A. A. Novakova

Low temperature formation of nanocrystalline Fe–W and Fe–Mo compounds

Abstract Nanocrystalline Fe–W and Fe–Mo compounds obtained by coupled reduction of fine dispersed FeOOH with H 2 WO 4 (or with H 2 MoO 4 ) in continuous H 2 flow at the temperature range 700–740°C were studied by means of Mossbauer spectroscopy and X-ray diffraction. The formation of partially disordered and even amorphous intermetallic phases and solid solutions with extended concentrations was observed. Hydrogen incorporation in the structure of disordered intermetallic phases during the reduction process was revealed.

Depth-selective 57Fe CEMS (DCEMS) on samples with rough surfaces using a gas flow proportional counter

The possibility of semi-quantitative depth-selective analysis of surface layers of specimens unenriched by 57Fe by means of a gas flow proportional counter is demonstrated. The optimal energy intervals for electron detection and corresponding depth-integral weight functions were determined. The influence of surface roughness on the surface selectivity of DCEMS as well as for conventional CEMS was experimentally studied. The dependence of depth selectivity on certain parameters of the detection system was investigated in detail.

Accumulation of Ferrous Iron in Chlamydomonas reinhardtii. Influence of CO2 and Anaerobic Induction of the Reversible Hydrogenase

The green alga, Chlamydomonas reinhardtii, can photoproduce molecular H2 via ferredoxin and the reversible [Fe]hydrogenase enzyme under anaerobic conditions. Recently, a novel approach for sustained H2 gas photoproduction was discovered in cell cultures subjected to S-deprived conditions (A. Melis, L. Zhang, M. Forestier, M.L. Ghirardi, M. Seibert [2000] Plant Physiol 122: 127–135). The close relationship between S and Fe in the H2-production process is of interest because Fe-S clusters are constituents of both ferredoxin and hydrogenase. In this study, we used Mössbauer spectroscopy to examine both the uptake of Fe by the alga at different CO2concentrations during growth and the influence of anaerobiosis on the accumulation of Fe. Algal cells grown in media with57Fe(III) at elevated (3%, v/v) CO2concentration exhibit elevated levels of Fe and have two comparable pools of the ion: (a) Fe(III) with Mössbauer parameters of quadrupole splitting = 0.65 mm s−1 and isomeric shift = 0.46 mm s−1 and (b) Fe(II) with quadrupole splitting = 3.1 mm s−1 and isomeric shift = 1.36 mm s−1. Disruption of the cells and use of the specific Fe chelator, bathophenanthroline, have demonstrated that the Fe(II) pool is located inside the cell. The amount of Fe(III) in the cells increases with the age of the algal culture, whereas the amount of Fe(II) remains constant on a chlorophyll basis. Growing the algae under atmospheric CO2 (limiting) conditions, compared with 3% (v/v) CO2, resulted in a decrease in the intracellular Fe(II) content by a factor of 3. IncubatingC. reinhardtii cells, grown at atmospheric CO2 for 3 h in the dark under anaerobic conditions, not only induced hydrogenase activity but also increased the Fe(II) content in the cells up to the saturation level observed in cells grown aerobically at high CO2. This result is novel and suggests a correlation between the amount of Fe(II) cations stored in the cells, the CO2 concentration, and anaerobiosis. A comparison of Fe-uptake results with a cyanobacterium, yeast, and algae suggests that the intracellular Fe(II) pool in C.reinhardtii may reside in the cell vacuole.

Effect of formate on Mössbauer parameters of the non-heme iron of PS II particles of cyanobacteria.

Mössbauer spectra were measured for PSII particles having an active water‐splitting system. The particles were isolated from the thennophilic cyanobacterium Synechococcus elongatus enriched in57Fe. The Mössbauer resonance absorption spectrum is a superposition of 3 doublets with the following quadrupole splitting and chemical shift: 1, δ = 0.40, Δ = 0.85; II, δ = 1.35,Δ =2.35; III, δ = 0.25, Δ = 1.65. The δ and Δ values of doublets I, II, III are characteristic of proteins with iron‐sulphur center, non‐heme iron of the reaction center of higher plants and of the oxidized cytochrome 6–559. Treatment with sodium formate to remove bicarbonate affects only the doublet of non‐heme iron, causing its quadrupole splitting to reduce to 1.75 and the chemical shift to reduce to 0.90. After washing out the formate, the Mossbauer spectrum of non‐heme iron is restored. The data suggest that bicarbonate is a ligand for the non‐heme iron of the reaction center of cyanobacteria.

Supersaturated solid solutions and metastable phases formation through different stages of mechanical alloying of FeTi

Abstract Elemental equiatomic Fe-Ti powder mixture was mechanically alloyed in high energy ball mill. XRD, DTA and Mossbauer spectroscopy (at liquid nitrogen temperature) were utilized to monitor the kinetics as well as the accompanied structural and phase transformations through different stages of milling. Our experiments showed that formation of nanocrystalline FeTi compound proceeds via the formation of the supersaturated solid solutions β-Ti(Fe) and α-Fe(Ti) at the interface. After 36 hours of milling, the main part of powder mixture transformed not only to FeTi but also to Fe2Ti intermetallic compound. The transition of last part of super saturated solid solutions β-Ti(Fe) to those intermetallic phases was observed after annealing of this sample at 600 °C.

Study by Mössbauer spectroscopy of the properties of magnetic carriers for medicines

The morphology, Mossbauer spectra and magnetic properties of ultrafine particles (10nm) as a core of magnetic carriers (MC) and dextran-ferrite microspheres are studied. The result suggested the presence of two ferrimagnetic at 300K ferric phases, inheriting their valency, crystallographic state and magnetic properties at creating iron-dextran complexes.

Mössbauer effect in poly-and single crystals YBa2(Cu1−x Fe x )3O7−y

Angle dependence of Mössbauer spectra parameters on angle δO between the ψ-rays wave vectork and the unit cellc-axis of single crystal YBa2(Cu0.98Fe0.02)3O7−y is studied at room temperature. The present results give more detailed information about the correct manner of spectra fitting and EFG tensor parameters in positions of Fe-atoms in 1-2-3 crystal matrix.

A Mössbauer spectroscopy study of the corrosion products formed at an iron surface in soil

The structural and phase composition of corrosion scale formed in soil on a nail of archaeological origin were investigated layer by layer using the methods of Mossbauer spectroscopy, X-ray diffraction, thermomagnetic and chemical analysis. The following iron compounds were determined: Fe3O4, α-Fe2O3 (< 50 and ~ 150 A different dispersed stages), FeS2, FeOOH, FeSO4 × 3H2O, FeCl2 × 2H2O, Fe3(PO4)2 × 8H2O and Fe(CO)3. Near the iron core, crystallized iron oxides, such as magnetite (Fe3O4) and hematite (Fe2O3) are predominant; on approaching the surface of the sample, the quantity of magnetite diminishes and virtually disappears. Haematite can be found on the sample surface only in finely dispersed form, while the concentration of iron-sulfur and ironphosphate compounds increases. This model can be explained only by an active bacterial role in the process of soil corrosion.

Study of the products of interaction between iron and gallium during mechanical activation

Mechanochemical interaction between iron and gallium has been investigated. The multistage character and the dynamics of mechanochemical formation of the gallium solid solution in iron have been established. X-ray diffraction, electron microscopy, and atomic force microscopy have been used for studying structural and morphological peculiarities of products formed at various stages of mechanical activation. Mössbauer spectroscopy has been used for the investigation of local variations in the nearest surroundings of iron atoms during phase transformations.

Mössbauer spectroscopy of iron metabolism and iron intracellular distribution in liver of rats

Mössbauer spectroscopy was used to investigate the distribution of iron in rat organs and its localisation in liver subcellular fraction. A 57Fe-sucrose complex solution was injected by 0.5 ml doses into tail veins of animals every day, during a 6-day period. Mössbauer spectra were measured in spleen, blood, liver and liver subcellular fractions. The mössbauer spectrum of a spleen sample has two symmetrical doublets, one with delta = 0.6 mm/s and delta = 0.7 mm/s, and the other with delta = 1.0 mm/s and delta = 2.35 mm/s. The Mössbauer spectrum of blood has parameters which are close to those for carboxyhemoglobin and oxyhemoglobin complexes. After the addition of sodium citrate, the proportion of the carboxyhemoglobin complex increases. The Mössbauer spectrum of liver has a two-component pattern with two symmetrical doublets, the first with delta = 0.6 mm/s and delta = 0.63 mm/s and the second with delta = 1.4 mm/s and delta = 3.45 mm/s. The first component, which was identified as ferritin, is present in all subcellular fractions (800 x gav sediment fraction, mitochondrial/lysosomal, microsomal and supernatant fractions), with its greatest content in microsomal fraction. After the addition of NaBH4 to mitochondrial/lysosomal fraction, about 20% of the iron contained in ferritin was reduced. In the Mössbauer spectrum this is reflected by an appearance of a doublet with delta = 0.85 mm/s and delta = 3.7 mm/s.