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1.
Environ Sci Technol ; 54(5): 2832-2842, 2020 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-32019302

RESUMO

Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.


Assuntos
Compostos Férricos , Geologia , Oxirredução , Espectroscopia de Mossbauer , Espectroscopia por Absorção de Raios X , Raios X
2.
Biochemistry ; 59(5): 704-716, 2020 02 11.
Artigo em Inglês | MEDLINE | ID: mdl-31887031

RESUMO

A defining characteristic of bacterial cytochromes (cyt's) in the P460 family is an unusual cross-link connecting the heme porphyrin to the side chain of a lysyl residue in the protein backbone. Here, via proteomics of the periplasmic fraction of the ammonia-oxidizing bacterium (AOB) Nitrosomonas europaea, we report the identification of a variant member of the P460 family that contains a methionyl residue in place of the cross-linking lysine. We formally designate this protein cytochrome "c'ß-Met" to distinguish it from other members bearing different residues at this position (e.g., cyt c'ß-Phe from the methane-oxidizing Methylococcus capsulatus Bath). As isolated, the monoheme cyt c'ß-Met is high-spin (S = 5/2). Optical spectroscopy suggests that a cross-link is absent. Hydroxylamine, the substrate for the cross-linked cyt P460 from N. europaea, did not appreciably alter the optical spectrum of cyt c'ß with up to 1000-fold excess at pH 7.5. Cyt c'ß-Met did however bind 1 equiv of H2O2, and with a slight excess, Mössbauer spectroscopy indicated the formation of a semistable ferryl (FeIV═O) Compound II-like species. The corresponding electron paramagnetic resonance showed a very low intensity signal indicative of a radical at g = 2.0. Furthermore, cyt c'ß-Met exhibited guaiacol-dependent peroxidase activity (kcat = 20.0 ± 1.2 s-1; KM = 2.6 ± 0.4 mM). Unlike cyt c'ß-Met, cyt P460 showed evidence of heme inactivation in the presence of 2 equiv of H2O2 with no appreciable guaiacol-dependent peroxidase activity. Mutagenesis of the cross-linking lysyl residue to an alanine in cyt P460, however, reversed this lack of activity.


Assuntos
Citocromos c/metabolismo , Heme/metabolismo , Compostos de Ferro/metabolismo , Lisina/metabolismo , Nitrosomonas/química , Peroxidase/metabolismo , Citocromos c/química , Citocromos c/genética , Espectroscopia de Ressonância de Spin Eletrônica , Heme/química , Compostos de Ferro/química , Lisina/química , Modelos Moleculares , Nitrosomonas/citologia , Nitrosomonas/metabolismo , Peroxidase/química , Proteômica , Espectroscopia de Mossbauer
3.
Eur Biophys J ; 48(7): 635-643, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31302726

RESUMO

In this work, wild-type and heterozygous ß-thalassaemic mice were enriched with 57Fe via gastrointestinal absorption to characterize in greater detail the iron complexes then identifiable via Mössbauer spectroscopy. The 57Fe enrichment method was validated and Mössbauer spectra were obtained at 80 K from blood samples from wild-type and ß-thalassaemic mice at 1, 3, 6, and 9 months of age. As expected, the haemoglobin levels of the thalassaemic mice were lower than from normal mice, indicating anaemia. Furthermore, significant amounts of ferritin-like iron were observed in the thalassaemic mice samples, which decreased with mouse age, reflecting the pattern of reticulocyte count reduction reported in the literature.


Assuntos
Isótopos de Ferro/metabolismo , Isótopos de Ferro/farmacologia , Espectroscopia de Mossbauer , Talassemia beta/sangue , Talassemia beta/metabolismo , Animais , Absorção Intestinal , Camundongos , Camundongos Endogâmicos C57BL
4.
Proc Natl Acad Sci U S A ; 116(32): 15836-15841, 2019 08 06.
Artigo em Inglês | MEDLINE | ID: mdl-31324742

RESUMO

In this report we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M-M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from highly symmetric to fully asymmetric by 57Fe Mössbauer and X-ray diffraction to explore the relationship between MAD-derived data and the data available from these widely used characterization techniques. The compounds examined include the all-ferrous clusters [ n Bu4N][(tbsL)Fe3(µ3-Cl)] (1) ([tbsL]6- = [1,3,5-C6H9(NC6H4-o-NSi t BuMe2)3]6-]), (tbsL)Fe3(py) (2), [K(C222)]2[(tbsL)Fe3(µ3-NPh)] (4) (C222 = 2,2,2-cryptand), and the mixed-valent (tbsL)Fe3(µ3-NPh) (3). Redox delocalization in mixed-valent 3 was explored with cyclic voltammetry (CV), zero-field 57Fe Mössbauer, near-infrared (NIR) spectroscopy, and X-ray crystallography techniques. We find that the MAD results show an excellent correspondence to 57Fe Mössbauer data; yet also can distinguish between subtle changes in local coordination geometries where Mössbauer cannot. Differences within aggregate oxidation levels are evident by systematic shifts of scattering factor envelopes to increasingly higher energies. However, distinguishing local oxidation levels in iso- or mixed-valent materials can be dramatically obscured by the degree of covalent intracore bonding. MAD-derived atomic scattering factor data emphasize in-edge features that are often difficult to analyze by X-ray absorption near edge spectroscopy (XANES). Thus, relative oxidation levels within the cluster were most reliably ascertained from comparing the entire envelope of the atomic scattering factor data.


Assuntos
Difração de Raios X , Cristalografia por Raios X , Modelos Moleculares , Oxirredução , Espectroscopia de Mossbauer
5.
Biometals ; 32(1): 171-184, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30637584

RESUMO

Scopelophila ligulata is an Fe-hyperaccumulator moss growing in acidic environments, but the mechanism of Fe accumulation remains unknown. To understand the mechanism, we determined Fe species in S. ligulata samples. The moss samples were collected from four sites in Japan. The concentrations of Fe, P, S, Cl, and K in them were measured by induced coupled plasma mass spectrometry. Fe species in some of them were determined by Mössbauer spectroscopy and were confirmed by X-ray diffraction analysis. Fe species in S. ligulata samples were determined to be jarosite, ferritin, high-spin Fe(II) species, and akaganeite. To our knowledge, this is the first report on the biomineralization of jarosite in mosses. This result, combined with the fact that bacteria, a fungus, and a grass mineralize jarosite, suggests that its biomineralization is a common characteristic in a wide variety of living organisms. These findings indicate that the biomineralization of jarosite occurs not only in the region-specific species but in species adapted to a low-pH and metal-contaminated environment in different regions, provide a better understanding of the mechanism of Fe accumulation in the Fe-hyperaccumulator moss S. ligulata, and offer new insights into the biomineralization of jarosite.


Assuntos
Bryopsida/química , Compostos Férricos/química , Ferro/análise , Sulfatos/química , Biomineralização , Espectroscopia de Mossbauer , Difração de Raios X
6.
Biochemistry ; 58(7): 940-950, 2019 02 19.
Artigo em Inglês | MEDLINE | ID: mdl-30628436

RESUMO

Mycofactocin is a putative redox cofactor and is classified as a ribosomally synthesized and post-translationally modified peptide (RiPP). Some RiPP natural products, including mycofactocin, rely on a radical S-adenosylmethionine (RS, SAM) protein to modify the precursor peptide. Mycofactocin maturase, MftC, is a unique RS protein that catalyzes the oxidative decarboxylation and C-C bond formation on the precursor peptide MftA. However, the number, chemical nature, and catalytic roles for the MftC [Fe-S] clusters remain unknown. Here, we report that MftC binds a RS [4Fe-4S] cluster and two auxiliary [4Fe-4S] clusters that are required for MftA modification. Furthermore, electron paramagnetic resonance spectra of MftC suggest that SAM and MftA affect the environments of the RS and Aux I cluster, whereas the Aux II cluster is unaffected by the substrates. Lastly, reduction potential assignments of individual [4Fe-4S] clusters by protein film voltammetry show that their potentials are within 100 mV of each other.


Assuntos
Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Proteínas com Ferro-Enxofre/química , Proteínas com Ferro-Enxofre/metabolismo , Proteínas de Bactérias/genética , Catálise , Domínio Catalítico , Cisteína/química , Técnicas Eletroquímicas , Espectroscopia de Ressonância de Spin Eletrônica , Proteínas com Ferro-Enxofre/genética , Mycobacterium ulcerans/química , Oxirredução , S-Adenosilmetionina/metabolismo , Espectroscopia de Mossbauer
7.
Mater Sci Eng C Mater Biol Appl ; 94: 798-810, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30423766

RESUMO

Self-hardening calcium phosphate cements present ideal bone tissue substitutes from the standpoints of bioactivity and biocompatibility, yet they suffer from (a) weak mechanical properties, (b) negligible osteoinduction without the use of exogenous growth factors, and (c) a lack of intrinsic antibacterial activity. Here we attempt to improve on these deficiencies by studying the properties of self-setting Fe-doped bone-integrative cements containing two different concentrations of the dopant: 0.49 and 1.09 wt% Fe. The hardening process, which involved the transformation of Fe-doped ß-tricalcium phosphate (Fe-TCP) to nanocrystalline brushite, was investigated in situ by continuously monitoring the cements using the Energy Dispersive X-Ray Diffraction technique. The setting time was 20 min and the hardening time 2 h, but it took 50 h for the cement to completely stabilize compositionally and mechanically. Still, compared to other similar systems, the phase transformation during hardening was relatively fast and it also followed a relatively simple reaction path, virtually free of complex intermediates and noisy background. Mössbauer spectrometry demonstrated that 57Fe atoms in Fe-TCP were located in two non-equivalent crystallographic sites and distributed over positions with a strong crystal distortion. The pronounced presence of ultrafine crystals in the final, brushite phase contributed to the reduction of the porosity and thereby to the enhancement of the mechanical properties. The compressive strength of the hardened TCP cements increased by more than twofold when Fe was added as a dopant, i.e., from 11.5 ±â€¯0.5 to 24.5 ±â€¯2.0 MPa. The amount of iron released from the cements in physiological media steadied after 10 days and was by an order of magnitude lower than the clinical threshold that triggers the toxic response. The cements exhibited osteoinductive activity, as observed from the elevated levels of expression of genes encoding for osteocalcin and Runx2 in both undifferentiated and differentiated MC3T3-E1 cells challenged with the cements. The osteoinductive effect was inversely proportional to the content of Fe ions in the cements, indicating that an excessive amount of iron can have a detrimental effect on the induction of bone growth by osteoblasts in contact with the cement. In contrast, the antibacterial activity of the cement in the agar assay increased against all four bacterial species analysed (E. coli, S. enteritidis, P. aeruginosa, S. aureus) in direct proportion with the concentration of Fe ions in it, indicating their key effect on the promotion of the antibacterial effect in this material. This effect was less pronounced in broth assays. Experiments involving co-incubation of cements with cells in an alternate magnetic radiofrequency field for 30 min demonstrated a good potential for the use of these magnetic cements in hyperthermia cancer therapies. Specifically, the population of human glioblastoma cells decreased six-fold at the 24 h time point following the end of the magnetic field treatment, while the population of the bone cancer cells dropped approximately twofold. The analysis of the MC3T3-E1 cell/cement interaction reiterated the effects of iron in the cement on the bone growth marker expression by showing signs of adverse effects on the cell morphology and proliferation only for the cement containing the higher concentration of Fe ions (1.09 wt%). Biological testing concluded that the effects of iron are beneficial from the perspective of a magnetic hyperthermia therapy and antibacterial prophylaxis, but its concentration in the material must be carefully optimized to avoid the adverse effects induced above a certain level of iron concentrations.


Assuntos
Antibacterianos/farmacologia , Cimentos para Ossos/farmacologia , Fosfatos de Cálcio/química , Ouro/farmacologia , Ferro/química , Osseointegração/efeitos dos fármacos , Prata/farmacologia , Animais , Linhagem Celular , Subunidade alfa 1 de Fator de Ligação ao Core/metabolismo , Humanos , Cinética , Camundongos , Osteoblastos/citologia , Osteoblastos/metabolismo , Osteocalcina/genética , Osteocalcina/metabolismo , Pós , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Espectroscopia de Mossbauer , Análise Espectral Raman , Temperatura , Difração de Raios X
8.
Planta ; 249(3): 751-763, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30382344

RESUMO

MAIN CONCLUSION: Fe uptake machinery of chloroplasts prefers to utilise Fe(III)-citrate over Fe-nicotianamine complexes. Iron uptake in chloroplasts is a process of prime importance. Although a few members of their iron transport machinery were identified, the substrate preference of the system is still unknown. Intact chloroplasts of oilseed rape (Brassica napus) were purified and subjected to iron uptake studies using natural and artificial iron complexes. Fe-nicotianamine (NA) complexes were characterised by 5 K, 5 T Mössbauer spectrometry. Expression of components of the chloroplast Fe uptake machinery was also studied. Fe(III)-NA contained a minor paramagnetic Fe(II) component (ca. 9%), a paramagnetic Fe(III) component exhibiting dimeric or oligomeric structure (ca. 20%), and a Fe(III) complex, likely being a monomeric structure, which undergoes slow electronic relaxation at 5 K (ca. 61%). Fe(II)-NA contained more than one similar chemical Fe(II) environment with no sign of Fe(III) components. Chloroplasts preferred Fe(III)-citrate compared to Fe(III)-NA and Fe(II)-NA, but also to Fe(III)-EDTA and Fe(III)-o,o'EDDHA, and the Km value was lower for Fe(III)-citrate than for the Fe-NA complexes. Only the uptake of Fe(III)-citrate was light-dependent. Regarding the components of the chloroplast Fe uptake system, only genes of the reduction-based Fe uptake system showed high expression. Chloroplasts more effectively utilize Fe(III)-citrate, but hardly Fe-NA complexes in Fe uptake.


Assuntos
Ácido Azetidinocarboxílico/análogos & derivados , Brassica napus/metabolismo , Cloroplastos/metabolismo , Compostos Férricos/metabolismo , Ferro/metabolismo , Ácido Azetidinocarboxílico/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Espectroscopia de Mossbauer , Transcriptoma
9.
Cell Biochem Biophys ; 77(1): 33-46, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30191452

RESUMO

In this overview, we present the results of the study of spleen and liver tissues taken from healthy donors in comparison with those from patients with (i) non-Hodgkin B-cell lymphomas, namely, mantle cell lymphoma and marginal zone B-cell lymphoma, (ii) acute myeloid leukemia, and (iii) primary myelofibrosis. The study was carried out using Mössbauer spectroscopy and magnetization measurements for the analysis of ferritin-like iron in spleen and liver tissues. Magnetization measurements demonstrated small differences in the saturation magnetic moments and revealed additional paramagnetic components. Two liver samples demonstrated unusual behavior of the magnetic moment when the zero-field-cooled curve was over the field-cooled curve in the temperature range between ~40 and ~70 K. Relative iron content variations in the tissue cells as well as small variations in the 57Fe hyperfine parameters were demonstrated for healthy and patients' spleen and liver tissues on the base of measured Mössbauer spectra. The results obtained permit us to suggest small differences in the ferritin iron core structure in spleen and liver tissues from healthy donors and patients with hematological malignancies.


Assuntos
Neoplasias Hematológicas/patologia , Ferro/química , Fígado/química , Espectroscopia de Mossbauer , Baço/química , Ferritinas/química , Humanos , Leucemia Mieloide Aguda/patologia , Fígado/metabolismo , Linfoma de Células B/patologia , Magnetismo , Microscopia , Mielofibrose Primária/patologia , Baço/metabolismo , Temperatura
10.
Environ Sci Pollut Res Int ; 26(5): 4277-4287, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30291616

RESUMO

Fly ash, a coal combustion residue produced by Termotasajero in Colombia, has been hydrothermally treated after an alkaline fusion to produce zeolite without addition of silicon or aluminum. The starting material was thoroughly mixed with NaOH, in a 1:1.2 mass ratio, to obtain a homogeneous mixture that was heated to 100 °C during different times (6, 8, and 10 h) and three zeolite samples were produced. The samples were characterized by XRD, SEM, XRF, Mössbauer spectroscopy, and N2 physisorption. According to characterization results (high surface area and appropriate morphological properties including crystallinity) and synthesis time, zeolitic catalyst synthesized with 8 h of hydrothermal treatment was selected to perform further analysis. This sample consisted of a mixture of zeolite X and zeolite A of high surface area (301 m2 g-1) and a Fe content of 6% wt/wt. The zeolite was used as a catalyst for the Fenton oxidation of Orange II. Experiments were performed in a laboratory batch reactor at 70 °C and constant pH = 3, using different concentrations of H2O2. When the stoichiometric amount of H2O2 was used, good mineralization (XTOC = 45%), complete discoloration, and oxidant consumption were obtained after 240 min of reaction. The sample retained activity after 16 h of usage. The presence of Fe in the reaction media was always detected and a homogeneous Fenton mechanism induced by surface-leached iron is suggested.


Assuntos
Compostos Azo/química , Benzenossulfonatos/química , Cinza de Carvão/química , Zeolitas/síntese química , Catálise , Colômbia , Peróxido de Hidrogênio/química , Concentração de Íons de Hidrogênio , Microscopia Eletrônica de Varredura , Oxidantes/química , Oxirredução , Peróxidos/química , Espectroscopia de Mossbauer , Difração de Raios X , Zeolitas/química
11.
Cell Biochem Biophys ; 77(1): 15-32, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-29704106

RESUMO

A brief review on the applications of Mössbauer spectroscopy in biomedical research discusses the results of more than fifty years of experience in this field. Basing on the numerous results the main directions of biomedical applications of Mössbauer spectroscopy are considered as follows: 1) studies of the quantitative changes of iron-containing biomolecules related to pathological processes; 2) studies of the qualitative changes in iron-containing biomolecules related to pathological processes; 3) studies of the effect of various environmental factors (physical, chemical, and biological) on iron-containing biomolecules; 4) studies of metabolic processes by means of analysis of the Mössbauer nuclides pathways in organisms; 5) studies of dynamic processes; 6) studies of pharmaceutical compounds and blood substitutes containing Mössbauer nuclides; 7) miscellaneous studies. Some examples of biomedical research using 57Fe, 57Co, 119Sn, 153Sm, and 197Au Mössbauer nuclides are presented.


Assuntos
Espectroscopia de Mossbauer/métodos , Animais , Pesquisa Biomédica , Hemoglobinas/química , Humanos , Ferro/química , Sobrecarga de Ferro/patologia , Nanopartículas Metálicas/química , Estresse Oxidativo , Talassemia beta/patologia
12.
Molecules ; 23(12)2018 Nov 30.
Artigo em Inglês | MEDLINE | ID: mdl-30513645

RESUMO

A new hybrid inorganic-organometallic salt has been obtained from the reaction of the Keggin-type silicotungstate anion with ferrocene in a water/methanol mixture as a result of the partial oxidation of ferrocene molecules to ferrocenium cations. Single-crystal X-ray diffraction analysis reveals the presence of four ferrocenium (FeIII) cations and one ferrocene (FeII) molecule per plenary Keggin anion in the crystal structure of [FeIII (Cp)2]4[SiW12O40]·[FeII(Cp)2]·2CH3OH (1). Compound 1 thus constitutes the first example in the literature in which ferrocenium and ferrocene species coexist in the structure of a polyoxometalate-based salt. The two crystallographically independent ferrocenium species in the asymmetric unit of 1 exhibit different configurations: One displays an eclipsed conformation with ideal D5h symmetry, whereas the conformation in the other one is staggered D5d. The crystal packing of 1 can be best described as an organometallic sub-lattice of ferrocenium and ferrocene species linked by a network of π-π interactions that generates rectangular cavities of about 14 × 10 Å in which strings of Keggin anions and methanol molecules are hosted, further connected to each other via weak OPOM···CMeOH-OMeOH···OPOM type hydrogen bonds. The charge-transfer nature of the salt has been studied by solid-state diffuse reflectance UV-Vis spectroscopy and the presence of magnetically isolated FeIII/FeII centres has been confirmed by Mössbauer spectroscopy. A topological study carried out on all of the pristine ferrocenyl species deposited in the Cambridge Structural Database (CSD) has allowed two main conclusions to be drawn: (1) these species tend to adopt extreme conformations (either eclipsed or staggered) with less than a 15% of examples showing intermediate states and (2) the oxidation state of the iron centres can be unequivocally assigned on the basis of a close inspection of the Fe···Cp distances, which allows ferrocene neutral molecules and ferrocenium cations to be easily distinguished.


Assuntos
Compostos Ferrosos/química , Metalocenos/química , Sais/química , Compostos de Tungstênio/química , Cristalografia por Raios X , Espectrofotometria Ultravioleta , Espectroscopia de Infravermelho com Transformada de Fourier , Espectroscopia de Mossbauer
13.
J Am Chem Soc ; 140(48): 16792-16806, 2018 12 05.
Artigo em Inglês | MEDLINE | ID: mdl-30403845

RESUMO

Chemical oxidation and reduction of the all-ferrous (HL)2Fe6 in THF affords isostructural, coordinatively unsaturated clusters of the type [(HL)2Fe6] n: [(HL)2Fe6][BArF24] (1, n = +1; where [BArF24]- = tetrakis[(3,5-trifluoromethyl)phenyl]borate), [Bu4N][(HL)2Fe6] (2a, n = -1), [P][(HL)2Fe6] (2b, n = -1; where [P]+ = tributyl(1,3-dioxolan-2-ylmethyl)phosphonium), and [Bu4N]2[(HL)2Fe6] (3, n = -2). Each member of the redox-transfer series was characterized by zero-field 57Fe Mössbauer spectroscopy, near-infrared spectroscopy, single-crystal X-ray crystallography, and magnetometry. Redox-directed trends are observed when comparing the structural metrics within the [Fe6] core. The metal octahedron [Fe6] decreases marginally in volume as the molecular reduction state increases as gauged by the Fe-Feavg distance varying from 2.608(11) Å ( n = +1) to 2.573(3) ( n = -2). In contrast, the mean Fe-N distances and ∠Fe-N-Fe angles correlate linearly with the [Fe6] oxidation level, or alternatively, the changes observed within the local Fe-N4 coordination planes vary linearly with the aggregate spin ground state. In general, as the spin ground state ( S) increases, the Fe-N(H)avg distances also increase. The structural metric perturbations within the [Fe6] core and measured spin ground states were rationalized extending the previously proposed molecular orbital diagram derived for (HL)2Fe6. Chemical reduction of the (HL)2Fe6 cluster results in an abrupt increase in spin ground state from S = 6 for the all-ferrous cluster, to S = 19/2 in the monoanionic 2b and S = 11 for the dianionic 3. The observation of asymmetric intervalence charge transfer bands in 3 provides further evidence of the fully delocalized ground state observed by 57Fe Mössbauer spectroscopy for all species examined (1-3). For each of the clusters examined within the electron-transfer series, the observed spin ground states thermally persist to 300 K. In particular, the S = 11 in dianionic 3 and S = 19/2 in the monoanionic 2b represent the highest spin ground states isolated up to room temperature known to date. The increase in spin ground state results from population of the antibonding orbital band comprised of the Fe-N σ* interactions. As such, the thermally persistent ground states arise from population of the resultant single spin manifolds in accordance with Hund's rules. The large spin ground states, indicative of strong ferromagnetic electronic alignment of the valence electrons, result from strong direct exchange electronic coupling mediated by Fe-Fe orbital overlap within the [Fe6] cores, equivalent to a strong double exchange magnetic coupling B for 3 that was calculated to be 309 cm-1.


Assuntos
Complexos de Coordenação/química , Ferro/química , Complexos de Coordenação/síntese química , Cristalografia por Raios X , Fenômenos Magnéticos , Estrutura Molecular , Espectroscopia de Mossbauer , Temperatura
14.
Water Res ; 144: 312-321, 2018 11 01.
Artigo em Inglês | MEDLINE | ID: mdl-30053622

RESUMO

Phosphate recovery from sewage sludge is essential in a circular economy. Currently, the main focus in centralized municipal wastewater treatment plants (MWTPs) lies on struvite recovery routes, land application of sludge or on technologies that rely on sludge incineration. These routes have several disadvantages. Our study shows that the mineral vivianite, Fe2(PO4)3 × 8H2O, is present in digested sludge and can be the major form of phosphate in the sludge. Thus, we suggest vivianite can be the nucleus for alternative phosphate recovery options. Excess and digested sewage sludge was sampled from full-scale MWTPs and analysed using x-ray diffraction (XRD), conventional scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), environmental SEM-EDX (eSEM-EDX) and Mössbauer spectroscopy. Vivianite was observed in all plants where iron was used for phosphate removal. In excess sludge before the anaerobic digestion, ferrous iron dominated the iron pool (≥50%) as shown by Mössbauer spectroscopy. XRD and Mössbauer spectroscopy showed no clear correlation between vivianite bound phosphate versus the iron content in excess sludge. In digested sludge, ferrous iron was the dominant iron form (>85%). Phosphate bound in vivianite increased with the iron content of the digested sludge but levelled off at high iron levels. 70-90% of all phosphate was bound in vivianite in the sludge with the highest iron content (molar Fe:P = 2.5). The quantification of vivianite was difficult and bears some uncertainty probably because of the presence of impure vivianite as indicated by SEM-EDX. eSEM-EDX indicates that the vivianite occurs as relatively small (20-100 µm) but free particles. We envisage very efficient phosphate recovery technologies that separate these particles based on their magnetic properties from the complex sludge matrix.


Assuntos
Compostos Ferrosos/química , Fosfatos/química , Esgotos/química , Eliminação de Resíduos Líquidos/métodos , Anaerobiose , Ferro/química , Microscopia Eletrônica de Varredura , Minerais/química , Fosfatos/análise , Espectrometria por Raios X , Espectroscopia de Mossbauer , Águas Residuárias/química , Difração de Raios X
15.
Nanotechnology ; 29(36): 365701, 2018 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-29894981

RESUMO

Magnetic nanoparticles (NPs) have attracted great attention owing to their applications in the biomedical field. In the present work, maghemite (γFe2O3) NPs of 6.5 nm were prepared using a sonochemical method and used to prepare magnetic beads through silanization with 3-aminopropyltrimethoxysilane (APTS). Subsequently, amino groups in the resulting APTS-γFe2O3 beads were converted to carboxylic acid (CARB-γFe2O3) through the succinic anhydride reaction, as confirmed by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy and dynamic light scattering (DLS) measurements. The size of these beads was measured as 12 nm and their hydrodynamic diameter as 490 nm, using TEM analysis and DLS, respectively. The CARB-γFe2O3 beads were further functionalized by immobilizing rabbit antibodies on their surfaces; the immobilization was confirmed by flow cytometry and ionic strength. The samples were further characterized by Mössbauer spectroscopy and DC magnetization measurements. Studies on magnetic relaxivities showed that magnetic beads present great potential for application in MR imaging.


Assuntos
Anticorpos/metabolismo , Compostos Férricos/síntese química , Microesferas , Animais , Ácidos Carboxílicos/química , Difusão Dinâmica da Luz , Compostos Férricos/química , Fluorescência , Imagem por Ressonância Magnética , Magnetismo , Nanopartículas/química , Nanopartículas/ultraestrutura , Tamanho da Partícula , Propilaminas/química , Coelhos , Silanos/química , Espectroscopia de Infravermelho com Transformada de Fourier , Espectroscopia de Mossbauer , Eletricidade Estática , Vibração , Difração de Raios X
16.
Water Res ; 141: 357-365, 2018 09 15.
Artigo em Inglês | MEDLINE | ID: mdl-29804022

RESUMO

Arsenic compounds are carcinogenic to humans and are typically removed from contaminated water using various sorbents. The ionic composition plays a significant role in arsenate removal efficiency during the process of water remediation. Here, we quantify the effects of natural ions (chlorides, nitrates, carbonates, sulfates, and phosphates) and humic acid on the removal of arsenates by ferrate(VI) at pH = 6.6. In the experiments, the initial concentration of arsenates was 10 mg L-1 (as As) and the concentrations of ions varied in the range from 5 to 100 mg L-1 of element in ionic form and humic acid. The achieved results show that only phosphate ions had principle influence on the efficiency of arsenate removal by ferrate(VI). The effect of phosphates was elucidated by applying transmission electron microscopy, energy-dispersive X-ray spectroscopy, and low temperature in-field 57Fe Mössbauer spectroscopy to solid samples, prepared under different weight ratios of ferrate(VI), arsenates, and phosphates. These results show three crucial effects of phosphates on the arsenate removal mechanisms. At low P:As weight ratio (up to 1:1), the incorporation of arsenate ions into the crystalline structure of γ-Fe2O3/γ-FeOOH nanoparticles was found to be suppressed by the presence of phosphates. Thus, arsenates were mainly adsorbed onto the surface of γ-Fe2O3/γ-FeOOH nanoparticles. Further increase in the P:As weight ratio (more than 1:1) resulted in the competition between arsenates and phosphates sorption. With the increased concentration of phosphate ions, the number of arsenates on the surface of γ-Fe2O3/γ-FeOOH nanoparticles was reduced. Finally, the complexation of iron(III) ions with phosphate ions occurred, leading to a decrease in the arsenates removal efficiency, which resulted from a lower content of precipitated γ-Fe2O3/γ-FeOOH nanoparticles. All these aspects need to be considered prior to application of ferrate(VI) for arsenates removal in real natural waters.


Assuntos
Arseniatos/química , Compostos Férricos/química , Substâncias Húmicas , Ferro/química , Fosfatos/química , Poluentes Químicos da Água/química , Adsorção , Carbonatos/química , Cloretos/química , Concentração de Íons de Hidrogênio , Nitratos/química , Espectroscopia de Mossbauer , Sulfatos/química , Purificação da Água/métodos
17.
Methods Enzymol ; 599: 197-226, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29746240

RESUMO

Iron-sulfur (Fe/S) proteins are involved in numerous key biological functions such as respiration, metabolic processes, protein translation, DNA synthesis, and DNA repair. The simplest types of Fe/S clusters include [2Fe-2S], [3Fe-4S], and [4Fe-4S] forms that sometimes are present in multiple copies. De novo assembly of Fe/S cofactors and their insertion into apoproteins in living cells requires complex proteinaceous machineries that are frequently highly conserved. In eukaryotes such as yeast and mammals, the mitochondrial iron-sulfur cluster assembly machinery and the cytosolic iron-sulfur protein assembly system consist of more than 30 components that cooperate in the generation of some 50 cellular Fe/S proteins. Both the mechanistic dissection of the intracellular Fe/S protein assembly pathways and the identification and characterization of Fe/S proteins rely on tool boxes of in vitro and in vivo methods. These cell biological, biochemical, and biophysical techniques help to determine the extent, stability, and type of bound Fe/S cluster. They also serve to distinguish bona fide Fe/S proteins from other metal-binding proteins containing similar cofactor coordination motifs. Here, we present a collection of in vitro methods that have proven useful for basic biochemical and biophysical characterization of Fe/S proteins. First, we describe the chemical assembly of [2Fe-2S] or [4Fe-4S] clusters on purified apoproteins. Then, we summarize a reconstitution system reproducing the de novo synthesis of a [2Fe-2S] cluster in mitochondria. Finally, we explain the use of UV-vis, CD, electron paramagnetic resonance, and Mössbauer spectroscopy for the routine characterization of Fe/S proteins.


Assuntos
Proteínas com Ferro-Enxofre/química , Animais , Dicroísmo Circular/métodos , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Humanos , Mitocôndrias/química , Espectrofotometria Ultravioleta/métodos , Espectroscopia de Mossbauer/métodos
18.
Methods Enzymol ; 599: 409-425, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29746248

RESUMO

For over 20 years, nuclear resonance vibrational spectroscopy (NRVS) has been used to study vibrational dynamics of iron-containing materials. With the only selection rule being iron motion, 57Fe NRVS has become an excellent tool to study iron-containing enzymes. Over the past decade, considerable progress has been made in the study of complex metalloenzymes using NRVS. Iron cofactors in heme-containing globins; [2Fe2S], [3Fe4S], [4Fe4S] proteins; the [NiFe] and [FeFe] hydrogenases; and nitrogenases have been explored in a fashion not possible through traditional vibrational spectroscopy. In this chapter, we discuss the basics of NRVS, a strategy to perform NRVS, and a discussion of the application of NRVS on rubredoxin and [FeFe] hydrogenase.


Assuntos
Proteínas com Ferro-Enxofre/química , Espectroscopia de Mossbauer/métodos , Proteínas Arqueais/química , Chlamydomonas reinhardtii/química , Hidrogenase/química , Modelos Moleculares , Oxirredução , Fótons , Proteínas de Plantas/química , Pyrococcus furiosus/química , Rubredoxinas/química , Software , Síncrotrons
19.
J Trace Elem Med Biol ; 48: 105-110, 2018 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-29773168

RESUMO

In the present paper, Mössbauer spectroscopic studies of dry biomass samples of the cyanobacterium Arthrospira platensis (formerly known as Spirulina platensis) were performed with regard to metabolic iron accumulation. 57Fe Mössbauer parameters of iron in the biomass correspond to ferrihydrite. Spectra of iron hydroxides in A. platensis biomass differ from those of iron complexes with ethylenediaminetetraacetic acid injected to Zarrouk culture medium. The limit of saturation of A. platensis trichomes with iron in the form of ferrihydrite was found to be 5 µg/ml (0.09 µmol/ml) Fe in the culture medium. Conglomerates precipitated in the medium at higher iron concentrations also contain ferrihydrite but the ratio of the crystal lattice forms is different from that in the biomass.


Assuntos
Compostos de Ferro/análise , Spirulina/química , Ácido Edético/administração & dosagem , Ácido Edético/análise , Ácido Edético/metabolismo , Compostos de Ferro/administração & dosagem , Compostos de Ferro/metabolismo , Espectroscopia de Mossbauer , Spirulina/metabolismo
20.
J Am Chem Soc ; 140(11): 3916-3928, 2018 03 21.
Artigo em Inglês | MEDLINE | ID: mdl-29463085

RESUMO

The reaction of [(PyNMe3)FeII(CF3SO3)2], 1, with excess peracetic acid at -40 °C generates a highly reactive intermediate, 2b(PAA), that has the fastest rate to date for oxidizing cyclohexane by a nonheme iron species. It exhibits an intense 490 nm chromophore associated with an S = 1/2 EPR signal having g-values at 2.07, 2.01, and 1.94. This species was shown to be in a fast equilibrium with a second S = 1/2 species, 2a(PAA), assigned to a low-spin acylperoxoiron(III) center. Unfortunately, contaminants accompanying the 2(PAA) samples prevented determination of the iron oxidation state by Mössbauer spectroscopy. Use of MeO-PyNMe3 (an electron-enriched version of PyNMe3) and cyclohexyl peroxycarboxylic acid as oxidant affords intermediate 3b(CPCA) with a Mössbauer isomer shift δ = -0.08 mm/s that indicates an iron(V) oxidation state. Analysis of the Mössbauer and EPR spectra, combined with DFT studies, demonstrates that the electronic ground state of 3b(CPCA) is best described as a quantum mechanical mixture of [(MeO-PyNMe3)FeV(O)(OC(O)R)]2+ (∼75%) with some FeIV(O)(•OC(O)R) and FeIII(OOC(O)R) character. DFT studies of 3b(CPCA) reveal that the unbound oxygen of the carboxylate ligand, O2, is only 2.04 Å away from the oxo group, O1, corresponding to a Wiberg bond order for the O1-O2 bond of 0.35. This unusual geometry facilitates reversible O1-O2 bond formation and cleavage and accounts for the high reactivity of the intermediate when compared to the rates of hydrogen atom transfer and oxygen atom transfer reactions of FeIII(OC(O)R) ferric acyl peroxides and FeIV(O) complexes. The interaction of O2 with O1 leads to a significant downshift of the Fe-O1 Raman frequency (815 cm-1) relative to the 903 cm-1 value predicted for the hypothetical [(MeO-PyNMe3)FeV(O)(NCMe)]3+ complex.


Assuntos
Compostos de Ferro/química , Oxigênio/química , Teoria Quântica , Espectroscopia de Ressonância de Spin Eletrônica , Conformação Molecular , Espectroscopia de Mossbauer
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