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The ability to clearly relate local structure to function is desirable for many catalytically relevant Pd-containing systems. This report represents the first direct 105Pd solid state NMR measurements of diamagnetic inorganic (K2Pd(IV)Cl6, (NH4)2Pd(IV)Cl6 and K2Pd(IV)Br6) complexes, and micron- and nano-sized Pd metal particles at room temperature, thereby introducing effective 105Pd chemical shift and Knight shift ranges in the solid state. The very large 105Pd quadrupole moment (Q) makes the quadrupole parameters (CQ, ηQ) extremely sensitive to small structural distortions. Despite the well-defined high symmetry octahedral positions describing the immediate Pd coordination environment, 105Pd NMR measurements can detect longer range disorder and anisotropic motion in the interstitial positions. The approach adopted here combines high resolution X-ray pair distribution function (PDF) analyses with 105Pd, 39K and 35Cl MAS NMR, and shows solid state NMR to be a very sensitive probe of short range structural perturbations. Solid state 105Pd NMR observations of ∼44–149 μm Pd sponge, ∼20–150 nm Pd black nanoparticles, highly monodisperse 16 ± 3 nm PVP-stabilised Pd nanoparticles, and highly polydisperse ∼2–1100 nm biomineralized Pd nanoparticles (bio-Pd) on pyrolysed amorphous carbon detect physical differences between these systems based on relative bulk:surface ratios and monodispersity/size homogeneity. This introduces the possibility of utilizing solid state NMR to help elucidate the structure–function properties of commercial Pd-based catalyst systems.\ud \ud

A Serratia sp. expresses a high level of acid phosphatase when grown continuously under carbon limitation. In the presence of CaCl2, biosynthesis of nanocrystalline hydroxyapatite (bio-HA) was achieved by utilizing phosphate released via enzymatic cleavage of an applied substrate (glycerol 2-phosphate: G2P). Hydroxyapatite crystals were identified by energy dispersive X-ray emission (EDX) and selected area diffraction (SAD). X-ray powder diffraction (XRD) analysis gave a mean crystallite size of ∼21–32 nm, with the smallest crystals (21–24 nm) obtained using 1 mM Ca2+ and 1 mM G2P. The uptake of Eu3+ and Sr2+ by bio-HA made by continuously pregrown cells (0.42 mg/mg and 0.043 mg/mg respectively) was ∼20% greater for Sr2+ than was previously reported for bio-HA material of size ∼40 nm made by batch-pregrown cells, while the corresponding uptake of Eu3+ was increased by > 1.8-fold. This was attributed to the localization of Eu (III) at grain boundaries by reference to previous work and highlights th...

Five gram negative and two gram positive bacterial strains known for their heavy metal tolerance or ability to reduce metal ions were coated with Pd(0) nanoparticles (NPs) via reduction of soluble Pd(II) ions under H2 following an initial uptake of PdCl42- without added electron donor ('biosorption'), where the gram negative strains had a ~5-fold greater capacity for Pd(II). Cupriavidis metallidurans accumulated Pd(II) exceptionally; the possibility of reduction to Pd(0) via an endogenous electron donor was not discounted. The initial rate of subsequent H2-mediated Pd(II) reduction correlated with the Pd(II) removed during biosorption (r2=0.9). TEM showed strain-specific variations of Pd-NPs. At a 1:3 loading of Pd:biomass the cell surfaces of Escherichia coli and Desulfovibrio desulfuricans showed uniform coverage with small NPs with the other strains showing larger aggregates. NPs made by the gram positive cells appeared larger than their gram negative counterparts. At a loading of 1:19 all were active catalysts in Cr(VI) reduction and in two Heck coupling reactions. BioPdE. coli and bioPdD. desulfuricans and bioPdA. oxydans were consistently the best and worst catalysts respectively. BioPdE. coli was further tested as a process catalyst according to industrial protocols in Heck and Suzuki coupling reactions. Laboratory and industrial tests (coupling of phenyl iodide and ethyl acrylate) gave 75% and 78% conversion to ethyl cinnamate, respectively. The biomaterial catalysed Heck and Suzuki reactions using bromoacetophenone and 4-bromoanisole (Heck) and 4-chloroanisole (Suzuki) but not 3-chlorotoluene. In accordance with known chemical catalysis the catalytic efficacy was related to electron-withdrawing substituents on the phenyl ring, with more than 90% conversion (Suzuki) using 4-bromobenzotrifluoride.

The Heck coupling of iodobenzene with ethyl acrylate or styrene was used to assess the catalytic properties of biogenic nanoparticles of palladium supported upon the surface of bacterial biomass (bioPd), this approach combining advantages of both homogeneous and heterogeneous catalysts. The biomaterial was comparably active or superior to colloidal Pd in the Heck reaction, giving a final conversion of 85% halide and initial rate of 0.17 mmol/min for the coupling of styrene and iodobenzene compared to a final conversion of 70% and initial rate of 0.15 mmol/min for a colloidal Pd catalyst under the same reaction conditions at 0.5 mol.% catalyst loading. It was easily separated from the products under gravity or by filtration for reuse with low loss or agglomeration. When compared to two alternative palladium catalysts, commercial 5% Pd/C and tetraalkylammonium-stabilised palladium clusters, the bioPd was successfully reused in six sequential alkylations with only slight decreases in the rate of reaction as compared to virgin catalyst (initial rate normalised for g Pd decreased by 5% by the 6th run with bioPd catalyst cf. a decrease of 95% for Pd/C). A re-usable Pd-catalyst made cheaply from bacteria left over from other processes would impact on both conservation of primary sources via reduced metal losses in industrial application and the large environmental demand of primary processing from ores.

This paper describes the preparation and morphological and fine structural characteristics of biologically derived ruthenium and bimetallic palladium/ruthenium nanoparticles. Cells of E. coli strain MC400 were used for production of bio-supported Ru and Pd/Ru bimetallic nanoparticles (bio-Ru NPs and bio-Pd/Ru NPs). High-resolution scanning transmission electron microscopy with a high-angle annular dark field detector and energy dispersive X-ray spectrometry attachment and elemental mapping was used to investigate the bio-supported synthesis of Ru and Ru/Pd NPs. Ru3+ ions were reduced by E. coli cells to the metallic state via bio-mineralisation process using hydrogen as a reducing agent. It was observed that Ru NPs were associated with the periplasmic region of E. coli, whereas Pd NPs were abundant in the periplasm and cytoplasm of the cells. Bimetallic Pd/Ru nanoparticles were observed only on the perimeter of the cells. Bio-Pd/RuE.coli preparations contain simultaneously Pd NPs, Ru NPs and Pd/Ru NPs which makes them a unique candidate for a heterogeneous catalyst. Possible configurations of the bimetallic NPs are discussed.

BACKGROUND Desulfovibrio spp. biofabricate metallic nanoparticles (e.g. ‘Bio-Pd’) which catalyse the reduction of Cr(VI) to Cr(III) and dehalogenate polychlorinated biphenyls (PCBs). Desulfovibrio spp. are anaerobic and produce H2S, a potent catalyst poison, whereas Escherichia coli can be pre-grown aerobically to high density, has well defined molecular tools, and also makes catalytically-active ‘Bio-Pd’. The first aim was to compare ‘Bio-Pd’ catalysts made by Desulfovibrio spp. and E. coli using suspended and immobilised catalysts. The second aim was to evaluate the potential for Bio-Pd-mediated dehalogenation of PCBs in used transformer oils, which preclude recovery and re-use. RESULTS Catalysis via Bio-PdD. desulfuricans and Bio-PdE. coli was compared at a mass loading of Pd:biomass of 1:3 via reduction of Cr(VI) in aqueous solution (immobilised catalyst) and hydrogenolytic release of Cl - from PCBs and used transformer oil (catalyst suspensions). In both cases Bio-PdD. desulfuricans outperformed Bio-Pd E. coli by ~3.5-fold, attributable to a ~3.5-fold difference in their Pd-nanoparticle surface areas determined by magnetic measurements (Bio-PdD. desulfuricans) and by chemisorption analysis (Bio-PdE. coli). Small Pd particles were confirmed on D. desulfuricans and fewer, larger ones on E. coli via electron microscopy. BioPdD. desulfuricans-mediated chloride release from used transformer oil (5.6 0.8 g mL -1 ) was comparable to that observed using several PCB reference materials. CONCLUSIONS At a loading of 1:3 Pd: biomass Bio-PdD. desulfuricans is 3.5-fold more active than BioPdE. coli, attributable to the relative catalyst surface areas reflected in the smaller nanoparticle sizes of the former. This study also shows the potential of Bio-PdD. desulfuricans to remediate used transformer oil.

We report a novel biochemical method based on the sacrificial hydrogen strategy to synthesise bimetallic Au/Pd nanoparticles supported on bacterial cells. The synergistic effect of Au/Pd over monometallic preparations was demonstrated in the oxidation of benzyl alcohol. The bioinorganic catalysts outperformed a commercial Pd catalyst (5% Pd/C) showing no deactivation and high selectivity towards benzaldehyde.

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 noncarbon 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. The research highlights biogenic nuclear waste remediation, Pd and Pt bionanocatalysts for environment and energy, Au oxidation bionanocatalysts from jewelery waste, optically active bioproducts from Se oxyanions, and nanoscale magnets biofabricated from Fe (III) wastes.

Escherichia coli produces at least three [NiFe] hydrogenases (Hyd-1, Hyd-2 and Hyd-3). Hyd-1 and Hyd-2 are membrane-bound respiratory isoenzymes with their catalytic subunits exposed to the periplasmic side of the membrane. Hyd-3 is part of the cytoplasmically oriented formate hydrogenlyase complex. In this work the involvement of each of these hydrogenases in Pd(II) reduction under acidic (pH 2.4) conditions was studied. While all three hydrogenases could contribute to Pd(II) reduction, the presence of either periplasmic hydrogenase (Hyd-1 or Hyd-2) was required to observe Pd(II) reduction rates comparable to the parent strain. An E. coli mutant strain genetically deprived of all hydrogenase activity showed negligible Pd(II) reduction. Electron microscopy suggested that the location of the resulting Pd(0) deposits was as expected from the subcellular localization of the particular hydrogenase involved in the reduction process. Membrane separation experiments established that Pd(II) reductase activity is membrane-bound and that hydrogenases are required to initiate Pd(II) reduction. The catalytic activity of the resulting Pd(0) nanoparticles in the reduction of Cr(VI) to Cr(III) varied according to the E. coli mutant strain used for the initial bioreduction of Pd(II). Optimum Cr(VI) reduction, comparable to that observed with a commercial Pd catalyst, was observed when the bio-Pd(0) catalytic particles were prepared from a strain containing an active Hyd-1. The results are discussed in the context of economic production of novel nanometallic catalysts.

This study was aimed at the development of a new heterogeneous Pd catalyst based on biologically mineralised palladium (Bio-Pd). Desulfovibrio desulfuricans was used to reduce Pd(II) to nanocrystalline Pd embedded in the bacterial surface. In this way the biomass provides support and prevents coalescence of the palladium nanoparticles. Palladised biomass exhibits catalytic activity, which was demonstrated in a range of applications including reduction, oxidation and hydrogenation reactions. Preparation of Bio-Pd under various conditions leads to the formation of a supported palladium catalyst with potentially different catalytic properties according to the preparation method.

Nanoparticles of palladium were obtained with the help of hydrogen-oxidising, metal- reducing bacteria and used for the production of electricity in a proton exchange membrane (PEM) fuel cell. Earlier works have shown that palladised cells of Escherichia coli and Desulfovibrio desulfuricans (Bio-PdE.coli and Bio-PdD.desulfuricans, respectively) appeared similar by electron microscopy and were comparably active in a chemical test reaction. When tested in a PEM fuel cell they produced 0.018 and 0.108 W, respectively. Electron paramagnetic resonance analysis of Bio-PdE.coli mixed with activated carbon showed paramagnetic activity. However, Bio-PdD.desulfuricans under the same conditions quenched the intrinsic EPR signal. This quenching is indicative of the magnetic properties of the particles. The magnetic behaviour of Pd nanoparticles was theoretically predicted for particles between 10 and 20 nm in diameter and can be experimentally confirmed by EPR measurements.

Bio-manufacturing of nano-scale palladium was achieved using bacterial cells. Highly active Pd-catalyst (Bio-Pd) produced by an E. coli mutant gave power output in a fuel cell. Up to ~115% of the maximum power generation was achieved by electrodes of Bio-Pd catalysts from Escherichia coli, compared to that from a commercial-Pd electrode (~0.099 W). A bio-precious-metals (Bio-PM) catalyst made directly from an industrial reprocessing solution by the E. coli was also made into fuel cell electrodes and ~0.06W of maximum power generation was observed.

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.

Escherichia coli can perform at least two modes of anaerobic hydrogen metabolism and expresses at least two types of hydrogenase activity. Respiratory hydrogen oxidation is catalysed by two 'uptake' hydrogenase isoenzymes, hydrogenase -1 and -2 (Hyd-1 and -2), and fermentative hydrogen production is catalysed by Hyd-3. Harnessing and enhancing the metabolic capability of E. coli to perform anaerobic mixed-acid fermentation is therefore an attractive approach for bio-hydrogen production from sugars. In this work, the effects of genetic modification of the genes encoding the uptake hydrogenases, as well as the importance of preculture conditions, on hydrogen production and fermentation balance were examined. In suspensions of resting cells pregrown aerobically with formate, deletions in Hyd-3 abolished hydrogen production, whereas the deletion of both uptake hydrogenases improved hydrogen production by 37% over the parent strain. Under fermentative conditions, respiratory H2 uptake activity was absent in strains lacking Hyd-2. The effect of a deletion in hycA on H2 production was found to be dependent upon environmental conditions, but H2 uptake was not significantly affected by this mutation.

Homogeneous and heterogeneous catalysis approaches to hydrogenation have different advantages and disadvantages and hybrid approaches are sought to maximise the advantages of both. Bacterial cells, of length 1–2 μm, present an economical alternative to conventional micro-scale supports such as graphite and alumina. Certain strains of bacteria can reduce soluble Pd(II), from stock solutions or acid extracts of spent catalysts, forming nanocrystals of Pd, which are supported within the bacterial cell surface layers. The biologically supported nano-Pd contains particles of size ∼5 nm and below, as determined using magnetic measurements (SQUID) and EXAFS spectroscopy. Bio-nano-Pd supported on exemplar Gram negative and Gram positive bacterial types catalysed the hydrogenation of itaconic acid (initial rates 1.1 and 1.2 × 10−2 mol gPd−1 s−1) comparing well with commercial 5% Pd-graphite (1.3 × 10−2 mol gPd−1 s−1).

Nano-scale palladium was bio-manufactured via enzymatically-mediated deposition of Pd(II) from solution. The bio-accumulated metal palladium crystals were processed and applied onto carbon paper and tested as anodes in a proton exchange membrane (PEM) fuel cell for power production. Up to 85% and 31% of the maximum power generation was achieved by Bio-Pd catalysts made using two strains of bacteria, compared to commercial fuel cell grade Pt catalyst. Therefore, it is feasible to use bio-synthesized catalysts in fuel cells for electricity production.

Since 1998 demand for the platinum group metals (PGM) has exceeded supply resulting in large price increases. Undersupply, combined with rising costs prompts environmentally friendly recycling technologies. Leachates containing PGM were produced from secondary waste sources using microwave leaching technology with the aim of recovering precious metals using bacterial biomass. Previous studies showed that metallised biomass exhibits catalytic activity; hence metal is not only recovered but can be converted into a valuable product. Cells of Escherichia coli MC4100 that had been pre-metallised with Pt were more effective at reducing PGM from the leachates. The solid recovered from the leachate onto the bacteria was characterised using X-ray Powder Diffraction (XRD) and Energy Dispersive X-ray Microanalysis (EDX). Metallised biomass was tested for catalytic activity (reduction of Cr(VI) to Cr(III)) to compare the ‘quality’ of polymetallic bacterial-based catalysts versus counterparts made from single and mixed metal model solutions.

Palladized biomass of typical Gram negative bacteria (Desulfovibrio desulfuricans and Escherichia coli) is well documented as a potentially useful catalyst for reduction of metallic species such as Cr(VI). This bionanocatalyst can be sourced from Pd-waste and scrap leachates via biocrystallization. A major industrial application of precious metal catalysts is in hydrogenation and hydrogenolysis reactions whereby, respectively, H is added across unsaturated bonds and halogen substituents can be removed from aromatic rings. Gram positive bacteria have not been evaluated previously as potential supported Pd-bionanocatalysts. We compare the activity of ‘Bio-Pd(0)’ supported on the fundamentally different Gram negative (Desulfovibrio) and Gram positive (Bacillus) bacterial surfaces, and evaluate the activity of the two types of ‘Bio-Pd(0)‘ in a standard reference reaction, the hydrogenation of itaconic acid, against a commercially available catalyst (5% Pd on carbon). The results show that the bionanocatalysts have a similar activity to the commercial material and biomanufacturing from waste sources may be an economic alternative to conventional processing for catalyst production as precious metal prices continue to rise.

Soil microorganisms and plants were studied in samples of arsenic-contaminated soil from two cattle dip sites. The aim was to delineate the parameters that will determine the feasibility of future remediation by growing arsenic-accumulating plants, including the identity and characteristics of some rhizosphere soil microbes. The soil samples contained high total, but low soluble arsenic concentrations which, together with other properties, resembled the previously reported characteristics of dip-site soils from this region of rural Australia. A glasshouse trial demonstrated that dip-site rhizosphere microbes promoted arsenic accumulation by the grass Agrostis tenuis on contaminated dip-site soil without inhibition of growth. The arsenic content of the shoots was increased by 45%. We studied the colonization of roots of dip-site plants by mycorrhizal fungi and tentatively identified six genera of other fungi present in the soil samples. Two plant species growing at the sites, Kikuyu grass (the most abundant plant) and Rainbow fern, exhibited mixed infections of their roots by endomycorrhizal fungi (tentatively identified as Acaulospora and Gigaspora) and by soil-born pathogens. Five rhizosphere bacteria were identified to genus level and we determined the effect of arsenic on their growth. The two most prevalent strains differed greatly in their growth sensitivity to arsenate; Arthrobacter sp. being the most sensitive while Ochrobactrum sp. exhibited exceptional resistance to arsenate. Of the other, less prevalent strains, two were Bacillus spp. and the last, Serratia sp., was the most resistant to arsenite. These findings show the importance of understanding plant-soil microbe interactions for developing future strategies aimed at a phytoremediation-based approach to removing arsenic from soil at dip sites.

Biosynthesis of nano-scale platinum and palladium was achieved via enzymatically-mediated deposition of metal ions from solution. The bio-accumulated Pt(0) and Pd(0) crystals were dried, applied onto carbon paper and tested as anodes in a polymer electrolyte membrane (PEM) fuel cell for power production. Up to 100% and 81% of the maximum power generation was achieved by the bio-Pt and bio-Pd catalysts, respectively, compared to commercial fuel cell grade Pt catalyst. Hence, biomineralisation could pave the way for economical production of fuel cell catalysts since previous studies have shown that precious metals can be biorecovered from wastes into catalytically active bionanomaterials.

The surfaces of cells of Desulfovibrio desulfuricans,Desulfovibrio vulgaris and a new strain, Desulfovibrio sp. `Oz-7' were used to manufacturea novel bioinorganic catalyst via the reduction of Pd(II) to Pd(0) at the cell surface usinghydrogen as the electron donor. The ability of the palladium coated (palladised) cells to reductivelydehalogenate chlorophenol and polychlorinated biphenyl species was demonstrated. Dried, palladisedcells of D. desulfuricans, D. vulgaris and Desulfovibrio sp. `Oz-7'were more effective bioinorganic catalysts than Pd(II) reduced chemically under H2 orcommercially available finely divided Pd(0). Differences were observed in the catalyticactivity of the preparations when compared with each other. Negligible chloride release occurredfrom chlorophenol and polychlorinated biphenyls using biomass alone.

A species of Serratia bacteria has been used to manufacture hydroxyapatite in the form of coatings on solid supports, powder and scaffolds. The biomineralization mechanism involves an acid phosphatase enzyme located in the bacterial cell wall that cleaves organic phosphate groups liberating inorganic phosphates that then combine with calcium ions to form calcium-deficient hydroxyapatite. The same mechanism can be used to form other insoluble metal phosphates, reducing the concentration of free ions in solution and thus providing a means of water bioremediation. Encapsulation of the enzyme within liposomes was shown to be an effective means of removal of cadmium and uranium from solution and to recover silver phosphate and a form of palladium phosphate. Here, we also describe an alternative method of recovery of palladium ions via their reduction to metal (Pd(0)) using hydrogenase enzymes entrapped within membrane vesicles. This preliminary study gave catalytically active “bio-Pd(0)” with a catalytic efficacy of ~ 30% of that of equivalent “bio-Pd” on whole cells of Desulfovibrio spp. and Bacillus sphaericus , and of a commercial 5% Pd on a carbon catalyst and shows that, in principle, a liposome-based system could be used to make an organic/inorganic hybrid catalyst for use where whole bacteria may be undesirable.

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 noncarbon energy technologies are driven by the need to reduce CO2 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. The research highlights biogenic nuclear waste remediation, Pd and Pt bionanocatalysts for environment and energy, Au oxidation bionanocatalysts from jewelery waste, optically active bioproducts from Se oxyanions, and nanoscale magnets biofabricated from Fe (III) wastes.

Bio-manufacturing of nano-scale palladium was achieved via enzymatically-mediated deposition of Pd from solution using Desulfovibrio desulfuricans, Escherichia coli and Cupriavidus metallidurans. Dried ‘Bio-Pd’ materials were sintered, applied onto carbon papers and tested as anodes in a proton exchange membrane (PEM) fuel cell for power production. At a Pd(0) loading of 25% by mass the fuel cell power using Bio-Pd D. desulfuricans (positive control) and Bio-Pd E. coli (negative control) was ~140 and ~30 mW respectively. Bio-Pd C. metallidurans was intermediate between these with a power output of ~60 mW. An engineered strain of E. coli (IC007) was previously reported to give a Bio-Pd that was >3-fold more active than Bio-Pd of the parent E. coli MC4100 (i.e. a power output of >110 mW). Using this strain, a mixed metallic catalyst was manufactured from an industrial processing waste. This ‘Bio-precious metal’ (‘Bio-PM’) gave ~68% of the power output as commercial Pd(0) and ~50% of that of Bio-Pd D. desulfuricans when used as fuel cell anodic material. The results are discussed in relation to integrated bioprocessing for clean energy.

The use of bacterial flagella as templates for the immobilization of Pd and Au nanoparticles is described. Complete coverage of D. desulfuricans flagellar filaments by Pd(0) nanoparticles was obtained via the H(2)-mediated reduction of Pd(NH3)4]Cl2 but similar results were not obtained using HAuCl4. The introduction of additional cysteine-derived thiol residues in the E. coli FliC protein increased Au(III) sorption and reduction onto the surface of the flagellar filament and resulted in the production of stabilized Au(0) nanoparticles of approximately 20-50 nm diameter. We demonstrate the application of molecular engineering techniques to manufacture biologically passivated Au(0) nanoparticles of a size suitable for catalytic applications.

Resting cells of Desulfovibrio vulgaris NCIMB 8303 and Desulfovibrio desulfuricans NCIMB 8307 were used for the hydrogenase-mediated reduction of Pd(II) to Pd(0). The resulting hybrid palladium bionano- catalyst (Bio-Pd(0)) was used in the reduction of Cr(VI) to the less environmentally problematic Cr(III) species. The reduction of Cr(VI) by free and agar-immobilized Bio-Pd(0) was evaluated. Investigations using catalyst suspensions showed that Cr(VI) reduction was similar (� 170 nmol Cr(VI)/h/mg Bio-Pd(0)) when Bio-Pd(0) was produced using D. vulgaris or D. desulfuricans. Continuous-flow studies using D. vulgaris Bio-Pd(0) with agar as the immobilization matrix investigated the effect of Bio- Pd(0) loading, inlet Cr(VI) concentration, and flow rate on the efficiency of Cr(VI) reduction. Reduction of Cr(VI) was highest at a D. vulgaris Bio-Pd(0) loading of 7.5 mg Bio-Pd(0)/mL agar (3:1 dry cell wt: Pd(0)), an input (Cr(VI)) of 100 mM, and a flow rate of 1.75 mL/h (approx. 3.5 column volumes/h). A mathematical interpretation predicted the activity of the immobilized Bio-Pd(0) for a given set of conditions within 5% of the value found by experiment. Considering the system as an 'artificial enzyme' analog and application of applied enzyme kinetics gave an apparent Km value (Km app) of 430 mM Cr(VI) and a deter- mined value of flow-through reactor activity which differed by 11% from that predicted mathematically. 2006 Wiley Periodicals, Inc.

Bacterial hydrogenases have been harnessed to the removal of heavy metals from solution by reduction to less soluble metal species. For Pd(II), its bioreduction results in the deposition of cell-bound Pd(0)-nanoparticles that are ferromagnetic and have a high catalytic activity. Hydrogenases can also be used synthetically in the production of hydrogen from sugary wastes through breakdown of formate produced by fermentation. The Bio-H2 produced can be used to power an electrical device using a fuel cell to provide clean electricity. Production of hydrogen from confectionery wastes by one organism (Escherichia coli) can be used as the electron donor for the production of Bio-Pd0 from soluble Pd(II) by a second organism. The resulting Bio-Pd0 can then be used as a bioinorganic catalyst in the remediation of Cr(VI)-contaminated solutions or polychlorinated biphenyls at the expense of Bio-H2, as a hydrogenation catalyst for industry or as a component of a fuel cell electrode.

A novel bioinorganic catalyst was obtained via reduction of Pd(II) to Pd0 on to the surface of cells of Desulfovibrio desulfuricans at the expense of H2. Palladised biomass, supplied with formate or H2 as an electron donor, catalysed the dehalogenation of 2-chlorophenol and polychlorinated biphenyls. In the example of 2,3,4,5-tetrachlorobiphenyl, the bioinorganic catalyst promoted a rate of chloride release of 9.33 +/- 0.17 nmol min(-1) mg (-1) and only approximately 5% of this value was obtained using chemically reduced or commercially available Pd0. In the case of 2,2',4,4',6,6'-hexachlorobiphenyl the rate was more than four orders of magnitude faster than the degradation reported using a sulfidogenic culture. Negligible chloride release occurred from any of the chloroaromatic compounds using biomass alone, or from palladised biomass challenged with hexane carrier solvent only. Analysis of the spent solution showed that in addition to catalysis of reductive dehalogenation the new material was able to remove very effectively the organic residua, with neither any PCB nor any breakdown products identifiable by GC/MS.

For the first time, the method of shell-isolated nanoparticle Raman spectroscopy (SHINERS) is used in combination with cyclic voltammetry (CV) and reactivity studies to investigate the adsorption behaviour of a series of three alkynes undergoing hydrogenation on nanoparticle, single crystal and bacteria/graphite-supported platinum surfaces. It is found that a strong association of alkynes with defect sites to produce a long-lived di-sigma/pi-alkene surface complex allows for deep hydrogenation of this intermediate to the alkane product. In contrast, when platinum surface defect sites are blocked by either bismuth or polyvinylpyrrolidone (PVP) (and thus leaving behind only Pt{111} terrace adsorption sites), large increases in selectivity to the semi-hydrogenation product are observed for all three alkynes. This finding is consistent with SHINERS collected from both well-ordered and roughened Pt{111} electrodes which revealed that the di-sigma/pi-bonded surface intermediate is hardly formed at all on Pt{111} unless defect sites are introduced via electrochemical roughening. As a general method of producing selective catalysts, the elimination of toxic heavy metals from Lindlar-type catalyst, used commonly in organic chemistry, and their replacement by more benign, organic species adsorbed at defect sites is discussed.