Copper self-exchange rates

The NO/NO+ and NO/NO- self-exchange rates are quite slow (42). Therefore, the kinetics of nitric oxide electron transfer reactions are strongly affected by transition metal complexes, particularly by those that are labile and redox active which can serve to promote these reactions. Although iron is the most important metal target for nitric oxide in mammalian biology, other metal centers might also react with NO. For example, both cobalt (in the form of cobalamin) (43,44) and copper (in the form of different types of copper proteins) (45) have been identified as potential NO targets. In addition, a substantial fraction of the bacterial nitrite reductases (which catalyze reduction of NO2 to NO) are copper enzymes (46). The interactions of NO with such metal centers continue to be rich for further exploration. 

Blue copper proteins, 36 323, 377-378, see also Azurin Plastocyanin active site protonations, 36 396-398 charge, 36 398-401 classification, 36 378-379 comparison with rubredoxin, 36 404 coordinated amino acid spacing, 36 399 cucumber basic protein, 36 390 electron transfer routes, 36 403-404 electron transport, 36 378 EXAFS studies, 36 390-391 functional role, 36 382-383 occurrence, 36 379-382 properties, 36 380 pseudoazurin, 36 389-390 reduction potentials, 36 393-396 self-exchange rate constants, 36 401-403 UV-VIS spectra, 36 391-393 Blue species... 

Self-exchange rate constants, blue copper pro-tiens, 36 401-403... 

Table IV. Electron Transfer Cross-Reaction and Self-Exchange Rate Constants for Blue Copper Proteins (25°, /aO.IM, pH 7)a...

Electron Self-Exchange Rate Constants kese (298K) for Blue Copper Proteins Retrieved from NMR Spectra... 

Self-Exchange Rate Constants for Cu(I) and Cu(II) States of Different Blue Copper Proteins"... 

A further influence on electron exchange is the ligand type present. Thus with bidentate aromatic 2,2 -bipyridine and 1,10-phenanthroline ligands (L), the [RuL3] + + self-exchange rate constants are 1 x 10 sec (95, 96). In the case of the copper proteins the imidazole and S-donor ligands presumably have similar beneficial effects. 

An elegant example of the measurement of an electron self-exchange rate of a redox protein was reported by Dahlin et al. The copper ion of stellacyanin was removed and then replaced with either Cu or Cu. Oxidized [ Cu] stellacyanin was allowed to react with reduced [ Cu] stellacyanin for various times (10 ms to 7 min) at 20°C, after which the reaction was quenched by lowering the solution temperature to - 120°C using a rapid-freeze apparatus ... 

The electron self-exchange rate constants of proteins are considerably larger than those of the inorganic copper complexes (Tables IV and V) (11,25,106,111). This is attributed to the large changes in the coordination sphere structures of the Cu(II) and Cu(I) inorganic complexes in comparison to the relative rigid active sites of the proteins. 

Electron Self-exchange Rate Constants of Blue Copper Proteins... 

The kinetic behavior of the reductions of several Cu(II)N2S2 complexes, containing thioether/pyridyl chelate ligands, by ferrocene and l,r-dimethyl-ferrocene in acetonitrile points to the formation of a precursor complex prior to electron transfer.The rate constant for the oxidation of (hydroxyethyl)-ferrocene by [2-pyridyl(methylbis(2-ethyl)thioethyl)amine]copper(II) yields a [Cu(pmas)] self-exchange rate constant of 47 M s from the Marcus theory relation.The addition of NJ increases the rate of oxidation (F" and I" have no effect) by shifting the reduction potential upon the formation of [Cu(pmas)N3] and Cu(pmas)(N3)2 (NJ displacement of a thioether sulfur occurs in the latter species). The application of the Marcus relationship to the reductions of the [l,8-bis(2-pyridyl)-3,6-dithiaoctane]copper(II) complex by a series of Ru(II) ammine and bipyridyl complexes in 50% aqueous CH3OH yields a self-exchange rate constant of 0.63 s for the [Cu(pdto)] couple. " From the rate... 

The electron self-exchange rates for the [l,7-bis(5-methylimidazol-4-yl)-2,6-dithiaheptane]copper(I)/(II) couple in DMSO have been determined by H NMR line broadening as a function of temperature, with fcn = 4 x 10 M s" at 28 An electron self-exchange rate constant of 1.3 x 10" M s has been measured for the [Cu((imidH)2DAP)] /" couple (imidH)2DAP = 2,6-bis[l-((2-... 

Marcus theory has been used to interpret the reactions of cytochromes c and blue copper proteins. For thirteen protein-protein electron-transfer reactions, the data can be fitted with the self-exchange rate constants of 2.8 x 10 s ... 

The self-exchange rate for the copper(III)/(II)-tripeptite complex, [Cu(H 2Aib3)]° , where Aib is a-aminobutyric acid, has been examined ... 

Cu(III)(peptide)], with [Cu(I)(dmp)2], where dmp is 2,9-dimethyl-1,10-phen-anthroline, are rapid, outer-sphere processes which show some adherence to Marcus behavior,although the [Cu(dmp)2] self-exchange rate appears to be very dependent on the cross reaction,a lower limit of 3 X 10" mol" liter s arising from the [Cu(III)(peptide)] reactions, while a value of 9 x 10 mol liter s" is obtained from reaction with [IrCle], both at 25°C and 0.10 M ionic strength.Reactions of the copper(I) complex of the sterically hindered phenyl sulfonate derivative of dmp, [Cu(dpmp)2], with [Cu(III) (peptide)] are complicated by limiting rate behavior which is ascribed to activation of the copper(III) complex [reaction (25)]... 

Cross reactions of nickel(III)- and nickel(II)-peptide complexes conform readily to Marcus theory and are thought to be outer sphere but, in contrast to the copper system, give no unique self-exchange rate. Instead values range from 550 s for [Ni(III)/(II)(H 2Aib3)] through 1.3 x... 

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