Structural characterization and diffusional analysis of the inclusion complexes of fluoroadamantane with β-cyclodextrin and its derivatives studied via 1H, 13C and 19F NMR spectroscopy

This research conducts method development to study the diffusions of β-cyclodextrin and its derivatives (collectively called β-CDs) in biological systems. We proposed using fluoroadamantane (FA) β-CD inclusion complexes as a model system to study the diffusion of β-CDs by using 19 F self-diffusion NMR technique. The use of 19 F signal over 1 H signal arises from the advantage of being able to avoid the interference of 1 H signals from biological molecules and water. Another benefit of using FA is that the 19 F relaxation times are not significantly influenced by viscous biological solutions due to the tumbling nature of FA in β-CD cavities. To synthesize the FA β-CD inclusion complexes, a FA THF (tetrahydrofuran) solution and a β-CD water solution were mixed together followed by lyophilization. The formation of the inclusion complexes in water were determined using HMQC and ROESY NMR experiments with the assistance of molecular modeling. To assess the method, both 1 H and 19 F diffusion NMR were carried out to study the diffusions of four typical FA β-CD inclusion complexes. The results of this study illustrate that the diffusion coefficients obtained from the FA 19 F signal truly measure those of the β-CDs’ diffusion coefficients in water. Thus, the proposed technique using our model system is valid to be used to study the diffusions of β-CDs in biological systems.