Solution structures of 1:1 complexes of oxyphenonium bromide with beta- and gamma-cyclodextrins.

The solution structures of complexes of oxyphenonium bromide (OB) with β- and γ-cyclodextrins (β- and γ-CDs, respectively) in deuterium oxide have been investigated by 500 MHz proton NMR spectroscopy and molecular mechanics calculations. The chemical shifts induced by complex formation provide the 1:1 binding constants and the chemical shift variations, ΔδOB-CD, with complexation for the protons of OB and the CDs. The observed binding constants are very close to those obtained by other methods and are in the following order:  β-CD > γ-CD > α-CD. Initial structures of the complexes are constructed on the basis of the ROESY spectra and the ΔδOB-CD values and are optimized by molecular mechanics calculations. The intermolecular distances between the protons of OB and CD calculated for these structures are well-correlated with the observed ROESY intensities. The cyclohexyl group of OB penetrates deeply into a β-CD cavity, and the phenyl group is close to the wide rim of the cavity. The phenyl and cyclohexyl g...