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PubMed2002

Synthesis and structure of singly bridged and doubly bridged [MoFe(3)S(4)] double cubanes with bidentate phosphine ligands.

The reactions of the (Et(4)N)(2)[(Cl(4)-cat)(MeCN)MoFe(3)S(4)Cl(3)] (I) cluster with Fe(pp)(2)Cl(2) (pp = depe (bis(1,2-diethylphosphino)ethane) or dmpe (bis(1,2-dimethylphosphino)ethane)) produced the [(Cl(4)-cat)MoFe(3)S(4)(pp)(2)Cl](2)(mu-pp) (pp = depe (III) or dmpe (V)) singly bridged double cubanes. The reactions of I with the same bidentate phosphine ligands in the presence of NaBPh(4) also produced III and the [(Cl(4)-cat)MoFe(3)S(4)(dmpe)(2)](2)(mu-S)(mu-dmpe) (VI) doubly bridged double cubane, respectively. The byproduct (BPh(4))[Fe(dmpe)(2)(MeCN)Cl] (VII) has been isolated from the reaction mixture and crystallographically characterized. The depe analogue of VI, [(Cl(4)-cat)MoFe(3)S(4)(depe)(2)](2)(mu-S)(mu-depe) (IV), has been successfully prepared from III in the presence of excess Li(2)S. Similar reactions with (Et(4)N)(2)[Fe(4)S(4)(SPh)(4)] (VIII) have resulted in the formation of the neutral Fe(4)S(4)(depe)(2)(SPh)(2) (IX) cluster. The chloride analogue of IX, Fe(4)S(4)(depe)(2)Cl(2) (XI), has been obtained by a reaction of IX with benzoyl chloride. The crystal and molecular structures of III, VI, VII, and XI have been determined by single-crystal X-ray crystallography. The electrochemical and spectroscopic properties, including the Mossbauer spectra of the new clusters, have been determined and analyzed.

Bridged-Ring Compounds↗

PubMed2005

Ligand orientation control in low-spin six-coordinate (porphinato)iron(II) species.

The synthesis of a low-spin six-coordinate iron(II) porphyrinate in which the two axial ligands are forced to have a relative perpendicular orientation has been successfully accomplished for the first time. The reaction of four-coordinate (tetramesitylporphinato)iron(II) with 2-methylimidazole leads to the preparation of [Fe(TMP)(2-MeHIm)(2)] which cocrystallizes with five-coordinate [Fe(TMP)(2-MeHIm)]. The six-coordinate complex accommodates the sterically crowded pair of imidazoles with a strongly ruffled core and relative perpendicular orientation. This leads to shortened equatorial bonds of 1.963(6) A and slightly elongated axial Fe-N bond lengths of 2.034(9) A that are about 0.04 A shorter and 0.03 A longer, respectively, in comparison to those of the bis-imidazole-ligated iron(II) species with parallel oriented axial ligands. The Mossbauer spectrum shows a pair of quadrupole doublets that can be assigned to the components of the cocrystallized crystalline solid. High-spin five-coordinate [Fe(TMP)(2-MeHIm)] has DeltaE(Q) = 2.25 mm/s and delta = 0.90 mm/s at 15 K. The quadrupole splitting, DeltaE(Q), for [Fe(TMP)(2-MeHIm)(2)] is 1.71 mm/s, and the isomer shift is 0.43 mm/s at 15 K. The quadrupole splitting value is significantly larger than that found for low-spin iron(II) derivatives with relative parallel orientations for the two axial ligands. Mossbauer spectra thus provide a probe for ligand orientation when structural data are otherwise not available.

Crystallography, X-Ray↗

PubMed2004

Spectroscopic, redox and magnetic properties of a tetraiminediphenolate iron(II) macrocyclic complex: a model compound for iron proteins.

The title complex [Fe(II)(tidf-H2)(H2O)2](ClO4)2*H(2)O (tidf-H2 = tetraiminediphenolate ligand) has been prepared from a transmetallation reaction between [Mg2(tidf)](NO3)2*4H2O and an iron(II) salt in methanolic solutions under inert atmosphere conditions. It was characterized by analytical, magnetic and spectroscopic methods (Mossbauer, FTIR, UV-vis), by cyclic voltammetry as well as spectroelectrochemistry.

Electrochemistry↗

PubMed2005

Magnetic field induced synthesis and self-assembly of super paramagnetic particles in a protein matrix.

Aqueous solution of a globular protein named bovine serum albumin was homogeneously mixed with ferrous and ferric ions and allowed to gel at ambient conditions. Gels were then oxidized using sodium hydroxide, in the presence of magnetic field of magnitude 0.13 T. The effect of magnetic field on the above biomimetic synthesis was a reduction in particle size and a directional assembly of synthesized super paramagnetic particles into a regular pattern in the protein film. The microstructural revelation was complimentary to Mossbauer results and magnetic measurement studies, i.e., an interesting variation in the magnetic behaviour of self-assembled super paramagnetic particles as a function of dc magnetic field induced ordering.

Biomimetic Materials↗

PubMed1992

[Investigation on the incidence of high altitude polycythemia and its hemoglobin characteristics in a Tibetan population].

The incidences of high altitude polycythemia (HAPC) and its hemoglobin characteristics in natives and immigrants at 2 different altitudes in the Tibet Autonomous Region were investigated. The results were as follows: 1) The incidences of HAPC among residents in Lhasa (3650 meters above sea level) and in Naqu-Ando district (4500-4800 meters above sea-level) were 2.39% and 12.95%, respectively. The incidence of HAPC increased with increasing altitude. The incidences in immigrants and in men were higher than those in natives and in women. 2) The MetHb concentration in RBC from patients with HAPC was 10.14%, distinctly higher than that in healthy adults (6.35%) in the same area. This may be one of the causes leading to oxygen carrying malfunction in the RBCs of HAPC patients. 3) The Mossbauer spectra of RBCs from patients with HAPC had a third component "c" in addition to the two normal components, oxy-Hb "a" and deoxy-Hb "b." The third component "c" may be adenatured Hb in the RBCs of the patients. The question of whether it is related to oxygen carrying power requires further study.

Adolescent↗

PubMed1989

[The effect of time-relaxation spectral width on temperature dependences of parameters of Mossbauer spectra of biopolymers].

A new model for description of dynamic properties of macromolecule, especially globular proteins, is proposed. The model proposes the existence of time-relaxation spectra determining the time characteristics of biomacromolecule dynamics. The time dependence of mean-square deviation of atom from the initial state and spectra of Rayleigh scattering of Mossbauer radiation (RSNR) have been calculated. The temperature dependence of model spectra properties has been investigated. It has been shown that with the increase of time-relaxation spectra range of macromolecules the square under RSNR spectra with temperature growth decreases more quietly. It has been concluded that the idea concerning the time-relaxation spectra existence doesn't explain the sharp decrease of square of protein experimental spectra.

Biopolymers↗

PubMed1999

Beagle 2: a proposed exobiology lander for ESA's 2003 Mars Express mission.

The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies.

Equipment Design↗

PubMedDate not supplied

[Theory of Mossbauer effect in hydrated globular proteins].

The spectrum of Mössbauer absorption by the label incorporated into macromolecule is constructed. The dependence of the spectrum parameters on the hydration degree is found. The results are compared with experiments. The fluid flow inside the globule, excited by rotational vibrations of the globule surface is described by the linearized Debye-Brinkman equation. The local coefficients of rotational and translational diffusion of the globule fragments are found. The hydration coefficient is determined by the ratio of the effective inertia of the porous sphere with the fluid to the inertia of solid sphere.

Models, Chemical↗

PubMed2005

Multielectron redox chemistry of iron porphyrinogens.

Iron octamethylporphyrinogens were prepared and structurally characterized in three different oxidation states in the absence of axial ligands and with sodium or tetrafluoroborate as the only counterions. Under these conditions, the iron- and ligand-based redox chemistry of iron porphyrinogens can be defined. The iron center is easily oxidized by a single electron (E(1/2) = -0.57 V vs NHE in CH(3)CN) when confined within the fully reduced macrocycle. The porphyrinogen ligand also undergoes oxidation but in a single four-electron step (E(p) = +0.77 V vs NHE in CH(3)CN); one of the ligand-based electrons is intercepted for the reduction of Fe(III) to Fe(II) to result in an overall three-electron oxidation process. The oxidation equivalents in the macrocycle are stored in C(alpha)-C(alpha) bonds of spirocyclopropane rings, formed between adjacent pyrroles. EPR, magnetic and Mossbauer measurements, and DFT computations of the redox states of the iron porphyrinogens reveal that the reduced ligand gives rise to iron in intermediate spin states, whereas the fully oxidized ligand possesses a weaker sigma-donor framework, giving rise to high-spin iron. Taken together, the results reported herein establish a metal-macrocycle cooperativity that engenders a multielectron chemistry for iron porphyrinogens that is unavailable to heme cofactors.

Crystallography, X-Ray↗

PubMed1989

Fe2+ binding to apo and holo mammalian ferritin.

The binding of Fe2+ to both apo and holo mammalian ferritin has been investigated under anaerobic conditions as a function of pH. In the pH range 6.0-7.5, 8.0 +/- 0.5 Fe2+ ions bind to each apoferritin molecule, but above pH 7.5, a pH-dependent Fe2+ binding profile is observed with up to 80 Fe2+ ions binding at pH 10.0. This Fe2+ binding is reversible and is accompanied by up to two H+ being released per Fe2+ bound at pH 10.0. The Fe2+ binding to apoferritin probably occurs in the 3-fold channels. A much larger and more complex pH-dependent Fe2+ binding stoichiometry was observed for holoferritin with up to 300 Fe2+ ions binding at pH 10.0. This pH-dependent Fe2+ binding was interpreted as Fe2+ interaction at the FeOOH mineral surface with displacement of H+ from -OH or phosphate surface groups by the incoming Fe2+ ions. Mossbauer spectroscopic measurements using 57Fe-labeled Fe2+ under anaerobic conditions showed that 57Fe2+ binding to holoferritin was accompanied by electron transfer to the core, yielding 57Fe3+, presumably bound to the mineral surface. Removal of added iron by Fe2+-specific chelating agents yielded 57Fe2+, demonstrating the reversibility of this electron-transfer process. The Fe2+ bound to apo- and holoferritin is readily converted to Fe3+ by exposure to O2 and strongly retained by the respective ferritin species.

Animals↗

PubMed1984

Smectite interactions with flavomononucleotide.

Adsorption isotherms and UV-visible and Mossbauer spectroscopic data point to specific interactions between flavomononucleotide (FMN) and Fe(3+)-smectite. The maximum amount of FMN adsorption was 0.3 mmole/g of Fe(3+)-smectite giving a 1:1 molar proportion of Fe3+ and FMN. The results suggest a Fe(3+)-FMN complex residing at the smectite surface. Other homoionic smectites (Cu2+, Zn2+, and Ca2+) exhibited lower levels of adsorption and less apparent specific interaction.

Adsorption↗

PubMed1997

Mössbauer studies of alkane omega-hydroxylase: evidence for a diiron cluster in an integral-membrane enzyme.

The gene encoding the alkane omega-hydroxylase (AlkB; EC 1.14.15.3) from Pseudomonas oleovorans was expressed in Escherichia coli. The integral-membrane protein was purified as nearly homogeneous protein vesicles by differential ultracentrifugation and HPLC cation exchange chromatography without the detergent solubilization normally required for membrane proteins. Purified AlkB had specific activity of up to 5 units/mg for octane-dependent NADPH consumption. Mössbauer studies of AlkB showed that it contains an exchange-coupled dinuclear iron cluster of the type found in soluble diiron proteins such as hemerythrin, ribonucleotide reductase, methane monooxygenase, stearoyl-acyl carrier protein (ACP) delta9 desaturase, rubrerythrin, and purple acid phosphatase. In the as-isolated enzyme, the cluster contains an antiferromagnetically coupled pair of high-spin Fe(III) sites, with an occupancy of up to 0.9 cluster per AlkB. The diferric cluster could be reduced by sodium dithionite, and the diferrous state was found to be stable in air. When both O2 and substrate (octane) were added, however, the diferrous cluster was quantitatively reoxidized, proving that the diiron cluster occupies the active site. Mossbauer data on reduced AlkB are consistent with a cluster coordination rich in nitrogen-containing ligands. New sequence analyses indicate that at least 11 nonheme integral-membrane enzymes, including AlkB, contain the 8-histidine motif required for catalytic activity in stearoyl-CoA desaturase. Based on our Mössbauer studies of AlkB, we propose that the integral-membrane enzymes in this family contain diiron clusters. Because these enzymes catalyze a diverse range of oxygenation reactions, this proposal suggests a greatly expanded role for diiron clusters in O2-activation biochemistry.

Iron↗

PubMed1997

The effect of histological processing on the form of iron in iron-loaded human tissues.

Iron-loaded human spleen tissue was immersed in neutral buffered formalin over a period of 200 days. Over the first 60 days, iron leached steadily from the tissue until 3% had been lost. Thereafter, no further iron leaching was detected. Comparisons of Mossbauer spectra of freeze-dried tissue and tissue freeze-dried after immersion in formalin for 200 days showed no evidence of chemical transformation of the iron remaining in the tissue. The spectra indicated a difference in the heme-iron to non-heme iron ratio between the two samples probably reflecting inhomogeneity of the ratio throughout the spleen as measured on the centimetre scale. Mossbauer spectra of freeze-dried samples of iron-loaded human liver and pancreas tissue were compared with those for samples from the same patient that had been processed by routine hospital procedures for histology and archival. These spectra showed no evidence for chemical transformation of the iron present in the tissues. These results demonstrate that it is feasible to use archived fixed and embedded human tissue samples for studies aimed at gauging the relative fraction of goethite-like hemosiderin present in the tissue.

Formaldehyde↗

PubMed2005

Synthesis and characterization of Sn(IV) complexes of lower rim 1,3-diacid derivative of calix[4]arene and their protective effects on tissue oxidative stress and essential metal concentration in lead exposed male Wistar rats.

The two Sn(IV) complexes synthesized using calix[4]arene-1,3-di-acid derivative were characterized by analytical, (1)H, (13)C and (119)Sn NMR, matrix assisted laser desorption ionization mass, and (119)Sn Mossbauer techniques and found that the complexes are tetranuclear possessing structurally two different types of tin centers. These complexes were evaluated for their protective value against blood and tissue oxidative stress in lead exposed male albino rats of Wistar strain. The results suggest that the two tin complexes significantly protect changes in lead induced biochemical variables indicative of heme synthesis pathway and exhibit only moderate effect on tissue oxidative stress. The beneficial effects could be attributed mainly to the ability of Sn(IV) complexes in preventing absorption of lead to the target sites/tissues.

Animals↗

PubMed2005

Vitrified metal finishing wastes II. Thermal and structural characterisation.

Waste filter cakes from two metal finishing operations were heat treated and vitrified. Substantial weight loss during heating was due to emission of water, volatile sulphur-rich and chlorine-rich compounds, and the combustion of carbonaceous components. Estimations of CO(x), SO(x) and HCl emissions were based on chemical analyses. Upon cooling from molten, one sample remained amorphous but all others partially crystallised. Crystalline nature was dependent upon waste composition and the level of P(2)O(5) addition. Thermal stabilities of the waste forms were good, but less so than MW, a borosilicate glass developed for its high temperature stability. Mossbauer and FTIR analyses showed that iron environments in the different vitrified waste forms were very similar. Iron was present predominantly as Fe(3+), although the exact redox ratio varied slightly between waste forms. Iron in both redox states occupied distorted octahedral coordination polyhedra with similar levels of site distortion. Phosphate networks in the vitreous materials were highly de-polymerised, consisting largely of (PO(4))(3-) monomer and (P(2)O(7))(2-) dimer units. This explained the high chemical durability of these waste forms and their structural insensitivity to compositional change, underlining their suitability as hosts for the immobilisation of toxic and nuclear wastes.

Differential Thermal Analysis↗

PubMedDate not supplied

[Mossbauer data on the effect of NAD.H on the state of iron in bacteria].

The state of Fe of bacterial cultures of different systematic positions (Bacillus megaterium, Bacillus polymyxa, Pseudomonas putida, Pseudomonas fluorescens, Alcaligenes faecalis, Arthrobacter siderocapsulatus) grown on the medium containing Fe(III) citrate (up to 100 mg/l) with additional or without NAD.H was studied. The samples were in damp air-dry, second moistened, dried at 383 K states. Spectra have been obtained at 290 K and 100-200 K. The studied microorganisms have two types of atoms of Fe(III) which dissociated into protoplasm or into cell slug at damp state. All studied microorganisms except Arthrobacter siderocapsulatus do not reduce iron at all variants of experiments. Arthrobacter siderocapsulatus reduces about 50% of cell iron only the presence of NAD.H creating two types of Fe(II) complexes firmly connected with cell.

Bacteria↗

PubMed2005

Water affects the stereochemistry and dioxygen reactivity of carboxylate-rich diiron(II) models for the diiron centers in dioxygen-dependent non-heme enzymes.

Carboxylate-bridged high-spin diiron(II) complexes with distinctive electronic transitions were prepared by using 4-cyanopyridine (4-NCC(5)H(4)N) ligands to shift the charge-transfer bands to the visible region of the absorption spectrum. This property facilitated quantitation of water-dependent equilibria in the carboxylate-rich diiron(II) complex, [Fe(2)(mu-O(2)CAr(Tol))(4)(4-NCC(5)H(4)N)(2)] (1), where (-)O(2)CAr(Tol) is 2,6-di-(p-tolyl)benzoate. Addition of water to 1 reversibly shifts two of the bridging carboxylate ligands to chelating terminal coordination positions, converting the structure from a paddlewheel to a windmill geometry and generating [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-NCC(5)H(4)N)(2)(H(2)O)(2)] (3). This process is temperature dependent in solution, rendering the system thermochromic. Quantitative treatment of the temperature-dependent spectroscopic changes over the temperature range from 188 to 298 K in CH(2)Cl(2) afforded thermodynamic parameters for the interconversion of 1 and 3. Stopped flow kinetic studies revealed that water reacts with the diiron(II) center ca. 1000 time faster than dioxygen and that the water-containing diiron(II) complex reacts with dioxygen ca. 10 times faster than anhydrous analogue 1. Addition of {H(OEt(2))(2)}{B}, where B(-) is tetrakis(3,5-di(trifluoromethyl)phenyl)borate, to 1 converts it to [Fe(2)(mu-O(2)CAr(Tol))(3)(4-NCC(5)H(4)N)(2)](B) (5), which was also structurally characterized. Mossbauer spectroscopic investigations of solid samples of 1, 3, and 5, in conjunction with several literature values for high-spin iron(II) complexes in an oxygen-rich coordination environment, establish a correlation between isomer shift, coordination number, and N/O composition. The products of oxygenating 1 in CH(2)Cl(2) were identified crystallographically to be [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(4-NCC(5)H(4)N)(2)].2(HO(2)CAr(Tol)) (6) and [Fe(6)(mu-O)(2)(mu-OH)(4)(mu-O(2)CAr(Tol))(6)(4-NCC(5)H(4)N)(4)Cl(2)] (7).

Carboxylic Acids↗

PubMedDate not supplied

[Study of the dynamics of human serum albumin by coherent Rayleigh dispersion of Mossbauer radiation].

The measurements of angle dependencies of total and elastic Rayleigh scattering of Mossbauer radiation intensities have been performed for human serum albumin (HSA) with hydration degrees h = 0.13 and h = 0.4. The extended model was developed for calculating the inelastic intensity of Rayleigh scattering. Original data for HSA and published data on met-Mb were fitted within the frame of this model. The best agreement with experiment was obtained when two types of intraglobular motions were taken into account: individual motions of small side-chain groups and cooperative (mechanical) motions of segments (most probable alpha-helices). Long-range correlated motions are essential at low hydration degree. The possibilities of application of the coherent version of RSMS technique are described.

Humans↗