Theoretical elucidation of the amino acid interaction with graphene and functionalized graphene nanosheets: insights from DFT calculation and MD simulation.

Graphene-amino acid interaction is gaining significance mainly based on its possible biomedicine applications. The density functional theory (DFT) calculation and molecular dynamics simulation (MD) are applied to obtain a comprehensive understanding of the adsorption mechanism of three kinds of amino acids, namely, alanine (Ala), glycine (Gly), and valine (Val) over the surface of graphene and functionalized graphene nanosheets. In this study, several analyses such as solvation energy, adsorption energy, intermolecular distances, and charge properties are used to explore the adsorption behavior of amino acid on the nanosheets. The calculated adsorption energies show that the interaction of amino acids with functionalized graphene is greater than the pristine graphene. Regarding DFT computations, the adsorption of Val on the graphene about - 10 kJ/mol is stronger than Gly and Ala. Meanwhile, it is found that the geometrical parameters and electronic properties of graphene change drastically upon functionalization, and the formation of hydrogen bonds between -COOH functional group and amino acids enhances the adsorption energy about 12-30%. To obtain a deeper comprehension of the interaction nature, the atoms in molecules (AIM) and the natural bond orbital (NBO) studies have been performed. Furthermore, the MD simulations are employed to assess the dynamic properties of our designed systems. The results from the present study demonstrate that the movement of the amino acids into the carriers is spontaneous and forms stable complexes.