Binding Interactions between a Ferrocenylguanidinium Guest and Cucurbit[n]uril Hosts

The binding interactions between a novel ferrocenylguanidinium derivative (FcG+) and the macrocyclic hosts cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solution. 1H NMR spectroscopic experiments indicated that both hosts form stable 1:1 inclusion complexes with FcG+, in which the ferrocenyl group is engulfed by the host cavity. The stoichiometry of the CB7·FcG+ complex was also confirmed by electrospray mass spectrometric (ESI MS) experiments. The association equilibrium constants (K) were determined from NMR competition experiments. The measured K values were 3.5 × 109 and 2.5 × 108 M–1 for CB7 and CB8, respectively, in 50 mM sodium acetate-d3 D2O solution (pD 4.7). DFT computational studies confirmed the 1:1 stoichiometry and the inclusion character of both complexes. Voltammetric experiments were carried out to measure the complexation-induced shifts on the half-wave potentials for the one-electron oxidation of the ferrocenyl moiety. Complexation by CB7 led to a 12 mV an...