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Digitale Medien

Intraspecific variation in production of astringent phenolics over a vegetation-resource availability gradient (1987)

Muller, R. N. ; Kalisz, P. J. ; Kimmerer, T. W.

Springer

Oecologia 72 (1987), S. 211-215

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ISSN: 1432-1939

Schlagwort(e): Phenolics ; Stress gradient ; Vegetation

Quelle: Springer Online Journal Archives 1860-2000

Thema: Biologie

Notizen: Summary The chemical constituency of flowering dogwood (Cornus florida L.) and red maple (Acer rubrum L.) foliage was analyzed over a species compositional gradient to test the hypothesis that over subtle gradients of moisture and nutrient availability production of phenolic compounds will be increased on sites of greatest stress. Calcium and nitrogen concentrations declined along the gradient in both species, while phosphorus showed a significant decline only in red maple. Lignin concentrations in both species were unrelated to the vegetation gradient, but astringent phenolics increased by 156% and 159% in dogwood and red maple, respectively. The correlation between production of polyphenolds and site quality supports previous observations that under conditions of environmental stress production of many secondary compounds is increased, and suggests that this relationship is significant over subtle environmental gradients.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00379270

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Digitale Medien

Investigation of prototropic equilibria by carbon-13 relaxation time analysis (1987)

Elst, L. Vander ; Van Haverbeke, Y. ; Maquestiau, A. ; [weitere]

Chichester : Wiley-Blackwell

Organic Magnetic Resonance 25 (1987), S. 16-20

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ISSN: 0749-1581

Schlagwort(e): 13C NMR ; 13C Relaxation Times ; Prototropic equilibria ; Chemistry ; Analytical Chemistry and Spectroscopy

Quelle: Wiley InterScience Backfile Collection 1832-2000

Thema: Chemie und Pharmazie

Notizen: Quaternary 13C dipole-dipole spin-lattice relaxation times are used to analyse prototropic equilibria of 2-acetylbenzimidazole (1) and 4-azabenzimidazole in DMSO-d6 solutions. For the first compound, fast exchange between the two chelated structures prevails for 13C relaxation times, whereas proton and 13C chemical shifts characterize a slow exchange. For 4-azabenzimidazole, 13C and 1H spectra do not exhibit absorptions from structures in slow exchange. Analysis of the T1 values of carbons 8 and 9 before and after isotopic exchange of the labile amino hydrogen clearly show that the major component of the equilibrium is the 3H structure.

Zusätzliches Material: 5 Ill.