Adsorption of histidine on cerium oxide model surfaces was investigated by synchrotron radiation photoemission, resonant photoemission, and near edge X-ray absorption fine structure spectroscopies. Histidine was evaporated in a vacuum onto ordered stoichiometric CeO2(111) and partially reduced CeO1.9 thin films grown on Cu(111). Histidine binds to CeO2 in anionic form via the carboxylate group and all three nitrogen atoms, with the imidazole ring parallel to the surface. The amino nitrogen atom of the imidazole ring (IM) is deprotonated, and both IM nitrogen atoms form strong bonds via π orbitals, while the α-amino nitrogen interacts with the oxide via its hydrogen atoms. In the case of CeO1.9, the deprotonation of the amino nitrogen of the imidazole ring is less pronounced and N K-edge spectra do not show a clear orientation of the ring with respect to the surface. A minor reduction of the cerium surface on adsorption of histidine was observed and explained by charge exchange as a result of hybridization of the π orbitals of the IM ring with the f and d orbitals of ceria. Knowledge of histidine adsorption on the cerium oxide surface can be used for design of mediator-less biosensors where the histidine-containing proteins can be strongly bound to the oxide surface via the imidazole side chain of this residue.

The adsorption of histidine (His), and its peptide glycyl-glycyl-histidine (Gly-Gly-His), on Au(111) and Au(110) has been studied by soft X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the nitrogen and oxygen K-edges. The molecules were adsorbed on surfaces from acidic (pH ∼3) solution. The results are compared with our previous studies of the adsorption of histidine and its peptides on Au(111) deposited on Au(111) from neutral solutions. When deposited from acidic solution, His adsorbs as carboxylic and carboxylate forms on both Au(111) and Au(110) surfaces, whereas its peptide is present mainly in the carboxylic form. In contrast, both molecules deposited from neutral solution adsorbed mainly as carboxylates. The imino nitrogen atom of the imidazole ring plays a crucial role in the interaction with gold surfaces. The Au 4f core level shift indicates that a chemisorption rather than a physisorption process occurs.

ABSTRACT. The adsorption of cytosine, 6-azacytosine, 6-azacytidine and 5-azacytidine on the Au(111) surface has been studied by soft X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). Monolayer films of these molecules were adsorbed on Au(111) from aqueous solution, and the nature of bonding with this surface has been determined. Cytosine was adsorbed from the gas phase by evaporation, as well as from solution, on both the Au(111) and Au (110) through the N (3) atom of the pyrimidine ring dominates, but a second state is also 2 present. For deposition from solution, this second state dominates, and the molecular plane is no longer parallel to the surface. This state also bonds through the N (3) atom, but in addition interacts with the surface via the amino group. Two tautomers of 6-azacytosine were observed, and they and 6-azacytidine adsorb with similar geometries and chemical bonding via the azacytosine ring. The ribose ring does not appear to perturb the adsorption of azacytidine compared with azacytosine. The azacytosine ring is nearly but not perfectly parallel to the surface. 5-azacytidine adsorbs with the azacytosine ring very nearly parallel to the surface, as an imino tautomer.3

The dispersion dependences of electron excitations in crystalline graphite and single-layer graphene have been studied taking the electron spin into consideration. The correlations of the energy spectra of electron excitations and, for the first time, the compatibility conditions for two-valued irreducible projective representations characterizing the symmetry of spinor excitations in the indicated structures are determined, as well as the distributions of spinor quantum states over the projective classes and irreducible projective representations for all high-symmetry points in the corresponding Brillouin zones. With the help of theoretical symmetry-group methods for the spatial symmetry groups of crystalline graphite and single-layer graphene (in particular, the splitting of п-bands at the Dirac points), the spin-dependent splittings in their electron energy spectra are found. The splitting magnitude can be considerable, e.g., for dichalcogenides of transition metals belonging to the same spatial symmetry group. But it is found to be small for crystalline graphite and single-layer graphene because of a low spin-orbit interaction energy for carbon atoms and, as a consequence, carbon structures.