Oxidative activation structural data

The detailed mechanism of P aeruginosa CCP has been studied by a combination of stopped-flow spectroscopy (64, 65, 84, 85) and paramagnetic spectroscopies (51, 74). These data have been combined by Foote and colleagues (62) to yield a quantitative scheme that describes the activation process and reaction cycle. A version of this scheme, which involves four spectroscopically distinct intermediates, is shown in Fig. 10. In this scheme the resting oxidized enzyme (structure in Section III,B) reacts with 1 equiv of an electron donor (Cu(I) azurin) to yield the active mixed-valence (half-reduced) state. The active MV form reacts productively with substrate, hydrogen peroxide, to yield compound I. Compound I reacts sequentially with two further equivalents of Cu(I) azurin to complete the reduction of peroxide (compound II) before returning the enzyme to the MV state. A further state, compound 0, that has not been shown experimentally but would precede compound I formation is proposed in order to facilitate comparison with other peroxidases. 

Figure 8. SEM surface images of partly crystallized sections of an activated Fe Zr alloy used for ammonia synthesis [23, 24J The main image reveals the formation of a stepped iron metal structure with a porous zirconium oxide spacer structure An almost ideal transport system for gases into the interior of the catalyst is created with a large metal-oxide interface which provides high thermal and chemical stability of this structure The edge contrast in the 200 keV backscatlered raw data image arises from the large difference in emissivity between metal and oxide It is evident that only fusion and segregation-crystallization can create such an interface structure.

The ESR data shows that both the number of centers and the local structure of active sites associated with Cu isolated ions are not changed noticeably at T < 500°C as a result of cobalt introduction. At the same time, catalytic testing shows a 3-fold rise in oxidative activity of bi-cationic sample (Fig. 1) demonstrating an increase either in the number of sites or in the intrinsic activity of catalytic centers. The effect can be explained only in assumption of the high dispersion of cobalt ions in microporous matrix it is difficult to imagine a considerable contribution from the big particles of cobalt oxide on the outer surface of zeolitic crystals. 

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