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We report an anti‐folded bowl‐shaped bisdibenzocorannulene (BDBC) featuring a new chair‐cyclohexane‐like hexagon as a bridge of two dibenzocorannulene moieties. The neutral compound showed multiple redox‐active properties and could be converted to the corresponding redox states through chemical reduction or oxidation. Chemical reduction of BDBC by stoichiometric addition of metallic potassium in the presence of [18]crown‐6 ether, provided a radical anion BDBC.− and a dianion BDBC2−, respectively; while chemical oxidation by silver hexafluoroantimonate(V), converted the neutral compound to an open‐shell singlet diradical dication (BDBC..)2+. The structural consequences of both electron‐reduction and oxidation were closely related to the release of ring‐strain of the bowl‐shaped π‐scaffold and imposed steric hindrance of the hexagonal bridge. In addition, the unusual open‐shell nature of the dication could mainly be attributed to the changing of localized antiaromaticity in the closed‐shell structure to delocalized character in the biradical, and thus the emergence of weakly bonded π‐electrons. [ABSTRACT FROM AUTHOR]

We report an anti‐folded bowl‐shaped bisdibenzocorannulene (BDBC) featuring a new chair‐cyclohexane‐like hexagon as a bridge of two dibenzocorannulene moieties. The neutral compound showed multiple redox‐active properties and could be converted to the corresponding redox states through chemical reduction or oxidation. Chemical reduction of BDBC by stoichiometric addition of metallic potassium in the presence of [18]crown‐6 ether, provided a radical anion BDBC.− and a dianion BDBC2−, respectively; while chemical oxidation by silver hexafluoroantimonate(V), converted the neutral compound to an open‐shell singlet diradical dication (BDBC..)2+. The structural consequences of both electron‐reduction and oxidation were closely related to the release of ring‐strain of the bowl‐shaped π‐scaffold and imposed steric hindrance of the hexagonal bridge. In addition, the unusual open‐shell nature of the dication could mainly be attributed to the changing of localized antiaromaticity in the closed‐shell structure to delocalized character in the biradical, and thus the emergence of weakly bonded π‐electrons. [ABSTRACT FROM AUTHOR]

Uranium tetraboride (UB4) was successfully synthesized by boro/carbothermal reduction of UO2 with B4C and carbon as combined reduction agents under flowing argon. The effects of processing temperature and mole ratios of starting materials on phase evolution were studied. XRD results demonstrated that UB4 was obtained with 3.75 mol% B4C in excess based on the UO2/B4C/C molar ratios of 1:1:1 at 1500°C. SEM observation revealed that submicrometer‐sized quasi‐spherical UB4 particles cemented together to be an aggregate. The laser particle size analysis showed that the particle size was in the range of 1‐10 μm. The oxidation behavior of UB4 was also investigated by TG and XRD. The oxidation of UB4 started at about 500°C and it showed better oxidation resistance than other basic uranium nuclear fuels (UO2, UC, UN and U3Si2). The oxidation chemical process of UB4 was presented as a three‐step process: (a) the formation of U3O8 and B2O3 oxidation products; (b) the formation of UB2O6 intermediate product by the interaction of U3O8 and B2O3; (c) the decomposition of UB2O6 to get U3O8. [ABSTRACT FROM AUTHOR]

By using spatially resolved photoelectron spectromicroscopy, we have investigated the formation of Cu(I) oxide phases when a bulk Cu foil is exposed to a near ambient pressure of molecular oxygen. The experiment was performed by using a novel cell for in operando measurements capable to overcome the so called ‘pressure gap’. We have found that the oxidation of Cu proceeds through the formation of Cu(I) oxide domains in the micron and submicron range size, the evolution of which affects the overall morphology of the Cu surface as well. Chemical and morphological changes have been simultaneously detected. It was, surprisingly, found that during the oxidation process in many areas domains having +1 valence state do not spread on the metallic regions which homogenously oxidize; no chemical oxidizing wave was detected by the available lateral resolution and time frame. [ABSTRACT FROM AUTHOR]

A high‐yielding and high‐rate reduction method that operates with alkenes, alkynes, azides, nitriles, and nitroarenes was developed and optimized. The method makes use of sodium borohydride reduction of CoSO4 under release of hydrogen along with the formation of Co2B as a nanoparticle material. The produced Co2B activates the various functional groups for hydride reduction. The protocol was proven to operate with an assortment of functional groups to provide good to excellent yields. Furthermore, the reduction method was successfully adapted, implemented, and developed for a continuous flow approach using the multi‐jet oscillating disk (MJOD) flow reactor platform at atmospheric pressure. [ABSTRACT FROM AUTHOR]

Abstract: A dinuclear CoII complex, [Co2(tphz)(tpy)2]n+ (n=4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T1/2≈470 K for the pristine compound (n=4) to single‐molecule magnet with an ST=5/2 spin ground state when once reduced (n=3) to finally a diamagnetic species when twice reduced (n=2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature. [ABSTRACT FROM AUTHOR]

Abstract: Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its Cα‐hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct α‐carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine‐based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the Cα proton leaves in the plane of the Cα, N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO2 and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA. [ABSTRACT FROM AUTHOR]

Abstract: We report on a headspace gas chromatographic method for determining the content of 3‐chloro‐1,2‐propanediol in polyamideamine epichlorohydrin resin solution. It was based on quantitatively converting 3‐chloro‐1,2‐propanediol to formaldehyde by periodate oxidation in a closed headspace sample vial at a room temperature for 10 min, and then to methanol by borohydride reduction at 90°C for 40 min followed by the headspace gas chromatographic measurement. The results showed that the present method has an excellent measurement precision (relative standard deviation < 2.60%) and accuracy (recoveries from 96.4–102%) in 3‐chloro‐1,2‐propanediol analysis. The limit of quantitation was 0.031 mg/mL. It is simple and suitable for determining the 3‐chloro‐1,2‐propanediol content in polyamideamine epichlorohydrin resin solution. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the oxidation degree of multiwalled carbon nanotubes (MWCNTs) for the detection of NADH was evaluated in this paper. MWCNTs were oxidized by microwave‐assisted sulfonitic treatment at different times (5, 10, 15, and 30 min) and deposited onto a graphite screen printed electrodes. Oxidized MWCNTs were characterized and the electrochemical performance evaluated. The best sensor in terms of sensitivity and stability was obtained after 15 minutes of oxidation (SPE/CNT15). A significant reduction of the NADH oxidation potential was recorded for oxidized MWCNTs compared with unmodified MWCNTs (0.270 V and 0.500 V, respectively vs. Ag/AgCl pseudo reference electrode), increasing the selectivity of the system. Chronoamperometric calibration curves carried out applying a potential of 0.3 V for 1 min were linear in the 4–35 μM range of NADH. A limit of detection of 1 μM was achieved with negligible surface fouling (three consecutive calibration curves, 30 total measurements: slope decrease 5.9 %). Inter electrode reproducibility (n=13) was good resulting in RSD of 15.2 % and 5.0 % for the peak intensity and the oxidation potential, respectively. Quantification of glucose in white wine samples was carried out to demonstrate the ability of the NADH sensor to work in real samples. A good correlation with a spectrophotometric kit for the glucose quantification was achieved. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy was performed on a model system of a novel CuMn2O4 spinel catalyst in order to study the effects of reduction by carbon monoxide and subsequent reoxidation by oxygen both processed at 600°C. A phase transition from CuMn2O4 spinel into separated MnO and Cu-rich phases, which are CuO or Cu depending on the reduction period, was observed in the reduced samples. Furthermore, a surface coverage of the MnO grains by epitaxially grown, nanocrystalline Mn3O4 was found in all reduced samples. These Mn3O4 nanocrystals are assumed to act as seed crystals in the subsequent reoxidation step completely reversing the phase transitions and reconstituting single-phase CuMn2O4 spinel. In addition, superlattice reflections due to cation ordering occurred as a typical feature in the as-prepared spinel. In the reoxidized spinel, the superlattice reflections were absent, hence indicating a disordered cation distribution. [ABSTRACT FROM AUTHOR]

The activation of readily prepared, air-stable cobalt(II) bis(carboxylate) pre-catalysts for the functionalization of C( sp2)−H bonds has been systematically studied. With the pyridine bis(phosphine) chelate, iPrPNP, treatment of 1- (O2CtBu)2 with either B2Pin2 or HBPin generated cobalt boryl products. With the former, reduction to (iPrPNP)CoIBPin was observed while with the latter, oxidation to the cobalt(III) dihydride boryl, trans-(iPrPNP)Co(H)2BPin occurred. The catalytically inactive cobalt complex, Co[PinB(O2CtBu)2]2, accompanied formation of the cobalt-boryl products in both cases. These results demonstrate that the pre-catalyst activation from cobalt(II) bis(carboxylates), although effective and utilizes an air-stable precursor, is less efficient than activation of cobalt(I) alkyl or cobalt(III) dihydride boryl complexes, which are quantitatively converted to the catalytically relevant cobalt(I) boryl. Related cobalt(III) dihydride silyl and cobalt(I) silyl complexes were also synthesized from treatment of trans-(iPrPNP)Co(H)2BPin and (iPrPNP)CoPh with HSi(OEt)3, respectively. No catalytic silylation of arenes was observed with either complex likely due to the kinetic preference for reversible C−H reductive elimination rather than product- forming C−Si bond formation from cobalt(III). Syntheses of the cobalt(II) bis(carboxylate) and cobalt(I) alkyl of iPrPONOP, a pincer where the methylene spacers have been replaced by oxygen atoms, were unsuccessful due to deleterious P−O bond cleavage of the pincer. Despite their structural similarity, the rich catalytic chemistry of iPrPNP was not translated to iPrPONOP due to the inability to access stable cobalt precursors as a result of ligand decomposition via P−O bond cleavage. [ABSTRACT FROM AUTHOR]

The 20 standard amino acids encoded by the Genetic Code were adopted during the RNA World, around 4 billion years ago. This amino acid set could be regarded as a frozen accident, implying that other possible structures could equally well have been chosen to use in proteins. Amino acids were not primarily selected for their ability to support catalysis, as the RNA World already had highly effective cofactors to perform reactions, such as oxidation, reduction and transfer of small molecules. Rather, they were selected to enable the formation of soluble structures with close-packed cores, allowing the presence of ordered binding pockets. Factors to take into account when assessing why a particular amino acid might be used include its component atoms, functional groups, biosynthetic cost, use in a protein core or on the surface, solubility and stability. Applying these criteria to the 20 standard amino acids, and considering some other simple alternatives that are not used, we find that there are excellent reasons for the selection of every amino acid. Rather than being a frozen accident, the set of amino acids selected appears to be near ideal. [ABSTRACT FROM AUTHOR]

Electrochemical surface stress is important in nanomaterials because of their large surface-to-volume ratios, which lead to unique mechanical and electrocatalytic properties, but directly measuring this quantity has been challenging. Here we report on experimental determination of the surface stress, and associated electrochemical processes of a single gold nanowire with an optical imaging technique. We show that surface stress changes linearly and reversibly with the potential between 0 and 0.8 V versus Ag/AgCl, but abruptly with large hysteresis, associated with the oxidation and reduction of the nanowire, between 0.8 and 1.5 V. The potential derivative of the surface stress closely resembles the cyclic voltammograms. We described the observations in terms of anion adsorption and surface oxidation/reduction. This work demonstrates a new approach to study electrochemical processes and the associated surface stress changes of nanomaterials. [ABSTRACT FROM AUTHOR]

A flexible and efficient synthesis of the potent human topoisomerase inhibitor (5 Z,9 Z)-eicosa-5,9-dienoic acid was explored; the presented method represents a generally applicable approach towards demospongic acids and related natural products. Key steps of the synthesis involve chemoselective hydroboration, Corey-Fuchs alkynylation, Z-selective Lindlar reduction, tetrapropylammonium perruthenate catalyzed direct oxidation of a primary alcohol to the corresponding acid, and Arndt-Eistert homologation. Thus, the total synthesis of (5 Z,9 Z)-eicosa-5,9-dienoic acid was achieved in 10 steps in an overall yield of 20 %. [ABSTRACT FROM AUTHOR]

The present study provides new experimental data on the reactivity of sulfur-based ligands connected to Re atoms. It was recently discovered that oxidation of µ-S ligands within the bioctahedral [Re12CS14(µ-S)3(CN)6]6- cluster anion using H2O2 led to the formation of µ-SO2 and µ-SO3 products. This work is focused on the investigation of the opposite process - reduction of the [Re12CS14(µ-SO2)3(CN)6]6- anion to [Re12CS14(µ-S)3(CN)6]6- by sulfide ions in an aqueous medium under mild conditions. The reduction results in a slow change of the solution colour, making it possible to investigate in detail the intermediate products. Analysis of the reaction mixture by ESI mass spectrometry revealed that a series of cluster anions [Re12CS17O n(CN)6]6- ( n = 0-5) was generated during the process. This indicates stepwise chemical reduction of bridging SO2 ligands proceeding through the formation of µ-SO ligands. In this way, twelve-nuclear rhenium clusters demonstrate a unique, fully reversible redox cycle of their µ-bridging ligands, keeping the cluster core unchanged. Two mixed-ligand cluster anions, [Re12CS14(µ-SO2)2(µ-S)(CN)6]6- and [Re12CS14(µ-SO2)(µ-S)2(CN)6]6-, were found to be the major reaction intermediates. The former was crystallised with [Cu(NH3)5]2+ and [Cd(NH3) n]2+ ammine cations and investigated by single-crystal X-ray diffraction. To understand the electronic structure and charge distribution in [Re12CS17O n(CN)6]6- cluster anions, DFT calculations were also carried out. [ABSTRACT FROM AUTHOR]

The oxidation of Pd particles and subsequent reduction of PdO were studied in 0.2-0.7 bar O2 and H2 gas at 20-650 °C by in-situ transmission electron microscopy. The 15 nm thick Pd particles were 50-300 nm wide, and (111) oriented on the SiN support. Two oxidation mechanisms were observed: 1) the slow formation of epitaxial PdO at the Pd particle edges with orientations OR(1): PdO[201]//Pd[111] and PdO(020)//Pd{022}, 5.8° from OR(2): PdO[110]//Pd[100] and PdO[001]//Pd[001]. 2) the fast formation of randomly oriented PdO nucleating at the Pd particle edges. During the reduction process we observed epitaxial formation [OR(1) and OR(2)] as well as nonepitaxial formation of Pd (and Pd hydride). The formation of randomly oriented (5-10 nm) Pd particles on a (001) surface of PdO was much slower than of the epitaxial Pd grains on other PdO surfaces. A systematic study of the electron beam irradiation effect on the phase transformations showed that this effect can be avoided. [ABSTRACT FROM AUTHOR]

Repetitive syntheses of six AuPt/Vulcan carbon (VC) and six AuPd/VC nanocomposites by NaBH4 solution reduction of equimolar mixtures of HAuCl4 · xH2O and H2PtCl6 · 6H2O salts or HAuCl4 · xH2O and Na2PdCl4 salts gives nanocomposites having highly dispersed metal alloy nanoparticles of similar average size (4-7 ± 2 nm). Significant variation in nanocomposite physical and electrochemical properties is observed. AuM alloy stoichiometries and total metal wt% vary by as much as ±11 at% and ±5 wt%, respectively. Activities toward electrocatalytic oxidation of formic acid, evaluated by cyclic voltammetry, reveal one electrochemically inactive nanocomposite, higher activities for AuPd/VC nanocomposites than for AuPt/VC nanocomposites, and a maximum mass-specific current of 3.8 mA cm−2 per mg total metal for one AuPd/VC nancomposite. TEM image of AuPt/Vulcan carbon (left image) and AuPd/Vulcan carbon (right image) nanocomposites. Bar represents 20 nm. [ABSTRACT FROM AUTHOR]

This study aimed to determine whether catalytic pretreatment can be used as a method to reduce the amount of wastewater sludge. In this study, H2O2 oxidation in the presence of a heterogeneous Fe/MgO catalyst was added to the pretreatment step. Initially a laboratory-scale test showed a TCOD (total chemical oxygen demand) was reduced 27.4% during catalytic oxidation compared to 2.1% in a catalyst-free option. Catalytic pretreatment was then evaluated in a bench-scale flow-loop test. Two bench systems were composed of identical serial processes that included anaerobic digestion, aerobic digestion, and coagulating sedimentation. The only difference between the two processes was whether catalytic pretreatment of sediment sludge was used or not. Results showed that catalyst-free oxidation TCOD gradually increased from 4200 to 7800 mg/L while catalytic oxidation maintained TCOD values at 4200 ± 200 mg/L. In addition, catalytic pretreatment reduced total nitrogen from 46.9 to 41.0 mg/L and phosphate from 3.1 to 2.3 mg/L. [ABSTRACT FROM AUTHOR]

The reduction and oxidation properties of four nitrocompounds (trinitrotoluene [TNT], 2,4-dinitrotoluene, 2,4-dinitroanisole, and 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one [NTO]) dissolved in water as compared with the same properties for compounds adsorbed on a silica surface were studied. To consider the influence of adsorption, cluster models were developed at the M05/tzvp level. A hydroxylated silica (001) surface was chosen to represent a key component of soil. The PCM(Pauling) and SMD solvation models were used to model water bulk influence. The following properties were analyzed: electron affinity, ionization potential, reduction Gibbs free energy, oxidation Gibbs free energy, and reduction and oxidation potentials. It was found that adsorption and solvation decrease gas phase electron affinity, ionization potential, and Gibbs free energy of reduction and oxidation, and thus, promote redox transformation of nitrocompounds. However, in case of solvation, the changes are more significant than for adsorption. This means that nitrocompounds dissolved in water are easier to transform by reduction or oxidation than adsorbed ones. Among the considered compounds, TNT was found to be the most reactive in an electron attachment process and the least reactive for an electron detachment transformation. During ionization, a deprotonation of adsorbed NTO was found to occur. [ABSTRACT FROM AUTHOR]

Graphene nanoribbon is a novel variety of graphene with high length-to-width ratio and straight edges. Herein, we report an improved method for the synthesis of graphene oxide nanoribbons (GONRs) from longitudinal unraveling of multiwalled carbon nanotubes by means of a one-step, one-pot pressurized oxidation reaction. The obtained GONRs were characterized by different techniques. Furthermore, owing to their unique properties such as strong optical absorption and good water dispersibility, we show that GONRs can be used as an excellent matrix or probe in matrix-assisted or surface-enhanced laser desorption/ionization mass spectrometry (MALDI or SELDI MS) for the first time. In MALDI MS, GONRs generated significantly higher signals than conventional organic matrix and other graphene-based matrices in the detection of low-mass compounds. We also demonstrate the use of GONRs as a sensitive SELDI probe for simultaneous detection of multiple small molecules and profiling of small molecules in complex environmental samples, thus revealing its application potential in rapid screening of low-mass pollutants in complex media. [ABSTRACT FROM AUTHOR]

Coordination of the novel redox-active phosphine-appended aminophenol pincer ligand (PNOH2) to PdII generates a paramagnetic complex with a persistent ligand-centered radical. The complex undergoes fully reversible single-electron oxidation and reduction. Homolytic bond activation of diphenyldisulfide by the single-electron reduced species leads to a ligand-based mixed-valent dinuclear palladium complex with a single bridging thiolate ligand. Mechanistic investigations support an unprecedented intramolecular ligand-to-disulfide single-electron transfer process to induce homolytic SS cleavage, thereby releasing a thiyl (sulfanyl) radical. This could be a new strategy for small-molecule bond activation. [ABSTRACT FROM AUTHOR]

Catalytic nitrite was found to enable carbon-oxygen bond-forming reductive elimination from unstable alkyl palladium intermediates, providing dioxygenated products from alkenes. A variety of functional groups were tolerated, and high yields (up to 94 %) were observed with many substrates, also for a multigram-scale reaction. Nitrogen dioxide, which could form from nitrite under the reaction conditions, was demonstrated to be a potential intermediate in the catalytic cycle. Furthermore, the reductive elimination event was probed with 18O-labeling experiments, which demonstrated that both oxygen atoms in the difunctionalized products were derived from one molecule of acetic acid. [ABSTRACT FROM AUTHOR]

The tandem reduction/oxidation of fluorenyl compounds was performed with LiAlH4 under air to afford the corresponding 9-hydroxyfluorenyl derivatives in good yields. This methodology with LiAlH4 is unprecedented and most likely proceeds by an organoaluminium intermediate, and in the proposed mechanism. [ABSTRACT FROM AUTHOR]

Both the efficiency and the stereoselectivity in baker's-yeast-mediated reduction of ketones are strongly influenced by both the presence and the position of sulfur substituents, or indeed by the use of sulfur-containing additives. Interestingly the oxidation level of the sulfur substituent has a powerful impact on the outcome of the yeast reduction. It is apparent that use of the sulfone moiety as a substituent to influence the efficiency and stereoselectivity in ketone reduction is substantially more effective than use of the analogous sulfide and sulfoxide moieties. [ABSTRACT FROM AUTHOR]

A sandwiched electrode containing pristine Li2S powder in between two layers of binder‐free carbon nanotube electrodes is developed. The carbon matrix provides an ion and electron accessible environment, and a space for trapping the active material. Exceptionally high capacities with superior stability and rate capability are obtained. [ABSTRACT FROM AUTHOR]

Iridium-catalyzed direct dehydroxylation of alcohols with hydrazine was developed through a combination of the oxidation of alcohols and the Wolff-Kishner reduction. This protocol is simple to perform and highly efficient for a series of primary, benzylic and allylic alcohols. [ABSTRACT FROM AUTHOR]

Nitrate-reducing, Fe(II)-oxidizing bacteria were suggested to couple with enzymatic Fe(II) oxidation to nitrate reduction. Denitrification proceeds via intermediates ( [ABSTRACT FROM AUTHOR]

The photophysical and electrochemical properties of a novel metallopolymer containing [Re(bpy)(CO)3]+ moieties coordinated to a poly(4-vinylpyridine) polymer chain are reported. Significantly, the release of the metal complexes can be triggered by oxidation or reduction of the rhenium complex. Solvent rapidly binds to the vacant coordination site to give a luminescent product. The redox and photophysical properties of the parent metallopolymer and the released solvated complex are compared. Along with photoemission, the metallopolymer generates significant electrogenerated chemiluminescence upon reduction in the presence of benzoyl peroxide as coreactant. [ABSTRACT FROM AUTHOR]

The article offers information regarding the use of heterogeneous catalysts, such as palladium on carbon for several oxidation and reduction reactions. It discusses the use of DNA-mediated palladium nanoparticles as an efficient catalyst. It also investigates ways of using the waste DNA from discarded industrial salmon milt.

The relations between the oxygen potentials and the excess oxygen-nonstoichiometry ( y) of the pyrochlore-type Am2Zr2O7+ y at 1333 K were measured by the electrochemical method using a zirconia solid electrolyte and the change of mass by oxidation and reduction. The oxygen potentials at 1333 K smoothly increased from −516.5 to 0.00 kJ/mol with increasing y from 0.00 to 0.56. It was found that the oxygen potentials of Am2Zr2O7+ y were higher than those of AmO2− x and Am0.5Np0.5O2− x measured in our previous studies at 1333 K. The results were discussed with the valence state and ionic radius of cations as well as the phase relations. [ABSTRACT FROM AUTHOR]

A kinetic study of the reduction of pyrocatechol and catechin by dpph radical has been carried out in various ratios of CHOH/HO mixed solvent at pH 5.5-7.5, μ = 0.10 M [( n-Bu)N]ClO, and T = 25°C. The rate constants of oxidation in aqueous solvent, k, were obtained from the extrapolation of the linear plots of the specific rate constants k vs. % HO plots at each pH value. A linear relationship between k and 1/[H] was observed for both flavonoids with k = kK/[H], where K was the first acid dissociation constant on the catechol ring and k is the rate constant of the oxidation of the mononegative species HX. The values of k obtained from the slopes of the plots are (8.2 ± 0.2) × 10 and (6.1 ± 0.1) × 10 M s for pyrocatechol and catechin, respectively. The analysis of the reaction on the basis of Marcus theory for an outer-sphere electron transfer reaction yielded a value of 3.7 × 10 M s for the self-exchange rate constant of dpph/dpphH couple. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 147-153, 2011 [ABSTRACT FROM AUTHOR]

A stereoselective total synthesis of +cryptocarya diacetate 1 was achieved by two different routes Schemes 2and 3. The sequences involve LiAlH4LiI reduction, ringclosing metathesis, Prinscyclization, Wackeroxidation, and Wittigolefination reactions as key steps. [ABSTRACT FROM AUTHOR]

A promising general approach is proposed that enables the controlled reduction of dopants to tune the photoluminescence properties of single-phase materials. The change of oxidation state of dopants in phosphor phases leads to different emission colors that can be finely tuned. This approach was illustrated with the progressive reduction of the red phosphor SrAl2O4:Eu3+ to green phosphor SrAl2O4:Eu2+ to target yellow luminescence. [ABSTRACT FROM AUTHOR]

The total chromium oxide (Cr2O3) solubility is measured in Na2O– xSiO2 melts as a function of temperature (1125°< T<1250°C), glass composition (1.5< x<3.5), and oxygen fugacity (−15< fO2<−0.61) using a closed and single-use reactor. The presence of Cr(II), Cr(III), and Cr(VI) species is evidenced and their respective contributions in the total Cr content dissolved in the melt are determined. The experimental results are described using a model of chromium chemistry in silicate melts involving dissolution, redox, and oxo-complex reactions, whose equilibrium constants are A mathematical treatment, using the results obtained, allows the correlation between the proposed model and thermodynamic properties of the system. The standard enthalpies and entropies associated with the oxidation and reduction reactions are: Δ Hox=−36 kJ/mol; Δ Hred=208 kJ/mol; Δ Sox=68 J·(mol·K)−1; and Δ Sred=87 J·(mol·K)−1. [ABSTRACT FROM AUTHOR]

Diversity, distribution and genetic comparison of Archaea associated with the surface mucus of corals from three genera, namely Acanthastrea sp., Favia sp. and Fungia sp., from the Gulf of Eilat, Israel and from Heron Island, Australia were studied. Sequencing of the 16S rRNA gene of the coral-associated Archaea revealed dominance of Crenarchaeota (79%, on average). In this phylum, 87% of the sequences were similar (≥ 97%) to the Thermoprotei, with 76% of these being similar (≥ 97%) to the ammonium oxidizer, Nitrosopumilus maritimus. Most of the coral-associated euryarchaeotal sequences (69%) were related to marine group II, while other euryarchaeotal clades were found to be related to anaerobic methanotrophs (8%), anaerobic nitrate reducers (i.e. denitrification, 15%) and marine group III (8%). Most of the crenarchaeotal and euryarchaeotal coral-associated 16S rRNA gene sequences from Heron Island (61%) and from the Gulf of Eilat (71%) were closely related (≥ 97%) to sequences previously derived from corals from the Virgin Islands. Analysis of archaeal amoA sequences obtained from the fungiid coral, Fungia granulosa, divided into three clades, all related to archaeal sequences previously obtained from the marine environment. These sequences were distantly related to amoA sequences previously found in association with other coral species. Preliminary experiments suggest that there is active oxidation of ammonia to nitrite in the mucus of F. granulosa. Thus, coral-associated Archaea may contribute to nitrogen recycling in the holobiont, presumably by acting as a nutritional sink for excess ammonium trapped in the mucus layer, through nitrification and denitrification processes. [ABSTRACT FROM AUTHOR]

Recently, a microbial consortium was shown to couple the anaerobic oxidation of methane to denitrification, predominantly in the form of nitrite reduction to dinitrogen gas. This consortium was dominated by bacteria of an as yet uncharacterized division and archaea of the order Methanosarcinales. The present manuscript reports on the upscaling of the enrichment culture, and addresses the role of the archaea in methane oxidation. The key gene of methanotrophic and methanogenic archaea, mcrA, was sequenced. The associated cofactor F430 was shown to have a mass of 905 Da, the same as for methanogens and different from the heavier form (951 Da) found in methanotrophic archaea. After prolonged enrichment (> 1 year), no inhibition of anaerobic methane oxidation was observed in the presence of 20 mM bromoethane sulfonate, a specific inhibitor of MCR. Optimization of the cultivation conditions led to higher rates of methane oxidation and to the decline of the archaeal population, as shown by fluorescence in situ hybridization and quantitative MALDI-TOF analysis of F430. Mass balancing showed that methane oxidation was still coupled to nitrite reduction in the total absence of oxygen. Together, our results show that bacteria can couple the anaerobic oxidation of methane to denitrification without the involvement of Archaea. [ABSTRACT FROM AUTHOR]

This special issue highlights several recent discoveries in the microbial nitrogen cycle including the diversity of nitrogen-fixing bacteria in special habitats, distribution and contribution of aerobic ammonium oxidation by bacteria and crenarchaea in various aquatic and terrestrial ecosystems, regulation of metabolism in nitrifying bacteria, the molecular diversity of denitrifying microorganisms and their enzymes, the functional diversity of freshwater and marine anammox bacteria, the physiology of nitrite-dependent anaerobic methane oxidation and the degradation of recalcitrant organic nitrogen compounds. Simultaneously the articles in this issue show that many questions still need to be addressed, and that the microbes involved in catalyzing the nitrogen conversions still harbour many secrets that need to be disclosed to fully understand the biogeochemical nitrogen cycle, and make future predictions and global modelling possible. [ABSTRACT FROM AUTHOR]

A new thermocatalytic method to destroy chlorinated solvents has been developed in the laboratory and tested in a pilot field study. The method employs a conventional Pt/Rh catalyst on a ceramic honeycomb. Reactions proceed at moderate temperatures in the simultaneous presence of oxygen and a reductant (mixed redox conditions) to minimize catalyst deactivation. In the laboratory, stable operation with high conversions (above 90% at residence times shorter than 1 s) for perchloroethylene (PCE) is achieved using hydrogen as the reductant. A molar ratio of H2/O2= 2 yields maximum conversions; the temperature required to produce maximum conversions is sensitive to influent PCE concentration. When a homologous series of aliphatic alkanes is used to replace hydrogen as the reductant, the resultant mixed redox conditions also produce high PCE conversions. It appears that the dissociation energy of the C–H bond in the respective alkane molecule is a strong determinant of the activation energy, and therefore the reaction rate, for PCE conversion. This new method was employed in a pilot field study in Tucson, Arizona. The mixed redox system was operated semicontinuously for 240 days with no degradation of catalyst performance and complete destruction of PCE and trichloroethylene in a soil vapor extraction gas stream. Use of propane as the reductant significantly reduced operating costs. Mixed redox destruction of chlorinated solvents provides a potentially viable alternative to current soil and groundwater remediation technologies. [ABSTRACT FROM AUTHOR]

Methane has long been known to be used as a carbon and energy source by some aerobic alpha- and delta-proteobacteria. In these organisms the metabolism of methane starts with its oxidation with O2 to methanol, a reaction catalyzed by a monooxygenase and therefore restricted to the aerobic world. Methane has recently been shown to also fuel the growth of anaerobic microorganisms. The oxidation of methane with sulfate and with nitrate have been reported, but the mechanisms of anaerobic methane oxidation still remains elusive. Sulfate-dependent methane oxidation is catalyzed by methanotrophic archaea, which are related to the Methanosarcinales and which grow in close association with sulfate-reducing delta-proteobacteria. There is evidence that anaerobic methane oxidation with sulfate proceeds at least in part via reversed methanogenesis involving the nickel enzyme methyl-coenzyme M reductase for methane activation, which under standard conditions is an endergonic reaction, and thus inherently slow. Methane oxidation coupled to denitrification is mediated by bacteria belonging to a novel phylum and does not involve methyl-coenzyme M reductase. The first step in methane oxidation is most likely the exergonic formation of 2-methylsuccinate from fumarate and methane catalyzed by a glycine-radical enzyme. [ABSTRACT FROM AUTHOR]

The nitrate conjugative element (NCE) encodes the ability to respire nitrate in the facultative Thermus thermophilus NAR1 strain. This process is carried out by two heterotetrameric enzymes that catalyse the oxidation of NADH (Nrc) and the reduction of nitrate (Nar), whose expression is activated by the NCE-encoded transcription factors DnrS and DnrT. We report the presence of NCE in other facultative strains of T. thermophilus and analyse its role in subsequent steps of the denitrification pathway. We encountered that nrc mutants of denitrifying strains show a decrease in anaerobic growth rates not only with nitrate, but also with nitrite, NO and N2O, which is concomitant to their lower NADH oxidation activities in vitro. We show that nitrate, nitrite and NO are activating signals for transcription of nrc in these strains. Finally, we demonstrate that DnrS and DnrT are required for anaerobic growth not only with nitrate, but also with nitrite, NO and N2O. These data allow us to conclude that: (i) Nrc constitutes the main electron donor for the four reductases of the denitrification pathway, and (ii) the NCE controls the expression of the whole denitrification pathway and the repression of the aerobic respiration through the transcription factors DnrS and DnrT. [ABSTRACT FROM AUTHOR]

Abstract: It is becoming increasingly evident that the absorption of certain nutrients and drugs and their effects are largely influenced by the concomitant ingestion of other substances. As various xeno- and endobiotics belong to the class of organic cations, the aim of this work was to study the modulation of the intestinal apical uptake of organic cations by diet procyanidins. Five procyanidin fractions with different structural complexity were obtained after fractionation of a grape seed extract. The effect of these compounds on 1-methyl-4-phenylpyridinium (MPP+) uptake was evaluated in Caco-2 cells. Apical uptake of 3H-MPP+ by Caco-2 cells was increased by a 60min exposure to 600μgml−1 of procyanidin fractions, that increase being positively related with procyanidins structural complexity. It was verified that 3H-MPP+ uptake increased with preincubation time. It was speculated that procyanidins were oxidized during preincubation, this change could interfered with transport activity. Tested oxidizing agents showed that the redox state of the transporter could affect its activity. Additionally, trans-stimulation experiments showed that catechin and fraction I (the simpler fraction) can use the same transporter as MPP+. The results are compatible with the hypothesis of these compounds being competitive inhibitors of MPP+ transport. In conclusion, procyanidins are capable to modulate MPP+ apical uptake in Caco-2 cells, this transport being most probably modulated through oxidation–reduction phenomena. Interactions between these compounds and drugs present in the diet may affect their absorption and bioavailability. Both the concentration and complexity of the procyanidin compounds should be taken into account in medical practice. [Copyright &y& Elsevier]

As part of a study to evaluate an integrated zero-valent iron (Fe0)-biological oxidation process for treating azo dye wastewaters, we conducted batch and column experiments with the azo dye orange G to assess the effects of solution conditions on the performance of iron pretreatment. The influence of iron type and surface area, solution pH, dissolved inorganic salts, and phosphate ion on the reduction (decolorization) of orange G solution were examined. In batch experiments, increased iron surface area, decreased pH, and chloride and sulfate salts enhanced dye decolorization, whereas high pH (9.9) and phosphate concentrations (>3 mg/L PO4-P) inhibited dye reduction. Results from batch experiments were confirmed in column experiments. An increase in temperature from 22 to 35°C resulted in a near doubling of the reduction rate constant in a column study. The abiotic reduction results illustrate the feasibility and potential limitations of an integrated iron column, activated sludge treatment process for wastewaters containing azo dyes. [ABSTRACT FROM AUTHOR]

Azetidine-2-carboxylic acid (Aze) analogs possessing various heteroatomic side chains at the 3-position have been synthesized by modification of 1-9-(9-phenylfluorenyl) (PhF)-3-allyl-Azetert-butyl ester (2S,3S)-1. 3-Allyl-Aze1was synthesized by regioselective allylation ofα-tert-butylβ-methylN-(PhF)aspartate13, followed by selectiveω-carboxylate reduction, tosylation, and intramolecularN-alkylation. Removal of the PhF group and olefin reduction by hydrogenation followed by Fmoc protection produced nor-leucine–Aze chimera2. Regioselective olefin hydroboration of (2S,3S)-1produced primary alcohol23, which was protected as a silyl ether, hydrogenated andN-protected to give 1-Fmoc-3-hydroxypropyl-Aze26. Enantiopure (2S,3S)-3-(3-azidopropyl)-1-Fmoc-azetidine-2-carboxylic acidtert-butyl ester3was prepared as a Lys–Aze chimera by activation of 3-hydroxypropyl–Aze26as a methanesulfonate and displacement with sodium azide. Moreover, orthogonally protected azetidine dicarboxylic acid4was synthesized as anα-aminoadipate–Aze chimera by oxidation of alcohol26. These orthogonally protected amino acid–Aze chimeras are designed to serve as tools for studying the influence of conformation on peptide activity. [ABSTRACT FROM AUTHOR]

We measured rates of N2 production through anaerobic NH2+ oxidation with NO2-(anammox) and denitrification in permanently cold (from -1.7°C to 4°C) sediments off the east and west coasts of Greenland. The investigated sites (36- to 100-m water depth) covered sediments in which carbon contents ranged from 0.3 to 3.2 dry weight %, O2 uptake rates ranged from 3.4 to 8.3 mmol m-2 d-1, O2 penetration depths ranged from 0.25 to 1.70 cm, and bottom-water NO3- concentrations ranged from 0.3 to 15.3 µmol L-1. Total N2 production was 34-344 µmol N m-2 d-1, of which anammox accounted for 1-92 µmol N m-2 N m-2 d-1. At one of the high-Arctic sites, anammox activity had an optimum temperature (Topt) of 12°C, while that of bacterial denitrification was 24°C. According to the classical temperature scheme for metabolic growth, the anammox response was psychrophilic, while denitrification was psychrotrophic. Although Topt was considerably higher than in situ temperatures, rates of denitrification and anammox were still high at -1.3°C, reaching 17% and 40%, respectively, of those found at Topt. The activation energies, Ea, of anammox and denitrification were 51.0 and 60.6 kJ mol-1, respectively, and the corresponding Q10 values were 2.2 and 2.4. Rates of anammox were linearly correlated with bottom-water NO3- concentrations (r² = 0.96, p < 0.0001, n = 11) at the investigated sites. We suggest that the slow-growing anammox bacteria are favored in sediments with high and stable NO3- conditions. This may be a general pattern in deeper waters at other latitudes as well. [ABSTRACT FROM AUTHOR]

The photochemical reduction of Ag[sup +] and oxidation of Pb[sup 2+] from aqueous solution by SrTiO[sub 3] leave insoluble reaction products (silver and PbO[sub 2], respectively) on the surface. Microscopic analysis has been used to relate the rates of these two reactions to the structure and orientation of SrTiO[sub 3] surfaces. The nonpolar (100) surface is the most reactive for silver reduction and the composition of the termination layer does not influence this reaction. On the polar (111) surface, the reduction and oxidation reactions occur on terraces with different terminations and opposite charges; this leads to a nonuniform distribution of reaction products. The polar (110) surface is the least reactive, and the majority of the reaction products are observed at steps along <100> directions where the more reactive {100} surfaces are exposed. The distribution of oxidation products found on (110) terraces is also influenced by the composition and charge of the surface termination. The results show that the photochemical reactivity of SrTiO[sub 3] is anisotropic and that, on polar surfaces, dipolar fields arising from charged surface domains influence the transport of photogenerated charge carriers and promote spatially selective oxidation and reduction reactions. [ABSTRACT FROM AUTHOR]

We previously reported a nickelladithiolene nanosheet based on a π-conjugated hexagonal network. A liquid-liquid and a gas-liquid interfacial reaction, using benzenehexathiol and nickel(II) acetate, produced the stacked and atomically thin nanosheets, respectively ( J. Am. Chem. Soc. 2013, 135, 2462). Here, we report the modulation of the electronic states on the nickelladithiolene nanosheet by means of the chemical reduction and oxidation reactions. The electronic states were determined by the binding energy of the sulfur peaks in the X-ray photoelectron spectra. [ABSTRACT FROM AUTHOR]

Coupled rat liver mitochondria were incubated with [U-14C]hexadecanoate and carnitine which resulted in the formation of acyl-, 2-enoyl- and 3-hydroxyacyl-CoA and carnitine esters. The production of 2-enoyl-CoA and 3-hydroxyacyl-CoA esters was associated with a significant lowering of the NAD+/NADH ratio, in contrast to rat muscle mitochondria [Eaton, S., Bhuiyan, A. K. M. J., Kler, R. S., Turnbull, D. M. & Bartlett, K. (1993) Biochem. J. 289, 161-172], suggesting that control by the respiratory chain is important under normal conditions. When NAD+/NADH ratios were held low by succinate-induced reverse electron flow, 3-enoyl-CoA esters were also detected, probably formed by the action of 3,2-enoyl-CoA isomerase. Measurement of the flux of β-oxidation at different osmolalities showed that flux was strongly dependent on osmolality changes in the physiological range. Measurement of the CoA and carnitine esters resulting from incubators made at different osmolalities showed that there was an increase in the amounts of the saturated acyl-CoA esters with respect to 2-enoyl-CoA and 3-hydroxyacyl-CoA esters, consistent with control by the electron-transfer flavoprotein-ubiquinone segment {Halestrap, A. P. & Dunlop J. L. (1986) Biochem. J. 239, 559-565]. This however could not be the only factor operating as indicated by the continued presence of 2-enoyl-CoA and 3-hydroxyacyl-CoA esters at high osmolalities. [ABSTRACT FROM AUTHOR]

In order to compare the oxidation and reduction reactions of c-type cytochromes (cytochromes c552 from the green alga Monoraphidium braunii and horse heart cytochrome c) by different flavins (lumiflavins, riboflavin and FMN), laser flash photolysis studies have been carried out using either reduced or oxidized protein in the presence of triplet or semiquinone flavin, respectively. The reaction kinetics clearly demonstrate the cytochrome oxidation is mediated by the flavin triplet state. The rate constants for reduction are 20-100 times smaller than those for oxidation, indicating that the triplet state is a more effective reactant than is the semiquinone. This is attributed to its excited state nature and correspondingly high free energy content. The rate constants for both the reduction and oxidation of cytochrome c552 by riboflavin are significantly smaller than those obtained with lumiflavin, suggesting a steric interference of the ribityl side chain in the flavin &mdah; cytochrome interaction. The comparison between oxidation and reduction indicates that the former process is less affected by steric hindrance than the latter. Both reduction and oxidation of cytochrome c552 by FMN show an ionic strength dependence with the same sign, consistent with a negatively charged reaction site on the cytochrome. The magnitude of the electrostatic effect is slightly smaller for reduction than it is for oxidation. A pattern quite similar to that observed with cytochrome c552 was obtained when parallel experiments were carried out with horse cytochrome c, although differences were observed in the steric and electrostatic properties of the electron transfer site(s) in these two cytochromes. These results suggest that the same or closely adjacent sites on the proteins are involved in the oxidation and reduction reactions. The biochemical implications of this are discussed. [ABSTRACT FROM AUTHOR]

Hydroxypyruvate reductase of a serine-producing methylotroph, Hyphomicrobium methylovorum GM2, was purified to complete homogeneity, crystallized and characterized, the first time for an enzyme from a methylotroph. The enzyme was found to be a dimer composed of identical subunits (38 kDa). the molecular mass of the enzyme being about 70 kDa. The enzyme was stable against heating at 25 C for 10 min at pH values between 5 and 9. Optimal activity was observed at pH 6.8 and around 45 C. The enzyme catalyzed the reduction of hydroxypyruvate with the oxidation of only NADH. Other than hydroxypyruvate. only glyoxylate served as a substrate. The Km values were found to be 0.175 mM for hydroxypyruvate and 10.8 mM for glyoxylate. Taking advantage of the high substrate specificity of this enzyme, a means of enzymatic determination of hydroxypyruvate was established. [ABSTRACT FROM AUTHOR]

Describes the purification of an NAD-linked acetoacetyl-CoA reductase of Zoogloea ramigera to electrophoretic homogeneity. Stereospecificity; Reduction-oxidation reaction; Culture of organism.