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PubMed1997

An Fe2IVO2 diamond core structure for the key intermediate Q of methane monooxygenase.

A new paradigm for oxygen activation is required for enzymes such as methane monooxygenase (MMO), for which catalysis depends on a nonheme diiron center instead of the more familiar Fe-porphyrin cofactor. On the basis of precedents from synthetic diiron complexes, a high-valent Fe2(micro-O)2 diamond core has been proposed as the key oxidizing species for MMO and other nonheme diiron enzymes such as ribonucleotide reductase and fatty acid desaturase. The presence of a single short Fe-O bond (1.77 angstroms) per Fe atom and an Fe-Fe distance of 2.46 angstroms in MMO reaction intermediate Q, obtained from extended x-ray absorption fine structure and Mössbauer analysis, provides spectroscopic evidence that the diiron center in Q has an Fe2IVO2 diamond core.

Binding Sites↗

PubMed1997

Iron-sulfur clusters: nature's modular, multipurpose structures.

Iron-sulfur proteins are found in all life forms. Most frequently, they contain Fe2S2, Fe3S4, and Fe4S4 clusters. These modular clusters undergo oxidation-reduction reactions, may be inserted or removed from proteins, can influence protein structure by preferential side chain ligation, and can be interconverted. In addition to their electron transfer function, iron-sulfur clusters act as catalytic centers and sensors of iron and oxygen. Their most common oxidation states are paramagnetic and present significant challenges for understanding the magnetic properties of mixed valence systems. Iron-sulfur clusters now rank with such biological prosthetic groups as hemes and flavins in pervasive occurrence and multiplicity of function.

Catalysis↗

PubMed2000

A short Fe-Fe distance in peroxodiferric ferritin: control of Fe substrate versus cofactor decay?

The reaction of oxygen with protein diiron sites is important in bioorganic syntheses and biomineralization. An unusually short Fe-Fe distance of 2.53 angstroms was found in the diiron (mu-1,2 peroxodiferric) intermediate that forms in the early steps of ferritin biomineralization. This distance suggests the presence of a unique triply bridged structure. The Fe-Fe distances in the mu-1, 2 peroxodiferric complexes that were characterized previously are much longer (3.1 to 4.0 angstroms). The 2.53 angstrom Fe-Fe distance requires a small Fe-O-O angle (approximately 106 degrees to 107 degrees). This geometry should favor decay of the peroxodiferric complex by the release of H2O2 and mu-oxo or mu-hydroxo diferric biomineral precursors rather than by oxidation of the organic substrate. Geometrical differences may thus explain how diiron sites can function either as a substrate (in ferritin biomineralization) or as a cofactor (in O2 activation).

Chemical Phenomena↗

PubMed2000

O2 activation by nonheme iron complexes: A monomeric Fe(III)-Oxo complex derived from O2.

Iron species with terminal oxo ligands are implicated as key intermediates in several synthetic and biochemical catalytic cycles. However, there is a dearth of structural information regarding these types of complexes because their instability has precluded isolation under ambient conditions. The isolation and structural characterization of an iron(III) complex with a terminal oxo ligand, derived directly from dioxygen (O2), is reported. A stable structure resulted from placing the oxoiron unit within a synthetic cavity lined with hydrogen-bonding groups. The cavity creates a microenvironment around the iron center that aids in regulating O2 activation and stabilizing the oxoiron unit. These cavities share properties with the active sites of metalloproteins, where function is correlated strongly with site structure.

Anthracenes↗

PubMed2003

Crystallographic and spectroscopic characterization of a nonheme Fe(IV)-O complex.

Following the heme paradigm, it is often proposed that dioxygen activation by nonheme monoiron enzymes involves an iron(IV)=oxo intermediate that is responsible for the substrate oxidation step. Such a transient species has now been obtained from a synthetic complex with a nonheme macrocyclic ligand and characterized spectroscopically. Its high-resolution crystal structure reveals an iron-oxygen bond length of 1.646(3) angstroms, demonstrating that a terminal iron(IV)=oxo unit can exist in a nonporphyrin ligand environment and lending credence to proposed mechanisms of nonheme iron catalysis.

Catalysis↗

PubMed1993

Purification and characterization of protocatechuate 2,3-dioxygenase from Bacillus macerans: a new extradiol catecholic dioxygenase.

Protocatechuate 2,3-dioxygenase (2,3-PCD) from Bacillus macerans JJ1b has been purified to homogeneity for the first time. The enzyme catalyzes proximal extradiol ring cleavage of protocatechuate (PCA) with the attendant incorporation of both atoms of oxygen from O2. The holoenzyme has a mass of 143 +/- 7 kDa as determined by ultracentrifugation and other techniques. It is composed of four apparently identical subunits with M(r)s of 35,500, each containing one iron atom. Mössbauer spectroscopy of 57Fe-enriched enzyme showed that the irons are indistinguishable and are high spin (S = 2) Fe2+ in both the uncomplexed and substrate-bound enzyme. However, the quadrupole splitting, delta EQ, and isomer shift, delta, of the Mössbauer spectrum changed from delta EQ = 2.57 mm/s and delta = 1.29 mm/s to delta EQ = 2.73 mm/s and delta = 1.19 mm/s upon PCA binding to the enzyme, showing that the iron environment is altered when substrate is present. The enzyme was also found to bind variable and substoichiometric amounts of Mn2+, but this metal could be removed without loss of activity or stability. The inherently electron paramagnetic resonance (EPR)-silent Fe2+ of the enzyme reversibly bound nitric oxide to produce an EPR-active species (g = 4.11, 3.95; S = 3/2). The specific activity of the enzyme was found to be correlated with the amount of the S = 3/2 species formed, showing that activity is dependent on Fe2+. Anaerobic addition of substrates to the enzyme-nitric oxide complex significantly altered the EPR spectrum, suggesting that substrates bind to or near the iron. The enzyme was inactivated by reagents that oxidize the Fe2+, such as H2O2 and K3FE(CN)6; full activity was restored after reduction of the iron by ascorbate. Steady-state kinetic data were found to be consistent with an ordered bi-uni mechanism in which the organic substrate must add to 2,3-PCD before O2. The enzyme has the broadest substrate range of any of the well-studied catecholic dioxygenases. All substrates have vicinal hydroxyl groups on the aromatic ring except 4-NH2-3-hydroxybenzoate. This is the first substrate lacking vicinal hydroxyl groups reported for catecholic extradiol dioxygenases. 2,3-PCD is the final member of the PCA dioxygenase family to be purified. It is compared with other members of this family as well as other catecholic dioxygenases.

Amino Acid Sequence↗

PubMed1999

Ferritin mutants of Escherichia coli are iron deficient and growth impaired, and fur mutants are iron deficient.

Escherichia coli contains at least two iron storage proteins, a ferritin (FtnA) and a bacterioferritin (Bfr). To investigate their specific functions, the corresponding genes (ftnA and bfr) were inactivated by replacing the chromosomal ftnA and bfr genes with disrupted derivatives containing antibiotic resistance cassettes in place of internal segments of the corresponding coding regions. Single mutants (ftnA::spc and bfr::kan) and a double mutant (ftnA::spc bfr::kan) were generated and confirmed by Western and Southern blot analyses. The iron contents of the parental strain (W3110) and the bfr mutant increased by 1.5- to 2-fold during the transition from logarithmic to stationary phase in iron-rich media, whereas the iron contents of the ftnA and ftnA bfr mutants remained unchanged. The ftnA and ftnA bfr mutants were growth impaired in iron-deficient media, but this was apparent only after the mutant and parental strains had been precultured in iron-rich media. Surprisingly, ferric iron uptake regulation (fur) mutants also had very low iron contents (2.5-fold less iron than Fur+ strains) despite constitutive expression of the iron acquisition systems. The iron deficiencies of the ftnA and fur mutants were confirmed by Mössbauer spectroscopy, which further showed that the low iron contents of ftnA mutants are due to a lack of magnetically ordered ferric iron clusters likely to correspond to FtnA iron cores. In combination with the fur mutation, ftnA and bfr mutations produced an enhanced sensitivity to hydroperoxides, presumably due to an increase in production of "reactive ferrous iron." It is concluded that FtnA acts as an iron store accommodating up to 50% of the cellular iron during postexponential growth in iron-rich media and providing a source of iron that partially compensates for iron deficiency during iron-restricted growth. In addition to repressing the iron acquisition systems, Fur appears to regulate the demand for iron, probably by controlling the expression of iron-containing proteins. The role of Bfr remains unclear.

Aerobiosis↗

PubMed2002

Structural and magnetic properties of evaporated nanostructured Fe/V multilayers.

The structural and magnetic properties of the evaporated Fe/V multilayers with a fixed V-layer thickness (tV = 1.5 nm) and variable Fe layer thicknesses (0.75 nm < or = tFe < or = 6 nm) have been studied by X-ray reflectivity and high-angle X-ray diffraction, conversion-electron Mössbauer spectrometry, and vibrating sample magnetometry. The results show that multilayers are formed with a broad Fe/V interface and pure crystalline bcc-Fe layers in the center of the individual subsystems. The Fe spin orientation is aligned in the film plane in the individual centers as well in the interfacial regions. The interfacial anisotropy constant Ks was estimated to be equal to 0.04 mJ/m2. This parallel magnetic anisotropy is discussed in terms of reduced symmetry effects on the hybridized 3d states.

Anisotropy↗

PubMed2005

Synthesis and characterisation of polyol-capped transition metal oxide nanoparticles.

In-situ capped nanocrystalline gamma-Fe2O3, Co3O4, and Cu2O were prepared in 1,4-butanediol in aerobic conditions. X-ray diffraction (XRD) patterns show that the synthesised samples are nanocrystalline cubic oxides with crystallite sizes 9.5 nm, 13.4 nm, and 11 nm, respectively. Raman spectroscopy shows peaks at 350 cm(-1), 500 cm(-1), and 700 cm(-1), indicating that the iron oxide is gamma-Fe2O3; Mössbauer spectroscopy shows the presence of two Fe3(3+) sites. Transmission electron microscopy images show that the particle sizes of gamma-Fe2O3 and Co3O4 samples are 8.9 nm and 7 nm, respectively. The absence of agglomeration indicates that the synthesised nanoparticles are capped. FT-IR spectra show the presence of an organic moiety in the sample which acts as a capping agent. Thermogravimetry shows that the capping is stable up to 873 K in gamma-Fe2O3, and up to 400 K in Co3O4. The samples are soluble in water to form stable hydrosols. During synthesis of gamma-Fe2O3 a 6-line ferrihydrite is formed as an intermediate, which is stable in solution up to 473 K, and transforms to gamma-Fe2O3 at 483 K, by rapid dissolution-reprecipitation. In the syntheses of Co3O4 and Cu2O, no intermediates are formed.

Cobalt↗

PubMed1991

Oxidative stress in newborn erythrocytes.

Phenylhydrazine (PHZ) exposure is used to study in vitro red cell aging mechanisms dependent on Hb oxidation. The effect of PHZ on normal neonatal red blood cells was studied in unseparated blood and after separation into light and heavy cells. PHZ caused more extensive morphologic changes in neonatal than in adult red blood cells. PHZ exposure of neonatal cells caused less reduced glutathione depletion than in adult cells. Although we found the same total amount of oxidized Hb in both cells, a well-defined oxidation product of Hb was demonstrated by Mössbauer spectra only in neonatal cells. This oxidation product was not methemoglobin but a trivalent, high-spin iron compound. All neonatal cell populations were more sensitive to PHZ than were adult ones, as demonstrated by the presence of Heinz bodies at low PHZ concentration, which did not affect adult cells. These studies demonstrate greater sensitivity of neonatal cells to PHZ in all density-separated populations.

Adult↗

PubMed2000

Chemical states and lattice dynamics of alpha-diimine Fe2+ complexes intercalated into gamma-zirconium phosphate.

The alpha-diimine Fe2+ complexes, [Fe(phen)3]2+, [Fe(bpy)3]2+, and [Fe(terpy)2]2+, (phen: 1,10-phenanthroline, bpy: 2,2'-bipyridyl, terpy: alpha,alpha',alpha''-tripyridine) were intercalated into zirconium dihydrogenphosphate phosphate dihydrate (gamma-zirconium phosphate, gamma-ZrP), Zr(PO4)(H2PO4).2H2O. The rate of the intercalation, the molar ratio of Fe to Zr, was found to be 3.82-7.76%. Mössbauer spectra indicated that one part of [Fe(phen)3]2+ and [Fe(bpy)3]2+ changed from a low-spin Fe2+ to high-spin Fe2+ state on intercalation, but [Fe(terpy)2]2+ did not change in chemical state. The lattice dynamics of the complexes and the intercalation compounds were investigated in terms of the temperature dependence of the area intensity on the Mössbauer spectra. A linear relationship was established for all the complex salts and the intercalation compounds investigated between the ln[A(T)/A(82)] and absolute temperature, T, where A(T) and A(82) show the intensities of a doublet at T and 82 K of the Mössbauer spectra, respectively. From the slope of the linear relation, the theta2M values, which were derived based on the Debye approximation of lattice vibration, were evaluated for the complex salts and the intercalation compounds. The Fe2+ complexes showed theta2M values of 1.27 to 2.32 x 10(6), whereas the intercalation compounds showed very similar values to each other, ranging from 2.19 to 2.39 x 10(6), irrespective of different alpha-diimine ligands. The results were explained in terms of the characteristic layered structure of zirconium phosphate, and by the tight bond between the alpha-diimine Fe2+ complexes and the host gamma-ZrP.

Algorithms↗

PubMed1997

Chemical characterization and reactivity of iron chelator-treated amphibole asbestos.

Iron in amphibole asbestos is implicated in the pathogenicity of inhaled fibers. Evidence includes the observation that iron chelators can suppress fiber-induced tissue damage. This is believed to occur via the diminished production of fiber-associated reactive oxygen species. The purpose of this study was to explore possible mechanisms for the reduction of fiber toxicity by iron chelator treatments. We studied changes in the amount and the oxidation states of bulk and surface iron in crocidolite and amosite asbestos that were treated with iron-chelating desferrioxamine, ferrozine, sodium ascorbate, and phosphate buffer solutions. The results have been compared with the ability of the fibers to produce free radicals and decompose hydrogen peroxide in a cell-free system in vitro. We found that chelators can affect the amount of iron at the surface of the asbestos fibers and its valence, and that they can modify the chemical reactivity of these surfaces. However, we found no obvious or direct correlations between fiber reactivity and the amount of iron removed, the amount of iron at the fiber surface, or the oxidation state of surface iron. Our results suggest that surface Fe3+ ions may play a role in fiber-related carboxylate radical formation, and that desferrioxamine and phosphate groups detected at treated fiber surfaces may play a role in diminishing and enhancing, respectively, fiber redox activity. It is proposed that iron mobility in the silicate structure may play a larger role in the chemical reactivity of asbestos than previously assumed.

Asbestos, Amphibole↗

PubMed1997

Can microwave radiation at high temperatures reduce the toxicity of fibrous crocidolite asbestos?

Exposure of animals and humans to crocidolite asbestos fibers produces fibrosis and two types of cancers: bronchogenic carcinoma and mesothelioma. It is therefore desirable to reduce toxicity of these fibers without affecting their other characteristics. In this study, commercial crocidolite asbestos fibers were radiated with microwave radiation at different temperatures. Radiated fibers and nonradiated original fibers were then studied by Mössbauer spectroscopy to quantify the amount of ferric and ferrous ions present at structurally different sites in each crocidolite sample. They were also studied for their ability to initiate the peroxidation of linoleic acid to assess the effect of radiation on this process. Results showed that microwave radiation reduced the total Fe2+/Fe3+ ratio. This reduction produced a concomitant decrease in the ability of the radiated samples to peroxidize linoleic acid.

Aldehydes↗

PubMed1994

Characterization and extracorporeal application of a new phosphate-binding agent.

A new phosphate-binding agent which does not cause any severe side effects in vivo was developed by modifying a crosslinked dextran with polynuclear iron(III)oxide-hydroxide. Its particle size ranges from 150 to 300 microns, and the iron content was about 18% by dry weight. The oxidation state of iron was characterized by ESCA and Mössbauer spectroscopy. The maximum phosphate binding capacity of the iron(III)oxide-hydroxide-modified dextran was determined with respect to aqueous phosphate solutions, human serum and whole blood. The effects on whole blood count, haemolysis, protein concentration and enzyme activities were examined. In addition, the influence of phosphate concentration, pH and temperature on the phosphate uptake of the material was determined. The results show that this new adsorbent might provide an alternative to conventional phosphate-binding agents. This paper also describes the first experiments on the therapeutic application of the material in an extracorporeal blood perfusion system for the treatment of hyperphosphataemia during haemodialysis.

Adsorption↗

PubMedDate not supplied

[Preparation and spectroscopic studies of diorganotin(IV) complexes with adenosine and related compounds].

Nine complexes of adenosine and related compounds (adenosine-5'-monophosphate, adenosine-5'-triphosphate, 1-methyl-adenosine, pyridoxal-5-phosphate and beta-nicotinamide-adenine-dinucleotide-phosphoric acid) with di-n-butyltin(IV) oxide and/or di-n-butytin(IV) dichloride were prepared in the solid state. The compositions of the complexes were determined by standard analytical methods. It was found that the complexes contain organotin(IV) moiety and the ligand in a ratio of 1:1 or 2:1. The FTIR spectra demonstrated that di-n-butyltin(IV) oxide reacts with the D-ribose moiety of the ligands, while di-n-butyltin(IV) dichloride is co-ordinated to the deprotonated phosphate group. The basic part of the ligands does not participate directly in complex formation. Comparison of the experimental Mössbauer delta E values with those calculated on the basis of the PQS concept revealed that the organotin(IV) moiety has trigonal-bipyramidal, octahedral and in some cases tetrahedral geometry also. Some of the complexes contain the organotin(IV) cation in two different surroundings.

Adenosine↗

PubMedDate not supplied

[Preparation, X-ray structural and spectroscopic studies of some D-lactobionic acid complexes with Cs(I), Fe(III) and di-n-butyltin(IV)].

D-Lactobionic acid (4-O-beta-D-galactopyranosyl-D-gluconic acid) complexes of Cs(I), Fe(III) and di-n-butyltin(IV)2+ ions were prepared in the solid state. The bonding sites of the ligands were verified by means of FTIR, Raman and 13C NMR spectroscopic measurements. The Cs(I)-D-lactobionate was obtained in single-crystal form. The X-ray crystallographic results on Cs(I)-D-lactobionate demonstarted that each Cs(I) ion is bonded to four D-lactobionate ions, forming an intricate 3D network. The asymmetric unit consists of one Cs(I), one D-lactobionate ion and one water molecule. For the di-n-butyltin(IV) complex, Mössbauer pqs calculations indicated octahedral and trigonalbipyramidal stereochemistry around the central tin atom in the oligomeric compound. In DMSO solution, the polymeric structure does not remain as shown by 13C NMR measurement. One solvent molecule is coordinated additionally to the tin center, and the carboxylate group has become monodentate. According to the EPR measurement, the Fe(III) complexes obtained at different pH have at least dimeric or oligomeric structure.

Cesium↗

PubMedDate not supplied

Neolithic ceramic findings from western Sicily. Chemical-physical and mineralogical characterization.

This paper presents the results of a study that is part of a wider research program regarding the knowledge of the initial living phases of Sicilian agricultural and pastoral societies. Three ceramic samples attributed to the medium initial Neolithic (NEO1 and NEO2) and to the first neolithic (NEO3), recovered in two different archaeological sites of the western Sicily, have been analysed. Chemical, mineralogical and spectroscopic data point out a similarity between NEO1 and NEO3 samples; compositional and morphological differences instead have been observed in the NEO2 sample. The firing temperatures of the samples have been estimated by Mössbauer spectroscopy; they are lower than 500 degrees C for the samples NEO1 and NEO3, and about 700 degrees C for NEO2.

Archaeology↗

PubMedDate not supplied

Red cell Hb oxidation of healthy subjects compared to breast cancer patients.

The end result of our research would be the development of a new diagnostic technique that could be used as a screening test, starting from a simple blood collection, a common procedure without any risk to the subject. Red blood cells (RBC) of patients affected by breast cancer are more sensitive to the denaturing action of acetylphenylhydrazine (APH), hence the formation time of hemin, one of the last oxidation products, is significantly shorter then in normal subjects. Our previous experiment showed the differences during iron oxidation between breast cancer patients and healthy persons (Croci et al. 2001). Different amounts of hemin, after the same incubation time, can discriminate between samples collected from people suffering from cancer and a healthy population. These results have given birth to the necessity to standardise a procedure useful as a screening method. The aim of the present work was to define a range of values that characterise the samples collected from healthy people.

Breast Neoplasms↗