title: Electron-transfer mechanism of the triplet state quenching of aluminium tetrasulfonated phthalocyanine by cytochrome c.
abstract: The mechanism of electron-transfer from aluminium tetrasulfonated phthalocyanine triplet state to cytochrome c was investigated in this work. This reaction successfully quenches the dye triplet state due to the formation of complexes between the solute and the protein at the active site. The electron-transfer rate constant is around 3x10(7) s(-1), and is in accordance with previous results for the singlet excited state quenching [C.A.T. Laia, S.M.B. Costa, D. Phillips, A. Beeby. Electron-transfer kinetics in sulfonated aluminum phthalocyanines/cytochrome c complexes, J. Phys. Chem. B 108 (2004) 7506-7514.] in the framework of the Marcus theory, with a reorganization energy equal to 0.94 eV. The complex formation is diffusion controlled, but heterogeneities of the protein surface charge distribution lead to quenching rate constants smaller than predicted on a hard-spheres model with electrostatic interactions. Also the binding equilibrium constant is strongly affected by this phenomenon. Ionic strength plays an important role on the complex formation, but its effect on the unimolecular electron-transfer rate constant is negligible within experimental error.
authors.affiliation: Centro de Química-Estrutural, Complexo 1, Instituto Superior Técnico, 1049-001 Lisboa, Portugal. cesar.laia@dq.fct.unl.pt
authors.forename: César A T
authors.initials: CA
authors.lastname: Laia
authors.forename: Sílvia M B
authors.initials: SM
authors.lastname: Costa
authors.forename: L F
authors.initials: LF
authors.lastname: Vieira Ferreira
mesh_terms: D002942:Circular Dichroism; D003574:Cytochrome c Group / Q000737:chemistry* / Q000502:physiology; D004579:Electron Transport / Q000502:physiology; D007211:Indoles / Q000737:chemistry*; D008954:Models, Biological; D009942:Organometallic Compounds / Q000737:chemistry*; D009994:Osmolar Concentration; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D013057:Spectrum Analysis / Q000379:methods; D055672:Static Electricity; D013997:Time Factors
chemical_list: D003574:Cytochrome c Group; D007211:Indoles; D009942:Organometallic Compounds; C048577:aluminum tetrasulfophthalocyanine