Inhibition of C(2)-H/D exchange of a bis(imidazolium) dication upon complexation with cucubit[7]uril

Inclusion of the alpha, alpha'-bis(3-(1-methylimidazolium))-p-xylene dication in cucurbit[ 7] uril (CB[ 7], K-CB[7] = (4.3 x 10(9) M-1), with C - H center dot center dot center dot O=C hydrogen bonding between the guest C(2)-protons and the carbonyl oxygens of the host portals, inhibits the H/D exchange for the C(2)-proton with k(OD) (25 degrees C, D2O) decreasing from 1.2 x 10(3) M-1 s(-1) (pK(a) = 22.3) in the absence of CB[7] to 0.9 M-1 s(-1) (pK(a) = 25.4) in the presence of 1.1 equiv. CB[7].