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

1980 ◽  
Vol 102 (13) ◽  
pp. 4350-4355 ◽  
Author(s):  
John G. Reynolds ◽  
Catherine L. Coyle ◽  
R. H. Holm
Keyword(s):  
Exchange Rate ◽  
Rate Constant ◽  
Electron Exchange ◽  
Exchange Rate Constant ◽  
Exchange Kinetics ◽  
Fe Sites ◽  
Kinetics Of

Pressure effect on hydrogen isotope exchange kinetics in chymotrypsinogen investigated by FT-IR spectroscopy

1991 ◽  
Vol 69 (11) ◽  
pp. 1699-1704 ◽  
Author(s):  
P. T. T. Wong
Keyword(s):  
High Pressure ◽  
Exchange Rate ◽  
Rate Constant ◽  
Bound Water ◽  
Pressure Effects ◽  
Protein Molecules ◽  
Fast Exchange ◽  
Exchange Rate Constant ◽  
Hydrogen Deuterium ◽  
Exchange Kinetics

Hydrogen/deuterium (H/D) exchange rate constants in chymotrypsinogen have been determined at several pressures up to 28.9 kbar by FTIR spectroscopy. The secondary structure of the protein molecules was monitored simultaneously at the corresponding pressures by the intensity redistribution of the infrared amide I band at these pressures. As in other proteins, the labile protons on the amide groups in chymotrypsinogen can, to a good approximation, be separated into two classes, each with distinct first order H/D exchange rates constants in the time period from 10 min to ~24 h. The fast exchange rate constant increases while the slow exchange rate constant decreases with increasing pressure. The increase in the fast exchange rate constant at high pressure is largely associated with the pressure-induced unfolding of the protein molecules. At extremely high pressure (12.8 kbar), in addition to the unfolding of protein molecules, pressure induced a distortion and weakening of the hydrogen bonds of the fold protein segments also contribute to an increase in the overall H/D exchange rate. The present results confirm that when chymotrypsinogen is dissolved in D2O, a considerable amount of D2O molecules is bound to the protein molecules on the surface as well as in the interior cavities of the molecules. The H/D exchange takes place between these bound D2O and the protons in the protein molecules. The mechanism of the H/D exchange and the interior dynamics in proteins are discussed on the basis of the present results. Key words: hydrogen/deuterium exchange, exchange kinetics, rate constant, pressure effects, infrared spectroscopy, protein, conformation structure, bound water.

Cobalt, Iron and Ruthenium Complexes of Picolinic and Dipicolinic Acids: Syntheses, Solution Properties and Kinetics of Electron Transfer Reactions With Cytochrome C(II) and Some Inorganic Reductants

1989 ◽  
Vol 42 (1) ◽  
pp. 1 ◽  
Author(s):  
RM Ellis ◽  
JD Quilligan ◽  
NH Williams ◽  
JK Yandell
Keyword(s):  
Exchange Rate ◽  
Cytochrome C ◽  
Rate Constant ◽  
Order Rate Constant ◽  
The Self ◽  
Transfer Reactions ◽  
Solution Properties ◽  
Cobalt Iron ◽  
Exchange Rate Constant ◽  
Kinetics Of

Tris picolinate complexes of CO111 and RU111 have been synthesized, and their standard potentials measured (432 �10, 403 �2 mV) at 25�C and ionic strength 0.1 mol dm-3. The self-exchange rate constant of Ru ( pic )3O/- was found to be (1 .4 �0.9)×108 dm3 mol-1 s-l, from reaction with cytochrome C(II), Co( bpy )32+ and ~Co( phen )32+. For the reaction between Fe( dipic )2- and cytochrome ~(II), at 2S260C, pH 5.5 and I 0.1 mol dm-3 (KNO3), the second-order rate constant was (3.2 �0.l)×105 dm3 mol-1 s-1,with ΔH+ 19.9 �0.9 kJ mol-1 and ΔS+ -72.8 �.7 J K-1 mol-l. The self-exchange rate constant of Fe( dipic )2-/2- was reevaluated as (5.8 �0.2)×106 dm3 mol-l s-1.

The oxidation of hydrogen peroxide by tris(polypyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel(III) in aqueous media

1986 ◽  
Vol 64 (9) ◽  
pp. 1936-1942 ◽  
Author(s):  
Donal H. Macartney
Keyword(s):  
Hydrogen Peroxide ◽  
Exchange Rate ◽  
Rate Constant ◽  
Aqueous Media ◽  
Activation Parameters ◽  
Exchange Rate Constant ◽  
Oxidation Of Hydrogen ◽  
Polypyridine Complexes ◽  
Ph Range ◽  
Kinetics Of

The stoichiometry and kinetics of the oxidation of hydrogen peroxide by tris(2,2′-bipyridine) and tris(4,4′-dimethyl-2,2′-bipyridine) complexes of osmium(III), iron(III), ruthenium(III), and nickel (III) were studied in acidic and neutral aqueous media at 25 °C and I = 0.50 M (LiCF3SO3). The reaction 2M(bpy)33+ + H2O2 → 2M(bpy)32+ + O2 + 2H+ is observed with quantitative yields of dioxygen gas. The observed rate constants displayed an inverse acid dependence over the pH range 6.0–8.5; kobsd = k1 + k2K1/[H+], attributed to the oxidations of H2O2(k1) and HO2− (k2). An application of the Marcus theory relationship to the cross-reaction data gave a self-exchange rate constant of 10−2–10−1 M−1 s−1 for the HO2−/HO2 couple. The electron exchange rate constant is evaluated in terms of the inner-sphere and solvent reorganizational barriers and is compared to values reported for other small molecule couples. Rate and activation parameters for the reduction of the nickel(III) complexes by the hydroxide ion have been determined and are compared with the corresponding values for other metal tris(poly pyridine) complexes.

Reduction of hexaammineruthenium(III) ions by a series of tris(polypyridyl)chromium(II) ions – Revisiting the Cr(NN)33+/2+ self-exchange rate

2001 ◽  
Vol 79 (7) ◽  
pp. 1124-1127 ◽  
Author(s):  
K Omar Zahir
Keyword(s):  
Exchange Rate ◽  
Excited States ◽  
Rate Constants ◽  
Driving Force ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Outer Sphere ◽  
Laser Flash ◽  
Exchange Rate Constant ◽  
Kinetics Of

The kinetics of the outer-sphere oxidation of Cr(NN)32+ ions (NN = 2,2'-bipyridine, 1,10-phenanthroline, and their substituted analogs) by hexaammineruthenium(III) was studied using laser flash photolysis. The Cr(NN)32+ ions were generated via the reductive quenching of the *Cr(NN)33+ excited states by oxalate ions or by H2edta2–. The second-order rate constants were found to vary with the driving force of the reaction. The rate constants increase from (7.1 ± 0.5) × 106 M–1 s–1 for Cr(5-Clphen)32+ to (2.6 ± 0.2) × 108 M–1 s–1 for Cr(4,7-Me2phen)32+. The self-exchange rate constant for the couple (Cr(NN)33+/2+) was calculated by applying Marcus cross relation to present and other known reactions of Cr(NN)3n+ ions, where n = 3 or 2 with various reactants and is estimated to be (6 ± 4) × 107 M–1 s–1.Key words: tris(polypyridyl)chromium(II)/(III) self-exchange rate, hexaammineruthenium(III), oxidation of Cr(NN)32+.

Electron Exchange Kinetics of the NO3Free Radical in Solution

1964 ◽  
Vol 86 (13) ◽  
pp. 2595-2600 ◽  
Author(s):  
T. W. Martin ◽  
R. E. Rummel ◽  
R. C. Gross
Keyword(s):  
Electron Exchange ◽  
Exchange Kinetics ◽  
Kinetics Of
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