Preparation and characterization of β-sitosterol/β-cyclodextrin crystalline inclusion complexes

Abstract

Inclusion complexes of β-sitosterol and β-cyclodextrin were prepared by mixing an equimolar ratio of the components in distilled water followed by freeze-drying. The solid state complexes were characterized by differential scanning calorimetry, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Physical mixtures of the two components showed two distinct melting endothermic peaks at 139 and 169 °C. The two melting peaks were attributable to the individual component (i.e., β-sitosterol and β-cyclodextrin). The inclusion complex, however, shows a single sharp melting endothermic peak at 186 °C indicating the formation of a crystalline complex. Scanning electron micrographs show the formation of well-defined needle-like crystals for the inclusion complexes. The crystalline inclusion complexes were readily soluble in water. The inclusion complexes were characterized in the solution state by nuclear magnetic resonance (NMR) spectroscopy. The continuous variation method, using NMR data, suggests the formation of a 1:1 β-sitosterol to β-cyclodextrin inclusion complex. Cross peaks observed in the rotating-frame overhauser effect spectroscopy NMR spectra suggests that both ends of the β-sitosterol i.e., the aliphatic tail and the cyclic head were encapsulated within the β-cyclodextrin cavity. Computational modeling on the inclusion complexes carried out using density functional theory support the conclusions obtained from NMR spectroscopy. The results of the study show that the β-sitosterol and β-cyclodextrin form water soluble inclusion complex.