Interactions of phenylglycine with amorphous solid water studied by temperature-programmed desorption and photoelectron spectroscopy

Abstract

Temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) have been employed to study the interactions of phenylglycine (PheGly) with amorphous solid water (ASW) nanolayers (10–50ML). First, the adsorption and growth of PheGly layers on an AlOx/NiAl(110) surface have been examined. After that, mixed PheGly–ASW layers have been grown on the alumina surface at 110K. Alternatively, PheGly molecules (from submonolayer to multilayer coverages) have been deposited on top of the ASW surfaces. In mixed PheGly–ASW nanolayers the PheGly phase displays hydrophobic behavior and accumulates near the surfaces of the films, while top-deposited PheGly wets the ASW films forming closed overlayers at low coverages. H2O desorption from the PheGly–ASW films is strongly influenced by the PheGly molecules, i.e., the crystallization of ASW is partially inhibited in the vicinity of the amino acid and a lower desorption temperature of H2O molecules than from pure ASW layers was detected. Thicker PheGly overlayers on ASW provide a kinetic restriction to H2O desorption from the underlying ASW layers until the PheGly molecules become mobile and develop pathways for water desorption at higher temperatures. The results are discussed with respect to the previously obtained data for glycine–ASW layered systems. It has been demonstrated that the substitution of the hydrogen atom in glycine with a phenyl group does not lead to detectable changes in the pathways of ASW desorption. However, desorption of PheGly differs from the desorption of glycine from the similarly structured glycine–ASW nanolayers. The differences are interpreted in terms of adsorbate–adsorbate and adsorbate–substrate interactions.