MÖSSBAUER SPECTROSCOPIC STUDIES OF HUMIC ACID AND FULVIC ACID SOIL FRACTIONS

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MÖSSBAUER STUDIES OF THE ONE-DIMENSIONAL ANTIFERROMAGNETIC SYSTEMS : A2FeF5

Les études Mössbauer de A2FeF5 (Az = K2, Rb2, N2H6) montrent que ces systèmes ont une température de Néel basse, une faible valeur du champ hyperfin à saturation et une variation signigicative du champ hyperfin avec le champ appliqué. Tout cela est bien caractéristique d'un système anti-ferromagnétique uni-dimensionnel, et est compatible avec les prédictions d'un modèle d'onde de spin.Mössbauer measurements on the compounds A2FeF5 (A2 = K2, Rb2 or N2H6) show that they exhibit a low Néel temperature, a low saturation value of the hyperfine field and a variation of the hyperfine field with an applied field. These are al1 typical characteristics of one-dimensional antiferromagnetic systems, and are consistent with the predictions of spin wave theory

Thalassaemic human spleen ferritin and haemosiderin in applied magnetic fields

Mössbauer spectra of the microcrystalline cores of thalassaemic human spleen ferritin and haemosiderin in applied magnetic fields have shown that the magnetic anisotropy dominates over the energy term arising from the net magnetic moments of the microcrystals in the applied field. The spectra have been analysed to give information on the net magnetic moments of the protein cores

MÖSSBAUER SPECTROSCOPIC STUDIES OF DIMENSIONALITY AND SPIN REDUCTION EFFECTS IN THE ANTIFERROMAGNETIC SYSTEMS : (AF)n-FeF3

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Biomineralization of iron: Moessbauer spectroscopy and electron microscopy of ferritin cores from the chiton Acanthopleura hirtosa and the limpet Patella laticostata

Ferritins isolated from the hemolymph of the chiton Acanthopleura hirtosa and the limpet Patella laticostata have been studied by 57Fe Mössbauer spectroscopy, electron diffraction, transmission electron microscopy (TEM), and inductively coupled plasma (ICP) spectrometry. Mössbauer spectra of the samples at 78 K were quadrupole-split doublets with similar quadrupole splittings and chemical isomer shifts, characteristic of octahedral high-spin iron(III), while at 4.2 K the spectra were magnetically split sextets. The spectra yield mean superparamagnetic blocking temperatures of about 32 and 30 K for the A. hirtosa and P. laticostata ferritins, respectively, and indicate magnetic ordering temperatures of about 37 and 34 K. Core size distributions were measured for both the A. hirtosa and P. laticostata ferritins by using TEM and gave mean core size ranges of 8.0-8.5 and 7.5-8.0 nm, respectively. Diffuse lines in the electron diffraction patterns of the ferritin cores indicated the presence of ferrihydrite (5Fe2-O3·9H2O) of limited crystallinity. Phosphorus to iron atomic ratios were measured by ICP spectrometry. The phosphorus levels were close to the limit of detection, giving approximate mean values of P:Fe of 1:44 for the P. laticostata ferritin and 1:36 for the A. hirtosa ferritin. These levels of phosphate are significantly less than those for the crystalline cores of mammalian ferritins and considerably less than those for the noncrystalline core of bacterioferritins

Variation of the Neel temperature of the one-dimensional antiferromagnet K2FeF5 with applied field

Single-crystal Mossbauer measurements show that the Neel temperature of K2FeF5 increases for magnetic fields applied perpendicular to the easy axis and decreases for magnetic fields applied parallel to the easy axis. This behaviour is consistent with theoretical results for a quasi-one-dimensional Heisenberg antiferromagnet. Calculations of the magnetic phase diagram have been performed and these are in excellent agreement with the experimental data

Core structures of haemosiderins deposited in various organs in β-thalassaemia/haemoglobin e disease

Mössbauer spectra were recorded of tissue from β-thalassaemia/haemoglobin E spleen, liver, pancreas and heart and of crude haemosiderins (insoluble iron fractions) isolated from the organs. Iron in the crude haemosiderins from the spleen and heart remains paramagnetic below 4.2K indicating that the iron is in a non-crystalline form. Superparamagnetic behaviour of the crude haemosiderins from the pancreas and liver indicate the presence of ferrihydrite cores with some cores with a structure based on defect-goethite

Some magnetic properties of the cores of various ferritins

57Fe Mössbauer spectra of the mineral cores of various ferritins show both paramagnetic and superparamagnetic relaxation effects and in some cases a combination of both. Correlations have been observed between data on the crystallinity, phosphate content and percentage iron in the cores and their magnetic ordering and mean blocking temperatures derived from the Mössbauer spectra

OBSERVATION OF IRON-STORAGE PROTEIN IN E. COLI BY MÖSSBAUER SPECTROSCOPY

Des mesures Mössbauer ont été faites à des températures allant jusqu'à 0,08 K sur des échantillons de E. Coli contenant 10 - 1000 µg de 57Fe par gramme de cellules. Les résultats indiquent la présence d'un composé dominant de fer magnétiquement ordonné ayant une température de transition de 2,6 ± 0,2 K. Cela suggère l'existence d'un type nouveau de composé de stockage du fer. Une protéine d'environ 500.000 daltons possédant un noyau de haute densité électronique, probablement constitué par le composé de fer magnétiquement ordonné, a été isolée à partir des bactéries.57Fe Mössbauer spectra have been measured at temperatures down to 0.08 K in E. Coli cells containing 10 - 1000 µg Fe/1 gram of packed cells. The results indicate the presence of a dominant magnetically ordered iron compound having a transition temperature of 2.6 ± 0.2 K. This provides evidence for the presence of a new type of an iron-storage compound in E. Coli. A protein of approximately 500,000 daltons containing an electron dense core, which is probably the magnetically ordered iron compound, has been isolated from the bacteria