Investigations of intercalation in inorganic solids with layered structures: iron-57 mössbauer spectroscopy studies of size fractionated and iron-exchanged montmorillonite clays

⁵⁷Fe mössbauer spectroscopy has been used to examine some naturally occurring layer silicates in which cations located in exchange sites in the interlayer regions can be replaced by other species. The ⁵⁷Fe Mössbauer spectra recorded from differing size fractions of two types of non-exchanged and sodium-exchanged montmorillonite clays were found to be independent of the fraction size. The spectra have been interpreted in terms of the occupation by iron(III) of a heterogeneity of similar sites within the montmorillonite lattice. No justification has been obtained for computer analysis of the data in terms of more than one characterisable lattice site and no evidence has been found for the association of any iron oxyhydroxide impurity with the montmorillonite fractions.The ⁵⁷Fe Mössbauer parameters recorded from iron(III)-exchanged montmorillonite, in which iron(III) species are intercalated within the layers, show that the process is best performed at fairly low pH using low concentrations of iron(III). Failure to control such conditions can result in the formation of iron oxyhydroxides or hydrolysed iron(III) species. The preparation of iron(II)-exchanged montmorillonite was accompanied by partial oxidation of the iron(II) to iron(III).     

Unraveling Geometrical Site Confinement in Highly Efficient Iron‐Doped Electrocatalysts toward Oxygen Evolution Reaction

Introduction of iron in various catalytic systems has served a crucial function to significantly enhance the catalytic activity toward oxygen evolution reaction (OER), but the relationship between material properties and catalysis is still elusive. In this study, by regulating the distinctive geometric sites in spinel, Fe occupies the octahedral sites (Fe³⁺_(Oh)) and confines Co to the tetrahedral site (Co²⁺_(Td)), resulting in a strikingly high activity (η_{j = 10 mA cm}^?2 = 229 mV and η_{j = 100 mA cm}^?2 = 281 mV). Further enrichment of Fe ions would occupy the tetrahedral sites to decline the amount of Co²⁺_(Td) and deteriorate the OER activity. It is also found that similar tafel slope and peak frequency in Bode plot of electrochemical impedance spectroscopy indicate that Co²⁺_(Td) ions are primarily in charge of water oxidation catalytic center. By means of electrochemical techniques and in situ X‐ray absorption spectroscopy, it is proposed that Fe³⁺_(Oh) ions mainly confine cobalt ions to the tetrahedral site to restrain the multipath transfer of cobalt ions during the dynamic structural transformation between spinel and oxyhydroxide, continuously activating the catalytic behavior of Co²⁺_(Td) ions. This material‐related insight provides an indication for the design of highly efficient OER electrocatalysts.     

Characterization of biogenic iron oxides collected by the newly designed liquid culture method using diffusion chambers

We designed a new culture method for neutrophilic iron‐oxidizing bacteria using liquid medium (i) to study the formation and mineralogical characteristics of biogenic iron oxides (BIOS) and (ii) to apply BIOS to various scientific and engineering applications. An iron‐oxidizing bacterium, Mariprofundus ferrooxydans PV‐1^T (ATCC, BAA–1020), was cultured using a set of diffusion chambers to prepare a broad anoxic–oxic interface, upon which BIOS formation is typically observed in natural environments. Iron oxide precipitates were generated in parallel with bacterial growth. A scanning electron microscopy analysis indicated that the morphological features of the iron oxide precipitates in the medium (in vitro BIOS) were similar to those of BIOS collected from natural deep‐sea hydrothermal environments in the Northwest Eifuku Seamount field in the northern Mariana Arc (in situ BIOS). Further chemical speciation of both the in vitro and in situ BIOS was examined with X‐ray absorption fine structure (XAFS). A bulk XAFS analysis showed that the minerals in both BIOS were mainly ferrihydrite and oligomeric stages of amorphous iron oxyhydroxides with edge‐sharing octahedral linkages. The amount of in vitro BIOS produced with the diffusion‐chamber method was greater than those produced previously with other culture methods, such as gel‐stabilized gradient and batch liquid culture methods. The larger yields of BIOS produced with the new culture method will allow us to clarify in the future the mineralization mechanisms during bacterial growth and to examine the physicochemical properties of BIOS, such as their adsorption to and coprecipitation with various elements and substances.     

Effects of Iron and Manganese Plaques on Arsenic Uptake by Rice Seedlings (Oryza sativa L.) Grown in Solution Culture Supplied with Arsenate and Arsenite

We have shown previously that phosphorus nutrition and iron plaque on the surface of rice roots influence arsenate uptake and translocation by rice in hydroponic culture. We have now investigated the role of iron (Fe) and manganese (Mn) plaque on arsenate and arsenite uptake and translocation in rice seedlings grown hydroponically. Fe and Mn plaques were clearly visible as reddish or brown coatings on the root surface after 12 h induction, and Fe plaque was much more apparent than Mn plaque. Arsenite or arsenate supply did not decrease plant dry weights significantly. There were significant differences in shoot dry weights but little difference in root dry weights between some plaque treatments. Arsenic (As) concentrations in Fe plaque when arsenate was supplied were significantly higher than those in no plaque (control) and Mn plaque treatments, and much higher than those supplied with arsenite. This showed that Fe plaque on the rice root had higher affinity to arsenate than to arsenite. In Fe plaque treatment, the results indicated that most As was sequestered in roots when arsenite was supplied and most As concentrated in Fe plaque when arsenate was supplied. Most As was accumulated in rice roots in Mn plaque and no plaque treatments for both As species.     

Mutational and gene expression analysis of mtrDEF,omcA and mtrCAB during arsenate and iron reduction in Shewanella sp. ANA‐3

Arsenate respiration and Fe(III) reduction are important processes that influence the fate and transport of arsenic in the environment. The goal of this study was to investigate the impact of arsenate on Fe(III) reduction using arsenate and Fe(III) reduction deficient mutants of Shewanella sp. strain ANA‐3. Ferrihydrite reduction in the absence of arsenate was similar for an arsenate reduction mutant (arrA and arsC deletion strain of ANA‐3) compared with wild‐type ANA‐3. However, the presence of arsenate adsorbed onto ferrihydrite impeded Fe(III) reduction for the arsenate reduction mutant but not in the wild‐type. In an Fe(III) reduction mutant (mtrDEF, omcA, mtrCAB null mutant of ANA‐3), arsenate was reduced similarly to wild‐type ANA‐3 indicating the Fe(III) reduction pathway is not required for ferrihydrite‐associated arsenate reduction. Expression analysis of the mtr/omc gene cluster of ANA‐3 showed that omcA and mtrCAB were expressed under soluble Fe(III), ferrihydrite and arsenate growth conditions and not in aerobically grown cells. Expression of arrA was greater with ferrihydrite pre‐adsorbed with arsenate relative to ferrihydrite only. Lastly, arrA and mtrA were simultaneously induced in cells shifted to anaerobic conditions and exposed to soluble Fe(III) and arsenate. These observations suggest that, unlike Fe(III), arsenate can co‐induce operons (arr and mtr) implicated in arsenic mobilization.     

The influence of iron content on the biofouling resistance of 90/10 copper‐nickel alloys

A series of 90/10 cupronickel alloys containing iron at levels between 0% and 5% were immersed in the sea in Chichester Harbour. Samples were retrieved over a 14‐month period and subjected to scanning electron microscopy, energy dispersive X‐ray analysis and X‐ray photoelectron spectroscopy. The alloy with no iron corroded very rapidly and showed little, if any, colonisation. The 0·5% Fe and 1·5% Fe alloys developed microfouling communities dominated by the diatom Amphora, while the 2·5% and 5% Fe‐containing materials showed not only diatoms but also macro‐fouling in the form of barnacle settlement. However, the very loosely adherent nature of the iron and nickel‐rich corrosion products of these high iron alloys resulted in very poor tenacity of adhesion by the macrofouling. However, thick films of diatoms of lower copper tolerance became well established on the iron‐rich alloys. The alternative anti‐fouling mechanisms of the 90/10 copper‐nickels are discussed.     

Preliminary characterization and biological reduction of putative biogenic iron oxides (BIOS) from the Tonga-Kermadec Arc, southwest Pacific Ocean

Sediment samples were obtained from areas of diffuse hydrothermal venting along the seabed in the Tonga sector of the Tonga‐Kermadec Arc, southwest Pacific Ocean. Sediments from Volcano 1 and Volcano 19 were analyzed by X‐ray diffraction (XRD) and found to be composed primarily of the iron oxyhydroxide mineral, two‐line ferrihydrite. XRD also suggested the possible presence of minor amounts of more ordered iron (hydr)oxides (including six‐line ferrihydrite, goethite/lepidocrocite and magnetite) in the biogenic iron oxides (BIOS) from Volcano 1; however, Mössbauer spectroscopy failed to detect any mineral phases more crystalline than two‐line ferrihydrite. The minerals were precipitated on the surfaces of abundant filamentous microbial structures. Morphologically, some of these structures were similar in appearance to the known iron‐oxidizing genus Mariprofundus spp., suggesting that the sediments are composed of biogenic iron oxides. At Volcano 19, an areally extensive, active vent field, the microbial cells appeared to be responsible for the formation of cohesive chimney‐like structures of iron oxyhydroxide, 2–3 m in height, whereas at Volcano 1, an older vent field, no chimney‐like structures were apparent. Iron reduction of the sediment material (i.e. BIOS) by Shewanella putrefaciens CN32 was measured, in vitro, as the ratio of [total Fe(II)]:[total Fe]. From this parameter, reduction rates were calculated for Volcano 1 BIOS (0.0521 day^?1), Volcano 19 BIOS (0.0473 day^?1), and hydrous ferric oxide, a synthetic two‐line ferrihydrite (0.0224 day^?1). Sediments from both BIOS sites were more easily reduced than synthetic ferrihydrite, which suggests that the decrease in effective surface area of the minerals within the sediments (due to the presence of the organic component) does not inhibit subsequent microbial reduction. These results indicate that natural, marine BIOS are easily reduced in the presence of dissimilatory iron‐reducing bacteria, and that the use of common synthetic iron minerals to model their reduction may lead to a significant underestimation of their biological reactivity.     

Plasmid-determined resistance to arsenic and antimony inPseudomonas aeruginosa

Resistance to arsenic salts in aPseudomonas aeruginosa clinical isolate was shown to be determined by a 100 kb transferable plasmid. The resistance pattern included arsenate, arsenite, and antimonate ions. Arsenate and arsenite resistances were inducible by previous exposure of cultures to subinhibitory amounts of either of the two ions. Phosphate ions protectedP. aeruginosa cells from the toxic effects of arsenate but did not alter arsenite toxicity.     

Morphology of biogenic iron oxides records microbial physiology and environmental conditions: toward interpreting iron microfossils

Despite the abundance of Fe and its significance in Earth history, there are no established robust biosignatures for Fe(II)‐oxidizing micro‐organisms. This limits our ability to piece together the history of Fe biogeochemical cycling and, in particular, to determine whether Fe(II)‐oxidizers played a role in depositing ancient iron formations. A promising candidate for Fe(II)‐oxidizer biosignatures is the distinctive morphology and texture of extracellular Fe(III)‐oxyhydroxide stalks produced by mat‐forming microaerophilic Fe(II)‐oxidizing micro‐organisms. To establish the stalk morphology as a biosignature, morphologic parameters must be quantified and linked to the microaerophilic Fe(II)‐oxidizing metabolism and environmental conditions. Toward this end, we studied an extant model organism, the marine stalk‐forming Fe(II)‐oxidizing bacterium, Mariprofundus ferrooxydans PV‐1. We grew cultures in flat glass microslide chambers, with FeS substrate, creating opposing oxygen/Fe(II) concentration gradients. We used solid‐state voltammetric microelectrodes to measure chemical gradients in situ while using light microscopy to image microbial growth, motility, and mineral formation. In low‐oxygen (2.7–28 μm ) zones of redox gradients, the bacteria converge into a narrow (100 μm–1 mm) growth band. As cells oxidize Fe(II), they deposit Fe(III)‐oxyhydroxide stalks in this band; the stalks orient directionally, elongating toward higher oxygen concentrations. M. ferrooxydans stalks display a narrow range of widths and uniquely biogenic branching patterns, which result from cell division. Together with filament composition, these features (width, branching, and directional orientation) form a physical record unique to microaerophilic Fe(II)‐oxidizer physiology; therefore, stalk morphology is a biosignature, as well as an indicator of local oxygen concentration at the time of formation. Observations of filamentous Fe(III)‐oxyhydroxide microfossils from a ~170 Ma marine Fe‐Si hydrothermal deposit show that these morphological characteristics can be preserved in the microfossil record. This study demonstrates the potential of morphological biosignatures to reveal microbiology and environmental chemistry associated with geologic iron formation depositional processes.     

A novel pathway of arsenate detoxification

Microorganisms have evolved various mechanisms to detoxify arsenic, an ubiquitous environmental toxin. Known mechanisms include arsenite efflux, arsenate reduction followed by arsenite efflux and arsenite methylation. In this issue, Chen et al. describe a novel mechanism for arsenate detoxification via synergistic interaction of glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) and a major facilitator superfamily protein (ArsJ). They propose that GAPDH catalyzes the formation of 1‐arseno‐3‐phosphoglycerate, which is then extruded out of the cell by ArsJ. The significance of this pathway and questions for further research are discussed.     

The effect of arsenate and arsenite on photosynthesis in Scenedesmus obliquus. A Potentiometric study in a closed CO2-system

Abstract

A Potentiometric titration method was used to study the adverse effect of arsenate (As(V)) and arsenite (As(III)) on inorganic carbon uptake in suspensions of the green alga Scenedesmus obliquus. The measurements were performed in a closed CO₂-system with diluted synthetic seawater (1‰ salinity) as ionic medium. Usually, the algal chlorophyll concentration was 0.4 mg dm^?3, while the arsenate- and arsenite-concentrations were varied within the limits 0.1 to 200 μmol dm^?3. In some experiments arsenate toxicity was studied in the presence of 1 to 100 μmol dm^?3 of phosphate (P(V)).

With concentrations of arsenate or arsenite less than 0.1 μmol dm^?3 no toxic effects were observed. However, at As-concentrations of 200 μmol dm^?3, the algal carbon uptake was reduced by 41% with arsenate and 29% with arsenite, i.e., arsenate is more toxic to Scenedesmus obliquus than arsenite. The toxicity of arsenate was negligible in the presence of a ten fold excess of phosphate. This is probably due to chemical similarities between arsenate and phosphate causing competition between the ions for the binding sites.

The importance of taking the speciation as well as the buffer capacity of the algal system into account, when calculating the carbon uptake, is also discussed.     

Partitioning of taxifolin-iron ions complexes in octanol-water system

The composition of taxifolin-iron ions complexes in an octanol-water biphasic system was studied using the method of absorption spectrophotometry. It was found that at pH 5.0 in an aqueous biphasic system the complex of [Tf · Fe₂(OH) _k (H₂O)_{8 ? k} ] is present, but at pH 7.0 and 9.0 the complexes of [Tf₂ · Fe(OH) _k (H₂O)_{2 ? k} ] and [Tf · Fe(OH) _k (H₂O)_{4 ? k} ] are predominantly observed. The formation of a stable [Tf₃ · Fe] complex occurred in octanol phase. The charged iron ion of this complex is surrounded by taxifolin molecules, which shield the iron ion from lipophilic solvent. During transition from water to octanol phase the changes of the composition of complexes are accompanied by reciprocal changes in portion of taxifolin and iron ions in these phases. It was shown that the portion of taxifolin in aqueous solution in the presence of iron ions is increased at high pH values, and the portion of iron ions is minimal at pH 7.0. In addition, the parameters of solubility limits of taxifoliniron ions complexes in an aqueous solution were determined. The data obtained gain a better understanding of the role of complexation of polyphenol with metal of variable valency in passive transport of flavonoids and metal ions across lipid membranes.     

Linking microbial oxidation of arsenic with detection and phylogenetic analysis of arsenite oxidase genes in diverse geothermal environments

The identification and characterization of genes involved in the microbial oxidation of arsenite will contribute to our understanding of factors controlling As cycling in natural systems. Towards this goal, we recently characterized the widespread occurrence of aerobic arsenite oxidase genes (aroA‐like) from pure‐culture bacterial isolates, soils, sediments and geothermal mats, but were unable to detect these genes in all geothermal systems where we have observed microbial arsenite oxidation. Consequently, the objectives of the current study were to measure arsenite‐oxidation rates in geochemically diverse thermal habitats in Yellowstone National Park (YNP) ranging in pH from 2.6 to 8, and to identify corresponding 16S rRNA and aroA genotypes associated with these arsenite‐oxidizing environments. Geochemical analyses, including measurement of arsenite‐oxidation rates within geothermal outflow channels, were combined with 16S rRNA gene and aroA functional gene analysis using newly designed primers to capture previously undescribed aroA‐like arsenite oxidase gene diversity. The majority of bacterial 16S rRNA gene sequences found in acidic (pH 2.6–3.6) Fe‐oxyhydroxide microbial mats were closely related to Hydrogenobaculum spp. (members of the bacterial order Aquificales), while the predominant sequences from near‐neutral (pH 6.2–8) springs were affiliated with other Aquificales including Sulfurihydrogenibium spp., Thermocrinis spp. and Hydrogenobacter spp., as well as members of the Deinococci, Thermodesulfobacteria and β‐Proteobacteria. Modified primers designed around previously characterized and newly identified aroA‐like genes successfully amplified new lineages of aroA‐like genes associated with members of the Aquificales across all geothermal systems examined. The expression of Aquificales aroA‐like genes was also confirmed in situ, and the resultant cDNA sequences were consistent with aroA genotypes identified in the same environments. The aroA sequences identified in the current study expand the phylogenetic distribution of known Mo‐pterin arsenite oxidase genes, and suggest the importance of three prominent genera of the order Aquificales in arsenite oxidation across geochemically distinct geothermal habitats ranging in pH from 2.6 to 8.     

Remodulation of central carbon metabolic pathway in response to arsenite exposure in Rhodococcus sp. strain NAU‐1

Arsenite‐tolerant bacteria were isolated from an organic farm of Navsari Agricultural University (NAU), Gujarat, India (Latitude: 20°55′39.04″N; Longitude: 72°54′6.34″E). One of the isolates, NAU‐1 (aerobic, Gram‐positive, non‐motile, coccobacilli), was hyper‐tolerant to arsenite (As^III, 23 mM) and arsenate (As^V, 180 mM). 16S rRNA gene of NAU‐1 was 99% similar to the 16S rRNA genes of Rhodococcus (Accession No. HQ659188). Assays confirmed the presence of membrane bound arsenite oxidase and cytoplasmic arsenate reductase in NAU‐1. Genes for arsenite transporters (arsB and ACR3(1)) and arsenite oxidase gene (aoxB) were confirmed by PCR. Arsenite oxidation and arsenite efflux genes help the bacteria to tolerate arsenite. Specific activities of antioxidant enzymes (catalase, ascorbate peroxidase, superoxide dismutase and glutathione S‐transferase) increased in dose‐dependent manner with arsenite, whereas glutathione reductase activity decreased with increase in As^III concentration. Metabolic studies revealed that Rhodococcus NAU‐1 produces excess of gluconic and succinic acids, and also activities of glucose dehydrogenase, phosphoenol pyruvate carboxylase and isocitrate lyase were increased, to cope with the inhibited activities of glucose‐6‐phosphate dehydrogenase, pyruvate dehydrogenase and α‐ketoglutarate dehydrogenase enzymes respectively, in the presence of As^III. Enzyme assays revealed the increase in direct oxidative and glyoxylate pathway in Rhodococcus NAU‐1 in the presence of As^III.     

Characterization of As efflux from the roots of As hyperaccumulator <Emphasis Type="Italic">Pteris vittata</Emphasis> L.

In some plant species, various arsenic (As) species have been reported to efflux from the roots. However, the details of As efflux by the As hyperaccumulator Pteris vittata remain unknown. In this study, root As efflux was investigated for different phosphorus (P) supply conditions during or after a 24-h arsenate uptake experiment under hydroponic growth conditions. During an 8-h arsenate uptake experiment, P-supplied (P+) P. vittata exhibited much greater arsenite efflux relative to arsenate uptake when compared with P-deprived (P–) P. vittata, indicating that arsenite efflux was not proportional to arsenate uptake. In the As efflux experiment following 24 h of arsenate uptake, arsenate efflux was also observed with arsenite efflux in the external solution. All the results showed relatively low rates of arsenate efflux, ranging from 5.4 to 16.1% of the previously absorbed As, indicating that a low rate of arsenate efflux to the external solution is also a characteristic of P. vittata, as was reported with arsenite efflux. In conclusion, after 24 h of arsenate uptake, both P+ and P– P. vittata loaded/effluxed similar amounts of arsenite to the fronds and the external solution, indicating a similar process of xylem loading and efflux for arsenite, with the order of the arsenite concentrations being solution ≪ roots ≪ fronds.     

Dominance of ‘Gallionella capsiferriformans’ and heavy metal association with Gallionella‐like stalks in metal‐rich pH 6 mine water discharge

Heavy metal‐contaminated, pH 6 mine water discharge created new streams and iron‐rich terraces at a creek bank in a former uranium‐mining area near Ronneburg, Germany. The transition from microoxic groundwater with ~5 mm Fe(II) to oxic surface water may provide a suitable habitat for microaerobic iron‐oxidizing bacteria (FeOB). In this study, we investigated the potential contribution of these FeOB to iron oxidation and metal retention in this high‐metal environment. We (i) identified and quantified FeOB in water and sediment at the outflow, terraces, and creek, (ii) studied the composition of biogenic iron oxides (Gallionella‐like twisted stalks) with scanning and transmission electron microscopy (SEM, TEM) as well as confocal laser scanning microscopy (CLSM), and (iii) examined the metal distribution in sediments. Using quantitative PCR, a very high abundance of FeOB was demonstrated at all sites over a 6‐month study period. Gallionella spp. clearly dominated the communities, accounting for up to 88% of Bacteria, with a minor contribution of other FeOB such as Sideroxydans spp. and ‘Ferrovum myxofaciens’. Classical 16S rRNA gene cloning showed that 96% of the Gallionella‐related sequences had ≥97% identity to the putatively metal‐tolerant ‘Gallionella capsiferriformans ES‐2’, in addition to known stalk formers such as Gallionella ferruginea and Gallionellaceae strain R‐1. Twisted stalks from glass slides incubated in water and sediment were composed of the Fe(III) oxyhydroxide ferrihydrite, as well as polysaccharides. SEM and scanning TEM‐energy‐dispersive X‐ray spectroscopy revealed that stalk material contained Cu and Sn, demonstrating the association of heavy metals with biogenic iron oxides and the potential for metal retention by these stalks. Sequential extraction of sediments suggested that Cu (52–61% of total sediment Cu) and other heavy metals were primarily bound to the iron oxide fractions. These results show the importance of ‘G. capsiferriformans’ and biogenic iron oxides in slightly acidic but highly metal‐contaminated freshwater environments.     

The metabolic acclimation of Arabidopsis thaliana to arsenate is sensitized by the loss of mitochondrial LIPOAMIDE DEHYDROGENASE2, a key enzyme in oxidative metabolism

Mitochondrial lipoamide dehydrogenase is essential for the activity of four mitochondrial enzyme complexes central to oxidative metabolism. The reduction in protein amount and enzyme activity caused by disruption of mitochondrial LIPOAMIDE DEHYDROGENASE2 enhanced the arsenic sensitivity of Arabidopsis thaliana. Both arsenate and arsenite inhibited root elongation, decreased seedling size and increased anthocyanin production more profoundly in knockout mutants than in wild‐type seedlings. Arsenate also stimulated lateral root formation in the mutants. The activity of lipoamide dehydrogenase in isolated mitochondria was sensitive to arsenite, but not arsenate, indicating that arsenite could be the mediator of the observed phenotypes. Steady‐state metabolite abundances were only mildly affected by mutation of mitochondrial LIPOAMIDE DEHYDROGENASE2. In contrast, arsenate induced the remodelling of metabolite pools associated with oxidative metabolism in wild‐type seedlings, an effect that was enhanced in the mutant, especially around the enzyme complexes containing mitochondrial lipoamide dehydrogenase. These results indicate that mitochondrial lipoamide dehydrogenase is an important protein for determining the sensitivity of oxidative metabolism to arsenate in Arabidopsis.     

In Vitro Cytotoxic Activities,DNA‐, and BSA‐Binding Studies of a New Dinuclear Copper(II) Complex with N‐[3‐(Dimethylamino)propyl]‐N′‐(2‐carboxylatophenyl)‐ Oxamide as Ligand

A new dinuclear copper(II) complex bridged by N‐[3‐(dimethylamino)propyl]‐N′‐ (2‐carbo‐xylatophenyl)oxamide (H₃dmapob), and endcapped with 2,2′‐diamino‐4,4′‐bithiazole (dabt), namely [Cu₂(dmapob)(dabt)(CH₃OH)(pic)]·(DMF)_0.75·(CH₃OH)_0.25 has been synthesized and characterized by elemental analysis, molar conductivity measurement, infrared and electronic spectra studies, and single‐crystal X‐ray diffraction. In the crystal structure, both copper(II) ions have square–pyramidal coordination geometries. The Cu···Cu separation through the oxamido bridge is 5.176(9) Å. A two‐dimensional supramolecular framework is formed through hydrogen bonds and π–π stacking interactions. The reactivities toward herring sperm DNA and bovine serum albumin (BSA) show that the complex can interact with the DNA via intercalation mode and bind to the BSA responsible for quenching of tryptophan fluorescence by the static quenching mechanism. The in vitro anticancer activities suggest that the copper(II) complex is active against the selected tumor cell lines. The influence of different bridging ligands in dinuclear complexes on the DNA‐ and BSA‐binding properties as well as anticancer activities is preliminarily discussed.     

Mineral evolution and processes of ferruginous microbialite accretion – an example from the Middle Eocene stromatolitic and ooidal ironstones of the Bahariya Depression,Western Desert,Egypt

Peritidal ferruginous microbialites form the main bulk of the Middle Eocene ironstone deposits of the Bahariya Depression, Western Desert, Egypt. They include ferruginous stromatolites and microbially coated grains (ferruginous oncoids and ooids). Their internal structures reveal repeated cycles of microbial and Fe oxyhydroxide laminae. The microbial laminae consist of fossilised neutrophilic filamentous iron‐oxidising bacteria. These bacteria oxidised the Fe(II)‐rich acidic groundwater upon meeting the marine water at an approximately neutral pH. The iron oxyhydroxide laminae were initially precipitated as amorphous iron oxhydroxides and subsequently recrystallised into nanocrystalline goethite during early diagenesis. Organic remains such as proteinaceous compounds, lipids, carbohydrates and carotenoids are preserved and can be identified by Raman spectroscopy. The ferruginous microbialites were subjected to post‐depositional subaerial weathering associated with sea‐level retreat and subsurface alteration by continued ascent of the Fe(II)‐rich acidic groundwater. At this stage, another iron‐oxidising bacterial generation prevailed in the acidic environment. The acidity of the groundwater was caused by oxidation of pyrite in the underlying Cenomanian Bahariya formation. The positive iron isotopic ratios and presence of ferrous and ferric iron sulphates may result from partial iron oxidation along the redox boundary in an oxygen‐depleted environment.     

Phylogenetic and phenotypic analyses of arsenic-reducing bacteria isolated from an old tin mine area in Thailand

An agar plate screening assay was used to determine whether 100 arsenic-resistant bacterial isolates, previously obtained from arsenic-contaminated soils, had the ability to transform arsenite and arsenate. Ninety-five percent of the isolates were capable of reducing arsenate on agar plates. The isolates also grew in the presence of high concentrations of arsenite, but none of the bacterial isolates oxidized arsenite to arsenate under the growth conditions tested. About 14 % (13 of 95) of the tested isolates transformed high levels of arsenate (33–70 μM) when tested using the molybdenum blue method. Partial sequence analysis of 16S rDNA genes indicated that the isolates belonged to two broad taxonomic groups: Firmicutes and Proteobacteria. Ten isolates were assigned to four species in the genus Bacillus, and three isolates belonged to two species in the genera Enterobacter and Ochrobactrum. Taken together these results indicate that phylogenetically diverse bacteria isolated from arsenic-contaminated soils in an old tin mine area in Thailand have the ability to transform arsenate to arsenite.