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

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。对映体代表了分子之间的终极相似性，因此，通常要求纯化。色谱分离也依赖于统计，溶解客体物质通过扩散与表面的大量接触保证了某些事件在分子间相互作用中以适当的取向发生，从而诱导立体化学分化。需要在固相表面用最少数量的手性选择剂对要分离的对映体进行最大的迁移率鉴别。对于立体选择色谱中新概念的确定，参考不对称催化是有帮助的。在这种情况下，手性配体的单独存在不足以达到最佳的对映体过量。精确控制起始化合物朝向活性中心的方向是关键。将后一种概念转移到多孔材料的主客体化学中，导致了我们的长期愿景：表面的设计能够定向手性客体，以最大限度地提高它们的移动性，并达到最佳的对映选择性分离。对于如此复杂的宿主材料的靶向合成，人们必须能够以分子精度观察分离，并量化被限制在接近色谱工艺条件的材料孔隙中的客体的分子动力学和迁移率。我们的小组已经在初步工作中表明，这是可能的，使用电子自旋共振光谱（ESR）技术。该方法现在已经得到了充分的发展，它可以应用于收集手性、氨基酸修饰的有机二氧化硅材料作为模型系统的分离的详细信息。我们的第一个工作包是关于控制禁闭条件的。我们提出了一种新的模板方法，用于合成50-150 nm范围内孔径分布狭窄的有机二氧化硅材料。在第二个工作包中实现了手性氮氧化物作为顺磁自旋探针与表面相互作用的系统变化。一个特别有趣的问题是，表面上的非手性邻基如何影响分离过程，并最终作为超分子的指导者，以特定的方式定向氮氧化物客体。我们主要观察到的是从w-ESR实验中获得的对映体选择性因子alpha，以及纳米和宏观传输系数，例如从成像ESR光谱中确定。最后，我们想使用单片有机二氧化硅材料进行HPLC分离实验，以了解基本的主-客研究如何转化为应用。

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.