DFT Investigation of the Interaction of Gold Nanoclusters with Nucleic Acid Base Guanine and the Watson-Crick Guanine-Cytosine Base Pair

The interaction of gold nanoclusters (Au, n = 2, 4, 6, 8, 10, 12) with nucleic acid purine base guanine (G) and the Watson-Crick guanine-cytosine (GC) base pair through the major groove site (N7 site of guanine) of DNA was investigated theoretically. Geometries of complexes were optimized at the density functional theory (DFT) level employing the hybrid B3LYP functional. The 6-31G(d) basis set was used for all atoms except gold, for which the LANL2DZ effective core potential (ECP) was used. Natural population analysis was performed to determine NBO charges. The vertical first ionization potential and electron affinity of guanine and the guanine-cytosine base pair and their complexes with gold nanoclusters were also analyzed. It was revealed that gold clusters interact more strongly with the GC base pair than with isolated guanine. It was found that consequent to the binding of gold nanoclusters a substantial amount of electronic charge was transferred from guanine (or the guanine-cytosine base pair) to the gold clusters. Furthermore, the amount of the electronic charge transferred to the gold cluster was found to be larger for GC-Au-n complexes than that in the G-Au-n complexes. The vertical ionization potential, electron affinity, and biological significance of the interaction of gold nanoclusters with nucleic acid building blocks have also been discussed.