D. Hechel

Does iron play a role in Parkinson's disease?

Mössbauer studies of Parkinsonian and control Substantia Nigra (SN) show that the overall amount of iron in SN is about the same in PD and control. At least 90% of this iron is ferritin-like and Fe2+ and/or neuromelanin iron, if present at all, can constitute only less than 10% of the overall iron. During storage in formalin, iron is slowly removed from ferritin and bound to a chelating agent.

Effect of Zn, Ga and Ni substitution on the superconducting properties of the electron doped system Nd-Ce-Cu-O

Abstract We report experimental data about the influence of Zn, Ga and Ni substitution of T c of the electron doped system Nd 1.85 Ce 0.15 Cu 1- y M y O 4- δ , 0≤ y ≤0.15. The relative suppression of T c for a given dopant concentration decreases from Ni to Ga to Zn. Superconductivity is totally suppressed above y =0.01, 0.03 and 0.05 for M= Ni, Ga, Zn, respectively. The solubility of M=Fe in the matrix is extremely small. The effect of M=Ga 3+ on T c is similar to that of Ce 4+ . We compare doping results for magnetic and nonmagnetic ions and discuss the origin of the depression of T c . The effect of these dopants on T c in the Nd-Ce-Cu-O system is completely diffrent from that observed in the La-Sr-Cu-O system.

Iron (III) can be transferred between ferritin molecules

The iron-storage molecule ferritin can sequester up to 4500 Fe atoms as the mineral ferrihydrite. The iron-core is gradually built up when FeII is added to apoferritin and allowed to oxidize. Here we present evidence, from Mössbauer spectroscopic measurements, for the surprising result that iron atoms that are not incorporated into mature ferrihydrite particles, can be transferred between molecules. Experiments were done with both horse spleen ferritin and recombinant human ferritin. Mössbauer spectroscopy responds only to 57Fe and not to 56Fe and can distinguish chemically different species of iron. In our experiments a small number of 57FeII atoms were added to two equivalent apoferritin solutions and allowed to oxidize (1—5 min or 6 h). Either ferritin containing a small iron-core composed of 56Fe, or an equal volume of NaCl solution, was added and the mixture frozen in liquid nitrogen to stop the reaction at a chosen time. Spectra of the ferritin solution to which only NaCl was added showed a mixture of species including 57FeIII in solitary and dinuclear sites. In the samples to which 150 56FeIII-ferritin had been added the spectra showed that all, or almost all, of the 57FeIII was in large clusters. In these solutions 57FeIII initially present as intermediate species must have migrated to molecules containing large clusters. Such migration must now be taken into account in any model of ferritin iron-core formation.

How does the ferritin core form

Ferritin stores iron as ferrihydrite inside a shell composed of H and L protein chains. H chains contain ferroxidase centres catalysing Fe2+ oxidation, while L chains lack these centres but seem to promote ferrihydrite nucleation. Mössbauer spectroscopic studies of recombinant H-chain ferritins show the following: (1) fast Fe2+ oxidation is associated with the formation of Fe3+ dimers at the ferroxidase centre; (2) within 30 min, a portion of the dimers have split to Fe3+ monomers and some monomers have moved to the threefold channels; (3) over longer times, a trend dimer → monomer → core is established. Core formation is accelerated if L chains are present.

Mechanism of Fe(II) oxidation and core formation in ferritin

The iron-storage protein, ferritin, sequesters iron (III) as an inorganic complex (ferrihydrite) inside a protein shell composed of twenty-four subunits. 1 Mammalian ferritins are copolymers of two chains, H and L, each of Mr ~ 20,000, with 55% amino acid sequence identity. 2 Ferritins of invertebrates, plants and bacteria have similar structures, but their chains are probably only of the H-type. The three-dimensional structures of the ferritin from Escherichia coli known as FTN and the type 1 ferritin from the parasite Schistosoma mansoni have been determined and shown to be similar to mammalian ferritins. 3 Both are H type ferritins as shown by their ferroxidase activities. This paper summarises our current understanding and uncertainties concerning the mechanisms of iron sequestration. It has previously been established that this involves the uptake of Fe(II) and its catalytic oxidation by the protein. Much of our recent data has been obtained with recombinant ferritins overexpressed in E. coli and their site-directed variants. These variants are described here by means of the one-letter amino acid code.

Magnetic properties, specific heat studies and Mössbauer measurements of PrBa2NbCu2O8

Abstract PrBa2NbCu2O8 has been studied by DC susceptibility and specific heat measurements to determine the magnetic behavior of the Pr sublattice, and by a 1% 57Fe-doped sample to determine the magnetic behavior of the Cu(2) sites. The Pr sublattice and the CuO2 planes are both antiferromagnetically ordered at 11.6 and 360 K, respectively. The Pr contribution to the specific heat ΔCp(T) was calculated by subtracting the data of LaBa2NbCu2O8 as background. The entropy associated with the magnetic transition is 6.7 J/mol K, intermediate between the expected values for Pr4+ and Pr3+. At low temperatures the magnetic contribution has the form of ΔCp(T)=MT3.1 characteristic of 3D antiferromagnetic magnons. In contrast to PrBa2Cu3Oz, no linear term for the electronic specific heat is observed in PrBa2NbCu2O8.

Coexistence and competition between superconductivity and magnetic order in YBa2Cu4O8

Abstract Magnetic susceptibility and 57 Fe Mossbauer spectroscopy were used to study superconductivity and magnetic order in YBa 2 (Cu 1−x Fe x ) 4 O 8+δ . T c is decreasing with x, disappearing for x > x c 0.04. For x c the crystal structure is orthorhombic and Mossbauer spectra show that iron substitutes Cu, predominantly in the Cu(1) site. Moreover, for the superconducting compound with x=0.025 and T c =27 (2) K, the Cu (1) site orders magnetically at T N =30(2) and H eff (Cu(1), 4.2 K)=461(2) kOe, thus superconductivity and magnetism coexist. For x>x c the crystal structure changes to tetragonal, and magnetic order is observed in the Cu (2) site,T N =380(5) K for x=0.1 and H eff (Cu(2), 4.2 K)=510(2) kOe. The coexistence of superconductivity and magnetic order in the Cu(1) site and the competition between superconductivity and magnetic order in the Cu(2) sites in YBa 2 Cu 4 O 8 are discussed in terms of the previously observed phase diagrams for Y 1−x Pr x Ba 2 (Cu 1−y Fe y ) 3 O 7+δ .

Antiferromagnetic order in Ca2CuO2Cl2, Sr2CuO2Cl2 and Sr2CuO3+x

Abstract The magnetic order in the tetragonal M 2 CuO 2 Cl 2 , M=Ca,Sr and in Sr 2 CuO 3+x compounds was studied by using Mossbauer spectroscopy of 0.5% 57 Fe-doped samples. These compounds crystallize in a K 2 NiF 4 - type tetragonal structure, isostructural to La 2−x Sr x CuO 4 superconductors. In this structure, one crystallographic site exists for copper atoms, which form CuO 2 planes. Sr 2 CuO 3 prepared under ambient pressure has an orthorhombic structure, while the tetragonal Sr 2 CuO 3+x is obtained when prepared under high oxygen pressure. Both copperoxychlorides are antiferromagnetically ordered with T N ≈260K, very similar to T N in La 2 CuO 4 or Nd 2 CuO 4 . The strontium-cuprates are magnetically ordered at 4.2K with T N below 10K.

Superconductivity and antiferromagnetism in Cu(2) layers of RBa2Cu3O2

The systems Y1-xPrxBa2Cu3Oz with x=0 to 1 and YBa2(Cu1-yMy)3Oz, M Fe and Co, with y=0 to 0.26, and z=6 and 7, doped with 57Fe, have been studied by dc magnetometry to determine the superconducting phase transition temperature and by 57Fe Mossbauer spectroscopy to determine the antiferromagnetic phase transition temperature TN of the Cu(2) site. In those cases where substitution is made out of the CuO2 planes, for z=7, Tc is reduced with increasing the dopant concentration. Antiferromagnetism is found at concentrations where the superconductivity disappears, which means that the materials exhibit either superconductivity or antiferromagnetic order, depending on composition. The phase diagrams obtained are very similar to the well-known oxygen content dependence phase diagram. For z=6, TN changes very little with x or y. There is no conclusive evidence for overlap of superconductivity and antiferromagnetism. For substitution of Zn in the CuO2 plane (Zn) a different behavior is observed. Here the magnetic order is never found in oxygen rich samples, and appears in oxygen poor samples only for y<0.08.

The function of H and L chains in iron sequestration in ferritin

Abstract In order to understand the iron sequestering mechanism within the protein shell in ferritins, Mossbauer studies were performed on horse spleen ferritin (about 15% H and 85% L chains) and variants of human H chain ferritins in which putative oxidation and nucleation site ligands have been changed by site directed mutagenesis and which were loaded with small amounts of iron and frozen at short times after iron loading. It was found that the catalysis by apoferritin of Fe(II) oxidation is associated with residues within the H chains, that both Fe(III) monomers and dimers are located on H chains and that these dimers form at ferroxidase centers. Nevertheless iron core formation does occur also in ferritins that lack the ferroxidase center of the H chains, though initial Fe(II) oxidation is slower.