The interaction of lipoic acid with beta-cyclodextrin (beta-CD) has been studied by capillary electrophoresis in aqueous phosphate buffer (20 mm, pH = 9.0) at 20 degreesC, The results allowed us to detect the formation of an inclusion complex with a 1:1 lipoic acid/beta-CD stoichiometry and an association constant of 1645 M-1. The geometry of the inclusion complex in D2O was investigated by means of 2D-ROESY (Rotating-frame Overhauser Enhancement Spectroscopy) NMR experiments, which showed the occurrence of a bimodal complexation of lipoic acid inside the beta-CD cavity. Semi-empirical calculations using the PM3 method show that the orientations of the included lipoic acid are very close in energy, thus confirming the experimental observations.
Capillary electrophoresis, ROESY NMR and molecular modelling study of the inclusion complex beta-cyclodextrin/lipoic acid
CAROFIGLIO, TOMMASO;FORNASIER, ROBERTO;G. SAIELLI;TONELLATO, UMBERTO;
2002
Abstract
The interaction of lipoic acid with beta-cyclodextrin (beta-CD) has been studied by capillary electrophoresis in aqueous phosphate buffer (20 mm, pH = 9.0) at 20 degreesC, The results allowed us to detect the formation of an inclusion complex with a 1:1 lipoic acid/beta-CD stoichiometry and an association constant of 1645 M-1. The geometry of the inclusion complex in D2O was investigated by means of 2D-ROESY (Rotating-frame Overhauser Enhancement Spectroscopy) NMR experiments, which showed the occurrence of a bimodal complexation of lipoic acid inside the beta-CD cavity. Semi-empirical calculations using the PM3 method show that the orientations of the included lipoic acid are very close in energy, thus confirming the experimental observations.
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