The influence of supramolecular directors bound to surfaces of porous hosts with chiral walls on the dynamic of enantiomers as guests

与手性壁多孔主体表面结合的超分子导向剂对作为客体的对映体动力学的影响

• 批准号: 428188436
• 负责人: Professor Dr. Sebastian Polarz
• 金额: --
• 依托单位: Arbeitsgruppe Physikalische und Biophysikalische Chemie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/428188436?language=en
• 关键词: influence; supramolecular; directors; bound; surfaces

An important application of porous solids is for separation of (similar) chemical compounds by chromatography. Enantiomers represent the case of ultimate similarity between molecules and, thus, purification is in general demanding. Chromatographic separation also relies on statistics, a high number of contacts of the dissolved guest species with the surfaces via diffusion ensures, some events occur in proper orientation to induce stereochemical differentiation in intermolecular interaction. Maximum mobility discrimination of the enantiomers to be separated with a minimum amount of a chiral selector necessary at the surfaces of the solid phase is desired. For the identification of new concepts in stereoselective chromatography, it is helpful referring to a different area, asymmetric catalysis. There, the sole presence of a chiral ligand is not enough for achieving best enantiomeric excess. A precise control over the orientation of the starting compounds towards the active center is pivotal. The transfer of the latter concept to host-guest chemistry in porous materials leads to our long-term vision: The design of surfaces to become capable of orienting chiral guests for maximizing the effect on their mobility and reaching optimum enantioselective separation. For the target-oriented synthesis of such a complex host material, one has to be able to watch separation with molecular precision and quantify the molecular dynamics and mobility of guests confined to the pores of the material close to chromatographic process conditions. Our group has shown in preliminary work, this is possible using electron spin resonance spectroscopy (ESR) techniques. The methodology is now developed sufficiently, it can be applied to gather detailed information about separation using chiral, amino-acid modified organosilica materials as model systems. Our first work-package is concerned with gaining control over confinement conditions. We present new templating approaches for the synthesis of organosilica materials with narrow size distribution of pores in the 50-150 nm range. A systematic variation of the interaction of chiral nitroxides as paramagnetic spin-probes with the surfaces is realized in the second work-package. A particularly interesting question is, how non-chiral neighboring groups on the surface can influence the separation process and ultimately act as supramolecular directors for orienting the nitroxide guests in a specific way. Our main observable is the enantiomer selectivity factor alphaT obtained from cw-ESR experiments, and also coefficients for nanoscopic and macroscopic transport will be determined, for instance from imaging ESR spectroscopy. Finally, we want to perform a HPLC separation experiment using a monolithic organosilica material, to learn how the fundamental host-guest study translate to application.

多孔固体的一个重要应用是通过色谱法分离（类似的）化合物。对映异构体代表分子之间的最终相似性的情况，因此，纯化通常是苛刻的。色谱分离还依赖于统计学，溶解的客体物质通过扩散与表面的大量接触确保了一些事件以适当的取向发生以诱导分子间相互作用中的立体化学差异。需要待分离的对映异构体的最大迁移率区分，其中在固相表面处需要最小量的手性选择剂。 对于立体选择性色谱中新概念的识别，参考一个不同的领域，不对称催化是有帮助的。在那里，手性配体的单独存在不足以实现最佳对映体过量。对起始化合物朝向活性中心的取向的精确控制是关键。将后一概念转移到多孔材料中的主客体化学导致我们的长期愿景：表面设计能够定向手性客体，以最大限度地提高其流动性并达到最佳的对映选择性分离。对于这种复杂主体材料的靶向合成，必须能够以分子精度观察分离，并量化限制在接近色谱工艺条件的材料孔中的客体的分子动力学和流动性。我们的小组在初步工作中已经表明，使用电子自旋共振光谱（ESR）技术是可能的。该方法已得到充分发展，可用于收集有关手性氨基酸改性有机硅材料分离的详细信息。我们的第一个工作包是关于获得对限制条件的控制。我们提出了新的模板法合成的有机硅材料的孔径分布窄，在50-150 nm的范围内。在第二个工作包中实现了手性氮氧化物作为顺磁性自旋探针与表面的相互作用的系统变化。一个特别有趣的问题是，表面上的非手性相邻基团如何影响分离过程，并最终作为超分子导向剂以特定的方式定向氮氧客体。我们主要观察到的是从cw-ESR实验获得的对映体选择性因子α T，并且还将确定纳米级和宏观运输的系数，例如从成像ESR光谱。最后，我们希望使用整体有机硅材料进行HPLC分离实验，以了解基本的主客体研究如何转化为应用。