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

手性，或镜像的不可重叠性，是自然的基本对称性。正如人类的左手和右手是不可重叠的镜像一样，蛋白质和DNA等生物分子以及其他具有生物活性的分子也是手性的。这些分子的非重叠结构形式称为对映体。人工合成的分子通常是对映体的混合物。将混合物分离成对映体纯化合物或单一对映体的能力对化工和制药行业特别重要，因为一个对映体可能会产生与另一个完全不同的效果。然而，对映体分离仍然是化学生产过程中代价高昂的一个方面。在化学、生物工程、环境和运输系统部门的分子分离计划的支持下，以及化学部门的化学测量和成像计划的部分共同资助下，PIS将研究使用磁性固体表面分离对映体的一种新的、可能是通用的原理的应用。在手性分子中，施加电压会影响分子与铁磁表面相互作用的强度。相互作用的强度取决于分子是左撇子还是右撇子。然而，要使用磁性表面和外加电压来分离对映体，手性分子和表面必须直接接触。该项目的目标是确定影响分离的分子参数，并确定理想的磁性材料。利用这种方法分离对映体的能力有可能降低生产药物和其他与农业相关的分子的成本，改善人类健康和促进可持续发展。所提出的活动建立在对手性诱导自旋选择性效应的基本见解以及最近发现手性分子中的电荷极化伴随着自旋极化的基础上。最近的研究结果表明，手性分子对映体专一地吸附在铁磁体上，吸附的对映体由底物的磁化方向决定。分子的自旋极化主要通过泡利排斥力的变化来影响与磁性表面的吸附能。自旋极化改变了电子波函数的对称性约束，当分子的电子云与衬底的电子波函数重叠时，这强烈地影响了泡利排斥能。基于这一行为，将开发一种利用磁性材料进行对映体选择性分离和纯化的新方法。这一目标将通过四个目标来实现：1)研究手性分子的对映体选择性吸附如何依赖于分子性质；2)检查用于分离对映体混合物的不同层析结构；3)探索和确定有效分离的实验条件；以及4)研究具有磁性表面的结晶用于分离的使用。这项研究将导致对使用磁性材料的对映体分离的基本理解。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.