The interaction of graphene with biomolecules has a variety of useful applications. In particular, graphitic surfaces decorated with peptides are being considered for high performance biochemical sensors. The interaction of peptides with graphene can also provide insight into the binding behavior of larger biomolecules. In this investigation, we have computed the binding enthalpies of a series of GXG tripeptides with graphene using classical molecular dynamics. Explicit water molecules were included to capture the effect of solvent. Of the twenty amino acid residues examined (X in GXG), arginine, glutamine, and asparagine exhibit the strongest interactions with graphene. Analysis of the trajectories shows that the presence of graphene affects the peptide conformation relative to its conformation in solution. We also find that the peptides favor the graphene interface predominantly due to the influence of the solvent, with hydrophilic residues binding more strongly than hydrophobic residues. These results demonstrate the need to include explicit solvent atoms when modeling peptide-graphene systems to mimic experimental conditions. Furthermore, the scheme outlined herein may be widely applicable for the determination and validation of surface interaction parameters for a host of molecular fragments using a variety of techniques, ranging from coarse-grained models to quantum mechanical methods.

The characteristic properties of graphene make it useful in an assortment of applications. One particular application--the use of graphene in biosensors--requires a thorough understanding of graphene-peptide interactions. In this study, the binding of glycine (G) capped amino acid residues (termed GXG tripeptides) to trilayer graphene surfaces in aqueous solution was examined and compared to results previously obtained for peptide binding to single-layer free-standing graphene [A. N. Camden, S. A. Barr, and R. J. Berry, J. Phys. Chem. B 117, 10691-10697 (2013)]. In order to understand the interactions between the peptides and the surface, binding enthalpy and free energy values were calculated for each GXG system, where X cycled through the typical 20 amino acids. When the GXG tripeptides were bound to the surface, distinct conformations were observed, each with a different binding enthalpy. Analysis of the binding energy showed the binding of peptides to trilayer graphene was dominated by van der Waals interactions, unlike the free-standing graphene systems, where the binding was predominantly electrostatic in nature. These results demonstrate the utility of computational materials science in the mechanistic explanation of surface-biomolecule interactions which could be applied to a wide range of systems.

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