Redox Reagents Research Articles

Density functional theory evidence for an electron hopping process in single-walled carbon nanotube-mediated redox reactions

The electron hopping mechanism in the single-walled carbon nanotube (SWCNT)-mediated redox reaction between anthraquinonyl (AQH2) and 4-arylhydroxyl amine (4AHA) groups is studied by density functional theory calculations. The (8,0) SWCNT is used to mimic the real system of interest. It is found that electrons from the oxidized AQH2 group can be transferred to the oxidizing 4AHA group, at the other end of the nanotube, by a hopping process through the mediating SWCNT. Disparity of electron densities ascribable to non-localized electrons confirms this finding. The disparity, partial electron density difference, and Hirshfeld partial charges analyses show that the SWCNT can hold 87% of the extra electron density of the hypothetical negative intermediate produced from the oxidation of the AQH2 process. Chemical attachments of these two redox reagents to the SWCNT also cause new impurity states within the band gap, thereby giving more metallic characteristics to the system. These findings provide a detailed understanding of the electron hopping process and agree well with a previous experimental study.

Use of redox reagents for stabilization of Pu and Np valence forms in aqueous reprocessing of spent nuclear fuel: Chemical and technological aspects

Published data on properties of reagents used in aqueous reprocessing of spent nuclear fuel for controlling the Pu and Np valence are summarized. The chemical principles of the reactions of U(IV), NH2OH, HNO2 (nitrogen oxides), and H2O2 with Pu and Np ions in nitric acid solutions and specific features of the behavior of these elements in the course of fuel reprocessing are considered. The properties of new promising organic redox reagents for stabilization of Pu and Np valence forms in the PUREX process are briefly described.

Industrial case study: Evaluation of a mixed-mode resin for selective capture of a human growth factor recombinantly expressed in E. coli

Mixed-mode chromatography resins are gaining popularity as effective purification tools for challenging feedstocks. This study presents the development of an industrial application to selectively capture recombinant human vascular endothelial growth factor (rhVEGF) on Capto MMC from an alkaline feedstock. Capto MMC resin contains a ligand that has the potential to participate in ionic, hydrophobic, and hydrogen boding interactions with proteins and is coupled to a highly cross-linked agarose bead matrix. VEGF is a key growth factor involved in angiogenesis and has therapeutic applications for wound healing. In this process, it is expressed in Escherichia coli as inclusion bodies. Solids are harvested from the cell lysate, and the rhVEGF is solubilized and refolded at pH 9.8 in the presence of urea and redox reagents. The unique mixed-mode characteristics of Capto MMC enabled capture of this basic protein with minimal load conditioning and delivered a concentrated pool for downstream processing with >95% yields while reducing host cell protein content to <1.2%. This study explores the impact of loading conditions and residence time on the dynamic binding capacity as well as the development of elution conditions for optimal purification performance. After evaluating various elution buffers, l-arginine HCl was shown to be an effective eluting agent for rhVEGF desorption from the Capto MMC mixed-mode resin since it successfully disrupted the multiple interactions between the resin and rhVEGF. The lab scale effort produced a robust chromatography step that was successfully implemented at commercial manufacturing scale.

Electrochemical studies of ferrocene in a lithium ion conducting organic carbonate electrolyte

We carried out a detailed study of the kinetics of oxidation of ferrocene (Fc) to ferrocenium ion (Fc +) in the non-aqueous lithium ion conducting electrolyte composed of a solution of 1 M LiPF 6 in 1:1 EC:EMC solvent mixture. This study using cyclic (CV) and rotating disk electrode (RDE) voltammetry showed that the Fc 0/Fc + redox couple is reversible in this highly concentrated electrolyte. The ferrocene and ferrocenium ion diffusion coefficients ( D) were calculated from these results. In addition, the electron transfer rate constant ( k 0) and the exchange current density for the oxidation of ferrocene were determined. A comparison of the kinetic data obtained from the two electrochemical techniques appears to show that the data from the RDE experiments are more reliable because they are collected under strict mass transport control. A Tafel slope of c.a. 79 mV/decade and a transfer coefficient α of 0.3 obtained from analysis of the RDE data for ferrocene oxidation suggest that the structure of the activated complex is closer to that of the oxidized specie due to strong interactions with the carbonate solvents. The experiments reported here are relevant to the study of redox reagents for the chemical overcharge protection of Li-ion batteries.

Characteristics of H and L Subunits with Mass Spectrometry, Electrophoresis and Transmission Electron Microscopy in Liver Ferritin of Dasyatis Akajei

Liver ferritin of Dasyatis akajei (DALF) with mass spectrum purity was prepared in batches. Transmission electron microscopy (TEM) was used to determine the molecular sizes of DALF, protein shell, and iron core, respectively. SDS-PAGE analysis reveals that DALF consists of two different types of subunits, H and L subunits. Moreover, the two types of both H and L subunits and their homology were further identified by peptide mass fingerprinting. Redox reagents such as natural red, thionine, and methyl viologen and the acidity at pH 1.5 does not have abilities for weakening the interaction intensity of both H-L and L-L subunit polymers to form L subunit ions for mass spectrum (MS) analysis with MALDI-TOF MS, respectively. However, using a combined approach of both increasing the laser intensity and decreasing the matrix pH synchronously, an MALDI-TOF mass spectrometer can directly determine molecular weights of both H and L subunits in DALF, indicating that the interaction intensity both H-L and L-L subunit polymers is higher than that of H-H subunit type in DALF.

Two tetranuclear Mn-complexes as biomimetic models of the oxygen evolving complex in Photosystem II. A synthesis, characterisation and reactivity study

In this work we report the preparation of two metallamacrocyclic tetranuclear manganese(II) complexes, [L1(4)Mn4](ClO4)4 and [L2(4)Mn4](ClO4)4 where L1 and L2 are the anions of the heptadentate ligands 2-((2-(bis(pyridin-2-ylmethyl)amino)ethyl)(methyl)amino)acetic acid and 2-(benzyl(2-(bis(pyridin-2-ylmethyl)amino)ethyl)amino)acetic acid), respectively. The complexes have been fully characterized by ESI-MS, elemental analysis, single-crystal X-ray diffraction, magnetic susceptibility, and EPR spectroscopy. Electrochemical reactions as well as reactions with different chemical redox reagents have been performed and a reversible two electron oxidation per manganese ion has been identified. The reaction of [L1(4)Mn4](ClO4)4 with oxone or cerium(IV) results in the evolution of oxygen which makes this system interesting for future studies in the search for a functional mimic of the oxygen evolving complex in Photosystem II.

Dimerization and endocytosis of the sucrose transporter StSUT1 in mature sieve elements

The sucrose transporter StSUT1 from Solanum tuberosum was shown to be regulated post-translationally by redox reagents. Its activity is increased at least 10fold in the presence of oxidizing agents if expressed in yeast. Oxidation has also an effect on plasma membrane targeting and dimerization of the protein. In response to oxidizing agents, StSUT1 is targeted to lipid raft-like microdomains and SUT1 protein is detectable in the detergent resistant membrane fraction of plant plasma membranes. Interestingly, StSUT1 treated with brefeldin A seems to aggregate in endocytic compartments in mature sieve elements. Further analysis of the SUT1 targeting will certainly provide more information about the putative involvement of lipid raft-like microdomains for endocytic events. We provide here additional information about the dimerization and endocytosis of the SUT1 protein. The oligomerization of overexpressed SoSUT1 from Spinacia oleracea in transgenic potato plants was analyzed by two-dimensional gel electrophoresis and endocytosis of the StSUT1 protein was confirmed by immunogold labeling.Addendum to: Krügel U, Veenhoff LM, Langbein J, Wiederhold W, Liesche J, Friedrich T, Grimm B, Martinoia E, Poolman B, Kühn C. Transport and Sorting of the plant sucrose transporter StSUT1 is affected by post-translational modification. Plant Cell 2008; 20:1-17.

Type and concentration of redox reagents influencing nitrile formation upon myrosinase ( Brassica carinata)-catalyzed hydrolysis of glucosibarin

The ratio of isothiocyanates (ITCs) to nitriles formed in the myrosinase-catalyzed hydrolysis of glucosinolates is a key factor determining the physiological effect of glucosinolate containing plants and materials. In this context, the mechanism by which nitrile formation occurs is not well understood. In the present paper we have studied the effect of three redox reagents – Fe 2+, glutathione (GSH) and ascorbic acid – on the profile of products obtained upon the hydrolysis of a model glucosinolate (glucosibarin ((2 R)-2-hydroxy-2-phenylethylglucosinolate)) catalyzed by Brassica carinata myrosinase. A Micellar Electrokinetic Capillary Chromatography method that allows following on-line the hydrolysis of the glucosinolate, the formation of the degradation products and the oxidation of GSH was used. Increasing the concentration of Fe 2+ and GSH (from 0.25- to 2-fold molar excess with respect to the glucosinolate) increased the ratio of nitrile ((2 R)-2-hydroxy-2-phenylethylcyanide) to oxazolidine-2-thione ((5 S)-5-phenyloxazolidine-2-thione), whereas increasing the concentration of ascorbic acid decreased this ratio. Low concentrations of ascorbic acid favored nitrile formation. A mechanism for nitrile formation involving a disulfide bond in the myrosinase complex is proposed.

Use of zeolite to refold a disulfide-bonded protein

Zeolites are microporous crystalline aluminosilicates with a highly ordered structure. Using zeolite beta as an adsorbent, denatured/reduced hen egg lysozyme was refolded to the active form at high concentrations. The denatured/reduced lysozyme was adsorbed onto the zeolite and the protein was refolded by desorbing it into refolding buffer, consisting of redox reagents, guanidine hydrochloride, polyethylene glycol, and l-arginine. This zeolite refolding method could be highly effective for various kinds of proteins, refolding them with high efficiency even when they contain disulfide bonds.

Transport and Sorting of the Solanum tuberosum Sucrose Transporter SUT1 Is Affected by Posttranslational Modification

The plant sucrose transporter SUT1 from Solanum tuberosum revealed a dramatic redox-dependent increase in sucrose transport activity when heterologously expressed in Saccharomyces cerevisiae. Plant plasma membrane vesicles do not show any change in proton flux across the plasma membrane in the presence of redox reagents, indicating a SUT1-specific effect of redox reagents. Redox-dependent sucrose transport activity was confirmed electrophysiologically in Xenopus laevis oocytes with SUT1 from maize (Zea mays). Localization studies of green fluorescent protein fusion constructs showed that an oxidative environment increased the targeting of SUT1 to the plasma membrane where the protein concentrates in 200- to 300-nm raft-like microdomains. Using plant plasma membranes, St SUT1 can be detected in the detergent-resistant membrane fraction. Importantly, in yeast and in plants, oxidative reagents induced a shift in the monomer to dimer equilibrium of the St SUT1 protein and increased the fraction of dimer. Biochemical methods confirmed the capacity of SUT1 to form a dimer in plants and yeast cells in a redox-dependent manner. Blue native PAGE, chemical cross-linking, and immunoprecipitation, as well as the analysis of transgenic plants with reduced expression of St SUT1, confirmed the dimerization of St SUT1 and Sl SUT1 (from Solanum lycopersicum) in planta. The ability to form homodimers in plant cells was analyzed by the split yellow fluorescent protein technique in transiently transformed tobacco (Nicotiana tabacum) leaves and protoplasts. Oligomerization seems to be cell type specific since under native-like conditions, a phloem-specific reduction of the dimeric form of the St SUT1 protein was detectable in SUT1 antisense plants, whereas constitutively inhibited antisense plants showed reduction only of the monomeric form. The role of redox control of sucrose transport in plants is discussed.

Extended-gate FET-based enzyme sensor with ferrocenyl-alkanethiol modified gold sensing electrode

We developed a field-effect transistor (FET)-based enzyme sensor that detects an enzyme-catalyzed redox-reaction event as an interfacial potential change on an 11-ferrocenyl-1-undecanethiol (11-FUT) modified gold electrode. While the sensitivity of ion-sensitive FET (ISFET)-based enzyme sensors that detect an enzyme-catalyzed reaction as a local pH change are strongly affected by the buffer conditions such as pH and buffer capacity, the sensitivity of the proposed FET-based enzyme sensor is not affected by them in principle. The FET-based enzyme sensor consists of a detection part, which is an extended-gate FET sensor with an 11-FUT immobilized gold electrode, and an enzyme reaction part. The FET sensor detected the redox reaction of hexacyanoferrate ions, which are standard redox reagents of an enzymatic assay in blood tests, as a change in the interfacial potential of the 11-FUT modified gold electrode in accordance with the Nernstian response at a slope of 59 mV/decade at 25 °C. Also, the FET sensor had a dynamic range of more than five orders and showed no sensitivity to pH. A FET-based enzyme sensor for measuring cholesterol level was constructed by adding an enzyme reaction part, which contained cholesterol dehydrogenase and hexacyanoferrate (II)/(III) ions, on the 11-FUT modified gold electrode. Since the sensitivity of the FET sensor based on potentiometric detection was independent of the sample volume, the sample volume was easily reduced to 2.5 μL while maintaining the sensitivity. The FET-based enzyme sensor successfully detected a serum cholesterol level from 33 to 233 mg/dL at the Nernstian slope of 57 mV/decade.

Chemical Reaction of Reagents Covalently Confined to a Nanotube Surface: Nanotube-Mediated Redox Chemistry

We present the use of carbon nanotubes (CNTs) as nanoreaction vessels to confine chemical reactions within the carbon nano-“test tube”. This is achieved by functionalizing two redox reagents, anthraquinonnyl and 4-nitrophenyl groups, on the same CNT. It was found that the CNT can mediate the chemical reaction between the two redox reagents and generate 4-arylamine groups at the CNT surface. The reaction can proceed only when both the reagents are confined on the same CNT; if the reagents are located on different tubes, reaction ceases.

Regulation of heat shock-induced apoptosis by sensitive to apoptosis gene protein

Heat shock may increase oxidative stress due to increased production of reactive oxygen species and/or the promotion of cellular oxidation events. Sensitive to apoptosis gene (SAG) protein, a novel zinc RING finger protein that protects mammalian cells from apoptosis by redox reagents, is a metal chelator and a potential reactive oxygen species scavenger, but its antioxidant properties have not been completely defined. In this report, we demonstrate that modulation of SAG expression in U937 cells regulates heat shock-induced apoptosis. When we examined the protective role of SAG against heat shock-induced apoptosis with U937 cells transfected with the cDNA for SAG, a clear inverse relationship was observed between the amount of SAG expressed in target cells and their susceptibility to apoptosis. We also observed a significant decrease in the endogenous production of reactive oxygen species and oxidative DNA damage in SAG-overexpressed cells compared to control cells on exposure to heat shock. In addition, transfection of PC3 cells with SAG small interfering RNA markedly decreased the expression of SAG, enhancing the susceptibility of heat shock-induced apoptosis. Taken together, these results indicate that SAG may play an important role in regulating the apoptosis induced by heat shock presumably through maintaining the cellular redox status.

Redox Reactions of a Dinuclear Manganese Complex – the Influence of Water

AbstractThe redox properties of the dinuclear manganese complex [MnIII,III2L(μ‐OAc)2]+ (1) (where L is the trianion of the heptadentate ligand 2,6‐bis{[(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)(2‐pyridylmethyl)amino]methyl}‐4‐methylphenol) were studied in acetonitrile solutions containing different concentrations of water. Electrochemical reactions as well as reactions with different chemical and photochemical redox reagents were monitored, using a variety of analytical techniques, namely cyclic voltammetry, UV/Vis spectroelectrochemistry, and EPR spectroscopy. We found that even small concentrations of water influence the compound's redox behaviour significantly, especially the oxidation reactions. As a consequence, the presence of water reduces the overall potential span needed to reach the highest oxidation state observed for 1 (MnIII,IV2) from its most reduced state (MnII,II2) to about 1.1 V. Higher oxidation states of 1 are stabilized, most likely by water coordination and the formation of μ‐oxido bridge(s) between the two manganese atoms. For reducing conditions, an unprecedented 25‐line EPR signal was observed, which might originate from reduced 1 in its MnII,II2 or MnII,III2 state after considerable ligand rearrangement. As complexes like 1 have been designed to act as potential water oxidation catalysts, the complicated redox‐ and ligand‐exchange chemistry found for 1 in the presence of water, its intended substrate, might be exemplary for many of the dinuclear manganese compounds currently under investigation. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

In vitro-refolding of a single-chain Fv fragment in the presence of heteroaromatic thiols

The aim of the present work was to explore the use of heteroaromatic thiol compounds, namely derivatives of pyridine and pyrimidine, as redox reagents for the in vitro-refolding of a recombinantly expressed single-chain Fv fragment (scFvOx). The mixed disulfide of scFvOx with glutathione was used as a starting material, while reduced glutathione, 4-mercaptopyridine, 2-mercaptopyrimidine, 2-mercaptopyridine N-oxide, and the mercaptobenzene derivative thiosalicylic acid, respectively, served as catalysts for the formation of native disulfide bonds during renaturation. In contrast to thiosalicylic acid, and despite their significantly lower thiol p K a values, none of the heteroaromatic thiol compounds accelerated the apparent kinetics of in vitro-refolding compared to the naturally occurring peptide glutathione. However, significantly improved renaturation yields were observed in the presence of 4-mercaptopyridine and 2-mercaptopyrimidine, demonstrating the usefulness of aromatic thiol compounds as reagents for the in vitro-refolding of antibody fragments.

SH-Containing Cellulose Acetate Derivatives: Preparation and Characterization as a Shape Memory-Recovery Material

Cellulose derivatives having a cross-linkable mercapto group were prepared by esterification of cellulose acetate (CA) with mercaptoacetic acid. The molecular structure of a series of products (CA-MA) was characterized by (1)H and (1)H- (13)C HMQC NMR spectroscopy and gel permeation chromatography. The solubility of CA-MA in water and organic solvents could be controlled by changing the preparation conditions including the degree of acetyl substitution of the starting CA. The CA-MA samples thus synthesized showed a sol-gel transition in solution and a shape memory-recovery behavior in film form through adequate redox treatments due to the reversible, cross-linking association and dissociation between mercapto groups. Dimethyl sulfoxide was usable as the organic solvent and oxidant, while the major reducing reagent was 2-mercaptoethanol or ammonium mercaptoacetic acid. The progress of the redox reactions was followed by using a confocal depth scanning technique in Raman spectroscopy. It was found that the compatibility between the cellulose derivatives and the redox reagents used was an important factor for the successful reactions, especially in the samples of film form. The cross-linking effect on the thermal and viscoelastic properties of the CA-MA films was also estimated by differential scanning calorimetry and dynamic mechanical analysis. Discussion focused on the alternately declining and recovering behavior of a principal loss tan delta peak, observed following the redox treatments repeated for the CA-MA film specimens.

Isolation and characterization of the DNA-binding protein (DBP) of the Autographa californica multiple nucleopolyhedrovirus

DNA-binding protein (DBP) of Autographa californica multiple nucleopolyhedrovirus (Ac MNPV) was expressed as an N-terminal His 6-tag fusion using a recombinant baculovirus and purified to near homogeneity. Purified DBP formed oligomers that were crosslinked by redox reagents resulting in predominantly protein dimers and tetramers. In gel retardation assays, DBP showed a high affinity for single-stranded oligonucleotides and was able to compete with another baculovirus SSB protein, LEF-3, for binding sites. DBP binding protected ssDNA against hydrolysis by a baculovirus alkaline nuclease AN/LEF-3 complex. Partial proteolysis by trypsin revealed a domain structure of DBP that is required for interaction with DNA and that can be disrupted by thermal treatment. Binding to ssDNA, but not to dsDNA, changed the pattern of proteolytic fragments of DBP indicating adjustments in protein structure upon interaction with ssDNA. DBP was capable of unwinding short DNA duplexes and also promoted the renaturation of long complementary strands of ssDNA into duplexes. The unwinding and renaturation activities of DBP, as well as the DNA binding activity, were sensitive to sulfhydryl reagents and were inhibited by oxidation of thiol groups with diamide or by alkylation with N-ethylmaleimide. A high affinity of DBP for ssDNA and its unwinding and renaturation activities confirmed identification of DBP as a member of the SSB/recombinase family. These activities and a tight association with subnuclear structures suggests that DBP is a component of the virogenic stroma that is involved in the processing of replicative intermediates.

Solvent‐Dependent Interconversions between RhI, RhII, and RhIII Complexes of an Aryl–Monophosphine Ligand

Reaction of the aryl-monophosphine ligand alpha(2)-(diisopropylphosphino)isodurene (1) with the Rh(I) precursor [Rh(coe)(2)(acetone)(2)]BF(4) (coe=cyclooctene) in different solvents yielded complexes of all three common oxidation states of rhodium, depending on the solvent used. When the reaction was carried out in methanol a cyclometalated, solvent-stabilized Rh(III) alkyl-hydride complex (2) was obtained. However, when the reaction was carried out in acetone or dichloromethane a dinuclear eta(6)-arene Rh(II) complex (5) was obtained in the absence of added redox reagents. Moreover, when acetonitrile was added to a solution of either the Rh(II) or Rh(III) complexes, a new solvent-stabilized, noncyclometalated Rh(I) complex (6) was obtained. In this report we describe the different complexes, which were fully characterized, and probe the processes behind the remarkable solvent effect observed.

Organometallic Electron-Reservoir Complexes. Concepts and Applications

Abstract The 19-electron complexes [FeI(η5-C5R5)(η6-arene)] (R=H, arene = C6Me6, 1,3,5-tBu3C6H3; R=Me, arene = C6Me6, C6Et5H) are thermally stable and serve as strong single-electron reductant in a variety of stoichiometric and catalytic electron-transfer processes that are detailed in this review (prototype: [FeI(η5-C5H5)(η6-C6Me6)]). They are electron-reservoirs because their redox potential is very negative and they form a redox system for which both redox forms are stable. In this sense, they are Green redox reagents, since the oxidized form is recovered after use and is even frequently catalytically used. Symmetrically, the 17-electron complex [FeIII(η5-C5R5)(η6-C6Me6)][SbCl6]2, the strongest organometallic single-electron oxidant with a redox potential 1 V more positive than that of its isoelectronic ferrocenium analog, is a reservoir of electron hole.

Molecular and Biochemical Analysis of the Plastidic ADP-glucose Transporter (ZmBT1) from Zea mays

Physiological studies on the Brittle1 maize mutant have provided circumstantial evidence that ZmBT1 (Zea mays Brittle1 protein) is involved in the ADP-Glc transport into maize endosperm plastids, but up to now, no direct ADP-Glc transport mediated by ZmBT1 has ever been shown. The heterologous synthesis of ZmBT1 in Escherichia coli cells leads to the functional integration of ZmBT1 into the bacterial cytoplasmic membrane. ZmBT1 transports ADP-Glc in counterexchange with ADP with apparent affinities of about 850 and 465 mum, respectively. Recently, a complete ferredoxin/thioredoxin system has been identified in cereal amyloplasts and BT1 has been proposed as a potential Trx target protein (Balmer, Y., Vensel, W. H., Cai, N., Manieri, W., Schurmann, P., Hurkman, W. J., and Buchanan, B. B. (2006) Proc. Natl. Acad. Sci. U. S. A. 103, 2988-2993). Interestingly, we revealed that the transport activity of ZmBT1 is reversibly regulated by redox reagents such as diamide and dithiothreitol. The expression of ZmBT1 is restricted to endosperm tissues during starch synthesis, whereas a recently identified BT1 maize homologue, the ZmBT1-2, exhibits a ubiquitous expression pattern in hetero- and autotrophic tissues indicating different physiological roles for both maize BT1 isoforms. BT1 homologues are present in both mono- and dicotyledonous plants. Phylogenetic analyses classify the BT1 family into two phylogenetically and biochemically distinct groups. The first group comprises BT1 orthologues restricted to cereals where they mediate the ADP-Glc transport into cereal endosperm storage plastids during starch synthesis. The second group occurs in mono- and dicotyledonous plants and is most probably involved in the export of adenine nucleotides synthesized inside plastids.