DFT study of the interaction between guanine and water

The geometries, energies and vibrational properties of the four cyclic complexes formed between guanine and water are computed using density functional theory (B3LYP) combined with the 6-31+G(d,p) basis set. The results obtained with geometry optimization (FULL) made without any constraint are compared with the ones previously obtained when considering only the amino group hydrogen atoms as non planar (NPA), Intermolecular distances and hydrogen bond energies for the FULL and NPA geometries do not greatly differ and can be accounted for by a small difference in the basicity of the N3 acceptor atom. The same remark also holds for most of the vibrational modes except for the wagging and twisting modes of the amino group, which are very sensitive to the geometry of this group. (C) 2000 Elsevier Science B.V. All rights reserved.