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ABSTRACT: Luminescent quantum dots were synthesized using bacterially derived selenide (Se(II-)) as the precursor. Biogenic Se(II-) was produced by the reduction of Se(IV) by Veillonella atypica and compared directly against borohydride-reduced Se(IV) for the production of glutathione-stabilized CdSe and β-mercaptoethanol-stabilized ZnSe nanoparticles by aqueous synthesis. Biological Se(II-) formed smaller, narrower size distributed QDs under the same conditions. The growth kinetics of biologically sourced CdSe phases were slower. The proteins isolated from filter sterilized biogenic Se(II-) included a methylmalonyl-CoA decarboxylase previously characterized in the closely related Veillonella parvula. XAS analysis of the glutathione-capped CdSe at the S K-edge suggested that sulfur from the glutathione was structurally incorporated within the CdSe. A novel synchrotron based XAS technique was also developed to follow the nucleation of biological and inorganic selenide phases, and showed that biogenic Se(II-) is more stable and more resistant to beam-induced oxidative damage than its inorganic counterpart. The bacterial production of quantum dot precursors offers an alternative, 'green' synthesis technique that negates the requirement of expensive, toxic chemicals and suggests a possible link to the exploitation of selenium contaminated waste streams.
Nanotechnology 03/2013; 24(14):145603. · 3.98 Impact Factor
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J M Byrne, V S Coker,
S Moise,
P L Wincott,
D J Vaughan,
F Tuna,
E Arenholz,
G van der Laan,
R A D Pattrick,
J R Lloyd,
N D Telling
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ABSTRACT: Cobalt-doped magnetite (CoxFe3 -xO4) nanoparticles have been produced through the microbial reduction of cobalt-iron oxyhydroxide by the bacterium Geobacter sulfurreducens. The materials produced, as measured by superconducting quantum interference device magnetometry, X-ray magnetic circular dichroism, Mössbauer spectroscopy, etc., show dramatic increases in coercivity with increasing cobalt content without a major decrease in overall saturation magnetization. Structural and magnetization analyses reveal a reduction in particle size to less than 4 nm at the highest Co content, combined with an increase in the effective anisotropy of the magnetic nanoparticles. The potential use of these biogenic nanoparticles in aqueous suspensions for magnetic hyperthermia applications is demonstrated. Further analysis of the distribution of cations within the ferrite spinel indicates that the cobalt is predominantly incorporated in octahedral coordination, achieved by the substitution of Fe(2+) site with Co(2+), with up to 17 per cent Co substituted into tetrahedral sites.
Journal of The Royal Society Interface 01/2013; 10(83):20130134. · 4.40 Impact Factor
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ABSTRACT: A combination of scanning transmission X-ray microscopy and X-ray magnetic circular dichroism was used to spatially resolve the distribution of different carbon and iron species associated with Shewanella oneidensis MR-1 cells. S. oneidensis MR-1 couples the reduction of Fe(III)-oxyhydroxides to the oxidation of organic matter in order to conserve energy for growth. Several potential mechanisms may be used by S. oneidensis MR-1 to facilitate Fe(III)-reduction. These include direct contact between the cell and mineral surface, secretion of either exogenous electron shuttles or Fe-chelating agents and the production of conductive 'nanowires'. In this study, the protein/lipid signature of the bacterial cells was associated with areas of magnetite (Fe₃O₄), the product of dissimilatory Fe(III) reduction, which was oversaturated with Fe(II) (compared to stoichiometric magnetite). However, areas of the sample rich in polysaccharides, most likely associated with extracellular polymeric matrix and not in direct contact with the cell surface, were undersaturated with Fe(II), forming maghemite-like (γ-Fe₂O₃) phases compared to stoichiometric magnetite. The reduced form of magnetite will be much more effective in environmental remediation such as the immobilisation of toxic metals. These findings suggest a dominant role for surface contact-mediated electron transfer in this study and also the inhomogeneity of magnetite species on the submicron scale present in microbial reactions. This study also illustrates the applicability of this new synchrotron-based technique for high-resolution characterisation of the microbe-mineral interface, which is pivotal in controlling the chemistry of the Earth's critical zone.
Geobiology 04/2012; 10(4):347-54. · 4.11 Impact Factor
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ABSTRACT: The bioproduction of nanoscale magnetite by Fe(III)-reducing bacteria offers a potentially tunable, environmentally benign route to magnetic nanoparticle synthesis. Here, we demonstrate that it is possible to control the size of magnetite nanoparticles produced by Geobacter sulfurreducens by adjusting the total biomass introduced at the start of the process. The particles have a narrow size distribution and can be controlled within the range of 10-50 nm. X-ray diffraction analysis indicates that controlled production of a number of different biominerals is possible via this method including goethite, magnetite and siderite, but their formation is strongly dependent upon the rate of Fe(III) reduction and total concentration and rate of Fe(II) produced by the bacteria during the reduction process. Relative cation distributions within the structure of the nanoparticles have been investigated by x-ray magnetic circular dichroism and indicate the presence of a highly reduced surface layer which is not observed when magnetite is produced through abiotic methods. The enhanced Fe(II)-rich surface, combined with small particle size, has important environmental applications such as in the reductive bioremediation of organics, radionuclides and metals. In the case of Cr(VI), as a model high-valence toxic metal, optimized biogenic magnetite is able to reduce and sequester the toxic hexavalent chromium very efficiently to the less harmful trivalent form.
Nanotechnology 11/2011; 22(45):455709. · 3.98 Impact Factor
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ABSTRACT: The ability of microbial cells to synthesize highly reactive nanoscale functional materials provides the basis for a novel synthetic biology tool for developing the next generation of multifunctional industrial biocatalysts. Here, we demonstrate that aerobic cultures of Escherichia coli, genetically engineered to overproduce a recombinant monoamine oxidase possessing high enantioselectivity against chiral amines, can be augmented with nanoscale Pd(0) precipitated via bioreduction reactions. The result is a novel biometallic catalyst for the deracemization of racemic amines. This deracemization process is normally achieved by discrete sequential oxidation/reduction steps using a separate enantiomer-specific biocatalyst and metal catalyst, respectively. Here, use of E. coli cultures carrying the cloned monoamine oxidase gene and nanoscale bioreduced Pd(0) particles was used successfully for the conversion of racemic 1-methyltetrahydroisoquinoline (MTQ) to (R)-MTQ, via the intermediate 1-methyl-3,4-dihydroisoquinoline, with an enantiomeric excess of up to 96%. There was no loss of catalyst activity following the five rounds of oxidation and reduction, and importantly, there was minimal loss of palladium into the reaction supernatant. This first demonstration of a whole cell biometallic catalyst mixture for "single-pot", multistep reactions opens up the way for a wide range of integrated processes, offering a scalable and highly flexible platform technology.
Acs Catalysis. 01/2011; 1(11):1589-1594.
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L. E. Macaskie,
I. P. Mikheenko,
P. Yong,
K. Deplanche,
A. J. Murray,
M. Paterson-Beedle, V. S. Coker,
C. I. Pearce,
R. Cutting,
R. A. D. Pattrick,
D. Vaughan,
G. van der Laan,
J. R. Lloyd
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ABSTRACT: Over the past 30 years the literature has burgeoned with bioremediation approaches to heavy metal removal from wastes. The price of base and precious metals has also increased. With the resurgence of nuclear energy uranium has become a strategic resource. Other 'non-carbon energy' technologies are driven by the need to reduce CO(2) emissions. The 'New Biohydrometallurgy' we describe unites these drivers by the concept of conversion of wastes into new materials for environmental applications. The new materials, fashioned, bottom-up, into nanomaterials under biocontrol, can be termed 'Functional Bionanomaterials'. This new discipline, encompassing waste treatment along with nanocatalysis or other applications, can be summarized as 'Environmental Bionanotechnology'. Several case histories illustrate the scope and potential of this concept. (c) 2010 Elsevier By. All rights reserved.
Hydrometallurgy 01/2010; 104(3-4):483-487. · 2.03 Impact Factor
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Abstracts of Papers of the American Chemical Society. 01/2009; 237.
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Geochimica et Cosmochimica Acta 01/2009; 73(13):A786-A786. · 4.26 Impact Factor
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L. E. Macaskie,
I. P. Mikheenko,
P. Yong,
K. Deplanche,
A. J. Murray,
M. Paterson-Beedle, V. S. Coker,
C. I. Pearce,
R. A. D. Pattrick,
D. Vaughan,
G. van der Laan,
J. R. Lloyd
[show abstract]
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ABSTRACT: Over the past 30 years the literature has burgeoned with bioremediation approaches to heavy metal removal from wastes. The price of base and precious metals has dramatically increased. With the resurgence of nuclear energy uranium has become a strategic resource. Other 'non-carbon energy' technologies are driven by the need to reduce CO(2) emissions. The 'New Biohydrometallurgy' we describe unites these drivers by the concept of conversion of wastes into new materials for environmental applications. The new materials, fashioned, bottom-up, into nanomaterials under biocontrol, can be termed 'Functional Bionanomaterials'. This new discipline, encompassing waste treatment along with nanocatalysis or other applications, can be Summarized as 'Environmental Bionanotechnology'. Several case histories illustrate the scope and potential of this concept.
01/2009: pages 541-548;
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ABSTRACT: Biologically synthesized magnetite (Fe(3)O(4)) nanoparticles are studied using x-ray absorption and x-ray magnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, nontoxic form, such as a Cr(3+)-spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3249578]
Applied Physics Letters 01/2009; 95(16). · 3.84 Impact Factor
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J. R. Lloyd, V. S. Coker,
R. S. Cutting,
A. Geissler,
K. M. Handley,
G. T. W. Law,
F. R. Livens,
K. Morris,
R. A. D. Pattrick,
C. I. Pearce,
D. A. Polya,
D. J. Vaughan
Geochimica et Cosmochimica Acta 01/2009; 73(13):A785-A785. · 4.26 Impact Factor
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J R Lloyd,
C I Pearce, V S Coker,
R A D Pattrick,
G van der Laan,
R Cutting,
D J Vaughan,
M Paterson-Beedle,
I P Mikheenko,
P Yong,
L E Macaskie
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ABSTRACT: The microbial cell offers a highly efficient template for the formation of nanoparticles with interesting properties including high catalytic, magnetic and light-emitting activities. Thus biomineralization products are not only important in global biogeochemical cycles, but they also have considerable commercial potential, offering new methods for material synthesis that eliminate toxic organic solvents and minimize expensive high-temperature and pressure processing steps. In this review we describe a range of bacterial processes that can be harnessed to make precious metal catalysts from waste streams, ferrite spinels for biomedicine and catalysis, metal phosphates for environmental remediation and biomedical applications, and biogenic selenides for a range of optical devices. Recent molecular-scale studies have shown that the structure and properties of bionanominerals can be fine-tuned by subtle manipulations to the starting materials and to the genetic makeup of the cell. This review is dedicated to the late Terry Beveridge who contributed much to the field of biomineralization, and provided early models to rationalize the mechanisms of biomineral synthesis, including those of geological and commercial potential.
Geobiology 07/2008; 6(3):285-97. · 4.11 Impact Factor
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Geochimica et Cosmochimica Acta 01/2008; 72(12):A730-A730. · 4.26 Impact Factor
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ABSTRACT: The Fe(III)-reducing bacterium Geobacter sulfurreducens produces nanometer-sized magnetite by transferring electrons from organic matter or hydrogen to ferrihydrite, resulting in the reductive transformation of the ferrihydrite to magnetite, and the generation of ATP for growth. Electron transfer can occur by direct contact between the cell surface and the mineral or via a soluble "electron shuttle," for example a quinone-containing humic species. The minerals produced at different stages of ferrihydrite reduction during two experiments, one with and one without the humic analog anthraquinone-2, 6-disulphonate (AQDS), were measured using high-resolution synchrotron powder X-ray diffraction. Amorphous 2-line ferrihydrite converts to goethite, then to a mixture of goethite and magnetite, and finally to magnetite. Samples with and without AQDS showed the same general mineralogical trends, and the rate of reaction was faster in the presence of AQDS. In addition, two transient minerals structurally similar to goethite and magnetite were observed to form as intermediates between ferrihydrite and goethite and goethite and magnetite, but only in samples produced in the absence of the electron shuttle. These transient minerals were named proto-goethite and proto-magnetite. Proto-goethite has a shorter c-axis [4.467(20) angstrom] than crystalline goethite, a function of size (<2 nm) where quantum properties prevail. Proto-magnetite is identified by long tetrahedral (2.113 angstrom) and short octahedral (1.943 angstrom) Fe-O bonds compared to stoichiometric magnetite, possibly indicative of a coordination crossover caused by charge density [Fe(II)] migration to tetrahedral sites. Fe(II) in solution or sorbed to the mineral surface is considered to be the catalyst causing the mineral transformations. The Fe(II) is thought to form predominantly from the reductive dissolution of 2-line ferrihydrite by G. sulfurreducens.
American Mineralogist 01/2008; 93(4):540-547. · 2.17 Impact Factor
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Abstracts of Papers of the American Chemical Society. 01/2007; 233:462-462.
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ABSTRACT: Ferrite spinels, especially magnetite (Fe3O4), can be formed either by geological, biological or chemical processes leading to chemically similar phases that show different physical characteristics. We compare, for the first time, magnetite produced by these three different methods using X-ray magnetic circular dichroism (XMCD), a synchrotron radiation based technique able to determine the site occupancy of Fe cations in the ferrite spinels. Extracellular nanoscale magnetite produced by different Fe(Ill)reducing bacteria was shown to have different degrees of stoichiometry depending on the bacteria and the method of formation, but all were oxygen deficient due to formation under anoxic conditions. Intracellular nano-magnetite synthesized in the magnetosomes of magnetotactic bacteria was found to have a Fe cation site occupancy ratio most similar to stoichiometric magnetite, possibly due to the tight physiological controls exerted by the magnetosome membrane. Chemically-synthesised nano-magnetite and bulk magnetite produced as a result of geological processes were both found to be cation deficient with a composition between magnetite and maghemite (oxidised magnetite).
European Journal of Mineralogy 01/2007; 19(5):707-716. · 1.49 Impact Factor
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ABSTRACT: Poorly crystalline Fe(III) oxyhydroxides, ubiquitously distributed as mineral coatings and discrete particles in aquifer sediments, are well-known hosts of sedimentary As. Microbial reduction of these phases is widely thought to be responsible for the genesis of As-rich reducing groundwaters found in many parts of the world, most notably in Bangladesh and West Bengal, India. As such, it is important to understand the behavior of As associated with ferric oxyhydroxides during the early stages of Fe(lll) reduction. We have used X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) to elucidate the changes in the bonding mechanism of As(III) and As(V) as their host Fe(III) oxyhydroxide undergoes bacterially induced reductive transformation to magnetite. Two-line ferrihydrite, with adsorbed As(III) or As(V), was incubated under anaerobic conditions in the presence of acetate as an electron donor, and Geobacter sulfurreducens, a subsurface bacterium capable of respiring on Fe(lll), but not As(V). In both experiments, no increase in dissolved As was observed during reduction to magnetite (complete upon 5 days incubation), consistent with our earlier observation of As sequestration by the formation of biogenic Fe(III)-bearing minerals. XAS data suggested that the As bonding environment of the As(III)-magnetite product is indistinguishable from that obtained from simple adsorption of As(lll) on the surface of biogenic magnetite. In contrast, reduction of As(V)-sorbed ferrihydrite to magnetite caused incorporation of As5+ within the magnetite structure. XMCD analysis provided further evidence of structural partitioning of As5+ as the small size of the As5+ cation caused a distortion of the spinel structure compared to standard biogenic magnetite. These results may have implications regarding the species-dependent mobility of As undergoing anoxic biogeochemical transformations, e.g., during early sedimentary diagenesis.
Environmental Science and Technology 01/2007; 40(24):7745-50. · 5.23 Impact Factor
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ABSTRACT: Ordering of Fe3+ and Fe2+ cations between octahedral and tetrahedral sites in synthetic members of the magnetite-ulvospinel (Fe3O4-Fe2TiO4) solid-solution series was determined using Fe L-2,L-3-edge X-ray magnetic circular dichroism (XMCD) coupled with electron microprobe and chemical analysis, Ti L-2,L-3-edge and Fe K-edge X-ray absorption spectroscopy (XAS), and unit-cell parameters. Microprobe analyses, cell edges, and chemical FeO determinations showed that bulk compositions were stoichiometric magnetite-ulvospinel solid solutions. XMCD showed that the surface was sensitive to redox conditions, and samples required re-equilibration with solid-solid buffers. Detailed site-occupancy analysis gave Fe2+/Fe3+ XMCD-intensity ratios close to stoichiometric values. L-2,L-3-edge XAS confirmed that Ti4+ was restricted to octahedral sites. XMCD showed that significant Fe2+ only entered the tetrahedral sites when Ti content was >0.40 atoms per formula unit (apfu), whereas Fe2+ in octahedral sites increased from 1 apfu in magnetite to a maximum of similar to 1.4 apfu when Ti content was 0.45 apfu. As Ti content increased, a steady increase in Fe2+ in tetrahedral sites was observable in the XMCD spectra, concurrent with a slow decrease in Fe2+ in octahedral sites. Calculated magnetic moments decreased rapidly from magnetite (4.06 mu(B)) to USP45 (1.5 mu(B)), then more slowly toward ulvospinel (0 mu(B)). Two synthesized samples were maghemitized by re-equilibrating with an oxidizing buffer. XMCD showed that Fe2+ oxidation, with concomitant vacancy formation, was restricted to octahedral sites. Through the direct measurement of Fe oxidation states, XMCD results can be used to rationalize the magnetic properties of titanomagnetites, along with oxidized titanomaghemitized analogs, in Earth's crustal rocks.
American Mineralogist. 95(4):425-439.
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ABSTRACT: The biologically-mediated reduction of synthetic samples of the Fe(III)-bearing minerals hematite, goethite, lepidocrocite, feroxhyte, ford ferrihydrite, akaganeite and schwertmannite by Geobacter sulfurreducens has been investigated using microbiological techniques in conjunction with X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). This combination of approaches offers unique insights into the influence of subtle variations in the crystallinity of a given mineral on biogeochemical processes, and has highlighted the importance of (oxyhydr)oxide crystallite morphology in determining the changes occurring in a given mineral phase. Problems arising from normalising the biological Fe(III) reduction rates relative to the specific surface areas of the starting materials are also highlighted. These problems are caused primarily by particle aggregation, and compounded when using spectrophotometric assays to monitor reduction. For example, the initial rates of Fe(III) reduction observed for two synthetic feroxyhytes with different crystallinities (as shown by XRD and TEM studies) but almost identical surface areas, differ substantially. Both microbiological and high-resolution TEM studies show that hematite and goethite are susceptible to limited amounts of Fe(III) reduction, as evidenced by the accumulation of Fe(II) during incubation with G. sulfurreducens and the growth of nodular structures on crystalline goethite laths during incubation. Lepidocrocite and akaganeite readily transform into mixtures of magnetite and goethite, and XRD data indicate that the proportion of magnetite increases within the transformation products as the crystallinity of the starting material decreases. The presence of anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle increases both the initial rate and longer term extent of biological Fe(III) reduction for all of the synthetic minerals examined. High-resolution XPS indicates subtle but measurable differences in the Fe(III):Fe(II) ratios at the mineral surfaces following extended incubation. For example, for a poorly crystalline schwertmannite, deconvolution of the Fe2p3/2 peak suggests that the Fe(III):Fe(II) ratio of the near-surface regions varies from 1.0 in the starting material to 0.9 following 144 h of incubation with G.sulfurreducens, and to 0.75 following the same incubation period in the presence of 10 μM AQDS. These results have important implications for the biogeochemical cycling of iron.
Geochimica et Cosmochimica Acta.
