Intrinsically Chiral Surface Chemistry

       Synthesis of chiral reagents and separation of chiral compounds play a key role in the multibillion-dollar chemical industry. To date, almost all of this chemistry has been performed homogeneously. The production of chiral compounds by enantioselective heterogeneous catalysts is an emerging area that shows great promise for the cheap, efficient production of single enantiomers. A handful of enantioselective reactions are now possible using supported catalysts, however, there is a lack of understanding of the mechanism by which these catalysts operate. The challenge for surface chemistry is to elucidate the steps that lead to enantiospecific chemistry. Accomplishing this will allow the current crop of heterogeneous catalysts to be improved, and others designed.

(A) Computer simulation of the structure of an intrinsically chiral copper surface. The kink sites are believed to be active for enantioselective reactions. (B) Sykes group images of an intrinsically chiral surface. Inset shows two atomically resolved chiral kink sites.

      Our research is aimed at understanding the surface chemistry of these catalysts by studying molecular interactions with a new class of surface; the intrinsically chiral surface. These intrinsically chiral surfaces have recently been shown to interact enantiospecifically with chiral molecules, and therefore constitute good test beds for investigating enantiospecific chemistry.[1] The Sykes group was the first to obtain atomically resolved STM images of these active kink sites.[2] This work revealed that miscut metal crystals are truly chiral at the atomic scale. This was a very important breakthrough given the previous work on molecular adsorption on these surfaces showed enantiospecificity. Our work was able to both confirm the presence of chiral sites and quantify the number and nature of these sites. The group is now poised to investigate the adsorption and reaction of molecules on these surfaces. Coupling the spectroscopic capabilities of our STM with isotopic labeling will allow us to probe the chirality of individual molecules in situ. Studying relevant systems with these surface science tools will allow us to shed light on the molecular-scale workings of enantiospecific heterogeneous catalysts.
            The Sykes group is currently collaborating with two of the world leaders in the field of chiral surface chemistry on this project (Andrew Gellman from Carnegie Mellon University and David Sholl from Georgia Institute of Technology). The most recent Sykes group data is featured in a review of Chiral Surface Chemistry: “Enantioselectivity on Naturally Chiral Metal Surfaces” due for publication in 2008.

1. Horvath, J. D.; Gellman, A. J. Enantiospecific Desorption of R- and S-Propylene Oxide from a Chiral Cu(643) Surface. Journal of the American Chemical Society 2001, 123, 7953-7954.
2. Baber, A. E.; Gellman, A. J.: Sholl, D. S.; Sykes, E. C. H. The Real Structure of Naturally Chiral Cu{643} Journal of Physical Chemistry C, 2008, 112, 11086-11089