Structural characterization of biomolecules on solid surfaces

Abstract

● Intrarow Adsorption Structure of Glycine on Ge(100) The adsorption structure of glycine on Ge(100) was investigated using scanning tunneling microscopy (STM), density functional theory (DFT) calculations, and high-resolution photoemission spectroscopy (HRPES). We found a major adsorption feature of glycine on Ge(100) in the STM images. This feature appeared as a bright protrusion between two dimer rows with a dark adjacent dimer. The position of the bright protrusion located in the middle of the two dimer rows indicates a multibonding adsorption structure. The results of the theoretical calculations confirm that the adsorption structure of glycine on Ge(100) (between two possible multibonding adsorption structures) is an ‘intrarow O??H dissociated and N dative bonded structure’. In the HRPES experiments, we found an N 1s peak (at 399.5 eV) and two O 1s peaks (at 531.1 and 532.0 eV), which represent strong evidence that the adsorption configuration of glycine on Ge(100) is composed of both O-H dissociation and N dative bonding. All our STM, DFT, and HRPES results suggest that the adsorption structure of glycine molecules on Ge(100) is an ‘intrarow O??H dissociated and N dative bonded structure’.

● The Adsorption Configuration of Valine on Ge(100) The adsorption geometry of valine molecules on Ge(100) surface were investigated by observing four core-level spectra (Ge 3d, C 1s, N 1s, and O 1s) using high-resolution photoemission spectroscopy (HRPES). In the HRPES spectrum, the binding energy of the single N 1s peak for valine adsorbed on a Ge(100) surface is similar to the energies of glycine, ammonia, or alanine adsorbed on the Ge(100) surface via N dative bonding. The O 1s signal is divided into two non-equivalent oxygen peaks, indicating that only one oxygen atom in the carboxyl group of valine participates in bonding with the Ge(100) surface. As a result, we conclude that both amine and carboxyl groups in valine molecules concurrently take part in the adso...