PITA Fiscal Year 2008 Projects - Nanotechnology

Enantioselective adsorption of chiral compounds

Principal Investigators: Andrew J. Gellman, Paul J Sides

Sensing and separating chiral compounds are vital parts of drug development and manufacture. Responding to this need, we propose investigation of enantioselective adsorption of chiral molecules on chiral mineral surfaces. A chiral molecule has a structure admitting two non-superimposable mirror images. Nearly all physical properties such as density, chemical reactivity, boiling point, and melting point, are identical. Analytical techniques and processes that distinguish between enantiomers have been few and cumbersome. Enantiospecific adsorption is a potential basis for such analysis and processing. Chiral surfaces discriminate between enantiomers of chiral compounds; therefore chiral surfaces can function as enantioselective reagents. Many common inorganic materials have chiral bulk structures. Quartz, for example, has an enantiomorphic bulk structure; two of its three lowest Miller index surfaces are chiral. Other minerals such as calcite are not enantiomorphic in the bulk structure, but have low Miller index surfaces that are chiral.

Evidence for the enantiospecific adsorption of amino acids on single crystalline quartz and calcite will be produced. UHV surface science tools will be used to quantify the differences in the adsorption energies of R- and S- amino acids onto chiral surfaces of quartz and calcite. The extent of the adsorption will be evaluated in vacuum by temperature programmed desorption and in aqueous solutions by detection of the zeta potential differences between surfaces of opposite handedness when amino acids are adsorbed. The zeta potential (related to apparent surface charge) measurements will be made using a novel technique recently developed at CMU and offered commercially by a CMU spinoff company called ZetaMetrix Inc that will function as the commercial partner for the project. This technique will be adapted to make a differential measurement of enantioselective adsorption on R- and S- surfaces. A quartz crystal microbalance will be used in both vacuum and liquid phase as an alternative technique.