Exogenous ligands

Figure 18.5 Plausible sequence of steps responsible for rapid and selective reduction of O2 to H2O by mixed-valence CcO. The square frames signify the catalytic site (Fig. 18.4c) imidazole ligation of Cub is omitted for clarity in some or aU intermediates, Cub may additionally be ligated by an exogenous ligand, such as H2O (in Cu ) or OH (in Cu ) such ligation is not established, and hence is omitted in all but compound Pm and the putative hydroperoxo intermediate. The dashed frames signify the noncatalytic redox cofactors. Typically used phenomenological names of the spectroscopically observed intermediates (compounds A, E, H, etc.) are also indicated.

Figure 18.20 A plausible ORR catalytic cycle by biomimetic catalysts 2 (Fig. 18.17). Cu is ligated by three imidazoles (omitted for clarity) and potentially an exogenous ligand, whose nature is not known. All intermediates other than ferric-peroxo and ferric-hydroperoxo were prepared independently.

E. Reduction of Heme-Hemopexin and Binding of Exogenous Ligands... 

In particular, the 1/2-met T3 site In T2 has EPR spectra and equilibrium binding constants =10 M for exogenous ligands... 

From Table 4, both the relative magnitude of the hyperflne coupling to each copper and the IT absorption Intensity correlate with the covalent nature of the tightly bound exogenous ligand. 

Low Temperature MCD Studies of Exogenous Ligand Binding to Native Laccase. Native laccase reduces dloxygen to water but the reduced T3... 

Figure 16 Comparison of exogenous ligand binding modes In l/2-met hemocyanln (left) and 1/2-met laccase (right).

The oxidized T1 site In laccase Is spectroscopically similar to that of plastocyanin and azurln. Indicating that exogenous ligands can coordinate only to the T2 and T3 coppers at the native active site, (see Splra, D.J. Co, M.S. Solomon, E.I. Hodgson, K.O. Blochem. Blophys. Res. Commun. 1983, 112, 746.)... 

The S2-state EPR signals have also been used to probe the coordination of exogenous ligands to the Mn complex (27-31). Ammonia, but not more bulky amines, dramatically alters the... 

Excitonic emission, F state, 35 380-381 Exogenous ligand binding, [M-3Fe0134S] clusters, 38 365-368 Explosion calorimetry, 24 10 Extended fullerenes, 44 2... 

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