Rotaxane Formation by Cucurbit[7]uril in Water and DMSO Solutions

The cucurbit[7]uril (CB7) host forms rotaxane-type complexes with dumbbell-shaped, cationic guests bis(3,5-dimethoxybenzyl)-4,4′-bipyridinium (12+) and bis(3,5-diethoxybenzyl)-4,4′-bipyridinium (22+). The kinetics of complex formation is slower with the latter guest because of its bulkier end groups. Rotaxane formation was found to be thermodynamically more favorable and kinetically faster in D2O than in DMSO-d6 solution, which highlights the importance of hydrophobic interactions in the assembly of cucurbituril complexes.

七元瓜环（cucurbit[7]uril，CB7）主体与哑铃形阳离子客体bis(3,5-二甲氧基苄基)-4,4'-联吡啶鎓（1²⁺）及bis(3,5-二乙氧基苄基)-4,4'-联吡啶鎓（2²⁺）形成轮烷型复合物。后者客体的复合物形成动力学更慢，因其端基更庞大。研究发现，在D2O溶液中轮烷的形成相较于DMSO-d6溶液在热力学上更有利且动力学上更快，这凸显了疏水相互作用在瓜环复合物组装过程中的重要性。