- Electropolymerization of cobalt tetraamino-phthalocyanine at reduced graphene oxide for electrochemical determination of cysteine and hydrazine
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We describe a simple and elegant electropolymerization method to prepare highly stable tetraamino functionalized cobalt phthalocyanine (pTACoPc) at electrochemically reduced graphene oxide (RGO). The described method efficiently bridges the excellent physicochemical properties of RGO with the rich redox chemistry of TACoPc. Graphene oxide was electrochemically reduced to RGO at the electrode surface along with concominent electropolymerization of TACoPc. The electrochemical studies showed that RGO on pTACoP/GCE increased effective surface area, reduced charge transfer resistance and enhanced electrochemical signal. The RGO-pTACoPc film modified electrode exhibits excellent electrocatalytic ability to oxidize cysteine and hydrazine. To determine cysteine, the RGO-pTACoPc sensor displayed a linear concentration range of 50 nM to 2.0 μM, detection limit of 18.5 nM and sensitivity of 10.19 nA nM-1 cm-2. Besides, the sensor displayed a linear concentration range of 50 nM to 2.6 μM, detection limit of 10 nM and sensitivity of 1.62 nA nM-1 cm-2 to determine hydrazine. The electrocatalytic ability of RGO-pTACoPc shows better performance over other cobalt phthalocyanine derivatives. Furthermore, the described sensor exhibited long-term storage stability, good repeatability and reproducibility. The practical applicability of the sensor has been assessed in biological and water samples.
- Mani, Veerappan,Huang, Sheng-Tung,Devasenathipathy, Rajkumar,Yang, Thomas C. K.
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p. 38463 - 38469
(2016/05/19)
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- Nitrite reduction mediated by the complex RuIII(EDTA)
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Reported is the first example of a ruthenium(iii)-complex, Ru III(EDTA) (EDTA4- = ethylenediaminetetraacetate), that mediates O-atom transfer from nitrite to the biological thiols cysteine and glutathione, leading to the formation of [RuIII(EDTA)(NO +)]0. However, at pH below 5.0, the coordinated nitrite ion in the [RuIII(EDTA)(NO2)]2- complex undergoes proton-assisted decomposition, resulting in the formation of a [RuIII(EDTA)(NO+)]0 species. the Partner Organisations 2014.
- Chatterjee, Debabrata,Shome, Sanchari,Jaiswal, Namita,Banerjee, Priyabrata
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p. 13596 - 13600
(2014/11/08)
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- S-aroylthiooximes: A facile route to hydrogen sulfide releasing compounds with structure-dependent release kinetics
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We report the facile preparation of a family of S-aroylthiooxime (SATO) H2S donors, which are synthesized via a click reaction analogous to oxime formation between S-aroylthiohydroxylamines (SATHAs) and aldehydes or ketones. Analysis of cysteine-triggered H2S release revealed structure-dependent release kinetics with half-lives from 8-82 min by substitution of the SATHA ring. The pseudo-first-order rate constants of substituted SATOs fit standard linear free energy relationships (p = 1.05), demonstrating a significant sensitivity to electronic effects.
- Foster, Jeffrey C.,Powell, Chadwick R.,Radzinski, Scott C.,Matson, John B.
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supporting information
p. 1558 - 1561
(2014/04/17)
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- Investigation of reactions postulated to occur during inhibition of ribonucleotide reductases by 2′-azido-2′-deoxynucleotides
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Model 3′-azido-3′-deoxynucleosides with thiol or vicinal dithiol substituents at C2′ or C5′ were synthesized to study reactions postulated to occur during inhibition of ribonucleotide reductases by 2′-azido-2′-deoxynucleotides. Esterification of 5′-(tert-
- Dang, Thao P.,Sobczak, Adam J.,Mebel, Alexander M.,Chatgilialoglu, Chryssostomos,Wnuk, Stanislaw F.
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experimental part
p. 5655 - 5667
(2012/09/25)
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- Live-cell imaging of cyclopropene tags with fluorogenic tetrazine cycloadditions
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Spotlight on lipids: One of the major limitations of tetrazine bioorthogonal cycloadditions is the requirement of bulky dienophile reaction partners. Methylcyclopropene tags were designed capable of reacting rapidly with tetrazines while maintaining stability in aqueous solution. The suitability of these probes for bioconjugation is shown by imaging cyclopropene-modified phospholipids in live human cancer cells (see picture). Copyright
- Yang, Jun,?e?kute, Jolita,Cole, Christian M.,Devaraj, Neal K.
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supporting information; scheme or table
p. 7476 - 7479
(2012/09/08)
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- Identification and characterization of the first ovothiol biosynthetic Enzyme
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Ovothiols are histidine-derived thiols that were first isolated from marine invertebrates. We have identified a 5-histidylcysteine sulfoxide synthase (OvoA) as the first ovothiol biosynthetic enzyme and characterized OvoAs from Erwinia tasmaniensis and Trypanosoma cruzi. Homologous enzymes are encoded in more than 80 genomes ranging from proteobacteria to animalia.
- Braunshausen, Andrea,Seebeck, Florian P.
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supporting information; experimental part
p. 1757 - 1759
(2011/04/15)
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- Fe(HSO4)3 and Fe(HSO4)3/DMSO as efficient, heterogeneous, and reusable catalyst systems for the oxidative coupling of thiols
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Fe(HSO4)3 has been used as a heterogeneous, efficient, and recyclable catalyst in ethanol for the selective oxidation of thiols to their corresponding disulfides. The same results were obtained under identical conditions using catalytic amounts of Fe(HSO4)3 in the presence of DMSO. Different types of aliphatic, aromatic, and heteroaromatic thiols have been used in the reaction, and in all cases the products were obtained in good to excellent yields.
- Eshghi,Bakavoli,Moradi,Davoodnia
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experimental part
p. 3110 - 3118
(2010/04/24)
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- NOVEL FORMULATION OF DEHYDRATED LIPID VESICLES FOR CONTROLLED RELEASE OF ACTIVE PHARMACEUTICAL INGREDIENT VIA INHALATION
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A new formulation of dehydrated lipid vesicles employs a vesicle preserver and permits the control of release and delivery of active pharmaceutical ingredients into the respiratory system for treatment in particular of asthma. The typical formulation provides controlled release of the active pharmaceutical ingredient from 0% to 100% from 0 to 72 hours after inhalation, changes the systemic administration to topical administration, allows prolonged therapeutic period for one administration, increased stability, with reduced dose, reduced systemic side effects, reduced toxicity.
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- Acylated Exendin-4 Compounds
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This invention provides new therapeutic peptides, i.e. new protracted Exendin-4 compounds, pharmaceutical compositions and the use of such.
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- The fragmentation of gold nanoparticles induced by small biomolecules
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Spherical gold nanoparticles (3-5 nm) undergo a surprising fragmentation without extra energy imput and are converted into ultrasmall particles (less than 1.5 nm), which is a direct result of electron transfer between gold nanoparticles and cysteine. The Royal Society of Chemistry.
- Wang, Tie,Hu, Xiaoge,Dong, Shaojun
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supporting information; body text
p. 4625 - 4627
(2009/03/11)
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- Kinetics and mechanism for the reaction of cysteine with hydrogen peroxide in amorphous polyvinylpyrrolidone lyophiles
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Purpose. Peroxide impurities play a critical role in drug oxidation. In metal-free aqueous solutions, hydrogen peroxide (H2O2) induced thiol oxidation involves a bimolecular nucleophilic reaction to form a reactive sulfenic acid intermediate (RSOH), which reacts with a second thiol to form a disulfide (RSSR). This study examines the reaction of cysteine (CSH) and H2O2 in amorphous polyvinylpyrrolidone (PVP) lyophiles to explore the possible relevance of the solution mechanism to reactivity in an amorphous glass. Materials and Methods. Amorphous PVP lyophiles containing CSH and H2O2 at varying initial 'pH' and reactant concentrations were prepared by methods designed to minimize reaction during lyophilization. Kinetic studies were conducted anaerobically at 25°C and reactants and products were monitored by HPLC. Products were characterized and the kinetic data were fit to models adapted from the solution mechanism. Results. Key differences in the reactions in aqueous solution and amorphous PVP are: (1) while only cystine (CSSC) forms in solution, three degradants-cysteine sulfinic acid (CSO2H), cysteine sulfonic acid (CSO3H) and cystine (CSSC)-form in amorphous PVP; (2) simple bimolecular kinetics govern the solution reaction while initial rates in amorphous PVP suggested more complex kinetics (i.e., non-unity values for reaction order); and (3) heterogeneous (i.e., biphasic) reaction dynamics are evident in amorphous PVP. The differences in product formation and apparent reaction orders in the solid-state could be rationalized by partitioning of the same reactive intermediate to multiple products in the solid-state due to the restricted mobility of CSH. Beyond the initial rate region, the kinetics in amorphous PVP could be described by the Kohlrausch-Williams-Watts (KWW) stretched-exponential equation or by assuming two populations of reactant molecules having different reactivities. Conclusions. When reactive intermediates are involved, differences in degradant profiles and other characteristics (e.g., rate constants, apparent reaction order) in the amorphous-state may simply reflect altered rates for individual reaction steps due to glass-induced changes in relative reactant mobilities rather than a change in overall mechanism.
- Luo, Dayong,Anderson, Bradley D.
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p. 2239 - 2253
(2007/10/03)
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- Process for promoting proper folding of human serum albumin using a human serum albumin ligand
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The present invention is a process for refolding and renaturing human serum albumin protein to substantially native conformation by the addition of a human serum albumin refolding ligand to a solution containing the protein under conditions conducive to refolding of the protein.
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- The oxidation of cysteine by electrogenerated octacyanomolybdate (V)
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We report on the response of solid carbon electrodes (glassy carbon and boron doped diamond to the one electron oxidation of octacyanomolybdate(IV) in a wide pH range (1-11). Under alkaline conditions the oxidation of octacyanomolybdate(IV) was found to proceed via a EC reaction mechanism, where one electron oxidation to octacyanomolybdate(V) was followed by inner sphere decomposition of the oxidised species. Further, the electrochemical oxidation of octacyanomolybdate(IV) was studied in the presence of thiols (cysteine, homocysteine and glutathione); an electrocatalytic process occurs, where electrochemically generated octacyanomolybdate(V) species is reduced by cysteine back to the parent octacyanomolybdate(IV) species via a E(C)C′ reaction mechanism. DIGISIM modelling was utilised in order to confirm the suggested mechanism and obtain relevant kinetic data.
- Nekrassova, Olga,Kershaw, Jessica,Wadhawan, Jay D.,Lawrence, Nathan S.,Compton, Richard G.
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p. 1316 - 1320
(2007/10/03)
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- Process for production diphtheria toxin
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The present invention provides a method of purifying diphtheria toxin comprising (1) fermenting a microorganism strain capable of producing diphtheria toxin using glucose as a carbon source, the method comprising adding glucose to a growing culture whereby the addition of glucose maintains microorganism growth effective to support diphtheria toxin production; and (2) purifying the diphtheria toxin from the culture by contacting a toxin containing preparation derived therefrom with an ion exchange matrix, eluting a fraction containing the toxin, applying the eluate to a hydrophobic matrix, and eluting a fraction containing the toxin.
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- Effect of the structure of the macroheterocyclic ligand on the catalytic properties of tetraarenoporphyrazine metal complexes: II. Oxidation of cysteine, catalyzed by cobalt tetraarenoporphyrazines
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The catalytic activity of cobalt tetraarenoporphyrazine complexes in heterogeneous oxidation of cysteine is much dependent on the macrocycle structure and is inversely related to the electron-acceptor power of the ligand.
- Korzhenevskii,Shikova,Koifman,Bykova
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p. 1315 - 1318
(2007/10/03)
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- Oxidation of cysteine and glutathione by soluble polymeric MnO2
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The kinetics of reduction of soluble polymeric Mn02 by cysteine and glutathione has been studied in the pH range of 4.0-9.0. The concentration of thiols was varied between 1 and 2 mM, while the Mn02 concentration was varied between 2 and 12 μM. In this pH range, the reaction products were identified as MN(II) and the corresponding disulfides (cystine and glutathione disulfide). Cysteic or cysteinesulfonic acid was formed only when pH ?～ -160 J mol-1 K-1) and proceeds via an inner-sphere redox process. The reaction proceeds via the formation of two different inner-sphere complexes ≡MnIVSR- and ≡MnIVSR and their further reaction to products. Both surface species are linked to each other via acid-base equilibria, and the rate constant decreases as pH increases, The presence of two ligand surface species is determined using surface complexation modeling, A reaction mechanism in agreement with the experimental results is proposed.
- Herszage, Julian,Dos Santos Afonso, Maria,Luther III, George W.
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p. 3332 - 3338
(2007/10/03)
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- S-nitrosocysteine and cystine from reaction of cysteine with nitrous acid. A kinetic investigation.
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The formation of the S-nitrosocysteine (CySNO) in aqueous solution starting from cysteine (CySH) and sodium nitrite is shown to strongly depend on the pH. Experiments conducted within the pH range 0.5-7.0 show that at pH below 3.5 the NO+ (or H2NO 2 +) is
- Grossi, Loris,Montevecchi, Pier Carlo
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p. 8625 - 8630
(2007/10/03)
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- Solvent systems for pharmaceutical agents
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The invention provides compositions, solvent systems, and methods for solubilizing compounds which are otherwise difficult to solubilize. The invention involves the use of a structured fluid (e.g. a liquid crystalline phase, an L1 phase, an L2 phase, an L3 phase, an emulsion, or a microemulsion), comprising a polar solvent, a lipid or a surfactant, and an essential oil or a dissolution/solubilization agent.
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- Electrocatalytic oxidation and sensitive detection of cysteine on a lead ruthenate pyrochlore modified electrode
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Electrocatalytic oxidation of cysteine (CySH) at Nation/ lead ruthenate pyrochlore (Py) chemically modified electrodes was thoroughly studied. Electrochemical ac impedance spectroscopy analysis indicated the formation of Py microparticles in the interfacial galleries of Nation. Experiments with benchmark systems of Fe(CN)63-/4- and Ru(bpy)2+/3+ reveal the suppression of Nation's anionic character after the in situ precipitation of Py. Michaleis-Menten-type kinetics with the rate determination step of CyS-Py-RuVI → Py-RuIV + CyS-SCy was proposed for this catalytic oxidation. The electrocatalytic behavior is further developed as a sensitive detection scheme for CySH by square-wave voltammetry (SWV) and flow injection analysis (FIA). Under the optimized conditions, the calibration curve is linear up to 560 μM with a detection limit (signal/noise 3) of 1.91 μM in SWV. The detection limit can be improved to 1.70 nM (i.e., 24.22 ng in a 20-μL sample loop) in FIA. This is the lowest value ever reported for direct CySH determination without preliminary accumulation.
- Zen,Senthil Kumar,Chen
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p. 1169 - 1175
(2007/10/03)
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- Composition of matter having bioactive properties
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Particles of coordinated complex comprising a basic, hydrous polymer and a capacitance adding compound, as well as methods for their production, are described. These complexes exhibit a high degree of bioactivity making them suitable for a broad range of applications through their incorporation into conventional vehicles benefiting from antimicrobial and similar properties.
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- Kinetics and mechanism for reduction of the anticancer prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by thiols.
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The reduction of the platinum(IV) prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by L-cysteine, DL-penicillamine, DL-homocysteine, N-acetyl-L-cysteine, 2-mercaptopropanoic acid, 2-mercaptosuccinic acid, and glutathione has been investigated at 25 degrees C in a 1.0 M aqueous perchlorate medium with 6.8 a reductive elimination process through an attack by sulfur at one of the mutually trans chloride ligands, yielding trans-[Pt(OH)2(c-C6H11NH2)(NH3)] and RSSR as the reaction products, as confirmed by 1H NMR. Second-order rate constants for the reduction of JM335 by the various protolytic species of the thiols span more than 3 orders of magnitude. Reduction with RS- is approximately 30-2000 times faster than with RSH. The linear correlation log(kRS) = (0.52 +/- 0.06)-pKRSH--(2.8 +/- 0.5) is observed, where kRS denotes the second-order rate constant for reduction of JM335 by a particular thiolate RS- and KRSH is the acid dissociation constant for the corresponding thiol RSH. The slope of the linear correlation indicates that the reactivity of the various thiolate species is governed by their proton basicity, and no significant steric effects are observed. The half-life for reduction of JM335 by 6 mM glutathione (40-fold excess) at physiologically relevant conditions of 37 degrees C and pH 7.30 is 23 s. This implies that JM335, in clinical use, is likely to undergo in vivo reduction by intracellular reducing agents such as glutathione prior to binding to DNA. Reduction results in the immediate formation of a highly reactive platinum(II) species, i.e., the bishydroxo complex in rapid protolytic equilibrium with its aqua form.
- Lemma,Shi,Elding
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p. 1728 - 1734
(2008/10/08)
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- Reaction of ascorbic acid with S-nitrosothiols: Clear evidence for two distinct reaction pathways
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Ascorbate reacts with S-nitrosothiols generally, in the pH range 3-13 by way of two distinct pathways, (a) at low [ascorbate], typically below ～1 × 10-4 mol dm-3 which leads to the formation of NO and the disulfide, and (b) at higher [ascorbate] when the products are the thiol and NO. Reaction (a) is Cu2+-dependent, and is completely cut out in the presence of EDTA, whereas reaction (b) is totally independent of [Cu2+] and takes place readily whether EDTA is present or not. For S-nitrosoglutathione (GSNO) the two reactions can be made quite separate, although for some reactants the two reactions overlap. In reaction (a), ascorbate acts as a reducing agent, generating Cu+ from Cu2+, which in turn reacts with RSNO forming initially NO, Cu2+ and RS-. The latter can then play the role of reducing agent for Cu2+, leading to disulfide formation. Ascorbate will initiate reaction when the free thiolate has initially been reduced to a very low level by the synthesis of RSNO from a large excess of nitrous acid over the thiol. Reaction (b) is interpreted in terms of nucleophilic attack by ascorbate at the nitroso-nitrogen atom, leading to thiol and O-nitrosoascorbate which breaks up, by a free-radical pathway, to give dehydroascorbic acid and NO. A similar pathway is the accepted mechanism in the literature for the nitrosation of ascorbate by nitrous acid and alkyl nitrites. The rate constant for the Cu2+-independent pathway increases sharply with pH and analysis of the variation of the rate constant with pH identifies a reaction pathway via both the mono- and di-anion forms of ascorbate, with the latter being the more reactive. As expected the entropy of activation is large and negative. Some aspects of structure-reactivity trends are discussed.
- Holmes, Anthony J.,Williams, D. Lyn H.
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p. 1639 - 1644
(2007/10/03)
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- Disulfide-bridge formation through solvent-free oxidation of thiol amino acids catalysed by peroxidase or hemin on mineral supports
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Air oxidation of hydrophilic thiols to disulfides was performed in neutral conditions on mineral supports activated by hemin or peroxidase. The Royal Society of Chemistry 1999.
- Guibe-Jampel, Eryka,Therisod, Michel
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p. 3067 - 3068
(2007/10/03)
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- Aminopyri(mi)dine derivatives combined with amino acids, and pharmacological activities thereof
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Synthetic compounds combining sulphur-containing or sulphur-free amino acids with aminopyrimidine and aminopyridine derivatives, as well as mineral or organic acid addition salts produced in the presence of an amino grouping, were synthesized. Non-sulphur amino acids such as glutamic acid, pyroglutamic acid, tyrosine, histidine and arginine, and sulphur amino acids such as methionine, cysteine, S-methyl-cysteine and cystine, were attached to minoxidil to give monosubstituted and disubstituted derivatives. The amides with a pyrimidine or pyridine structure coupled to an amide structure in which the carbonyl is from sulphur-containing or sulphur-free amino acid have the properties of; (1) excellent adhesion to the skin, particularly the epidermis; (2) capturing free radicals, in particular the superoxide anion and the hydroxyl radical; (3) selectively relaxing smooth muscle fibers; and (4) in vitro and in vivo keratinocyte growth, hair growth in humans, and fresh and accelerated fur growth in animals.
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- The mechanism of nitric oxide formation from S-nitrosothiols (thionitrites)
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S-Nitrosothiols (RSNO) are easily made by electrophilic nitrosation of thiols and are a convenient source of nitric oxide. Reaction occurs readily (in many cases) in aqueous buffer at pH 7.4 to give in addition the corresponding disulfide RSSR. If oxygen is not rigorously excluded from the solution, then the nitric oxide is converted quantitatively to nitrite ion, whereas in the absence of oxygen nitric oxide can be detected using a commercial NO-probe. Reaction, however, only occurs (apart from the photochemical pathway) if Cu2+ is present. There is often enough Cu2+ in the distilled water-buffer components to bring about reaction, but decomposition is halted if Cu2+ is complexed with EDTA. Experiments with the specific Cu+ chelator neocuproine however show that the true effective reagent is Cu+, formed by reduction of Cu2+ with thiolate ion. Kinetic experiments show that the most reactive nitrosothiols are those which can coordinate bidentately with Cu+, and there is a wide range of reactivity amongst the structures studied. Reactivity is crucially dependent on the concentrations of Cu2+ and RS-. Reaction also occurs, although somewhat more slowly, if the source of copper is the CuII complex with the tripeptide diglycyl-L-histidine (GGH) or as the CuII complex with human serum albumin (HSA). This allows the possibility that nitrosothiols could in principle generate nitric oxide in vivo using the naturally occurring sources of CuII. Rapid exchange of the NO-group in RSNO with thiols occurs, again in aqueous buffer at pH 7.4. This reaction has been established as a nucleophilic substitution reaction by the thiolate ion at the nitroso nitrogen atom. The implications of these results with regard to possible involvement of nitrosothiols in vivo are discussed.
- Williams, D. Lyn H.
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p. 1085 - 1091
(2007/10/03)
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- Cosmetic composition
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An emulsion suitable for topical application to human skin or hair comprises, in addition to water from 0.01 to 20% by weight of a skin benefit ingredient, preferably a 2-hydroxyalkanoic acid having from 3 to 20 carbon atoms, or a salt thereof; from 0.1 to 20% by weight of polyoxyethylene-21-stearyl ether, as a principle emulsifier and from 0.5 to 70% by weight of an emollient oil.
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- Novel spergualin-related compounds and compositions
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The present invention relates to novel spergualin-related compounds represented by the general formula [I]: STR1 wherein X is --(CH2)1?5 or STR2 Y is a hydrogen atom or a residue obtained by removing a hydroxyl group from the carboxyl group of an amino acid or a peptide; m is 0, 1 or 2 and n is 1 or 2, with the proviso that Y is not a hydrogen atom when n is 2 and m is 0. This compounds are stable and exhibit a high immunosuppressive activity.
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- Electron transfer. 100. Iron-catalyzed reduction of peroxide-bound chromium(IV) with mercapto acids
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Mercapto carboxylic acids reduce the diperoxochromium(IV) derivative of diethylenetriamine, CrIV(dien)(O2)2 (chelate I), slowly in acetate buffers, but the reaction is dramatically catalyzed by dissolved iron. With both mercaptoacetic acid and cysteine, the observed stoichiometry (RSH:CrIV) approaches 5:1. Both Cr(IV) and the peroxo groups are reduced, forming Cr(III) and the dithio acids (R2S2). The Cr(III) products contain both acetate and chelating mercapto carboxylate groups, with the ratio of the competing carboxylato ligands dependent on the composition of the reaction medium; Cr(III) spectra indicate predominant O,S-chelation with mercaptoacetate but O,N-chelation with cysteine. Iron exists principally as FeIII in these systems, and its reduction to FeII, via strongly absorbing FeIII-thiol complexes (in the absence of CrIV), is too slow to allow a significant catalytic role for FeII in our reactions. The catalyzed reduction by excess mercaptoacetate is first order in dissolved iron and is accelerated by acetate but exhibits a rate independent of [RSH] at concentrations of the latter greater than 5 × 10-5 M. The rate law accommodates a rapid formation of an FeIII-thiol complex (K > 105.6 M-1), which undergoes electron transfer to Cr(IV) (k = 1.9 × 103 M-1 s-1), yielding an RS? radical (which dimerizes) and a Cr(III)-peroxo complex (which is quickly reduced). Acceleration by acetate is attributed to partial conversion to an FeIII(SR)(OAc) complex, which is somewhat more active than FeIII(SR). The rate law for reduction by L-cysteine (eq 13) is likewise consistent with a reaction involving an FeIII(SR) species, but the kinetic picture here is complicated by incomplete formation of this complex (K = 34 M-1) and by partial dimerization of FeOH2+ in our solutions. The incorporation of acetate and mercapto carboxylate groups into the Cr(III) products is believed to arise from the intervention, during the reduction of bound peroxide, of a CrIII-O? transient, which is rapidly protonated to a substitution-labile CrIV-OH intermediate. Inhibition of redox by 10-3 M EDTA suggests that chelation of FeIII by the reductant is necessary for catalytic action and that the reduction of FeIII by unidentate-bound mercapto acid is too slow to sustain a catalytic path entailing recycling between FeII and FeIII.
- Ghosh,Gould
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p. 3651 - 3655
(2008/10/08)
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- Kinetics of the Copper- and Iron-Catalysed Oxidation of Cysteine by Dioxygen
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For the purpose of controlling levels of thiols and peroxide in bilogical experiments, the kinetics of 'autoxidation' of cysteine (RSH) catalysed by copper or iron ions, added to the reaction medium as Cu(II) and Fe(II) or Fe(III) salts, has been studied.The reaction may be described as proceeding in two steps, only the second of which is spontaneous: 2 RSH + O2 --> RSSR + H2O2 (i) 2 RSH + H2O2 --> RSSR + 2 H2O (ii).The Cu(II)-catalysed reaction (i) follows Michaelis-Menten kinetics with respect to RSH, and probably O2, and is, partly at least, second order with respect to Cu.The rate (ii) is first-order with respect to RSH and H2O2, and is enhanced by Fe(II) and Fe(III) but practically not all by Cu(II).With Cu(II) as the catalyst of the overall reaction, H2O2 is one of the final products.With Fe(II) or Fe(III) as the catalyst, the overall reaction, which proceeds without formation of H2O2, is first-order with respect to RS- and Fe(II)/Fe(III) (at least at high ).When catalysed by an FeO(OH) sol the kinetics change to zeroth-order with respect to RSH.The Cu- and Fe-catalysed rates are not additive; at certain concentrations Fe slows down the overall Cu-catalysed reaction and changes the kinetics towards zeroth order, reducing the levels of H2O2.The mechanisms of the catalysis by Cu of (i) and by Fe of (i) and (ii) have not yet been fully explained.The present study indicates a possible role for binuclear complexes (Cu + Cu or Cu + Fe) and shows further the usefullness of fitting data to numerical solutions of differential equations for models describing reaction rates, in work aimed at the elucidation of mechanisms.
- Ehrenberg, L.,Harms-Ringdahl, M.,Fedorcsak, I.,Granath, F.
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p. 177 - 187
(2007/10/02)
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- Anaerobic Oxidation of Cysteine to Cystine by Iron(III). Part 2. The Reaction in Basic Solution
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The anaerobic oxidation of cysteine to cystine (H2L) by iron(III) has been followed over the pH range 8.2-11.6 by use of a stopped-flow high-speed spectrophotometric method (the results obtained below pH 8.6, however, were not reproducible and no attempt was made to establish a rate law over this range).Between pH 8.6 and 11.2 the experimental data were accurately reproduced by assuming that the bis-cysteine complex, 2-, reacts with the mono-cystein complex, , to yield two iron(II) ions, one cystine, and an unoxidised cysteine with a second-order rate constant of 8.36 x 1E3 dm3mol-1s-1.The predominant complex species present in solution is the purple 2- which exhibits an absorption maximum at 545 nm (shoulder at 445 nm) and has a molar absorption coefficient of 3175 dm3mol-1cm-1.The other complex present is also purple and is .The absorption spectrum of this species (obtained over the pH range 5.5-8.0) exhibits a maximum at 503 nm (shoulder at 575 nm) and has a molar absorption coefficient of 1640 dm3mol-1cm-1.The kinetic results were also used to calculate values of this first and second protonation constant for cysteine (log KH1 = 10.34, log KH2 = 8.32) which compare very favourably with previously published values (obtained by potentiometric titration).Finally, a value of log KM2 = 4.76 for the reaction + L2- 2- was also extracted from the kinetic data.All measurements were carried out at 25 deg C in solution of ionic strength 0.10 mol dm-3 (KCl).
- Jameson, Reginald F.,Linert, Wolfgang,Tschinkowitz, Axel
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p. 2109 - 2112
(2007/10/02)
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- Transvesicular Reactions of Thiols with Ellman's Reagent
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The cleavage of Ellman's reagent , 1, to chromophoric anion 2 by various thiols has been studied in pH 8 buffer, micellar cetyltrimethylammonium bromide (4), and vesicular dihexa-decyldimethylammonium bromide (5) or dioctadecyldimethylammonium chloride (6) solutions.The thiols included thiocholesterol, thiophenol, 2-thionaphthol, DL-cysteine, glutathione, 1-butanethiol, and 1-octanethiol.Vesicles of 6 at 25 deg C sequester 1 in distinct exovesicular and endovesicular binding sites, where reactions with added thiols are kinetically differentiated.Differences in thiol acidity and structure influence their rates of permeation and reaction with vesicle-bound 1.Small quantities of covesicallized 1-hexanol (0.2 wt percent) lower the gel to liquid crystalline transition temperature of vesicular 1 (from ca. 39 deg C to 24 deg C), enhance vesicular fluidity, accelerate the thiol/1 reactions, and destroy the kinetic distinction between the exovesicular and endovesicular reactions.
- Moss, Robert A.,Swarup, Shanti
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p. 5860 - 5866
(2007/10/02)
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- Complex Formation between Anthraquinone-2,6-disulfonate and a Neutral Zinc Porphyrin. Effects of CTAB Micelles on Complex Stability and Photoinduced Electron Transfer
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Zinc(II) mexo-tetrakisporphyrin, Zn-TPSPyP0, forms a complex with anthraquinone-2,6-disulfonate, AQS22-.The porphyrin is statically quenched by the quinone acceptor in the complex structure.In the presence of CTAB micelles the complex is separated and AQS22- is bound to micelles.The excited sensitizer decays to a long-lived triplet state (0.5 ms) and induces the reduction of AQS22-.The micelles also function in the charge separation of the electron-transfer products.
- Degani, Yinon,Willner, Itamar
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p. 5685 - 5689
(2007/10/02)
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- Process for the production of aqueous solutions of sodium salts of α-a
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Aqueous solutions of sodium salts of α-aminocarboxylic acids practically free of foreign salts are produced by saponifying the corresponding hydantoin at a temperature between 110° C. and 180° C. with a mixture, in each case based on the hydantoin, of 1 equivalent of sodium hydroxide and 2 equivalents of calcium oxide or hydroxide, separating off the precipitated calcium carbonate after the end of the saponification and concentrating the aqueous sodium salt solution remaining to drive off the ammonia contained therein.
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- Monomeric interferons
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A method for producing monomeric interferons from oligomeric interferons, for preventing formation of oligomeric interferon from monomeric interferon, and for increasing the yield of monomeric interferon upon purification of interferon is described. The method employs a redox reagent to treat the interferon sample.
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- Oxidation of Thiols by Nitric Oxide and Nitrogen Dioxide: Synthetic Utility and Toxicological Implications
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Thiols are readily oxidized to disulfides by either nitric oxide or nitrogen dioxide.Reaction conditions are mild, and quantitative yields can be obtained.The reactions are useful for preparative purposes and may have toxicological significance.
- Pryor, William A.,Church, Daniel F.,Govindan, C. K.,Crank, George
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p. 156 - 159
(2007/10/02)
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- Rate Constants and Equilibrium Constants for Thiol-Disulphide Interchange Reactions Involving Oxidized Glutathione
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The rate of reduction of oxidized glutathione (GSSG) to glutathione (GSH) by thiolate (RS-) follows a Broensted relation in pKas of the conjugate thiols (RSH): βnuc ca. 0.5.This value is similar to that for reduction of Ellman's reagent: βnuc ca. 0.4 - 0.5.Analysis of a number of rate and equilibrium data, taken both from this work and from the literature, indicates that rate constants, k, for a range of thiolate-disulphide interchange reactions are correlated well by equations of the form log k = C + βnucpKanuc + βcpKac + βlgpKalg ( nuc = nucleophile, c = central, and lg = leaving group sulfur): eq 36 - 38 give representative values of the Broensted coefficients.The values of these Bronsted coefficients are not sharply defined by the available experimental data, although eq 36 - 38 provide useful kinetic models for rates of thiolate-disulfide interchange reactions.The uncertainty in these parameters is such that their detailed mechanistic interpretation is not worthwhile, but their qualitative interpretation - that all three sulphur atoms experience a significant effective negative charge in the transition state, but that the charge is concentrated on the terminal sulfurs - is justified.Equilibrium constants for reduction of GSSG using α,ω-dithiols have been measured.The reducing potential of the dithiol is strongly influenced by the size of the cyclic disulfide formed on its oxidation: the most strongly reducing dithiols are those which can form six-membered cyclic disulfides.Separate equilibrium constants for thiolate anion-disulphide interchange (KS-) and for thiol-disufide interchange (KSH) have been estimated from literature data: KS- is roughly proportional to 2ΔpKa is the difference between the pKas of the two thiols involved in the interchange.The contributions of thiol pKa values to the observed equilibrium constants for reduction of GSSG with α,ω-dithiols appear to be much smaller than those ascribable to the influence of structure on intramolecular ring formation.These equilibrium and rate constants are helpful in choosing dithiols for use as antioxidants in solutions containing proteines: dithiothreitol (DTT), 1,3-dimercapto-2-propanol (DMP), and 2-mercaptoethanol have especially useful properties.
- Szajewski, Richard P.,Whitesides, George M.
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p. 2011 - 2026
(2007/10/02)
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- Oxidation of thiols to disulfides
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A simple and selective technique for the oxidation of thiols resulted in high yields of the corresponding disulfides. The reaction is tailored so that all byproducts are either volatile or insoluble and the end product recovered easily in essentially pure form. A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.
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