Sequence Dependent Photochemistry of Adenine-Thymine and Thymine-Adenine Dinucleotides

Abstract

Under ultraviolet irradiation, DNA thymine-adenine dinucleotide (TpdA) might undergo a cycloaddition while its isomer adenine-thymine deoxy-dinucleotide (dApT) is of high photostability. By using time-dependent density functional theory and molecular dynamics simulations, we found that the cycloaddition of TpdA is a barrierless process via a charge-transfer state. In contrast, the cycloaddition of dApT was found to be energy consuming. We also revealed that in aqueous solution, the average interbase distance of dApT is larger than that of TpdA, further contributing to the high photostability of dApT.