Photo- and radiation chemistry of retinoids, polyenes and related molecules

Laser flash photolysis and pulse radiolysis have led to the characterisation of several short-lived intermediates formed after irradiation of retinoic acid and retinyl acetate in methanol or hexane. Absorption maxima extinction coefficients and decay constants are reported and discussed. The results suggest that skin photosensitivity caused by retinyl acetate might be greater than that due to retinoic acid. Preliminary experiments have also been carried out in somewhat more biological relevant environments with retinoids (i.e. detergent micelles, DNA and vesicles) by conventional flash photolysis. The rate of decay of the transient (triplet) species for each of the compounds have been determined. The decay rate did not increase in the presence of oxygen so that no bimolecular rate constant for oxygen quenching could be obtained. The lifetimes of each transient species are much longer-lived in the 'biological environments' than in organic solvents. The triplet absorption characteristics of a series of polyene C15 aldehydes and C18 ketones were obtained by laser flash photolysis and pulse radiolysis, and compared with those previously obtained for retinal, the chromophore of the visual pigment rhodopsin. Preliminary studies on photochemical and photobiological properties of some 1.4-benzodiazepines - Librium, Mogadon and Valium by laser flash photolysis are reported. (author)