title: Photophysical, photochemical, and thermodynamic properties of shikimic acid derivatives: calycin and rhizocarpic acid (lichens).
abstract: 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.
authors.affiliation: Chemistry and Biology Institute, Faculty of Sciences, University of Valparaiso, Chile. maria.hidalgo@uv.cl
authors.forename: M E
authors.initials: ME
authors.lastname: Hidalgo
authors.forename: E
authors.initials: E
authors.lastname: Fernández
authors.forename: M
authors.initials: M
authors.lastname: Ponce
authors.forename: C
authors.initials: C
authors.lastname: Rubio
authors.forename: W
authors.initials: W
authors.lastname: Quilhot
mesh_terms: D006863:Hydrogen-Ion Concentration; D019476:Insect Proteins / Q000737:chemistry / Q000528:radiation effects*; D008011:Lichens / Q000528:radiation effects*; D008314:Malonates / Q000737:chemistry / Q000528:radiation effects*; D015394:Molecular Structure; D010100:Oxygen; D010777:Photochemistry; D012765:Shikimic Acid / Q000737:chemistry; D013816:Thermodynamics; D014466:Ultraviolet Rays
chemical_list: D019476:Insect Proteins; D008314:Malonates; C442323:p18 protein, Leucophaea maderae; C466066:rhizocarpic acid; D012765:Shikimic Acid; D010100:Oxygen