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High-valent intermediates

Watanabe Y. 2000. High-valent intermediates. In Radish KM, Smith KM, Guilard R, editors. The Porphyrin Handbook. San Diego Academic Press, p. 97. [Pg.692]

M(IV)-peptide radicals, and decay to final products have been determined (96). Interestingly, the rate constants for both the formation and decay of the high-valent intermediate are much larger than the corresponding values in the chromium system in Scheme 1. Thus the lifetimes of both the hydroperoxo species and M(IV)-peptide radicals are much shorter in the enzymatic system than for the chromium macrocycles. [Pg.12]

Watanabe, Y. High-valent intermediates, The Porphyrin Handbook. Volume 4. Biochemistry and Binding Activation of Small Molecules , Eds. Kadish, . M. Smith, . M. Guilard, R. Academic Press San Diego, 2000, pp. 97-117. [Pg.54]

The corresponding high-valent intermediate in the assembly of the di-iron(III) center-tyrosyl radical cofactor of RNR R2 has also been identified by Stubbe and coworkers and designated as X [86,89], This intermediate decays to the (p,-oxo)diiron(III) form at a rate commensurate with the appearance of the tyrosyl radical. Intermediate X, formally Fe(III)Fe(IV), exhibits an isotropic S = 1/2 spin EPR signal near g = 2, which is split by the introduction of 57Fe and broadened by 1702 in the assembly reaction. These observations as well as Mossbauer results show that the unpaired spin must be associated with the diiron center [88,89],... [Pg.285]

Table 4 Mossbauer parameters of high-valent intermediates of peroxidases, met-myoglobin treated with H2O2 and two tetramesitylporphyrin(TMP) model systems ... Table 4 Mossbauer parameters of high-valent intermediates of peroxidases, met-myoglobin treated with H2O2 and two tetramesitylporphyrin(TMP) model systems ...
In both peroxidases, the decay of Compound I is drastically increased by the deletion of the distal arginine, emphasizing its role as a stabilizer of the high-valent intermediate [169-171, 173, 175]. Crystallographic and resonance Raman data have shown that the distal arginine is very flexible, and can move towards or away from the ligand in the sixth position as needed [135, 176]. This flexibility allows the gua-... [Pg.1755]

FIGURE 3.11 High -valent intermediates detected in nonheme enzymes. [Pg.86]

The electronic structure of hemes is well suited for the stabilization of high-valent intermediates. Cytochrome P450 and related heme enzymes take advantage of this... [Pg.165]

The evidence for the presence of an intermediate (Hperoxo or P) as a precursor of the high-valent intermediate Q (see Scheme 16-1) in the reaction cycle of MMOHted... [Pg.259]

We have explored the reactivity of Fe(TPA) complexes with peroxides and found that such centers are capable of activating peroxides to functionalize alkanes in a catalytic fashion. Because of the efficient stoichiometric transfer of coordinated halide onto the alkane substrate, we have been able to deduce the participation of an [(TPA)Fe(X)=0] + species in these reactions. Finally the high valent intermediate can be stabilized under appropriate conditions to allow its spectroscopic characterization. These experiments provide significant insight into how nonheme iron centers may function in enzyme active sites for the functionalization of unactivated C-H bonds. [Pg.330]


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See also in sourсe #XX -- [ Pg.262 , Pg.264 , Pg.269 ]




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