Dimitri Hautot

Increased Levels of Magnetic Iron Compounds in Alzheimer's Disease

A study of the magnetic properties of superior temporal gyrus brain tissue from 11 Alzheimers disease (AD) and 11 age-matched control subjects demonstrates an exponential correlation between the concentrations of the Fe;{2+}-ion-containing iron oxide, magnetite (Fe{3}O{4}), and the fraction of those particles that are smaller than 20 nm in diameter. These data provide circumstantial evidence in favor of their genesis within the 8 nm diameter cores of the iron storage protein ferritin. We also show, for the first time, that the total concentration of biogenic magnetite is generally higher in the AD brain (in some cases as much as 15 times greater than controls) and that there are gender-based differences, with AD female subjects having significantly higher concentrations than all other groups. These results provide insights which may guide current efforts to develop iron-based MRI diagnosis of AD.

Physical and Chemical Characterization of Therapeutic Iron Containing Materials: A Study of Several Superparamagnetic Drug Formulations with the β-FeOOH or Ferrihydrite Structure

The effectiveness of therapeutically used iron compounds is related to their physical and chemical properties. Four different iron compounds used in oral, intravenous, and intramuscular therapy have been examined by X-ray powder diffraction, iron-57 Mössbauer spectroscopy, transmission electron microscopy, BET surface area measurement, potentiometric titration and studied through dissolution kinetics determinations using acid, reducing and chelating agents. All compounds are nanosized with particle diameters, as determined by X-ray diffraction, ranging from 1 to 4.1 nm. The superparamagnetic blocking temperatures, as determined by Mössbauer spectroscopy, indicate that the relative diameters of the aggregates range from 2.5 to 4.1 nm. Three of the iron compounds have an akaganeite-like structure, whereas one has a ferrihydrite-like structure. As powders the particles form large and dense aggregates which have a very low surface area on the order of 1 m2 g−1. There is evidence, however, that in a colloidal solution the surface area is increased by two to three orders of magnitude, presumably as a result of the break up of the aggregates. Iron release kinetics by acid, chelating and reducing agents reflect the high surface area, the size and crystallinity of the particles, and the presence of the protective carbohydrate layer coating the iron compound. Within a physiologically relevant time period, the iron release produced by acid or large chelating ligands is small. In contrast, iron is rapidly mobilized by small organic chelating agents, such as oxalate, or by chelate-forming reductants, such as thioglycolate.

A MOSSBAUER SPECTRAL STUDY OF THE JILIN METEORITE

The iron‐57 Mössbauer spectra of three different samples of the Jilin meteorite have been measured at 78 and 295 K. Five iron containing major components are identified, two magnetic components, kamacite and troilite, and three non‐magnetic components, olivine, pyroxene, and an iron(III) component. The relative absorption areas of these five components show that sample A contains a larger fraction of magnetic components, ca. 50 percent, than samples B and C, which contain ca. 30 percent. This difference indicates a significant compositional inhomogeneity in the Jilin meteorite. The fit of the troilite component sextet is extensively discussed in the paper and requires the adjustment of not only the isomer shift and hyperfine field, but also of the quadrupole interaction, the asymmetry parameter of the electric field gradient tensor, and the orientation of the hyperfine field in the principal axes of the electric field gradient tensor. The smaller isomer shift and hyperfine field of the kamacite mineral in sample B indicate that this sample contains less nickel than the kamacite in samples A and C, in which the amount of nickel is estimated to be ca. 9 percent. On the basis of its hyperfine parameters, the iron(III) component is assigned to iron(III) substituted on the M1 site of pyroxene.

Hydrogen dynamics in the hydrides of Pr2Fe17 as revealed by Mössbauer spectroscopy

The rhombohedral Pr2Fe17Hx compounds with the Th2Zn17 structure have been prepared for x=0–5. Their lattice parameters and Curie temperatures have been determined from powder x-ray diffraction and thermomagnetic measurements, respectively, and their Mossbauer spectra have been measured between 4.2 and 295 K. The Mossbauer spectra for x=0, 1, and 2, obtained between 4.2 and 295 K, and those of Pr2Fe17H3, obtained above 90 K, have been analyzed with a seven sextet model, indicative of a basal magnetization in these compounds. The Mossbauer spectra of Pr2Fe17H3 below 90 K, of Pr2Fe17H4 between 4.2 and 295 K, and of Pr2Fe17H5 above 155 K, have been analyzed with a four sextet model, indicative of an axial magnetization in these compounds over the indicated temperature ranges. The axial magnetic anisotropy results from a combination of lattice expansion upon hydrogenation and contraction upon cooling, and the relative importance of the praseodymium Stevens coefficients. A magnetic phase diagram for the Pr2Fe17...

A structural, magnetic, and Mössbauer spectral study of Dy2Fe17 and its hydrides

The structural and magnetic properties of the Dy2Fe17Hx compounds, where x is 0, 1, 2, 3, and 3.8, have been investigated by means of powder x-ray diffraction, thermomagnetic and ac magnetic susceptibility measurements, and iron-57 Mossbauer spectroscopy. The Dy2Fe17Hx compounds crystallize in a hexagonal Th2Ni17 -like structure which has both an iron-rich stoichiometry and disorder of the Dy and Fe–Fe dumbbell sites. The increase in the lattice parameters, the magnetic ordering temperature, the saturation magnetization, and the dependence of the Mossbauer hyperfine parameters upon hydrogen content support a two-step filling by hydrogen of the interstitial sites with hydrogen first filling the octahedral 6h sites for x<3 and then partially filling the tetrahedral 12i sites for x=3 and 3.8. Neither the Mossbauer spectra nor the ac magnetic susceptibility measurements reveal any spin reorientation in any of the compounds. The extent of the excess iron and the disorder observed in all the compounds is confir...

Magnetic and Mossbauer spectral properties of the compound Nd6Fe13Au

Abstract The magnetic properties of Nd 6 Fe 13 Au were studied by means of magnetic measurements and iron-57 Mossbauer spectroscopy. It is shown that magnetic ordering of the Fe moments occurs at temperatures much above room temperature ( T N = 408 K). At low temperatures, the net moment of Nd 6 Fe 13 Au is very small owing to mutual compensation of the contributions of the various magnetic sublattices involved. High-field measurements made at 4.2 K show that ferromagnetic alignment of the sublattice moments is reached in two steps via first-order magnetic phase transitions. The Mossbauer spectra reveal that the Zeeman splitting gradually decreases with increasing temperature and that the average hyperfine field is zero at 435 K and above. Between 325 K and 411 K the area in the Mossbauer spectra due to the ordered magnetic component decreases gradually as it is replaced by a quadrupole doublet.

Mössbauer spectral evidence for rhombohedral symmetry in R3Fe5O12 garnets with R = Y, Eu and Dy

The iron-57 Mossbauer spectra of R3Fe5O12, where R is Y, Eu and Dy, have been measured between 4.2 and 550 K. The substantial quadrupole splittings observed in the paramagnetic spectra confirm that the local symmetry at both the tetrahedral and octahedral iron(III) sites is not cubic. The low temperature Mossbauer spectra of Dy3Fe5O12 clearly confirm the spin reorientation between 10 and 15 K and the 4.2 and 10 K spectra are consistent with the known orientation of the magnetization at 14 K in the cubic Iad unit cell. The Mossbauer spectra of R3Fe5O12, where R is Y, Eu and Dy, obtained between 45 and 295 K, reveal four different tetrahedral iron(III) Mossbauer spectral components, four components which are inconsistent with a magnetization oriented along the [111] axis of a cubic Iad unit cell. In contrast, these four components are consistent with a crystal symmetry which is reduced from cubic to rhombohedral R. The temperature dependence of the hyperfine fields in Dy3Fe5O12 indicates a small biquadratic exchange contribution to the magnetic exchange. The temperature dependence of the isomer shifts in Dy3Fe5O12 gives Mossbauer lattice temperatures of 405 and 505 K for the 16a and 24d sites, respectively, values which are in excellent agreement with the Debye temperature measured for Y3Fe5O12.

A Mössbauer spectral study of Nd6Fe13X, where X is Cu, Ag, and Au and of the spin reorientation in Nd6Fe13Si

The Mossbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 80 and 500 K. A model corresponding to a basal alignment of the magnetic moments leads to excellent, internally consistent, fits for the Cu, Ag, and Au compounds. The resulting temperature dependences of the spectral hyperfine parameters are uniform and reveal for each Fe site the expected correlations between the isomer shift and the Wigner–Seitz cell volume and the hyperfine field and the number of Fe near neighbors. For Nd6Fe13Si, a different model must be used because of the presence of a spin reorientation below 155 K. Above 155 K, because of the axial alignment of the moments, and in agreement with the 295 K powder neutron diffraction results, the spectra can be analyzed with four sextets. Below 155 K, five additional sextets are required to fit the spectra because of a progressive transition towards a basal alignment of the Fe moments. At 80 K the mixed magnetic phase is 75% basal and 25% axial, whereas at ...

A neutron diffraction and Mössbauer spectral study of the magnetic spin reorientation in Nd6Fe13Si

Powder neutron diffraction and Mossbauer spectral studies have been carried out on Nd6Fe13Si between 2–295 K. The nuclear neutron scattering shows that Nd6Fe13Si has the tetragonal I4/mcm crystal structure at all temperatures. A collinear antiferromagnetic structure with the wavevector q = (0, 0, 1) is observed below the Neel temperature of 421 K. A spin reorientation is observed at ~100 K in both the neutron diffraction patterns and the Mossbauer spectra. Above and below 100 K, the magnetic moments of the four iron and the two neodymium crystallographic sites are ferromagnetically coupled within one block along the c axis and the resulting magnetic moment of this block is antiferromagnetically coupled with that of the adjacent block along the c axis through a layer of silicon atoms. Above and below 100 K, the magnetic moments are found to be parallel or very close to the c axis and within or close to the (a, b) basal plane of the tetragonal unit cell, respectively. This first-order spontaneous zero-field spin reorientation occurs cooperatively and involves both the neodymium and iron magnetic moments. The powder neutron diffraction between 10 and 200 K indicates anisotropic lattice changes associated with a change in the magnetoelastic coupling in this compound. The Mossbauer spectral hyperfine parameters are those expected for axial and basal magnetization directions in Nd6Fe13Si and further indicate the existence of a 75% basal and 25% axial mixed magnetic phase even at 4.2 K, a mixed magnetic phase which results from the influence of the secondary ferromagnetic Nd2Fe17 phase on the primary Nd6Fe13Si phase.

A Mössbauer spectral study of Tb2Fe17 and the Tb2Fe17−xSix solid solutions

The Mossbauer spectra of a series of rhombohedral Tb2Fe17−xSix solid solutions, with x equal to 0, 1, 2, and 3, have been measured as a function of temperature. Although the spectra of Tb2Fe17 change substantially upon cooling from 295 to 85 K, it has been possible to fit them with a consistent seven sextet model corresponding to a basal magnetization. The spectral analysis yields reasonable hyperfine parameters and the expected changes with temperature. The resulting weighted average effective iron recoil mass of 66 g/mol and the Mossbauer temperature of 395 K are typical of this type of intermetallic compound. In addition, the isomer shifts and the hyperfine fields observed for the crystallographically distinct iron sites in Tb2Fe17 agree well with those expected from the differences in the Wigner–Seitz cell volumes and the near-neighbor environments of the four sites. The spectra of the silicon substituted solid solutions have been fit with the same model and similar hyperfine parameters, but with a bi...