The kinetic an mechanism of aspartic acid (Asp, HO2CCH(NH2)CH2CO2H) adsorption and decomposition on Cu{hkl}R&S surface have been studied using a set of L-Asp isotopomers and on various surfaces. By using mixtures of D-Asp and 1,4-13C2-L-Asp we have demonstrated that adsorption on Cu{3,1,17}R&S surfaces is enantiospecific. Adsorption at temperatures &gt; 400 K results in the adsorption of Aps in the form of a bi-aspartate species that is deprotonated at both ends. During heating on Cu surfaces adsorbed Asp decomposes to yield CO2 and N≡CCH3. Using 4-13C-L-Asp reveals that the decomposition occurs sequentially, first by cleavage of the C3-C4 bond to yield 13CO2, followed by cleavage of the C1-C2 bond to yield CO2, and finally by dehydrogenation of the remaining NH2CH=CH2 to yield N≡CCH3. Use of 2,2,3-d3-L-Asp demonstrates that the final step involves scrambling of H and D atoms in the NH2CD=CD2 intermediate to yield various deuterated isotopomers of acetonitrile. The decomposition mechanism occurs by a vacancy-mediated, autocatalytic explosion mechanism. The non-linear kinetics of the process results in high enantioselectivity on the Cu{643}R&S surfaces. Finally, we have been able to demonstrate that the steady-state isothermal decomposition of Asp on the Cu(100) surface at temperatures &gt;450 K can occur catalytically to yield multiple turnovers without apparent contamination of the surface. Using effusive molecular beam methods we have observed the multiple steady-states that are predicted by the non-linear kinetics of the autocatalytic explosion mechanism: For give conditions of Asp flux and Cu(100) surface temperature we observe both a ‘high-coverage / low rate’ steady-state and a ‘low-coverage / high rate steady-state.’

Kinetics and mechanism of aspartic acid decomposition on chiral Cu{hkl}R&S surfaces

255th National Meeting (2018)

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