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Porphyrins-cyclodextrin—III. Breaking of cofacial dimers and multi-electron-reduction of free-base porphyrin within and outside of cyclodextrin cavities

International Journal of Radiation Applications and Instrumentation Part C Radiation Physics and Chemistry
Publication Date
DOI: 10.1016/1359-0197(92)90045-h


Abstract γ-Radiolysis, pulse radiolysis, proton nuclear magnetic resonance, absorption and fluorescence spectroscopies were used for the study and the characterization of the inclusion complex of the free base porphyrin H 2TSPP in aqueous solution of β-cyclodextrin (β-CD). In reducing media and independently of the presence or the absence of β-CD the porphyrin ring is reduced to give the radical anion P -., the dianion P 2-, the tetraanion P 4- and finally the colorless hexaanion P 6-. The absorption spectra of the various reduction states and the degree of their reversibility to P 0 upon admission of oxygen in the solution are reported. The effect of β-CD on the electron transfer from the CH 2OH . radical to the porphyrin ring was examined. Our NMR data show that up to pH=10.5 the complexation of the porphyrin with β-CD is intracavity but the reactivity of the porphyrin monomers towards reducing species is only slightly affected. At pH=13 dimer breaking is observed in the presence of β-CD due to the anti-shielding of the sulfonatophenyl groups.

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