Fig 5.

Qualitative representation of HOMOs of 5′ApG-3′ versus 5′-GAp-3′ (a) and 5′ApA-3′ versus 5′-AAp-3′ (b) steps. The extent of orbital overlap and delocalization is notably greater for the 5′ApG-3′ and 5′-ApA-3′ steps. The HOMOs were calculated by using HYPERCHEM 5.1 (restricted Hartree–Fock level with 3-21G* basis set). The atomic coordinates of the bases were obtained from insight ii based on standard B-DNA geometry and the sugar-phosphate backbones were replaced with a methyl group.