NSF-BSF: Investigating Magnetic Surfaces as a New Approach to Enantioseparations

University Of Pittsburgh, Pittsburgh PA

Investigators

Abstract

Chirality, or the nonsuperimposability of mirror images, is a fundamental symmetry property of Nature. Just as human left and right hands are nonsuperimposable mirror images, biomolecules such as protein and DNA and other biologically-active molecules are chiral. The nonsuperimposable structural forms of these molecules are referred to as enantiomers. Artificially synthesized molecules are often a mixture of enantiomers. The ability to separate the mixtures into enantiomerically-pure compounds, or a single enantiomer, is particularly important to the chemical and pharmaceutical industries, as one enantiomer may have an entirely different effect than another. Yet, enantiomeric separations remain a costly aspect of the chemical production process. With support from the Molecular Separations program in the Division of Chemical, Bioengineering, Environmental, and Transport Systems, and partial co-funding from the Chemical Measurement and Imaging program in the Division of Chemistry, the PIs will examine the application of a novel and potentially generic principle for the separation of enantiomers using magnetic solid surfaces. In chiral molecules, applying a voltage affects how strongly the molecule interacts with a ferromagnetic surface. The strength of the interaction depends on whether the molecule is left-handed or right-handed. To separate enantiomers using magnetic surfaces and applied voltages, however, the chiral molecules and surface must be in direct contact. The goal of the project is to establish the molecular parameters affecting the separation and to identify the ideal magnetic materials. The ability to separate enantiomers using such an approach has the potential to reduce the cost of producing drugs and other agriculturally-relevant molecules, improving human health and promoting sustainability. The proposed activity builds on fundamental insights into the chiral induced spin selectivity effect and the recent finding that charge polarization in chiral molecules is accompanied by spin polarization. Recent results show that chiral molecules enantiospecifically adsorb on ferromagnets, where the adsorbed enantiomer is determined by the direction of magnetization of the substrate. The molecule's spin polarization affects the adsorption energy with a magnetic surface primarily through a change in the Pauli repulsion. The spin polarization changes the symmetry constraints on the electronic wavefunction, and this strongly affects the Pauli repulsion energy as the electron cloud of the molecule overlaps with the electronic wavefunctions of the substrate. Based on this behavior, a new approach to enantioselective separations and purification using magnetic materials will be developed. This goal will be accomplished through four objectives: 1) examining how the enantioselective adsorption of chiral molecules depends on the molecular properties; 2) examining different chromatographic constructs for separating mixtures of enantiomers; 3) exploring and defining the experimental conditions for efficient separations; and 4) examining the use of crystallization with magnetic surfaces for separations. The research will result in fundamental understanding of enantiomeric separations using magnetic materials. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.