title: Study of the complexation of fisetin with cyclodextrins.
abstract: In this work, the interaction between fisetin (3,3',4',7-tetrahydroxyflavone) (Fis) and cyclodextrins (CDs) (alpha and beta) was studied through UV-vis absorption, steady-state fluorescence, induced circular dichroism, and (1)H NMR experiments with dependence on temperature and pH. Some experimental data were compared with quantum-mechanics studies based on the SAM1 (AMPAC) semiempirical model, as well as with the B3LYP and MPW1PW91 functional models from density functional theory using the 6-311G and 3-21G basis sets. The spectroscopic measurements show that Fis does not form stable complexes with alpha-CD. On the other hand, at pH 4.0 and 6.5, the complex Fis-beta-CD is formed in a Fis:beta-CD 1:1 stoichiometry and an equilibrium constant (K) of 900 +/- 100 M(-1). In basic medium (pH 11.5), K decreases to 240 +/- 90 M(-1) because Fis deprotonation leads to its better solubilization in water. Molecular modeling points out that Fis is not totally inserted into the inner cavity of beta-CD. The formation of the inclusion complex renders an environment that enhances intramolecular excited state proton transfer. The inclusion complex is formed preferentially via entry of the Fis phenyl group into beta-CD.
authors.affiliation: Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14040-901 Ribeirão Preto, SP, Brazil.
authors.forename: Mariana R
authors.initials: MR
authors.lastname: Guzzo
authors.forename: Miriam
authors.initials: M
authors.lastname: Uemi
authors.forename: Paulo M
authors.initials: PM
authors.lastname: Donate
authors.forename: Sofia
authors.initials: S
authors.lastname: Nikolaou
authors.forename: Antonio Eduardo H
authors.initials: AE
authors.lastname: Machado
authors.forename: Laura T
authors.initials: LT
authors.lastname: Okano
mesh_terms: D003505:Cyclodextrins / Q000737:chemistry*; D005419:Flavonoids / Q000737:chemistry*; D044948:Flavonols; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D015394:Molecular Structure; D012680:Sensitivity and Specificity; D012995:Solubility; D013816:Thermodynamics
chemical_list: D003505:Cyclodextrins; D005419:Flavonoids; D044948:Flavonols; C017875:fisetin