Aspartic acid adsorbed on Cu surfaces is doubly deprotonated. On chiral Cu(643) its enantiomers undergo enantiospecific decomposition via an autocatalytic explosion. Once initiated, the decomposition mechanism proceeds via sequential cleavage of the C3-C4 and C1-C2 bonds each yielding CO, followed by conversion of the remaining species into N[triple bond, length as m-dash]CCH.

The initial stage in the oxidation of Cu single crystal surfaces has been studied on a surface structure spread single crystal (S 4 C) exposing a continuous distribution of all Cu(hkl) surface orientations lying within 10°polar angle of the (111) plane, Cu(111) ± 10°-S 4 C. The uptake of oxygen across the Cu(111) ± 10°-S 4 C during exposure to O 2 at 300 K has been measured using spatially resolved X-ray photoelectron spectroscopy (XPS), and the resulting Cu 2 O surface oxide layer has been imaged using scanning tunneling microscopy (STM). Uptake of oxygen is dependent on surface step density and increases with increasing polar angle relative to the (111) pole. In contrast, the oxygen uptake does not depend on the crystallographic orientation of the step edge or, in other words, the kink density along the step edge. STM images reveal that once oxidation of the step edges begins, all of the boundaries of the Cu 2 O step oxide layer are oriented along (100) step edges in the Cu(111) terrace independent of the initial orientation of the step. In other words, the oxidizing step edges have no memory of their original orientation, and thus, the step growth depends only on step density and not on the kink density along the step edge. The combined use of both spatially resolved XPS and atomic scale imaging with STM on a Cu(111) ± 10°-S 4 C has provided unique insight into the origins of structure-sensitive surface chemistry.

No abstract

The mechanism and kinetics of aspartic acid (Asp, HO2CCH­(NH2)­CH2CO2H) decomposition on Cu(100) 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)­CH2 13CO2H), l-Asp-d 7 (DO2CCD­(ND2)­CD2CO2D), l-Asp-2,3,3-d 3 (HO2CCD­(NH2)­CD2CO2H), and l-Asp-15N-2,3,3-d 3 (HO2CCD­(15NH2)­CD2CO2H). The monolayer of Asp adsorbed on the Cu(100) surface is in a doubly deprotonated bi-aspartate form (−O2CCH­(NH2)­CH2CO2−). During heating, Asp decomposes on Cu(100) 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 to acetonitrile of the CD­(NH2)­CD2 intermediate formed by decarboxylation of l-Asp-2,3,3-d 3 and l-Asp-15N-2,3,3-d 3.