Ab initio study of the binding of collagen amino acids to graphene and A-doped (A = H, Ca) graphene

We present a theoretical study of the binding of collagen amino acids (AA, namely glycine, Gly; proline, Pro; and hydroxyproline, Hyp) to graphene (Gr). Ca-doped graphene and graphane (Gra) using density functional theory calculations and ab initio molecular dynamics (AIMD) simulations. It is found that binding of Gly, Pro and Hyp to Gr and Gra is thermodynamically favorable yet dependent on the amino acid orientation and always very weak (adsorption energies E-ads range from -90 to -20 meV). AIMD simulations reveal that room-temperature thermal excitations are enough to induce detachment of Gly and Pro from Gr and of all three amino acids from Gra. Interestingly, we show that collagen AA binding to Gr is enhanced dramatically by doping the carbon surface with calcium atoms (corresponding E-ads values decrease by practically two orders of magnitude with respect to the non-doped case). This effect is result of electronic charge transfers from the Ca impurity (donor) to Gr (acceptor) and the carboxyl group (COOH) of the amino acid (acceptor). The possibility of using Gr and Gra as nanoframes for sensing of collagen amino acids has also been investigated by performing electronic density of states analysis. It is found that, whether Gr is hardly sensitive, the electronic band gap of Gra can be modulated by attaching different number and species of AAs onto it. The results presented in this work provide fundamental insights on the quantum interactions of collagen protein components with carbon-based nanostructures and can be useful for developments in bio and nanotechnology fields. (C) 2010 Elsevier B.V. All rights reserved.