The mechanism and kinetics of aspartic acid (Asp, HO2CCH(NH2)CH2CO2H) decomposition on several Cu(hkl) surfaces have been studied using x-ray photoemission spectroscopy and temperature programmed reaction spectroscopy. We investigate the Asp decomposition mechanism in detail using unlabeled D-Asp and isotopically labeled L-Asp-4-13C (HO2CCH(NH2)CH213CO2H), L-Asp-d7 (DO2CCD(ND2)CD2CO2D), L-Asp-2,3,3-d3 (HO2CCD(NH2)CD2CO2H), and L-Asp-15N-2,3,3-d3 (HO2CCD(15NH2)CD2CO2H). The monolayer of Asp adsorbed on Cu(hkl) surfaces is in a doubly deprotonated bi-aspartate form (-O2CCH(NH2)CH2CO2-). During heating, Asp decomposes on Cu(hkl) with kinetics consistent with a vacancy-mediated explosion mechanism. The mechanistic steps yield CO2 by sequential cleavage of the C3-C4 and C1-C2 bonds, and N≡CCH3 and H2 via decomposition of the remaining CH(NH2)CH2 intermediate. Deuterium labeling has been used to demonstrate that scrambling of H(D) occurs during the decomposition of the CD(NH2)CD2 intermediate formed by L-Asp-2,3,3-d3 and L-Asp-15N-2,3,3-d3. This reaction proceeds without contamination of the Cu surfaces and can be conducted catalytically and in steady state by exposing Cu(hkl) surfaces to a constant flux of Asp. This opens a window for the further exploration of enantiospecific catalysis on chiral Cu(hkl)R&S surfaces.

Kinetics and mechanism of aspartic acid adsorption and its explosive decomposition on Cu(hkl) surfaces

2019 Spring National Meeting

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