Synthesis of oligomeric and monomeric functionalized graphene oxides and a comparison of their abilities to perform as protein ligands and enzyme inhibitors

Graphene oxide (GO) is a versatile, monomolecular layered nanomaterial that possess various oxygen containing functionality on its large surface. These characteristics allow GO to interact with a variety of materials, for application to a number of areas. The strength and selectivity of these interactions can be improved significantly through further functionalization. In this paper we describe the functionalization of GO and its application as a protein ligand and an enzyme inhibitor. The work reported in this paper details how chymotrypsin inhibition can be improved using GO functionalized with a monomeric and oligomer layer of tyrosine. The results indicated that the mono and oligo functionalized systems performed extremely well, with Ki values nearly four times better than GO alone. Our original premise was that the oligomeric system would bind better, due to the length of the oligomeric arms and potential for a high degree of flexibility. However, the results clearly showed that the shorter monomeric system was the better ligand/inhibitor. This was due to weaker intramolecular interactions between the aromatic side chains of tyrosine and the aromatic surface of GO. Although these are possible for both systems, they are cooperative and therefore stronger, for the oligomeric functionalized GO. As such, the protein must compete and overcome these cooperative intramolecular interactions before it can bind to the functionalized GO. Whereas, the tyrosines on the surface of the monomeric system interact with the surface of GO through a significantly weaker mono-valent interaction, but interact cooperatively with the protein surface.