title: Phase solubility studies of pure (-)-alpha-bisabolol and camomile essential oil with beta-cyclodextrin.
abstract: (-)-Alpha-bisabolol was found to form an inclusion complex with beta-cyclodextrin (beta-CD) in solution as well as in the solid state. To investigate molecular associations of beta-CD with pure (-)-alpha-bisabolol or (-)-alpha-bisabolol as a component of camomile essential oil, phase solubility studies were undertaken. A B(s) type solubility with an apparent complex constant of 273 M(-1) for the pure (-)-alpha-bisabolol and 304 M(-1) for (-)-alpha-bisabolol as a constituent of the essential oil were obtained. The two curves in the phase solubility diagram reach their plateau at different concentrations of (-)-alpha-bisabolol, 7.04 x 10(-4) M for the pure substance and 2.88 x 10(-4) M for the substance as a component of the essential oil. Although the shapes of the curves are almost similar, the intrinsic solubility's of pure (-)-alpha-bisabolol (4.85 x 10(-4) M) and (-)-alpha-bisabolol as a component of the essential oil (1.82 x 10(-4) M) differ significantly. An inclusion complex having a stoichiometric composition of 2:1 (beta-CD: drug) was obtained. A mechanism of complexation has been proposed on the basis of the stability constant calculated from phase solubility data and the stoichiometric ratio of the solid state complexation.
authors.affiliation: Department of Pharmaceutical Technology, Eberhard-Karls-University Tuebingen, Tuebingen, Germany.
authors.forename: K J
authors.initials: KJ
authors.lastname: Waleczek
authors.forename: H M Cabral
authors.initials: HM
authors.lastname: Marques
authors.forename: B
authors.initials: B
authors.lastname: Hempel
authors.forename: P C
authors.initials: PC
authors.lastname: Schmidt
mesh_terms: D020843:Chamomile / Q000737:chemistry*; D002626:Chemistry, Pharmaceutical; D002849:Chromatography, Gas; D003505:Cyclodextrins / Q000737:chemistry*; D004355:Drug Stability; D000431:Ethanol; D008958:Models, Molecular; D000081222:Monocyclic Sesquiterpenes; D009822:Oils, Volatile / Q000737:chemistry*; D012717:Sesquiterpenes / Q000737:chemistry*; D012995:Solubility; D013500:Surface Tension; D013997:Time Factors; D014867:Water; D047392:beta-Cyclodextrins
chemical_list: D003505:Cyclodextrins; D000081222:Monocyclic Sesquiterpenes; D009822:Oils, Volatile; D012717:Sesquiterpenes; D047392:beta-Cyclodextrins; D014867:Water; C004497:bisabolol; D000431:Ethanol; C031215:betadex