Tuning the Surface Chemistry of Chiral Cu(531)S for Enhanced Enantiospecific Adsorption of Amino Acids

Abstract

Amino acids are important bioorganic compounds composed of amine and carboxylic acid because they are the main building blocks of many biomolecules. All of them are chiral except glycine. Thus, they have two enantiomers which provide dramatically different biological effects, thereby requiring their separation. High Miller index metal surfaces often define intrinsically chiral structures. A number of previous studies have proved the enantiospecific adsorption difference of chiral molecules on those surfaces. To further enhance the enantiospecificity, step decoration, which is doping the kink site of chiral metal surface with a second metal, can be one route. It may induce one enantiomer adsorbed on the surface to become more stable than the other, inducing the larger enantiospecific energy difference. In this study, we performed density functional theory (DFT) calculations to systemically examine the adsorption geometries and energetics of each enantiomer of alanine, serine, and cysteine, and their enantiospecific energy differences on pure, Pd-, Pt-, and Au-decorated Cu(531)(S), respectively. By decorating the kinked site with an Au atom, the enantiospecificity of adsorbed cysteine was meaningfully enhanced by 0.08 eV, in the case when the side chain has a high affinity with the surface. Our results provide useful insight of how to tune chiral metal surfaces to enlarge the enantiospecificity of chiral molecules.