Interaction of Heptakis (2, 3, 6-Tri-0-methyl) -β-cyclodextrin with Cholesterol in Aqueous Solution

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The interaction of cholesterol with heptakis (2, 3, 6-tri-0-methyl) -β-cyclodextrin (TOM-β-CyD) was investigated in water using solubility method. It was found that TOM-β-CyD forms two kinds of soluble complexes, with molar ratios of 1 : 1 and 1 : 2 (cholesterol : TOM-β-CyD). The thermodynamic parameters for 1 : 1 and 1 : 2 complex formation of cholesterol with TOM-β-CyD were : ΔG^0_<1 : 1>=-11.0kJ/mol at 25℃ (K_<1 : 1>=7.70×10_M^<-1>) ; ΔH^0_<1 : 1>= -1.28kJ/mol ; TΔS^0_<1 : 1>=9.48kJ/mol ΔG^0_<1 : 2>=-27.8kJ/mol at 25℃ (K_<1 : 2>=7.55×10^4_M^<-1>) ; ΔH^0_<1 : 2>=-0.57kJ/mol ; TΔS^0_<1 : 1>=27.3kJ/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 suggested to be exclusively hydrophobic interaction. Based on the measurements of proton nuclear magnetic resonance spectra and studies with Corey-Pauling-Koltun atomic models, the probable structures of the 1 : 2 complex were estimated. In addition, the interaction of TOM-β-CyD with cholesterol was compared with that of heptakis (2, 6-di-O-methyl) -β-CyD (DOM-β-CyD). The interaction of TOM-β-CyD is more hydrophobic than that of DOM-β-CyD, and the life time of the complexed TOM-β-CyD is sufficiently long to give separated signals, at the NMR time scale, which differs from that of complexed DOM-β-CyD.
公益社団法人日本薬学会の論文
2004-12-01