Mdssbauer parameters

The protein is composed of three independent components component A, the hydroxylase component B, a mediating protein and component C, the reductase (Green and Dalton, 1985 Fox et al., 1989). These proteins have been isolated in high purity and activity. The hydroxylase contains iron centers which have Mdssbauer parameters simi-... 

In crystalline oxides and hydroxides of iron (III) octahedral coordination is much more common than tetrahedral 43). Only in y-FegOs is a substantial fraction of the iron (1/3) in tetrahedral sites. The polymer isolated from nitrate solution is the first example of a ferric oxyhydroxide in which apparently all of the irons are tetrahedrally coordinated. From the oxyhydroxide core of ferritin, Harrison et al. 44) have interpreted X-ray and electron diffraction results in terms of a crystalline model involving close packed oxygen layers with iron randomly distributed among the eight tetrahedral and four octahedral sites in the unit cell. In view of the close similarity in Mdssbauer parameters between ferritin and the synthetic poljmier it would appear unlikely that the local environment of the iron could be very different in the two materials, whatever the degree of crystallinity. Further study of this question is needed. 

Figure 17. The molecular structure and temperature dependence of the "Fe Mdssbauer parameters (IS and QS) and half-width of the absorption line (h) and some parameters of the nonprimitive unit cell of the FeNx i(BHd)2 crystal [67],...

To verify this assumption, the temperature dependence of the Mdssbauer parameters (Figs. 21 and 22) were measured for the clathrochelate FeNx3(BOH)2, Fe(4MNx)3(BOH)2, and FeGx3(BOH)2 complexes and their nonmacrocyclic [Fe(H2Nx)3](S04) analog [56]. 

The sTjTe Mdssbauer parameters for the tin-, germanium-, and antimony-capped clathrochelate compounds (Tables 22-24) are typical low-spin iron(II) complexes. The increase in the ligand field strength (a "macrocyclic" effect), causes the increase in s-electron density on the iron nucleus, is less pronounced for these compounds than for their boron-capped analogs experimental ISs are only slightly lower than those calculated from a PIS concept. 

The Fe Mdssbauer parameters for the clathrochelate [FeMn(trom)](BF4) and [Fe2(trom)](BF4) complexes are characteristic of high-spin iron complexes. The spectrum of the [FeMn(trom)](BF4) clathrochelate exhibits one doublet line, which indicates the sole type of coordination centre. The QS value increases regularly with a temperature decrease. A major contribution to the QS value is made by the valence component (the lattice component is small and practically independent of temperature). For [FeMn(trom)](BF4) clathrochelate, all three spin-quintet states are presumably within kT, and the QS value depends on temperature [192]. 

The Mdssbauer spectrometer was equipped with a 10 mC 5 Co/Rh source maintained at room temperature, A Northern NS-yOO multichannel analyser was used for taking the spectra. The Mdssbauer parameters were determined by least square computer programme. Tht isomer shift (5) was calculated with reference to a-Fe. The diaracieristics of iron in various iron molybdates and iron antimonate arc given in table I. 

TABLE 1 Mdssbauer parameters of the catalysts obtained by fttting with the experimental data... 

Two crystalline modifications of tin(II) fluoride are known [53]. The orthorhombic form of SnF2 shows significantly different Mdssbauer parameters from the better-known monoclinic form. In particular the smaller chemical isomer shift in the former is indicative of increased covalent character, while the larger quadrupole splitting suggests a more distorted environment about... 

Table 14.16 Iron and tin Mdssbauer parameters for iron-organotin complexes (data at 80 K and values for (Fe) converted from nitroprusside)...

Finally, others and us calculated Mdssbauer parameters of TauD and P4H in comparison with experiment (58,59). Although the agreement for these types of calculations is not perfect, generally the correct trend is reproduced. Recent quantum mechan-ics/molecular mechanics studies on a doubly reduced form of structure B in the catalytic cycle of P450 were performed and focused on the possible low-lying electronic states (60). In particular, the relative energy difference and spectroscopic parameters (EPR) of an Fe -porphyrin versus Fe -porphyrin anion radical were compared. 

A wide range of tin(IV) systems has been excunined and mcuiy data are available. The aim of this section is to show the relation between the Mdssbauer parameters and the nature, nimiber, and disposition of the ligands surrounding the tin atom. 

Table 3. Mdssbauer parameters for both the C-Fe(7)/Alj03 precursor and K-C-Fe(7)/Alj03 most active catalyst. The number in the brackets inform about accuracy of value, for example the value 0.33(2) is the same as 0.33 0.02...

The Mdssbauer parameters are shown in Table 30.2 and are consistent with the literature [8]. 

TABLE XII. In Situ Mdssbauer Parameters for Fe in Anodically Polarized Cobalt Surfaces Doped with Co in Borate Buffer (pH 8.5)... 

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