University of Konstanz , Department of Chemistry, D-78457 Konstanz, Germany.
Langmuir. 2017 Oct 31;33(43):11968-11976. doi: 10.1021/acs.langmuir.7b02713. Epub 2017 Oct 16.
Separation of compounds using liquid chromatography is a process of enormous technological importance. This is true in particular for chiral substances, when one enantiomer has the desired set of properties and the other one may be harmful. The degree of development in liquid chromatography is extremely high, but still there is a lack in understanding based on experimental data how selectivity works on a molecular level directly at the surfaces of a porous host material. We have prepared amino-acid containing organosilica as such host materials. Watching the rotational dynamics of chiral spin probes using electron paramagnetic resonance spectroscopy allows us to differentiate between surface adsorbed and free guest species. Diastereotopic selectivity factors were determined, and the influence of chiral surface group density, chemical character of the surface groups, pore-size, and temperature was investigated. We found higher selectivity values in macroporous solids with a rather rigid organosilica network and at lower temperature, indicating the significant effect of confinement effects. In mesoporous materials features are opposed with regards to the T-dependent behavior. From EPR imaging techniques and the resulting (macroscopic) diffusion coefficients, we could confirm that the correlations found on the microscopic level transform also to the macroscopic behavior. Thus, our study is of value for the development of future chromatography materials by design.
使用液相色谱法分离化合物是一项具有巨大技术重要性的过程。对于手性物质来说尤其如此,因为一种对映异构体具有所需的特性,而另一种可能有害。液相色谱法的发展程度非常高,但仍然缺乏基于实验数据的理解,即手性表面活性剂在多孔主体材料的表面上如何在分子水平上直接发挥选择性。我们已经制备了含有氨基酸的有机硅作为这种主体材料。使用电子顺磁共振波谱法观察手性旋转探针的旋转动力学,使我们能够区分表面吸附的和游离的客体物种。确定了非对映选择性因素,并研究了手性表面基团密度、表面基团的化学性质、孔径和温度的影响。我们发现,在具有相当刚性的有机硅网络的大孔固体中和在较低温度下,选择性值更高,这表明限域效应的显著影响。在介孔材料中,关于 T 依赖性行为的特征是相反的。从 EPR 成像技术和由此产生的(宏观)扩散系数,我们可以确认在微观水平上发现的相关性也转化为宏观行为。因此,我们的研究对于通过设计开发未来的色谱材料具有价值。