ELECTRONIC-SPECTRA, STRUCTURE AND PHOTOISOMERIZATION OF UROCANIC ACID

Electronic absorption and fluorescence spectra of urocanic acid are st udied in aqueous solution at different pH. The observed results are ex plained using molecular orbital geometry optimization calculations for the ground states of a number of tautomers of urocanic acid including those of its anion, followed by calculation of electronic transitions . The isomers of urocanic acid which would strongly absorb UV-B radiat ion have thus been identified. Further, the possible mechanisms of iso merization of urocanic acid from the trans- to cis-form which is relat ed to its role in immunosuppression and UV-B induced skin cancer have been suggested.