Cucurbiturils Monofunctionalized on the Methylene Bridge and Their Host-Guest Properties

Monofunctionalization of cucurbiturils is essential for transferring these potent supramolecular macrocyclic hosts into real-world application. Here, we present the synthesis of cucurbit[6]urils 1 and 2 in which one methylene bridge is modified by a single substituent containing a nitro or an ammonium group. We investigated host-guest properties in water and 0.2 M NaCl using H-1 NMR and isothermal titration calorimetry, particularly for 2. The macrocycle 2 self-associated into dimeric aggregates in pure water, but readily disassembled in the presence of NaCl or organic cations. Cucurbit[7]uril was able to encapsulate the ammonium substituent of 2 inside its cavity resulting in a complex of 1 : 1 stoichiometry with an association constant of 3.1x10(5) M-1. The presented host-guest properties together with further possible derivatization showcase the potential of cucurbiturils modified in the methylene position such as 1 and 2 for the development of advanced supramolecular systems.