Dynamics in Flexible Pillar[n]arenes Probed by Solid-State NMR,The Journal of Physical Chemistry C

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Dynamics in Flexible Pillar[n]arenes Probed by Solid-State NMR
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2021-06-15 , DOI: 10.1021/acs.jpcc.1c02046
Ashlea R Hughes ₁ , Ming Liu _{1,

2} , Subhradip Paul ₃ , Andrew I Cooper _{1,

2} , Frédéric Blanc _{1,

4}

Affiliation

Pillar[n]arenes are supramolecular assemblies that can perform a range of technologically important molecular separations which are enabled by their molecular flexibility. Here, we probe dynamical behavior by performing a range of variable-temperature solid-state NMR experiments on microcrystalline perethylated pillar[n]arene (n = 5, 6) and the corresponding three pillar[6]arene xylene adducts in the 100–350 K range. This was achieved either by measuring site-selective motional averaged ¹³C ¹H heteronuclear dipolar couplings and subsequently accessing order parameters or by determining ¹H and ¹³C spin–lattice relaxation times and extracting correlation times based on dipolar and/or chemical shift anisotropy relaxation mechanisms. We demonstrate fast motional regimes at room temperature and highlight a significant difference in dynamics between the core of the pillar[n]arenes, the protruding flexible ethoxy groups, and the adsorbed xylene guest. Additionally, unexpected and sizable ¹³C ¹H heteronuclear dipolar couplings for a quaternary carbon were observed for p-xylene adsorbed in pillar[6]arene only, indicating a strong host–guest interaction and establishing the p-xylene location inside the host, confirming structural refinements.

中文翻译：

通过固态核磁共振探测柔性柱[n]芳烃的动力学

柱[ n ]芳烃是超分子组装体，可以通过其分子灵活性进行一系列技术上重要的分子分离。在这里，我们通过对微晶全乙基化柱[ n ]芳烃（ n = 5, 6）和相应的三柱[6]芳烃二甲苯加合物在 100–350 范围内进行一系列变温固态核磁共振实验来探讨动力学行为。 K 范围。这是通过测量位点选择性运动平均¹³ C ¹ H 异核偶极耦合并随后访问有序参数或通过确定¹ H 和¹³ C 自旋晶格弛豫时间并基于偶极和/或化学位移各向异性弛豫提取相关时间来实现的机制。我们展示了室温下的快速运动状态，并强调了柱[ n ]芳烃核心、突出的柔性乙氧基和吸附的二甲苯客体之间动力学的显着差异。此外，对于仅吸附在柱[6]芳烃中的对二甲苯，观察到了季碳的意外且相当大的¹³ C ¹ H 异核偶极偶合，表明存在强烈的主客体相互作用，并确定了对二甲苯在主体内部的位置，证实了结构改进。

更新日期：2021-06-24

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