(678f) Enantiospecificity of Thin Metal Films On Chiral SrTiO3 Surfaces

The separation of racemic mixture is an important step in today’s pharmaceutical fields since the physiological and toxicological properties of enantiomer can be significantly different to its mirror-image counterpart. One option for separating enantiomers is the use of chiral metal surfaces, but while these surfaces have been shown to be enantiospecific they are limited in the degree of enantiospecificity, cost, and low-surface area. One possible method to enhance the degree of enantiospecificity and reduce cost is to grow metal nanostructures or thin films on chiral oxide surfaces. Using density functional theory (DFT) we are examining Pt grown on the chiral SrTiO₃ substrate due to the lattice matching between these materials.

            As a first effort to understand the effects of oxide substrate on the adsorption properties of Pt films, we studied CO adsorption on Pt thin films supported on the SrO- and TiO₂-terminated SrTiO₃(100). With one monolayer (ML) of Pt, the presence of SrTiO₃ substrate enhances the CO adsorption energy by ~ 40% and in addition results in large differences in the adsorption energy at various sites on the Pt layer due to the underlying atoms of the oxide. Pt atoms sitting on top of oxide O atoms show the strongest biding to the CO molecule. This degree of heterogeneity will be important in enhancing the enantioselectivity of the chiral Pt/SrTiO₃ surfaces. The effects of oxide substrate are negligible after 2 ML of Pt, indicating the importance of deposited Pt thickness for maintaining any potential oxide effect.

We also examined the adsorption behaviors of R- and S-FAM (fluro-amino-methoxy) on the Cu(874), Pd(874), Pt(874), and a ML of Pt on SrTiO₃(874) in order to understand the enantioselectivity of oxide-supported chiral metal structures. Our preliminary results show that the adsorption behaviors of FAM are dependent on the position of fluorine atom of FAM and the electronic nature of chiral surfaces. The presence of underlying SrTiO₃ also strongly modifies the energetics of R- and S-FAM adsorbed on the chiral Pt ML compared to the bare Pt (874). We will present results from ongoing studies of the enantioselectivity for FAM and other small chiral molecules on ML thick metal films on chiral SrTiO₃(874) and discuss any general guidelines observed for enhancing enantiospecificity.