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PubMed1997

Cooperativity in the Iron(II) Spin-Crossover Compound [Fe(ptz)(6)](PF(6))(2) under the Influence of External Pressure (ptz = 1-n-Propyltetrazole).

The iron(II) spin-crossover compound [Fe(ptz)(6)](PF(6))(2) (ptz = 1-propyltetrazole) crystallizes in the triclinic space group P&onemacr;, with a = 10.6439(4) Å, b = 10.8685(4) Å, c = 11.7014(4) Å, alpha = 75.644(1) degrees, beta = 71.671(1) degrees, gamma = 60.815(1) degrees, and Z = 1. In [Fe(ptz)(6)](PF(6))(2), the thermal spin transition is extremely steep because of cooperative effects of elastic origin. The transition temperature at ambient pressure is 74(1) K. An external pressure of 1 kbar shifts the transition temperature to 102(1) K, corresponding to a stabilization of the low-spin state, which is smaller in volume. The volume difference between the high-spin and the low-spin state, DeltaV degrees (HL), is 24(2) Å(3)/molecule. The interaction constant Gamma, as a measure of cooperativity, is within experimental error independent of external pressure and has a value of 101(5) cm(-)(1). In contrast to the case of the related compound [Fe(ptz)(6)](BF(4))(2) (Decurtins et al. Inorg. Chem.1985, 24, 2174), there is no hysteresis due to a first-order crystallographic phase transition, nor is there a hysteresis induced by external pressure as in the mixed crystal [Zn(1)(-)(x)()Fe(x)()(ptz)(6)](BF(4))(2), x = 0.1 (Jeftic et al. J. Phys.Chem. Solids 1996, 57, 1743). However, in [Fe(ptz)(6)](PF(6))(2), the interaction constant Gamma is found to be very close to the critical value above which a hysteresis solely due to the cooperative effects is expected. In addition, high-spin --> low-spin relaxation measurements were performed under external pressures of up to 1 kbar in the temperature interval between 50 and 60 K. An external pressure of 1 kbar accelerates the high-spin --> low-spin relaxation by 1 order of magnitude.

Journal Article↗
PubMed1994

Iron at the cell surface controls DNA synthesis in CCl 39 cells.

Treatment of CCl 39 cells with the impermeable iron II chelator bathophenanthroline disulfonate (BPS) inhibits both DNA synthesis and transplasma membrane electron transport. The inhibition persists when the BPS is removed, and the extract from 10(6) cells contains up to 1.28 nmoles iron II chelated to BPS. The BPS iron II chelate itself is not inhibitory. Both DNA synthesis and electron transport are restored by addition of microM iron II or iron III compounds to extracted cells. Other impermeable chelators for iron II give similar inhibition, whereas the iron III-specific Tiron or copper-specific bathocuproine sulfonate do not inhibit. The inhibition differs from the permeable iron III chelator inhibition of ribonucleotide reductase, because inhibition of DNA synthesis by the permeable chelators is reversed when chelator is removed. The response to growth factors also differs, with no impermeable chelator inhibition on 10% fetal calf serum contrasting to inhibition by permeable chelators. DNA synthesis with both activation of tyrosine kinase with EGF plus insulin or by thrombin or ceruloplasmin led to protein kinase C activation as inhibited by the impermeable chelators. It is proposed that an iron available on the cell surface is required for DNA synthesis and plasma membrane electron transport.

Animals↗
PubMed1981

Antimicrobial properties of iron-binding proteins.

The transferrins are iron-binding proteins with molecular weights of around 80,000, which interact with a maximum of two ferric atoms per each protein molecule. The best known transferrins are the serotransferrins from animal sera, lactoferrins from milk, and conalbumin from egg-white. The iron-deficient transferrins will inhibit the growth of certain bacteria and fungi by making iron unavailable for bacterial metabolism. Such activity is abolished if the transferrin is saturated with iron. Many organisms can produce small molecular-weight iron-binding compounds called siderophores that can successfully utilize the iron sequestered by the transferrins. Such organisms are very virulent. Overwhelming evidence is now available to indicate that the transferrins play an important role in mammalian host-defense mechanisms. Thus, iron injections into animals infected with virulent bacteria result in increased death rates, and parenteral iron administration to human infants predisposes them to fatal septicemia. On the other hand, in cases of systemic infection, the organism responds by lowering its total serum iron, so as to make the serotransferrin present less saturated with iron. This phenomenon is called nutritional immunity. The iron apparently moves into the storage tissues from the circulation, and furthermore, it is withheld from circulation by the reticuloendothelial system. Laboratory results in such cases indicate low total serum iron levels and high unsaturated iron-binding activity values, thus increasing the bacteriostatic effects of the serotransferrins. Increased lactoferrin levels are observed in the milks of mastitic cattle.

Anemia, Hypochromic↗
PubMed1997

The primitive matrix components of the unique carbonaceous chondrite Acfer 094: a TEM study.

The mineralogical and chemical characteristics of the fine-grained matrix (< or = 3 micrometers) of the unique primitive carbonaceous chondrite Acfer 094 have been investigated in detail by scanning electron microscopy (SEM) and analytical transmission electron microscopy (ATEM). Generally, the fine-grained matrix represents a highly unequilibrated assemblage of an amorphous material, small forsteritic olivines (200-300 nm), low Ca-pyroxenes (300-400 nm), and Fe,Ni-sulfides (100-300 nm). The matrix is basically unaffected by secondary processes. Only minor amounts of serpentine and ferrihydrite, as products of hydrous alteration, are present. Texturally, the amorphous material acts as a groundmass to olivines, pyroxenes, and sulfides, mostly exhibiting rounded or elongated morphologies. Only very few clastic mineral grains have been found. The texture and chemical composition of the amorphous material are consistent with an origin by disequilibrium condensation in either the cooling solar nebula or a circumstellar environment. As such, the amorphous material may be considered as a possible precursor of matrix materials in other types of chondrites. The non-clastic matrix olivines (Fo98-99) and pyroxenes (En97-100) are suggested to have formed either by condensation in the solar nebula under highly oxidizing conditions or by recrystallization from the amorphous material. The formation of these grains by fragmentation of chondrule components is unlikely due to chemical and microstructural reasons. Rapid cooling caused the observed intergrowths of clino/orthoenstatite in the Mg-rich matrix pyroxenes. Although some similarities exist comparing the fine-grained matrix of Acfer 094 with the matrices of the unequilibrated CO3 chondrite ALHA77307 and the unique type 3 chondrite Kakangari, Acfer 094 remains unique. Since it contains the highest measured concentrations of circumstellar SiC and the second highest of diamond (highest is Orgueil), it seems reasonable to suggested that at least parts of the amorphous material in the fine-grained matrix may be of circumstellar origin.

Carbon↗
PubMed2004

Structural insights into nonheme alkylperoxoiron(III) and oxoiron(IV) intermediates by X-ray absorption spectroscopy.

Transient mononuclear low-spin alkylperoxoiron(III) and oxoiron(IV) complexes that are relevant to the activation of dioxygen by nonheme iron enzymes have been generated from synthetic iron(II) complexes of neutral tetradentate (TPA) and pentadentate (N4Py, Bn-TPEN) ligands and structurally characterized by means of Fe K-edge X-ray absorption spectroscopy (XAS). Notable features obtained from fits of the EXAFS region are Fe-O bond lengths of 1.78 A for the alkylperoxoiron(III) intermediates and 1.65-1.68 A for the oxoiron(IV) intermediates, reflecting different strengths in the Fe-O pi interactions. These differences are also observed in the intensities of the 1s-to-3d transitions in the XANES region, which increase from 4 units for the nearly octahedral iron(II) precursor to 9-15 units for the alkylperoxoiron(III) intermediates to 25-29 units for the oxoiron(IV) species.

Biomimetic Materials↗
PubMed2004

Thermal and light induced polymorphism in iron(II) spin crossover compounds.

The spin crossover complexes [Fe[H(2)B(pz)(2)](2)L]([H(2)B(pz)(2)](-)= dihydrobis(pyrazolyl)borate, L = 2,2[prime or minute]-bipyridine (1), bipy and 1,10-phenanthroline, phen (2)) undergo both thermal and light induced spin crossover, but the structure of the low spin and light induced high spin states for are different from that of the thermally induced high spin state and from those of.

Journal Article↗
PubMed1952

The influence of diet on iron absorption. III. Comparative studies with rats, mice, guinea pigs, and chickens.

The response of rats, chicks, mice, and guinea pigs to two diets containing various amounts of iron has been compared. With diets composed chiefly of corn grits animals of all these species absorb and store considerably more iron than those with normal diets of the same iron content. If sufficient iron is added to a normal diet, all species will absorb large amounts of iron. However, there appear to be great species differences in the level of iron which must be fed to cause the increase in absorption. Chicks and mice appear to have less effective control over iron absorption on high iron diets. Attention is called to large individual differences in ability to control iron absorption under the conditions of these experiments.

Animals↗
PubMed1985

The iron-chelating agent picolinic acid enhances transferrin receptors expression in human erythroleukaemic cell lines.

Picolinic acid, a metal chelating molecule, was administered to human erythroleukaemic cell lines (K 562 and HEL) that were grown in serum-containing media. Picolinic acid inhibited both iron uptake and cell growth. Furthermore, picolinic acid was shown to markedly decrease the level of ferritin in the cells. In spite of the inhibition of cell growth, picolinic acid induced a marked increase in the transferrin-binding capacity of the cells. This phenomenon was due to a two-five-fold enhancement of the rate of transferrin receptor biosynthesis. Other iron-chelating compounds, capable of reducing the level of intracellular iron, also elicited a marked enhancement of the transferrin-binding capacity of the cells. However, the addition of iron, as ferric ammonium citrate, in the culture medium elicited a marked increase in the level of ferritin and a strong decrease in the transferrin-binding capacity of the cells. On the basis of these data we propose that a feed-back mechanism is involved in the regulation of transferrin receptors: when the cells accumulate iron they decrease the number of transferrin receptors in order to prevent further accumulation of iron; when no or low iron is available to the cells, the number of transferrin receptors markedly increases as a compensatory mechanism.

Cell Line↗