Thinking outside the Blue Box: from molecular to supramolecular pH-responsiveness


We present herein the development of a new polycationic cyclophane: the red box, second in a series of hydrazone-based analogues of the well-known organic receptor cyclobis(paraquat-p-phenylene) cyclophane (blue box). The macrocycle has been prepared in an excellent yield in aqueous media, and shows both a remarkable pH-responsiveness and unusual hydrolytic stability of the two hydrazone C=N bonds, associated with charge delocalization of the amine lone pair. Whilst in aqueous media the red box is able to complex a variety of aromatic substrates, both in its acidic and basic form, in organic media the cyclophane is only able to capture those in the acidic form, resulting in supramolecular pHresponsiveness.



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Blanco-Gomez, A; Neira, I; Barriada, JL; Melle-Franco, M; Peinador, C; Garcia, MD

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This research was supported by the Ministerio de Economia y Competitividad (MINECO FEDER, Grant CTQ2016-75629-P) and Xunta de Galicia (ED431C 2018/39). MMF acknowledges support from the Portuguese Foundation for Science and Technology (FCT), under the projects PTDC/FIS-NAN/4662/2014, IF/00894/2015, and FCT Ref. UID/CTM/50011/2019 for CICECO-Aveiro Institute of Materials. I. N. thanks the MECD (FPU program) for financial support. Dedicated to Professor Jose Maria Quintela on the occasion of his retirement.

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