Kinetics of self-exchange of bis(1,4,7-trithiacyclononane)iron(III)/(II) in acetonitrile and in acidic aqueous solution

1990 ◽  
Vol 68 (12) ◽  
pp. 2228-2233 ◽  
Author(s):  
Hideo Doine ◽  
Thomas W. Swaddle
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Ionic Strength ◽  
Line Broadening ◽  
Acidic Water ◽  
Exchange Reactions ◽  
Acidic Aqueous Solution ◽  
Spontaneous Reduction ◽  
Kinetics Of ◽  
C Nmr

The rate constant kex of the [Formula: see text] self-exchange reaction cannot be measured in most common solvents because of spontaneous reduction of the [Formula: see text] ion, which is also sensitive to photolysis by visible light. However, in CD3CN at −41 to −19 °C, reproducible proton-decoupled 13C NMR line broadening measurements are possible, and give kex = (5.3 ± 0.3) × 104 kg mol−1s−1 at 0 °C, ΔH* = 10.3 ± 1.8 kJ mol−1, and ΔS* = −116 ± 7 J K−1 mol−1, at ionic strength I = 0.1 mol kg−1. Proton NMR line broadening experiments are marginally practicable in very acidic water (2.0 mol kg−1 D2SO4/D2O) near 0 °C, and give kex = 3.2 × 106 kg mol−1 s−1 at 1 °C. The relative kex values of these and other low-spin/low-spin FeIII/II self-exchange reactions follow the predictions of the Marcus–Hush theory at least qualitatively. The effect of ionic strength, however, is less than predicted, probably because of the formation of less reactive anion–cation pairs. Keywords: electron transfer kinetics, crown thioether complexes.

Pressure effects on the rate of electron transfer between tris(1,10-phenanthroline)iron(II) and -(III) in aqueous solution and in acetonitrile

1988 ◽  
Vol 66 (11) ◽  
pp. 2763-2767 ◽  
Author(s):  
Hideo Doine ◽  
Thomas Wilson Swaddle
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Ionic Strength ◽  
Classical Theory ◽  
Activation Parameters ◽  
Pressure Effects ◽  
Line Broadening ◽  
Water As Solvent ◽  
Aqueous Solvent ◽  
Mean Pressure

Proton nmr line-broadening experiments at ambient and elevated (to 215 MPa) pressures show that the rate of electron transfer between Fe(phen)32+ and Fe(phen)33+ as bisulfates in D2O/D2SO4 is represented by the activation parameters (at ionic strength I ~ 0.4 mol kg−1) ΔH≠ = 1.6 ± 0.5 kJ mol−1, ΔS≠ = −102.2 ± 1.6 JK−1mol−1, k(276 K) = 1.31 × 107 kg mol−1s−1, and (at I ~ 0.3 mol kg−1 and a mean pressure of 100 MPa) ΔV≠ = −2.2 ± 0.1 cm3mol−1. For the same reaction of the perchlorate salts (total [Fe] 0.046–0.065 mol kg−1) in CD3CN, ΔH≠ = 11.0 ± 1.0 kJ mol−1, ΔS≠ = −72.5 ± 3.6 J K−1 mol−1, k(277 K) = 8.0 × 106 kgmol−1s−1, and ΔV≠ = −5.9 ± 0.5 cm3 mol−1. For water as solvent, ΔV≠ is satisfactorily accounted for by a classical theory of the Stranks–Hush–Marcus type. Volumes of activation for electron self-exchange are shown to provide criteria for non-adiabaticity and for dominance of (non-aqueous) solvent reorganization dynamics; on this basis, it is seen that neither of these factors is important in the title reactions.

Meso tetrakis ortho-, meta-, and para-N-alkylpyridiniopor-phyrins: kinetics of copper(II) and zinc(II) incorporation and zinc porphyrin demetalation

2003 ◽  
Vol 07 (03) ◽  
pp. 139-146 ◽  
Author(s):  
Peter Hambright ◽  
Ines Batinić-Haberle ◽  
Ivan Spasojević
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Effective Charge ◽  
Methyl Ethyl ◽  
Ionic Strength Dependence ◽  
Zinc Porphyrin ◽  
Cationic Porphyrin ◽  
Strength Dependence ◽  
Acid Catalyzed ◽  
Kinetics Of

The relative reactivities of the tetrakis( N -alkylpyridinium- X - yl )-porphyrins where X = 4 (alkyl = methyl, ethyl, n -propyl) , X = 3 (methyl) , and X = 2 (methyl, ethyl, n -propyl, n -butyl, n -hexyl, n -octyl) were studied in aqueous solution. From the ionic strength dependence of the metalation rate constants, the effective charge of a particular cationic porphyrin was usually larger when copper(II) rather than zinc(II) was the reactant. The kinetics of ZnOH + incorporation and the acid catalyzed removal of zinc from the porphyrins in 1.0 M HCl were also studied. In general, the more basic 4- (para-) and 3- (meta-) isomers were the most reactive, followed by the less basic 2- (ortho-) methyl to n -butyl derivatives, with the lipophilic ortho n -hexyl and n -octyl porphyrins the least reactive.

Effect of ionic strength on the kinetics of ionic and micellar reactions in aqueous solution

1982 ◽  
Vol 76 (2) ◽  
pp. 984-996 ◽  
Author(s):  
Mei Hsu Dung ◽  
John J. Kozak
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Kinetics Of

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

1987 ◽  
Vol 243 (2) ◽  
pp. 379-384 ◽  
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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