Journal
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY
Volume 66, Issue 3, Pages 213-217Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/S1011-1344(02)00264-6
Keywords
lichens; rhizocarpic acid; calycin; photodegradation; photoconsumption quantum yields
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Photophysical and photochemical parameters of the lichen metabolites calycin and rhizocarpic acid were determined. Experiments were carried out in micellar solutions of 3% Brij 35, at pH 2 and 12, and in acetonitrile. Both metabolites absorb in the UV-A and UV-B regions, and emit fluorescence in the visible region of the solar spectrum. Shifts were not observed in the absorption spectra, at pH 2 and 12. The low phi(c), between 10(-5) and 10(-2), shows that both compounds are photostable in the experimental conditions. For rhizocarpic acid, two values of pK(a) were obtained: 5.1 corresponding to the hydroxyl group, and 9.0 corresponding to the protonated nitrogen. Calycin presents only one value of pK(a): 4.9, that is attributed to the hydroxyl group. L-(+)-Gluconic-gamma-lactonic acid was used as a reference model; the compound showed greater photoinstability, demonstrating that the photodegradation observed occurs mainly in the oxolane carbonylic ring. (C) 2002 Published by Elsevier Science B.V.
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