The influence of equatorial substitution and K+ ion concentration: an encapsulation study of CH4, CH3F, CH3Cl, CH2F2 and CF4, in Q[5], CyP5Q[5] and a CyP5Q[5]-carboxylate derivative

Abstract

Equatorial substitution on cucurbit[5]uril (Q[5]) gives binding constants for cavity-bound guests examined, with 1.05–2-fold increases over normal Q[5]. K+ and Na+ ions also have comparable binding constant increases. This work compares the binding properties and the portal diameters of the recently reported cyclopentanocucurbit[5]uril (CyP5Q[5]) and the herein, new CyP5Q[5]-carboxylate derivative with those of normal Q[5]. Portal sizes and cavity binding were probed using a series of guests of methane and halomethanes of increasing kinetic diameters from 3.76 to 4.66 Å. A new limit of 4.18 Å was found superseding the prior binding of Xe (diameter 4.05 Å) in normal Q[5]. In addition, K+ ion concentrations are demonstrated to have a large positive effect on the binding constants of a hydrophobic guest such as CH4 encapsulation in the three Q[5] hosts.