Redox Flexibility Research Articles

Redox proteomic analysis of the gastrocnemius muscle from adult and old mice.

The data provides information in support of the research article, “Differential Cysteine Labeling and Global Label-Free Proteomics Reveals an Altered Metabolic State in Skeletal Muscle Aging”, Journal of Proteome Research, 2014, 13 (11), 2008–21 [1]. Raw data is available from ProteomeXchange [2] with identifier PDX001054. The proteome of gastrocnemius muscle from adult and old mice was analyzed by global label-free proteomics and the relative quantification of specific reduced and reversibly oxidized Cysteine (Cys) residues was performed using Skyline [3]. Briefly, reduced Cysteine (Cys) containing peptides was alkylated using N-ethylmalemide (d0-NEM). Samples were desalted and reversibly oxidized Cys residues were reduced using tris(2-carboxyethyl)phosphine (TCEP) and the newly formed reduced Cys residues were labeled with heavy NEM( d5-NEM). Label-free analysis of the global proteome of adult (n=5) and old (n=4) gastrocnemius muscles was performed using Peaks7™ mass spectrometry data analysis software [4]. Relative quantification of Cys containing peptides that were identified as reduced (d(0) NEM labeled) and reversibly oxidized d(5)–NEM labeled was performed using the intensity of their precursor ions in Skyline. Results indicate that muscles from old mice show reduced redox flexibility particularly in proteins involved in the generation of precursor metabolites and energy metabolism, indicating a loss in the flexibility of the redox energy response.

Geometric and redox flexibility of pyridine as a redox-active ligand that can reversibly accept one or two electrons.

A low-coordinate iron(I) species can reversibly reduce pyridine, either by one electron to give a new C-C bond, or by two electrons to give a pyridine-derived bridge with an unprecedented μ-η(1):η(3) binding mode.

Facile two-electron reduction of a closo-rhodathiadecaborane

Closo-to-arachno redox flexibility in metallaheteroboranes may be viewed as a metal-to-ligand cooperative action with application in catalysis. The treatment of [PSH][arachno-4-SB(8)H(11)] with [RhCl(PPh(3))(3)] affords, after chromatography, three new 10-vertex rhodathiaboranes, [2,2,2-(H)(PPh(3))(2)-closo-2,1-RhSB(8)H(8)] (3), [6,6,9-(PPh(3))(3)-arachno-6,5-RhSB(8)H(9)] (4) and [2,2,2-(Cl)(H)(PPh(3))-6-(PPh(3))-closo-2,1-RhSB(8)H(7)] (5). 3 reacts quantitatively with PPh(3) to form 4, which, in turn, reacts with chlorinated solvents to give the chloro-ligated cluster 5. Kinetic studies demonstrate that the reaction of 3 with PPh(3) obeys a second-order rate law, with an associative mechanism. The Lewis acidity of 3 is quite remarkable, and, given its closo-to-arachno structural and electronic response, this cluster is expected to exhibit a rich chemistry.

Brønsted Acid/Base Driven Chemistry with Rhodathiaboranes: A Labile {SB9H9}–Thiadecaborane Fragment System

Reversible H2 cleavage promoted by closo to nido transformations of [1,1-(PPh3)2-3-(NC5H5)-closo-1,2-RhSB9H8] (2)/[8,8,8-(PPh3)2(H)-9-(NC5H5)-nido-8,7-RhSB9H9] (1) is a cooperative action with application in catalysis; the treatment of 2 and [1,1-(PPh3)(CO)-3-(NC5H5)-closo-RhSB9H8] (3) with either HCl or HOTf in CH2Cl2 affords the 11-vertex nido-rhodathiaboranes [8,8-(PPh3)(Cl)-9-(NC5H5)-nido-8,7-RhSB9H9] (4) and [8,8,8-(PPh3)(CO)(Cl)-9-(NC5H5)-nido-8,7-RhSB9H9] (5), respectively. In contrast, the reaction of 1 with triflic acid yields the salt [8,8-(PPh3)2(H)-9-(NC5H5)-nido-RhSB9H10][OTf] (6). These results illustrate the bifunctional nature of the clusters and their nido to closo redox flexibility, which open new routes for the tuning of the reactivity of these polyhedral compounds and widen their potential applications.

Magnetic and EPR study of ferric green rust- and ferrihydrite-coated sand prepared by different synthesis routes

Due to increased active surface area and high redox flexibility, the green rust- and ferrihydrite- (FH) coated sands appear promising materials in environmental applications such as reactive filtration processes for the elimination and fixation of pollutants in soils, sediments and contaminated water. Recently, different synthesis routes to prepare coatings of the ferric green rust (FGR) and FH minerals on quartz sand were reported (Khare et al 2008 Solid State Sci. 10 1342), where the pre-synthesized minerals and the sand were mixed via either a dry or a wet contact, or the minerals were synthesized by a chemical reaction in the presence of sand. We performed scanning electron microscopy, magnetic and electron paramagnetic resonance (EPR) measurements of the coated sands, with the aim of determining magnetic properties of the coatings and to investigate whether the three deposition methods yield chemically identical coatings within each group (FGR-type or FH-type), just appearing in different volumes, or whether the different deposition methods also introduce physical/chemical differences within the coatings of the same group. The FGR-type coatings behave magnetically as a superparamagnetic system. The significantly different spin blocking temperatures of the FGR samples prepared by the ‘dry-contact’ and ‘wet-contact’ methods (those prepared by the ‘wet-contact’ method were about 40 K higher) reveal physical/chemical differences between the two nominally same coatings. The FH-type coatings are magnetically more homogeneous, being of a spin-glass type. Marginal differences between the FH coatings produced by the ‘wet-contact’ and ‘reactive’ synthesis routes were observed as well.

Structure and thermodynamics of ferrous, stoichiometric and ferric oxyhydroxycarbonate green rusts; redox flexibility and fougerite mineral

Ferric oxyhydroxycarbonate GR( CO 3 2 − ) *, Fe III 6O 12H 8CO 3, is prepared from Fe II–III hydroxycarbonate GR( CO 3 2 − ), Fe II 4 Fe III 2 (OH) 12CO 3, by violent oxidation adding H 2O 2 or by aerial oxidation once dried. Crystals have practically the same aspect and structural features are mainly conserved as testified by X-ray diffraction. Continuous in situ deprotonation of GR( CO 3 2 − ) by adding the exact amount of H 2O 2 to reach any value of x = { [ Fe III ] / [ Fe total ] } is followed, leading to the general formula Fe II 6 ( 1 − x ) Fe III 6 x O 12 H 2 ( 7 − 3 x ) CO 3 that can be extended all over the range x ∈ [ 0 , 1 ] giving also a ferrous GR( CO 3 2 − ) §. Mössbauer spectra allow us to devise a model of the long range order of anions that remains unchanged over the whole range of composition whereas protonation or deprotonation accompanies the progressive filling of the three sublattices by Fe III ions with periodicity a 0 × 3 , if a 0 is that of the hexagonal cation pavement. Monitoring the electrode potential E h during oxidation by H 2O 2 allowed determining the chemical potential μ ○ [ GR ∗ ( x ) ] for any value of x leading to two domains approximated by μ ○ [ GR ∗ ( x ) ] = { − 618 + 54 x } kJ mole −1 in range [ ( 1 / 3 ) , ( 2 / 3 ) ], and μ ○ [ GR ∗ ( x ) ] = { − 632 + 75 x } kJ mole −1 in range [ ( 2 / 3 ) , 1 ] . Occurrences of fougerite mineral in the field (IMA 2003-057) limited to x ∈ [ ( 1 / 3 ) , ( 2 / 3 ) ] are discussed in agreement with their Mössbauer spectra identical to those obtained in this study.

In Situ Redox Flexibility of FeII-III Oxyhydroxycarbonate Green Rust and Fougerite

Bacterial activity is commonly thought to be directly responsible for denitrification in soils and groundwater. However, nitrate reduction in low organic sediments occurs abiotically by FeII ions within the fougerite mineral (IMA 2003-057), giving the bluish-green color of gleysols. Fougerite, the mineral counterpart of FeII-III oxyhydroxycarbonate, FeII6(1-x)FeIII6xO12H2(7-3x)CO3, provides a unique in situ redox flexibility, which can adapt x = {[FeIII]/[Fetotal]} between 1/3 and 2/3 as shown using Mössbauer spectroscopy. Chemical potential and Eh-pH diagrams for this system were determined from electrode potential monitored during deprotonation of hydroxycarbonate FeII4FeIII2(OH)12CO3 to assess the possibility of reducing pollutants in the field. Bioreduction of ferric oxyhydroxides in anoxic groundwater yields dissolved FeII, whereas HCO3- anions produced from organic matter are incorporated into fougerite layered double oxyhydroxide structure. Thus, fougerite is the solid-state redox mediator acting as electron shuttle that helps bacterial activity for reducing nitrate by coupling dissimilatory FeIII reduction and oxidation of FeII with reduction of NO3-. It is proposed that this system could be used in the remediation of soils and nitrified waters.

Synthesis, structure and electrochemical studies of the first mixed-metal clusters with the P–N–P assembling ligands (Ph 2P) 2NH (dppa), (Ph 2P) 2N(CH 3) (dppam) and (Ph 2P) 2N(CH 2) 3Si(OEt) 3 (dppaSi)

Heterometallic triangular palladium–cobalt clusters stabilized by three bridging diphosphine ligands such as Ph 2PNHPPh 2 (dppa), (Ph 2P) 2N(CH 3) (dppam), (Ph 2P) 2N(CH 2) 3Si(OEt) 3 (dppaSi), or mixed ligand sets Ph 2PCH 2PPh 2 (dppm)/dppa, dppm/dppam or dppm/dppaSi have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of making possible their use in the sol–gel process (case of dppaSi). The crystal structure determination of [CoPd 2( μ 3-CO) 2( μ-dppam) 3]PF 6 confirms the triangular arrangement of the metal core, with each edge bridged by a dppam ligand, although disorder problems prevent a detailed discussion of the bonding parameters. Different approaches are given to functionalize the heterometallic clusters: alkylation of the nitrogen atom of co-ordinated dppa ligands or introduction of a third bridging diphosphine in a precursor tetranuclear cluster containing only two bridging diphosphine ligands. In the latter case, it was found that their nature critically determined whether or not the reaction occurred. The diversity of bridging ligands allowed an investigation of their influence on the electrochemical properties of the clusters. By comparison with [CoPd 2( μ 3-CO) 2(CO) 2( μ-dppm) 2] + which contains only two assembling ligands, it is generally observed that trinuclear cationic CoPd 2 clusters containing three (identical or different) edge-bridging bidentate diphosphine ligands show increased redox flexibility. A notable stabilisation of the metal core is observed when three dppm ligands bridge the metal–metal bonds and [CoPd 2( μ 3-CO) 2( μ-dppm) 3] reversibly undergoes either a single-step two-electron oxidation or two distinct one-electron reductions. Complexes with the other diphosphines exhibit similar redox behaviour, but the stability of their redox congeners depends upon the nature of the diphosphine: a lower redox aptitude is exhibited by the dppa and dppam derivatives [CoPd 2( μ 3-CO) 2( μ-dppa) 3] + and [CoPd 2( μ 3-CO) 2( μ-dppam) 3] +.

Transition metal sulfur chemistry and its relevance to molybdenum and tungsten enzymes

Abstract

Structural aspects of the redox flexibility of group VIII metal complexes with tripodal polyphosphine ligands

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A new class of homoleptic 12-electron molybdenum and tungsten alkoxide clusters of formula [M4(OR)12

The authors are interested in developing efficient synthetic routes to alkoxide-supported molybdenum and tungsten clusters that may prove to be excellent models for fragments of reduced oxides of the same metals. These clusters should include both coordinative unsaturation and redox flexibility at the metal centers to initiate organometallic chemistry upon substrate reduction. Complementary metal oxide model systems such as polyoxoanions may prove effective for oxidation catalysis. They have recently demonstrated that W/sub 2/(O-i-Pr)/sub 6/ (I) exists in reversible equilibrium with its 12-electron cluster W/sub 4/(O-i-Pr)/sub 12/ (II) in solution at room temperature, eq 1, whereas Mo/sub 2/(O-i-Pr)/sub 6/ is indefinitely stable with respect to cluster formation. Even by reducing the steric demands at the molybdenum center they were unable to induce the formation of new metal-metal bonds in (Mo/sub 2/(O-i-Pr)/sub 5/(OMe))/sub 2/ (III), which instead retains isolated, unbridged Mo-Mo triple bonds. The authors report here the isolation and characterization of members of a new class of 12-electron tetranuclear alkoxide clusters, IV-XI, which are spectroscopically isostructural for both molybdenum and tungsten together with the single-crystal X-ray diffraction structure of one derivative, (Mo/sub 4/(O-CH/sub 2/-c-Bu)/sub 12/(HO-CH/sub 2/-c-Bu)) (XI) (where c-Bu = cyclobutyl). This represents the first group of structurally related homoleptic alkoxidemore » clusters for molybdenum and tungsten in oxidation state (3+).« less