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Thiols
Kinds of Thiols Terms modified by Thiols Selected AbstractsKinetics and mechanism of oxidation of 2-mercaptosuccinic acid by bis(,-oxo)- manganese(III,IV)-cyclam complex in aqueous medium: Influence of externally added copper(II)INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2004Nizamuddin Shaikh Kinetic studies on the oxidation of 2-mercaptosuccinic acid by dinuclear [Mn2III/IV(,-O)2(cyclam)2](ClO4)3] (1) (abbreviated as MnIII,MnIV) (cyclam = 1,4,8,11-tetraaza-cyclotetradecane) have been carried out in aqueous medium in the pH range of 4.0,6.0, in the presence of acetate buffer at 30°C by UV,vis spectrophotometry. In the pH region, two species of complex 1 (MnIII,MnIV and MnIII,MnIVH, the later being ,-O protonated form) were found to be kinetically significant. The first-order dependence of the rate of the reactions on [Thiol] both in presence and absence of externally added copper(II) ions, first-order dependence on [Cu2+] and a decrease of rate of the reactions with increase in pH have been rationalized by suitable sequence of reactions. Protonation of ,-O bridge of 1 is evidenced by the perchloric acid catalyzed decomposition of 1 to mononuclear Mn(III) and Mn(IV) complex observed by UV,vis and EPR spectroscopy. The kinetic features have been rationalized considering Cu(RSH) as the reactive intermediate. EPR spectroscopy lends support for this. The formation of a hydrogen bonded outer-sphere adduct between the reductant and the complex in the lower pH range prior to electron transfer reactions is most likely to occur. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 170,177 2004 [source] Thiol,ene coupling reaction of fatty acid monomersJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 24 2004Johan Samuelsson Abstract The reactivities and reaction rates of the thiol,ene coupling reaction of 2-ethyl-(hydroxymethyl)-1,3-propanediol trimercapto acetate and 2-ethyl-(hydroxymethyl)-1,3-propanediol trimercapto propionate with two common unsaturated fatty acid methyl esters (methyl oleate and methyl linoleate) were evaluated. The reactions were monitored with real-time IR and 1H NMR, which both showed that the mercapto acetate was more reactive than the mercapto propionate. Both thiols were more prone to add to the monounsaturated methyl oleate than to methyl linoleate, which contained two unconjugated double bonds. According to bond energy calculations, the thiol hydrogen of mercapto acetate was somewhat more difficult to abstract than the hydrogen of mercapto propionate. Consequently, the formed SC bond in the acetate case was stronger than in the propionate case, and so the equilibrium was more shifted toward the addition products. The real-time IR measurements also showed that the cis unsaturation in methyl oleate isomerized much more quickly than that in methyl linoleate, and this also had an impact on the overall addition rate of the thiols because a trans unsaturation was more reactive than a cis unsaturation. The higher isomerization rates in the oleate systems, compared with those of the linoleate systems, was suggested to be due to a more restricted rotation along the CC bond of the reacted unsaturation in linoleate. This study showed the importance of trans unsaturations in obtaining reasonable reaction rates in thiol,ene reactions with fatty acid derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6346,6352, 2004 [source] Regioselectivity in Lewis Acid Catalyzed X,H (O, S, N) Insertions of Methyl Styryldiazoacetate with Benzyl Alcohol, Benzyl Thiol, and Aniline.CHEMINFORM, Issue 36 2007Yongli Yue Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of [2]Rotaxanes by Tritylative Endcapping of in situ Formed Pseudorotaxanes Having Thiol or Hydroxyl Functionality on the Axle Termini.CHEMINFORM, Issue 47 2002Yoshio Furusho No abstract is available for this article. [source] Electrode Modified with Cobalt Cyclohexylbutyrate for the Determination of Low Molecular Weight Thiol Group Bearing Compounds Using Catalytic Stripping VoltammetryELECTROANALYSIS, Issue 3 2010Petr Jakubec Abstract Glassy carbon electrode, modified with cobalt(II) cyclohexylbutyrate monohydrate immobilized in polystyrene matrix is usable for determination of thiol group bearing compounds both in oxidized and reduced forms using catalytic stripping voltammetry. The measurements are carried out in acetate buffer (pH,4.3) containing Tween 40. After the accumulation step at ,850,mV vs. Ag/AgCl a peak at ,170,mV is observed on linear sweep voltammogram, the height of which is proportional to the concentration of added thiol. Addition of carbon nanotubes into polystyrene film enhances the sensitivity of the modified electrode. The detection limit is 1×10,6,mol dm,3 for all studied thiols. The electrode can be regenerated by exposing it to the potential between 300,600,mV. [source] Voltammetric Investigation of Zinc Release from Metallothioneins Modulated by the Glutathione Redox Couple and Separated with a Porous MembraneELECTROANALYSIS, Issue 20 2008Lin Liu Abstract Glutathione (GSH), in addition to serving as a redox buffer in cellular environment, has been suggested as a modulator in metal regulation and homeostasis by metallothioneins (MTs). The interactions of MTs with both GSH and its oxidized form GSSG have been shown to govern the direction of metal transfer. Common methods for the determination of zinc release from MTs modulated by GSH/GSSG either involve radioactive species or enzymes or are labor-intensive. In this study, upon separation of Zn2+ from the reaction mixture of MTs and GSH with a centrifugal filter membrane, differential pulse voltammetry (DPV) was used for the Zn2+ quantification. The same approach is extended to the studies of metal transfer between Zn7MT with a GSH/GSSG mixture and that between Zn7MT with GSSG. The concomitant conversion between the free thiol and disulfide bonds was confirmed with UV-vis spectrophotometry. The results demonstrate that GSSG, GSH, and the GSH/GSSG mixture all modulate zinc release from Zn7MT. The percentage of zinc release increases in the order of GSH, GSSG, and the GSH/GSSG mixture. The new approach is demonstrated to be well suited for investigation of redox regulation of MT and its reaction with zinc-containing enzymes. [source] Disposable Amperometric Sensors for Thiols with Special Reference to GlutathioneELECTROANALYSIS, Issue 18 2008Dipankar Bhattacharyay Abstract The antioxidant ,reduced glutathione' tripeptide is conventionally called glutathione (GSH). The oxidized form is a sulfur-sulfur linked compound, known as glutathione disulfide (GSSG). Glutathione is an essential cofactor for antioxidant enzymes; it provides protection also for the mitochondria against endogenous oxygen radicals. The ratio of these two forms can act as a marker for oxidative stress. The majority of the methods available for estimation of both the forms of glutathione are based on colorimetric and electrochemical assays. In this study, electrochemical sensors were developed for the estimation of both GSH and GSSG. Two different types of transducers were used: i) screen-printed three-electrode disposable sensor (SPE) containing carbon working electrode, carbon counter electrode and silver/silver chloride reference electrode; ii) three-electrode disposable system (CDE) consisting of three copper electrodes. 5,5,-dithiobis(2-nitrobenzoic acid) (DTNB) was used as detector element for estimation of total reduced thiol content. The enzyme glutathione reductase along with a co-enzyme reduced nicotinamide adenine dinucleotide phosphate was used to estimate GSSG. By combining the two methods GSH can also be estimated. The detector elements were immobilized on the working electrodes of the sensors by bulk polymerization of acrylamide. The responses were observed amperometrically. The detection limit for thiol (GSH) was less than 0.6,ppm when DTNB was used, whereas for GSSG it was less than 0.1,ppm. [source] Design, characterization, and utilization of a fast fluorescence derivatization reaction utilizing o -phthaldialdehyde coupled with fluorescent thiolsELECTROPHORESIS, Issue 7 2007Suminda Hapuarachchi Abstract We have developed a chemical derivatization scheme for primary amines that couples the fast kinetic properties of o -phthaldialdehyde (OPA) with the photophysical properties of visible, high quantum yield, fluorescent dyes. In this reaction, OPA is used as a cross-linking reagent in the labeling reaction of primary amines in the presence of a fluorescent thiol, 5-((2-(and-3)- S -(acetylmercapto)succinoyl)amino)fluorescein (SAMSA fluorescein), thereby incorporating fluorescein (,,=,78,000,M,1, quantum yield of 0.98) into the isoindole product. Detection is based on excitation and emission of the incorporated fluorescein using the 488,nm laser line of an Ar+ laser rather than the UV-excited isoindole, thereby eliminating the UV light sources for detection. Using this method, we have quantitatively labeled biologically important primary amines in less than 10,s. Detection limits for analysis of glutamate, glycine, GABA, and taurine were less than 2,nM. We present the characterization of OPA/SAMSA-F reaction and the potential utility of the derivatization reaction for dynamic chemical monitoring of biologically relevant analytes using CE. [source] Chromosomal antioxidant genes have metal ion-specific roles as determinants of bacterial metal toleranceENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Joe J. Harrison Summary Microbiological metal toxicity involves redox reactions between metal species and cellular molecules, and therefore, we hypothesized that antioxidant systems might be chromosomal determinants affecting the susceptibility of bacteria to metal toxicity. Here, survival was quantified in metal ion-exposed planktonic cultures of several Escherichia coli strains, each bearing a mutation in a gene important for redox homeostasis. This characterized ,250 gene,metal combinations and identified that sodA, sodB, gor, trxA, gshA, grxA and marR have distinct roles in safeguarding or sensitizing cells to different toxic metal ions (Cr2O72,, Co2+, Cu2+, Ag+, Zn2+, AsO2,, SeO32, or TeO32,). To shed light on these observations, fluorescent sensors for reactive oxygen species (ROS) and reduced thiol (RSH) quantification were used to ascertain that different metal ions exert oxidative toxicity through disparate modes-of-action. These oxidative mechanisms of metal toxicity were categorized as involving ROS and thiol-disulfide chemistry together (AsO2,, SeO32,), ROS predominantly (Cu2+, Cr2O72,) or thiol-disulfide chemistry predominantly (Ag+, Co2+, Zn2+, TeO32,). Corresponding to this, promoter- luxCDABE fusions showed that toxic doses of different metal ions up- or downregulate the transcription of gene sets marking distinct pathways of cellular oxidative stress. Altogether, our findings suggest that different metal ions are lethal to cells through discrete pathways of oxidative biochemistry, and moreover, indicate that chromosomally encoded antioxidant systems may have metal ion-specific physiological roles as determinants of bacterial metal tolerance. [source] Analysis of glutathione endpoints for measuring copper stress in Chlamydomonas reinhardthENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2007Tasha L. Stoiber Abstract Glutathione (GSH) is the most abundant nonprotein thiol in eukaryotic cells and it protects cells by functioning as an antioxidant and a metal-binding ligand. Because glutathione readily undergoes oxidation-reduction reactions to combat oxidative stress, intracellular ratios of the reduced (GSH) to the oxidized (GSSG) forms of glutathione may serve as an important biomarker of exposure and effect of trace metals in eukaryotic cells. We compared sensitivity of glutathione ratios in the freshwater alga Chlamydomonas reinhardtii to the traditional endpoints of cell growth rates and chlorophyll a following exposure to Cu for periods of 6 and 24 h. A response of the GSH:GSSG ratio to Cu concentration was observed at Cu levels of 40 and 80 nM after exposure for both 6 and 24 h. The concentration of total GSH at 24 h was roughly half the value at 6 h after exposure to either 40 or 80 nM Cu. A response for cell growth rate was observed only at 24 h, whereby the average specific growth rate decreased from about 1.1 to 0.4 d,1. The total Cu concentrations eliciting a cell response of 50%, effect concentrations (EC50s), after 24 h of exposure were similar (49.2, 49.8, and 38.2 nM Cu) and not significantly different for GSH:GSSG ratio, GSH levels, and specific growth, respectively. Total cell-associated Cu concentrations after exposure for 24 h were calculated from the EC50 endpoints and ranged from 13.3 to 17.0 fg/cell. Overall, thiol ratios were indicative of toxicity resulting from exposure to Cu, but precision may be greater for the cell growth rate endpoints. [source] Role of ethylenediaminetetraacetic acid on lead uptake and translocation by tumbleweed (Salsola kali L.)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2007Guadalupe de la Rosa Abstract Tumbleweed plants (Salsola kali L.) grown in agar and liquid media demonstrated a high capacity to accumulate Pb in their different parts without affecting biomass. Whereas shoot elongation and biomass were not significantly affected by high tissue concentrations of Pb, root growth was significantly affected relative to controls. Roots, stems, and leaves demonstrated Pb concentrations of 31,000, 5,500, and 2,100 mg/kg dry weight, respectively, when plants were grown in the agar medium containing 80 mg Pb/L. Application of ethylenediaminetetraacetic acid (EDTA) to Pb-contaminated media dramatically reduced the total acquisition of Pb from both types of media. However, EDTA significantly increased the translocation of Pb from roots to the aerial parts, as evidenced by a multifold increase (23- and 155-fold for agar and liquid media, respectively) in the translocation concentration factor. The concentration of the antioxidant thiol compounds significantly increased (p < 0.05) in plants grown with uncomplexed Pb treatments relative to control plants. Scanning-electron microscopy and electron dispersive x-ray spectroscopic evaluation of leaf samples demonstrated an interesting pattern of Pb translocation in the presence or absence of EDTA. Large Pb crystals were found across the leaf tissues (palisade, spongy parenchyma, and conducting tissues) in the absence of EDTA. Lead nanoparticles also were seen when plants were grown in Pb-EDTA solution. Ultramicroscopic features of tumbleweed provide clear evidence for the unrestricted conduction of Pb from the root to the aerial parts, and this property makes the plant a good candidate for phytoremediation. [source] Facile Functionalization and Phase Reduction Route of Magnetic Iron Oxide Nanoparticles for Conjugation of Matrix Metalloproteinase,ADVANCED ENGINEERING MATERIALS, Issue 6 2010Dan Li Abstract A protocol for the simultaneous functionalization and phase reduction route of iron oxide magnetic nanoparticles (MNPs) and its further bioconjugation is presented. It was found that surface functionalization of maghemite (,-Fe2O3) nanoparticles with mercaptopropyltrimethoxysilane (MPTMS) under anoxic environment at above 80,°C promotes in situ conversion to magnetite (Fe3O4). Full conversion to Fe3O4, as probed by Mössbauer spectroscopy, with accompanied increase in the composite saturation magnetization, was achieved at 120,°C. By controlling the MPTMS concentration, the resultant silane-MNPs morphology can be tuned from having homogeneous thin layer (<1,nm) to thick continuous silane with embedded MNP multicores. Likewise the amount of surface distal thiol moieties was dependent on the silanization conditions. The density of distal thiols (i.e., amount of thiol per surface area) and resultant aggregate size have direct impact on the attachment, as well as the activity and reusability of the conjugated matrix metalloproteinase (MMP-2, using sulfo-SMCC as crosslinker). The work has important implication to the field of magneto-chemotherapeutics, where spatial control of conjugated active biomolecules under magnetic field and T2 -weighted MRI contrast can be achieved simultaneously. [source] Enhanced Activity and Stereoselectivity of Polystyrene-Supported Proline-Based Organic Catalysts for Direct Asymmetric Aldol Reaction in WaterEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2009Michelangelo Gruttadauria Abstract Several polystyrene-supported proline dipeptides and a prolinamide derivative were prepared by thiol,ene coupling. These materials were used as catalysts for the direct asymmetric aldol reaction in water, and results compared with unsupported catalysts in water. Such an approach gave more active or stereoselective catalysts compared to the unsupported compounds, showing that our immobilization procedure may be useful to develop catalytic materials with enhanced performance. Moreover, these catalysts can be recovered and reused for at least nine times without loss of activity or can be easily regenerated when their activity has decreased. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Contribution of exofacial thiol groups in the reducing activity of Lactococcus lactisFEBS JOURNAL, Issue 10 2010D. Michelon Lactococcus lactis can decrease the redox potential at pH 7 (Eh7) from 200 to ,200 mV in oxygen free Man,Rogosa,Sharpe media. Neither the consumption of oxidizing compounds or the release of reducing compounds during lactic acid fermentation were involved in the decrease in Eh7 by the bacteria. Thiol groups located on the bacterial cell surface appear to be the main components that are able to establish a greater exchange current between the Pt electrode and the bacteria. After the final Eh7 (,200 mV) was reached, only thiol-reactive reagents could restore the initial Eh7 value. Inhibition of the proton motive force showed no effect on maintaining the final Eh7 value. These results suggest that maintaining the exofacial thiol (,SH) groups in a reduced state does not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wall-bound proteins and may participate in protecting cells against oxidative stress. [source] Escherichia coli thioredoxin inhibition by cadmiumFEBS JOURNAL, Issue 7 2004Asp2, Two mutually exclusive binding sites involving Cys3 Observations of thioredoxin inhibition by cadmium and of a positive role for thioredoxin in protection from Cd2+ led us to investigate the thioredoxin,cadmium interaction properties. We used calorimetric and spectroscopic methods at different pH values to explore the relative contribution of putative binding residues (Cys32, Cys35, Trp28, Trp31 and Asp26) within or near the active site. At pH 8 or 7.5 two binding sites were identified by isothermal titration calorimetry with affinity constants of 10 × 106 m,1 and 1 × 106 m,1. For both sites, a proton was released upon Cd2+ binding. One mole of Cd2+ per mole of reduced thioredoxin was measured by mass spectrometry at these pH values, demonstrating that the two binding sites were partially occupied and mutually exclusive. Cd2+ binding at either site totally inhibited the thiol,disulfide transferase activity of Trx. The absence of Cd2+ interaction detected for oxidized or alkylated Trx and the inhibition of the enzymatic activity of thioredoxin by Cd2+ supported the role of Cys32 at the first site. The fluorescence profile of Cd2+ -bound thioredoxin differed, however, from that of oxidized thioredoxin, indicating that Cd2+ was not coordinated with Cys32 and Cys35. From FTIR spectroscopy, we inferred that the second site might involve Asp26, a buried residue that deprotonates at a rather high and unusual pKa for a carboxylate (7.5/9.2). The pKa of the two residues Cys32 and Asp26 have been shown to be interdependent [Chivers, T. P. (1997) Biochemistry36, 14985,14991]. A mechanism is proposed in which Cd2+ binding at the solvent-accessible thiolate group of Cys32 induces a decrease of the pKa of Asp26 and its deprotonation. Conversely, interaction between the carboxylate group of Asp26 and Cd2+ at a second binding site induces Cys32 deprotonation and thioredoxin inhibition, so that Cd2+ inhibits thioredoxin activity not only by binding at the Cys32 but also by interacting with Asp26. [source] Variation in 4-mercapto-4-methyl-pentan-2-one release by Saccharomyces cerevisiae commercial wine strainsFEMS MICROBIOLOGY LETTERS, Issue 2 2004Kate S. Howell Abstract The volatile thiol 4-mercapto-4-methylpentan-2-one (4MMP) is a potent contributor to wine aroma. In grape juice, 4MMP is bound to cysteine as a non-volatile compound and requires the action of yeast during fermentation to release the aroma active thiol. A method was developed to measure 4MMP release from the precursor by headspace solid-phase microextraction and separation by gas chromatography with atomic emission detection to screen the ability of wine yeast to release 4MMP. Yeast commonly used in white wine making were grown with the precursor at two different temperatures, and the amount of 4MMP released was measured. The results demonstrate that yeast strain selection and fermentation temperature can provide an important tool to enhance or modulate the grape-derived aromas formed during wine fermentation. [source] The effect of antibiotics and bismuth on fecal hydrogen sulfide and sulfate-reducing bacteria in the ratFEMS MICROBIOLOGY LETTERS, Issue 1 2003Hiroki Ohge Abstract Colonic bacteria produce the highly toxic thiol, hydrogen sulfide. Despite speculation that this compound induces colonic mucosal injury, there is little information concerning manipulations that might reduce its production. We studied the effect of antibiotics and bismuth on the production of hydrogen sulfide in rats. Baseline fecal samples were analyzed for hydrogen sulfide concentration and release rate during incubation and numbers of sulfate-reducing bacteria. Groups of six rats received daily doses of ciprofloxacin, metronidazole, or sulfasalazine for one week, and feces were reanalyzed. Bismuth subnitrate was then added to the antibiotic regimens. While sulfide production and sulfate-reducing bacteria were resistant to treatment with ciprofloxacin or metronidazole, bismuth acted synergistically with ciprofloxacin to inhibit sulfate-reducing bacteria growth and to reduce sulfide production. Combination antibiotic,bismuth therapy could provide insights into the importance of sulfide and sulfate-reducing bacteria in both human and animal models of colitis and have clinical utility in the treatment of antibiotic-resistant enteric pathogens. [source] Mycothiol-dependent proteins in actinomycetesFEMS MICROBIOLOGY REVIEWS, Issue 3 2007Mamta Rawat Abstract The pseudodisaccharide mycothiol is present in millimolar levels as the dominant thiol in most species of Actinomycetales. The primary role of mycothiol is to maintain the intracellular redox homeostasis. As such, it acts as an electron acceptor/donor and serves as a cofactor in detoxification reactions for alkylating agents, free radicals and xenobiotics. In addition, like glutathione, mycothiol may be involved in catabolic processes with an essential role for growth on recalcitrant chemicals such as aromatic compounds. Following a little over a decade of research since the discovery of mycothiol in 1994, we summarize the current knowledge about the role of mycothiol as an enzyme cofactor and consider possible mycothiol-dependent enzymes. [source] Nanolithography: Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-Objects (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Mater. On page 3696, Wang et al. report on the nanoscale chemical surface patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns by the iterative application of thermochemical nanolithography. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for the selective attachment of nanometer-sized objects, such as proteins or DNA, using standard chemical protocols. [source] Thermochemical Nanolithography of Multifunctional Nanotemplates for Assembling Nano-ObjectsADVANCED FUNCTIONAL MATERIALS, Issue 23 2009Debin Wang Abstract Nanoscale chemical patterning of different chemical species (amine, thiol, aldehyde, and biotin) in independent nanopatterns is achieved by the iterative application of thermochemical nanolithography (TCNL) to inscribe amine patterns followed by their chemical conversion to other functional groups. Due to the unique chemical stability of the patterns, the resultant substrates can be stored for weeks and subsequently be used for covalent and molecular-recognition-based attachment of nano-objects using standard chemical protocols. In particular, the ability of this method to attach proteins and DNA to the chemical nanopatterns and to create co-patterns of two distinctive bioactive proteins is demonstrated. [source] MBSJ MCC Young Scientist Award 2009 REVIEW: Structural basis of protein disulfide bond generation in the cellGENES TO CELLS, Issue 9 2010Kenji Inaba The formation of protein disulfide bonds is an oxidative reaction that is crucial for the folding and maturation of many secreted and membrane proteins. Both prokaryotic and eukaryotic cells possess various disulfide oxidoreductases and redox-active cofactors to accelerate this oxidative reaction in a correct manner. Crystal or solution structures have been solved for some of the oxidoreductases in the past 10 years, leading to remarkable progress in the field of thiol-based redox cell biology. Consequently, structural and mechanistic similarities in the disulfide bond formation pathways have been uncovered. This review highlights the molecular basis of the elaborate oxidative systems operating in the Escherichia coli periplasm, the endoplasmic reticulum lumen and the mitochondrial intermembrane space. The accumulated knowledge provides important insights into how protein and redox homeostasis are maintained in the cell. [source] Controlling Electron and Hole Charge Injection in Ambipolar Organic Field-Effect Transistors by Self-Assembled MonolayersADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Xiaoyang Cheng Abstract Controlling contact resistance in organic field-effect transistors (OFETs) is one of the major hurdles to achieve transistor scaling and dimensional reduction. In particular in the context of ambipolar and/or light-emitting OFETs it is a difficult challenge to obtain efficient injection of both electrons and holes from one injecting electrode such as gold since organic semiconductors have intrinsically large band gaps resulting in significant injection barrier heights for at least one type of carrier. Here, systematic control of electron and hole contact resistance in poly(9,9-di- n -octylfluorene- alt -benzothiadiazole) ambipolar OFETs using thiol-based self-assembled monolayers (SAMs) is demonstrated. In contrast to common believe, it is found that for a certain SAM the injection of both electrons and holes can be improved. This simultaneous enhancement of electron and hole injection cannot be explained by SAM-induced work-function modifications because the surface dipole induced by the SAM on the metal surface lowers the injection barrier only for one type of carrier, but increases it for the other. These investigations reveal that other key factors also affect contact resistance, including i) interfacial tunneling through the SAM, ii) SAM-induced modifications of interface morphology, and iii) the interface electronic structure. Of particular importance for top-gate OFET geometry is iv) the active polymer layer thickness that dominates the electrode/polymer contact resistance. Therefore, a consistent explanation of how SAM electrode modification is able to improve both electron and hole injection in ambipolar OFETs requires considering all mentioned factors. [source] Determination of Selenium Concentration in Sixty Five Reference Materials for Geochemical Analysis by GFAAS after Separation with Thiol CottonGEOSTANDARDS & GEOANALYTICAL RESEARCH, Issue 2-3 2001Luc Marin sélénium; SAA four graphite; séparation; matériaux géologiques de référence; coton thiol Selenium has been determined in sixty five geological reference materials of different origins by graphite furnace atomic absorption spectrometry. Samples were decomposed with a mixture of nitric and hydrofluoric acids. Selenium was reduced to SeIV with hydrochloric acid, and then fixed and separated from the matrix on thiol cotton. After digestion of the thiol cotton in hot nitric acid, the Se concentration was measured using palladium and magnesium nitrates as a matrix modifier. The limit of determination was 0.02 ,g g,1, the precision of the results (relative standard deviation of 3 to 8 replicates) varied from 2.6 to 17.7% with an average of 7.9% in the range 0.02-42.7 ,g g,1 and was similar to the value obtained for synthetic samples. Our results are in good agreement with available literature values. Le sélénium a été dosé sur 65 standards géochimiques de référence de différentes provenances par spectrométrie d'absorption atomique avec four graphite. Les échantillons ont été mis en solution par une attaque acide HNO3 -HF. Le sélénium a été réduit en SeIV avec de l'acide chlorhydrique, fixé et séparé de la matrice sur du coton thiol. Après décomposition du coton thiol par chauffage avec de l'acide nitrique, les concentrations en sélénium ont été mesurées en utilisant du nitrate de palladium et de magnésium comme modificateur de matrice. La limite de détermination est de 0.02 ,g g,1, la précision des résultats (écart type relatif sur 3 à 8 mesures) pour les standards géochimiques varie de 2.6 à 17.7% avec une moyenne de 7.9% dans la game 0.02-42.7 ,g g,1et est comparable à celle obtenue pour des échantillons synthétiques. Nos résultats sont en bonne concordance avec les résultats déjà publiés dans la littérature. [source] Synthesis and Evaluation of S - and C(1) -Substituted Analogues of LincomycinHELVETICA CHIMICA ACTA, Issue 2 2009Marie-Pierre Collin Abstract New thioglycosides and C(1) -alkylated thioglycosides (S -ulosides) of lincomycin were synthesized, and their antibiotic activities were determined. The S -aryl and S -arylalkyl analogues 11a,11i were obtained by S -glycosylation of the sulfoxides 7 with arenethiols, or by S -alkylation of the thiol 14 with alkyl bromides. Lincomycin derivatives 27, 32a, 32b, 38a, 38b, 44, and 47 were prepared via Henry reaction or Michael addition of the lincosamine-derived 1-deoxy-1-nitropyranoses 22. The S -alkyl derivatives showed a similar activity and specificity as lincomycin. Lipophilic S -uloside analogues were two- to fourfold less active than the parent antibiotic, whilst the hydrophilic analogues were inactive. [source] Synthesis of a Potential 10E4 Tetrasaccharide Antigen Involved in Scrapie PathogenesisHELVETICA CHIMICA ACTA, Issue 11 2006Pascal Bindschädler Abstract To test the hypothesis that tetrasaccharide 3 is involved in scrapie pathogenesis, tetrasaccharide derivative 32 functionalized with an amine linker at the reducing end was synthesized. A (2,+,2) glycosylation approach was chosen to furnish the target compound in fully protected form. To investigate its biological role, tetrasaccharide 32 was further functionalized to the corresponding thiol 33 using Traut's reagent. During the course of the synthesis, the N,N -diacetyl protecting group proved surprisingly labile to radical and acidic conditions. [source] Development of odorless organosulfur reagents and asymmetric reaction using odorless thiolsHETEROATOM CHEMISTRY, Issue 5 2007Manabu Node Odorless organosulfur reagents were developed by increasing their molecular weights to suppress volatility. 1-Dodecanethiol (4), dodecyl methyl sulfide (5), p -heptylphenylmethanethiol (6), p -dodecylbenzenethiol (7), p -heptylbenzenethiol (8), 2-dodecyl-1,3-propanedithiol (11), p -octyloxyphenyl-methanethiol (18b), and p -octyloxybenzenethiol (19) are typical examples of the odorless thiols and sulfides. 6-Morpholinohexyl thiol (15), methyl 6-morpholinohexyl sulfide (16), and methyl 6-morpholinohexyl sulfoxide (17) were also developed as separable reagents from reaction products by facile acid-base extraction. In addition, p -tetramethylsilylphenylmethanethiol (18) and p -tetramethylsilylbenzenethiol (14) were synthesized as the odorless synthetic substitutes of benzyl mercaptan and benzenethiol, respectively. In a similar way, silylated diphenyl disulfide (26) and diselenide (27) were prepared as odorless disulfide and diselenide. Moreover, 10-sulfanylisoborneol (1) was found to be an excellent chiral odorless substitute of hydrogen sulfide in Michael addition. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:572,583, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20348 [source] Synthesis and metal transport ability of a new series of thiamacrocycles containing thiol and disulfide groups inside the ringHETEROATOM CHEMISTRY, Issue 4 2001Tatsuya Nabeshima Synthetic methods for thiamacrocycles containing two thiol groups or a disulfide linkage and their abilities to effect single heavy-metal-ion transport across a liquid membrane were examined. High Ag+ selectivity was accomplished by the thiol or disulfide hosts, although all the corresponding crown ether analogs bearing a disulfide group showed no Ag+ selectivity. The difference of the transport preferences among the thiacrown ethers prepared here is considered to be reflected by the position and the number of the sulfur atoms ligating to Ag+ and the cavity size of the hosts. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:276,281, 2001 [source] Fabrication of Micropatterned Stimulus-Responsive Polymer-Brush ,Anemone'ADVANCED MATERIALS, Issue 18 2009Tao Chen A simple strategy to fabricate stimulus-responsive patterned PNIPAAM-brush microstructures (,anemones') is presented. The size of the microstructures can be adjusted by setting the composition of thiol and the contact pressure. We demonstrate that the patterned PNIPAAM-brush microstructures have a triggerable and reversible conformation transition, and can potentially be used as microcontainers to reversibly dock and release microparticles. [source] Antioxidants in aerial parts of Hypericum sampsonii, Hypericum japonicum and Hypericum perforatumINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 11 2009Chung Li Chen Summary Antioxidants contents and antioxidative enzymes and their activities in fresh aerial tissues of Hypericum sampsonii (Sampson's St John's Wort), Hypericum japonicum (Japanese St John's Wort) and Hypericum perforatum were investigated. Hypericum sampsonii contained more total ascorbate [34.33 ,mol g,1 fresh weight (FW)] than H. perforatum (57% less) and H. japonicum (82% less). It also contained more thiol and phenolics than two other species. Hypericum japonicum had highest superoxide dismutase (SOD) activity (8.74 mmol min,1 g,1 FW), followed by H. sampsonii (2% less) and H. perforatum (37% less). Hot-air dried H. perforatum materials contained more thiol [208.7 ,mol g,1 dry weight (DW)] and phenolics (352.82 mg g,1 DW) than freeze-dried and fresh materials. Both drying treatments decreased the activities of antioxidative enzymes in aerial tissues of H. perforatum. However, freeze-dried H. perforatum contained the highest SOD activity (5.42 mmol min,1 g,1 DW) among the antioxidative enzymes measured from both freeze-dried and hot-air dried tissues (ranged from 0.02 to 2.65 ,mol min,1 g,1 DW). [source] Inhibition of the decrease of volatile esters and terpenes during storage of a white wine and a model wine medium by glutathione and N -acetylcysteineINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 6 2008Despima Papadopoulou Summary Glutathione and N -acetylcysteine, each at 20 mg L,1, were tested as inhibitors of the decrease of volatile esters and terpenes during storage of Debina white wine. Moreover, the inhibition of the decrease of isoamyl acetate, ethyl hexanoate and linalool in a model wine medium by glutathione and N -acetylcysteine, each at 0,20 mg L,1, was also tested. Several volatiles, such as isoamyl acetate, ethyl hexanoate, ethyl octanoate, ethyl decanoate and linalool, decreased during wine storage. Glutathione or N -acetylcysteine significantly restricted the decrease of these volatiles. In the model medium, each thiol inhibited the decrease of the three volatiles in a dose-dependent manner. N -acetylcysteine inhibited the decrease of all three volatiles at 2.5 mg L,1 while glutathione at 2.5 or 5.0 mg L,1. The present results indicate that glutathione and N -acetylcysteine may be taken into account as potent inhibitors of the disappearance of aromatic esters and terpenes in wines. [source] | |||||||||||||||||||||||||||||||||||||||||||