Tunneling timetables

The validity of the azurin tunneling timetable rests on the assumption that Ru-azurin structures are not very different in crystals and aqueous solutions. Measurements of ET kinetics on crystalline samples of labeled azurins directly test this assumption " the rate constants for oxidation of Cu(I) by Ru(III) and Os(III) in solutions and crystals are nearly identical for each donor acceptor pair. It follows that the crystal structures of reduced and oxidized azurin are the relevant reactant and product states for solution ET. 

Figure 6. Tunneling timetable for ET in Ru-modified azurin. The solid line is the TP prediction for coupling along a p strand (P = 1.0 A ) the dashed line illustrates a 1.1 A distance decay.

Figure 8. Tunneling timetable for ET in Ru-modified myoglobin ( ) and cytochrome bs62 ( ) The solid lines illustrate the TP predictions for coupling along / strands (ft = 1.0 A ) and a helices (/ =1.3A- ).

The driving-force-optimized electron tunneling timetable for azurin reveals a nearly perfect exponential distance dependence, with a decay constant (P) of... 

The rates of high-driving-force ET reactions have been measured for more than 30 Ru(diimine)-labeled metalloproteins.Only modest corrections are required to scale these rates to driving-force-optimized values, permitting comparisons of ET in different proteins. The results are summarized in the electron tunneling timetable of Fig. 1-2. 

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