The adsorption of glutamic acid onto two-dimensional (2-D) Ni clusters on Au{111} has been investigated
by reflection absorption infrared spectroscopy (RAIRS) and scanning tunneling microscopy (STM). Adsorption
at 300 K leads to two distinct adsorbate species, which we conclude are zwitterionic species adsorbed either
at Ni-like sites in the center of the clusters or at interfacial sites at the edges of clusters. Adsorption of
(S)-glutamic acid causes the complete destruction of clusters of initial diameter <3 nm. We conclude that the
Ni islands have been corroded, resulting in the formation of a Ni salt, presumably nickel(II) glutamate. On
annealing to 350 K, chains of one-dimensional (1-D) molecular features are observed in STM experiments.
We discuss the possible composition and structure of this salt and conclude that the chains most likely consist
of nickel(II) pyroglutamate. Pyroglutamate is well-known to be produced by heating of glutamate salts. The
intermolecular bonding and azimuthal alignment of the 1-D chains are discussed.
The adsorption of (S)-glutamic acid onto Ni{111} from solution was investigated with reflection absorption infrared spectroscopy as functions of modification temperature and pH. Modification at 300 K results in the formation of approximately one monolayer of adsorbate. The extent of protonation of the adsorbate decreases with increasing pH. Modification at 350 K produces a thicker adsorbate layer, which is assigned to nickel glutamate (low pH) and a mixture of nickel and sodium glutamate (high pH). Adsorption of methylacetoacetate onto the chirally modified surfaces occurs predominantly in the diketone tautomeric form when adsorbed glutamic acid exists in the protonated form. By contrast, methylacetoacetate exists primarily in the enol tautomeric form when glutamate (i.e., anionic) species are present. The implications of our findings for understanding the mechanism of Ni-catalyzed β-ketoester hydrogenation are discussed.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.