Differential pressure effect on bimodal inclusion complex of β-cyclodextrin with a nitroxide radical probe as studied with electron paramagnetic resonance

Differential pressure effect was found in the inclusion equilibrium of bimodal inclusion (phenyl-in and t-butyl-in) complexes of β-cyclodextrin with the free-radical probe diphenylmethyl t-butyl nitroxide. A high-pressure electron paramagnetic resonance (EPR) system was employed to determine the shift of the EPR spectra under high static pressure. With increasing external pressure, the equilibrium between phenyl-in and t-butyl-in complexes shifts to the t-butyl-in side.