An ab initio study of adsorption of alanine on the chiral calcite surface

Abstract

Density functional theory calculations has been used to examine the adsorption of d- and l-alanine (Ala) on the chiral calcite surface. We find negligible differences ( < 1 kcal/mol) in adsorption energies for the most stable minima of d- and l-Ala on the calcite surface. The strongest interaction in the adsorbed system is between the surface Ca and the O atom of the carboxyl group on Ala. The source of the weak enantiospecificity is the relative difference in dimensions of the Ala and the atoms on the calcite surface. The surface O and Ca atoms on the calcite surface are separated by 6 Å, while the Ala molecule is roughly 3–4 Å in size. This disparity in dimensions prevents the Ala molecule from making three strong points of contact with the surface, a prerequisite for strong enantiospecificity.

Keywords:

• Chirality
• Density functional theory
• Mineral surfaces
• Calcite
• Amino acid

Acknowledgements

We thank Henry Teng, Andrew Gellman, David Sholl, and Robert Downs for helpful discussions. This work was supported by NSF (EAR0229634), the NASA Astrobiology Institute, and the Carnegie Institution of Washington.