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Chemical Reduction (chemical + reduction)
Kinds of Chemical Reduction Selected AbstractsDevelopment of partial rock veneers by root throw in a subalpine settingEARTH SURFACE PROCESSES AND LANDFORMS, Issue 1 2006W. R. Osterkamp Abstract Rock veneers stabilize hillslope surfaces, occur especially in areas of immature soil, and form through a variety of process sets that includes root throw. Near Westcliffe, Colorado, USA, data were collected from a 20 × 500 m transect on the east slope of the Sangre de Cristo Mountains. Ages of pit/mound complexes with rock fragments exposed at the surface by root throw ranged from recent (freshly toppled tree) to unknown (complete tree decay). Calculations based on dimensions of the pit/mound complexes, estimated time of tree toppling, sizes of exposed rock fragments, and percentage rock covers at pit/mound complexes, as well as within the transect area, indicate that recent rates of root throw have resulted in only partial rock veneering since late Pleistocene deglaciation. Weathering of rock fragments prevents development of an extensive rock veneer and causes a balance, achieved within an estimated 700 years, between the rates of rock-fragment exposure by root throw and clast disintegration by chemical reduction. The estimated rate of rock-fragment reduction accounts for part of the fluvial sediment yields observed for forested subalpine areas of western North America. Copyright © 2005 John Wiley & Sons, Ltd. [source] Reducing conditions significantly attenuate the neuroprotective efficacy of competitive, but not other NMDA receptor antagonists in vitroEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2000Ashley K. Pringle Abstract Inappropriate activation of NMDA receptors during a period of cerebral ischaemia is a crucial event in the pathway leading to neuronal degeneration. However, significant research has failed to deliver a clinically active NMDA receptor antagonist, and competitive NMDA antagonists are ineffective in many experimental models of ischaemia. The NMDA receptor itself has a number of modulatory sites which may affect receptor function under ischaemic conditions. Using rat organotypic hippocampal slice cultures we have investigated whether the redox modulatory site affects the neuroprotective efficacy of NMDA receptor antagonists against excitotoxicity and experimental ischaemia (OGD). NMDA toxicity was significantly enhanced in cultures pretreated with a reducing agent. The noncompetitive antagonist MK-801 and a glycine-site blocker were equally neuroprotective in both normal and reduced conditions, but there was a significant rightward shift in the dose,response curves of the competitive antagonists APV and CPP and the uncompetitive antagonist memantine. OGD produced neuronal damage predominantly in the CA1 region, which was prevented by MK-801 and memantine, but not by APV or CPP. Inclusion of an oxidizing agent during the period of OGD had no effect alone, but significantly enhanced the neuroprotective potency of the competitive antagonists. These data clearly demonstrate that chemical reduction of the redox modulatory site of the NMDA receptor decreases the ability of competitive antagonists to block NMDA receptor-mediated neuronal damage, and that the reducing conditions which occur during simulated ischaemia are sufficient to produce a similar effect. This may have important implications for the design of future neuroprotective agents. [source] Structural Evolution and Copper-Ion Release Behavior of Cu-pHEMA Hybrids Synthesized In Situ,ADVANCED ENGINEERING MATERIALS, Issue 11 2009Yen-Yu Liu Abstract A novel Cu-pHEMA hybrid was successfully prepared by in situ photopolymerization of 2-hydroxyethyl methacrylate (HEMA) monomer in the presence of Cu(II) copper ions, following an in situ chemical reduction. Experimental observations indicate that intermolecular interactions such as the coupling force and hydrogen bonding between the Cu and the hydroxyl groups further stabilize the hybrid structure to a considerable extent. Localization of the metallic copper particles within the pHEMA network structure as a result of those intermolecular interactions gives rise to the formation of discretely distributed nanocrystallites with particle sizes ranging from 5 to 25,nm in diameter. A crystallographic change of the Cu nanophase from an amorphous-like to a crystalline structure is observed as the H2O:HEMA molar ratio increases, upon synthesis, accompanied with an increase in the particle size. A relatively slow and sustained release of the Cu (in the form of cupric ions) from the hybrids was measured for a time period of about 10 days, which also illustrates a Cu(II)-induced proliferation of the endothelial cells over a relatively small range of release rate of the Cu from the hybrids. Such a new type of Cu-loaded hybrid hydrogel is expected to be compatible and may be considered as a candidate biomaterial for biomedical/therapeutic uses. [source] A Transparent, Flexible, Low-Temperature, and Solution-Processible Graphene Composite ElectrodeADVANCED FUNCTIONAL MATERIALS, Issue 17 2010Haixin Chang Abstract The synthesis and preparation of a new type of graphene composite material suitable for spin-coating into conductive, transparent, and flexible thin film electrodes in ambient conditions is reported here for the first time. Solution-processible graphene with diameter up to 50 ,m is synthesized by surfactant-assisted exfoliation of graphite oxide and in situ chemical reduction in a large quantity. Spin-coating the mixing solution of surfactant-functionalized graphene and PEDOT:PSS yields the graphene composite electrode (GCE) without the need for high temperature annealing, chemical vapor deposition, or any additional transfer-printing process. The conductivity and transparency of GCE are at the same level as those of an indium tin oxide (ITO) electrode. Importantly, it exhibits high stability (both mechanical and electrical) in bending tests of at least 1000 cycles. The performance of organic light-emitting diodes based on a GCE anode is comparable, if not superior, to that of OLEDs made with an ITO anode. [source] Preparation, Structure, and Electrochemical Properties of Reduced Graphene Sheet FilmsADVANCED FUNCTIONAL MATERIALS, Issue 17 2009Longhua Tang Abstract This paper describes the preparation, characterization, and electrochemical properties of reduced graphene sheet films (rGSFs), investigating especially their electrochemical behavior for several redox systems and electrocatalytic properties towards oxygen and some small molecules. The reduced graphene sheets (rGSs) are produced in high yield by a soft chemistry route involving graphite oxidation, ultrasonic exfoliation, and chemical reduction. Transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy clearly demonstrate that graphene was successfully synthesized and modified at the surface of a glassy carbon electrode. Several redox species, such as Ru(NH3)63+/2+, Fe(CN)63,/4,, Fe3+/2+ and dopamine, are used to probe the electrochemical properties of these graphene films by using the cyclic voltammetry method. The rGSFs demonstrate fast electron-transfer (ET) kinetics and possess excellent electrocatalytic activity toward oxygen reduction and certain biomolecules. In our opinion, this microstructural and electrochemical information can serve as an important benchmark for graphene-based electrode performances. [source] Surface-enhanced Raman scattering study of the red dye laccaic acidJOURNAL OF RAMAN SPECTROSCOPY, Issue 10 2007M. V. Cañamares Abstract FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied to the study of lac dye, a highly fluorescent anthraquinone red dye. The SERS spectra were obtained at different pH values, on Ag nanoparticles prepared by chemical reduction with citrate and hydroxylamine, and at several excitation wavelengths, in order to find the best experimental conditions for the detection of the lac dye. The lower detection limit was achieved using nanoparticles prepared by reduction with hydroxylamine, excitation at 514.5 nm, and slightly acidic pH conditions, thus exploiting a combination of factors including lower electrostatic repulsion between dye and nanoparticles and resonance Raman enhancement. A comparison between the adsorption of laccaic acid (LA) and carminic acid (CA), another anthraquinone red dye, was also done, based on the SERS spectra of both dyes. Copyright © 2007 John Wiley & Sons, Ltd. [source] Surface-enhanced Raman scattering study of the adsorption of the anthraquinone pigment alizarin on Ag nanoparticlesJOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2004M. V. Cañamares Abstract FT-Raman and surface-enhanced Raman scattering (SERS) spectroscopy were applied in the vibrational characterization and study of the adsorption and acidity behavior of the highly fluorescent anthraquinone dye alizarin on Ag colloids prepared by chemical reduction with hydroxylamine hydrochloride. The SERS spectra were obtained at different conditions of pH, excitation wavelength and pigment concentration in order to deduce the adsorption mechanism of this molecule. On the basis of the results found we propose an adsorption model for alizarin, which has a different acidic behavior on the metal surface to that in solution. On the metal the deprotonation order of the OH groups changes with respect to the aqueous solution, the OH in position 1 being the first to be ionized instead of that in position 2 as occurs in solution. The two main alizarin forms identified on the metal surface correspond to the mono- and dianionic alizarin species. Copyright © 2004 John Wiley & Sons, Ltd. [source] Photooxidation and Photoconductivity of Polyferrocenylsilane Thin FilmsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 7 2003Paul W. Cyr Abstract Irradiation of thin films of poly(ferrocenylmethylphenylsilane) ([Fe(,5 -C5H4)2SiMePh]n) cast from chloroform solution with UV light leads to photooxidation of ferrocene centers in the polymer main chain. The extent of the polymer oxidation can be controlled in the range ca. 0,5% by the duration of the irradiation exposure and by the concentration of chloroform. The photooxidized polyferrocenylsilane material is conductive, with an increased conductivity of greater than three orders of magnitude relative to the unoxidized material. In addition, the photooxidized polymers have been found to be photoconductive. The photooxidation process can be reversed by means of chemical reduction using hydrazine or decamethylferrocene, leading to the regeneration of the neutral polymers. However, substantial molecular weight decline was detected during the photooxidation/reduction process, presumably as a result of chain cleavage reactions induced by the anionic or radical chlorinated photoproducts. Methylation of the cyclopentadienyl rings of the ferrocene moiety in the polymer was found to lead to materials which are significantly more stable. Time trace of the current at constant applied voltage of 100 V for a PFS film upon illumination. The ON and OFF states were created by using a mechanical shutter. [source] In situ remediation of PCE at a site with clayey lithology and a significant smear zoneREMEDIATION, Issue 3 2010Josephine Molin Groundwater at the former Serry's Dry Cleaning site in Corvallis, Oregon, was impacted by chlorinated volatile organic compounds (CVOCs). The primary CVOCs impacting the site include tetrachloroethene, trichloroethene, dichloroethene, and vinyl chloride, which were detected at concentrations up to 22,000, 1,700, 3,100, and 7 ,g/L, respectively, prior to treatment. Large seasonal fluctuations in groundwater CVOC concentrations indicated that a significant fraction of the CVOC mass was present in the smear zone. Field-scale pilot tests were performed for the Oregon Department of Environmental Quality's Dry Cleaner Program to evaluate the performance of EHC® in situ chemical reduction (ISCR) technology. The pilot study involved evaluating field performance and physical distribution into low-permeability soil using basic Geoprobe® injection tooling. The testing results confirmed that bioremediation enhanced by ISCR supported long-term treatment at the site. This article describes the implementation and results of the tests. Performance data are available from a three-year period following the injections, allowing for a discussion about sustained performance and reagent longevity. © 2010 Wiley Periodicals, Inc. [source] Successful ISCR-enhanced bioremediation of a TCE DNAPL source utilizing EHC® and KB-1®REMEDIATION, Issue 3 2010James G. D. Peale Remediation of chlorinated solvent DNAPL sites often meets with mixed results. This can be attributed to the diametrically opposed nature of the impacts, where the disparate dissolved-phase plume is more manageable than the localized, high-concentration source area. A wide range of technologies are available for downgradient plume management, but the relative mass of contaminants in a DNAPL source area generally requires treatment for such technologies to be effective over the long term. In many cases, the characteristics of DNAPL source zones (e.g., depth, soil heterogeneity, structural limitations) limit the available options. The following describes the successful full-scale implementation of in situ chemical reduction (ISCR) enhanced bioremediation of a TCE DNAPL source zone. In this demonstration, concentrations of TCE were rapidly reduced to below the maximum contaminant level (MCL) in less than six months following implementation. The results described herein suggest that ISCR-enhanced bioremediation is a viable remedial alternative for chlorinated solvent source zones. © 2010 Wiley Periodicals, Inc. [source] TCE plume remediation via ISCR-enhanced bioremediation utilizing EHC® and KB-1®REMEDIATION, Issue 4 2008James G. D. Peale Groundwater below an operating manufacturing facility in Portland, Oregon, was impacted by chlorinated volatile organic compounds (CVOCs), with concentrations indicative of a dense, nonaqueous-phase liquid (DNAPL) release. The downgradient plume stretched under the adjacent Willamette River, intersecting zones of legacy impacts from a former manufactured gas plant (MGP). An evaluation of source-area and downgradient plume treatment remedies identified in situ bioremediation as most likely to be effective for the CVOC plume, while leaving the legacy impacts for other responsible parties. With multiple commercially available products to choose from, the team developed and implemented a bench test to identify the most appropriate technology, which was further evaluated in a field pilot study. The results of the testing demonstrated conclusively that bioremediation enhanced by in situ chemical reduction (ISCR) using EHC® and KB-1® was most appropriate for this site, providing outstanding results. The following describes the implementation and results of the tests. © 2008 Wiley Periodicals, Inc. [source] Investigation on the proton exchange membrane water electrolyzer using supported anode catalystASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2009Sheng Sui Abstract The proton exchange membrane water electrolyzer (PEMWE) was investigated using a novel supported anode catalyst. The supported catalyst for the oxygen evolution reaction (OER) was synthesized by chemical reduction and deposition under ultrasonic dispersion. Transmission electron microscopy (TEM) reveals that iridium (Ir) particles with sizes of about 10,40 nm are mainly dispersed on the outside surface of titanium carbide (TiC). The PEMWE using the supported Ir/TiC (40 wt% Ir) as the anode catalyst shows the best performance among the supported catalysts of three different Ir contents. Increasing the cell temperature in the PEMWE can enhance the activity of the catalyst and lower the over-potential of the electrodes, which can improve the performance of the PEMWE. At a cell temperature of 80 °C and atmospheric pressure, the current densities of the best PEMWE at the potential of 1.8 and 2.0 V are 1002 and 1736 mA/cm2, respectively. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Use of recombinant rotavirus VP6 nanotubes as a multifunctional template for the synthesis of nanobiomaterials functionalized with metalsBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Germán Plascencia-Villa Abstract The structural characteristics and predefined constant size and shape of viral assemblies make them useful tools for nanobiotechnology, in particular as scaffolds for constructing highly organized novel nanomaterials. In this work it is shown for the first time that nanotubes formed by recombinant rotavirus VP6 protein can be used as scaffolds for the synthesis of hybrid nanocomposites. Rotavirus VP6 was produced by the insect cell-baculovirus expression vector system. Nanotubes of several micrometers in length and various diameters in the nanometer range were functionalized with Ag, Au, Pt, and Pd through strong (sodium borohydride) or mild (sodium citrate) chemical reduction. The nanocomposites obtained were characterized by transmission electron microscopy (TEM), high-resolution TEM (HRTEM) with energy dispersive spectroscopy (EDS), dynamic light scattering, and their characteristic plasmon resonance. The outer surface of VP6 nanotubes had intrinsic affinity to metal deposition that allowed in situ synthesis of nanoparticles. Furthermore, the use of preassembled recombinant protein structures resulted in highly ordered integrated materials. It was possible to obtain different extents and characteristics of the metal coverage by manipulating the reaction conditions. TEM revealed either a continuous coverage with an electrodense thin film when using sodium citrate as reductant or a discrete coverage with well-dispersed metal nanoparticles of diameters between 2 and 9,nm when using sodium borohydride and short reaction times. At long reaction times and using sodium borohydride, the metal nanoparticles coalesced and resulted in a thick metal layer. HRTEM-EDS confirmed the identity of the metal nanoparticles. Compared to other non-recombinant viral scaffolds used until now, the recombinant VP6 nanotubes employed here have important advantages, including a longer axial dimension, a dynamic multifunctional hollow structure, and the possibility of producing them massively by a safe and efficient bioprocess. Such characteristics confer important potential applications in nanotechnology to the novel nanobiomaterials produced here. Biotechnol. Bioeng. 2009; 104: 871,881. © 2009 Wiley Periodicals, Inc. [source] Topical application of acidified nitrite to the nail renders it antifungal and causes nitrosation of cysteine groups in the nail plateBRITISH JOURNAL OF DERMATOLOGY, Issue 3 2007M.J. Finnen Summary Background, Topical treatment of nail diseases is hampered by the nail plate barrier, consisting of dense cross-linked keratin fibres held together by cysteine-rich proteins and disulphide bonds, which prevents penetration of antifungal agents to the focus of fungal infection. Acidified nitrite is an effective treatment for tinea pedis. It releases nitric oxide (NO) and other NO-related species. NO can react with thiol (-SH) groups to form nitrosothiols (-SNO). Objectives, To determine whether acidified nitrite can penetrate the nail barrier and cure onychomycosis, and to determine whether nitrosospecies can bind to the nail plate. Methods, Nails were treated with a mixture of citric acid and sodium nitrite in a molar ratio of 0·54 at either low dose (0·75%/0·5%) or high dose (13·5%/9%). Immunohistochemistry, ultraviolet-visible absorbance spectroscopy and serial chemical reduction of nitrosospecies followed by chemiluminescent detection of NO were used to measure nitrosospecies. Acidified nitrite-treated nails and the nitrosothiols S-nitrosopenicillamine (SNAP) and S-nitrosoglutathione (GSNO) were added to Trichophyton rubrum and T. mentagrophytes cultures in liquid Sabouraud medium and growth measured 3 days later. Thirteen patients with positive mycological cultures for Trichophyton or Fusarium species were treated with topical acidified nitrite for 16 weeks. Repeat mycological examination was performed during this treatment time. Results, S-nitrothiols were formed in the nail following a single treatment of low- or high-dose sodium nitrite and citric acid. Repeated exposure to high-dose acidified nitrite led to additional formation of N-nitrosated species. S-nitrosothiol formation caused the nail to become antifungal to T. rubrum and T. mentagrophytes. Antifungal activity was Cu2+ sensitive. The nitrosothiols SNAP and GSNO were also found to be antifungal. Topical acidified nitrite treatment of patients with onychomycosis resulted in > 90% becoming culture negative for T. rubrum. Conclusions, Acidified nitrite cream results in the formation of S-nitrosocysteine throughout the treated nail. Acidified nitrite treatment makes a nail antifungal. S-nitrosothiols, formed by nitrosation of nail sulphur residues, are the active component. Acidified nitrite exploits the nature of the nail barrier and utilizes it as a means of delivery of NO/nitrosothiol-mediated antifungal activity. Thus the principal obstacle to therapy in the nail becomes an effective delivery mechanism. [source] Downregulation of cell survival signalling pathways and increased cell damage in hydrogen peroxide-treated human renal proximal tubular cells by alpha-erythropoietinCELL PROLIFERATION, Issue 4 2009M. Andreucci Objective:, Erythropoietin has been shown to have a protective effect in certain models of ischaemia-reperfusion, and in some cases the protection has been correlated with activation of signalling pathways known to play a role in cell survival and proliferation. We have studied whether erythropoietin would overcome direct toxic effects of hydrogen peroxide (H2O2) treatment to human renal proximal tubular (HK-2) cells. Materials and methods:, HK-2 cells were incubated with H2O2 (2 mm) for 2 h with or without erythropoietin at concentrations of 100 and 400 U/ml, and cell viability/proliferation was assessed by chemical reduction of MTT. Changes in phosphorylation state of the kinases Akt, glycogen synthase kinase-3, (GSK-3,), mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2) were also analysed. Results:, Cells incubated with H2O2 alone showed a significant decrease in viability, which did not significantly change by addition of erythropoietin at concentration of 100 U/ml, but was further reduced when concentration of erythropoietin was increased to 400 U/ml. Phosphorylation state of the kinases Akt, GSK-3,, mTOR and ERK1/ERK2 of H2O2 -treated HK-2 cells was slightly altered in the presence of erythropoietin at concentration of 100 U/ml, but was significantly less in the presence of erythropoietin at a concentration of 400 U/ml. Phosphorylation of forkhead transcription factor FKHRL1 was diminished in cells incubated with H2O2 and erythropoietin at a concentration of 400 U/ml. Conclusions:, Erythropoietin, at high concentrations, may significantly increase cellular damage in HK-2 cells subjected to oxidative stress, which may be due in part to decrease in activation of important signalling pathways involved in cell survival and/or cell proliferation. [source] Diboryl and Diboranyl Porphyrin Complexes: Synthesis, Structural Motifs, and Redox Chemistry: Diborenyl Porphyrin or Diboranyl Isophlorin?CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2007Andre Weiss Dr. Abstract The syntheses of diboryl porphyrin complexes [(BX2)2(ttp)] (ttp: dianion of tetra- p -tolylporphyrin) and the BB single-bond diboranyl complexes [(BX)2(ttp)] (X=F, Cl, Br, I) are given. The former are prepared from the reactions of BX3 (X=F, Cl) with [Li2(ttp)] and the latter from B2Cl4 (X=Cl), the reaction of SbF3 with [(BCl)2(ttp)] (for X=F), and, in the cases of X=Br or I, in a remarkable reductive coupling reaction resulting directly from the reaction of BBr3 or BI3 with [Li2(ttp)]. Density functional theory (DFT) calculations on the thermochemical parameters for the reductive coupling reactions (and those calculated for related dipyrromethene complexes) indicate that a combination of the reducing ability of bromide and iodide ions combined with the constrained environment of the porphyrin ligand contribute to the driving force. The reductive coupling is also observed in the reaction of [(BCl2)2(ttp)] with nBuLi to give [(BnBu)2(ttp)], which was characterised crystallographically. The reaction of [(BCl)2(ttp)] with catechol gives a boron catecholato porphyrin complex, [B2(O2C6H4)(ttp)]. Chloride abstraction from [(BCl)2(ttp)] gives the planar dication [B2(ttp)]2+, whereas chemical reduction of [(BCl)2(ttp)] by using magnesium anthracenide gives a neutral complex, [B2(ttp)], in which the TTP ligand has been reduced by two electrons to give an unusual example of an isophlorin complex. The cationic and neutral complexes [B2(ttp)]2+ and [B2(ttp)] were characterised through a combination of spectroscopic data that is supported by DFT calculations on the porphine analogues. [source] Chemical Derivatisation of Multiwalled Carbon Nanotubes Using Diazonium Salts,CHEMPHYSCHEM, Issue 11 2004Charles G. R. Heald A facile and versatile modification strategy: A chemically activated method of covalently derivatising carbon powder, via the chemical reduction of aryl diazonium salts with hypophosphorous acid, to include the covalent derivatisation of multiwalled carbon nanotubes (MWCNTs) is demonstrated. The specific molecular environments of 1-anthraquinonyl moieties attached to MWCNTs (see picture) produce interesting effects. [source] Fabrication of Cobalt and Cobalt Oxide/Graphene Composites: Towards High-Performance Anode Materials for Lithium Ion BatteriesCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 2 2010Shubin Yang Dr. Pave a way to high-performance anode materials: Organic metal/graphene composites are fabricated through an in,situ assembly of disc-shaped phthalocyanine molecules with graphene sheets during the chemical reduction of graphite oxide, which enables a homogenous dispersion of Co and Co3O4 nanoparticles in the sheets after simple pyrolysis and oxidation. The resulting Co3O4/graphene composites exhibit remarkable lithium storage performance. [source] | |||||||||||||||||||