Para-aminobenzoic acid-photosensitized dimerization of thymine I. In DNA-related model systems

Abstract

Abstract Para-aminobenzoic acid (PABA) is able to photosensitize the dimerization of two adjacent thymines in aqueous solutions of free thymine base or thymidylyl-3′,5′-thymidine at wavelengths greater than 300 nm where thymine does not absorb. The dependence of dimer yield on a variety of reaction conditions when these two DNA- related systems were irradiated in the presence of PABA has been investigated. Reaction mechanisms have been proposed to account for the major processes taking place. The rate constants for the various constituent reactions have been assigned on the basis of experiment, values cited in the literature and calculations based upon these values as well as calculation based upon Stern—Volmer steady state analysis of the proposed mechanisms. Computer simulation of these mechanisms gave dimer yields which were in reasonable agreement with the experimental data.