Temperature-Dependent and pH-Responsive Pillar[5]arene-Based Complexes and Hydrogen-Bond-Based Supramolecular Pentagonal Boxes in Water

Abstract

Supramolecular systems in water are of paramount importance and those based on hydrogen bonds are both intriguing and scarce. Here, after studying the peculiar host-guest complexes formed between per-dimethylamino-pillar[5]arene (1) and the bis-sulfonates2 a-c, we describe the formation of the first hydrogen-bond-based supramolecular pentagonal boxes (SPBs), which are stable in water. These pH-responsive SPBs are constructed from1as a body, benzene polycarboxylic acids3 a,bas lid compounds, and2 a-cas guests. We demonstrate that encapsulation of2 a-cin pillar[5]arene1and in the highly stable water-soluble SPBs, that is,1(3 a)(2)and1(3 b)(2), is both temperature and pH dependent and, quite interestingly, depends, on the nature of the lid compounds used for capping the boxes even at high pH. We also highlight the difference in the(1)H NMR characteristics of2 band2 cin the cavity of1and the SPBs.