CHARACTERIZATION OF PEPTIDE-SURFACE INTERACTIONS

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Biomolecule-surface interactions are essential to the efficacy of bioanalytical separations, biosensors, and prosthetic devices. Despite their importance, very little is known about fundamental chemical and physical interactions between biomolecules and surfaces. The goal of the proposed research is to characterize the non-covalent interactions of peptides with metal surfaces. This proposal describes systematic studies aimed at determining how specific functional groups and conformational constraints in amino acids, peptides, and small polypeptides control the adsorption, orientation, and surface interactions of these biomolecules. The results will significantly extend our understanding of peptide-metal interactions, and our understanding of the adsorption behavior of polyfunctional molecules at solution-solid interfaces. Peptides are excellent chemical and spectroscopic models for proteins. We will therefore use peptides to determine the relative importance of specific functional groups and conformational constraints in determining the absorptivity and surface interactions of peptides and proteins with non-reactive surfaces. For studies of the non-covalent adsorbate-surface interactions that are common to all substrates, noble metals are nearly ideal model surfaces. Their surface chemistry is relatively simple compared with that of quartz, silica, and polymers. The net surface charge and hydrophobicity can be varied simply by changing the applied potential, the supporting electrolyte, and the metal itself. The primary tools that will be used in these studies are Raman and infrared spectroscopy, with particular emphasis on surface-enhanced Raman spectroscopy (SERS) because of its unique sensitivity and selectivity for adsorbates on noble metal surfaces. Our preliminary SERS results demonstrate the feasibility of this approach, and reveal that peptide absorption is governed by specific functional group-surface interactions that prescribe the adsorbate orientation and conformation at the solution- metal interface. In particular, the results suggest that peptides interact strongly with silver through the terminal amine group and through aromatic side chains, particularly tyrosine, In the proposed work we will characterize these and other peptide functional group-surface interactions in detail, and evaluate their relative contributions to peptide absorptivity. A secondary objective is to determine how the surface charge, hydrophobicity, and roughness affect peptide and polypeptide adsorption.