Photophysical properties of aminomethylpsoralen in presence and absence of DNA

Abstract

Some properties of the first triplet and singlet excited states of 4′-aminomethyl-4,5′,8-trimethylpsoralen have been determined by laser flash photolysis and spectrofluorimetry. In water the lowest triplet has an intrinsic lifetime of 100 μs and is quenched by the molecule in its ground state with a rate constant k Q = 10 9 M −1·s −1 and by thymine with a rate constant k q = 2 · 10 8 M −1·s −1. Addition of 0.5 mg/ml of calf thymus DNA causes the disappearance of the aminomethylpsoralen triplet absorption immediately after the laser flash excitation and extinguishes the fluorescence emission of a 6 · 10 −5 M solution of aminomethylpsoralen. These experiments show that the first singlet excited state which is rapidly deactivated in the presence of DNA could be the precursor of the first pyrimidine photoadduct.