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We present herein the development of a new polycationic molecular receptor, inspired by the ubiquitous cyclobis(paraquat-p-phenylene)cyclophane (blue box). Our analogue, the white box, has been easily self-assembled on a preparative scale in water, using a template-assisted process by acyl hydrazone bonding of complementary bis(pyridinium)-xylylene tweezers, followed by kinetic trapping of the empty receptor. The obtained macrocycle was found to display a marked pH-responsiveness in water, because of an abnormal acidity of the amide protons within its structure. Consequently, and because of the concurrence of rotational isomerism on acidic conditions (fixed at higher pH values), the compound was found to display a dual behavior as a conformationally-locked/flexible molecular host, being able to recognize appropriate aromatic substrates, on a lock-and-key or induced fit fashion, by a conjunction of Π-Π, C-H···Π and, crucially, hydrophobic interactions.
PMID: 30730726 [PubMed - as supplied by publisher]