Stability of chiral domains produced by adsorption of tartaric acid isomers on the Cu(110) surface: a periodic density functional theory study.

In the present work the interaction of different bitartrate isomers on the Cu(110) surface has been investigated systematically by using the Vienna Ab-initio Simulation Package (VASP), which performs periodical density functional theory (DFT) calculations. Among all bitartrate isomers the R,R-configuration is the most stable under the (3 1, 1 2) domain on the Cu surface. Its optical isomer, the S,S-bitartrate, is 10 kJ mol(-)(1) less stable in the same domain. This energy difference is sufficient to produce the distinct chiral assemblies observed after the adsorption of each optical isomer on the Cu surface. The calculations also showed that these domains are not formed due to intermolecular H-bonds, in contrast with the previous proposal by Raval et al.(Nature 2000, 23, 376). In fact, there is a formation of optimal intramolecular H-bonds in the chemisorption structures. A favorable packing orientation is also needed for the respective chiral domains. For instance, the S,S-configuration suffers from a destabilizing packing energy of 21 kJ mol(-)(1) under the same domain, due to a short contact between the H atoms of the hydroxy groups. These intramolecular H-bonds cause also some distortions on the bitartrate molecule, which appear to be dependent on the relative position of the alpha-hydroxy groups. The stability of the extended asymmetric domains, when the surface is modified by a chiral additive, might have important consequences for understanding and optimizing the properties of enantioselective heterogeneous catalysts.