One of the key experimental challenges in the study of enantioselective surface chemistry is the development of tools or methods that can distinguish one enantiomer from the other. For two reasons we have identified aspartic acid (HO2CCH(NH2)CH2CO2H) as an ideal chiral probe for studying enantioselective surface chemistry on naturally chiral Cu single crystal surfaces. Firstly, it exhibits extremely highly enantiospecific surface reaction rates because of the fact that it decomposes by an explosive mechanism with highly non-linear kinetics. Secondly, it is an amino acid and as a consequence we are able to use *L-aspartic acid-1,4-13C2 (*L-Asp) which can be distinguished from D-aspartic acid (D-Asp) using mass spectrometry. These have been studied on the achiral Cu(110) and chiral Cu(3,1,17)R&S surfaces. Decomposition of Asp on the Cu(110) and chiral Cu(3,1,17)R&S surfaces yields CO2 and CH3-C�N as primary products. Not surprisingly, 13C labeling in *L-aspartic acid-1,4-13C2 show that the 13CO2 comes only from the carboxylate end-groups while labeling of other atoms shows that the CH3-C�N product arises only form the C2 and C3 carbon atoms. Exposure of a racemic mixtures of *L-Asp and D-Asp has been used to establish enantiospecific adsorption equilibria on the Cu(3,1,17)R&S surfaces. During exposure to the racemic mixture, the enantiomer with the higher binding energy is capable of displacing the more weakly bound enantiomer to establish a non-racemic adsorbed layer. In other words, exposure of the Cu(3,1,17)R&S surfaces to the racemic mixture in the gas phase results in a separation and enrichment of one of the two enantiomers on the surface. Recently we have shown that even the exposure of non-racemic mixtures of D- and *L-Asp to achiral Cu(111) surface can lead to amplification of enantiomeric excess on the surface. This can arise from the formation of homochiral clusters on the surface and can be modelled using a non-linear Langmuir-like isotherm that accounts for cluster formation.

Adsorption induced autoamplification of enantiomeric excess

248th National Meeting (2014)

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