Abstract
The disposition of cholesterol inside the β-cyclodextrin cavity(β-CD) was deduced from oxidation of cholesterol secondary alcoholgroups by Ca(OCl)2 and H2O2 in thepyridine–acetic acid system. The amount of cholest-4-ene-3-one formedwas found to be proportional to the concentration of β-cyclodextrin,resulting in 56.1% of ketone. The oxidation rate was enhanced byβ-cyclodextrin and its methyl, polymer and 1 : 1copper(II)–β-cyclodextrin derivatives. Detailed investigationsinvolving UV-visible, 13C- and 1H-NMR(T1, 1D NOE and ROESY) spectroscopic studies were carried out.A binding constant value of 15,385 ± 1500 M-2 wasobtained for the 2 : 1heptakis-2,6-di-O-methyl-β-cyclodextrin(DMβ-CD) : cholesterolcomplex in chloroform from UV studies. Proton and solid state13C-CP MAS spectra of the β-CD–cholesterol mixtureshowed large magnitude shifts for the protons from the wider end of theβ-CD cavity as well as those of ring A and ring B of cholesterol. Both1D NOE and ROESY measurements indicated the proximity between ring A andring B protons of cholesterol and the wider end protons of β-CD andDMβ-CD. Besides, analysis of τc,τi and tau;m from T1measurements showed not only a lowering of rotational motions but a ξvalue of 0.016–0.048 for some of the cholesterol protons, typical of aweak complex. Based on these studies, a probable structure for the 2 : 1complex involving two molecules of β-CD/DMβ-CD was proposed withportions of ring A and ring B being present inside the wider end of theβ-CD/DMβ-CD cavity and ring D and the side chain attached atposition 17, projecting into the wider end of the secondβCD/DMβ-CD molecule.
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Ravichandran, R., Divakar, S. Inclusion of Ring A of Cholesterol Inside the β-Cyclodextrin Cavity: Evidence from Oxidation Reactions and Structural Studies. Journal of Inclusion Phenomena 30, 253–270 (1998). https://doi.org/10.1023/A:1007912809965
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DOI: https://doi.org/10.1023/A:1007912809965