Vibrational spectroscopic characterization of self-assembling oligopeptides.

In the emerging field of tissue engineering, the development of synthetic materials promoting cell growth has led to the study of functionalised biomimetic materials and in particular to investigations on regular alternating polar/non-polar oligopeptides such as EAK-16. The characteristic of EAK-16 is to have a preferential beta-sheet structure, to be resistant to proteolytic cleavage and self-assemble into an insoluble macroscopic membrane. Its ability to create stable self-assembling layers derives from hydrophobic interactions between the -CH3 groups of non-ionic residues and complementary ionic bonds between acidic and basic amino acids. The stability of these layers is strongly influenced by the secondary structure of the peptide and can be enchanced by the regulation of pH and the presence of monovalent metallic ions. In order to evaluate the ability to form self-assembled layers on oxidised titanium surfaces, commonly present in bone prostheses, we investigated the conformations of five different oligopeptides (from 16 to 19 residues) derived from EAK-16 but modified in their sequence by substitution of acidic, basic and neutral amino acids or by the addition at the N-terminus of the RGD sequence, able to control osteoblast adhesion. The changes in the peptide structure were followed by Raman and IR spectroscopy. Indeed, these vibrational techniques have become a versatile tool in protein science and their application in characterising protein or peptides in biotechnology, pharmaceutical production and food industry has been highly developed.