Surface chemistry of glycine on Pt{111} in different aqueous environments

Abstract

Adsorption of glycine on Pt{111} under UHV conditions and in different aqueous environments was studied by XPS (UHV and ambient pressure) and NEXAFS. Under UHV conditions, glycine adsorbs in its neutral molecular state up to about 0.15 ML. Further deposition leads to the formation of an additional zwitterionic species, which is in direct contact with the substrate surface, followed by the growth of multilayers, which also consist of zwitterions. The neutral surface species is most stable and decomposes at 360 K through a multi-step process which includes the formation of methylamine and carbon monoxide. When glycine and water are co-adsorbed in UHV at low temperatures (< 170 K) inter-layer diffusion is inhibited and the surface composition depends on the adsorption sequence. Water adsorbed on top of a glycine layer does not lead to significant changes in its chemical state. When glycine is adsorbed on top of a pre-adsorbed chemisorbed water layer or thick ice layer, however, it is found in its zwitterionic state, even at low coverage. No difference is seen in the chemical state of glycine when the layers are exposed to ambient water vapor pressure up to 0.2 Torr at temperatures above 300 K. Also the decomposition temperature stays the same, 360 K, irrespective of the water vapor pressure. Only the reaction path of the decomposition products is affected by ambient water vapor.

Co-adsorption of water and glycine on Cu{110}

“…Surprisingly then, our results show that, over a wide range of temperature and pressure, the pure water and glycine overlayers are more stable than the mixed phases, suggesting that the ability to form intermixed hydrogen-bonded networks between the anionic amino acid and water is not the reason behind the extraordinary reactivity between H 2 O and gly (or ala). If we consider that Shavorskiy et al 67 found no evidence of reaction between glycine and water when the Cu{110} surface was presaturated by glycine, we can also exclude the fact that the reaction could proceed through an Eley-Rideal mechanism; therefore the only alternative remaining is that, at submonolayer coverage, the glycine islands are surrounded by a reactive water boundary region. 3 The phase diagram for the glycine/H 2 O equilibrium (without vdW corrections) as a function of the surface temperature (T) and water pressure P(H 2 O).…”

Adsorption of Methyl Acetoacetate at Ni{111}: Experiment and Theory

“…25,26 Our recent work on the adsorption of chiral modifiers on Ni, Pt and Cu surfaces has shown that the combination of XPS and NEXAFS is very powerful in characterizing the adsorption complex in terms of chemical state, bond coordination and molecular orientation. 19,[27][28][29][30] These spectroscopies do not depend on long-range order and can even be applied under near-ambient pressure conditions. They are therefore well suited for the study of chiral modifiers and reactants on Ni surfaces.…”

Chiral selectivity of amino acid adsorption on chiral surfaces—The case of alanine on Pt

“…[46] In line with these calculations, recent experiments show that glycine adsorbs in its pristine form on Pt(111) at low coverages, showing that, similar to Pd(111) surfaces the molecule-molecule interaction stabilizes the zwitterionic form. [46,51] In the present paper, we concern ourselves with low-coverage adsorption where molecule-molecule interaction is negligible.…”