Binding of Gold Nanoclusters with Size-Expanded DNA Bases:  A Computational Study of Structural and Electronic Properties

Binding of gold nanoclusters with size-expanded DNA bases, xA, xC, xG, and xT, is studied using quantum chemical methods. Geometries of the neutral xA-Au₆, xC-Au₆, xG-Au₆, and xT-Au₆ complexes were fully optimized using the B3LYP density functional method (DFT). The gold clusters around xA and xT adopt triangular geometries, whereas irregular structures are obtained in the case of gold clusters complexed around xC and xG. The lengths of the bonds between atoms in the x-bases increase on gold complexation. The aromatic character of the x-bases also increases on gold complexation except for the five-member rings. A significant charge transfer from the x-base to gold atoms is seen in these complexes. Second-order interactions are observed in addition to direct covalent bonds between gold atoms and x-bases.