Metalloproteins electron exchange

Electrochemical gating analysis to measure the conductivity as a function of redox potential [83] offers another approach to evaluate the possibility of conduction through G. sulfurreducens biofilms via c-type cytochromes. When conduction is via cytochromes or other redox carriers, there should be a maximum when the surface potential is near the formal potential for the redox process [29, 30, 81, 82, 84]. This reflects the equal density of reduced and oxidized species at the formal potential, which allows maximum possibility for electron exchange. When the film is poised at a potential that is much more positive or negative than the formal potential, the conduction is poor due to an overwhelming majority of the reduced (electron-loaded) or oxidized (hole-loaded) redox carriers. For example, electrochemical gating on redox-active metalloproteins exhibited a conductance peak, whereas nonredox controls did not show any peak in conductance [85]. 

Outer-sphere electron transfer reactions involving the [Co(NH3)6]3+/2+ couple have been thoroughly studied. A corrected [Co(NH3)6]3+/2+ self-exchange electron transfer rate (8 x 10-6M-1s-1 for the triflate salt) has also been reported,588 which is considerably faster than an earlier report. A variety of [Co(NH3)g]3+/2+ electron transfer cross reactions with simple coordination compounds,589 organic radicals,590,591 metalloproteins,592 and positronium particles (electron/ positron pairs)593 as redox partners have been reported. 

Kinetic data for electron transfer between two metalloproteins are presented in Table V. The rate constants and activation parameters for the Ps(II)-Ps(III) and Az(I)-Az(II) exchange reactions were calculated from the kinetic data for the first three reactions (for which K 1, AH° 0, AS° 0 in addition, the rate constant for the Hh(II)-Ps(III) reaction is independent of ionic strength (31)). The calculated exchange data were then used to predict the kinetic parameters for the Ps(II)-Az(II) reaction. As is evident from Table V, the agreement of the observed and predicted parameters is satisfactory, particularly since the Ps( II )-Az( II) reaction has a relatively complex mechanism (57) involving conformational changes on both Ps(III) and Az(I). 

In many metalloproteins, two or more metal ions are closely associated. The strength of the exchange interactions between the associated metal ions is the most important factor in determining the EPR properties of these systems. The exchange interactions arise from overlap of the magnetic orbitals (the orbitals containing the unpaired electrons These... 

Table 1. Experimental values of electron self-exchange rate constants for a selection of inorganic complexes and metalloproteins...

The electron self-exchange rate constants for two Cu(I)/Cu(II) complex couples, synthesized as models for active sites of copper metalloproteins, have been determined in acetonitrile using NMR techniques. An upper limit of... 

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