The Red Cage: Implementation of pH-Responsiveness Within a Macrobicyclic Pyridinium-Based Molecular Host

Abstract

[Abstract] 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 C[double bond, length as m-dash]N 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.