Abstract：
Controlling supramolecular systems between different functional forms by utilizing acids/bases as stimuli is a formidable challenge, especially where labile coordination bonds are involved. A pair of acid/base responsive, interconvertible 1,5-enedione/pyrylium based Pd2L4-type cages are prepared that exhibit differential guest binding abilities towards disulfonates of varied sizes. A three-state switch has been achieved, where (i) a weakly coordinating base induced cage-to-cage transformation in the first step, (ii) a strongly coordinating base triggered cage disassembly as the second step, and (iii) the third step shows acid(strong) promoted generation of initial cage, thereby completing the cycle. To our surprise, binding of a specific disulfonate guest facilitated cage-to-cage transformations by inducing strain on the cage assembly thereby opening the labile pyrylium rings of the cage. Through a competitive guest binding study, we demonstrated the superior guest binding capability of the octacationic pyrylium-based cage over a similar-sized tetracationic cage. These results provide a reliable approach to reversibly modulate the guest binding properties of acid/base-responsive self-assembled coordination cages.
摘要：
通过利用酸/碱作为刺激来控制不同功能形式之间的超分子系统是一个巨大的挑战。尤其是涉及不稳定的协调债券的地方。一对酸/碱响应，制备了可相互转化的1,5-烯二酮/基于Pd2L4的笼，该笼对不同大小的二磺酸盐表现出不同的客体结合能力。实现了三态切换,其中（i）第一步中的弱协调基础引起的笼到笼的转化，（ii）作为第二步，强烈协调的底座触发的保持架拆卸，和（iii）第三步显示了酸（强）促进的初始笼的生成，从而完成循环。令我们惊讶的是，特定的二磺酸盐客体的结合通过在笼组件上诱导应变从而打开笼的不稳定的吡咯环而促进了笼到笼的转化。通过竞争性宾客绑定研究，我们证明了八阳离子吡喃基笼比类似大小的四阳离子笼具有更高的客体结合能力。这些结果提供了一种可靠的方法来可逆地调节酸/碱响应自组装配位笼的客体结合特性。
