We present herein the implementation of pH-responsiveness into a new polycationic macrobicyclic structure, namely what we have termed the “red cage”. The hydrolytically-stable cryptand-like compound has been prepared in a relatively high yield in aqueous media by a kinetically-controlled hydrazone-exchange reaction, promoted by the unusual high stability of the new hydrazone CN bonds formed. In organic media the macrobicycle was found not able to complex model aromatic substrates. In buffered aqueous solutions, as a comparison, the “red cage” was found able to recognize them, but the binding was observed to be more efficient in acidic form of the cyclophane compared with its conjugate base.

中文翻译：

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“红笼”：在基于大双环吡啶鎓的分子宿主中实现 pH 响应

我们在此介绍了将 pH 响应性实施到新的聚阳离子大双环结构中，即我们称之为“红笼”的结构。通过动力学控制的腙交换反应，在水性介质中以相对高的产率制备了水解稳定的穴状化合物，这是由形成的新腙C N 键的异常高稳定性促进的。在有机介质中，发现大环不能复杂模拟芳香底物。在缓冲水溶液中，作为比较，发现“红色笼子”能够识别它们，但观察到环烷的酸性形式比其共轭碱的结合更有效。