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  • 1990-1994  (16)
  • Analytical Chemistry and Spectroscopy  (13)
  • Carbon isotope discrimination  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Carbon isotope discrimination, water-use efficiency, growth, and mortality in a natural shrub population (1994)
    Springer
    Oecologia 100 (1994), S. 347-354 
    Details
    ISSN: 1432-1939
    Keywords: Carbon isotope discrimination ; Growth mortality ; Size ; Water-use efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to scale up from the ecophysiological characters of individual plants to population-level questions, we need to determine if character patterns in natural populations are stable through time, and if the characters are related to growth and survival. We investigated these questions in a 3-year study for one character, integrated water-use efficiency (WUE) as estimated by carbon isotope discrimination (δ) in a population of the Great Basin shrub, Chrysothamnus nauseosus. WUE was a conservative character for a given plant within and across seasons, and a previously documented difference between two size classes (represented by juveniles and adults) was maintained; smaller juveniles had a lower WUE than larger adults. The lower WUE of juveniles was often accompanied by higher rates of photosynthesis and stomatal conductance as compared to adults even though juveniles generally had more negative xylem pressure potentials. Although many discussions of the role of WUE in natural populations have been based on the expectation that higher WUE (lower δ) is generally associated with less growth, we found no such relation-ship for juvenile plants in this population (i.e δ was not positively correlated with height increase). In addition, juvenile plant mortality was not correlated with δ. Although there were stable patterns of WUE for plants in this population, the positive correlation between WUE and size, and the lack of a negative correlation between WUE and height growth, make it unlikely that the WUE of an individual plant will be related in a simple manner to its growth and survival in the population.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316964
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  • 2
    Electronic Resource
    Electronic Resource
    Seasonal carbon isotope discrimination in a grassland community (1991)
    Springer
    Oecologia 85 (1991), S. 314-320 
    Details
    ISSN: 1432-1939
    Keywords: Carbon isotope discrimination ; Carbon isotope ratio ; Stable isotopes ; Grassland ; Community ecology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00320605
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  • 3
    Electronic Resource
    Electronic Resource
    Carbon isotope ratios are correlated with irradiance levels in the Panamanian orchid Catasetum viridiflavum (1990)
    Springer
    Oecologia 83 (1990), S. 247-249 
    Details
    ISSN: 1432-1939
    Keywords: Carbon isotope ratio ; Carbon isotope discrimination ; Catasetum ; C3 photosynthesis ; Gas exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Carbon isotope composition (13C/12C) in leaves of the Panamanian epiphytic orchid Catasetum viridiflavum were measured on individuals growing in canopies over a water surface to distinguish the effects of a change in source CO2 and humidity from those of intercellular CO2 concentration in determining isotopic composition. Carbon isotope ratios were observed to vary by over 4 in response to changes in total daily photon flux (PFD, 400–700 nm). Changes in isotopic composition of source CO2 or changes in humidity were not likely to have played a role in determining leaf isotopic composition. Observed changed in carbon isotope discrimination (Δ) of leaves experiencing different light levels ranged from 17 to 21. Because leaf nitrogen contents were similar among all orchids, we suggest that the carbon isotope discrimination data indicated that stomatal limitation to photosynthesis increased with increasing irradiance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317759
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  • 4
    Electronic Resource
    Electronic Resource
    Determination of the enantiomeric purity of scopolamine isolated from plant extract using achiral/chiral coupled column chromatography (1991)
    New York, NY : Wiley-Blackwell
    Biomedical Chromatography 5 (1991), S. 3-7 
    Details
    ISSN: 0269-3879
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The optical purity of scopolamine derived from Datura sanguinea was determined using coupled column chromatography. A C18 column was used to separate scopolamine from the additional alkaloids and other biological material present in the vegetal extract. The C18 column was coupled through a six-port switching valve to two β-cyclodextrin columns in series which were used to resolve the scopolamine enantiomers. A single acetylated β-cyclodextrin column gives equivalent results to the native cyclodextrin columns because of slightly higher enantioselectivity for scopolamine. A multistep extraction procedure is used to isolate scopolamine from the vegetal material. 4-6% of the scopolamine in the final extract was found to be the d enantiomer. Sample extracts as well as commercial scopolamine hydrobromide were treated under various conditions commonly encountered during typical commercial extraction procedures and analyzed in order to determine if the d enantiomer was present in the original material or if it was produced during the extraction process and, if so, determine which step and conditions contribute to acemization. Both the salt and the extract were found to be susceptible to racemization under basic conditions (≥pH 9) although the extract appeared to be more susceptible than the salt. Tropic acid formed from the hydrolysis of scopolamine seemed to be completely racemized even though the remaining scopolamine was only partially racemized. Within experimental error, no d enantiomer was found in the original fresh plant material.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bmc.1130050103
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  • 5
    Electronic Resource
    Electronic Resource
    Direct diagnosis of tuberculosis by computer assisted pattern recognition gas chromatographic analysis of sputum (1991)
    New York, NY : Wiley-Blackwell
    Biomedical Chromatography 5 (1991), S. 165-170 
    Details
    ISSN: 0269-3879
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: Chemical detection of tuberculosis (TB) products in sputum was attempted by using gas chromatographic analysis in conjunction with different pattern recognition computer models. For the chromatographic separations, we used a 2 mm × 1.8 m packed column and a 0.25 mm × 30 m fused silica capillary column to analyse the methylated glycosides and fatty acid methyl ester derivatives. Three computer pattern recognition methods were applied: error score, TB score and discriminant analysis. These methods predicted the presence of active TB most often in sputa of active TB patients and less so in those from inactive, suspected and non-TB patients, in that order. Although the best true positive of 75% was obtained from the TB score method and best true negative of 98% from discriminant analysis, the accompanying false positive and false negative results (36% and 50%, respectively) were unacceptable. The use of capillary column or fatty acid methyl ester derivatives of the samples did not improve on the predictive values of chromatograms obtained from the packed column on trimethylsilylglycosidic derivatives. Additional work is needed before this method can have a direct clinical application.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bmc.1130050406
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  • 6
    Electronic Resource
    Electronic Resource
    Carbon-13 NMR chemical shifts of 1-alkyl-3(5)-cyano-1H-pyrazole-4-carboxylic acid esters (1990)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 28 (1990), S. 90-92 
    Details
    ISSN: 0749-1581
    Keywords: 13C NMR 1-Alkyl-3(5)-cyano-1H-pyrazole-4-carboxylic ; acid ; esters ; Isomer differentiation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A compilation of 13C NMR chemical shifts for 13 pairs of 3- and 5-cyano-substituted pyrazole regioisomers is reported. All of the ring carbon and cyano carbon 13C chemical shifts show a regular, predictable correlation with the particular isomer, whether 3-cyano or 5-cyano. These shifts occurred in very narrow ranges, precluding any confusion of assignment within the group of compounds studied. x-ray crystallographic analysis was performed on one of the samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260280117
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  • 7
    Electronic Resource
    Electronic Resource
    Resonance Raman spectra and normal modes of vibration of 2,2′-bipyridine anion radicals (1990)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 21 (1990), S. 3-8 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The resonance Raman spectra of the lithium complexes of the 2,2′-bipyridine anion radical and five isotopically labeled analogues, including the 15N-labeled species, are reported. All of the fundamental modes of vibration, excluding the C—H stretching and several low-frequency modes, have been identified. Care must be taken to avoid contamination of the sample with the dianion Li2bpy. In order to eliminate possible misassignment of bands to traces of Li2bpy, the spectra of the latter species were also investigated. The assignments of the vibrational frequencies to the fundamental modes of Libpy are supported by a normal coordinate calculation and the structural implications of the vibrational frequency shifts, relative to the neutral parent, are discussed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250210103
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  • 8
    Electronic Resource
    Electronic Resource
    Vibrational spectra of para-disubstituted benzophenones (1991)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 22 (1991), S. 35-41 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman (3500-20 cm-1) and IR (4000-80 cm-1) spectra of benzophenone and a series of its para-disubstituted derivatives (substituents F, Cl, Br and CH3) as melts and in solution were recorded. A complete empirical assignment of the measured spectra was made and the influence of para substitution on the normal modes was investigated.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250220106
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  • 9
    Electronic Resource
    Electronic Resource
    Resonance Raman spectra of Ru(bpz)32+ in aqueous sulfuric acid solutions (1992)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 23 (1992), S. 681-689 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The resonance Raman spectra of tris(2,2′-bipyrazine)ruthenium(II) complex, Ru(bpz)32+, were obtained in solutions of H2SO4-H2O and 2H2SO4-2H2O at acid concentrations between 0 and 98 wt.%. The spectral results are consistent with sequential protonation (or deuteration) of the six peripheral nitrogen atoms, the first three protons being added to separate bipyrazine ligands to form Ru(bpzH+)35+. These findings are in agreement with the conclusions of previous studies based on electronic absorption and emission spectra.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250231205
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  • 10
    Electronic Resource
    Electronic Resource
    Vibrational spectra, ab initio calculations and normal coordinate analysis for 3-methyl-3-vinylcyclopropene (1993)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 24 (1993), S. 31-41 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Raman spectra (3400-10 cm-1) of liquid and solid 3-methyl-3-vinylcyclopropene, C3H2(CH3)CHCH2, and its isotopomer C3D2(CH3)CHCH2 were recorded. The temperature dependence of some band intensities and qualitiative depolarization ratios show that the thermodynamically preferred conformation is s-trans. The structural parameters and conformational stability of s-trans and gauche rotamers were obtained from ab initio calculations by employing both 3-21G and 6-31G* basis sets. Barriers to internal rotation and fundamental vibrational frequencies were calculated utilizing the 3-21G basis set. The ab initio results are consistent with the experimentally indicated greater stability of the s-trans relative to the gauche conformer.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250240105
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