Carboxymethyl- substituted benzo[3]uril and its application in ion-pair recognition

Carboxymethyl-substituted and ester-substituted benzo[3] urils have been successfully synthesized and investigated with regard to the supramolecular recognition of inorganic ions by means of fluorescence spectroscopy, H-1 NMR spectrometry, and quantum chemical calculations. The results indicated that benzo[3] uril 4 bearing six carboxyl groups binds to Cu2+, Fe3+, F-, and CH3COO- with strong affinities. Moreover, this macrocyclic host could be used to recognize ion pairs comprising Cu2+ and CH3COO-, Cu2+ and F-, Fe3+ and (CHCOO-)-C-3, and Fe3+ and F-through its fluorescence response. In contrast, benzo[3] uril 3, bearing ester groups, showed only host-guest interactions with Cu2+ and Fe3+. The absence of binding of the macrocycle 3 to anions highlights the important role of the carboxyl groups on benzo[3] uril 4, which provide active protons to form hydrogen bonds between the host and anion guests. (C) 2017 Elsevier B.V. All rights reserved.