title: Inclusion complex of 2-chlorobenzophenone with cyclomaltoheptaose (β-cyclodextrin): temperature, solvent effects and molecular modeling.
abstract: A thermodynamic study of the inclusion process between 2-chlorobenzophenone (2ClBP) and cyclomaltoheptaose (β-cyclodextrin, β-CD) was performed using UV-vis spectroscopy, reversed-phase liquid chromatography (RP-HPLC), and molecular modeling (PM6). Spectrophotometric measurements in aqueous solutions were performed at different temperatures. The stoichiometry of the complex is 1:1 and its apparent formation constant (K(c)) is 3846M(-1) at 30°C. Temperature dependence of K(c) values revealed that both enthalpy (ΔH°=-10.58kJ/mol) and entropy changes (ΔS°=33.76J/Kmol) are favorable for the inclusion process in an aqueous medium. Encapsulation was also investigated using RP-HPLC (C18 column) with different mobile-phase compositions, to which β-CD was added. The apparent formation constants in MeOH-H(2)O (K(F)) were dependent of the proportion of the mobile phase employed (50:50, 55:45, 60:40 and 65:35, v/v). The K(F) values were 419M(-1) (50% MeOH) and 166M(-1) (65% MeOH) at 30°C. The thermodynamic parameters of the complex in an aqueous MeOH medium indicated that this process is largely driven by enthalpy change (ΔH°=-27.25kJ/mol and ΔS°=-45.12J/Kmol). The results of the study carried out with the PM6 semiempirical method showed that the energetically most favorable structure for the formation of the complex is the 'head up' orientation.
authors.affiliation: Universidad Nacional de San Luis, San Luis, Argentina.
authors.forename: Matias I
authors.initials: MI
authors.lastname: Sancho
authors.forename: Estela
authors.initials: E
authors.lastname: Gasull
authors.forename: Sonia E
authors.initials: SE
authors.lastname: Blanco
authors.forename: Eduardo A
authors.initials: EA
authors.lastname: Castro
mesh_terms: D001577:Benzophenones / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D008956:Models, Chemical; D012997:Solvents / Q000737:chemistry*; D013696:Temperature; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D001577:Benzophenones; D012997:Solvents; D047392:beta-Cyclodextrins