Fe Ions (fe + ion)

Distribution by Scientific Domains

Selected Abstracts

Theoretical studies on effects of hydrogen bonds attaching to cysteine ligands on 4Fe-4S clusters

Y. Kitagawa
Abstract The effect of hydrogen bonds attaching to sulfur atoms of cysteine ligands on 4Fe-4S cluster is examined by using UB3LYP method. Calculated results indicate that an existence of the hydrogen bonds scarcely changes SOMO-SUMO gap, shapes of Kohn-Sham orbitals, and magnetic interactions between Fe ions, although it stabilizes Kohn-Sham orbital energies of SOMO and SUMO about 1.0 eV. And they also make a reduced state stable in comparison with an oxidized state. In addition, the point charges of +0.1e (e: elementary electric charge) at the position of the hydrogen atoms give almost same results to the hydrogen bonds quantitatively. The results suggest that a positive environment from the hydrogen bonds around the clusters is important for a redox potential of 4Fe-4S clusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Staphylococcal NreB: an O2 -sensing histidine protein kinase with an O2 -labile iron,sulphur cluster of the FNR type

Annegret Kamps
Summary The nreABC (nitrogen regulation) operon encodes a new staphylococcal two-component regulatory system that controls dissimilatory nitrate/nitrite reduction in response to oxygen. Unlike other two-component sensors NreB is a cytosolic protein with four N-terminal cysteine residues. It was shown that both the NreB,cysteine cluster and Fe ions are required for function. Isolated NreB was converted to the active form by incubation with cysteine desulphurase, ferrous ions and cysteine. This activation is typical for FeS-containing proteins and was reversed by oxygen. During reconstitution an absorption band at 420 nm and a yellow-brownish colour (typical for an FNR-type iron,sulphur cluster formation) developed. After alkylation of thiol groups in NreB and in the cysteine mutant NreB(C62S) almost no iron,sulphur cluster was incorporated; both findings corroborated the importance of the cysteine residues. Comparison of the kinase activity of (i) the reconstituted (ii) the unreconstituted, and (iii) the unreconstituted and deferrated NreB,His indicated that NreB kinase activity depended on iron availability and was greatly enhanced by reconstitution. NreB is the first direct oxygen-sensing protein described in staphylococci so far. Reconstituted NreB contains 4,8 acid-labile Fe and sulphide ions per NreB which is in agreement with the presence of 1,2 iron,sulphur [4Fe-4S]2+ clusters of the FNR-type. Unlike FNR, NreB does not act directly as transcriptional activator, but transfers the phosphoryl group to the response regulator NreC. [source]

Preparation and conversion electron Mössbauer study of Fe3O4/,-Fe2O3 composite films

Z. P. Niu
Abstract Fe3O4 and Fe3O4/,-Fe2O3 composite films have been prepared from a sintered Fe2O3 target, using an rf magnetron sputtering apparatus with various argon pressures. The phase and magnetic properties of the samples have been characterized by X-ray-diffraction (XRD) measurements, conversion electron Mössbauer spectroscopy (CEMS), and a vibrating sample magnetometer (VSM). With the increasing argon pressure during sputtering, the increase of the average center shift of Mössbauer lines indicates the decreasing valency state of Fe ions induced by the enhancement of presumed oxygen loss. An enhanced magnetoresistance (MR) has been found in the Fe3O4/,-Fe2O3 composite film that was prepared under an Ar pressure of 1.0 Pa. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Inhomogeneous surface electronic properties and charge ordering in epitaxial Fe3O4 films on MgO(001)

A. Subagyo
Abstract We report scanning tunneling microscopy (STM) study of surface electronic properties and charge ordering of epitaxially grown magnetite, Fe3O4, (001) films exhibiting high density of antiphase domain boundaries (APBs). STM measurements using a W tip reveal surface termination at B-sites. Fe ions with a 0.3 nm periodicity, i.e., a single atomic distance are observed. Current imaging tunneling spectroscopy reveals the alternation of two kinds of current peaks with a 0.6 nm periodicty indicating the presence of charge ordering consisted of Fe dimers with different charge states. STM measurements using a magnetic Ni tip provide higher contrast of the charge ordering. The APBs can modify the charge ordering as ordered and disordered areas are observed on adjacent domains separated by an APB. These strongly indicate that APBs can induce inhomogeneous properties on the surface of Fe3O4(001) films. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Relation between Mössbauer spectroscopy and geometrical frustration factors in MCr1.9857Fe0.02O4 (M = Co, Zn)

Kang Ryong Choi
Abstract In order to elucidate the role of Cr ions in MCr2O4(M = Co, Zn) exhibiting geometrically frustration and multiferroic property, we have substituted a small amount of Fe ions for Cr sites and investigated the magnetic behavior of Fe ions with Mössbauer spectroscopy. The crystal structure was found to be single-phase cubic spinel with space group of Fd3m. The lattice constants a0 and the internal structural parameter (x) of the oxygen were determined to be 8.340, 8.331 Å and 0.261 and 0.260, respectively. The Mössbauer absorption spectra at 4.2 K show that the well-developed two sextets are superposed with small difference of hyperfine fields(Hhf). The hyperfine fields of CoCr1.9857Fe0.02O4 and ZnCr1.9857Fe0.02O4 were determined to be 490 , 480 kOe and 460 , 450 kOe, respectively. Isomer shift values (,) of the two sextets are found to be 0.33 , 0.35 mm/s relative to those of Fe metal, which are consistent with the high spin Fe3+ charge state. From the results of Mössbauer measurement, it is suggested that Cr3+ ions have two different magnetic sites, and there is a correlation between hyperfine fields and degree of magnetic geometrical frustration. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

EPR study of Fe3+ centers in ternary layered TlInS2 single crystal

F.A. Mikailov
Abstract An iron doped TlInS2 single crystal has been studied at room temperature by Electron Paramagnetic Resonance (EPR) technique. The fine structure of EPR spectra of the paramagnetic Fe3+ ions was observed. The spectra were interpreted to correspond to the transitions among the spin multiplets (S=5/2, L=0) of the Fe3+ ion, which is split in the local ligand crystal field (CF) of orthorhombic symmetry. Four equivalent Fe3+ centers have been observed in the EPR spectra and the local symmetry of crystal field at the Fe3+ site and the CF parameters were determined. It was established that the symmetry axis of the axial component in the CF is making an angle of about 48 degree with the (ab) plane of TlInS2 crystal. Experimental results indicate that Fe ions substitute for In ions at the center of the InS4 tetrahedrons, and the rhombic distortion of the CF is caused by Tl ions located in the trigonal cavities between the tetrahedral complexes. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

MOCVD of BiFeO3 Thin Films on SrTiO3,

J. Thery
Abstract Bi-Fe-O thin films are grown by liquid-injection metal-organic (MO)CVD on (001) SrTiO3 substrates using two different bismuth precursors, Bi(tmhd)3 and Bi(mmp)3. The precursor Bi(mmp)3 is found to be more effective for Bi incorporation in the films. Epitaxial BiFeO3 films are obtained and no evidence for secondary phases such as Fe2O3 or Bi2O3 is found by X-ray diffraction (XRD) or transmission electron microscopy (TEM) studies. However, the presence of a multiple binding environment for Fe3+ is shown from the X-ray photoelectron spectroscopy (XPS) analyses. Moreover, XPS shows evidence of a Fe2+/Fe3+ valence mixed state. A saturation magnetization of 70 emu cm,3 is measured. This value is much higher than that reported for the bulk BiFeO3 material. Both the double valence for Fe ions and the enhanced magnetization may originate in the presence of non-fully-oxidized ,-Fe2O3. [source]