There are several green methods available to synthesize iron-based nanoparticles using different bio-based reducing agents. Although their useful properties in degradation of organic dyes, chlorinated organics, or arsenic have been described earlier, their characterization has been ambiguous, and further research is needed in this area. Synthesis and characterization details on iron-based nanoparticles produced by green tea extract are described in detail; characterization was carried out by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), and UV−vis spectrometry followed by ecotoxicological assay. XRD and TEM analyses revealed that iron forms amorphous nanosized particles with size depending on reaction time. Moreover, low-temperature Mossbauer spectroscopy confirmed progressive reduction of Fe 3+ to Fe 2+ during the reaction. Finally, the iron(II,III) nanoparticles prepared by green tea extract (GT−Fe nanoparticles) were found to have negative ecotoxicological impacts on important aquatic organisms such as cyanobacterium (Synechococcus nidulans), alga (Pseudokirchneriella subcapitata), and even invertebrate organisms (Daphnia magna). The EC 50 values are 6.1 ± 0.5 (72 h), 7.4 ± 1.6 (72 h), and 21.9 ± 4.3 (24 h) mg of Fe per L, respectively.

Methylobacterium extorquens AM1 is an aerobic facultative methylotroph known to secrete pyrroloquinoline quinone (PQQ), a cofactor of a number of bacterial dehydrogenases, into the culture medium. To elucidate the molecular mechanism of PQQ biosynthesis, we are focusing on PqqE which is believed to be the enzyme catalysing the first reaction of the pathway. PqqE belongs to the radical S-adenosyl-L-methionine (SAM) superfamily, in which most, if not all, enzymes are very sensitive to dissolved oxygen and rapidly inactivated under aerobic conditions. We here report that PqqE from M. extorquens AM1 is markedly oxygentolerant; it was efficiently expressed in Escherichia coli cells grown aerobically and affinity-purified to near homogeneity. The purified and reconstituted PqqE contained multiple (likely three) iron-sulphur clusters and showed the reductive SAM cleavage activity that was ascribed to the consensus 2+ cluster bound at the N-terminus region. Mo¨ssbauer spectrometric analyses of the as-purified and reconstituted enzymes revealed the presence of 2+ and [2Fe-2S] 2+clusters as the major forms with the former being predominant in the reconstituted enzyme. PqqE from M.extorquens AM1 may serve as a convenient tool for studying the molecular mechanism of PQQ biosynthesis, avoiding the necessity of establishing strictly anaerobic conditions.Keywords: Methylobacterium extorquens AM1/PQQ/ PqqE/radical SAM enzyme.Abbreviations: 5 0 dA, 5 0 -deoxyadenosine; HiPIPs, high-potential iron-sulphur proteins; IPTG, isopropyl--D-thiogalactopyranoside; PQQ, pyrroloquinoline quinone; SAM, S-adenosyl-L-methionine.Pyrroloquinoline quinone (PQQ) is an aromatic, tricyclic o-quinone that serves as a cofactor for a number of prokaryotic dehydrogenases, e.g. alcohol or glucose dehydrogenase (1, 2). The biosynthesis of PQQ is achieved in a series of reactions catalysed by enzymes encoded by genes located on pqq operon(s). The PQQ biosynthetic genes from several bacteria such as Acinetobacter calcoaceticus (3), Methylobacterium organophilum DSM 760 (4), Klebsiella pneumoniae (5), Pseudomonas fluorescens CHA0 (6) [reclassified as P.protegens CHA0 (7)], Methylobacterium extorquens AM1 (8), Enterobacter intermedium 60-2G (9) [reclassified as Kluyvera intermedia (10)] and Gluconobacter oxydans 621H (11) were reported and more than 125 bacterial species with PQQ biosynthetic capability were identified by bioinformatics analysis (12). Four to seven genes organized in operon(s) are responsible for PQQ biosynthesis in different bacteria (13). In K.pneumoniae, operon pqqABCDEF is involved in PQQ production. Among six genes, only pqqA, pqqC, pqqD and pqqE are exclusively required for PQQ production (14). Despite the fact that PQQ has been found decades ago, only little is known about its biosynthetic pathway. Although the putative function of each of the genes of pqq operon(s) has been proposed based on sequence analyses and homology modelling (15), the only biochemically confirmed function is that of pqqC, which encodes a protein catalysing o...

Two-step charge disproportionation mechanism of 3Fe(iv) to 2Fe(iii) and Fe(vi) via Fe(v) in ethanol.

PqqE is a radical S ‐adenosyl‐ l ‐methionine ( SAM ) enzyme that catalyzes the initial reaction of pyrroloquinoline quinone ( PQQ ) biosynthesis. PqqE belongs to the SPASM (subtilosin/ PQQ /anaerobic sulfatase/mycofactocin maturating enzymes) subfamily of the radical SAM superfamily and contains multiple Fe – S clusters. To characterize the Fe – S clusters in PqqE from Methylobacterium extorquens AM 1, Cys residues conserved in the N‐terminal signature motif ( CX 3 CX 2 C) and the C‐terminal seven‐cysteine motif ( CX 9–15 GX 4 CX n CX 2 CX 5 CX 3 CX n C; n = an unspecified number) were individually or simultaneously mutated into Ser. Biochemical and Mössbauer spectral analyses of as‐purified and reconstituted mutant enzymes confirmed the presence of three Fe – S clusters in PqqE: one [4Fe – 4S] 2+ cluster at the N‐terminal region that is essential for the reductive homolytic cleavage of SAM into methionine and 5′‐deoxyadenosyl radical, and one each [4Fe – 4S] 2+ and [2Fe – 2S] 2+ auxiliary clusters in the C‐terminal SPASM domain, which are assumed to serve for electron transfer between the buried active site and the protein surface. The presence of [2Fe – 2S] 2+ cluster is a novel finding for radical SAM enzyme belonging to the SPASM subfamily. Moreover, we found uncommon ligation of the auxiliary [4Fe – 4S] 2+ cluster with sulfur atoms of three Cys residues and a carboxyl oxygen atom of a conserved Asp residue.

No abstract

No abstract

This study presents an investigation of thermal decomposition of ferrous oxalate dihydrate in the combined atmosphere of inert and conversion gases to find an optimal route for a simple magnetite preparation. Homogenized precursor was isothermally treated inside the stainless-steel cells at 8 equidistant temperatures ranging from 300 to 650 °C for 1, 6, and 12 hours. The enclosure of samples inside the cells with the combined atmosphere eliminates the necessity of the inert gas to flow over the treated samples. Structural, magnetic, and morphological aspects of the prepared materials were examined by the combination of experimental techniques, such as Mössbauer spectroscopy, X-ray powder diffraction, and scanning electron microscopy.

Nickel ferrite NiFe 2 O 4 is a typical soft magnetic ferrite with high electrical resistivity used as high frequency magnetic material. Neodymium (Nd 3 þ ) doped NiFe 2 O 4 materials were fabricated using solid state reaction. The properties of the obtained material were investigated by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier-Transform Infrared Spectroscopy (FT-IR), magnetic measurements on SQUID and Mössbauer spectroscopy. It was found that the material consists of two different phases: Nd 3 þ doped NiFe 2 O 4 and NdFeO 3 . The Nd 3 þ ions occupy cation sites of the NiFe 2 O 4 inverse spinel structure. NdFeO 3 phase occurred when the level of Nd 3 þ atoms exceed a percolation limit. The presence of both phases was confirmed by SEM observations. The Mössbauer spectra analysis showed two sextets, which can be ascribed to iron atoms in tetrahedral and octahedral positions. From their intensities it is concluded that Nd 3 þ occupies octahedral sites in the spinel structure of NiFe 2 O 4 , which were originally occupied by Ni 2 þ .