title: Exclusion of aromatic radical cations from cyclodextrin nanocavity studied by pulse radiolysis.
abstract: The influence of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) on the one-electron oxidation reaction of aromatic sulfides (S) with Br2*- and the decay process of the S radical cation (S*+) was investigated by pulse radiolysis. The dissociation kinetics of S*+ from the CD cavity was examined in terms of the apparent equilibrium constants (Kapp) for the formation and decay processes of S*+. Inhibition of the one-electron oxidation reaction of S by Br2*- was clearly observed in the presence of HP-beta-CD. On the basis of a comparison between the determined Kapp values, it was found that the binding ability of S*+ with HP-beta-CD is much lower than that of S, because of the hydrophobic nature of the cavity. The formation process of the dimer radical cation of 4-(methylthio)phenylmethanol ((MTPM)2*+), which is generated between MTPM(*+) and neutral MTPM in solution, was also inhibited by the addition of HP-beta-CD.
authors.affiliation: The Institute of Scientific and Industrial Research (SANKEN), Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tachikawa
authors.forename: Sachiko
authors.initials: S
authors.lastname: Tojo
authors.forename: Mamoru
authors.initials: M
authors.lastname: Fujitsuka
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Majima
mesh_terms: D002412:Cations; D003505:Cyclodextrins / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D053758:Nanoparticles; D010084:Oxidation-Reduction; D011675:Pulse Radiolysis; D013056:Spectrophotometry, Ultraviolet; D019265:Spectroscopy, Near-Infrared; D013440:Sulfides / Q000737:chemistry
chemical_list: D002412:Cations; D003505:Cyclodextrins; D005609:Free Radicals; D006841:Hydrocarbons, Aromatic; D013440:Sulfides