Effect of quantum tunneling on single strand breaks in a modeled gas phase cytidine nucleotide induced by low energy electron: A theoretical approach.

Effect of quantum mechanical tunneling on single strand breaks induced by low energy electron (LEE) has been investigated in a modeled gas phase system, 2′-deoxycytidine-3′-monophosphate (3′-dCMPH). The potential energy curves for the sugar-phosphate C-O (3′ C-O) bond cleavage have been generated using second order Mo\ller-Plesset perturbation theory at the 6-31+G(d) accuracy level. Results from the electronic structure theory calculations in conjunction with our time dependent calculations for the 3′ C-O bond rupture in 3′-dCMPH using local complex potential based time dependent wave packet approach show significant quantum tunneling of the 3′ C-O bond from the bound vibrational states above 1 eV of the anionic potential energy curve. A comparison of the fragmentation profile with that of our earlier gas phase investigations based on Hartree-Fock and density functional theory - Becke, 3-parameter, Lee-Yang-Parr methods with 6-31+G(d) basis set is also provided. Further, inspection of the singly occupied molecular orbitals generated at different 3′ C-O bond lengths clearly indicates the electron transfer from the low lying base-π* shape resonance state to the phosphate P = O π* orbital of the DNA backbone during the strand breaks. The decisive step during LEE induced strand breaks follows via 'charge induced dissociation' (CID) for the metastable anion formed below 1 eV, whereas quantum mechanical tunnel-ing is out-weighted the CID mechanism for the LEE above 1 eV. [ABSTRACT FROM AUTHOR]