Interactions of Cholesterol with Cyclodextrins in Aqueous Solution

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The interaction of cholesterol with several cyclodextrins (CDs) was investigated in water using solubility method. It was found that heptakis (2,6-di-ο-methyl)-β-CD (DOM-β-CD) forms two types of soluble complex, with molar ratios of 1:1 and 1:2 (cholesterol: DOM-β-CD), and neither a soluble nor insoluble complex is formed between cholesterol and α-CD, β-CD, and γ-CD, although a minor soluble complex formation was observed between cholesterol and 2-hydroxylpropyl-β-CD. The thermodynamic parameters for 1:1 and 1:2 complex formation of cholesterol with DOM-β-CD obtained from the changes in K with temperature are as follows: ΔG°_<1:1>=-11.6kJ/mol at 25℃ (K_<1:1>=1.O9x1O^2M^<-1>); ΔH°_<1:1>=-3.38kJ/mol; TΔS°_<1:1>=8.25kJ/mol; AG°_<1:2>=-27.1 kJ/mol at 25℃ (K_<1:2>=5.68×10^4M^<-1>); ΔH°_<1:2>=-3.96 kJ/mol; and TΔSi°_<1:2>=23.2kJ/mol. The formation of the 1:2 complex occurred much more easily than that of the 1:1 complex. The driving force for 1:1 and 1:2 complex formation was considered to be mainly hydrophobic interaction. Also, based on the measurements of proton nuclear magnetic resonance spectra and studies with Corey-Pauling-Koltun atomic models, the probable structutures of the 1:2 complex were estimated.
公益社団法人日本薬学会の論文
2003-11-01