Competing Forces in Chiral Surface Chemistry: Enantiospecificity versus Enantiomer Aggregation

Abstract

The enantiospecific adsorption of enantiomer mixtures on surfaces is dictated by two competing forces: the enantiospecificity of adsorption energetics and the propensity of enantiomers to aggregate into homochiral (conglomerate) or heterochiral (racemate) clusters. These phenomena have been studied by measuring the surface enantiomeric excess, ees, of chiral amino acid mixtures adsorbed on Cu single-crystal surfaces and in equilibrium with gas-phase mixtures of varying enantiomeric excess, eeg. Alanine adsorption on Cu{3,1,17}RS ees ≠ eeg, even during exposure to a racemic mixture in the gas phase, eeg = 0. Exposure of the achiral Cu{111} surface to nonracemic aspartic acid, eeg ≠ 0, results in local amplification of enantiomeric excess on the surface, |ees| > |eeg|, as a result of h...