de Poel Wester, Tinnemans Paul T, Duchateau Alexander L L, Honing Maarten, Rutjes Floris P J T, Vlieg Elias, de Gelder René
Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands.
DSM Food Specialties, P.O. Box 1, Delft, 2600 MA, The Netherlands.
Cryst Growth Des. 2018 Jan 3;18(1):126-132. doi: 10.1021/acs.cgd.7b00942. Epub 2017 Dec 4.
The use of an achiral metal-organic framework for structure determination of chiral compounds is demonstrated for camphene and pinene. The structure of enantiopure β-pinene can be resolved using the crystalline sponge method. However, α-pinene cannot be resolved using enantiopure material alone because no ordering of guest molecules takes place in that case. Interestingly, enantiomeric pairs order inside the channels of the host framework when impure (+)-camphene is offered to the host, which is also the case when a racemic mixture of α-pinene is used. A mixture of (+)-α-pinene and (-)-β-pinene also leads to ordered incorporation in the host, showing the influence of the presence of an inversion center in the host framework. We further show that powder X-ray diffraction provides a direct view on incorporation of ordered guest molecules. This technique, therefore, provides a way to determine the optimal and/or minimal soaking time. In contrast, color change of the crystal only demonstrates guest uptake, not ordering. Moreover, we show that color change can also be caused by guest-induced host degradation.
本文展示了使用非手性金属有机框架来确定莰烯和蒎烯等手性化合物的结构。对映体纯的β-蒎烯的结构可以通过晶体海绵法解析。然而，仅使用对映体纯的材料无法解析α-蒎烯的结构，因为在这种情况下客体分子不会发生有序排列。有趣的是，当向主体提供不纯的（+）-莰烯时，对映体对会在主体框架的通道内有序排列，使用α-蒎烯的外消旋混合物时也是如此。（+）-α-蒎烯和（-）-β-蒎烯的混合物也会导致在主体中有序掺入，这表明主体框架中存在反转中心的影响。我们进一步表明，粉末X射线衍射可以直接观察到有序客体分子的掺入。因此，该技术提供了一种确定最佳和/或最短浸泡时间的方法。相比之下，晶体的颜色变化仅表明客体的摄取，而非有序排列。此外，我们表明颜色变化也可能是由客体诱导的主体降解引起的。
