Dynamics of CHFClBr and CDFClBr Inside a Thiomethylated Cryptophane, Studied by 19F−H CSA-DD Cross-Correlated Relaxation and 2H Quadrupolar Relaxation Measurements

Abstract

The host-guest complexation of bromochlorofluoromethane (CHFClBr) and bromochlorodeuteriofluoromethane (CDFCIBr) 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-(SCH 3 ) 6 } system. They revealed the presence of 1 9 F- 1 H CSA-DD cross-correlated relaxation, which was found to be more efficient inside the host cavity. The measurement of 1 9 F- 1 H CSA-DD cross-correlated relaxation rates at two different magnetic field strengths allowed the determination of the correlation time τ c of CHFClBr outside (τ c = 0.27 ns) and inside the cryptophane (τ c = 0.62-0.78 ns). These correlation times were confirmed by the measurement of the deuterium quadrupolar relaxation time Tq in the {CDFClBr@cryptophane-E-(SCH 3 ) 6 } system. The two methods were in very good agreement and showed that the substrate was slowed upon complexation.