Electrochemical Reduction of [Ni(Mebpy)3]2+. Elucidation of the Redox Mechanism by Cyclic Voltammetry and Steady-State Voltammetry in Low Ionic Strength Solutions.

Bipyridine complexes of Ni are used as catalysts in a variety of reductive transformations. Here, the electroreduction of [Ni(Mebpy)3]2+ (Mebpy = 4,4’-dimethyl-2,2’-bipyridine) in dimethylformamide is reported, with the aim of determining the redox mechanism and oxidation states of products formed under well-controlled electrochemical conditions. Results from cyclic voltammetry, steady-state voltammetry (SSV) and chronoamperometry demonstrate that [Ni(Mebpy)3]2+ undergoes two sequential 1e reductions at closely separated potentials (E0’1 = -1.06 ± 0.01 V and E0’2 = -1.15 ± 0.01 V vs Ag/AgCl (3.4 M KCl)). Homogeneous comproportionation to generate [Ni(Mebpy)3]+ is demonstrated in SSV experiments in low ionic strength solutions. The comproportionation rate constant is determined to be > 106 M-1s-1, consistent with rapid outer-sphere electron transfer. Consequentially, on voltammetric time scales, the 2e reduction of [Ni(Mebpy)3]2+ results in formation of [Ni(Mebpy)3]1+ as the predominant species released into bulk solution. We also demonstrate that [Ni(Mebpy)3]0 slowly loses a Mebpy ligand (~10 s-1).

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Electrochemical Reduction of [Ni(Mebpy) 3 ] 2+ : Elucidation of the Redox Mechanism by Cyclic Voltammetry and Steady‐State Voltammetry in Low Ionic Strength Solutions

ChemElectroChem ◽

10.1002/celc.202000171 ◽

2020 ◽

Vol 7 (6) ◽

pp. 1473-1479

Author(s):

Koushik Barman ◽

Martin A. Edwards ◽

David P. Hickey ◽

Christopher Sandford ◽

Yinghua Qiu ◽

...

Keyword(s):

Cyclic Voltammetry ◽

Steady State ◽

Ionic Strength ◽

Electrochemical Reduction ◽

Redox Mechanism ◽

Low Ionic Strength

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Electron Transfer within the Cytochrome c-Cytochrome c Peroxidase Complex: Dependence of the Transient-State and Steady-State Kinetics on Ionic Strength

Molecular Crystals and Liquid Crystals ◽

10.1080/00268949108041172 ◽

1991 ◽

Vol 194 (1) ◽

pp. 253-258 ◽

Cited By ~ 9

Author(s):

James E. Erman ◽

Doe Sun Kang ◽

Kil Lyong Kim ◽

Farrel E. Summers ◽

Andrea L. Matthis ◽

...

Keyword(s):

Electron Transfer ◽

Steady State ◽

Ionic Strength ◽

Cytochrome C ◽

Transient State ◽

Cytochrome C Peroxidase ◽

Steady State Kinetics ◽

Complex Dependence

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The mechanism of assembly of Acanthamoeba myosin-II minifilaments: minifilaments assemble by three successive dimerization steps.

The Journal of Cell Biology ◽

10.1083/jcb.109.4.1537 ◽

1989 ◽

Vol 109 (4) ◽

pp. 1537-1547 ◽

Cited By ~ 58

Author(s):

J H Sinard ◽

W F Stafford ◽

T D Pollard

Keyword(s):

Electron Microscopy ◽

Light Scattering ◽

Ionic Strength ◽

Analytical Ultracentrifugation ◽

Myosin Ii ◽

Alkaline Ph ◽

Predominant Species ◽

Assembly Mechanism ◽

Rapid Equilibrium ◽

Low Ionic Strength

We used 90 degrees light scattering, analytical ultracentrifugation, and electron microscopy to deduce that Acanthamoeba myosin-II minifilaments, composed of eight molecules each, assemble by a novel mechanism consisting of three successive dimerization steps rather than by the addition of monomers or parallel dimers to a nucleus. Above 200 mM KCl, Acanthamoeba myosin-II is monomeric. At low ionic strength (less than 100 mM KCl), myosin-II polymerizes into bipolar minifilaments. Between 100 and 200 mM KCl, plots of light scattering vs. myosin concentration all extrapolate to the origin but have slopes which decrease with increasing KCl. This indicates that structures intermediate in size between monomers and full length minifilaments are formed, and that the critical concentrations for assembly of these structures is very low. Analytical ultracentrifugation has confirmed that intermediate structures exist at these salt concentrations, and that they are in rapid equilibrium with each other. We believe these structures represent assembly intermediates and have used equilibrium analytical ultracentrifugation and electron microscopy to identify them. Polymerization begins with the formation of antiparallel dimers, with the two tails overlapping by approximately 15 nm. Two antiparallel dimers then associated with a 15-nm stagger to form an antiparallel tetramer. Finally, two tetramers associate with a 30-nm stagger to form the completed minifilament. At very low ionic strengths, the last step in the assembly mechanism is largely reversed and antiparallel tetramers are the predominant species. Alkaline pH, which can also induce minifilament disassembly, produces the same assembly intermediates as are found for salt induced disassembly.

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Zur Elektrochemie von Metall(O)-Verbindungen, V [1] Reaktionen von Diazadien-Metall(VIb)-carbonylkationen und -anionen / Electrochemistry of Metal(O) Compounds, V [1] Reactions of Diazadiene Metal(VIb) Carbonyl Cations and Anions

Zeitschrift für Naturforschung B ◽

10.1515/znb-1982-0312 ◽

1982 ◽

Vol 37 (3) ◽

pp. 324-331 ◽

Cited By ~ 23

Author(s):

Heindirk torn Dieck ◽

Ewald Kühl

Keyword(s):

Electron Transfer ◽

Cyclic Voltammetry ◽

Chemical Reactions ◽

Oxidation States ◽

Transfer Reactions ◽

Carbonyl Complexes ◽

Electron Transfer Reactions ◽

Reactions With Nucleophiles ◽

The Stability ◽

Subsequent Chemical

Abstract Carbonyl complexes of chromium, molybdenum and tungsten of the type DAD M(CO)4 with DAD - diazadiene (R-N=CR′-CR′=NR) are shown by cyclic voltammetry to undergo electron transfer reactions to [DAD M(CO)4]+ and [DAD M(CO)4]-. The rate of subsequent chemical reactions with nucleophiles or by loss of ligands depend on the sol-vent, the metal and the ligands' electronic and steric properties. Chromium(+I) is more readily stabilized than Mo(+I) or W(-I) while the opposite is true for the stability of the anions formed. The dimerisation of a low-coordinate species DAD Mo(CO)3 from the reduction of DAD Mo(CO)3(CH3CN) is detected electrochemically. The stabilization of oxidation states +1 and -I is briefly discussed in view of the DAD ligand properties.

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Proteolytic removal of three C-terminal residues of actin alters the monomer-monomer interactions

Biochemical Journal ◽

10.1042/bj2890897 ◽

1993 ◽

Vol 289 (3) ◽

pp. 897-902 ◽

Cited By ~ 42

Author(s):

M Mossakowska ◽

J Moraczewska ◽

S Khaitlina ◽

H Strzelecka-Golaszewska

Keyword(s):

Electron Microscopy ◽

Steady State ◽

Ionic Strength ◽

Rate Constants ◽

Initial Rate ◽

Critical Concentration ◽

Rate Of Polymerization ◽

Low Ionic Strength ◽

Hydrolysis Of

Homogeneous preparations of actin devoid of the three C-terminal residues were obtained by digestion of G-actin with trypsin after blocking proteolysis at other sites by substitution of Mg2+ for the tightly bound Ca2+. Removal of the C-terminal residues resulted in the following: an enhancement of the Mg(2+)-induced hydrolysis of ATP in low-ionic-strength solutions of actin; an increase in the critical concentration for polymerization; a decrease in the initial rate of polymerization; and an enhancement of the steady-state exchange of subunits in the polymer. Electron microscopy indicated an increased fragility of the filaments assembled from truncated actin. The results suggest that removal of the C-terminal residues increases the rate constants for monomer dissociation from the polymer ends and from the oligomeric species.

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Some electron-transfer reactions involving carbodi-imide-modified cytochrome c

Biochemical Journal ◽

10.1042/bj2430379 ◽

1987 ◽

Vol 243 (2) ◽

pp. 379-384 ◽

Cited By ~ 2

Author(s):

A J Mathews ◽

T Brittain

Keyword(s):

Electron Transfer ◽

Ionic Strength ◽

Protein Charge ◽

Native Proteins ◽

Wide Range ◽

Internal Electron ◽

Modified Proteins ◽

Time Courses ◽

Low Ionic Strength ◽

Kinetics Of

The reaction kinetics of native and carbodi-imide-modified tuna and horse heart cytochromes c with both a strong (dithionite) and a relatively weak (ascorbate) reducing agent were studied over a wide range of conditions. In their reactions with dithionite both the native and modified cytochromes exhibit single exponential time courses. The effects of dithionite concentration and ionic strength on the rate of the reduction are complex and can best be explained in terms of the model proposed by Lambeth & Palmer [(1973) J. Biol. Chem. 248, 6095-6103]. According to this model, at low ionic strength the native proteins are reduced almost exclusively by S2O4(2-) whereas the modified proteins showed reactivity towards both S2O4(2-) and SO2.-. These findings are interpreted in terms of the different charge characteristics of the carbodi-imide-modified proteins relative to the native proteins. The findings that the modified proteins react with ascorbate in a biphasic manner are explained as arising from ascorbate binding to a reducible form of the protein, before electron transfer, with an equilibrium between the ascorbate-reducible form of the protein and a non-reducible form. Estimates were obtained for both the ascorbate equilibrium binding constant and the rate constant for the internal electron transfer for both the native and modified horse and tuna proteins. The effect of pH on the reactions indicates that the active reductant in all cases is ascorbate2-. The studies of ascorbate reactivity yield important information concerning the proposed correlation between ascorbate reducibility and the presence of a 695 nm-absorption band, and the study of dithionite reactivity illustrates the effect of protein charge and solution ionic strength on the relative contributions made by the species SO2.- and S2O4(2-) to the reduction of ferricytochrome c.

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Formation of electrostatically-stabilized complex at low ionic strength inhibits interprotein electron transfer between yeast cytochrome c and cytochrome c peroxidase

Biochemical and Biophysical Research Communications ◽

10.1016/0006-291x(88)90611-0 ◽

1988 ◽

Vol 151 (1) ◽

pp. 429-434 ◽

Cited By ~ 51

Author(s):

J.T. Hazzard ◽

G. McLendon ◽

M.A. Cusanovich ◽

G. Tollin

Keyword(s):

Electron Transfer ◽

Ionic Strength ◽

Cytochrome C ◽

Cytochrome C Peroxidase ◽

Low Ionic Strength

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Outer-sphere electron-transfer reactions of ascorbate anions

Australian Journal of Chemistry ◽

10.1071/ch9821133 ◽

1982 ◽

Vol 35 (6) ◽

pp. 1133 ◽

Cited By ~ 143

Author(s):

NH Williams ◽

JK Yandell

Keyword(s):

Aqueous Solution ◽

Electron Transfer ◽

Exchange Rate ◽

Ionic Strength ◽

Rate Constants ◽

Outer Sphere ◽

The Self ◽

Transfer Reactions ◽

Redox Potentials ◽

The One

Rate constants for the one-electron oxidation of ascorbate dianion (A2-) by bis(terpyridine)cobalt(III)ion (8.5 × 106 dm3 mol-1 s-1) and pentaammine(pyridine)ruthenium(III) ion (6.0 × 109 dm3 mol-1 s-1), and of the monoanion (HA-) by tetraammine (bipyridine)ruthenium(III)ion (2.1 × 105 dm3 mol-1s-1) have been determined in aqueous solution at 25�C and ionic strength 0.1 (NaNO3 or NaClO4). It is shown that these rate constants, and other published rate constants for oxidation of HA- and A2-, are consistent with the Marcus cross relation, on the assumption that the self-exchange rate constants for both the HA-/HA and A2-/A-couples are 106 dm3 mol-1 s-1. One electron redox potentials for the ascorbate/dehydroascorbate system have been derived from scattered literature data.

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Cytochrome c reduction by cysteine plus copper: a pseudosubstrate system for cytochrome c oxidase

Canadian Journal of Biochemistry ◽

10.1139/o80-067 ◽

1980 ◽

Vol 58 (6) ◽

pp. 499-503 ◽

Cited By ~ 6

Author(s):

Bruce C. Hill ◽

Peter Nicholls

Keyword(s):

Electron Transfer ◽

Ionic Strength ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Oxygen Electrode ◽

Horse Heart Cytochrome ◽

Ferricytochrome C ◽

Cytochrome C Reduction ◽

Low Ionic Strength ◽

Horse Heart Cytochrome C

Cysteine alone reduces horse heart cytochrome c very slowly [Formula: see text] with a rate constant virtually identical in high and low ionic strength buffers. Copper catalyzes this reaction increasing the rate by a factor of 105 in 50 mM phosphate and by a factor of 106 in 10 mM Tris buffers. When ferricytochrome c and cysteine are mixed in an oxygen electrode a "burst" of oxygen uptake is seen, the decline in which parallels the reduction of cytochrome c. When cytochrome c oxidase is added to such a mixture two routes of electron transfer to oxygen exist: enzymatic and ferricytochrome c dependent nonenzymatic. Both processes are sensitive to cyanide, but azide inhibits only the authentic cytochrome c oxidase catalyzed process and BCS the ferricytochrome c stimulated reaction.

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