NEXAFS and XPS investigation of self-assembling biomaterial

Some of the most promising new synthetic biomaterial scaffolds are composed of self-assembling peptides that can be modified to contain biologically active motifs. The development of synthetic materials promoting cell growth aims at the realization of systems suitable for implantology or sensoristic applications. The final goal is to establish methodologies to control the adsorption/anchoring of special oligopeptide sequences capable to give self-organised layers on suitable surfaces. Peptide-based biomaterials can be fabricated to give rise to two- and three-dimensional structures. In this contribution we present results obtained by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption spectroscopy (NEXAFS), concerning the electronic structure of a 16 units peptide as deposited onto Au and TiO2 substrates. The peptide has been synthesized on purpose to give rise to a special sequence of the constituting amino acids (L-Alanine, L-Glutammic acid and L-Lysine). The TiO2 substrate has been grown onto a Si(111) disk; XPS data confirmed the surface stoichiometry. Data concerning some basic amino acids used in the sequence are also presented. XPS spectra have been measured either for the substrate and for the adsorbed peptide, at the C1s, N1s, O1s, Ti2p and Au4f core levels. Angular dependent NEXAFS has been performed at both C-K and N-K. Feature assignment is discussed and preliminary considerations concerning the angular dependence of specific resonances are also reported. Static exchange ab initio (STEX) calculations are in progress, in order to simulate the expected NEXAFS spectra and their polarization dependence.