Copper self-exchange

It has been recognized that sulfur donors aid the stabilization of Cu(i) in aqueous solution (Patterson Holm, 1975). In a substantial study, the Cu(ii)/Cu(i) potentials and self-exchange electron transfer rate constants have been investigated for a number of copper complexes of cyclic poly-thioether ligands (Rorabacher et al., 1983). In all cases, these macrocycles produced the expected stabilization of the Cu(i) ion in aqueous solution. For a range of macrocyclic S4-donor complexes of type... 

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... 

The nature of the self-exchange is still under consideration. The planned use of the copper(III)-nickel(II) and (reverse) reactions to... 

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

The oxidized and reduced forms of blue copper proteins can coexist in equilibrium in solution. This allows two identical molecules to exchange one electron, giving the so-called electron self-exchange (ESE) reaction (Marcus and Sutin, 1985). The rates of this process usually depend on the pH, temperature, and ionic strength of the solution. When the two forms... 

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

The coordination of copper ion by macrocyclic quadri- and quinque-dentate thi-oethers makes the Cu VCu reduction process easier, and also increases the rate of the redox self-exchange electron transfer process [55]. For example, [Cu(13-aneS4)] undergoes a one-electron reduction at 0.52 V versus NHE [58] (cf. E°(Cu /Cu ) = 0.15V versus NHE for the aquated ion in water) and the rate constant for the corresponding self-exchange electron transfer is 3 x 10 s [59] (to be compared... 

Figure 9. The inner-sphere self-exchange reorganisation energy of a number of complexes related to the blue copper proteins. The hatched bars indicate the reorganisation energy obtained when the reduced structure preferred a lower coordination number than the oxidised structure [68].

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 ... 

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