ULTRAVIOLET IRRADIATION OF NUCLEIC ACIDS COMPLEXED WITH HEAVY ATOMS-II. PHOSPHORESCENCE AND PHOTODIMERIZATION OF DNA COMPLEXED WITH Ag*

Abstract— We have studied the luminescence (at 77°K) and photochemistry (at 298°K) of a variety of polynucleotides complexed with Ag⁺. In all cases we observed that Ag⁺ induces a 'heavy atom effect' as indicated by quenching of fluorescence, enhancement of phosphorescence, and reduction of triplet lifetimes. The enhancement by Ag⁺ of the phosphorescence intensity of poly (dT) and DNA paralleled a 20-fold enhancement of the rate of thymine dimerization. These results suggest a possible triplet precursor for thymine dimerization in Ag⁺ complexes. Dimers were also made with a variety of triplet sensitizers, and Ag⁺ increased the dimer yield two- to four-fold, depending on the sensitizer used.