82796-47-2Relevant articles and documents
Kinetics of the reaction of copper(II) with cobalt(II) sepulchrate: Catalysis by chloride ion and imidazole
Sisley,Jordan
, p. 2880 - 2884 (2008/10/08)
The kinetics of the oxidation of cobalt(II) sepulchrate by aqueous copper(II) have been studied in the presence of chloride ion, imidazole, and acetonitrile at 25°C. The reaction rate increases with increasing concentrations of chloride ion (0.05-0.2 M in 0.50 M HClO4/LiClO4) and imidazole (0.025-0.09 M at pH 6.5, in 0.15 M LiClO4), but is unaffected by 0.4 M acetonitrile (0.50 M HClO4/LiClO4). The reaction of Cu2+(aq) and Co(sep)2+ is complicated by the rapid formation of copper metal, and it was necessary to use O2 as a scavenger for Cu+(aq) in order to determine the rate constant of 5.0 ± 0.25 M-1 s-1 (0.02 M HClO4, 0.48 M LiClO4, 25°C). This value and earlier results for reductions of Ru(III) complexes by Cu+(aq) give a self-exchange rate constant of 5 × 10-7 M-1 s-1 for Cu2+/+(aq) from the Marcus cross relationship. The CuII(Cl)n complexes have rate constants of 1.6 × 103, 1.5 × 104, and 4.5 × 105 M-1 s-1 for n = 1-3. The change in reactivity can be accounted for in terms of Marcus theory by the increased driving force and reduced charge, with a self-exchange rate constant for the CuII/I(Cl)n species of 2 × 10-4 M-1 s-1. The CuII(Im)n complexes show a much smaller change in reactivity (35, 70, and 120 M-1 s-1 for n = 2-4) and a smaller self-exchange rate constant of ～1 × 10 7 M 1 s-1.
Reactions of the superoxochromium(III) ion with transition-metal complexes
Brynildson, Mark E.,Bakac, Andreja,Espenson, James H.
, p. 2592 - 2595 (2008/10/08)
The reactions of the superoxochromium(III) ion, CrO22+, with a number of one-electron-reducing agents have been examined in acidic aqueous solutions at 25°C and 0.10 M ionic strength. The results are consistent with an outer-sphere mechanism for Ru(NH3)62+ (k = 9.5 × 105 M-1 s-1), Co(sep)2+ (8.5 × 105 M-1 s-1), and V(H2O)62+ (2.3 × 105 M-1 s-1). The reactions with Fe(H2O)62+, Co([14]aneN4)(OH2)22+, and Co([15]aneN4)(OH2)22+ take place by an inner-sphere mechanism characterized by the formation and subsequent decomposition of binuclear intermediates. The rate constants for these reactions have values 4.5 × 103, ～7 × 106, and 6.2 × 105 M-1 s-1, respectively.
Active-site chemistry of hemerythrin: Kinetic studies on the reduction of metmyohemerythrin from Themiste zostericola and the mechanism for met and deoxy interconversion
Armstrong, Graeme D.,Sykes, A. Geoffrey
, p. 3725 - 3729 (2008/10/08)
Three stages are observed in the 2-equiv reduction of the binuclear Fe(III,III) active site of Themiste zostericola metmyohemerythrin. At pH 8.2 the first stage is dependent on the concentration of reductant, and second-order rate constants k1 (M-1 s-1; 25°C) are as follows: [Co(sep)]2+, 1.4 × 103; [Co(9-aneN3)2]2+, 33; [V(pic)3]-, 4.4 × 103; and (from an earlier study) dithionite, 1.1 × 106 (I = 0.15 M (Na2SO4)). The second stage, which also consumes 1 mol of reductant, is (at pH 8.2) independent of reductant (k2 = 4 × 10-3 s-1). This step is believed to involve an isomerization of the kind Fe(II,III) → Fe(III,II), followed by rapid reduction. The third stage, having a relatively small absorbance change, may correspond to an isomerization of the Fe(II,II) state. Similar behavior is observed at pH 6.3, with some interplay of redox and isomerization in the second stage of reaction with the positively charged reactants. The mechanism that we propose takes into account recent structural information and previous kinetic results for the deoxymyo → metmyo conversion. This involves, for reduction of met, retention of the protein structure characteristic of methemerythrin until the third stage, when the protein adjusts to the stable deoxy form. A previous study has shown that the oxidation of the deoxy form involves the same number of stages, the last being attributed to formation of a stable met form. One possibility is that these slow isomerization processes involve interconversion of μ-oxo and μ-hydroxo forms.
