Nanoparticles functionalized by amino acids are studied. X-ray absorption near edge spectra (XANES) at the S L2,3 edge of the sulfur-containing proteinogenic amino acids were measured at the storage ring facility BESSY-II. The XANES spectra near the S L2,3 edge were calculated by both the full multiple scattering approach and the finite difference method within and beyond a muffin-tin approximation. Density functional theory (DFT) was applied for the optimization of the geometry of the sulfur-containing proteinogenic amino acids within LDA and GGA approaches. Several models of exchange-correlation potentials including hybrid ones were tested. The results of DFT optimization were analyzed by a comparison of the XANES spectra calculated for the sets of derived structural parameters with the experimental data.
The S L2,3 edge XANES is shown to be sensitive to study the variations of local and electronic structure of sulfur containing amino acid – methionine functionalizing SiO2 nanoparticles. It is shown that inclusion of the non-muffin-tin effects is important for modeling the S L2,3 edge XANES spectra of sulfur-containing amino acids and yields even better agreement with the experimental results, if beyond muffin-tin approximation approaches are used.

Fig. 2. Methionine is bound via a spacer molecule to silica nanoparticle



The research is in progress in collaboration with the group of Prof E. Ruehl ( Beril Free University, Germany)