Structures and Properties of the Planar G·C·G·C Tetrads: Ab Initio HF and DFT Studies

Abstract

To reveal the details of molecular geometries and properties of the GCGC tetrad, reliable quantum chemical methods (HF and DFT) in conjunction with a large basis set (6-311G(d,p)) were used to locate the local minima of the GCGC tetrad structures and to predict their energies and electrostatic potential maps. The study reveals that both A type forms of the GCGC tetrad form stable structures. The stabilization energies relative to the isolated bases amount to approximately 72 kcal/mol more than was predicted for the isolated G tetrad. The inter GC pair interaction contributes about 17−19 kcal/mol to the total stabilization energy. The large stabilization energies confirm that the stabilization of the tetrads plays a key role in the four-stranded helices. The GCGC-a1 conformer formed through the inter base pair H(N4)−O6 hydrogen bonding is about 2 kcal/mol more stable than the GCGC-a2 form. However, the relative stability of both forms could be affected by the presence of cations that might balance the elec...