DFT studies on hydrogen bonded complexes of thymine with formamide

Abstract

Hydrogen bond interactions of the thymine-formamide complexes have been investigated using B3LYP method. The structures of four possible cyclic double H-bonded<span style="color: rgb(35, 31, 32);"> complexes have been fully optimized at 6-31+G(d), 6-311++G(d, p) and 6-311++G(2d, 2p), respectively. Upon complexation with formamide, the thymine monomer undergoes some deformation of the bonds, especially in the interaction of strong H bonds. Within one complex, the N(T)-H…O(F) bond is stronger than the N(F)-H…O(T) bond. Natural bond orbital analysis indicates that all atoms of thymine experience a charge redistribution upon complexation with formamide, especially those involved in the formation of H bonds. The relative orders of the occupancies of <i style="">σ</i>* (Y-H) and <i style="">E</i>(2) are consistent with the order of the corresponding H bonds strengths. An analysis of vibrational frequency shifts and IR intensities shifts has also been carried out. </span>