Role of base arrangements and intermolecular hydrogen bonding in charge-transfer states of thymine-adenine dinucleotide in aqueous solution

Charge-transfer (CT) states of thymine-adenine deoxy-dinucleotide (TpdA) were studied by using the UV vis spectroscopy, molecular dynamics simulations and time-dependent density functional theory. Two CT states emitting distinguished fluorescence are found in TpdA. They are derived from two base arrangements of adenine and thymine. Intermolecular hydrogen bonding interactions with water prevent the stacked bases from approaching too closely in the CT states. The thymine ring is planar in the CT states and the sugar of adenine should adopt C2-endo puckering. Without water, TpdA might form a photoproduct or relax to a CT state with a "boat-like" thymine ring. (C) 2017 Elsevier B.V. All rights reserved.