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Mossbauer evidence

Iron atoms in states other than Fe(II) and Fe(III) are rare in biological material, but there is one case where Mossbauer evidence has pointed to an Fe(IV) electronic configuration. Horseradish peroxidase, when it forms peroxide derivatives (Compounds I and II of HRP), displays an isomer shift which is about equal to that obtained with Fe metal (23). A similar observation has also been found on an analogous compound, Japanese Radish Peroxidase (72). There is no evidence for Fe(I) or Fe (IV) states in any other hemoproteins, or in any of the iron-sulfur proteins. [Pg.11]

Prior to the structure determination, chemical, vibrational, spectroscopic, and Mossbauer evidence had indicated the formulation Xe2Fn AuFs" for the F, Xe2Au material. The X-ray structure is fully compatible with that formulation. [Pg.162]

These [4Fe-4S] clusters (P clusters) from the MoFe protein differ from normal [4Fe-4S] clusters, as demonstrated by MCD and Mossbauer measurements. The P clusters contain three iron atoms (D atoms) which differ from the fourth. In the MoFe protein from A vinelandii the minor component of the P cluster appears to be a high-spin Fe in a tetrahedral sulfur environment. The D centres also appear to be Fe in the resting enzyme, giving an unusually reduced level for the cluster. As all four iron atoms are Fe , the Mossbauer evidence for two types of iron atom in ratio 3 1 may be interpreted in terms of variation in the non-sulfide ligands, although other explanations are possible. [Pg.721]

The hydride anions are rather unstable at room temperature and are not so well known except for [Fe3(CO)nH] . Structures are shown in Fig. 9.1, that of [Fe4(CO)i3H] being unknown. The structure of [Fe2(CO)gHl" was suggested from infrared and Mossbauer evidence on the basis of its similarity to Fc2(CO)9 [12]. The Mbssbauer data are in Table 9.1. [Pg.225]

Apart from XeF, which is the light-emitting species in certain Xe/F2 lasers, there is no evidence for the existence of any odd-valent fluorides. Reports of XeFg have not been confirmed. Of the other halides, XeCl2, XeBr2 and XeCl4 have been detected by Mossbauer spectroscopy as products of the -decay of their... [Pg.896]

It is now fairly well established that atomic and few-atom cluster arrays can be generated and trapped in weakly interacting matrices 91), and subsequently scrutinized by various forms of spectroscopy. Up to this time, IR-Raman-UV-visible absorption and emission-esr-MCD-EXAFS-Mossbauer methods have been successfully applied to matrix-cluster samples. It is self-evident that an understanding of the methods of generating and identifying these species is a prerequisite for... [Pg.81]

In summary, the Mossbauer data presented by Fee et al. (5) gave the first conclusive evidence that Rieske clusters contain noncysteine ligands bound to the Fe" site of a localized mixed valence cluster. In addition, strong similarities with [2Fe-2S] clusters in bacterial dioxy-... [Pg.118]

Shanklin J, C Achim, H Schmidt, BG Fox, E Miinck (1997) Mossbauer studies of alkane w-hydroxylase evidence for a diiron cluster in an integral-membrane enzyme. Proc Natl Acad Sci USA 94 2981-2986. [Pg.144]

Fe(6-Mepy)2(py)tren] (004)2 Doped in PSS. Magnetic susceptibilities measured for a microcrystalline sample of the complex produce a magnetic moment value = 0.36 pg at 10 K and 0.61 pg at 150 K, followed by a gradual increase to Peff = 2.80 pe at 311 K [138]. Thus 26% of the complexes are in the HS state at 300 K if a magnetic moment of 5.1 Pe is assumed for the pure HS compound. On the other hand, the complex doped into a polystyrene sulfonate (PSS) film does not provide any evidence for a thermal population of the HS state up to 340 K as demonstrated by variable-temperature UV-VIS and Mossbauer spectra. In fact, all the complexes doped into the PSS film are in the LS state at temperatures below 340 K. However, if irradiated by a single pulse of a Q-switched Nd/YAG laser (532 mp), the complex is excited from the LS ground state to the HS J2 states via an intermediate MLCT state and the metal states. The subsequent back relaxation from the excited T2 state to the... [Pg.129]

For iron(III) eomplexes, uic venues /vlh [Fe(aepa)2]BPh4 H2O and k = 6.7 x 10 s for [Fe(mim)2(salacen)]PF6 have been obtained [156, 166]. The rate constants derived from the line shape analysis of Mossbauer spectra thus vary between 2.1 x 10 and 2.3 x 10 s at room temperature, no significant difference between iron(II) and iron(III) being apparent. In addition, it is evident that the rates of spin-state conversion in solution and in the crystalline solid are almost the same. For iron(II) eomplexes, for example, the solution rates vary between /cjjl = 5 x 10 and 2 x 10 s , whereas in solid compounds values between kjjL = 6.6 x 10 and 2.3 x 10 s have been obtained. Rates resulting from the relaxation of thermally quenched spin transition systems are considerably slower, since they have been measured only over a small range of relatively low temperatures. Extrapolation of the kinetic data to room temperature is, however, of uncertain validity. [Pg.147]

From the discussion in Sect. 4.2 in Chap. 4, it became evident that the isomer shift is linearly related to the electron density at the Mossbauer absorbing nucleus. Thus, one is tempted to write ... [Pg.150]


See other pages where Mossbauer evidence is mentioned: [Pg.198]    [Pg.222]    [Pg.479]    [Pg.53]    [Pg.630]    [Pg.721]    [Pg.45]    [Pg.857]    [Pg.196]    [Pg.630]    [Pg.41]    [Pg.147]    [Pg.170]    [Pg.26]    [Pg.408]    [Pg.248]    [Pg.6775]    [Pg.173]    [Pg.179]    [Pg.198]    [Pg.222]    [Pg.479]    [Pg.53]    [Pg.630]    [Pg.721]    [Pg.45]    [Pg.857]    [Pg.196]    [Pg.630]    [Pg.41]    [Pg.147]    [Pg.170]    [Pg.26]    [Pg.408]    [Pg.248]    [Pg.6775]    [Pg.173]    [Pg.179]    [Pg.170]    [Pg.180]    [Pg.1094]    [Pg.173]    [Pg.240]    [Pg.308]    [Pg.14]    [Pg.15]    [Pg.62]    [Pg.64]    [Pg.378]    [Pg.434]    [Pg.451]    [Pg.498]    [Pg.99]    [Pg.99]    [Pg.38]    [Pg.58]   
See also in sourсe #XX -- [ Pg.179 ]




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