Bibliothek

X
feed icon rss

Ihre E-Mail wurde erfolgreich gesendet. Bitte prüfen Sie Ihren Maileingang.

Leider ist ein Fehler beim E-Mail-Versand aufgetreten. Bitte versuchen Sie es erneut.

Vorgang fortführen?

Exportieren
Filter
  • 1995-1999  (21.580)
  • 1900-1904
  • 1850-1859  (835)
  • 1998  (6.593)
  • 1995  (14.987)
  • 1859  (452)
  • 1855  (383)
  • Chemistry  (18.727)
  • Life and Medical Sciences  (2.828)
  • General Chemistry  (2.299)
  • Analytical Chemistry and Spectroscopy  (1.717)
  • Engineering General  (737)
  • nitrogen
Datenquelle
Materialart
Erscheinungszeitraum
  • 1995-1999  (21.580)
  • 1900-1904
  • 1850-1859  (835)
Jahr
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    The impact of nitrogen fertilization of tomato on feeding site selection and oviposition by Trialeurodes vaporariorum (1998)
    Springer
    Entomologia experimentalis et applicata 86 (1998), S. 175-182 
    Details
    ISSN: 1570-7458
    Schlagwort(e): Aleyrodidae ; greenhouse whitefly ; nitrogen ; host selection ; oviposition
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Tomato plants, Lycopersicon esculentum Miller cv 'Tres Cantos', were supplied with high (308 ppm), medium (140 ppm) and low (84 ppm) nitrogen doses in order to determine the influence of nitrogen fertilization on feeding and oviposition site selection by greenhouse whitefly adults, T. vaporariorum (Westwood). The nitrogen and water content was higher in plants supplied with 308 N ppm than in plants with medium or low nitrogen doses and no differences were found in soluble sugar content. The leaves of the upper plant stratum (leaves 1–5) had the greatest nitrogen and water content, independent of the nitrogen dose applied. The plants were exposed to T. vaporariorum adults into a greenhouse under two current (late autumn-winter and spring-early summer) situations of the tomato crop in the Mediterranean area. The distribution of whitefly adults on the plants was affected by the nitrogen dose in both experimental conditions, the number of adults was higher on the plants supplied with high nitrogen dose. Within plants, adult distribution was affected by leaf position, the upper plant stratum being preferred for feeding. Whitefly females selected for oviposition and laid more eggs on plants and leaves of plants with higher nitrogen and water contents. We conclude that whitefly host selection for feeding and ovipositing are related to differences in nitrogen and water content of the host plant.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003145813704
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 2
    Digitale Medien
    Digitale Medien
    Fecundity and egg distribution of the herbivore Spodoptera pectinicornis as influenced by quality of the floating aquatic plant Pistia stratiotes (1998)
    Springer
    Entomologia experimentalis et applicata 86 (1998), S. 295-304 
    Details
    ISSN: 1570-7458
    Schlagwort(e): fecundity ; host plant quality ; Pistia stratiotes ; Spodoptera pectinicornis ; nitrogen ; trichomes ; oviposition ; biological control of weeds
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We determined the influence of larval host quality of the floating aquatic weed Pistia stratiotes L. (Araceae) on the fecundity and egg distribution of the biological control agent Spodoptera pectinicornis (Hampson) (Lepidoptera: Noctuidae). Different nutritional levels were produced by growing plants with relatively low and high levels of nitrogen, phosphorus and potassium fertilizer. Female and male pupal biomass were significantly greater when the larvae were fed leaves from the high fertilizer plants. Although the fertilizer treatments did not significantly influence total fecundity, there was an indirect effect as adults from larger pupae were more fecund. Regardless of treatment, ovipositing females formed a depression in the leaf surface by removing trichomes into which they deposited the egg masses. Most of the egg masses were laid on the lower leaf surface, on leaf positions 5–8 (counting from the young inner to the outer leaves) and during days 1–2 post-eclosion. Most of the eggs were laid in masses but about 12% were solitary. Females fed the low fertilizer treatment laid a greater proportion (mean ± s.e.) of their eggs as solitary eggs (17.3 ± 3.4% of total eggs) than did females fed the high fertilizer treatment (8.3 ± 2.3% of total eggs). The increased percentage of solitary eggs laid by the females from the low quality larval diet may be an adaptive response to decrease competition among the progeny.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003193220069
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 3
    Digitale Medien
    Digitale Medien
    Comparative effect of short term exposures of Callosobruchus subinnotatus to carbon dioxide, nitrogen, or low temperature on behavior and fecundity (1998)
    Springer
    Entomologia experimentalis et applicata 89 (1998), S. 243-248 
    Details
    ISSN: 1570-7458
    Schlagwort(e): Coleoptera ; bruchidae ; anesthesia ; carbon dioxide ; nitrogen ; cold ; oviposition and mating
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The effect of anesthetizing with carbon dioxide, nitrogen, or low temperature on the reproductive behavior and fecundity of Callosobruchus subinnotatus was investigated. Males and females anesthetized with N2 as virgins had shorter recovery time, copulated earlier, and had shorter mating time than those subjected to CO2 or low temperature. Exposure of males and females to 2.0±0.5 °C for 10 min had the most profound effect on the recovery periods, copulation time, and duration of mating. Adults anesthetized with CO2 and low temperature laid fewer eggs than those anesthetized with N2. Females were more affected than males by the treatments, except when males were chilled for 10 min, and this prolonged the time for commencement of mating. The mode of anesthesia could affect egg production because vitellogenesis and choriogenesis take place in the imago stage of bruchids.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003503623654
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 4
    Digitale Medien
    Digitale Medien
    Open-Air Litter Foraging in the Nasute Termite Longipeditermes longipes (Isoptera: Termitidae) (1998)
    Springer
    Journal of insect behavior 11 (1998), S. 179-189 
    Details
    ISSN: 1572-8889
    Schlagwort(e): open-air foraging ; caste ; polyethism ; litter feeder ; nitrogen ; termite
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The Southeast Asian nasute termite Longipeditermes longipes forages on the open ground on leaf litter. Its monomorphic workers carry back food balls in their mandibles while dimorphic soldiers defensively surround the marching columns and the foraging patches. When mechanically disturbed, workers hide under the litter, whereas antennating soldiers face as closely as possible the source of disturbance. Foragers prefer the lower, nitrogen-rich layer of the litter. Soldier behavior and column organization (returning workers in the center lanes, outgoing workers in the two flanking lanes) are similar to those in the related genera Hospitalitermes and Lacessititermes, which, however, tend to forage above ground.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021039722402
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 5
    Digitale Medien
    Digitale Medien
    Two kinds of adsorbed N atoms with different reactivities with H2 on a Pt0.25Rh0.75(100) surface (1998)
    Springer
    Catalysis letters 52 (1998), S. 151-155 
    Details
    ISSN: 1572-879X
    Schlagwort(e): platinum ; rhodium ; alloy ; surface composition ; nitrogen ; oxygen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Two kinds of adsorbed N atoms exist on a Pt0.25Rh0.75(100) surface. One desorbs at 490 K and the other desorbs at 650 K. The former reacts with H2 at 400 K, but the latter does not. It is supposed that the adsorption of these two N atoms is responsible of the surface composition, ratio of Pt and Rh.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1019000326574
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 6
    Digitale Medien
    Digitale Medien
    Nitrogen uptake and growth of two citrus rootstock seedlings in a sandy soil receiving different controlled-release fertilizer sources (1998)
    Springer
    Biology and fertility of soils 26 (1998), S. 169-172 
    Details
    ISSN: 1432-0789
    Schlagwort(e): Key words Urea ; Coated fertilizers ; Ammonium ; nitrogen ; Nitrate nitrogen ; Nitrogen uptake
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Understanding the fate of different forms of nitrogen (N) fertilizers applied to soils is an important step in enhancing N use efficiency and minimizing N losses. The growth and N uptake of two citrus rootstocks, Swingle citrumelo (SC), and Cleopatra mandarin (CM), seedlings were evaluated in a pot experiment using a Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments) without N application or with 400 mg N kg–1 applied as urea or controlled-release fertilizers (CRF; either as Meister, Osmocote, or Poly-S). Meister and Osmocote are polyolefin resin-coated urea with longevity of N release for 270 days (at 25°C). Poly-S is a polymer and sulfur-coated urea with release duration considerably shorter than that of either Meister or Osmocote. The concentrations of 2 M KCl extractable nitrate nitrogen (NO3 –-N) and ammonium nitrogen (NH4 +-N) in the soil sampled 180 days and 300 days after planting were greater in the soil with SC than with CM rootstock seedlings. In most cases, the extractable NH4 + and NO3 – concentrations were greater for the Osmocote treatment compared to the other N sources. For the SC rootstock seedlings, dry weight was greater with Meister or Poly-S compared with either Osmocote or urea. At the end of the experiment, ranking of the various N sources, with respect to total N uptake by the seedlings, was: Meister = Osmocote 〉 Poly-S 〉 Urea 〉 no N for CM rootstock, and Meister = Poly-S = Osmocote 〉 Urea 〉 no N for SC rootstock. The study demonstrated that for a given rate of N application the total N uptake by seedlings was greater for the CRF compared to urea treatment. This suggests that various N losses were lower from the CRF source as compared to those from soluble fertilizers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s003740050363
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 7
    Digitale Medien
    Digitale Medien
    AES investigations of the iron surface composition after laser irradiation under atmospheric conditions (1998)
    Springer
    Microchimica acta 130 (1998), S. 89-95 
    Details
    ISSN: 1436-5073
    Schlagwort(e): AES ; laser ; iron ; nitrogen ; oxygen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The laser induced modification of iron surfaces with atmospheric species was investigated by means of Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). Different laser systems were used for irradiating iron samples in a wide range of the laser processing parameters up to small foci and ultra short pulses. A nitriding of iron connected with an oxidation of the near surface region was observed in the wavelength range between 193 nm and 10.6 μm using large foci (∼0.1 cm2) and short pulses (10...1400ns). In case of small foci (∼7·10−6cm2) with ns-pulses (50 ns) an enrichment of the iron melt with nitrogen and an advanced oxidation of the surrounding area of the laser spot were detected. When using shorter pulses (200 fs, 40 ps) no indications for a nitriding were found.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01254595
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 8
    Digitale Medien
    Digitale Medien
    Evaluation of nitrate leaching risk at site and farm level (1998)
    Springer
    Nutrient cycling in agroecosystems 50 (1998), S. 271-276 
    Details
    ISSN: 1573-0867
    Schlagwort(e): nitrogen ; monitoring ; dairy farming ; simulation models ; risk assessment ; soil variability
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract At the ‘De Marke’ experimental farm a dairy farm was set up with the aim of meeting environmental and economic goals. The farm management with respect to nitrogen emphasized reduction of fertilization and a cattle grazing system that should result in nitrate concentrations in the groundwater below the EC-directive level of 11.3 mg l-1 nitrate-N. At six sites in six different fields of ‘De Marke’, these concentrations were monitored for 4 years. A direct comparison with the chosen limit was possible for these sites, but an evaluation of the environmental achievements of the farming system at farm level was also required. This was achieved by using simulation models and additional information about soils and field management. Based on multiple soil profile descriptions, frequency distributions of model output were generated, allowing a risk assessment for the total farm. The probability of exceeding the chosen threshold value of 11.3 mg l-1 nitrate-N during the period of summer 1991- spring 1995 was 63% for the whole farm, with marked differences between years, crops and hydrological conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009704714949
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 9
    Digitale Medien
    Digitale Medien
    Leaching of nitrogen and phosphorus from rural areas to surface waters in the Netherlands (1998)
    Springer
    Nutrient cycling in agroecosystems 50 (1998), S. 321-324 
    Details
    ISSN: 1573-0867
    Schlagwort(e): nutrient modelling ; leaching ; nitrogen ; phosphorus ; schematization
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In context of preparing the Fourth National Policy Document on Water Management in the Netherlands effects of different scenarios of fertilizer management on nitrogen (N) and phosphorus (P) leaching from rural areas into Dutch surface waters were analyzed. The manuscript offers insight into the model instrument that is used to simulate the different scenarios. Main parts of the modelinstrument are: a procedure to schematize the Netherlands in horizontal areal units, field scale mechanistic models for water and nutrient behaviour in the soil and an empirical model for fertilizer additions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009773202654
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 10
    Digitale Medien
    Digitale Medien
    Can organic farming help to reduce N-losses? (1998)
    Springer
    Nutrient cycling in agroecosystems 52 (1998), S. 277-287 
    Details
    ISSN: 1573-0867
    Schlagwort(e): dairy farming ; efficiency ; nitrogen ; organic ; pig farming ; surplus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract This study is in two parts. In the first part, nitrogen (N) losses per unit of milk and meat in Danish conventional and organic pig and dairy farming were compared on the basis of farm data. In the second part, organic and conventional dairy farming were compared in detail, using modelling. N-surpluses at different livestock densities, fodder intensities, and soil types were simulated. Finally, simulated N-surpluses were used in national scenarios for conversion to organic dairy farming in Denmark. In Part one, pig farming was found to have a higher N-efficiency than dairy farming. Organic pig production had a lower N-efficiency and a higher N-surplus per kg meat than conventional pig production. The possibilities to reduce N-loss by conversion to organic pig production therefore appear to be poor. Organic dairy farming had a higher N-efficiency and a lower N-surplus per kg milk than conventional dairy farming. Conversion from conventional to organic dairy farming may therefore reduce N-losses. In Part two, a positive correlation between livestock density and N-surplus ha-1 was found for dairy farming. For all simulated livestock densities, fodder feeding intensities and soil types, organic systems showed a lower N-surplus per unit of milk produced than conventional systems. National scenarios for dairy farming showed that the present Danish milk production could be achieved with a 24% lower total N-surplus if converted from intensive conventional farming to extensive organic farming. At the same time, N-surplus ha-1 and N-surplus (t milk)-1 would be lowered by 50% and 25% respectively. Changing from intensive to extensive conventional dairy farming with a livestock density equal to that in the organic scenario resulted in a reduction in N-surplus ha-1 of 15%. It was concluded that a reduction in total N-loss from agriculture is possible by converting from conventional to organic dairy farming but at the cost of either lower production on the present dairy farm area, or the current production on a substantially larger area.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009790722044
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 11
    Digitale Medien
    Digitale Medien
    Food production and consumption in Germany: N flows and N emissions (1998)
    Springer
    Nutrient cycling in agroecosystems 52 (1998), S. 289-301 
    Details
    ISSN: 1573-0867
    Schlagwort(e): food production and consumption ; mitigation strategies ; nitrogen ; nitrogen emission ; nitrous oxide ; sustainability of human N cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract During the past four decades the authors perceive that an increasing non-sustainability (Disintegration) within the agriculture , human nutrition, waste management complex has occurred both in Germany and the European Union. Compared to the basic needs of the population for nutritive energy, fat and protein, we estimate that the production and consumption of food and feed is more than 50% higher than necessary. Using nitrogen (N) input into German agriculture in 1991/92 as an example, we estimated that the N input of 191 kg ha-1 was 2 to 3 times too high. This high N input resulted in the net biomass production of 45 kg ha-1, a 25% efficiency. This inefficiency causes emissions of reactive N and other nutrient compounds into the hydrosphere and atmosphere that were 2 to 8 times too high. For example the contributions of agriculture to the total annual N2O–N emissions of Germany (during 1990–1992), Europe (1990) and of the world (1989) were 110, 691 Gg and 6.7 Tg or 52, 62 and 41%, respectively. The authors demonstrate that emissions of N and P from Germany and EU waste water management systems are also higher than necessary because nutrient recycling is not practiced extensively. Excessive food production and consumption has made the agriculture/human nutrition/waste and waste water complex, like the energy/transportation complex, a main cause of new transboundary environmental damage such as soil and water acidification, hypertrophication of near-natural terrestrial and aquatic ecosystems and climate change. We propose that a sustainable food production/consumption system can be developed that is based both on need-oriented production and consumption with no net exports and on recovery, recycling and more efficient use of nutrients. Using N as an example, the authors show which short and long term action aims must be set and realized by the year 2015, to meet environmental, economical and social sustainability requisites. The suggested, assumed sustainable N balance for German agriculture is characterized by a critical annual input and surplus maximum of 80 and 45 kg N ha-1 respectively, which should almost double biomass production efficiency for N utilization. This estimate is based on reducing animal stocking rates to 0.5 gross weight unit ha-1 to attain no net mineralization or immobilization of N in the soil.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009706001900
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 12
    Digitale Medien
    Digitale Medien
    Retention and leaching of N in Norwegian coniferous forests (1998)
    Springer
    Nutrient cycling in agroecosystems 52 (1998), S. 171-178 
    Details
    ISSN: 1573-0867
    Schlagwort(e): atmospheric deposition ; boreal forests ; critical loads ; forest growth ; gas losses ; leaching ; nitrogen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Nitrogen is brought into natural ecosystems from the atmosphere through N-fixation and deposition of NH 4 + and NO 3 - as wet and dry deposition. N is lost from terrestrial ecosystems unaffected by human activities by leaching or as gas, but the losses from different forest-and vegetation types are poorly quantified. The leaching is hampered by uptake in the vegetation and by immobilisation by soil organisms. The gas loss of N in the form of N2O and N2 appears to be rather small, but the loss of NO is unknown. Human activities such as those leading to the increased atmospheric dry and wet deposition of N, may affect the N-losses, but the increase in losses are likely to be very dependent on the amounts of N deposited. The present paper discusses the fate of the N deposited under the existing pollution climate in Norway where N deposition above the natural background has taken place for at least 50 years. The deposition today varies from about 15–20 kg N ha-1 yr-1 in the southernmost parts of the country to background values of about 2 kg ha-1 yr-1 in the north. Even in areas with the highest loads there are no clear indications that N-leaching in forest ecosystems has increased to ‘unacceptable’ levels. The main reason for this appears to be that most of the N deposited are immobilised in forest soils and utilised by forest trees and ground cover vegetation to increased biomass production. At present therefore, no clear signs of N-saturation can be found. This is in relatively good accordance with estimates of critical loads for N in Norwegian coniferous forests. Estimates of immobilisation, gas losses, net uptake in vegetation, biological fixation as well as a figure for ‘acceptable’ leaching, indicate that the long-term critical load of N might be of the order 10 to 30 kg N ha-1 yr-1. Most of the N deposited from the atmosphere appears therefore so far to be retained in the forests and only a small proportion seems to be lost to ground-and surface waters.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009715027516
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 13
    Digitale Medien
    Digitale Medien
    Intercropping sorghum with nitrogen fixing trees in semiarid India (1998)
    Springer
    Agroforestry systems 42 (1998), S. 181-194 
    Details
    ISSN: 1572-9680
    Schlagwort(e): Acacia ferruginea ; Albizia lebbeck ; Faidherbia albida ; nitrogen ; sorghum
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The influence of three nitrogen fixing tree (NFT) species viz., Faidherbia albida, Acacia ferruginea, Albizia lebbeck and four nitrogen levels (0, 20, 40 and 60 kg N ha−1) on intercropped rainfed sorghum was investigated at Hyderabad, India. The trees were established in shallow alfisols during 1985 with a spacing of 4 × 4 m. Intercropping was done in 1993 and 1994. The effect of trees on radiation interception, soil moisture, crop growth, yield components and yield of sorghum was examined. Association of tree species reduced grain and dryfodder yields of sorghum to an extent of 12 to 40% compared to sole crop situation. The reduction was maximum under A. lebbeck, minimum with F. albida and moderate under A. ferruginea. Application of 40 kg N ha−1 resulted in increased grain and dryfodder yields over other levels. Crop growth in terms of LAI and drymatter had similar response. The receipt of photosynthetically active radiation (PAR) was low under NFTs compared to open situation. The relative PAR intercepted under the trees was in the order: F. albida 〉 A. ferruginea 〉 A. lebbeck. Soil moisture status was more favourable under F. albida than under the other tree species. Soil moisture at all stages of crop growth was more in sole crop situation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006154725098
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 14
    Digitale Medien
    Digitale Medien
    Estimating regional forest productivity and water yield using an ecosystem model linked to a GIS (1998)
    Springer
    Landscape ecology 13 (1998), S. 323-334 
    Details
    ISSN: 1572-9761
    Schlagwort(e): forest productivity ; NPP ; runoff ; climate ; nitrogen ; northeastern U.S. ; modeling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We used the PnET-II model of forest carbon and water balances to estimate regional forest productivity and runoff for the northeastern United States. The model was run at 30 arc sec resolution (approximately 1 km) in conjunction with a Geographic Information System that contained monthly climate data and a satellite-derived land cover map. Predicted net primary production (NPP) ranged from 700 to 1450 g m2 yr1 with a regional mean of 1084 g m2 yr1. Validation at a number of locations within the region showed close agreement between predicted and observed values. Disagreement at two sites was proportional to differences between measured foliar N concentrations and values used in the model. Predicted runoff ranged from 24 to 150 cm yr1with a regional mean of 63 cm yr1. Predictions agreed well with observed values from U.S. Geologic Survey watersheds across the region although there was a slight bias towards overprediction at high elevations and underprediction at lower elevations. Spatial patterns in NPP followed patterns of precipitation and growing degree days, depending on the degree of predicted water versus energy limitation within each forest type. Randomized sensitivity analyses indicated that NPP within hardwood and pine forests was limited by variables controlling water availability (precipitation and soil water holding capacity) to a greater extent than foliar nitrogen, suggesting greater limitations by water than nitrogen for these forest types. In contrast, spruce-fir NPP was not sensitive to water availability and was highly sensitivity to foliar N, indicating greater limitation by available nitrogen. Although more work is needed to fully understand the relative importance of water versus nitrogen limitation in northeastern forests, these results suggests that spatial patterns of NPP for hardwoods and pines can be largely captured using currently available data sets, while substantial uncertainties exist for spruce-fir.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008004423783
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 15
    Digitale Medien
    Digitale Medien
    Thermogravimetric Analysis of Vanadium Phosphorus Oxide Catalysts Doped with Cobalt and Iron (1998)
    Springer
    Journal of thermal analysis and calorimetry 53 (1998), S. 111-121 
    Details
    ISSN: 1572-8943
    Schlagwort(e): air ; cobalt dopant ; iron dopant ; n-butane ; nitrogen ; thermogravimetric analysis ; vanadium phosphorus oxides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The transformation of VOHPO4·0.5H2O (VPO) precursor doped with cobalt or iron for n-butane oxidation to maleic anhydride was investigated by thermogravimetric analysis under air and nitrogen, with and without n-butane in the flow. While almost no effect was observed in nitrogen or air, a strong influence of the doping was observed when n-butane was added to the nitrogen or air. This resulted in a delay of the decomposition of the precursor and a further reoxidation of the VPO catalyst, particularly for doping with cobalt at low percentage (1%). This shows that doping can change the oxidation state of vanadium phosphorus oxide catalysts, which can explain differences in their catalytic performances and the favourable effect of doping by cobalt.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1010162018622
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 16
    Digitale Medien
    Digitale Medien
    Variation of Piperidine Alkaloids in Ponderosa (Pinus poderosa) and Lodgepole Pine (P. contorta) Foliage from Central Oregon (1998)
    Springer
    Journal of chemical ecology 24 (1998), S. 815-827 
    Details
    ISSN: 1573-1561
    Schlagwort(e): Piperidine alkaloids ; pinidine ; euphococcinine ; foliar chemistry ; nitrogen ; Pinus ponderosa ; Pinus contorta
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract We quantified 2,6-disubstituted piperidine alkaloids in Pinus ponderosa and P. contorta needles from three forest sites in April, June, August, and December. Alkaloids were detected on at least one date in 71% of the ponderosa pine and in 29% of the lodgepole pine trees sampled. Pinidine was the major alkaloid constituent of ponderosa pine, while euphococcinine was the predominant compound in lodgepole pine. For ponderosa pine, total alkaloid concentrations were very low at two sites on all dates. At the third site, concentrations were variable but significantly higher on all dates. Total alkaloid concentrations in previous-year foliage from this site were highest in April, then significantly lower from June through December. Current-year foliage collected in August and December had significantly higher alkaloid concentrations than previous-year foliage on the same dates. Variation in foliar nitrogen concentrations accounted for some of the alkaloid variation in current-year foliage sampled in August.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022369416745
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 17
    Digitale Medien
    Digitale Medien
    Effects of increased atmospheric CO2 and N supply on photosynthesis, growth and cell composition of the cyanobacterium Spirulina platensis (Arthrospira) (1998)
    Springer
    Journal of applied phycology 10 (1998), S. 461-469 
    Details
    ISSN: 1573-5176
    Schlagwort(e): Cyanobacterium ; Spirulina platensis ; Arthrospira ; CO2 ; organic carbon ; nitrogen ; photosynthesis ; batch culture
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The consequences of the addition of CO2 (1%) in cultures of S. platensis are examined in terms of biomass yield, cell composition and external medium composition. CO2 enrichment was tested under nitrogen saturating and nitrogen limiting conditions. Increasing CO2 levels did not cause any change in maximum growth rate while it decreased maximum biomass yield. Protein and pigments were decreased and carbohydrate increased by high CO2, but the capability to store carbohydrates was saturated. C:N ratio remained unchanged while organic carbon released to the external medium was enhanced, suggesting that organic carbon release in S. platensis is an efficient mechanism for the maintenance of the metabolic integrity, balancing the cell C:N ratio in response to environmental CO2 changes. CO2 affected the pigment content: Phycocyanin, chlorophyll and carotenoids were reduced in around 50%, but the photosynthetic parameters were slightly changed. We propose that in S. platensis CO2 could act promoting degradation of pigments synthetised in excess in normal CO2 conditions, that are not necessary for light harvesting. Nitrogen assimilation was significantly not affected by CO2, and it is proposed that the inability to stimulate N assimilation by CO2 enrichment determined the lack of response in maximum growth rate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008090402847
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 18
    Digitale Medien
    Digitale Medien
    Nitrogen availability influences the biochemical composition and photosynthesis of tank-cultivated Ulva rigida (Chlorophyta) (1998)
    Springer
    Journal of applied phycology 10 (1998), S. 383-389 
    Details
    ISSN: 1573-5176
    Schlagwort(e): ammonium ; C:N ratio ; tank culture ; dietary fibre ; fatty acids ; nitrogen ; photosynthesis ; Ulva rigida
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Physiological and biochemical changes in relation to inorganic nitrogen availability were studied for tank-cultivated Ulva rigida grown under nitrogen- enriched and nitrogen-depleted seawater. U. rigida was initially cultivated in nitrogen-enriched seawater (daily concentrations of NH4+ and NO3- + NO2- ranged between 0.5–1.7 and 0.06–0.15 mg L-1, respectively), then transferred to nitrogen-depleted seawater where photosynthetic capacity decreased to zero after 23 d. At the time (14 d) when photosynthetic rates were lower than 2.0 μmol O2 g-1 FW min-1 and strong bleaching had occurred, some algae were returned to the initial nitrogen-enriched seawater to study recovery from N-limited growth. Data on biochemical composition (chlorophylls, ash, caloric content, fatty acids and dietary fibres) and colouration varied significantly depending on the nitrogen conditions. C:N ratios correlated significantly with biochemical parameters. Fatty acid (FA) synthesis continued during the N-starvation period; saturated and mono-unsaturated FA increased to a maximun of 72.2%, while poly-unsaturated fatty acids (PUFA) decreased to 27.7%. During the N-enriched recovery period, the reverse was found. C:N ratios above 10 correlated with carbohydrate synthesis as shown by the dietary fibre level. Under nitrogen enriched conditions, C:N ratios decreased along with a decrease in fibre level. Under controlled conditions, nitrogen represents a major influence on the development of intensive tank cultivation of Ulva rigida, not only by affecting parameters closely related to nitrogen metabolism but also some clearly influenced by carbon uptake.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008008912991
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 19
    Digitale Medien
    Digitale Medien
    Effects of light intensity, CO2 and nitrogen supply on lipid class composition of Dunaliella viridis (1998)
    Springer
    Journal of applied phycology 10 (1998), S. 135-144 
    Details
    ISSN: 1573-5176
    Schlagwort(e): Light ; CO2 ; nitrogen ; lipids ; thin layer chromatography ; flame ionisation ; microalga ; batch culture ; Dunaliella viridis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Lipid class composition of Dunaliella viridis Teodoresco was analysed using thin layer chromatography coupled with flame ionisation detection (TLC/FID technique). D. viridis was cultured under four different photon fluence rates and in darkness, and under two different conditions of CO2 supply (atmospheric and 1%) with and without nitrogen sufficiency. Nine lipid classes were identified and quantified. Total lipids per cell and acetone-mobile polar lipids decreased with light, while the percentage of sterols and triglycerides increased with increasing irradiance. Total phospholipids increase was related with growth rate while hydrocarbons, wax esters and sterol esters accumulated in darkness. There were almost no changes in total lipids per cell because of nitrogen limitation; however, nitrogen limitation led to higher changes in lipid class composition under 1% CO2 than under atmospheric CO2 levels. The main reserve lipid, triglycerides, accumulated in high amounts under 1% CO2 and nitrogen limitation, increasing from 1% to 22% of total lipids. The ratio sterols/acetone-mobile polar lipids could be an index of the 'light status' independently of nitrogen limitation, while the ratio triglycerides/total phospholipids could indicate any physiological stress uncoupling C and N metabolism and affecting the growth rate.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1008067022973
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 20
    Digitale Medien
    Digitale Medien
    Short-term effect of nitrogen enrichment on the microbial communities of a peatland (1998)
    Springer
    Hydrobiologia 373-374 (1998), S. 111-119 
    Details
    ISSN: 1573-5117
    Schlagwort(e): peatland ; nitrogen ; microbial communities ; microbialloop
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The aim of this study was to assess the structure of the microbial loop in a Sphagnum fallax — Carex rostrata fen of the French Massif central, and the impact of nitrogen supplies on the different microbial communities. Microalgae (46% of the total microbial biomass), Protozoa (26%) and heterotrophic Bacteria (17%) were the dominant microorganisms. Rotifera (5%), Cyanobacteria (3%), Fungi (2%) and Nematoda (〈1%) were also present. Testate Amoebae were well represented in Sphagnum peatland (14% of total microbial biomass). Thus, the structure of the protist community in the surface of fen peatlands is notably different from that recorded in other environments. The input of nitrogen led to a steady increase in microbial biomasses, but only changed the structure of microbial communities significantly when the input was 50 kg ha-1. At high inputs, nitrogen supply increased the relative importance of Cyanobacteria, Euglenophyceae, Bacillariophyceae and Ciliates, and decreased the relative importance of heterotrophic Bacteria, other microalgae and testate Amoebae. The increase in the values of photosynthetic assimilation and heterotrophic activities could also reflect changes in community functioning.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1017091926454
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 21
    Digitale Medien
    Digitale Medien
    The role of mineral nutrients in the increased growth response of tomato plants in solarized soil (1998)
    Springer
    Plant and soil 206 (1998), S. 21-27 
    Details
    ISSN: 1573-5036
    Schlagwort(e): Lycopersicon esculentum ; nitrogen ; plant growth ; plant nutrition ; soil solarization ; tomato
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Soil solarization is a non-chemical disinfestation technique that frequently promotes plant growth in the absence of known major pathogens, a phenomenon termed increased growth response (IGR). The effect of solarization on plant nutrients and their role in the IGR was studied with tomato plants grown in solarized or non-solarized (control) sandy soil, under controlled conditions. Solarization considerably increased the soil concentrations of water extractable N, K, Ca, Mg and Na at most sites, whereas Cl and DTPA extractable Mn, Zn, Fe and Cu were decreased by the treatment. Plant growth and specific leaf area were enhanced in solarized as well as in N-supplemented control soil. In tomato plants grown in solarized soil, concentrations of most nutrients in the xylem sap, including N, were increased compared to the control, whereas Cl and SO4 levels decreased. The most significant increase in leaf nutrient concentration caused by soil solarization was recorded for N. Furthermore, leaf N concentration was highly and positively correlated with shoot growth. The concentration of Cu increased in leaves from the solarization vs. the control treatment, whereas that of SO4 and Cl decreased, the latter presumably below the critical toxicity level. The correlation between shoot growth and leaf concentration was positive for Cu and inverse for Cl and SO4. In conclusion, we found that soil solarization significantly affects nutrient composition in tomato plants, and provided strong evidence that N, and eventually also Cl, play a major role in IGR.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004321118896
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 22
    Digitale Medien
    Digitale Medien
    Water-use efficiency and transpiration efficiency of wheat under rain-fed conditions and supplemental irrigation in a Mediterranean-type environment (1998)
    Springer
    Plant and soil 201 (1998), S. 295-305 
    Details
    ISSN: 1573-5036
    Schlagwort(e): nitrogen ; soil evaporation ; transpiration ; water use
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Growth and water use were measured in wheat (Triticum aestivum L.) grown in northern Syria in a typical Mediterranean climate over five seasons 1991/92–1995/96. Water use was partitioned into transpiration (T) and soil evaporation (Es) using Ritchie's model, and water-use efficiency (WUE) and transpiration efficiency (TE) were calculated. The aim of the study was to examine the influence of irrigation and nitrogen on water use, WUE and TE. By addition of 100 kg N ha-1, Es was reduced from 120 mm to 101 mm under rain-fed conditions and from 143 mm to 110 mm under irrigated conditions, and T was increased from 153 mm to 193 mm under rain-fed conditions and from 215 mm to 310 mm under irrigated conditions. Under rain-fed conditions, about 35% of evapotranspiration (ET) may be lost from the soil surface for the fertilized crops and 44% of ET for the unfertilized crops. Transpiration accounted for 65% of ET for the fertilized crops and 56% for the unfertilized crops under rain-fed. As a result of this, WUE was increased by 44% for dry matter and 29% for grain yield under rain-fed conditions, and by 60% for dry matter and 57% for grain yield under irrigated conditions. Transpiration efficiency for the fertilized crops was 43.8 kg ha-1 mm-1 for dry matter and 15 kg ha-1 mm-1 for grain yield, while TE for the unfertilized crops was 33.6 kg ha-1 mm-1 and 12.2 kg ha-1 mm-1 for dry matter and grain yield, respectively. Supplemental irrigation significantly increased post-anthesis water use, transpiration, dry matter and grain yield. Water-use efficiency for grain yield was increased from 9.7 to 11.0 kg ha-1 mm-1 by supplemental irrigation, although WUE for dry matter was not affected by it. Irrigation did not affect transpiration efficiency for grain yield, but decreased transpiration efficiency for dry matter by 16%. This was associated with higher harvest index as a result of good water supply in the post-anthesis period and increased transpiration under irrigated conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004328004860
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 23
    Digitale Medien
    Digitale Medien
    Variability of traits associated with phosphorus efficiency in wild and cultivated genotypes of common bean (1998)
    Springer
    Plant and soil 203 (1998), S. 173-182 
    Details
    ISSN: 1573-5036
    Schlagwort(e): genetic diversity ; genotypic variability ; nitrogen ; nodulation ; Phaseolus vulgaris ; root area
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Genetic variation in plant growth under limited phosphorus (P) supply is necessary to obtain more productive cultivars on low P-available soils. Two pot experiments were conducted to evaluate the variability of some traits associated with efficiency of P absorption and utilization in wild and cultivated genotypes of common bean (Phaseolus vulgaris L.) under biological N2 fixation. At two P levels (20 and 80 mg P kg-1 soil, P1 and P2, respectively), 20 wild and 6 cultivated genotypes were grown in Experiment 1, and 4 wild and 27 cultivated genotypes were grown in Experiment 2. Plants were harvested at flowering, but in Experiment 1 wild accessions that did not flower were harvested at the beginning of leaf senescence. In Experiment 1, part of the genotypic variability of wild accessions was attributed to a less homogeneous ontogenetic stage at harvest, whereas in Experiment 2 some variation in biomass production was due to distinct phenologies of cultivated genotypes. Wild lines did not seem more tolerant to low P conditions, but the genotypic variation observed suggests these materials as a source of genetic diversity. Part of the variation in the root area and root efficiency ratio (total P content:root area) was compensatory, resulting in narrow genotypic differences in the total P content. The total P content and root efficiency ratio presented a wider amplitude of variation at P2 than at P1, and P uptake was more influenced by P supply than root production. Since the genotype × P level interaction was not significant for shoot biomass and shoot P concentration in Experiment 2, P utilization efficiency may be a useful selection criterion for cultivars between limited and adequate P supply. Within the sample of genetic diversity evaluated herein, there was large genotypic variability for traits related to P efficiency among wild and cultivated genotypes of common bean.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004398930218
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 24
    Digitale Medien
    Digitale Medien
    Root distribution following spatial separation of water and nitrogen supply in furrow irrigated corn (1998)
    Springer
    Plant and soil 199 (1998), S. 187-194 
    Details
    ISSN: 1573-5036
    Schlagwort(e): corn ; growth ; nitrogen ; root ; water
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Proper management of water and fertilizer placement in irrigated corn (Zea mays L.) has the potential to reduce nitrate leaching into the groundwater. Potential management practices tested in a two year field experiment included row or furrow fertilizer placement combined with every or alternate furrow irrigation. To understand how fertilizer availability to plants could be affected by these management practices, root growth and distribution in a Ulm clay loam soil were examined. Spring rains were greater than normal in both years providing adequate moisture for early root growth in both irrigated and non-irrigated furrows. As the non-irrigated furrow began to dry, root biomass increased as much as 126% compared with the irrigated furrow. The greatest increase was at lower depths, however, where moisture was still plentiful. When early season moisture was available, roots proliferated throughout the soil profile and quickly became available to take up fertilizer N in both irrigated and non-irrigated furrows. Root growth responded positively to fertilizer placement in the furrow in 1996 but not in 1995. Excessive N leaching in 1995 may have limited the response to fertilizer N.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004369227455
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 25
    Digitale Medien
    Digitale Medien
    Relationship between soil chemical factors and grassland diversity (1998)
    Springer
    Plant and soil 202 (1998), S. 69-78 
    Details
    ISSN: 1573-5036
    Schlagwort(e): grassland ; nitrogen ; nutrient competition ; phosphorus ; plant diversity ; potassium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Many studies carried out during these last few years have focused on the factors influencing plant diversity in species-rich grasslands. This is due to the fact that these ecosystems, among the most diversified in temperate climates, are extremely threatened; in some areas, they have almost disappeared. The re-establishment of these habitats implies to know the living conditions of the associations to be recreated. Very often, the typical species of these communities have become so rarefied that the seed bank or the seed rain are not sufficient to recreate the plant community. Most of the time, to achieve the restoration of these communities, they have to be totally recreated by sowing. For the restoration or the maintenance of the community, the soil chemical characteristics have also to be appropriate or if not modified. This research tends to establish a relation between some soil chemical factors and the plant diversity of a great number of stations. This research has illuminated the relationship between soil extractable phosphorus and potassium and plant diversity. Over 5 mg of phosphorus per 100 g of dry soil (acetate + EDTA extraction), no station containing more than 20 species per 100 m2 has been found. The highest number of species is found below the optimum content of the soil for plant nutrition (5–8 mg P/100 g). Concerning the potassium, the highest number of species is found at 20 mg/100, a value corresponcing to an optimum content of the soil for plant nutrition. High potassium contents, in opposition to phosphorus contents, are thus compatible with high values of diversity. Other factors (i.e. pH, organic matter, total nitrogen and calcium) do not show so clearly a relation with plant diversity. Excess of N–NO3 is known for its negative effect on the diversity of plant communities. In these environments, apart from the atmospheric deposits which can be important in some areas, N–NO3 is derived mainly from the symbiotic fixation of atmospheric nitrogen by legumes as well as from the mineralization of the organic matter of the soil. It is possible that, when in small quantities, the available soil phosphorus could be a limiting factor of the N–NO3 supply by these two sources. In this hypothesis, nitrogen would remain the main element limitating plant diversity but its availability would be controlled by phosphorus.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004389614865
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 26
    Digitale Medien
    Digitale Medien
    Modelling partitioning between structure and storage in sugar beet: Effects of drought and soil nitrogen (1998)
    Springer
    Plant and soil 207 (1998), S. 97-106 
    Details
    ISSN: 1573-5036
    Schlagwort(e): allometric growth ; Beta vulgaris L. ; drought ; models ; nitrogen ; partitioning
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In the UK sugar beet is grown on contrasting soils that vary both in their nutritional status and water-holding capacities. Water shortage and low nitrogen reduce canopy growth and dry matter production, which is compensated in part by an increase in the fraction of assimilates partitioned to storage. Conversely, high nitrogen and ample water encourage growth of the canopy, increase assimilation of carbon dioxide but reduce the proportion of assimilates stored as sugar. This paper sets out to examine simple relationships between sugar yield, total dry matter and soil nitrogen in rain-fed and irrigated sugar beet crops (Beta vulgaris L.) from 46 field experiments spanning 12 years and a range of soil types, in order to improve prediction of sugar yields. Two partitioning functions were fitted to the data. The first represents a useful alternative formulation of the allometric growth function that overcomes some of the difficulties in the interpretation of the parameters. This model adequately described the seasonal progress of sugar yield (Y) in relation to total dry matter (W), but it was difficult to postulate biological mechanisms as to how the parameters should vary in relation to varying soil nitrogen or to drought. The second partitioning function, given by Y = W − (1/k) log(1 + kW), also described the data well, but had the more useful parameter, k, the decay rate of the fraction of assimilates partitioned to structural matter. This was shown to be greater in crops which had experienced significant drought and was inversely proportional to the amount of nitrogen taken up by the crops. Relationships between k and amounts of nitrogen fertilizer applied and/or amounts of residual nitrogen in the soil at sowing, however, were more variable. These could be improved by additionally taking account of soil type and rainfall following nitrogen fertilizer application in late spring. The models are a useful extension to yield forecasting models because they provide a simple means of estimating sugar yield from total dry matter in relation to factors that affect partitioning of assimilates such as drought and soil nitrogen availability.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004444128026
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 27
    Digitale Medien
    Digitale Medien
    Nitrogen fixation and the mass balances of carbon and nitrogen in ecosystems (1998)
    Springer
    Biogeochemistry 43 (1998), S. 63-78 
    Details
    ISSN: 1573-515X
    Schlagwort(e): carbon ; mass balance ; nitrogen ; nitrogen fixation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Ecosystems with high rates of nitrogen fixation often have high loss rates through leaching or possibly denitrification. However, there is no formal theoretical context to examine why this should be the case nor of how nitrogen accumulates in such open systems. Here, we propose a simple model coupling nitrogen inputs and losses to carbon inputs and losses. The nitrogen balance of this model system depends on plant (nitrogen fixer) growth rate, its carrying capacity, N fixed/C fixed, residence time of nitrogen and carbon in biomass, litter decay rate, litter N/C, and fractional loss rate of mineralized nitrogen. The model predicts the requirements for equilibrium in a nitrogen-fixing system, and the conditions on nitrogen fixation and losses in order for the system to accumulate nitrogen and carbon. In particular, the accumulation of nitrogen and carbon in a nitrogen-fixing system depend on an interaction between residence time in vegetation and litter decay rate in soil. To reflect a possible increased uptake of soil nitrogen and decreased respiratory cost of symbiotic nitrogen fixers, the model was then modified so that fixation rate decreased and growth rate increased as nitrogen capital accumulated. These modifications had only small effects on carbon and nitrogen accumulation. This suggests that switching from uptake of atmospheric nitrogen to mineral soil nitrogen as nitrogen capital accumulates simply results in a trade-off between energetic limitations and soil nitrogen limitations to carbon and nitrogen accumulation. Experimental tests of the model are suggested.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006057428096
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 28
    Digitale Medien
    Digitale Medien
    Plant-soil Interactions in Deserts (1998)
    Springer
    Biogeochemistry 42 (1998), S. 169-187 
    Details
    ISSN: 1573-515X
    Schlagwort(e): aridisols ; desertification ; erosion ; geostatistics ; Larrea tridentata ; nitrogen ; phosphorus ; Prosopis glandulosa ; soil heterogeneity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract Geostatistical analyses show that the distribution of soil N, P and K is strongly associated with the presence of shrubs in desert habitats. Shrubs concentrate the biogeochemical cycle of these elements in ‘islands of fertility’ that are localized beneath their canopies, while adjacent barren, intershrub spaces are comparatively devoid of biotic activity. Both physical and biological processes are involved in the formation of shrub islands. Losses of semiarid grassland in favor of invading shrubs initiate these changes in the distribution of soil nutrients, which may promote the further invasion and persistence of shrubs and cause potential feedbacks between desertification and the Earth's climate system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005939924434
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 29
    Digitale Medien
    Digitale Medien
    Wetland effects on water quality: input-output studies of suspended particulate matter, nitrogen (N) and phosphorus (P) in Grand-Lieu, a natural plain lake (1998)
    Springer
    Hydrobiologia 373-374 (1998), S. 217-235 
    Details
    ISSN: 1573-5117
    Schlagwort(e): wetlands ; lake ; water quality ; sediment ; nitrogen ; phosphorus ; macrophytes ; nutrient retention
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The role of wetland on water quality of rivers was estimated in a natural lake, Grand-Lieu (5600 ha), discharging to the Loire estuary. Inputs of its two tributaries, budgets and retention within the lake for particulate matter (PM), nitrogen (N) and phosphorus (P) were compared during the inflow period (Oct–May), by an input-output study, in two hydrologically contrasted years, 1993–94 with high inflow (292 106 m3), and 1995–96 with low inflow (76 106 m3). Globally the loads per ha were similar for the two tributaries for the same year, with higher values at the beginning of the flows, and total inputs markedly higher in 1993–94. During this year, average loads for the main tributary were 154 kg ha-1 PM, 40 kg ha-1 total N and 1.35 kg ha-1 total P. In the two tributaries, NO3 represented 80% of total N for the two years, and PO4 65% and 44% of total P. Total inputs, total outputs and storages are highly related to annual inflow, with large differences between elements. The highest change of inputs occur for NO2, PO4 and PM, and the lowest for NH4. Storage and outputs of the lake were also much higher in 1993–94, the most important annual differences concerning P storage, and outputs of PM and all forms of nitrogen except NH4. However, only the retention rate of total P doubled with the high outflow of 1993–94 (40% against 18%), while those of PO4 and NH4 were equivalent (79–72% and 72–66% respectively). In contrast the retention rate of all the other elements was lower with the large flow of 1993–94: 61 against 86% for NO3, 85–90% for NO2, 32–60% for total N, and 14–20% for PM. Globally, this wetland received important discharge of inorganic nitrogen from its catchment area, trapping or converting most of it (62–85%) into organic matter, while it exported a large amount of dissolved and particulate organic nitrogen (16 g m-2 y-1 in 1993–94 and 4.5 in 1995–96), 2.6 and 1.9 times more than it received. The exportation of organic N per m2 and retention of total N (9.9–14.5 g m-2 y-1) represent record values. This seems mainly due to the importance of water flow, juxtaposition of habitats with different degree of closure, plant biomass and resuspended endogenous, organic sediments in exportation. The lake is not able to counterbalance the dramatic increase of agricultural and sewage inputs, that induce its eutrophication and silting up.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1017014027788
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 30
    Digitale Medien
    Digitale Medien
    Long term effects of inorganic fertilizer inputs on crop productivity in a rice-wheat cropping system (1998)
    Springer
    Nutrient cycling in agroecosystems 51 (1998), S. 193-200 
    Details
    ISSN: 1573-0867
    Schlagwort(e): cropping systems ; inorganic fertilizer ; nitrogen ; organic carbon ; phosphorus ; potassium ; rice-wheat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Three levels of N (40,80,120 kg N ha-1) and P (0,17.5,35 kg P ha-1), and 2 levels of K (0,33 kg K ha-1) were tested for 19 years in rice and wheat crops of a rice-wheat cropping system in a fixed layout of 3×2×2 factorial partially confounded design along with one control and 3 replications. From this trial, data of 7 treatments, i.e. 0-0-0, 40-35-33, 80-35-33, 120-35-33, 120-0-0, 120-35-0 and 120-0-33 kg ha-1 N-P-K respectively were compared for yield trends, changes in response functions, soil organic -C and available N,P,K status. Soil organic - C decreased in unfertilized plots by 62% (over initial value of 0.45%) but increased by 44, 40 and 36% in plots receiving 120-35-33, 120-35-0 and 80-35-33 kg ha-1 N-P-K respectively. Available N was also greatest in these same three treatments. Available soil P increased by about 5 fold in 15 years in treatments supplied with fertilizer P, but no significant change was detected in treatments without P addition. Yields of rice and wheat exhibited linear declining trend in all treatments. The highest rate of decline (89 kg ha-1 year-1 in rice and 175 kg ha-1 year-1 in wheat), however, was found when 120 kg ha-1 N was applied alone. The least rate of decline of 20 kg ha-1 year-1 in rice and 58 kg ha-1 year-1 in wheat was observed when 40-35-33 kg ha-1 N-P-K respectively was applied to both the crops. At currently recommended levels of NPK (120-35-33 kg ha-1), the rate of decline in yields was 25 kg ha-1 year-1 for rice and 62 kg ha-1 year-1 for wheat. Possible causes of these yield declines are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009744719420
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 31
    Digitale Medien
    Digitale Medien
    Global use and trade of feedstuffs and consequences for the nitrogen cycle (1998)
    Springer
    Nutrient cycling in agroecosystems 52 (1998), S. 261-267 
    Details
    ISSN: 1573-0867
    Schlagwort(e): cereals ; feedstuffs ; feeding intensity ; livestock ; meat ; nitrogen ; trade
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract This paper presents an estimate of the amount of nitrogen involved in the use and trade of feedstuffs for a number of world regions. Livestock production has shown a steady increase world-wide as a result of an annual increase of 1.4% in developing countries and 0.9% in developed countries during the period 1960–1990. Particularly in developing countries, the strong growth of animal production and a tendency towards decreasing reliance on grazing and increasing importance of fodder crops and feed concentrates, cause a major increase in the consumption of feedstuffs. Cereals form the major feedstuff world-wide. The current global use of cereals for feed is about 30% of the total use (57% in developed countries and 17% in developing countries). Net trade of cereals and other feedstuffs represents 4–8 Tg N per year, which is only 4–7% of the total N consumption by the world's animal population. A strong growth of the per capita food consumption, a relative increase of meat consumption, coupled with a strong population growth, may cause a strong increase of the net trade of cereals. In particular the countries of the Middle East, North Africa and China may become important importers of cereals. In future, the N transport between regions in the form of feedstuffs may become an important component in the global N cycle.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009763706114
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 32
    Digitale Medien
    Digitale Medien
    An assessment of human influences on fluxes of nitrogen from the terrestrial landscape to the estuaries and continental shelves of the North Atlantic Ocean (1998)
    Springer
    Nutrient cycling in agroecosystems 52 (1998), S. 213-223 
    Details
    ISSN: 1573-0867
    Schlagwort(e): atmospheric deposition ; coastal eutrophication ; denitrification ; fertilizer ; nitrogen ; nitrogen budgets ; regional biogeochemistry ; sewage
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Our analysis for the International SCOPE Nitrogen Project shows that the fluxes of nitrogen in rivers to the coast of the North Atlantic Ocean vary markedly among regions, with the lowest fluxes found in northern Canada (76 kg N km−2 yr−1) and the highest fluxes found in the watersheds of the North Sea (1450 kg N km−2 yr−1). Non-point sources of nitrogen dominate the flux in all regions. The flux of nitrogen from the various regions surrounding the North Atlantic is correlated (r 2 = 0.73) with human-controlled inputs of nitrogen to the regions (defined as net inputs of nitrogen in food, nitrogen fertilizer, nitrogen fixation by agricultural crops, and atmospheric deposition of oxidized nitrogen), and human activity has clearly increased these nitrogen flows in rivers. On average, only 20% of the human-controlled inputs of nitrogen to a region are exported to the ocean in riverine flows; the majority (80%) of these regional nitrogen inputs is stored in the landscape or denitrified. Of all the nitrogen inputs to regions, atmospheric deposition of NOy is the best predictor of riverine export of nitrogen from non-point sources (r 2 = 0.81). Atmospheric deposition of this oxidized nitrogen, most of which derives from fossil-fuel combustion, may be more mobile in the landscape than are regional inputs of nitrogen from fertilizer, nitrogen fixation in agriculture, and nitrogen in foods and feedstocks. Agricultural sources of nitrogen, although larger total inputs to most temperate regions surrounding the North Atlantic Ocean, appear to be more tightly held in the landscape. Deposition of ammonium from the atmosphere appears to be a very good surrogate measure of the leakiness of nitrogen from agricultural sources to surface waters. This suggests a management approach for controlling ‘surplus’ nitrogen used in agricultural systems. The sum of NOy and ammonium deposition proves to be an amazingly powerful predictor of nitrogen fluxes from non-point sources to the coastal North Atlantic Ocean for temperate-zone regions (r 2 = 0.92; p = 0.001). By comparing fluxes with some estimates of what occurs in watersheds with minimal human impact, it appears that human activity has increased riverine nitrogen inputs to the ocean by some 11-fold in the North Sea region, by 6-fold for all of Europe, and by 3-fold for all of North America. These increased flows of nitrogen have clearly led to severe eutrophication in many estuaries, and have probably contributed to some eutrophication on the continental shelf in the North Sea and in the Gulf of Mexico. In other regions, however, the input of nitrogen to continental shelves is dominated by cross-shelf advection from deep-Atlantic waters, and the increased inputs from rivers are relatively minor.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1009784210657
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 33
    Digitale Medien
    Digitale Medien
    An Equation for Calculating Nitrogen Density from Measurements of Dielectric Constants (1998)
    Springer
    International journal of thermophysics 19 (1998), S. 215-225 
    Details
    ISSN: 1572-9567
    Schlagwort(e): density ; dielectric constant ; nitrogen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A new equation for determining the density of nonpolar substances based on measurements of dielectric constants is presented. Applying the new equation to nitrogen at a density from 1 to 30 mol·L−1, the mean deviation of the results calculated from the equation is of the order of 10−4, which is the same as the uncertainty of the experimental data. Owing to its analytical form, the derived equation can be applied to indicate the density of nonpolar substances with a densitometer, without adding error to the experimental uncertainty. This equation is also capable of determining the mean polarizabilities and molecular diameters, which agree well with results from other investigators. We suggest that the equation derived here can be applied to some other nonpolar substances as well.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1021459304637
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 34
    Digitale Medien
    Digitale Medien
    A Reference Quality Equation of State for Nitrogen (1998)
    Springer
    International journal of thermophysics 19 (1998), S. 1121-1132 
    Details
    ISSN: 1572-9567
    Schlagwort(e): caloric properties ; density ; equation of state ; nitrogen ; thermodynamic properties
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A new formulation describing the thermodynamic properties of nitrogen has been developed. New data sets which have been used to improve the representation of the p–ρ–T surface of gaseous, liquid and supercritical nitrogen, including the saturated states are now available. New measurements on the speed of sound from spherical resonators have been used to improve the accuracy of caloric properties in gaseous and supercritical nitrogen. State-of-the-art algorithms for the optimization of the mathematical structure of the equation and special functional forms for an improved description of the critical region were used to represent even the most accurate data within their experimental uncertainty. The uncertainty in density of the new reference equation of state ranges from ±0.01% between 270 and 350 K at pressures less than 12MPa, within ±0.02% over all other temperatures less than 550 K and pressures less than 12 MPa, and up to a maximum of ±0.6% at the highest pressures. The equation is valid from the triple point to temperatures of 1000 K and pressures up to 2200 MPa. The new formulation yields a reasonable extrapolation up to the limits of chemical stability of nitrogen as indicated by comparison to experimental shock tube data. Constraints regarding the structure of the equation ensure reasonable extrapolated properties up to temperatures and pressures of 5000 K and 25 GPa. For typical calibration applications, the new reference equation is supplemented by a simple but also highly accurate formulation, valid only for supercritical nitrogen between 270 and 350 K at pressures up to 30 MPa.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1022689625833
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 35
    Digitale Medien
    Digitale Medien
    Tithonia and senna green manures and inorganic fertilizers as phosphorus sources for maize in Western Kenya (1998)
    Springer
    Agroforestry systems 44 (1998), S. 21-35 
    Details
    ISSN: 1572-9680
    Schlagwort(e): biomass transfer ; decomposition ; mineralization ; nitrogen
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Efforts to overcome declining soil fertility on small holder farms in western Kenya must be consistent with the reality of low utilization of inorganic fertilizers. Likewise organic inputs alone cannot supply adequate nutrients. The use of two organic resources, Tithonia diversifolia (tithonia) and Senna spectabilis (senna) leaves, and their combination with inorganic P for improving soil fertility and maize yields was investigated on a P limiting soil in Western Kenya. Treatments included: 1) control, no inputs; 2) 5 t ha−1 (dry matter) tithonia leaves; 3) 5 t ha−1 senna leaves; 4) 5 t ha−1 tithonia leaves + 25 kg P ha−1 as triple superphosphate (TSP); 5) 5 t ha−1 senna leaves + 25 kg P ha−1 (as TSP); and 6) 25 kg P ha−1 of TSP. Maize was used as a test crop. Decomposition and P and N release of tithonia and senna leaves were determined in a litterbag study. Tithonia + TSP applications tripled maize yields compared to the control, senna + TSP and tithonia sole application doubled yields, while senna sole applications did not increase yields substantially. A large residual yield was produced in the tithonia treatments in a subsequent crop. These yield results were consistent with the higher quality and faster release of N and P from the tithonia leaves compared to senna. The tithonia biomass transfer system can improve yields in the short term but has limitations because of the large amount of biomass and the associated labor requirements.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006123404071
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 36
    Digitale Medien
    Digitale Medien
    Estimates of current and historical fluxes of N, Ca, and K in the forest ecosystem Möhlin (1998)
    Springer
    GeoJournal 44 (1998), S. 73-89 
    Details
    ISSN: 1572-9893
    Schlagwort(e): element fluxes ; forest ecosystem ; acidification ; nitrogen ; base cations
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Geographie
    Notizen: Abstract Data on element fluxes (Ca, K, N) are presented which were obtained in the course of an extended project on element-cycling in a forested ecosystem near Möhlin, northwestern Switzerland. Current fluxes of Ca, K, and N could be compared with historical fluxes (1969–1993) with the help of soil chemistry inventories since 1969, data on the forest management, and atmospheric deposition. Since 1969, soil chemistry has significantly changed due to a distinct disintegration of humus. The decomposition of organic matter influenced strongly the element cycling. Due to this mineralization high amounts of N were released. It is, however, not fully clear in which chemical form N has been transferred out of the system. Two possible hypotheses on the N losses are defined. According to the calculated proton budget and measured element changes in the soil, it is hypothized that a large part of the mineralized organic N presumably was transformed into N2 or more likely into N2O. A complete nitrification of organically bound N to NO3 − is also discussed but is, however, considered as less probable. In contrast to K, Ca proved to be a very sensitive element: the exchangeable Ca stock has been decreased sharply. The analysis of the current fluxes of Ca, K, and N reveals that nitrogen is abundantly present in the forest system with the consequence that the ecological balance is shifted in favour of N. Accordingly, the supply of base cations is rather scarce for the plants. Furthermore, the influence of forest management on element fluxes seems to be substantial, especially on the fluxes of base cations, but can be reduced with simple measures (e.g. removal of the bark of coniferous trees).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006862704020
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 37
    Digitale Medien
    Digitale Medien
    A concept of selection for 'low input' wheat varieties (1998)
    Springer
    Euphytica 100 (1998), S. 95-100 
    Details
    ISSN: 1573-5060
    Schlagwort(e): genetic variation ; wheat genotypes ; nitrogen ; phosphorus ; potassium ; breeding ; low-input cultivars
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Nutrient efficiency in wheat is very complex. It includes two major types: nutrient acquisition efficiency and nutrient use efficiency. Various studies on wild, landraces, old, intermediate and new genotypes of cereals showed that the new varieties produced higher grain yields than the old varieties, and were also more efficient at using nutrients. Several spring wheat cultivars, representing almost all cultivars of spring wheat, released from the Federal Office for Cultivar Registration, Germany and published in the 'Descriptive List of Cultivars', were used to investigate the interactive effects between genotypes and the use efficiencies of the three macro nutrients N, P and K by the grain and straw. The results obtained in this study indicate that nutrient use efficiency of the single nutrients varies widely within recent cultivars. Some cultivars were identified as being multiple-nutrient use efficient. These are considered low-input cultivars. It appears that a special breeding programme of crop cultivars for low nutrient and stress conditions could be successful. Improved cultivar response to nutrients will help to reduce inputs and hence protect the environment.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1018308023391
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 38
    Digitale Medien
    Digitale Medien
    Fine root turnover of irrigated hedgerow intercropping in Northern Kenya (1998)
    Springer
    Plant and soil 198 (1998), S. 19-31 
    Details
    ISSN: 1573-5036
    Schlagwort(e): Acacia saligna ; agroforestry ; nitrogen ; root decomposition ; root distribution ; root turnover ; Sorghum bicolor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Fine root turnover (〈2 mm) was determined from repeated measurements of root distribution up to 120 cm soil depth by core sampling in four month intervals. Sole cropped Sorghum bicolor and Acacia saligna were compared with the agroforestry combination in an alley cropping system in semiarid Northern Kenya. Three methods for the calculation of root production were used: the max-min, balancing-transfer and compartment-flow method. The highest root biomass was found in the topsoil for all cropping systems, though trees had a deeper root system. Trees and crops had a similar amount of below-ground biomass during the vegetation period (0.3 and 0.4 Mg DM ha-1 120 cm-1), but in the agroforestry combination root biomass was more than the sum of the sole cropped systems (1.1 Mg DM ha-1 120 cm-1). The tree system showed a very static root development with little fluctuation between seasons, whereas root biomasses were very dynamic in the crop and tree + crop systems. Root production was highest in the tree + crop combination with 2.1 Mg DM ha-1 a-1, with about 50% less in sole cropped trees and crops. Root N input to soil decreased in the order tree + crop〉tree〉crop system with 13.5, 11.0 and 3.2 kg N ha-1 a-1, and cannot be estimated from total below-ground biomass or carbon turnover, as N is accumulated in senescing roots. Such low N input to soil stresses the need for investigating other processes of nutrient input from roots to soil. Areas of highest N input were identified in the topsoil under the tree row in the tree system. Resource utilisation and C and N input to soil were highest with a combination of annual and perennial crops.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004293910977
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 39
    Digitale Medien
    Digitale Medien
    Evaluation of the stem injection technique and subsequent15 N partitioning in red alder crowns (1998)
    Springer
    Plant and soil 198 (1998), S. 63-69 
    Details
    ISSN: 1573-5036
    Schlagwort(e): allocation ; Alnus ; nitrogen ; nitrogen fixation ; resorption ; translocation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Red alder (Alnus rubra Bong.) trees were labeled with15 NO- 3 or15 NH+ 4 using the stem-injection method. Leaves were sampled 3 and 15 months subsequent to injection within several crown positions, including top, bottom, proximal, medial, and distal. Stem injection of both15 NH+ 4 and15 NO- 3 at levels approaching 1% of crown N effectively labeled red alder trees. Although more variable, 15NO- 3 may have been more efficient in initial labeling. The distribution of 15N in the crown was uniform 3 months after labeling, but was diluted in the distal and top positions by the following year. In both years there was a clear increase in total N concentration toward the periphery of the tree. This increase became more pronounced with increasing crown size and crown closure. Crown position with respect to light availability may be the most important determinant in N allocation in red alder foliage.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004275316217
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 40
    Digitale Medien
    Digitale Medien
    Changes in carbon, nitrogen and phosphorus levels due to deforestation and cultivation: A case study in Simlipal National Park, India (1998)
    Springer
    Plant and soil 198 (1998), S. 137-145 
    Details
    ISSN: 1573-5036
    Schlagwort(e): carbon ; cultivation ; deforestation ; nitrogen ; phosphorus ; tropics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The study area, within the Simlipal National Park, India, provides a rare variety of soil sampling sites. These include virgin forests in the proximity of several cultivated areas (where no chemical fertilizers or any modern technology has been used and where periods of cultivation vary from 5 to a little over 100 yr); samples from evergreen forests, deciduous forests and natural grasslands could also be obtained. The availability of numerous such samples made it possible to use statistical methods to evaluate the changes. This study showed that deforestation and cultivation result in statistically significant (P0.05) reduction in organic C, total N and C:N ratios but no significant changes in total and available P levels; C:P and N:P ratios are also reduced. Loss of organic C and N occurs rapidly in the first 15 yr of cultivation and reaches quasi-steady state values around 1–2% organic C and 0.1–0.2% total N; extent of reduction is not related to initial levels. Significant reduction in C:N, C:P ratios following cultivation suggest that mineralisation losses of C are higher than loss of N whereas loss of P is lowest. Lack of significant correlation between organic C and P levels in all types of soils, suggests that the bulk of the P is in the inorganic form. Highest levels of organic C and N were observed in evergreen forests followed by deciduous forests, grasslands and cultivated areas in that order; total and available P levels, however, showed no significant differences. Evergreen vegetative cover appears to provide the ideal environment for organic matter accumulation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004391615003
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 41
    Digitale Medien
    Digitale Medien
    Salinity and fish effects on Salton Sea microecosystems: water chemistry and nutrient cycling (1998)
    Springer
    Hydrobiologia 381 (1998), S. 105-128 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Microcosms ; Salton Sea ; saline lakes ; microcosms ; salinity ; ionic composition ; oxygen ; pH ; nutrients ; nitrogen ; phosphorus ; silicon ; fish ; grazing ; Oreochromis mossambicus ; Gammarus mucronatus ; Artemia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A 15 month long experiment was undertaken to document responses of the Salton Sea biota to experimentally manipulated salinity levels (30, 39, 48, 57, and 65 g l-1) in 312-liter fiberglass tanks maintained outdoors. At two salinities (39 and 57 g l-1) microcosms were set up each having one small tilapia ( Oreochromis mossambicus) in order to assess its influence on the system. To 28 tanks filled with Salton Sea water diluted to 30 g l-1, different salts (NaCl, Na2SO_4, MgSO4 · 7H2O, KCl) were added in constant proportions to produce the desired salinity levels. Salton Sea shoreline sediment was added to the bottom of each tank, and inocula of algae and invertebrates were added on several occasions. Invertebrate populations, phytoplankton, periphyton, and water chemistry were monitored at regular intervals. This article present the results concerning water chemistry and nutrient cycling. There was no apparent increase in salinity over time, though ∼ 1190 l of tapwater with a salinity of ∼ 0.65 g l-1 were added to each tank during the experiment. Ionic composition varied both among treatments and over time to some degree. Ca2 concentrations were the same at all salinities, while K1 concentrations were 〉3 times greater at the highest salinity than at the lowest. pH showed little consistent variation among salinities until the last few months when it was higher by ∼ 0.4 units at the two higher salinities than at the lower ones; it was unaffected by fish. Absolute oxygen concentrations were negatively correlated with salinity, and occasionally depressed by the presence of fish. PO3-4, dissolved organic phosphorus, and particulate phosphorus concentrations were often reduced by 30–80% at 65 g l-1 relative to lower salinities and by the presence of fish. Early in the experiment NO2-3 concentrations were 〉2 times higher at 57 and 65 g l-1 than at lower salinities, but otherwise effects of salinity on dissolved forms of nitrogen were not marked; particulate nitrogen was much lower at 65 g l-1 than at other salinities and also was reduced by up to 90% by the presence of fish. Silica concentrations increased over time at all salinities, but, relative to those at lower salinities, were reduced by 60–90% at 65 g l-1 by abundant periphytic diatoms. The TN:TP ratio (molar basis) was 24–30 initially and 35–110 at the end of the experiment; it was positively correlated with salinity and the presence of fish. Mechanisms accounting for the above patterns involve principally the biological activities of phytoplankton and periphyton, as modified by grazing by Artemia franciscana and Gammarus mucronatus, and the feeding and metabolic activities of the tilapia. The large reduction in water column TN and TP levels brought about by the fast-growing, phyto- and zooplanktivorous tilapia suggest that amelioration of the Salton Sea's hypereutrophic state might be assisted by a large scale, sustained yield fish harvesting operation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003227624686
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 42
    Digitale Medien
    Digitale Medien
    Population growth and production of Habrotrocha rosa Donner (Rotifera: Bdelloidea) and its contribution to the nutrient supply of its host, the northern pitcher plant, Sarracenia purpurea L. (Sarraceniaceae) (1998)
    Springer
    Hydrobiologia 385 (1998), S. 193-200 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Habrotrocha rosa ; nitrogen ; phosphorus ; population dynamics ; predation ; rotifers ; Sarracenia purpurea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The population growth and biomass production of the pitcher-plant (Sarracenia purpurea L.) inquiline, Habrotocha rosa Donner (Rotifera: Bdelloidea), its consumption by other pitcher-plant inqulines, and its excretion of phosphorus (PO4–P) and nitrogen (NO3–N and NH4–N), were investigated in laboratory experiments. Observed population growth and production rate of H. rosa were higher at pH 4 (2.3 rotifers d-1) than at pH 3 (1.3 rotifers d-1), 5 (1.9 rotifers d-1), or 6 (0.8 rotifers d-1). Populations of H. rosa are an abundant and reliable food source for larvae of the dipteran inqulines Wyeomyia smithii (Coq.) and Blaesoxipha fletcheri (Aldrich) that co-occur with H. rosa in S. purpurea pitchers. Abundance of H. rosa within a pitcher is negatively associated with abundance of dipteran larvae, and these larvae consume rotifers in direct proportion to rotifer density (Type I functional response). Habrotrocha rosa may also account for the majority of the plant's supply of N and P. An average population of rotifers in the field (∼400 per pitcher) can excrete ∼5.2 μg NO3-N, ∼3.91 μg NH4-N, and ∼18.4 μg PO4–P per day into a single leaf, and excretion rate is independent of water pH. Over the six-month growing season of pitcher-plants in Massachusetts, U.S.A., we estimate that rotifers could supply 8.8–43 mg of N and 18.2–88 mg of P. These values far exceed the amount of N and P previously estimated to be supplied annually to the plants through insect capture or rainfall.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003566729588
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 43
    Digitale Medien
    Digitale Medien
    Population growth and production of Habrotrocha rosa Donner (Rotifera: Bdelloidea) and its contribution to the nutrient supply of its host, the northern pitcher plant, Sarracenia purpurea L. (Sarraceniaceae) (1998)
    Springer
    Hydrobiologia 385 (1998), S. 193-200 
    Details
    ISSN: 1573-5117
    Schlagwort(e): Habrotrocha rosa ; nitrogen ; phosphorus ; population dynamics ; predation ; rotifers ; Sarracenia purpurea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The population growth and biomass production of the pitcher-plant (Sarracenia purpurea L.) inquiline, Habrotocha rosa Donner (Rotifera: Bdelloidea), its consumption by other pitcher-plant inqulines, and its excretion of phosphorus (PO4–P) and nitrogen (NO3–N and NH4–N), were investigated in laboratory experiments. Observed population growth and production rate of H. rosa were higher at pH 4 (2.3 rotifers d-1) than at pH 3 (1.3 rotifers d-1), 5 (1.9 rotifers d-1), or 6 (0.8 rotifers d-1). Populations of H. rosa are an abundant and reliable food source for larvae of the dipteran inqulines Wyeomyia smithii (Coq.) and Blaesoxipha fletcheri (Aldrich) that co-occur with H. rosa in S. purpurea pitchers. Abundance of H. rosa within a pitcher is negatively associated with abundance of dipteran larvae, and these larvae consume rotifers in direct proportion to rotifer density (Type I functional response). Habrotrocha rosa may also account for the majority of the plant's supply of N and P. An average population of rotifers in the field (∼400 per pitcher) can excrete ∼5.2 μg NO3-N, ∼3.91 μg NH4-N, and ∼18.4 μg PO4–P per day into a single leaf, and excretion rate is independent of water pH. Over the six-month growing season of pitcher-plants in Massachusetts, U.S.A., we estimate that rotifers could supply 8.8–43 mg of N and 18.2–88 mg of P. These values far exceed the amount of N and P previously estimated to be supplied annually to the plants through insect capture or rainfall.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1003566729588
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 44
    Digitale Medien
    Digitale Medien
    Holling's Figure-Eight Model: A Technical Reevaluation in Relation to Climate Change and Biodiversity (1998)
    Springer
    Environmental monitoring and assessment 49 (1998), S. 157-168 
    Details
    ISSN: 1573-2959
    Schlagwort(e): biodiversity ; carbon storage ; climate change ; conservation ; creative destruction ; ecological succession ; ecosystem stability ; Holling figure-eight ; nitrogen ; resilience
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract Holling proposed a four-phase conceptual model of ecosystem dynamics that includes exploitation, conservation, and destructive and renewal components to explain the failure of many natural resource management schemes. The model is drawn as a sideways figure-eight i.e. ∞. There are two dimensions in this model, connectivity (abscissa) and the amount of capital stored in the system (ordinate). This conceptual model has been suggested as a guide to thinking about the impact of climate change on biodiversity, but the two dimensions are insufficient and the alignment of the figure-eight model is problematic when compared with actual data. Kay has adjusted the dimensions of the figure-eight model and renamed the abscissa as exergy stored and the ordinate as exergy consumed. We realign the original figure-eight model, labeling the abscissa as carbon stored and the ordinate as nutrients, such that the relative values of both axes are in qualitative agreement with data from four different studies. This new alignment is then shown to fit relatively well with Holling's original labels. This revision of the figure-eight model brings Holling's model into agreement with observations and provides insight into the linkages between biodiversity and climate change.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005813702080
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 45
    Digitale Medien
    Digitale Medien
    Spatial and Temporal Variabilities in Nitrogen and Phosphorous in the Nakdong River System, Korea (1998)
    Springer
    Water, air & soil pollution 102 (1998), S. 37-60 
    Details
    ISSN: 1573-2932
    Schlagwort(e): behavior ; distribution ; Nakdong River ; nitrogen ; phosphorus ; spatial ; temporal
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract The concentrations of nitrogen (N) and phosphorous (P) species and relevant hydrographic parameters were determined in main stream and tributary waters of the Nakdong River system during the periods of May through October 1994. During the entire period, the total N (TN) and total P (TP) concentrations in surface waters were found within the ranges of 0.4–7.0 (N=241) and 0.02–1.536 mg L-1 (N=241), respectively. To help derive meaningful interpretations of temporal and geographical variabilities in the nutrient bahavior, the entire data were evaluated for each individual parameter after employing several different grouping schemes. The results of this comparative analysis can be expressed in terms of: (1) high summer/fall ratios for most of nutrient species; and (2) low summer/fall ratios for most of nutrient-to-nutrient ratios and relevant hydrographic parameters. Interestingly, while the former case was found to be more significant in tributary waters than main stream waters, such geographical dependence was not strongly evident for the latter case. A z-statistic test, conducted to check the significance of temporal (between summer and fall) and spatial (between tributary and main stream regions) differences, confirm that the observed variabilities are in most cases strong enough for most of variables studied – nutrient species, their ratios, and relevant hydrographic parameters. In addition, comparison of nutrient species between dissolved and particulate phases reveals several interesting features. Unlike dissolved nutrient species, the concentrations of particulate N or P (PN or PP) exhibited quite extraoridanry behavior. While PN appears to be rather minor component of the total N budget for the Nakdong river, PP seems to make rather strong contributions to its total P budgets with its strong input from tributary waters during rainy summer season. Through an application of correlation analysis, relationships between different parameters were investigated for both before and after the grouping of data sets. The overall picture of this analysis showed that nutrient species were strongly correlated with each other, while the strongest correlations were among such hydrographic parameters as DO, BOD, COD, and conductivity. This analysis was further conducted to more deliberately divided data groups. The results of analyses on these sub-grouped data sets indicate that the occurrences of significant corelations were common from tributary waters relative to main streams for both (1) between different nutrient species and (2) between nutrient and hydrographic parameters. Using the line of evidence gathered from the statistical tests and from the correlation analysis, we conclude that the environmental health of the Nakdong river system is affected by the combined effects of various factors and processes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1004973616860
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 46
    Digitale Medien
    Digitale Medien
    Leaching of Nutrients, Organic Carbon and Iron from Finnish Forestry Land (1998)
    Springer
    Water, air & soil pollution 105 (1998), S. 239-250 
    Details
    ISSN: 1573-2932
    Schlagwort(e): Finland ; forested catchments ; iron ; leaching ; nitrogen ; nutrients ; organic carbon ; peatland ; phosphorus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Energietechnik
    Notizen: Abstract This study provides an assessment of the spatial variability of the long-term leaching of nutrients, total organic carbon (TOC) and iron (Fetot) from 22 forested catchments (0.69-56 km2), distributed across all but the northenmost areas of Finland. The natural, unmanaged Kruunuoja catchment is located in a national park, while the other catchments represent Finnish forestry land. The average leaching of Ptot (4.2 kg km-2 yr-1) from the Kruunuoja catchment was small compared to the catchments representing forestry land (on average 10 kg km-2 yr-1). Moreover, P fertilization was the most important predictor for the spatial variation in Ptot leaching (r2=0.45). Leaching of TOC, Fetot and N compounds was not closely related to forestry practices. Median C/N ratio in the study streams was high (range 34-66). The average inorganic N proportion and leaching of Ptot were lowest in the Kruunuoja catchment (7.3 % and 2.8 kg km-2 yr-1, respectively) and highest in the southernmost Teeressuonoja catchment (54 % and 100 kg km-2 yr-1, respectively) located in the highest N deposition area. The most important forestry practices since the 1960's have affected about 2.4 % of the area of study sites per year (cf. 2% in the entire country in 1991). Moreover, the mean annual runoff from the catchments (230-430 mm yr-1) agrees with the mean annual runoff from Finland (301 mm yr-1). Consequently, the results of the study catchments can be used to estimate average total annual leaching from Finnish forestry land: 2,700 t of Ptot, 48,000 t of Ntot, 110,000 t of Fetot and 1.5 million t of TOC.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005049408225
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 47
    Digitale Medien
    Digitale Medien
    Folding type-specific secondary structure propensities of amino acids, derived from α-helical, β-sheet, α/β, and α+β proteins of known structures (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 35-49 
    Details
    ISSN: 0006-3525
    Schlagwort(e): folding type-specific secondary structure propensities ; amino acids ; α-helical proteins ; β sheet proteins ; α/β proteins ; α+β proteins ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Folding type-specific secondary structure propensities of 20 naturally occurring amino acids have been derived from α-helical, β-sheet, α/β, and α+β proteins of known structures. These data show that each residue type of amino acids has intrinsic propensities in different regions of secondary structures for different folding types of proteins. Each of the folding types shows markedly different rank ordering, indicating folding type-specific effects on the secondary structure propensities of amino acids. Rigorous statistical tests have been made to validate the folding type-specific effects. It should be noted that α and β proteins have relatively small α-helices and β-strands forming propensities respectively compared with those of α+β and α/β proteins. This may suggest that, with more complex architectures than α and β proteins, α+β and α/β proteins require larger propensities to distinguish from interacting α-helices and β-strands. Our finding of folding type-specific secondary structure propensities suggests that sequence space accessible to each folding type may have differing features. Differing sequence space features might be constrained by topological requirement for each of the folding types. Almost all strong β-sheet forming residues are hydrophobic in character regardless of folding types, thus suggesting the hydrophobicities of side chains as a key determinant of β-sheet structures. In contrast, conformational entropy of side chains is a major determinant of the helical propensities of amino acids, although other interactions such as hydrophobicities and charged interactions cannot be neglected. These results will be helpful to protein design, class-based secondary structure prediction, and protein folding. © 1998 John Wiley & Sons, Inc. Biopoly 45: 35-49, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 48
    Digitale Medien
    Digitale Medien
    Torsional control of double-stranded DNA branch migration (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 69-83 
    Details
    ISSN: 0006-3525
    Schlagwort(e): DNA branched junctions ; branch migration ; superhelical torque ; control of DNA structure ; endonuclease VII ; nanomechanical device ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: DNA branched junctions are analogues of Holliday junction recombination intermediates. Partially mobile junctions contain a limited amount of homology flanking the branch point. A partially mobile DNA branched junction has been incorporated into a synthetic double-stranded circular DNA molecule. The junction is flanked by four homologous nucleotide pairs, so that there are five possible locations for the branch point. Two opposite arms of the branched junction are joined to form the circular molecule, which contains 262 nucleotides to the base of the junction. This molecule represents a system whereby torque applied to the circular molecule can have an impact on the junction, by relocating its branch point. Ligation of the molecule produces two topoisomers; about 87% of the product is a relaxed molecule, and the rest is a molecule with one positive supercoil. The position of the branch point is assayed by cleaving the molecule with endonuclease VII. We find that the major site of the branch point in the relaxed topoisomer is at the maximally extruded position in the relaxed molecule. Upon the addition of ethidium, the major site of the branch point migrates to the minimally extruded position. © 1998 John Wiley & Sons, Inc. Biopoly 45: 69-83, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 49
    Digitale Medien
    Digitale Medien
    Conformational change and aggregation of κ-carrageenan studied by flow field-flow fractionation and multiangle light scattering (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 85-96 
    Details
    ISSN: 0006-3525
    Schlagwort(e): conformation ; aggregation ; κ-carrageenan ; flow field-flow fractionation ; multiangle light scattering ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relatively novel combination of flow field-flow fractionation (FFF) and multiangle light scattering (MALS) was employed to study a nondegraded κ-carrageenan in different 0.1M salt solutions. The applicability of the technique was tested, and the effects of salt type and salt composition on the molar mass and radius of gyration were studied. A conformational ordering was induced at room temperature by switching the solvent from 0.1M NaCl (coil form) to 0.1M NaI (helix form). An approximate doubling of the average molar mass and an increase in radius of gyration was then observed, in agreement with results obtained previously using size exclusion chromatography-MALS. This increase in size was attributed to conformational ordering and to the formation of double helices. Severe aggregation was observed above 40% CsI in the 0.1M mixed salt solution of CsI and NaI. This was ascribed to the association of helices into large aggregates. For these large associates, having molar masses of several millions, a reversal of the elution order in flow FFF was detected. © 1998 John Wiley & Sons, Inc. Biopoly 45: 85-96 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 50
    Digitale Medien
    Digitale Medien
    Calculations on the low energy conformers of N-acetyl-D-alanyl-D-alanine (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 119-133 
    Details
    ISSN: 0006-3525
    Schlagwort(e): conformations of D-alanyl-D-alanine ; β-lactam ; structural overlay ; AMBER force field ; AM1 ; ab initio ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this article a conformational analysis of the D-alanyl-D-alanine dipeptide, both charged and neutral, has been carried out. The preferred conformations were determined by means of ab initio and semiempirical quantum, together with empirical force field calculations. The AMBER* force field and the 6-31 + G** and 6-31G** ab initio levels give rise to a coincident minimum energy structure, which, on the other hand, differs from that determined by AM1, 3-21 + G, and 3-21G. The solvent effect on the different charged and neutral conformations have been considered through the AMSOL semiempirical method. A quantification regarding the structural similarities between the different dipeptide conformations and the ampicillin has been performed. The results show that the best overlay is attained by the minimum structure energy obtained by using the 6-31 + G** methodology, which presents a planar amidic nitrogen. © 1998 John Wiley & Sons, Inc. Biopoly 45: 119-133, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 51
    Digitale Medien
    Digitale Medien
    C6-oxidized cellulose: Ion interactions with mono- and divalent cations (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 157-163 
    Details
    ISSN: 0006-3525
    Schlagwort(e): chemical oxidation ; cellulose ; conformational transition ; capillary viscosity ; microcalorimetry ; calcium ions ; gels ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The conformational behavior of different molecular weight fractions of a synthetic C6-oxidized derivative of cellulose were investigated by means of capillary viscometry, CD, and microcalorimetric measurements. Experiments were carried out in the presence of either monovalent or divalent counterions.The experimental data indicated that C6-oxidized cellulose can assume an ordered extended conformation at low ionic strength, induced by the intrachain repulsions of negative charges. This conformation was suggested to be very similar to the fully extended structure of cellulose. In addition to this, upon increasing the ionic strength, a conformational transition of the order-to-disorder type occurred. In fact, the screening of the electrostatic repulsions introduced a number of conformational kinks into the cellulosic backbone, which enabled the polymer to assume a more coiled conformation hence producing less viscous aqueous solutions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 157-163, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 52
    Digitale Medien
    Digitale Medien
    Conformational stability of biological polyelectrolytes: Evaluation of enthalpy and entropy changes of conformational transitions (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 203-216 
    Details
    ISSN: 0006-3525
    Schlagwort(e): conformational stability ; biological polyelectrolytes ; enthalpy ; entropy ; conformational transitions ; carrageenan ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new method is proposed for the determination of the enthalpy and entropy changes of nonionic origin upon conformational transition of linear biopolyelectrolytes in solution. For all transition midpoints, defined by given temperature and ionic strength, the total free energy change of the system is zero, which means that the nonionic contribution to the free energy change is equal in value and opposite in sign to the polyelectrolytic one. The counterion condensation theory of linear polyelectrolytes provides for the appropriate analytical expression to be used in such calculations. Linear plots of the proper functions of the calculated free energy changes vs the proper functions of temperature allows for the determination of the enthalpic and entropic terms of the nonionic free energy change of transition.The method has been applied to the extensive available data of the ion-induced conformational change of κ-carrageenan, a linear sulfated galactan extracted from seaweeds. The method has proved very successful, with the results showing a remarkable convergency of the enthalpy values for different monovalent counterions. On the other hand, the above approach has made it possible to explain the known effect of counterion specificity on the transition by a small difference in the nonionic entropic contributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 203-216, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 53
    Digitale Medien
    Digitale Medien
    UV resonance Raman spectroscopy of DNA and protein constituents of viruses: Assignments and cross sections for excitations at 257, 244, 238, and 229 nm (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 247-256 
    Details
    ISSN: 0006-3525
    Schlagwort(e): uv resonance Raman spectroscopy ; Raman cross section ; hypochromism ; DNA ; deoxynucleoside ; protein ; aromatic amino acid ; virus assembly ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Ultraviolet resonance Raman (UVRR) spectra of H2O and D2O solutions of the nucleoside (dA, dG, dC, dT) and aromatic amino acid (Phe, Trp, Tyr) constituents of DNA viruses have been obtained with laser excitation wavelengths of 257, 244, 238, and 229 nm. Using the 981 cm-1 marker of Na2SO4 as an internal standard, Raman frequencies and scattering cross sections were evaluated for all prominent UVRR bands at each excitation wavelength. The results show that UVRR cross sections of both the nucleosides and amino acids are strongly dependent on excitation wavelength and constitute sensitive and selective probes of the residues. The results provide a library of UVRR marker bands for structural analysis of DNA viruses and other nucleoprotein assemblies. © 1998 John Wiley & Sons, Inc. Biopoly 45: 247-256, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 54
    Digitale Medien
    Digitale Medien
    Lumbricus terrestris hemoglobin: A comparison of small-angle X-ray scattering and cryoelectron microscopy data (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 289-298 
    Details
    ISSN: 0006-3525
    Schlagwort(e): hemoglobin ; hexagonal bilayer ; Lumbricus ; electron microscopy ; three-dimensional reconstruction ; small-angle x-ray scattering ; three-dimensional models ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The quaternary structure of Lumbricus terrestris hemoglobin was investigated by small-angle x-ray scattering (SAXS). Based on the SAXS data from several independent experiments, a three-dimensional (3D) consensus model was established to simulate the solution structure of this complex protein at low resolution (about 3 nm) and to yield the particle dimensions. The model is built up from a large number of small spheres of different weights, a result of the two-step procedure used to calculate the SAXS model. It accounts for the arrangement of 12 subunits in a hexagonal bilayer structure and for an additional central unit of cylinder-like shape. This model provides an excellent fit of the experimental scattering curve of the protein up to h = 1 nm-1 and a nearly perfect fit of the experimental distance distribution function p(r) in the whole range. Scattering curves and p(r) functions were also calculated for low-resolution models based on 3D reconstructions obtained by cryoelectron microscopy (EM). The calculated functions of these models also provide a very good fit of the experimental scattering curve (even at h 〉 1 nm-1) and p(r) function, if hydration is taken into account and the original model coordinates are slightly rescaled. The comparison of models reveals that both the SAXS-based and the EM-based model lead to a similar simulation of the protein structure and to similar particle dimensions. The essential differences between the models concern the hexagonal bilayer arrangement (eclipsed in the SAXS model, one layer slightly rotated in the EM model), and the mass distribution, mainly on the surface and in the central part of the protein complex. © John Wiley & Sons, Inc. Biopoly 45: 289-298, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 55
    Digitale Medien
    Digitale Medien
    Conformational changes due to vicinal glycosylation: The branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide compared with its parent disaccharides* (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 417-432 
    Details
    ISSN: 0006-3525
    Schlagwort(e): conformational changes ; vicinal glycosylation ; branched α-l-Rhap(1-2)[β-d-Galp(1-3)]-β-d-Glc1-OMe trisaccharide ; parent disaccharides ; hydrogen bond ; isotope effect ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Conformations of the α-l-Rhap(1-2)-β-d-Glc1-OMe and β-d-Galp(1-3)-β-d-Glc1-OMe disaccharides and the branched title trisaccharide were examined in DMSO-d6 solution by 1H-nmr. The distance mapping procedure was based on rotating frame nuclear Overhauser effect (NOE) constraints involving C- and O-linked protons, and hydrogen-bond constraints manifested by the splitting of the OH nmr signals for partially deuteriated samples. An “isotopomer-selected NOE” method for the unequivocal identification of mutually hydrogen-bonded hydroxyl groups was suggested. The length of hydrogen bonds thus detected is considered the only one motionally nonaveraged nmr-derived constraint. Molecular mechanics and molecular dynamics methods were used to model the conformational properties of the studied oligosaccharides. Complex conformational search, relying on a regular Φ,Ψ-grid based scanning of the conformational space of the selected glycosidic linkage, combined with simultaneous modeling of different allowed orientations of the pendant groups and the third, neighboring sugar residue, has been carried out. Energy minimizations were performed for each member of the Φ,Ψ grid generated set of conformations. Conformational clustering has been done to group the minimized conformations into families with similar values of glycosidic torsion angles. Several stable syn and anti conformations were found for the 1→2 and 1→3 bonds in the studied disaccharides. Vicinal glycosylation affected strongly the occupancy of conformational states in both branches of the title trisaccharide. The preferred conformational family of the trisaccharide (with average Φ,Ψ values of 38°, 17° for the 1→2 and 48°, 1° for the 1→3 bond, respectively) was shown by nmr to be stabilized by intramolecular hydrogen bonding between the nonbonded Rha and Gal residues. © 1998 John Wiley & Sons, Inc. Biopoly 46: 417-432, 1998
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 56
    Digitale Medien
    Digitale Medien
    Buffer dependence of refractive index increments of protein solutions (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 489-492 
    Details
    ISSN: 0006-3525
    Schlagwort(e): refractive index increment ; proteins ; solvent ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The refractive index increment of a protein solution is a property not only of the protein, but also of the solvent. This is demonstrated theoretically and confirmed experimentally using analytical interferometry. © 1998 John Wiley & Sons, Inc. Biopoly 46: 489-492, 1998
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 57
    Digitale Medien
    Digitale Medien
    Editor's comments (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 1-1 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 58
    Digitale Medien
    Digitale Medien
    Conformational behavior of the HAV-VP3(110-121) peptidic sequence and synthetic analogs in membrane environments studied by CD and computational methods (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 479-492 
    Details
    ISSN: 0006-3525
    Schlagwort(e): hepatitis A ; synthetic peptides ; CD ; liposomes ; computational study ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The present study was undertaken to examine the structural features that may be important to explain the immunogenicity of the (110-121) peptide sequence (FWRGDLVFDFQV) of VP3 capsid protein of hepatitis A virus. A conformational analysis of the preferred conformations by CD and molecular mechanics was carried out. Present results suggest that the interaction with liposomes as biomembrane model induces and stabilizes the amphipathic β-structure of the peptide.To study the contribution of amino acid replacements at the RGD tripeptide as well as the influence of the peptide chain length on peptide conformation, solid-phase peptide synthesis of several peptide analogs was carried out and the peptide conformation was studied using CD spectroscopy. The results show that the RGD sequence is necessary to induce the β-structure in the presence of liposomes. © 1998 John Wiley & Sons, Inc. Biopoly 45: 479-492, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 59
    Digitale Medien
    Digitale Medien
    Liquid crystal formation in DNA fragment solutions (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 31-37 
    Details
    ISSN: 0006-3525
    Schlagwort(e): DNA liquid crystals ; DNA fragments ; screened Coulomb interactions ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The critical volume fractions pertaining to the formation of DNA liquid crystals were obtained from polarization microscopy, 31P-nmr, and phase separation experiments. The DNA length (approximately one to two times the persistence length 50 nm), ionic strength, and counterion variety dependencies are reported. The cholesteric-isotropic transition is interpreted in terms of the coexistence equations, which are derived from the solution free energy including orientational entropy and excluded volume effects. With the wormlike chain as reference system, the electrostatic contribution to the free energy is evaluated as a thermodynamic perturbation in the second virial approximation with a Debye-Hückel potential of mean force. The hard core contribution has been evaluated with scaled particle theory and/or a simple generalization of the Carnahan-Starling equation of state for hard spheres. For sufficiently high ionic strengths, the agreement is almost quantitative. At lower amounts of added salt deviations are observed, which are tentatively attributed to counterion screening effects. The contour length dependence agrees with a DNA persistence length 50 nm. © 1998 John Wiley & Sons, Inc. Biopoly 46: 31-37, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 60
    Digitale Medien
    Digitale Medien
    Gelation of gelatin observation in the bulk and at the air-water interface (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 245-252 
    Details
    ISSN: 0006-3525
    Schlagwort(e): gelatin ; gelation ; atomic force microscopy ; interfacial rheology ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Gelation of gelatin under various conditions has been followed by atomic force microscopy (AFM) with the objective of understanding more fully the structure formed during the gelation process. AFM images were obtained of the structures formed from both the bulk sol and in surface films during the onset of gelation. While gelation occurred in the bulk sol, the extent of helix formation was monitored by measurements of optical rotation, and the molecular aggregation was imaged by AFM. Interfacial gelatin films formed at the air-water interface were also studied. Measurements of surface tension and surface rheology were made periodically and Langmuir-Blodgett films were drawn from the interface to allow AFM imaging of the structure of the interfacial layer as a function of time. Structural studies reveal that at low levels of helical content the gelatin molecules assemble into aggregates containing short segments of dimensions comparable to those expected for gelatin triple helices. With time larger fibrous structures appear whose dimensions suggest that they are bundles of triple helices. As gelation proceeds, the number density of fibers increases at the expense of the smaller aggregates, eventually assembling into a fibrous network. The gel structure appears to be sensitive to the thermal history, and this is particularly important in determining the structure and properties of the interfacial films. © 1998 John Wiley & Sons, Inc. Biopoly 46: 245-252, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 61
    Digitale Medien
    Digitale Medien
    Ribozyme chemogenetics (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 65-81 
    Details
    ISSN: 0006-3525
    Schlagwort(e): nucleotide analogue interference mapping ; phosphorothioate ; group I intron ; interference suppression ; RNA ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this review I will outline several chemogenetic approaches used to determine the chemical basis of large ribozyme function and structure. The term chemogenetics was first used to describe site-specific functional group modification experiments in the analysis of DNA-protein interactions. Within the past few years equivalent experiments have been performed on large catalytic RNAs using both single-site substitution and interference mapping techniques with nucleotide analogues. While functional group mutagenesis is an important aspect of a chemogenetic approach, chemical correlates to genetic revertants and suppressors must also be realized for the genetic analogy to be intellectually valid and experimentally useful. Several examples of functional group revertants and suppressors have now been obtained within the Tetrahymena group I ribozyme. These experiments define an ensemble of tertiary hydrogen bonds that have made it possible to construct a detailed model of the ribozyme catalytic core. The model includes a functionally important monovalent metal ion binding site, a wobble-wobble receptor motif for helix-helix packing interactions, and a minor groove triple helix. © 1998 John Wiley & Sons, Inc. Biopoly 48: 65-81, 1998
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 62
    Digitale Medien
    Digitale Medien
    Design, synthesis, and analysis of conformationally constrained nucleic acids (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 83-96 
    Details
    ISSN: 0006-3525
    Schlagwort(e): nucleic acid ; disulfide cross-link ; structure ; dynamics ; stability ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this review I discuss straightforward and general methods to modify nucleic acid structure with disulfide cross-links. A motivating factor in developing this chemistry was the notion that disulfide bonds would be excellent tools to probe the structure, dynamics, thermodynamics, folding, and function of DNA and RNA, much in the way that cystine cross-links have been used to study proteins. The chemistry described has been used to synthesize disulfide cross-linked hairpins and duplexes, higher order structures like triplexes, nonground-state conformations, and tRNAs. Since the cross-links form quantitatively by mild air oxidation and do not perturb either secondary or tertiary structure, this modification should prove quite useful for the study of nucleic acids. © 1998 John Wiley & Sons, Inc. Biopoly 48: 83-96, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 63
    Digitale Medien
    Digitale Medien
    On the role of magnesium ions in RNA stability (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 113-135 
    Details
    ISSN: 0006-3525
    Schlagwort(e): divalent cations ; magnesium ; RNA ; ion binding ; RNA folding ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Divalent cations, like magnesium, are crucial for the structural integrity and biological activity of RNA. In this article, we present a picture of how magnesium stabilizes a particular folded form of RNA. The overall stabilization of RNA by Mg2+ is given by the free energy of transferring RNA from a reference univalent salt solution to a mixed salt solution. This term has favorable energetic contributions from two distinct modes of binding: diffuse binding and site binding. In diffuse binding, fully hydrated Mg ions interact with the RNA via nonspecific long-range electrostatic interactions. In site binding, dehydrated Mg2+ interacts with anionic ligands specifically arranged by the RNA fold to act as coordinating ligands for the metal ion. Each of these modes has a strong coulombic contribution to binding; however, site binding is also characterized by substantial changes in ion solvation and other nonelectrostatic contributions. We will show how these energetic differences can be exploited to experimentally distinguish between these two classes of ions using analyses of binding polynomials. We survey a number of specific systems in which Mg2+-RNA interactions have been studied. In well-characterized systems such as certain tRNAs and some rRNA fragments these studies show that site-bound ions can play an important role in RNA stability. However, the crucial role of diffusely bound ions is also evident. We emphasize that diffuse binding can only be described rigorously by a model that accounts for long-range electrostatic forces. To fully understand the role of magnesium ions in RNA stability, theoretical models describing electrostatic forces in systems with complicated structures must be developed. © 1999 John Wiley & Sons, Inc. Biopoly 48: 113-135, 1998
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 64
    Digitale Medien
    Digitale Medien
    Three-dimensional structure of the ion-chanel forming peptide trichorzianin TA VII bound to sodium dodecyl sulfate micelles (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 75-88 
    Details
    ISSN: 0006-3525
    Schlagwort(e): 1H-nmr ; molecular modeling ; peptaibol ; peptide-lipid interaction ; sodium dodecyl sulfate micelles ; trichorzianin TA VII ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Trichorzianin TA VII, Ac0 U1 A2 A3 U4 J5 Q6 U7 U8 U9 S10 L11 U12 P13 V14 U15 I16 Q17 Q18 Fol19, is a nonadecapeptide member of the peptaibol antibiotics biosynthesized by Trichoderma soil fungi, which is characterized by a high proportion of the α,α-dialkylated amino acids, α-aminoisobutyric acid (Aib, U) and isovaline (Iva, J), an acetylated N-terminus and a C-terminal phenylalaninol (Pheol, Fol). The main interest in such peptides stems from their ability to interact with phospholipid bilayers and form voltage-dependent transmembrane channels in planar lipid bilayers. In order to provide insights into the lipid-peptide interaction promoting the voltage gating, the conformational study of TA VII in the presence of perdeuterated sodium dodecyl sulfate (SDS-d25) micelles has been carried out. 1H sequential assignments have been performed with the use of two-dimensional homo- and -heteronuclear nmr techniques including double quantum filtered correlated spectroscopy, homonuclear Hartmann-Hahn, nuclear Overhauser effect spectroscopy, 1H-13C heteronuclear single quantum correlation, and heteronuclear multiple bond correlation. Conformational parameters, such as 3JNHCαH coupling constants, temperature coefficients of amide protons (Δδ/ΔTNH) and quantitative nuclear Overhauser enhancement data, lead to detailed structural information. Ninety-eight three-dimensional structures consistent with the nmr data were generated from 231 interproton distances and six Φ dihedral angle restraints, using restrained molecular dynamics and energy minimization calculations. The average rms deviation between the 98 refined structures and the energy-minimized average structure is 0.59 Å for the backbone atoms. The structure of trichorzianin TA VII associated with SDS micelles, as determined by these methods, is characterized by two right-handed helical segments involving residues 1-8 and 11-19, linked by a β-turn that leads to an angle about 90°-100° between the two helix axes; residues 18 and 19 at the end of the C-terminal helix exhibit multiple conformations. © 1998 John Wiley & Sons, Inc. Biopoly 46: 75-88, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 65
    Digitale Medien
    Digitale Medien
    Spectroscopic studies of 9-hydroxyellipticine binding to DNA (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 127-143 
    Details
    ISSN: 0006-3525
    Schlagwort(e): 9-hydroxyellipticine ; DNA ; CD ; linear dichroism ; resonance light scattering ; intercalation ; drug-drug interactions ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The binding of 9-hydroxyellipticine to calf thymus DNA, poly[d(A-T)]2, and poly-[d(G-C)]2 has been studied in detail by means of CD, linear dichroism, resonance light scattering, and molecular dynamics. The transition moment polarizations of 9-hydroxyelliptiycine were determined in polyvinyl alcohol stretched film. Spectroscopic solution studies of the DNA/drug complex are combined with theoretical CD calculations using the final 50 ps of a series of molecular dynamics simulations as input. The spectroscopic data shows 9-hydroxyellipticine to adopt two main binding modes, one intercalative and the other a stacked binding mode involving the formation of drug oligomers in the DNA major groove. Analysis of the intercalated binding mode in poly[d(A-T)]2 suggests the 9-hydroxyellipticine hydroxyl group lies in the minor groove and hydrogen bonds to water with the pyridine ring protruding into the major groove. The stacked binding mode was examined using resonance light scattering and it was concluded that the drug was forming small oligomer stacks rather than extended aggregates. Reduced linear dichroism measurements suggested a binding geometry that precluded a minor groove binding mode where the plane of the drug makes a 45° angle with the plane of the bases. Thus it was concluded that the drug stacks in the major groove. No obvious differences in the mode of binding of 9-hydroxyellipticine were observed between different DNA sequences; however, the stacked binding mode appeared to be more favorable for calf thymus DNA and poly[d(G-C)]2 than for poly[d(A-T)]2, an observation that could be explained by the slightly greater steric hindrance of the poly[d(A-T)]2 major groove. A strong concentration dependence was observed for the two binding modes where intercalation is favored at very low drug load, with stacking interactions becoming more prominent as the drug concentration is increased. Even at DNA : drug mixing ratios of 70:1 the stacked binding mode was still important for GC-rich DNAs. © 1998 John Wiley & Sons, Inc. Biopoly 46: 127-143, 1998
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 66
    Digitale Medien
    Digitale Medien
    Interaction of branched chain polymeric polypeptides with phospholipid model membranes (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 169-179 
    Details
    ISSN: 0006-3525
    Schlagwort(e): macromolecular carriers ; drug targeting and delivery ; branched chain synthetic polypeptides ; membrane-synthetic polypeptide interaction ; lipid monolayers/bilayers ; polymer therapeutics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The surface properties at the air/water interface and the interaction of branched chain polymeric polypeptides with a general formula poly[Lys-(DL-Alam-X1)], where X = Π (AK), Ser (SAK), or Glu (EAK), with phospholipids were investigated. Polylysine derivatives with polycationic (SAK, AK) or amphoteric (EAK) were capable to spread and form stable monomolecular layers. The stability of monolayers at the air/water interface was dependent on the side-chain terminal amino acid residue of polymers and can be described by SAK 〈 AK 〈 EAK order. The area per amino acid residue values calculated from compression isotherms were in the same range as compared to those of linear poly-α-amino acids and proteins. Moreover, these polymers interact with phospholipid monomolecular layers composed of dipalmitoyl phosphatidyl choline (DPPC) or DPPC/PG (PG: phosphatidyl glycerol; 95/5, mol/mol). Data obtained from compression isotherms of phospholipids spread on aqueous polymer solutions at different initial surface pressure indicated that insertion into lipid monolayers for SAK or AK is more pronounced than for EAK. The interaction between branched polypeptides and phospholipid membranes was further investigated using lipid bilayers with DPPC/PG and fluorescent probes located either at the polar surface [1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) sodium anilino naphthalene sulfonate (ANS)] or within the hydrophobic core (DPH) of the liposome. Changes in fluorescence intensity and in polarization were observed when TMA-DPH or ANS, but not DPH were used. Comparative data also indicate that all three polymers interact only with the outer surface of the bilayer, but even the most marked penetration of polycationic polypeptide (SAK) did not result in alteration of the ordered state of the alkyl chains in the bilayer. Taken together, data obtained from mono- or bilayer experiments suggest that the interaction between branched polymers and phospholipids are highly dependent on the charge properties (Ser vs Glu) and on the identity (Ser vs Ala) of side-chain terminating amino acids. The binding of polymers to the model membranes could be mainly driven by electrostatic forces, but the significant role of hydrophilic properties in case of SAK cannot be excluded. © 1998 John Wiley & Sons, Inc. Biopoly 46: 169-179, 1998
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 67
    Digitale Medien
    Digitale Medien
    Relationship between conformation and geometry as evidenced by molecular dynamics simulation of Cα,α-dialkylated glycines (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 239-244 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Cα,α-dialkylated glycines ; molecular dynamics ; geometry and conformation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The relationship between the local backbone conformation and bond angles at Cα of symmetrically substituted Cα,α-dialkylated glycines (Cα,α-dimethylglycine or α-aminoisobutyric acid, Aib; Cα,α-diethylglycine, Deg; Cα,α-di-n-propylglycine, Dpg) has been investigated by molecular dynamics (MD) simulation adopting flat bottom harmonic potentials, instead of the usual harmonic restraints, for the Cα bond angles. The MD simulations show that the Cα bond angles are related to the local backbone conformation, irrespectively of the side-chain length of Aib, Deg, and Dpg residues. Moreover, the N-Cα-C′ (τ) angle is the most sensitive conformational parameter and, in the folded form, is always larger and more flexible than in the extended one. © 1998 John Wiley & Sons, Inc. Biopoly 46: 239-244, 1998
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 68
    Digitale Medien
    Digitale Medien
    Methionine ligation strategy in the biomimetic synthesis of parathyroid hormones (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 319-327 
    Details
    ISSN: 0006-3525
    Schlagwort(e): methionine ligation ; parathyroid hormones ; biomimetic ligation ; S-methylation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In biological systems, both proteolysis and aminolysis of amide bonds produce activated intermediates through acyl transfer reactions either inter- or intramolecularly. Protein splicing is an illustrative example that proceeds through a series of catalyzed acyl transfer reactions and culminates at an O- or S-acyl intermediate. This intermediate leads to an uncatalyzed acyl migration to form an amide bond in the spliced product. A ligation method mimicking the uncatalyzed final steps in protein splicing has been developed utilizing the acyl transfer amide-bond feature for the blockwise coupling of unprotected, free peptide segments at methionine (Met). The latent thiol moiety of Met can be exploited using homocysteine at the α-amino terminal position of a free peptide for transthioesterification with another free peptide containing an α-thioester to give an S-acyl intermediate. A subsequent, proximity-driven S- to N-acyl migration of this acyl intermediate spontaneously rearranges to form a homocysteinyl amide bond. S-methylation with excess p-nitrobenezensulfonate yields Met at the ligation site. The methionine ligation is selective and orthogonal, and is usually completed within 4 h when performed at slightly basic pH and under strongly reductive conditions. No side reactions due to acylation were observed with any other α-amines of both peptide segments as seen in the synthesis of parathyroid hormone peptides. Furthermore, cyclic peptide can also be obtained through the same strategy by placing both homocysteine at the amino terminus and the thioester at the carboxyl terminus in an unprotected peptide precursor. These biomimetic ligation strategies hold promise for engineering novel peptides and proteins. © 1998 John Wiley & Sons, Inc. Biopoly 46: 319-327, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 69
    Digitale Medien
    Digitale Medien
    Modeling the free solution electrophoretic mobility of short DNA fragments (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 359-373 
    Details
    ISSN: 0006-3525
    Schlagwort(e): boundary element method ; DNA electrophoresis ; electrophoretic mobility of DNA ; free solution electrophoretic mobility of DNA ; ion relaxation, DNA electrophoresis ; modeling electrophoresis of polyions ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Boundary element methods are used to model the free solution electrophoretic mobility of short DNA fragments. The Stern surfaces of the DNA fragments are modeled as plated cylinders that reproduce translational and rotational diffusion constants. The solvent-accessible and ion-accessible surfaces are taken to be coincident with the Stern surface. The mobilities are computed by solving simultaneously the coupled Navier-Stokes, Poisson, and ion-transport equations. The equilibrium electrostatics are treated at the level of the full Poisson-Boltzmann equation and ion relaxation is included. For polyions as highly charged as short DNA fragments, ion relaxation is substantial. At .11 M KCl, the simulated mobilities of a 20 base pair DNA fragment are in excellent agreement with experiment. At .04 M Tris acetate, pH = 8.0, the simulated mobilities are about 10-15% higher than experimental values and this discrepancy is attributed to the relatively large size of the Tris counterion. The length dependence of the mobility at .11 M KCl is also investigated. Earlier mobility studies on lysozyme are reexamined in view of the present findings. In addition to electrophoretic mobilities, the effective polyion charge measured in steady state electrophoresis and its relationship to the preferential interaction parameter γgG is briefly considered. © 1998 John Wiley & Sons, Inc. Biopoly 46: 359-373, 1998
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 70
    Digitale Medien
    Digitale Medien
    Aggregation of dermorphin and L-Ala dermorphin examined by light scattering at sub-NMR concentrations (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 341-346 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 71
    Digitale Medien
    Digitale Medien
    Correlation between rate of enzyme-substrate diffusional encounter and average Boltzmann factor around active site (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 355-360 
    Details
    ISSN: 0006-3525
    Schlagwort(e): diffusional encounter ; Brownian dynamics ; average Boltzmann factor ; acetylcholinesterase ; Poisson-Boltzmann ; electrostatics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The utility of the average Boltzmann factor around the active site of an enzyme as the predictor of the electrostatic enhancement of the substrate binding rate is tested on a set of data on wild-type acetylcholinesterase and 18 charge mutants recently obtained by Brownian dynamics simulations. A good correlation between the average Boltzmann factors and the substrate binding rate constants is found. The effects of single charge mutations on both the Boltzmann factor and the substrate binding rate constant are modest, i.e., 〈5 fold increase or decrease. This is consistent with the experimental results of Shafferman et al. but does not support their suggestion that the overall rate of the catalytic reaction is not limited by the diffusional encounter of acetylcholinesterase and its substrate. © 1998 John Wiley & Sons, Inc. Biopoly 45: 355-360, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 72
    Digitale Medien
    Digitale Medien
    Reconstructing the protein-water interface (1998)
    New York : Wiley-Blackwell
    Biopolymers 45 (1998), S. 469-478 
    Details
    ISSN: 0006-3525
    Schlagwort(e): molecular dynamics ; hydrated proteins ; crystal structures ; density distributions ; globular proteins ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using molecular dynamics simulations of fully hydrated proteins and analysis of crystal structures contained in the Protein Data Bank, we develop a transferable set of perpendicular radial distribution functions for water molecules around globular proteins. These universal functions may be used to reconstruct the unique three-dimensional solvent density distribution around every individual protein with a modest error. We discuss potential applications of this solvent treatment in protein x-ray crystallographic refinements and in theoretical modeling. We also present a fast, grid-based algorithm for construction of the perpendicular solvent density distributions. © 1998 John Wiley & Sons, Inc. Biopoly 45: 469-478, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 73
    Digitale Medien
    Digitale Medien
    Design strategies for the construction of independently folded polypeptide motifs (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 23-29 
    Details
    ISSN: 0006-3525
    Schlagwort(e): independently folded polypeptide motifs ; miniproteins ; natural target domains ; BBA motif ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this paper we present a redesign strategy for the development of uniquely folded polypeptide motifs of less than 40 residues. These mini proteins are based on natural target domains, including the zinc finger domains (BBA motif) Nomenclature corresponds to the defined elements of secondary structure, beginning at the N-terminus of the peptide. Roman lettering refers to a specific motif while Greek characters correspond to the elements of secondary structure within that motif. and the disulfide-rich snake and scorpion toxins (BBB motif). These motifs are designed to act as the molecular framework for the construction of novel functional polypeptides. We will explore the structural determinants of the folded BBA motif, inspired by the zinc finger peptides, in relation to the redesign process. © 1998 John Wiley & Sons, Inc. Biopoly 47: 23-29, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 74
    Digitale Medien
    Digitale Medien
    Peptide ion channels: Design and creation of function (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 75-81 
    Details
    ISSN: 0006-3525
    Schlagwort(e): ion channel ; synthetic peptide ; de novo design ; template-assembled synthetic proteins ; supramolecular assembly ; membrane protein ; planer lipid bilayers ; amphiphilic peptide ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: To create ion channel function by synthetic peptides is a challenge in the de novo design of artificial membrane proteins. Amphiphilic α-helical motifs of ∼ 20 amino acid residues to span lipid bilayers are most often used for the creation of peptide ion channels. Template molecules to tether helical peptides have been employed to obtain more organized pore structures. Approaches to form molecular assembly of peptides in the membranes by hydrogen bonding have been also investigated. We have developed approaches to assemble helices with individual amino acid sequences to construct artificial helical proteins. Using one of these approaches, four helices corresponding to the voltage sensor segments (S4 in repeat I-IV) of the sodium channel were assembled on a peptide template to give a protein having ion channel activity with rectification. © 1998 John Wiley & Sons, Inc. Biopoly 47: 75-81, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 75
    Digitale Medien
    Digitale Medien
    Collagen mimetics (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 127-142 
    Details
    ISSN: 0006-3525
    Schlagwort(e): collagen mimetics ; triple helix ; peptoid ; template ; biophysics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Collagen peptidomimetics have been synthesized as an alternative to natural collagen. The incorporation of unnatural residues such as peptoids in the collagen sequences can demonstrate potent and specific biological activity and enhance the biostability against enzymatic degradation. Furthermore, the use of achiral peptoids simplifies synthetic strategies by reducing racemization problems. The peptoid residue N-isobutylglycine (Nleu) has been successfully incorporated into a series of collagen mimetics composed of Gly-Pro-Nleu, Gly-Nleu-Pro, and Gly-Nleu-Nleu. The discovery of template-assembled collagen mimetics and metal binding ability has laid the foundation for new opportunities in the design of novel collagen mimetic complexes. This review summarizes the synthesis and integrated biophysical analyses of the structures of these collagen mimetics. Solid phase segment condensation techniques have been utilized for the synthesis of the single chain and template-assembled analogues. The characterization of the collagen-like structures has been established by temperature-dependent optical rotation measurements, CD, NMR spectroscopy, and molecular modelling simulations. © 1998 John Wiley & Sons, Inc. Biopoly 47: 127-142, 1998
    Zusätzliches Material: 20 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 76
    Digitale Medien
    Digitale Medien
    Syntheses of squarylium-substituted alanine and its peptide, and formation of their thin films onto a poly(3-methylthiophene)/Au electrode (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 179-183 
    Details
    ISSN: 0006-3525
    Schlagwort(e): non-natural amino acid ; peptide ; squarylium dye ; thin film ; poly(3-methylthiophene) ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We designed a polypeptide that behaves as a photodevice by using a non-natural amino acid with replacement of an α-hydrogen by a squarylium dye and succeeded in syntheses of the non-natural amino acid derivative containing a squarylium and its peptide with trialanine Ala-Ala-Ala. Strong dye-dye interactions were confirmed by absorption and CD spectra for the peptide in 2,2,2-trifluoroethanol solution and in water suspension. The non-natural amino acid derivative could be deposited onto a PMeT/Au electrode by the micelle disruption method. © 1998 John Wiley & Sons, Inc. Biopoly 47: 179-183, 1998
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 77
    Digitale Medien
    Digitale Medien
    Editorial: Protein-protein interactions: Mimics and inhibitors (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 263-263 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 78
    Digitale Medien
    Digitale Medien
    New developments of the electrostatically driven monte carlo method: Test on the membrane-bound portion of melittin (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 117-126 
    Details
    ISSN: 0006-3525
    Schlagwort(e): electrostatically driven Monte Carlo method ; cluster analysis ; global energy minimum ; perturbed conformations ; conformational space ; lowest energy conformations ; polypeptide chain ; melittin, membrane-bound portion ; Empirical Conformational Energy Program for Peptides 3 ; annealing methods ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The electrostatically driven Monte Carlo (EDMC) method has been greatly improved by adding a series of new features, including a procedure for cluster analysis of the accepted conformations. This information is used to guide the search for the global energy minimum. Alternative procedures for generating perturbed conformations to sample the conformational space were also included. These procedures enhance the efficiency of the method by generating a larger number of low-energy conformations.The improved EDMC method has been used to explore the conformational space of a 20-residue polypeptide chain whose sequence corresponds to the membrane-bound portion of melittin. The ECEPP/3 (Empirical Conformational Energy Program for Peptides) algorithm was used to describe the conformational energy of the chain. After an exhaustive search involving 14 independent runs, the lowest energy conformation (LEC) (-91.0 kcal/mol) of the entire study was encountered in four of the runs, while conformations higher in energy by no more than 1.8 kcal/mol were found in the remaining runs with the exception of one of them (run 8). The LEC is identical to the conformation found recently by J. Lee, H.A. Scheraga, and S. Rackovsky [(1998) “Conformational Analysis of the 20-Residue Membrane-Bound Portion of Melittin by Conformational Space Annealing,” Biopolymers, Vol. 46, pp. 103-115] as the lowest energy conformation obtained in their study using the conformational space annealing method. These results suggest that this conformation corresponds to the global energy minimum of the ECEPP/3 potential function for this specific sequence; it also appears to be the conformation of lowest free energy. © 1998 John Wiley & Sons, Inc. Biopoly 46: 117-126, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 79
    Digitale Medien
    Digitale Medien
    Renaturation of condensed DNA studied through a decoupling scheme (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 195-200 
    Details
    ISSN: 0006-3525
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 80
    Digitale Medien
    Digitale Medien
    Band broadening in gel electrophoresis: Scaling laws for the dispersion coefficient measured by FRAP (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 201-214 
    Details
    ISSN: 0006-3525
    Schlagwort(e): band broadening ; dispersion ; DNA ; gels ; electrophoresis ; fluorescence recovery ; photobleaching ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We determined quantitatively the band broadening effect during gel electrophoresis by measuring the longitudinal dispersion coefficient Dx, with a fluorescence recovery after photobleaching setup, coupled to an electrophoretic cell. We carried out measurements as a function of the electric field, the average pore size, and the molecular length of DNA fragments. Our results are in good agreement with the predictions of the biased reptation model with fluctuations described by T. A. Duke et al. [(1992) Physics Review Letters, vol. 69, pp. 3260-3263]. This agreement is observed on single-stranded DNA [persistence length ≅ 4 nm; B. Tinland et al. (1997) Macromolecules, vol. 30, pp. 5763-5765] in polyacrylamide gels and on double-stranded DNA (persistence length ≅ 50 nm) in agarose gels, two systems where the ratio between the average pore size and the Kuhn length is larger than 1. © 1998 John Wiley & Sons, Inc. Biopoly 46: 201-214, 1998
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 81
    Digitale Medien
    Digitale Medien
    Inherent DNA curvature and flexibility correlate with TATA box functionality (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 403-415 
    Details
    ISSN: 0006-3525
    Schlagwort(e): molecular dynamics ; DNA curvature ; DNA flexibility ; TATA box functionality ; TATA box binding protein (TBP) ; TBP recognition ; TBP binding ; TBP transcriptional activation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Four 1.5 ns molecular dynamics (MD) simulations were performed on the d(GCTATAAAAGGG) · d(CCCTTTTATAGC) double helix dodecamer bearing the Adenovirus major late promoter TATA element and three iso-composition mutants for which physical and biochemical data are available from the same laboratory. Three of these DNA sequences experimentally induce tight binding with the TATA box binding protein (TBP) and induce high transcription rates; the other DNA sequence induces much lower TBP binding and transcription. The x-ray crystal structures have previously shown that the duplex DNA in DNA-TBP complexes are highly bent. We performed and analyzed MD simulations for these four DNAs, whose experimental structures are not available, in order to address the issue of whether inherent DNA structure and flexibility play a role in establishing these observed preferences. A comparison of the experimental and simulated results demonstrated that DNA duplex sequence-dependent curvature and flexibility play a significant role in TBP recognition, binding, and transcriptional activation. © 1998 John Wiley & Sons, Inc. Biopoly 46: 403-415, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 82
    Digitale Medien
    Digitale Medien
    The solution structure of small peptides: An IR CD study of aqueous solutions of (L-Ala)n [n = 3, 4, 5, 6] at different temperatures and ionic strengths (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 455-463 
    Details
    ISSN: 0006-3525
    Schlagwort(e): vibrational CD ; solution conformation ; alanine oligopeptides ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The solution conformation of a number of small, linear alanine oligomers was investigated via ir (or vibrational) CD (VCD). We find that these oligopeptides assume distinct solution conformations that depend primarily on chain lengths, and to a lesser degree on temperature, ionic strength, and pH. As expected, the longer chain oligomers exhibit more distinct VCD features and, presumably, more stable solution structures. At the level of the hexamer, however, aggregation of the peptide occurs. The fast time scale of VCD allows solution structures to be detected that may not be observable using slower techniques such as various forms of nmr spectroscopy. The VCD results reported here confirm that it is generally possible to obtain conformational information for small, linear homo- and heterooligopeptides via VCD spectroscopy. In this respect, the sensitivity of VCD is similar to that of electronic CD. Furthermore, the temperature dependence of the VCD results indicate that at elevated temperatures, the increasing number of conformational states results in a loss of discernible conformers, and consequently, a broadening and weakening of the VCD features. © 1998 John Wiley & Sons, Inc. Biopoly 46: 455-463, 1998
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 83
    Digitale Medien
    Digitale Medien
    Miniaturized hemoproteins (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 5-22 
    Details
    ISSN: 0006-3525
    Schlagwort(e): hemoproteins ; model systems ; miniaturized proteins ; mimochromes ; helix structures ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The present paper highlights and reviews current research in the field of hemoprotein models. Hemoproteins have been extensively studied in order to understand structure-function relationships, and to design new molecules with desired functions. A wide number of synthetic analogues have been developed, using quite different approaches. They differ in molecular structures, ranging from simple meso-substituted tetraaryl-metalloporphyrins and peptide-porphyrin conjugates.In this paper we summarize the state of the art on peptide based hemoprotein models. We also report here the approach used by us to develop a new class of molecules, named mimochromes. They can be regarded as miniaturized hemoproteins, because mimochromes are low molecular weight compounds with some structural and functional properties common to those of the parent high molecular weight protein. The basic structure of mimochromes is a deuteroporphyrin ring covalently linked to two helical peptide chains. Two molecules of this series have been fully characterized. All the information derived from their structural analysis has been applied to the design of new analogues with additional functions. © 1998 John Wiley & Sons, Inc. Biopoly 47: 5-22, 1998
    Zusätzliches Material: 15 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 84
    Digitale Medien
    Digitale Medien
    An electrostatic model for the dielectric effects, the adsorption of multivalent ions, and the bending of B-DNA (1998)
    New York : Wiley-Blackwell
    Biopolymers 46 (1998), S. 503-516 
    Details
    ISSN: 0006-3525
    Schlagwort(e): discrete charge model of DNA ; dielectric cylinder in water ; effective dielectric constant ; salt effects ; Debye shielding factor ; potential variations in DNA surface ; Boltzmann averaged bending angles ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: We have studied electrostatic properties of DNA with a discrete charge model consisting of a cylindrical dielectric core with a radius of 8 Å and a dielectric constant Di = 4, surrounded by two helical strings of phosphate point charges at 10 Å from the axis, immersed in an aqueous medium with dielectric constant Dw = 78.54. Eliminating the dielectric core makes potentials in the phosphate surface less negative by about 0.5 kT/e. Salt effects are evaluated for the model without a dielectric core, using the shielded Coulomb potential. Smearing the phosphate charges increases their potential by about 2.5 kT/e, due mostly to the self-potential of the smeared charge. Potentials in the center of the minor and major grooves vary less than 0.02 kT/e along their helical path. The potential in the center of the minor groove is from 1.0 to 1.7 kT/e, more negative than in the center of the major groove, depending on dielectric core and salt concentration. So multivalent cations and also larger cationic ligands, such as some antibiotics, are likely to adsorb in the minor groove, in agreement with earlier computations by A. and B. Pullman. Dielectric effects on the surface potential and the local potential variations are found to be relatively small. Bending of DNA is studied by placing a multivalent cation, MZ+, in the center of the minor or major groove, curving DNA around it for a certain length, and calculating the free energy difference between the bent and the straight configuration. Boltzmann averaged bending angles, 〈β〉, are found to be maximal in 0.03M monovalent salt, for a length of about 50 or 25 Å of curved DNA when an MZ+ ion is adsorbed in the minor or the major groove, respectively. When the dielectric constant of water is used throughout the calculation, we find maximal bends of 〈β〉 = 11° for M2+ and 〈β〉 = 16° for M3+ in the minor groove, 〈β〉 = 13° for M3+ in the major groove. The absence of bends in DNA adsorbed to mica in the presence of Mg salts supports the role of Mg2+ in “ion bridging” between DNA and mica. The treatment of the effective dielectric constant between two points outside a dielectric cylinder in water is appended. © 1998 John Wiley & Sons, Inc. Biopoly 46: 503-516, 1998
    Zusätzliches Material: 14 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 85
    Digitale Medien
    Digitale Medien
    Protein design: On the threshold of functional properties (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 63-73 
    Details
    ISSN: 0006-3525
    Schlagwort(e): protein de novo design ; novel macromolecules ; topological templates ; Template Assembled Synthetic Proteins (TASP) ; biosensors ; protein folding ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The ultimate goal in protein de novo design is the creation of novel macromolecules with tailor-made receptor, sensory, and catalytic functions. Despite considerable progress in understanding basic rules of secondary structure formation and protein stability, the well-known protein folding problem is still far from being solved and, in general, only a limited number of designed proteins are folded uniquely. In this article the state-of-the-art in protein design is demonstrated on some selected examples, indicating that the construction of protein-like macromolecules mimicking some essential features of natural proteins seems to be within reach. Thus, protein design and mimicry has become an interdisciplinary challenge with most intriguing perspectives. © 1998 John Wiley & Sons, Inc. Biopoly 47: 63-73, 1998
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 86
    Digitale Medien
    Digitale Medien
    Mode of action of linear amphipathic α-helical antimicrobial peptides (1998)
    New York : Wiley-Blackwell
    Biopolymers 47 (1998), S. 451-463 
    Details
    ISSN: 0006-3525
    Schlagwort(e): bacteria ; antibiotics ; linear amphipathic α-helical antimicrobial peptides ; peptide-lipid interactions ; membrane permeation ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The increasing resistance of bacteria to conventional antibiotics resulted in a strong effort to develop antimicrobial compounds with new mechanisms of action. Antimicrobial peptides seem to be a promising solution to this problem. Many studies aimed at understanding their mode of action were described in the past few years. The most studied group includes the linear, mostly α-helical peptides. Although the exact mechanism by which they kill bacteria is not clearly understood, it has been shown that peptide-lipid interactions leading to membrane permeation play a role in their activity. Membrane permeation by amphipathic α-helical peptides can proceed via either one of the two mechanisms: (a) transmembrane pore formation via a “barrel-stave” mechanism; and (b) membrane destruction/solubilization via a “carpet-like” mechanism. The purpose of this review is to summarize recent studies aimed at understanding the mode of action of linear α-helical antimicrobial peptides. This review, which is focused on magainins, cecropins, and dermaseptins as representatives of the amphipathic α-helical antimicrobial peptides, supports the carpet-like rather the barrel-stave mechanism. That these peptides vary with regard to their length, amino acid composition, and net positive charge, but act via a common mechanism, may imply that other linear antimicrobial peptides that share the same properties also share the same mechanism. © 1999 John Wiley & Sons, Inc. Biopoly 47: 451-463, 1998
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 87
    Digitale Medien
    Digitale Medien
    Modified oligoribonucleotides as site-specific probes of RNA structure and function (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 39-55 
    Details
    ISSN: 0006-3525
    Schlagwort(e): modified nucleotides ; site-specific probes ; RNA structure ; RNA function ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Modified nucleotides can be incorporated site specifically into RNA by the use of total chemical synthesis as well as by use of a variety of recombinant RNA techniques. The range of nucleotide analogues includes modifications to base, sugar, and phosphate for structure-function analysis and for cross-linking studies as well as to answer specific mechanistic questions in RNA catalysis. We describe how RNA containing site-specific modifications are prepared, concentrating in particular on routes involving chemically synthesized oligoribonucleotides, and give examples of their application in studies of the hammerhead and hairpin ribozymes. © 1998 John Wiley & Sons, Inc. Biopoly 48: 39-55, 1998
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 88
    Digitale Medien
    Digitale Medien
    Dressed for success: Realizing the catalytic potential of RNA (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 29-37 
    Details
    ISSN: 0006-3525
    Schlagwort(e): amide synthase ; catalytic antibodies ; Diels-Alderase ; ideal catalyst platform ; in vitro selection ; Lewis acid ; modified uridines ; modified RNA ; ribozymes ; SELEX ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: In this manuscript the catalytic ability of RNA is examined and compared to other biopolymers. Despite having considerably fewer catalytically enabling properties when compared to proteins, the power of in vitro selection has allowed for RNA and DNA catalysts to be isolated. RNA catalysis has been expanded by incorporating modified bases to enrich the structural and functional diversity of RNA. Successful examples of new RNA chemistry using base modifications include carbon-carbon bond forming reactions and creation of highly specific active sites that are capable of recognizing small organic molecules without the need for nucleic acid templating or intercalation. In fact, the scope of functional modifications available for use in the RNA platform may eventually surpass those that are found in proteins and there are already hints that well chosen modifications allow nucleic acid catalysts to take advantage of mechanisms not available to selected protein catalysts for similar reactions. The chemical versatility of RNA is just emerging and future research directions will likely entail more creative methods for functional modification that will lead to new catalysts. © 1998 John Wiley & Sons, Inc. Biopoly 48: 29-37, 1998
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 89
    Digitale Medien
    Digitale Medien
    New developments in structure determination of pseudoknots (1998)
    New York : Wiley-Blackwell
    Biopolymers 48 (1998), S. 137-153 
    Details
    ISSN: 0006-3525
    Schlagwort(e): RNA ; pseudoknot ; Turnip Yellow Mosaic Virus ; Mouse Mammary Tumor Virus ; Beet Western Yellows Virus ; Simian Retrovirus type-1 ; Hepatitis Delta Virus ; translational frameshifting ; ribozyme ; nmr ; x-ray diffraction ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Recently, several high-resolution structures of RNA pseudoknots have become available. Here we review the progress in this area. The majority of the structures obtained belong to the classical or H-type pseudoknot family. The most complicated pseudoknot structure elucidated so far is the Hepatitis Delta Virus ribozyme, which forms a nested double pseudoknot. In particular, the structure-function relationships of the H-type pseudoknots involved in translational frameshifting have received much attention. All molecules considered show interesting new structural motifs. © 1999 John Wiley & Sons, Inc. Biopoly 48: 137-153, 1998
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
  • 90
    Digitale Medien
    Digitale Medien
    Structure and Dynamics of Hydrogen Chelates. Part 1. NMR-spectroscopic studies in the quinazoline-2-acetonitrile series (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 236-250 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: To get informations on both the structure and dynamics of hydrogen chelates 1 of heteroaromatic systems, a great variety of quinazoline-2-acetonitrile chelates were synthesized (see 2-4). Similarly to the situation of the corresponding H-chelates in the pyrimidine-2-acetonitrile series, the investigation of these new derivatives 2-4 by NMR spectroscopic methods (DNMR, COSY, NOESY, ROESY, EXSY, HMQC, HMBC) confirms the presence of an equilibrium of the two possible H-chelate structures (two ‘rotamers’ I and II, i.e., (E)/(Z) isomers; see Scheme). The corresponding equilibria I ⇌ II were determined by complete 1H-NMR signal assignment at low temperatures (after freezing the rotational processes). In addition, the tautomer equilibria A ⇌ B (relative energies of the two minima of the nonsymmetrical double-well potential) for both ‘rotamers’ are ascertained by H,H and C,H couplings. The results are an important basis for the interpretation of both the UV/VIS absorptions and the dependence of fluorescence and fluorescence quantum yields on temperature.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810206
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 91
    Digitale Medien
    Digitale Medien
    Stereoselective Reactions of Phthalimido-Substituted Radicals Derived from (±)-Threonine: A comparison with reactions of N-phthaloyliminium ions (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 268-284 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Stereoselective reactions of phthalimido-substituted radicals derived from (±)-threonine with different radical traps are reported (Scheme 3, Table 1). A strong influence of the nature of the radical trap on the stereoselectivity was noticed. Small nucleophilic radical traps gave preferentially the syn products. The observed selectivities are explained with the A1,3 strain model and depend on steric and electronic effects (Fig. 2). Reactions with electrophilic radical traps such as diphenyl diselenide gave the anti diastereoisomers with moderate stereocontrol, presumably due to stereoelectronic effects. The same stereochemical outcome, i.e., preferential formation of the anti products, was observed for the reactions of the related N-phthaloyliminium ion (Scheme 5, Table 2). The stereochemistry of the ionic reaction is rationalized by a Felkin-Anh model (Fig. 3).
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810208
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 92
    Digitale Medien
    Digitale Medien
    Cyclopalladation of 1,1′-Azonaphthalene (= Di(naphthalen-1-yl)diazene): Isolation and characterization of two isomeric complexes (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 307-316 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The cyclopalladation of 1,1′-azonaphthalene (= di(naphthalen-1-yl)diazene; 2) with bis(hexafluoroacetyl-acetonato)palladium(II) (3; [Pd(hfa)2]) yields the ortho-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[1-(naphthalen-1-ylazo-κN2)naphthalen-2-yl-κC2]palladium(II) (4) as well as the peri-palladated complex (1,1,1,5,5,5-hexafluoropentane-2,4-dionato-κ2O,O′)[8-(naphthalen-1-ylazo-κN2)naphthalen-1-yl-κC1]-palladium(II) (5); their structures were corroborated by X-ray analyses. The formation of the novel peri-metallated product 5 containing a six-membered palladacycle strongly depends upon the reaction conditions.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810211
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 93
    Digitale Medien
    Digitale Medien
    The Photoisomerization Behavior of the (4-Hydroxycinnamoyl)-spermidines (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 342-352 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The photoisomerization behavior of three mono[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 1, 2, and 3, and three bis[(E)-3-(4-hydroxyphenyl)prop-2-enoyl]spermidines, 4, 5, and 6, are investigated. The synthetic product (E)-1 could be almost quantitatively (〉 96%) converted into its isomer (Z)-1 under UV light irradiation. In the cases of (E)-2 and (E)-3, a mixture of (E)/(Z) ca. 1:2 was obtained, when the same conditions were applied. The comparison of their UV spectra provides the possible explanation for these different behaviors. Furthermore, it was noticed that the (Z) → (E) isomerization of the C=C bond took place during the purification by reverse-phase high-performance liquid chromatography (RP-HPLC), and the (E)/(Z)-mixture is thus inseparable. The same feature could be observed during the isolation of the (Z,Z)-N,N′-bis[3-(4-hydroxyphenyl)prop-2-enoyl]-spermidines, (Z,Z)-4, (Z,Z)-5, and (Z,Z)-6. Nevertheless, the fractions of (Z,Z)-5 and (Z,Z)-6 were in almost pure state collected, and their 1-NMR spectra are presented.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810215
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 94
    Digitale Medien
    Digitale Medien
    Preparation and Absolute Configuration of (-)-(E)-α-trans-Bergamotenone (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 153-162 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis, absolute configuration, and olfactive evaluation of (-)-(E)-α-trans-bergamotenone (= (-)-(1′S,6′R,E)-5-(2′,6′-dimethylbicyclo[3.1.1]hept-2′-en-6′-yl)pent-3-en-2-one; (-)-1), as well as its homologue (-)-19 are reperted. The previously arbitrarily attributed absolute configuration of 1 and of (-)-α-trans-bergamotene (= (-)-(1 S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1. 1]hept-2-ene; (-)-2), together with those of the structurally related aldehydes (-)-3a,b and alcohols (-)-4a,b, have been rigorously assigned.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810114
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 95
    Digitale Medien
    Digitale Medien
    New Synthesis and Chirality of (-)-4,4,4,4′,4′,4′-Hexafluorovaline (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 182-186 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: (-)-(R)-4,4,4,4′,4′,4′-Hexafluorovaline hydrochloride ((R)-5) of 98% ee is prepared from β,β-bis(trifluoromethyl)acrylic acid (= benzyl 4,4,4-trifluoro-3-(trifluoromethyl)but-2-enoate; 1) in 4 steps with an overall yield of 9.6%. Key step is the separation of the TsOH salts of the diastereoisomers obtained by anti-Michael addition of (+)-(R)-1-phenylethylamine (2) to 1 (→ (R,R)-3). In contrast to the published (S)-chirality, the X-ray structure analysis of (R,S)-6 reveals, that (R)-chirality has to be assigned to the levorotatory (-)-4,4,4,4′,4′,4′-hexafluorovaline hydrochloride.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810117
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 96
    Digitale Medien
    Digitale Medien
    Tripodal Dodecadentate Ligands with Salicylamide and bipyridine binding sites for iron(II) and iron(III) coordination (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 207-218 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis and characterization of tripodal dodecadentate ligands with salicylamide and bipyridine binding sites for iron(II) and iron(III) are presented.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810203
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 97
    Digitale Medien
    Digitale Medien
    N,N-Dialkylcarbamato Complexes of the d10 cations of copper, silver, and gold (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 219-230 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reaction of CuO'Bu with CO2, and iPr2NH in the presence of PPh3, gives the dialkylcarbamato complex [Cu(O2CNiPr2)(PPh3)2] (1). The CO2/R2NH system (R = Me, Et) in an appropriate organic medium reacts with Ag2O giving the corresponding N,N-dialkylcarbamato complexes of analytical formula [Ag(C2CNR2)] (R = Me, 2; R = Et, 3). The methyl derivative 2 was characterized by X-ray diffraction methods. Crystal data of 2: for [Ag2(O2CNMe2)2], C6H12Ag2N2O4, mol. wt. 391.9; monoclinic, space group P21/c, a = 12.08(1), b = 3.797(2), c = 11.316(7) Å, β = 113.37(6)°, V = 476.3 Å3, Z = 2, Dc = 2.732 g cm-3; μ(MoKα) = 40.64 cm-1, F(000) = 376.0; R = 0.059, Rw = 0.067; g.o.f. 1.27. The structure consists of dinuclear [(Ag2OCNMe2)2] units with slightly distorted linearly two-coordinated Ag-atoms containing bridging carbamato groups to form a substantially planar eight-membered ring with an intra-annular Ag—Ag distance of 2.837(2) Å; the dinuclear units are further joined by Ag—O bonds to form an infinite array. Compound 3, which is presumably dinuclear, as suggested by cryoscopic measurements in benzene, undergoes a structural fission with PPh3, giving the mononuclear triphenylphosphine derivative [Ag(O2CNEt2)(PPh3)2] (4). The amine-catalyzed conversion of Ag2O into Ag2CO3, in the presence of the iPr2NH/CO2 system, is also reported. Cl-Exchange from [AuCl(PPh3)] with [Ag(O2CNEt2)] (3) gives the first N,N-dialkylcarbamato complex of gold, namely [Au(O2CNEt2)(PPh3)] (5), which crystallizes in the monoclinic system: C23H25AuNO2P · 0.5 C7H16, mol. wt. 625.5, space group P21/c; a = 13.212(5), b = 12.25(1), c = 16.795(6) Å, β = 109.09(2)°, V = 2568(2) Å3, Z = 4, Dc, = 1.618 g cm-3; μ(AgKα) = 31.40 cm-1, F(000) = 1236.0; R = 0.058; Rw = 0.064; g.o.f. 2.121. The compound contains two-coordinated Au-atom, namely to the P-atom and to the O-atom of the monodentate carbamato group, the P—Au—O bond angle being 174.7(3)°. The reaction with MeI showed these compounds to react predominantly at the carbamato O-atom giving the corresponding urethanes R2NCO2Me. Evidence was gathered for the transient coordination of CO to Ag in 3.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810204
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 98
    Digitale Medien
    Digitale Medien
    1,3-Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and α-diazo amides with thiocarbonyl compounds (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 285-302 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The reactions of α-diazo ketones 1a,b with 9H-fluorene-9-thione (2f) in THF at room temperature yielded the symmetrical 1,3-dithiolanes 7a,b, whereas 1b and 2,2,4,4-tetramethylcyclobutane-1,3-dithione (2d) in THF at 60° led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans-9a (Scheme 2). With 2-diazo-1,2-diphenylethanone (1c), thio ketones 2a-d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with 1c were more sluggish than those with 1a,b, they were catalyzed either by the addition of LiClO4 or by Rh2(OAc)4. In the case of 2d in THF/LiClO4 at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans-9b was formed. Monoadduct 4d could be transformed to cis- and trans-9b by treatment with 1c in the presence of Rh2(OAc)4 (Scheme 4). Xanthione (2e) and 1c in THF at room temperature reacted only when catalyzed with Rh2(OAc)4, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with α-diazo amides 1d,e (Schemes 5-7). It is worth mentioning that formation of 1,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α-diazo amide. In the case of 1d and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60°, 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide 11b were formed. Thiirane-carboxamides 11d-g were desulfurized with (Me2N)3P in THF at 60°, yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mechanism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a 1,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione (2f) is the thiocarbonyl ylide trapped by a second molecule of 2f to give 1,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810209
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 99
    Digitale Medien
    Digitale Medien
    Masthead (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998) 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810301
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
  • 100
    Digitale Medien
    Digitale Medien
    Synthesis of Chiral C2-Symmetric Binucleating Ligands (1998)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 81 (1998), S. 491-506 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The synthesis of a series of chiral enantiomerically pure C2-symmetric binucleating ligands is reported. Ligands of type 1-4, which consist of a phenolic or heterocyclic unit bridging two chiral dihydrooxazole rings. are readily accessible from chiral amino alcohols. Ligands 5a and 5b are composed of a cyclic urea or thiourea unit, respectively, and two 3,4-dihydro-2H-pyrrole rings containing a stereogenic center next to the N-atom. Compounds of this type are readily assembled from ethane-1,2-diamine and an imidothioic ester derived from pyroglutamic acid. These new ligands, which can coordinate two metals in close proximity to each other, are of interest regarding possible applications in asymmetric catalysis.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19980810304
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
    BibTip Andere fanden auch interessant ...
    Artikel (Nationallizenzen)
    Volltext
Schließen ⊗
Diese Webseite nutzt Cookies und das Analyse-Tool Matomo. Weitere Informationen finden Sie hier...