AVS 63rd International Symposium & Exhibition
    Surface Science Thursday Sessions
       Session SS-ThM

Paper SS-ThM4
Competing Forces in Chiral Surface Chemistry: Enantiospecificity versus Enantiomer Disproportionation

Thursday, November 10, 2016, 9:00 am, Room 104D

Session: Chirality and Enantioselectivity on Surfaces; Ionic Liquid Interfaces
Presenter: Andrew Gellman, Carnegie Mellon University
Authors: A.J. Gellman, Carnegie Mellon University
Y. Yun, Carnegie Mellon University
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{The enantiospecific adsorption of chiral molecules on chiral surfaces is dictated by two competing forces the enantiospecificity of adsorption energetics and the propensity of enantiomers to disproportionate into homochiral (conglomerate) or heterochiral (racemate) clusters. These phenomena have been studied by measuring the surface enantiomeric excess, ees, of mixtures of chiral amino acids adsorbed on Cu surfaces and in equilibrium with gas phase mixtures of varying enantiomeric excess, eeg. Alanine adsorption on Cu{3,1,17}R&S surfaces is non-enantiospecific, ees = eeg, because alanine enantiomers do not interact with either the surface or one another enantiospecifically. Aspartic acid adsorbs enantiospecifically on the Cu{3,1,17}R&S surfaces; eesnot= eeg, even during exposure to a racemic mixture in the gas phase, eeg=0. Exposure of the achiral Cu{111} surface to non-racemic aspartic acid, eeg not= 0, results in local amplification of enantiomeric excess, |ees| > |eeg|, as a result of homochiral disproportionation. Finally, in spite of the fact that the Cu{653}R&S surfaces are chiral, the adsorption of aspartic acid mixture is dominated by homochiral disproportionation of adsorbed enantiomers rather than enantiospecific adsorbate-surface interactions, |ees| > |eeg|. All of these types of behavior are captured by a Langmuir-like adsorption isotherm that also describes competition between enantiospecific adsorption and both homochiral (conglomerate) and heterochiral (racemate) clustering of adsorbed molecules.}