Self-exchange Constants Research Articles

Flash-photolysis studies of the electron-transfer reactions of dioxygen complexes of cobalt(III) with tris(2,2′-bipyridyl)ruthenium(III)

Electron-transfer reactions between the µ-peroxo-cobalt(III) complexes [(H3N)5Co(µ-O2)Co(NH3)5]4+(1), [(H3N)4Co(µ-O2)(µ-NH2)Co(NH3)4]3+(2), and [(L–L)2Co(µ-O2)(µ-NH2)Co(L–L)2]3+[L–L = ethylenediamine (3), 2,2′-bipyridyl (4), or 1,10-phenanthroline (5)] and [Ru(bipy)3]3+(bipy = 2,2′-bipyridyl) have been investigated. The reactants have been generated by the electron-transfer quenching of the excited state of [Ru(bipy)3]2+ by the corresponding µ-superoxo-complexes using flash photolysis. The half-wave potentials measured by polarography for complexes (3), (4), and (5) are 1.00 ± 0.05, 1.04 ± 0.05, and 1.04 ± 0.05 V respectively. The observed rate constants are used to calculate the self-exchange electron-transfer rate constants for the bridged cobalt(III) complexes. The Marcus cross relationship has been used to predict the rate constants determined earlier for the electron-transfer reaction between (3) and the superoxo-forms of complexes (1), (4), and (5).

The use of rotating disk voltammetry for the determination of homogeneous small molecule-redox protein reaction rates

Rotating disk voltammetry was used in this work to study the rates of reaction of ferricytochrome c with two very strong reductants, methyl and benzyl viologen. The rates of reaction for these reductants were found to be 4.0 × 10 7 and 5.4 × 10 7 m −1 s −1 at 24°C for benzyl and methyl viologen, respectively. The versatility of this method was demonstrated by the ease with which the activation parameters were obtained. The Δ H ≠ and Δ S ≠ were found to be 4.0 kcal/mol and −10.6 cal/mol-K, respectively, for benzyl viologen. All the observed reaction rates were corrected for coulombic effects by the method of Wherland and Gray, and the electrostatically corrected rate constants were compared with the Marcus and Hopfield theories for electron transfer. The agreement was excellent for the tunneling theory but there were some discrepancies with the absolute Marcus theory. The relative Marcus approach worked quite well and, by taking into account the nonadiabaticity of the electron transfer, reasonable values were obtained for the absolute Marcus theory when realistic values of the self-exchange constants were used.

Electron exchange kinetics of [Fe4S4(SR)4]2-/[Fe4S4(SR)4]3- and [Fe4Se4(SR)4]2-/[Fe4Se4(SR)4]3- systems. Estimates of the intrinsic self-exchange rate constant of 4-Fe sites in oxidized and reduced ferredoxins

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron exchange kinetics of [Fe4S4(SR)4]2-/[Fe4S4(SR)4]3- and [Fe4Se4(SR)4]2-/[Fe4Se4(SR)4]3- systems. Estimates of the intrinsic self-exchange rate constant of 4-Fe sites in oxidized and reduced ferredoxinsJohn G. Reynolds, Catherine L. Coyle, and R. H. HolmCite this: J. Am. Chem. Soc. 1980, 102, 13, 4350–4355Publication Date (Print):June 1, 1980Publication History Published online1 May 2002Published inissue 1 June 1980https://doi.org/10.1021/ja00533a010RIGHTS & PERMISSIONSArticle Views253Altmetric-Citations47LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (722 KB) Get e-Alerts Get e-Alerts

Identification of binding sites in reactions of blue copper proteins with inorganic complexes and implications of such findings

Kinetically determined pKa values provide evidence for different protein binding sites; implications regarding the application of Marcus theory and calculation of protein self-exchange rate constants are considered.

Metalloprotein electron transfer reactions: analysis of reactivity of horse heart cytochrome c with inorganic complexes.

The reactions of horse heart cytochrome c with Fe(ethylenediaminetetraacetate)2-, Co(1,10-phenanthroline)3(3+), Ru(NH3)6(2+), and Fe(CN)6(3-) have been analyzed within the formalism of the Marcus theory of outer-sphere electron transfer, including compensation for electrostatic interactions. Calculated protein self-exchange rate constants based on crossreactions are found to vary over three orders of magnitude, decreasing according to Fe(CN)6(3-) greater than Ru(NH3)6(2+) greater than Fe(EDTA)2-. The reactivity order suggests that the mechanism of electron transfer involves attack by the small molecule reagents near the most nearly exposed region of the heme; this attack is affected by electrostatic interactions with the positively charged protein, by hydrophobic interactions that permit reagent penetration of the protein surface, and by the availability of pi symmetry ligand (or extended metal) orbitals that can overlap with the pi redox orbitals of the heme group.

Electron-transfer reactions of excited states. Reductive quenching of the tris(2,2'-bipyridine)ruthenium(II) luminescence

Spectrofluorimetry was used to measure the quenching of *Ru(pby)/sub 3//sup 2 +/ luminescence using the reducing agents Fe(CN)/sub 6//sup 4 -/, Co(phen)/sub 3//sup 2 +/, Ru(NH/sub 3/)/sub 6//sup 2 +/, Eu(II), S/sub 2/O/sub 4//sup 2 -/, Fe/sup 2 +/ and Mo(CN)/sub 8//sup 4 -/. Data, including the reduction potential, the electron self-exchange rate constant, the Stern-Volmer constant, quenching rate constant, and spectral data concerning the position(s) of the lowest energy excited states available to the reducing agent quenchers, was tabulated using experimental data and some literature data. The experimental results indicate the role of *Ru(bpy)/sub 3//sup 2 +/ as a strong oxidizing agent in the electron transfer process. (DDA)