Dynamics of CHFClBr and CDFClBr inside a thiomethylated cryptophane, studied by 19F-1H CSA-DD cross-correlated relaxation and 2H quadrupolar relaxation measurements

The host-guest complexation of bromochlorofluoromethane (CHFClBr) and bromochlorodeuteriofluoromethane (CDFClBr) by a chiral thiomethylated cryptophane (cryptophane-E-(SCH3)(6)) was studied by fluorine NMR. Fluorine NMR T-1 experiments were performed on the {CHFClBr@cryptophane-E-(SCH3)(6)} system. They revealed the presence of F-19-H-1 CSA-DD cross-correlated relaxation, which was found to be more efficient inside the host cavity. The measurement of F-19-H-1 CSA-DD cross-correlated relaxation rates at two different magnetic field strengths allowed the determination of the correlation time tau(C) of CHFClBr outside (tau(C) = 0.27 ns) and inside the cryptophane (tau(C) = 0.62-0.78 ns). These correlation times were confirmed by the measurement of the deuterium quadrupolar relaxation time T, in the {CDFClBr@cryptophane-E-(SCH3)(6)} system. The two methods were in very good agreement and showed that the substrate was slowed upon complexation.