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  • 1
    Digitale Medien
    Digitale Medien
    Computational studies of the potential energy surface for O(3P)+H2S: Characterization of transition states and the enthalpy of formation of HSO and HOS (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 161-169 
    Details
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Structures and vibrational frequencies for minima and 11 transition states on the O(3P)+H2S potential energy surface have been characterized at the MP2=FULL/6-31G(d) level. GAUSSIAN-2 theory was employed to calculate ΔHf,298 for HSO and HOS of −19.9 and −5.5 kJ mol−1, respectively. The kinetics of HSO=HOS isomerization are analyzed by Rice–Ramsperger–Kassel–Marcus theory. Transition state theory analysis for O+H2S suggests OH+HS is the dominant product channel, with a rate constant given by 1.24×10−16 (T/K)1.746 exp(−1457 K/T) cm3 molecule−1 s−1. Kinetic isotope effects and the branching ratio for H+HSO production are also analyzed. The other possible products H2+SO and H2O+S do not appear to be formed in single elementary steps, but low-barrier pathways to these species via secondary reactions are identified. No bound adducts of O+H2S were found, but results for weakly bound triplet HOSH are presented. The likely kinetics for the reactions OH+SH→S(3P)+H2O, OH+SH→cis and trans 3HOSH, cis 3HOSH→HOS+H, and HSO and HOS+H→H2+3SO are discussed. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.469387
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  • 2
    Digitale Medien
    Digitale Medien
    A comparison of the infusion pharmacokinetics and pharmacodynamics of cisatracurium, the 1R-cis 1′R-cis isomer of atracurium, with atracurium besylate in healthy patients (1997)
    Oxford, UK : Blackwell Science Ltd
    Anaesthesia 52 (1997), S. 0 
    Details
    ISSN: 1365-2044
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: We have compared the pharmacokinetics of cisatracurium with atracurium when given by bolus dose followed by continuous infusion. Twenty healthy patients were anaesthetised with thiopentone, midazolam, fentanyl and 70% nitrous oxide in oxygen. Ten patients (Group C) were randomly allocated to receive cisatracurium 0.1 mgkg−1 and 10 patients (Group A) were given atracurium 0.5 mgkg−1. Neuromuscular block was monitored using a mechanomyograph. When the first twitch of the train-of-four had recovered to 5% of control, an infusion of cisatracurium 3 μgkg−1.min−1 was started in Group C and an infusion of atracurium 10 μgkg−1.min−1 was started in Group A. The infusion rates were adjusted to maintain the first twitch of the train-of-four at 5% of control. The times to 90% and maximum depression of the first twitch of the train-of-four were significantly longer after cisatracurium than atracurium (2.2 and 3.4 min compared with 1.3 and 1.8 min, respectively; p 〈 0.01 in each instance). No significant differences were found in recovery parameters between the two groups. Blood samples were taken at regular intervals following the bolus, during the infusion and for 8 h thereafter. The plasma samples were analysed using high-performance liquid chromatography for cisatracurium and atracurium (using a method which distinguishes between the three geometric isomer groups), laudanosine and monoquaternary alcohol. The results were analysed using the Non-linear Mixed Effects Model program. A two-compartment model was fitted to the data. The different isomer groups of atracurium have different pharmacokinetics, the trans–trans group having the highest clearance (1440 mlmin−1) and the cis–cis group the lowest (499 mlmin−1). The clearance of cisatracurium (425 mlmin−1) is less than that of cis–cis atracurium and its elimination half-life is longer (34.9 min and 21.9 min, respectively). The plasma concentration of laudanosine after cisatracurium was one-fifth of that after atracurium.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2044.1997.195-az0331.x
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  • 3
    Digitale Medien
    Digitale Medien
    Effect of floral orifice width and shape on hummingbird-flower interactions (1996)
    Springer
    Oecologia 106 (1996), S. 482-492 
    Details
    ISSN: 1432-1939
    Schlagwort(e): Pollination ; Archilochus colubris ; Monarda ; Feeding ; Nectar guides
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nectar guides are common among insect-pollinated plants, yet are thought to be rare or absent among hummingbird-pollinated plants. We hypothesize that the lower lips and trumpet-shaped orifices of many hummingbird flowers act as nectar guides to direct hummingbirds to the flowers' nectar and orient the birds for pollination. To test this hypothesis we conducted laboratory experiments using flowers of Monarda didyma (bee balm) and M. fistulosa (wild bergamot), which have orifice widths of about 4 mm and 2 mm, respectively, and latex flowers with orifice widths of 4 mm and 2 mm and three orifice shapes (trumpet, lipped, and lipless). Rubythroated hummingbirds (Archilochus colubris) made fewer errors during bill insertion and spent a smaller proportion of their feeding visit in error at M. didyma flowers than at M. fistulosa flowers, and at unaltered flowers of both species than at flowers with lower lips removed. Handling times were longer at both lipped and lipless flowers of M. didyma than at those of M. fistulosa, and at lipped than at lipless flowers of M. didyma. The average duration of contact between a hummingbird and a flower's anthers and stigma was longer at M. didyma than at M. fistulosa for both lipped and lipless flowers, and at lipped than at lipless M. didyma flowers. Hummingbirds missed the openings of latex flowers with their bills more frequently and spent a greater percentage of their total feeding visit in error at (i) 2-mm than at 4-mm flowers of all three shapes, (ii) lipless flowers than at trumpet or lipped flowers, and (iii) lipped flowers than at trumpet flowers of both widths. The duration of hummingbird/anther contact was longer at (i) 2-mm than at 4-mm flowers of all shapes, (ii) lipped than at trumpet or lipless flowers, and (iii) lipless than at trumpet flowers for both widths. No significant differences in handling times of hummingbirds were observed among any of the latex flower shapes or widths. Our results demonstrate that orifice shapes can act as guides by reducing the frequency of feeding errors by visiting hummingbirds, and that effects of orifice shape on pollination must be considered in conjunction with flower widths and locations of anthers and stigmas.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00329706
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  • 4
    Digitale Medien
    Digitale Medien
    Enamel matrix protein turnover during amelogenesis: Basic biochemical properties of short-lived sulfated enamel proteins (1995)
    Springer
    Calcified tissue international 57 (1995), S. 133-144 
    Details
    ISSN: 1432-0827
    Schlagwort(e): Enamel ; Sulfated glycoprotein ; N-linked sugar ; Rapid degradation ; Secretory stage of amelogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract The formation and turnover of sulfated enamel proteins was investigated by SDS-PAGE, fluorography, and TCA-precipitations using freeze-dried incisors of rats injected intravenously with 35S-sulfate (35SO4) and processed at various intervals from 1.6 minutes to 4 hours thereafter. Some rats were injected first with 35SO4 followed 5 minutes later by 0.3 mg of cycloheximide. This was done to terminate protein translation and allow events related to extracellular processing and degradation of the sulfated enamel proteins to be visualized more distinctly. Other rats were injected with cycloheximide followed at 0 minutes (simultaneous injection) to 30 minutes later by 35SO4. This was done to characterize the time required for proteins to travel from endoplasmic reticuium to Golgi apparatus, where they became sulfated. The results indicated that enamel organ cells (ameloblasts) rapidly incorporated 35SO4 into a major ∼65 kDa protein that was secreted into the enamel within 6–7.5 minutes. This parent protein appeared to be processed extracellularly within 15 minutes into major ∼49 kDa and ∼25 kDa fragments which themselves had apparent half-lives of about 1 and 2 hours, respectively. There were also many minor sulfated fragments varying in molecular weight (Mr) from ∼13–42 kDa, which appeared to originate from extracellular processing and/or degradation of the parent ∼65 kDa sulfated enamel protein or its major ∼49 kDa and ∼25 kDa fragments. Experiments with glycosidases further suggested that the majority of sulfate groups were attached to sugars N-linked by asparagine to the core of the ∼65 kDa sulfated enamel protein. The sulfated enamel proteins resemble acidic glycoproteins previously classified as “enamelins”. Unlike the enamelins, however, they are short-lived and do not appear to survive in enamel as it matures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00298434
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  • 5
    Digitale Medien
    Digitale Medien
    Immunoblotting studies on artifactual contamination of enamel homogenates by albumin and other proteins (1995)
    Springer
    Calcified tissue international 57 (1995), S. 145-151 
    Details
    ISSN: 1432-0827
    Schlagwort(e): Enamel proteins ; Amelogenin ; Ameloblasts ; Albumin ; Immunoblotting
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin , Physik
    Notizen: Abstract The reason for the presence of albumin and other serum, cytoskeletal, cytosolic, and extracellular matrix proteins in enamel fractions was investigated by immunoblotting using homogenates prepared from freeze-dried and freshly dissected rat incisors, and antibodies capable of resolving at least 1 ng of the primary antigen. The data indicated that most of the 16 antibodies examined in this study reacted with antigens present only within “cell” homogenates (enamel organ cells+adhering labial connective tissue and blood vessels). One exception was rat serum albumin which was detected routinely in enamel homogenates prepared from freshly dissected, wiped incisors but rarely within enamel homogenates prepared from freeze-dried incisors. Another exception was calbindin-D 28 kDa which was consistently found within secretory stage enamel homogenates irrespective of preparative technique. A third exception was enamel proteins (amelogenins) which were enriched in secretory and early maturation stage enamel homogenates compared with cell homogenates and distributed as multiple molecular weight, antigenic bands in enamel homogenates (14–30 kDa), but mostly as a single antigenic band in cell homogenates (near 27 kDa). Overall, the results of this study suggest that developing rat incisor enamel naturally contains few exogenous proteins such as albumin. High concentrations of albumin (or other serum proteins) in crude homogenates, or purified fractions, derive mostly from blood and/or tissue fluids soaking into the enamel during sample preparation. This type of artifact can be avoided by using freeze-dried teeth for biochemical analyses.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00298435
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  • 6
    Digitale Medien
    Digitale Medien
    The Use of Quality and Reputation Indicators by Consumers: The Case of Bordeaux Wine (1997)
    Springer
    Journal of consumer policy 20 (1997), S. 289-323 
    Details
    ISSN: 1573-0700
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract The absolute and relative impact of current quality and reputation variables on consumer decisions are examined using data from the market for Bordeaux wine. The estimates indicate that a model of consumer decision making which incorporates information on reputation (past quality) and collective reputation (average group quality) rejects alternative models that include current quality. The results also indicate that reputation has a large impact on the willingness to pay of consumers, that long term reputation is considerably more important than short term quality movements, and that consumers react slowly to changes in product quality. Collective reputation is shown to have an impact on consumer willingness to pay that is as large as that of individual firm reputation. If reputation and collective reputation effects are ignored, the estimated impact of current quality and short term changes in quality on consumer behaviour are overstated.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1006830218392
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