title: Effect of pH on the complexation of kaempferol-4'-glucoside with three β-cyclodextrin derivatives: isothermal titration calorimetry and spectroscopy study.
abstract: The utilization of kaempferol and its glycosides in food and pharmaceutical industries could be improved by the formation of inclusion complexes with cyclodextrins at different pH. This study explores the complexation of kaempferol-4'-glucoside with sulfobutyl ether-β-cyclodextrin (SBE-β-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and methylated-β-cyclodextrin (M-β-CD) in phosphate buffer solutions of different pH using isothermal titration calorimetry, UV-vis absorption and proton nuclear magnetic resonance spectroscopy at 298.2 K. Experimental results showed that kaempferol-4'-glucoside binds with the three β- cyclodextrins in the same 1:1 stoichiometry. The rank order of stability constants is SBE-β-CD > HP-β-CD > M-β-CD at the same pH level and pH 6.0 > pH 7.4 > pH 9.0 for the same cyclodextrin. The binding of kaempferol-4'-glucoside with the three β-cyclodextrin derivatives is synergistically driven by enthalpy and entropy at pH 6.0 and enthalpy-driven at pH 7.4 and 9.0. The possible inclusion mode was that in the cavity of β-CD is included the planar benzopyranic-4-one part of the kaempferol-4'-glucoside.
authors.affiliation: School of Chemistry and Chemical Engineering, Liaocheng University , Liaocheng, 252059 China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zheng
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Dong
authors.forename: Min
authors.initials: M
authors.lastname: Liu
authors.forename: Aiju
authors.initials: A
authors.lastname: Chen
authors.forename: Shangcai
authors.initials: S
authors.lastname: Feng
authors.forename: Bingquan
authors.initials: B
authors.lastname: Wang
authors.forename: Dezhi
authors.initials: D
authors.lastname: Sun
mesh_terms: D002151:Calorimetry; D019277:Entropy; D005960:Glucosides / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D044949:Kaempferols / Q000737:chemistry*; D015394:Molecular Structure; D012995:Solubility; D013057:Spectrum Analysis; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D005960:Glucosides; D044949:Kaempferols; D047392:beta-Cyclodextrins; C006552:kaempferol; C031215:betadex
keywords: NMR; UV−vis; complexation; isothermal titration calorimetry; kaempferol-4′-glucoside; β-cyclodextrin