Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology (BIST), Av. Països Catalans 16, 43007, Tarragona, Spain.
Universitat Rovira i Virgili (URV), Departament de Química Analítica i Química Orgánica, c/Marcel lí Domingo 1, 43007, Tarragona, Spain.
Chemistry. 2020 Jul 2;26(37):8220-8225. doi: 10.1002/chem.202000781. Epub 2020 Jun 9.
A deep cavitand binds long-chain trans,trans- and trans,cis-bis-formamide isomers in water solution giving a pair of caviplexes in a ca. 60:40 ratio. Both caviplexes display in/out guest exchange dynamics that are slow on the H NMR chemical shift timescale, but fast on the EXSY timescale. We apply diffusion-ordered NMR spectroscopy (DOSY) to characterize the caviplexes. On the diffusion timescale, the guest in/out exchange processes feature intermediate dynamics allowing the assessment of their kinetic stabilities. We found that the trans,cis-bis-formamide isomers form kinetically more stable caviplexes than the trans,trans-counterparts. We also show that the kinetic stabilities of the bis-formamide caviplexes relate well with their relative thermodynamic stabilities. Fortunately, the tuning of the DOSY parameters allowed the observation of the exchange dynamics as slow processes on the experiment timescale.
一种深穴状配体能在水溶液中结合长链反式,反式-和顺式,反式-双甲酰胺异构体，形成约 60:40 比例的一对 Caviplex。这两种 Caviplex 都表现出进出客体交换动力学，在 H NMR 化学位移时间尺度上较慢，但在 EXSY 时间尺度上较快。我们应用扩散有序 NMR 光谱学（DOSY）来表征 Caviplex。在扩散时间尺度上，客体的进出交换过程具有中间动力学，允许评估它们的动力学稳定性。我们发现，顺式,反式-双甲酰胺异构体形成的 Caviplex 比反式,反式-对应物具有更高的动力学稳定性。我们还表明，双甲酰胺 Caviplex 的动力学稳定性与其相对热力学稳定性密切相关。幸运的是，DOSY 参数的调整允许在实验时间尺度上观察到缓慢的交换动力学。
