Mossbauer properties

Attempts to elucidate the bonding have concentrated mainly on graphite-FeCla- This intercalate is especially suitable as a model compound, because the magnetic and Mossbauer properties of the iron nucleus constitute excellent probes for electronic structure and environment of the latter. 

Relativistic quantum mechanics yields the same type of expressions for the isomer shift as the classical approach described earlier. Relativistic effects have to be considered for the calculation of the electron density. The corresponding contributions to i/ (0)p may amount to about 30% for iron, but much more for heavier atoms. In Appendix D, a few examples of correction factors for nonrelativistically calculated charge densities are collected. Even the nonrelativistically calculated p(0) values accurately follow the chemical variations and provide a reliable tool for the prediction of Mossbauer properties [16]. 

Mossbauer Properties from Density Functional Theory... 

Mossbauer Properties from Density Functional Theory with the individual components being given by ... 

Iron(IV), (V), and (VI) centers are also found in solid-state materials, the coordination chemistry of which is of considerable interest because unusual structures and remarkable electronic and catalytic properties are encountered [184]. Reviews of the corresponding Mossbauer properties are found in [185-187]. 

Neese, F. 2003. Quantum chemical calculations of spectroscopic properties of metalloproteins and model compounds EPR and Mossbauer properties. Current Opinion in Chemical Biology 7 125-135. 

The presence of the oxo bridge in oxyHr and metHrX is reflected in then-magnetic susceptibility, NMR, and MOssbauer properties. The coirq)lexes exhibit strong andferromagnetic coupling, small NMR isotropic shifts, and large Mdssbauer quadrupole splittings. J values obtained for metHr and oxyHr from fits to variable temperature susceptibiliy data are -134 and -77 cm-i, respectively (34). The J for metHr compares favorably with those observed for the synthetic... 

An unusual cysteine sequence motif together with atypical EPR and Mossbauer properties has been reported earlier for a [Fe2S2] protein denoted FhuF. It is an iron-regulated E. coli protein which is probably involved in the reduction of ferric iron in ferrioxamine B.191 In a recent study the authors could provide evidence for the mixed valence state in the FhuF protein to be capable of... 

The characteristics of intermediates MMOH-Q and RNR R2-X continue to converge. The radiolytic reduction of MMOH-Q affords an Fe(III)/Fe(I V) form designated Qx, which has Mossbauer properties similar to RNR R2-X [25]. This work and the recent EXAFS characterization of MMOH-Q and RNR R2-X [26-28], revealing that the two intermediates have very similar core structures, provide strong support that the 02 reaction chemistry in these two enzymes is analogous. This notion very likely extends to the other diiron oxygen activating enzymes. 

For nonheme enzymes that fiuther activate dioxygen, it is apparent that the diferrous forms also bind O2 to eventually generate the active species responsible for the oxidative transformations. In the case of MMO, the first intermediate has been labeled compound P (Scheme 2), which subsequently converts to compound Q both are kinetically competent to hydroxylate methane. In the case of RNR, compound X (Scheme 1) is responsible for the one-electron oxidation of a tyrosine residue to generate a tyrosyl radical. Based on chemical considerations and its Mossbauer properties, it has been proposed that compound P is a diferric peroxide species. To date, three model complexes of compound P, with comparable spectroscopic properties, have been structurally characterized (Figure g). In two of these models O2 is bound in a cis... 

As discussed in Section IIIC, it has been suggested that the nickel site in carbon monoxide dehydrogenases is associated with an iron-sulfur cluster 266). Possible geometries include a mixed-metal cubane, [Ni-3Fe-4S] and a sulfur-bridged assembly (Fig. 60). A synthetic [Ni-3Fe-4S] cluster has been characterized and its Mossbauer properties are very similar to those of CODH from C. thermoaceticum 86). 

In vitro a crystalline iron core can be laid down in apoferritin by the addition of an oxidant, such as O2, to an aqueous solution of a ferrous salt and apoferritin (32, 132, 140). The reconstituted core of horse ferritin prepared in the absence of phosphate and with O2 as oxidant is very similar to the native core in terms of its size and Mossbauer properties (85). Electron microscopy, however, reveals that it is less well ordered. Reconstitution in the presence of phosphate leads to smaller cores. Reconstituted A. vinelandii cores in the absence of phosphate were more ordered than were the native cores, and clearly contained ferrihydrite particles and, in some cases, crystal domains (85). Thus the nature of the core is not determined solely by the protein coat the conditions of core formation are also important. This is also indicated by Mossbauer spectroscopy studies of P. aeruginosa cells grown under conditions different than those employed for the large-scale pu-... 

Table 3 Mossbauer properties of optimized Mb02 models...

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