Terminal Carboxylate Effects on the Thermodynamics and Kinetics of Cucurbit[7]uril Binding to Guests Containing a Central Bis(Pyridinium)-Xylylene Site

A series of bis(pyridinium)-xylylene derivatives bearing carboxylate terminal groups were investigated as guests for the cucurbit[7]uril host in aqueous solution. While the presence of the terminal carboxylates has a modest effect on the thermodynamic stability of the complexes, the kinetics of complex association/dissociation is strongly affected. The relative position (meta, para) of the carboxylate group in relation to the pyridinium nitrogen also exerts a considerable effect on the binding kinetics.