Psoralen photochemistry and nucleic acid structure

Many new psoralen derivatives have been synthesized in an effort to enhance their water solubility and their binding to nucleic acids. Availability of the very soluble strongly binding compounds has improved our abilities to follow the optical changes associated with the photochemistry of psoralens with DNA. Changes in both absorbance and fluorescence are presented in this review. A kinetic model for the photochemistry concludes that the detailed kinetics is dominated by the equilibrium constant for intercalation of the psoralen in the DNA, the quantum yield for photoaddition to DNA once intercalated and the quantum yield for photodestruction of the drug in water. With these 3 parameters the kinetics of photochemistry is predictable. The values of these parameters for numerous derivatives of 8-methoxypsoralen and 4,5',8 trimethylpsoralen are presented. Application of this photochemistry to a study of nucleic acid secondary structure in chromatin, fd bacteriophage, and in ribosomes is reviewed.