tailieunhanh - Báo cáo khoa học: Interaction of gymnemic acid with cyclodextrins analyzed by isothermal titration calorimetry, NMR and dynamic light scattering

The physiological phenomenon that the antisweet taste effect of gymnemic acid (GA) is diminished by application of c-cyclodextrin (c-CD) to the mouth was evaluated at the molecular level using isothermal titration calorimetry, NMR and dynamic light scattering. These analyses showed that GA specifically binds to c-CD. | iFEBS Journal Interaction of gymnemic acid with cyclodextrins analyzed by isothermal titration calorimetry NMR and dynamic light scattering Yusuke Izutani1 Kenji Kanaori2 Toshiaki Imoto3 and Masayuki Oda1 1 Graduate Schoolof Agriculture Kyoto PrefecturalUniversity Japan 2 Department of Applied Biology Kyoto Institute of Technology Japan 3 Faculty of Medicine Tottori University Yonago Japan Keywords aggregation cyclodextrin gymnemic acid molecular interaction thermodynamics Correspondence M. Oda Graduate Schoolof Agriculture Kyoto PrefecturalUniversity 1-5 Hangi-cho Shimogamo Sakyo-ku Kyoto 606-8522 Japan Fax 81 75 703 5673 Tel 81 75 703 5673 E-mail oda@ Received 30 August 2005 revised 6 October 2005 accepted 11 October 2005 doi The physiological phenomenon that the antisweet taste effect of gymnemic acid GA is diminished by application of y-cyclodextrin y-CD to the mouth was evaluated at the molecular level using isothermal titration calorimetry NMR and dynamic light scattering. These analyses showed that GA specifically binds to y-CD. Thermodynamic analysis using isothermal titration calorimetry revealed that the association constant of GA and y-CD is 105-106 M-1 with favorable enthalpy and entropy changes. The heat capacity change was negative and large despite the change in accessible surface area upon binding being small. These thermodynamics indicate that the binding is dominated by hydrophobic interactions which is in agreement with inclusion complex formation of y-CD. In addition NMR measurements showed that in solution the spectra of GA are broad and sharpened by the addition of y-CD indicating that unbound GA is in a water-soluble aggregate that is dispersed when it forms a complex with y-CD. Dynamic light scattering showed that the average diameter of unbound GA is 30 nm and that of GA and y-CD complex is nm similar to unbound y-CD supporting the aggregate property of GA and the inclusion complexation of GA by