On-site removal of H<Subscript>2</Subscript>S from biogas produced by food waste using an aerobic sludge biofilter for steam reforming processing

H₂S in biogas was removed by sludge-loaded biofiltration, rendering the biogas suitable for catalytic reforming into a mixture of CO and H₂ syngas that was then applied for the generation of electricity using a solid oxide fuel cell or for the chemical synthesis of methanol. The biogas was anaerobically produced in a 2 m³ bioreactor at 35°C for 2 years using restaurant food waste from Korea Advanced Institute of Science and Technology (KAIST), and the concentration of H₂S in the biogas ranged from 612 to 1,500 ppmv (Avg. 1,060 ppmv). Two immobilized cell bioreactors 0.2 and 8.5 L in volume were loaded with aerobic sludge and used to study characteristics of H₂S removal from biogas. At a retention time of 400 sec, the removal efficiency of H₂S was over 99% following initial stabilization for 7 days in the 8.5 L bioreactor installed at the on-site biogas facility. The maximum rate of H₂S removal in this study was 359 g-H₂S/m³/h with an average mass loading rate of 14.7 g-H₂S/m³/h (kinetic analysis: V _m = 842.6 g-H₂S/m³/h and K _s = 2.2 mg/L). Therefore, purified biogas with a negligible concentration H₂S was efficiently reformed to syngas. This study demonstrates the feasibility of biogas purification as a part of high-quality syngas production.     

Characterizing and modeling hydrogen sulfide production in anaerobic digestion of livestock manure,agro-industrial wastes,and wastewater sludge

Hydrogen sulfide (H₂S) is the most undesirable inorganic gas in biogas from anaerobic digestion (AD). However, H₂S production in AD is complex and understanding of its processes is still limited. This study performed six controlled batch anaerobic co-digestion experiments to investigate H₂S production. Materials were obtained from four field anaerobic digester systems and co-digestion feedstocks from agroindustry. An additional precipitation experiment was conducted to further examine H₂S production dynamics. Digesters containing highly soluble, carbohydrate-based wastes had a high H₂S final specific production (FSP) value. Additionally, the FSP values were negatively correlated with the initial Fe(II):S ratios in the digester liquid of the batch tests. The precipitation experiment indicated that iron sulfide precipitation was preferred in the presence of an anaerobic community. The H₂S production as a time series was successfully modeled using a generalized additive model (R² > 0.82). This study revealed that sulfate, phosphorus, and iron concentrations are important predictors and potential inhibitors of H₂S production in AD. Further examination of real-time H₂S modeling in AD is warranted.     

Novel iron complexes and chelators based on cis,cis-1,3,5-triaminocyclohexane: iron-mediated ligand oxidation and biochemical properties

 The interaction of Fe(II) and Fe(III) with the novel Fe(II) chelator N,N′N″-tris(2-pyridylmethyl)-cis,cis-1,3,5-triaminocyclohexane (referred to as tachpyr) gives rise to six-coordinate, low-spin, cationic complexes of Fe(II). Tachpyr also displays a cytotoxicity toward cultured bladder cancer cells that is believed to involve coordination of intracellular iron. The anaerobic reaction of tachpyr with Fe(II) salts affords the Fe(II)-tachpyr²⁺ complex, but in presence of oxygen, oxidative dehydrogenation of one or two of the aminomethylene group(s) of the ligand occurs, with formal loss of H₂: R—N(H)—C(H)₂—(2-py) → R—N=C(H)—(2-py)+H₂. The resulting mono- and diimino Fe(II) complexes (denoted as [Fe(tachpyr-H₂)]²⁺ and [Fe(tachpyr-2H₂)]²⁺) are an inseparable mixture, but they may be fully oxidized by H₂O₂ to the known tris(imino) complex Fe(II)[cis,cis-1,3,5-tris(pyridine-2-carboxaldimino)cyclohexane]²⁺ (or [Fe(tachpyr-3H₂)]²⁺). Cyclic voltammetry of the imino complex mixture reveals an irreversible anodic wave at +0.78 V vs. NHE. Tachpyr acts as a reducing agent toward Fe(IIII) salts, affording the same two Fe(II) imino complexes as products. Tachpyr also reductively removes Fe(III) from an Fe(III)(ATP)₃ complex (which is a putative form of intracellular iron), producing the two Fe(II) imino complexes. Novel N-alkylated derivatives of tachpyr have been synthesized. N-Alkylation has two effects on tachpyr: lowering metal affinity through increased steric hindrance, and preventing Fe(III) reduction because oxidative dehydrogenation of nitrogen is blocked. The N-methyl tachpyr derivative binds Fe(II) only weakly as a high-spin complex, and no complexation or reduction of Fe(III) is observed. Corresponding to their inability to bind iron, the N-alkylated chelators are nontoxic to cultured bladder cancer cells. A tach-based chelator with three N-propyleneamino arms is also synthesized. Studies of the chemical and biochemical properties of this chelator further support a relationship between intracellular iron chelation, iron reduction, and cytotoxicity. Received: 23 March 1998 / Accepted: 1 June 1998     

Bio-oxidation of H<Subscript>2</Subscript>S by <Emphasis Type="Italic">Sulfolobus metallicus</Emphasis>

Sulfolobus metallicus is a hyperthermophilic and chemolithoautotrophic archaeon that uses elemental sulfur as an energy source. Its ability to oxidize H₂S was measured either in the presence or absence of elemental sulphur, showing its ability for using both as an energy source. A biotrickling filter was set up and a biofilm of S. metallicus was established over the support. The maximum removal capacity of the biotrickling filter reached at 55°C was 40 g S/m³h for input loads higher than 70 g S/m³h. Thus, S. metallicus can be used in a biofiltration system for the treatment of waste gas emissions at high temperatures contaminated with H₂S.     

Linking geochemical processes with microbial community analysis: successional dynamics in an arsenic-rich, acid-sulphate-chloride geothermal spring

The source waters of acid‐sulphate‐chloride (ASC) geothermal springs located in Norris Geyser Basin, Yellowstone National Park contain several reduced chemical species, including H₂, H₂S, As(III), and Fe(II), which may serve as electron donors driving chemolithotrophic metabolism. Microorganisms thriving in these environments must also cope with high temperatures, low pH (～3), and high concentrations of sulphide, As(III), and boron. The goal of the current study was to correlate the temporal and spatial distribution of bacterial and archaeal populations with changes in temperature and geochemical energy gradients occurring throughout a newly formed (redirected) outflow channel of an ASC spring. A suite of complimentary analyses including aqueous geochemistry, microscopy, solid phase identification, and 16S rDNA sequence distribution were used to correlate the appearance of specific microbial populations with biogeochemical processes mediating S, Fe, and As cycling and subsequent biomineralization of As(V)‐rich hydrous ferric oxide (HFO) mats. Rapid As(III) oxidation (maximum first order rate constants ranged from 4 to 5 min^?1, t_1/2 = 0.17 ? 0.14 min) was correlated with the appearance of Hydrogenobaculum and Thiomonas–like populations, whereas the biogenesis of As(V)‐rich HFO microbial mats (mole ratios of As:Fe ～0.7) was correlated with the appearance of Metallosphaera, Acidimicrobium, and Thiomonas–like populations. Several 16S sequences detected near the source were closely related to sequences of chemolithotrophic hyperthermophilic populations including Stygiolobus and Hydrogenobaculum organisms that are known H₂ oxidizers. The use of H₂, reduced S(–II,0), Fe(II) and perhaps As(III) by different organisms represented throughout the outflow channel was supported by thermodynamic calculations, confirming highly exergonic redox couples with these electron donors. Results from this work demonstrated that chemical energy gradients play an important role in establishing distinct community structure as a function of distance from geothermal spring discharge.     

Treatment of H2S using a horizontal biotrickling filter based on biological activated carbon: reactor setup and performance evaluation

Biological treatment is an emerging and prevalent technology for treating off-gases from wastewater treatment plants. The most commonly reported odorous compound in off-gases is hydrogen sulfide (H₂S), which has a very low odor threshold. A self-designed, bench-scale, cross-flow horizontal biotrickling filter (HBF) operated with bacteria immobilized activated carbon (termed biological activated carbon—BAC), was applied for the treatment of H₂S. A mixed culture of sulfide-oxidizing bacteria dominated by Acidithiobacillus thiooxidans acclimated from activated sludge was used as bacterial seed and the biofilm was developed by culturing the bacteria in the presence of carbon pellets in mineral medium. HBF performance was evaluated systematically over 120 days, depending on a series of changing factors including inlet H₂S concentration, gas retention time (GRT), pH of recirculation solution, upset and recovery, sulfate accumulation, pressure drop, gas-liquid ratio, and shock loading. The biotrickling filter system can operate at high efficiency from the first day of operation. At a volumetric loading of 900 m³ m^–3 h^–1 (at 92 ppmv H₂S inlet concentration), the BAC exhibited maximum elimination capacity (113 g H₂S/m^–3 h^–1) and a removal efficiency of 96% was observed. If the inlet concentration was kept at around 20 ppmv, high H₂S removal (over 98%) was achieved at a GRT of 4 s, a value comparable with those currently reported for biotrickling filters. The bacterial population in the acidic biofilter demonstrated capacity for removal of H₂S over a broad pH range (pH 1–7). A preliminary investigation into the different effects of bacterial biodegradation and carbon adsorption on system performance was also conducted. This study shows the HBF to be a feasible and economic alternative to physical and chemical treatments for the removal of H₂S.     

Ferric Ion and Oxygen Reduction at the Surface of Protoplasts and Cells of Acer pseudoplatanus

This work was undertaken to verify whether surface NADH oxidases or peroxidases are involved in the apoplastic reduction of Fe(III). The reduction of Fe(III)-ADP, linked to NADH-dependent activity of horseradish peroxidase (HRP), protoplasts and cells of Acer pseudoplatanus, was measured as Fe(II)-bathophenanthrolinedisulfonate (BPDS) chelate formation. In the presence of BPDS in the incubation medium (method 1), NADH-dependent HRP activity was associated with a rapid Fe(III)-ADP reduction that was almost completely inhibited by superoxide dismutase (SOD), while catalase only slowed down the rate of reduction. A. pseudoplatanus protoplasts and cells reduced extracellular Fe(III)-ADP in the absence of exogenously supplied NADH. The addition of NADH stimulated the reduction. SOD and catalase only inhibited the NADH-dependent Fe(III)-ADP reduction. Mn(II), known for its ability to scavenge O^?₂, inhibited both the independent and NADH-dependent Fe(III)-ADP reduction. The reductase activity of protoplasts and cells was also monitored in the absence of BPDS (method 2). The latter was added only at the end of the reaction to evaluate Fe(II) formed. Also, in this case, both preparations reduced Fe(III)-ADP. However, the addition of NADH did not stimulate Fe(III)-ADP reduction but, instead, lowered it. This may be related to a re-oxidation of Fe(II) by H₂O₂ that could also be produced during NADH-dependent peroxidase activity. Catalase and SOD made the Fe(III)-ADP reduction more efficient because, by removing H₂O₂ (catalase) or preventing H₂O₂ formation (SOD), they hindered the re-oxidation of Fe(II) not chelated by BPDS. As with the result obtained by method 1, Mn(II) inhibited Fe(III)-ADP reduction carried out in the presence or absence of NADH. The different effects of SOD and Mn(II), both scavengers of O^?₂, may depend on the ability of Mn(II) to permeate the cells more easily than SOD. These results show that A. pseudoplatanus protoplasts and cells reduce extracellular Fe(III)-ADP. Exogenously supplied NADH induces an additional reduction of Fe(III) by the activity of NADH peroxidases of the plasmalemma or cell wall. However, the latter can also trigger the formation of H₂O₂ that, reacting with Fe(II) (not chelated by BPDS), generates hydroxyl radicals and converts Fe(II) to Fe(III) (Fenton's reaction).     

The effect of albumin,ceruloplasmin, and other serum constitutents on Fe(II) oxidation

This study has analyzed the role of several serum constituents, that have been proposed to effect the following reactionin situ: {fx1-1} {fx1-2} These reactions were monitored by measuring the rate of Fe(II) oxidation in the presence of apo-transferrin (reaction A) and Fe(III)-transferrin formation (reaction B) at 465 nm. Reactions A and B were found to be kinetically equivalent. The results show that, singly or in combination, bicarbonate, orthophosphate, citrate, apo-transferrin, and/or albumin have less than one-tenth of the ability to enhance the oxidation of Fe(II) compared to the serum enzyme, ceruloplasmin. It was also found that the rate of Fe(II) oxidation by serum Fe-ligands was influenced by the efficiency of oxygen utilization. Whereas ceruloplasmin produces a 4∶1 ratio of Fe(II) oxidized to oxygen utilized, the non-enzymic components yield a 2∶1 or 3.09∶1 ratio. These data support the role of ceruloplasmin as an antioxidant that prevents the formation of the intermediate active oxygen species O ₂ ⁻ · and H₂O ₂ ^· through the Fe(II) auto-oxidation reaction. A hitherto unrecognized factor in the control of nonenzymic oxidation of Fe(II) was serum albumin. This protein, at >25 μM, was found to sharply dampen the rate of Fe(II) oxidation in the presence of a physiological concentration of bicarbonate, citrate, and transferrin Albumin did not appear to affect the ceruloplasmin catalyzed oxidation of Fe(II) at pH 7.0. The addition of ceruloplasmin effected up to a 44 × increase in the rate of Fe(II) oxidation and Fe(III)-transferrin formation even in the presence of 0.60 mM albumin.     

Stabilization of hydrolytically labile iron(II)–cysteine peptide thiolate complexes in aqueous triton X-100 micelle solution: Spectroscopic properties mimicking of reduced rubredoxin

The absorption, CD, and ¹H- and ¹⁹F-nmr spectroscopic features of Fe(II) complexes with a series of cysteine-containing oligopeptides were investigated in aqueous (H₂O or D₂O) 10% Triton X-100 micelle solution. The complexes with distal aromatic rings, [Fe(Z-cys-Pro-Leu-cys-Gly-X)₂]²⁻ (Z = benzyloxycarbonyl; X = NH-C₆H₄-p-F, NH-CH₂-CH₂-C₆H₄-p-F, and Phe-OMe), were found to be quite stable in such aqueous micelle solution. The coordination of cysteine–peptide ligands to the Fe(II) ion is revealed by isotropically shifted ¹H-nmr signals due to the Cys C_βH₂ protons occurring at 120 ∼ 250 ppm in a D₂O Triton X-100 micelle solution (10%) at 60°C that are very similar to those reported for native reduced rubredoxin. The high stability of these cysteine peptide–Fe(II) complexes in aqueous micellar system was explained by the combined contributions from NH—S hydrogen bonds and the effect of the proximity of aromatic groups. The existence of such NH—S hydrogen bonds and interactions between aromatic ring and sulfur atom was confirmed by ¹⁹F-nmr spectral and ¹⁹F spin–lattice relaxation times (T₁) measurements. © 1998 John Wiley & Sons, Inc. Biopoly 46: 1–10, 1998     

EDTA activation of H2 photoproduction by Rhodospirillum rubrum

Summary The effect of trace elements (Fe, Ni) and chelating compounds on the activity of hydrogen (H₂) uptake (Hup) hydrogenase, nitrogenase and rate and yield of H₂ photoproduction from l-lactate in photosynthetic cultures of Rhodospirillum rubrum was investigated. Hup activity depended on the availability of Ni²⁺ and was inhibited by EDTA (0.3–0.5 mm ethylenedinitrilotetraacetic acid). Addition of EDTA (0.5 mm) to the culture medium caused a nearly complete inactivation of Hup activity and activation of nitrogenase, which was paralleled by a threefold increase in total H₂ photoproduced from lactate. Hup^– mutants, isolated by transposon Tn5 mutagenesis, produced maximally twofold more H₂ than the wild-type. Experiments with different chelating agents [EDTA, NTA (nitrilotriacetic acid), citrate, isocitrate] and varying concentrations of Fe²⁺ and Fe³⁺ showed that photosynthetic growth and nitrogenase activity of R. rubrum were strongly influenced by the iron supply. It is concluded that EDTA enhanced H₂ photoproduction by (I) inhibition of biosynthesis of Hup hydrogenase and (II) mobilization of iron, thereby activating the biosynthesis of the nitrogenase complex. Correspondence to: M. Kern     

Electrochemical detection of natural DNA damage induced by ferritin/ascobic acid/H2O2 system and amplification of DNA damage by endonuclease Fpg

Oppositely charged natural DNA and chitosan (CS) were assembled into (CS/DNA)_n layer-by-layer films on electrode surface, and Ru(bpy)₃²⁺ (bpy = bipyridyl) in solution was used as electroactive catalyst to detect damage of DNA in the films after incubation of the films in ferritin/AA/H₂O₂ solutions (AA = ascorbic acid). The mechanism of DNA damage caused by the ferritin/AA/H₂O₂ system was similar to that of Fenton reaction, where the reaction of ferritin with AA would release some Fe(II) ions from ferritin and the following reaction between Fe(II) ions and H₂O₂ would produce hydroxyl radical, which could induce DNA oxidative damage. This system provided an in vitro model to imitate the DNA damage indirectly induced by ferritin in real bio-systems. In addition, formamidopyrimidine DNA glycosylase (Fpg), a key endonuclease enzyme in repair of oxidatively damaged DNA, was used to amplify the DNA damage caused by ferritin/AA/H₂O₂ system through conversion of oxidative purine bases into single-strand breaks. The high sensitivity of electrocatalytic method with Ru(bpy)₃²⁺ as the catalyst in detection of DNA damage and the magnification function of Fpg may provide a novel idea to detect natural DNA lesion sensitively.     

Reduction of methemerythrin by dithionite ion

The reduction of methemerythrin (Hr⁺) by dithionite produces deoxyhemerythrin (Hr^o) in multi, possibly three, stages. The kinetics were examined at pH 8·2 and 25 °C. The first stage is reduction of methemerythrin to an intermediate A by SO₂^- (k = 1.3 × 10⁵m^?1s^?1). The much slower second and third stages have rates independent of dithionite concentrations. Reaction is completed after about 10 h. The kinetics of reactions of A with N₃^-, H₂O₂, and O₂ were examined, as well as the conversion of A to intermediate B (k = 4·4 × 10^?4s^?1). It is concluded that A is an (Fe(II)Fe(III))₈ species, and that in B the unit (Fe(II)Fe(II))₈ is well developed, judging by its unreactivity towards N₃^?, its reaction with H₂O₂, and its reversible uptake of O₂ (85–90% of the final product). There is little effect of adjusting the pH to 6·3 on the rates of the processes examined.     

Arthospira sp. intensive cultures for food and biogas purification

Summary The main contaminants (CO₂ and H₂S) in biogas produced by anaerooic digestion can be removed by an intensive mass culture of Arthospira sp.. At the same time productivities of 26–34 g dry mass/m² -d were reached.     

Physiological and Genomic Characterization of a Nitrate-Reducing Fe(II)-Oxidizing Bacterium Isolated from Paddy Soil

In this study, a neutrophilic, heterotrophic bacterium (strain Paddy-2) that is capable of ferrous iron [Fe(II)] oxidation coupled with nitrate (NO₃^?) reduction (NRFO) under anoxic conditions was isolated from paddy soil. The molecular identification by 16S rRNA gene sequencing identified the strain as Cupriavidus metallidurans. Strain Paddy-2 reduced 97.7% of NO₃^?and oxidized 89.7% of Fe(II) over 6?days with initial NaNO₃ and FeCl₂ concentrations of 9.37?mM and 4.72?mM, respectively. Acetate (5?mM) was also supplied as a carbon source and an alternative electron donor. A poorly crystalline Fe(III) mineral was the main component observed after 15?days of growth in culture, whereas lepidocrocite was detected in the X-ray diffraction spectrum after 3?months of culture. The homologous genes in electron transfer during Fe(II) oxidation (cyc1, cymA, FoxY, FoxZ, and mtoD) were also identified in the genomes of strain Paddy-2 and other reported NRFO bacteria. These genes encoding c-Cyts may play a role in electron transfer during the process of NRFO. These results provide evidence for the potential of NO₃^? to affect Fe(II) oxidation and biomineralization in bacterium from anoxic paddy soil.     

A chelate complex‐enhanced luminol system for selective determination of Co(II), Fe(II) and Cr(III)

A determination method for Co(II), Fe(II) and Cr(III) ions by luminol‐H₂O₂ system using chelating reagents is presented. A metal ion‐chelating ligand complex with a Co(II) ion and a chelating reagent like ethylenediaminetetraacetic acid (EDTA) produced highly enhanced chemiluminescence (CL) intensity as well as longer lifetime in the luminol‐H₂O₂ system compared to metals that exist as free ions. Whereas free Cu(II) and Pb(II) ions had a strong catalytic effect on the luminol‐H₂O₂ system, significantly, the complexes of Cu(II) and Pb(II) with chelating reagents lost their catalytic activity due to the chelating reagents acting as masking agents. Based on the observed phenomenon, it was possible to determine Co(II), Fe(II) and Cr(III) ions with enhanced sensitivity and selectivity using the chelating reagents of the luminol‐H₂O₂ system. The effects of ligand, H₂O₂ concentration, pH, buffer solution and concentrations of chelating reagents on CL intensity of the luminol‐H₂O₂ system were investigated and optimized for the determination of Co(II), Fe(II) and Cr(III) ions. Under optimized conditions, the calibration curve of metal ions was linear over the range of 2.0 × 10^‐8 to 2.0 × 10^‐5 M for Co(II), 1.0 × 10^‐7 to 2.0 × 10^‐5 M for Fe (II) and 2.0 × 10^‐7 to 1.0 × 10^‐4 M for Cr(III). Limits of detection (3σ/s) were 1.2 × 10^‐8, 4.0 × 10^‐8 and 1.2 × 10^‐7 M for Co(II), Fe(II) and Cr(III), respectively. Copyright © 2012 John Wiley & Sons, Ltd.     

Influence of trace elements on biogas production from mango processing waste in 1.5 m3 KVIC digesters

Summary The influence of trace elements (Co²⁺, Ni²⁺ and Fe³⁺) in varying concentrations and combination, was studied in 1.5 m³ Khadi & Village Industries Commission (KVIC) digesters for biogas generation from mangopeel. Addition of these trace metals enhanced the biogas yield and methane content moderately, the maximum being with the iron fed digester. The digesters were always found to be stable without much variation in total volatile fatty acids (VFA), pH, total alkalinity and other parameters. A methane content of 62% and biogas yield of 0.49 m³/kg VS added was obtained with 4000 mg/L FeCl₃ supplemented mangopeel fed digester as compared to control having biogas yield of 0.22 m³/kg VS added with a methane content of about 48–50%.     

Metal complexes of a new class of polydentate Mannich bases: Synthesis and spectroscopic characterisation

A new class of polydentate Mannich bases featuring an N₂S₂ donor system, bis((2-mercapto-N-phenylacetamido)methyl)phosphinic acid H₃L¹ and bis((2-mercapto-N-propylacetamido)methyl)phosphinic acid H₃L², has been synthesised from condensation of phosphinic acid and paraformaldehyde with 2-mercaptophenylacetamide W1 and 2-mercaptopropylacetamide W2, respectively. Monomeric complexes of these ligands, of general formula K₂[Cr^III(Lⁿ)Cl₂], K₃[M′^II(Lⁿ)Cl₂] and K[M(Lⁿ)] (M′ = Mn(II) or Fe(II); M = Co(II), Ni(II), Cu(II), Zn(II), Cd(II) or Hg(II); n = 1, 2) are reported. The structures of new ligands, mode of bonding and overall geometry of the complexes were determined through IR, UV–Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II) and Fe(II) complexes, square planar for Ni(II) and Cu(II) complexes and tetrahedral for the Co(II), Zn(II), Cd(II) and Hg(II) complexes. Complex formation studies via molar ratio in DMF solution were consistent to those found in the solid complexes with a ratio of (M:L) as (1:1).     

Egg Yolk Phosvitin Inhibits Hydroxyl Radical Formation from the Fenton Reaction

Phosvitin, a phosphoprotein known as an iron-carrier in egg yolk, binds almost all the yolk iron. In this study, we investigated the effect of phosvitin on Fe(II)-catalyzed hydroxyl radical (^?OH) formation from H₂O₂ in the Fenton reaction system. Using electron spin resonance (ESR) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and deoxyribose degradation assays, we observed by both assays that phosvitin more effectively inhibited ^?OH formation than iron-binding proteins such as ferritin and transferrin. The effectiveness of phosvitin was related to the iron concentration, indicating that phosvitin acts as an antioxidant by chelating iron ions. Phosvitin accelerates Fe(II) autoxidation and thus decreases the availability of Fe(II) for participation in the ^?OH-generating Fenton reaction. Furthermore, using the plasmid DNA strand breakage assay, phosvitin protected DNA against oxidative damage induced by Fe(II) and H₂O₂. These results provide insight into the mechanism of protection of the developing embryo against iron-dependent oxidative damage in ovo.     

Gas phase H<Subscript>2</Subscript>S product recovery in a packed bed bioreactor with immobilized sulfate-reducing bacteria

An N₂ strip gas was used in a packed bed sulfate-reducing bioreactor to recover the dissolved sulfide product and improve sulfate conversion. The highest volumetric productivity obtained was 261 mol H₂S m⁻³ d⁻¹. Lowering the initial pH of the medium from 7 to 6 increased the H₂S content of the strip gas from 3.6 to 5.8 mol%. The ratio of strip gas to liquid flow rates (G/L) was found be to a suitable basis for scaling the process. Calculations indicated that modest G/L values (<10²) were required to recover the residual dissolved sulfide in a downstream stripping column.     

The metal ion requirements of Arabidopsis thaliana Glx2-2 for catalytic activity

In an effort to better understand the structure, metal content, the nature of the metal centers, and enzyme activity of Arabidopsis thaliana Glx2-2, the enzyme was overexpressed, purified, and characterized using metal analyses, kinetics, and UV–vis, EPR, and ¹H NMR spectroscopies. Glx2-2-containing fractions that were purple, yellow, or colorless were separated during purification, and the differently colored fractions were found to contain different amounts of Fe and Zn(II). Spectroscopic analyses of the discrete fractions provided evidence for Fe(II), Fe(III), Fe(III)–Zn(II), and antiferromagnetically coupled Fe(II)–Fe(III) centers distributed among the discrete Glx2-2-containing fractions. The individual steady-state kinetic constants varied among the fractionated species, depending on the number and type of metal ion present. Intriguingly, however, the catalytic efficiency constant, k _cat/K _m, was invariant among the fractions. The value of k _cat/K _m governs the catalytic rate at low, physiological substrate concentrations. We suggest that the independence of k _cat/K _m on the precise makeup of the active-site metal center is evolutionarily related to the lack of selectivity for either Fe versus Zn(II) or Fe(II) versus Fe(III), in one or more metal binding sites.