RESUMO
For the ubiquitous diazotrophic rhizobacterium Azospirillum brasilense, which has been attracting the attention of researchers worldwide for the last 35 years owing to its significant agrobiotechnological and phytostimulating potential, the data on iron acquisition and its chemical speciation in cells are scarce. In this work, for the first time for azospirilla, low-temperature (at 80 K, 5 K, as well as at 2 K without and with an external magnetic field of 5 T) transmission Mössbauer spectroscopic studies were performed for lyophilised biomass of A. brasilense (wild-type strain Sp7 grown with (57)Fe(III) nitrilotriacetate complex as the sole source of iron) to enable quantitative chemical speciation analysis of the intracellular iron. In the Mössbauer spectrum at 80 K, a broadened quadrupole doublet of high-spin iron(III) was observed with a few percent of a high-spin iron(II) contribution. In the spectrum measured at 5 K, a dominant magnetically split component appeared with the parameters typical of ferritin species from other bacteria, together with a quadrupole doublet of a superparamagnetic iron(III) component and a similarly small contribution from the high-spin iron(II) component. The Mössbauer spectra recorded at 2 K (with or without a 5 T external field) confirmed the assignment of ferritin species. About 20% of total Fe in the dry cells of A. brasilense strain Sp7 were present in iron(III) forms superparamagnetic at both 5 and 2 K, i.e. either different from ferritin cores or as ferritin components with very small particle sizes.
Assuntos
Azospirillum brasilense/metabolismo , Ferritinas/metabolismo , Ferro/metabolismo , Espectroscopia de Mossbauer/métodos , Azospirillum brasilense/química , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Ferritinas/química , Liofilização , Ferro/química , Fenômenos Magnéticos , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Two all-ferrous, edge-bridged 8Fe-8S clusters, one capped with carbenes (2) and the other with phosphenes (3), have been characterized by (57)Fe Mossbauer spectroscopy. The clusters have diamagnetic ground states that yield spectra consisting of one quadrupole doublet with a large splitting (25% of absorption) and one (3) or two (2) doublets with much smaller splittings (75% of absorption). These patterns closely resemble those observed for all-ferrous 4Fe-4S clusters. Structurally, the 4Fe-4S fragments of 2 and 3 are remarkably similar to all-ferrous 4Fe-4S clusters, sharing with them the characteristic 3:1 pattern of the iron sites, a differentiation that has been shown previously to reflect spontaneous distortions of the cluster core. These spectroscopic and geometric similarities suggest that the diamagnetic ground state of the 8Fe-8S cluster results from antiferromagnetic exchange coupling of two identical 4Fe-4S modules, each carrying spin S(4Fe) = 4. The iron atoms with the largest quadrupole splittings are located at the opposite ends of the body diagonal containing the bridging sulfides.
Assuntos
Espectroscopia de Ressonância de Spin Eletrônica/métodos , Compostos Ferrosos/química , Proteínas Ferro-Enxofre/química , Ferro/química , Espectroscopia de Mossbauer/métodos , Sítios de Ligação , Dicroísmo Circular/métodos , Dissulfetos/química , Magnetismo , Modelos Químicos , Espectrofotometria Ultravioleta/métodos , Análise Espectral , Análise Espectral Raman , Sulfetos/química , TermodinâmicaRESUMO
We report the synthesis and spectroscopic/electrochemical properties of iron(II) complexes of polydentate Schiff bases generated from 2-acetylpyridine and 1,3-diaminopropane, acetylpyrazine and 1,3-diaminopropane, and from 2-acetylpyridine and L-histidine. The complexes exhibit bis(diimine)-iron(II) chromophores in association with pyrazine, pyridine or imidazole groups displaying contrasting pi-acceptor properties. In spite of their open geometry, their properties are much closer to those of macrocyclic tetraimineiron(II) complexes. An electrochemical/spectroscopic correlation between E degrees (FeIII/II) and the energies of the lowest MLCT band has been observed, reflecting the stabilization of the HOMO levels as a consequence of the increasing backbonding effects in the series of compounds. Mössbauer data have also confirmed the similarities in their electronic structure, as deduced from the spectroscopic and theoretical data.
Assuntos
Eletroquímica/métodos , Imidazóis/química , Ferro/química , Pirazinas/química , Piridinas/química , Bases de Schiff/análise , Espectrofotometria/métodos , Histidina/química , Espectroscopia de Ressonância Magnética , Modelos Químicos , Modelos Moleculares , Conformação Molecular , Bases de Schiff/química , Solventes/química , Espectrofotometria Infravermelho/métodos , Espectroscopia de Mossbauer/métodosRESUMO
A new series of substituted diiron(II) complexes [Fe(2)(tidf)(L)(2)(MeOH)(2)](n+) (tidf=a two compartment tetraiminediphenolate macrocycle; n=0 or 2+; L=NCS(-), CN(-), N(3)(-), pyrazine (pz), 4-cyanopyridine (4-cnpy) and 4-mercaptopyridine (4-shpy)) and one tetranuclear complex, {[Fe(2)(tidf)(CH(3)OH)(2)](2)(mu-4-cnpy)(2)}(ClO(4))(4) were isolated and characterized by elemental analysis, conductivity measurements, Mössbauer and FTIR.
Assuntos
Compostos Ferrosos/química , Compostos Macrocíclicos/química , Espectroscopia de Mossbauer/métodos , Condutividade Elétrica , Espectrofotometria InfravermelhoRESUMO
In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface.
Assuntos
Ligas/química , Cobalto/química , Hidrogênio/química , Ferro/química , Membranas Artificiais , Silício/química , Eletroquímica , Magnetismo , Tamanho da Partícula , Sensibilidade e Especificidade , Espectrofotometria/métodos , Espectroscopia de Mossbauer/métodos , Propriedades de Superfície , Difração de Raios X , Raios XRESUMO
In the present paper, the adsorption of amino acids (Ala, Met, Gln, Cys, Asp, Lys, His) on clays (bentonite, kaolinite) was studied at different pH (3.00, 6.00, 8.00). The amino acids were dissolved in seawater, which contains the major elements. There were two main findings in this study. First, amino acids with a charged R group (Asp, Lys, His) and Cys were adsorbed on clays more than Ala, Met and Gln (uncharged R groups). However, 74% of the amino acids in the proteins of modern organisms have uncharged R groups. These results raise some questions about the role of minerals in providing a prebiotic concentration mechanism for amino acids. Several mechanisms are also discussed that could produce peptide with a greater proportion of amino acids with uncharged R groups. Second, Cys could play an important role in prebiotic chemistry besides participating in the structure of peptides/proteins. The FT-IR spectra showed that the adsorption of amino acids on the clays occurs through the amine group. However, the Cys/clay interaction occurs through the sulfhydryl and amine groups. X-ray diffractometry showed that pH affects the bentonite interlayer, and at pH 3.00 the expansion of Cys/bentonite was greater than that of the samples of ethylene glycol/bentonite saturated with Mg. The Mössbauer spectrum for the sample with absorbed Cys showed a large increase ( approximately 20%) in ferrous ions. This means that Cys was able to partially reduce iron present in bentonite. This result is similar to that which occurs with aconitase where the ferric ions are reduced to Fe 2.5.
Assuntos
Silicatos de Alumínio/química , Aminoácidos/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Espectroscopia de Mossbauer/métodos , Difração de Raios X/métodos , Adsorção , Bentonita/química , ArgilaRESUMO
Synthetic route and detailed characterization of the macrocyclic complex [Fe(II)(dohpn)(py)(CO)](ClO4) (dohpn = 2,3,9,10-tetramethyl-1,4,8,11-tetraazaundecane-1,3,8,10-tetraen-11-ol-1-olate and py = pyridine) based on analytical, spectrometric and spectroscopic methods are herein reported. The corresponding vibrational and electronic features are discussed and a consistent assignment is proposed on the basis of semi-empirical theoretical calculations.
Assuntos
Carbono/química , Química/métodos , Espectrofotometria/métodos , Espectroscopia de Mossbauer/métodos , Monóxido de Carbono/química , Espectroscopia de Ressonância de Spin Eletrônica/métodos , Ferro/química , Espectroscopia de Ressonância Magnética , Espectrometria de Massas , Modelos Químicos , Modelos Moleculares , Distribuição Normal , Oxirredução , Fenantrolinas/química , Raios UltravioletaRESUMO
The infrared (IR), Raman and 57Fe-Mössbauer spectra of SrFe2(P2O7)2, BaFe2(P2O7)2 and PbFe2(P2O7)2 were recorded and discussed on the basis of the structural peculiarities of the compounds.
Assuntos
Cátions/química , Difosfatos/química , Radioisótopos de Ferro/química , Ferro/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Espectroscopia de Mossbauer/métodos , Fosfatos/química , Espectrofotometria Infravermelho , Análise Espectral Raman , Temperatura , Difração de Raios XRESUMO
This paper presents a novel reading of ideas on temporal binding as a key for cognitive operations by means of fast (gamma band) phase synchrony. We advocate a view of binding of widely distributed cell assemblies transiently locked in a neural hypergraph which serves as a reference point to incorporate or interpret other less coherent concurrent neural events. The paper traces in some detail the empirical evidence concerning the gamma binding process and presents some implications for the constitution of a unified cognitive-mental space.