DFT study of cyclic glycine-alanine dipeptide binding to gold nanoclusters

In this work, we studied the interactions between cyclic glycine-alanine dipeptide c(GA) and gold nanoclusters (Au_nNCs, where n = 2-10) using density functional theory (DFT), atoms-in-molecules theory (AIM), and natural bond orbital analysis (NBO). This dipeptide (DP) consists of two amino acid residues (glycine and alanine); thus, the preference of both residues for binding to gold atoms was examined. The preference of alanine residue to the studied Au_nNCs was found to be greater than that of glycine residue. Two types of interactions were exhibited between the Au_nNCs and c(GA), the partially-covalent partially-electrostatic type and electrostatic interaction. Performance of two DFT functionals and different basis sets is assessed. The results benchmark the importance of the DFT functional with dispersion and long-range corrections, as well as the polarization functions in the basis sets for the gold lusters-peptide binding. The binding energy (ΔE_bind) values of the c(GA)-Au_nNCs complexes in gas and water implicit solvent were compared with those previously published for cyclic glycine-glycine DP-Au_nNCs complexes. It was found that the ΔE_bind values of the former complexes are greater than those of latter ones in water solvent.