Theoretical Investigations of Chiral Self-Assembly at Solid Surfaces
EMSL Project ID
18399a
Abstract
Chiral symmetry breaking is the process by which an achiral phase is resolved into two enantiomeric domains. This refers to the separation of a racemic mixture, and also to induced chiral separations, in which a phase composed of achiral molecules becomes chiral either on a surface, or after being exposed to a chiral precursor to preferentially align the phase.Spontaneous chiral resolution of racemates during crystallization is rare. The steric or electrostatic preference of one molecule for its twin rather than its enantiomer is short ranged. When separation is attempted from a fluid phase, these preferences are often lost through rotational averaging or overwhelmed by thermal translational motion. This makes
chiral separations from such a phase difficult.
Breaking the symmetry of the phase using a surface has the potential to reduce these effects. The separation of monochiral domains at adsorption has been observed experimentally. Surfaces can aid in chiral resolutions in a number of ways. They can be used directly to limit to two dimensions, by adsorption, the configurational space available to the racemate. Both thermal and rotational averaging are significantly
reduced in these conditions. Consequently, chiral domains of the pure enantiomers form on the surface. The surface can also induce chiral symmetry breaking in achiral adsorbates which become chiral when adsorbed to the surface. This achiral compound, once bonded to the substrate, can form chiral domains. The surface thus patterned can be used as a low-cost chiral resolution catalyst. A similar principle is used in chiral chromatography.
We will work to elucidate the effect of various contributors to the molecular environment, to the success or failure of these separations.
From the results, we will formulate rules for chiral surface assembly. Not much is known about the impact of the surface geometry and energetics, the effect of choice of solvent or about the dynamics and cooperative effects. These effects will be studied independently, and in stepwise-increasing levels of complexity. We will begin by examining model systems, and then extend our approaches to molecular systems of interest to experimentalists. While our research will focus on chiral separations, our results should provide significant insight into the nature of surface assembly, in general.
Project Details
Project type
Exploratory Research
Start Date
2007-08-26
End Date
2008-08-31
Status
Closed
Released Data Link
Team
Principal Investigator