High-spin ferric

Pseudomonas sp. strain P.J. 874 grown with tyrosine carried out dioxygenation of 4-hydroxyphenylpyruvate to 2,5-dihydroxyphenylacetate accompanied by an NIH shift (Lindstedt et al. 1977). The involvement of a high-spin ferric center coordinated with tyrosine is conclusively revealed in the primary structure of the enzyme (Riietschi et al. 1992). 

Yang, A.-S. and B. J. Gaffney (1987). Determination of relative spin concentration in some high-spin ferric proteins using E/D distribution in electron paramagnetic resonance simulations. Biophys. J. 51 55-67. 

For example the X-band spectra of high-spin ferric hemes (S = 5/2 g 2 E/D < 0.1) show a single transition described by... 

An illustrative example is given in Figure 6.2 the spectrum (Arendsen et al. 1993) of a high-spin ferric heme with its typical very wide pattern of an intense feature around geff 6 and a weak negative peak near g 2 (Equations 5.34 and 5.35). 

The [2Fe-2S] dinuclear cluster itself is a classical example of such a system paramagnet in the reduced (1+) state it is made up of a high-spin ferric ion (S = 5/2) and a high-spin ferrous ion (S = 2), coupled antiparallel into a system spin S = 1/2. Under the simple model of Equations 11.15 and 11.16 the system g-values are (Gibson et al. 1966)... 

In addition, all complexes display a reversible, one-electron reduction at a very negative potential Em —1.70 to -1.90 V vs Fc+/Fc, which is metal centered and nearly invariant with respect to the substitution pattern of the coordinated pheno-lates. It demonstrates the enormous stabilization of the high-spin ferric state by three phenolato ligands. The electrochemistry also nicely shows that unprotected ortho- or para positions of these phenolates lead to irreversible electron-transfer waves on the time scale of a cyclic voltammogram and that methyl substituents are inefficient protecting groups. 

The observation that the isomer shift varies between 0.39 mm s 1 at 4 K and 0.54 mm s-1 at 80 or 298 K only, irrespective of the charge n of the complexes (n = 0, 1,2), immediately implies that all complexes contain an octahedral, high-spin ferric ion (d5, S = ). Furthermore, from the applied-field Mossbauer spectra of [Fem(LBuMet)] (.S t = f), [Fem(LBuMet )]+ (5t = 2), and [Fem(LBuMet )]2+ (5t = ) intrinsic isotropic hyperfine couphng constants, AFe/gNpN, of -21.4, -21.0, -20.8 T, respectively, have been established. These values are also typical of high-spin iron(III). 

In order to obtain the full hfs and quadrupole tensors of the nitrogen ligands, single crystals of diamagnetic CO-ligated ferrous Mb doped with about 10% high-spin ferric Mb have been prepared240. Preliminary data of the principal values in the heme plane are... 

Fd n can be studied in two oxidation states. In the oxidized state the cluster has electronic spin S = H. This spin results fiom antiferromagnetic coupling of three high-spin ferric (Si = 2 = S3 = 5H) iron sites. The magnetic hyperfine parameters obtained from an analysis of the low tempo ture MSssbauer spectra have been analyzed (18) in the frmiework of the Heisenberg Hamiltonian. 

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