Electron transfer from redox sites of proteins to excited simple molecules

3 ELECTRON TRANSFER FROM REDOX SITES OF PROTEINS TO EXCITED SIMPLE MOLECULES 

The other way to study the conductivity of protein molecules towards electron tunneling is to investigate the quenching of luminescence of electron-excited simple molecules by redox sites of proteins [95,96]. Experiments of this sort on reduced blue copper proteins have involved electron-excited Ru(II)(bpy)3, Cr(III)(phen)3, and Co(III)(phen)3 as oxidants. The kinetics of these reactions exhibit saturation at protein concentrations of 10 3 M, suggesting that, at high protein concentrations, the excited reagent is bound to reduced protein in an electron transfer precursor complex. Extensive data have been obtained for the reaction of reduced bean plastocyanin Pl(Cu(I)) with Cr(III)(phen)3. To analyze quenching experimental data, a mechanistic model that includes both 1 1 and 2 1 [Pl(Cu(I))/ Cr(III)(phen)3] complexes was considered [96] 

The same model has been used to fit the data obtained for the reactions of azurin, Az(Cu(I)) and Rhus vernicifera stellacyanin, St(Cu(I)), with Cr(III)(phen)3 and Ru(II)(bpy)3 oxidants. Values of the rate constants kt and stability constants K and K2 of the 1 1 and 2 1 complexes that have been extracted from the analyses are given in Table 2. 

Electron transfer rate constants, kt, free energy changes, - AG°, and stability constants, K1 and Kz, for the reactions of Cr(III)(phen)3 and Ru(II)(bpy)3 with reduced blue copper proteins at 295 K [96] 

5 ELECTRON TUNNELING BETWEEN METAL PORPHYRINS BOUND TO 

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Electron Transfer from Redox Sites of Proteins to Excited Simple Molecules... 

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