Adenine deactivation in DNA resolved at the CASPT2//CASSCF/AMBER level

Abstract

We have employed hybrid CASPT2//CASSCF/AMBER calculations to map the (1)L(a)(1pipi*) deactivation path of a single quantum mechanical adenine in a d(A)(10).d(T)(10) double strand in water that is treated at the molecular mechanics level. We find that (a) the L(a) relaxation route is flatter in DNA than in vacuo and (b) the L(a) relaxation energy in DNA is much larger than the stabilization energy of the corresponding L(a) excimer. An intra-monomer relaxation process is found to be compatible with the multiexponential decay recorded in DNA, possibly including the longer (4100 ps) lifetime component.