(732g) Kinetics and Mechanism of Aspartic Acid Adsorption and Its Explosive Decomposition on Cu(100)

Amino acids are chiral molecules and a popular choice for studies of enantioselective surface chemistry. In this work, we use isotopically labeled aspartic acid (Asp, HO₂CCH(NH₂)CH₂CO₂H) on a Cu(100) single crystal surface to understand its detailed decomposition mechanism and kinetics. X-ray photoemission spectroscopy (XPS) and temperature programmed reaction spectroscopy (TPRS) have enabled us to identify the products and the mechanism of L-Asp decomposition on Cu(100). XP spectra demonstrate that Asp adsorbed on Cu(100) surfaces is in bi-aspartate form (-O₂CCH₂CH(NH₂)CO₂-). Asp decomposes by a vacancy-mediated explosive surface reaction mechanism in which the reaction rate accelerates with increasing extent of reaction. Once initiated, the C3-C4 and C1-C2 bonds break sequentially to produce CO₂. The remaining intermediate (C₂H₅N) decomposes to produce N≡CCH₃ and H₂. This work advances our understanding of the Asp decomposition mechanism on Cu surfaces by probing the fate of the hydrogen atoms in the C₂H₅N intermediate generated by Asp decarboxylation.