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Reaction Mixture (reaction + mixture)
Kinds of Reaction Mixture Selected AbstractsEffect of citric acid and 1,2-dihydroxybenzene 3,5-disulfonic acid on crystallization of calcium sulfate dihydrate under simulated conditions of phosphoric acid productionCRYSTAL RESEARCH AND TECHNOLOGY, Issue 8 2005M. M. Rashad Abstract The effect of citric acid and 1,2-dihydroxybenzene 3,5-disulfonic acid (DHBDSA), as additives, on the crystallization of gypsum was studied under simulated conditions of the of phosphoric acid production. Calcium hydrogen phosphate and sulfuric acid were mixed with dilute phosphoric acid at 80 °C, and the turbidity of the reaction mixture was measured at different time periods to calculate the induction time of gypsum crystals formation. Addition of citric acid increased the induction time and decreased the growth efficiency while addition of DHBDSA decreased the induction time and increased the growth efficiency compared with in absence of additives. The crystals mean and median diameters were found to decrease in the presence of citric acid and increased in the presence of DHBDSA. The surface energy decreased with citric acid and increased with DHBDSA compared to the baseline (without additives). Interestingly, the majority of the formed crystals are tabular with DHBDSA and needle-like type with citric acid and baseline [source] Hydrothermal growth of boron nitride microcrystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2005Xiaopeng Hao Abstract Boron nitride (BN) crystals with size of several micrometers have been successfully synthesized by hydrothermal method. The reactants used in our experiments were boric acid (H3BO3), sodium azide (NaN3) and white phosphor (P). The samples were characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR), selective area electron diffraction (SAED). It is found that the existence of Cl - in the reaction mixture has much effect on the synthesis of BN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [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] Two-Surface Strategy in Electrochemical DNA Hybridization Assays: Detection of Osmium-Labeled Target DNA at Carbon ElectrodesELECTROANALYSIS, Issue 5-6 2003Miroslav Fojta Abstract Target DNAs, including a 71-mer oligonucleotide, a PCR product and a plasmid DNA, all containing oligo(A) stretches, were hybridized at magnetic Dynabeads oligo(dT)25 (DBT). The hybridization events were detected using a technique based on chemical modification of the target DNA with a complex of osmium tetroxide with 2,2,-bipyridine (Os,,bipy) and voltammetric detection at carbon electrodes. DNA was modified with Os,,bipy prior to capture at DBT, at the beads, or after release from the beads. In the latter case, DNA-Os,,bipy was detected in the reaction mixture using adsorptive transfer stripping voltammetry involving extraction of unreacted Os,,bipy from the electrode by organic solvents. Pre-labeling of the target plasmid DNA and the PCR product with Os,,bipy significantly increased the yield of DNA captured at the beads. Tens of femtomoles of both short (the 71-mer oligonucleotide) and long (the 3-kilobase plasmid) target DNAs in a 20-microliter hybridization sample can be easily detected by means of these techniques. Various carbon electrode materials, including pyrolytic graphite (PGE), highly oriented pyrolytic graphite (HOPGE), carbon paste (CPE), glassy carbon and pencil graphite, were tested regarding their suitability for the detection of osmium-labeled DNA. Among them, PGE and HOPGE appeared usable in the measurements of both purified DNA-Os,,bipy and its mixtures with unreacted Os,,bipy while CPE was suitable for the detection purified osmium-labeled DNA. [source] Development of a new hybrid technique for rapid speciation analysis by directly interfacing a microfluidic chip-based capillary electrophoresis system to atomic fluorescence spectrometryELECTROPHORESIS, Issue 11 2005Feng Li Abstract This paper represents the first study on direct interfacing of microfluidic chip-based capillary electrophoresis (chip-CE) to a sensitive and selective detector, atomic fluorescence spectrometry (AFS) for rapid speciation analysis. A volatile species generation technique was employed to convert the analytes from the chip-CE effluent into their respective volatile species. To facilitate the chip-CE effluent delivery and to provide the necessary medium for subsequent volatile species generation, diluted HCl solution was introduced on the chip as the makeup solution. The chip-CE-AFS interface was constructed on the basis of a concentric "tube-in-tube" design for introducing a KBH4 solution around the chip effluent as sheath flow and reductant for volatile species generation as well. The generated volatile species resulting from the reaction of the chip-CE effluent and the sheath flow were separated from the reaction mixture in a gas-liquid separator and swept into the AFS atomizer by an argon flow for AFS determination. Inorganic mercury (Hg(II)) and methylmercury (MeHg(I)) were chosen as the targets to demonstrate the performance of the present technique. Both mercury species were separated as their cysteine complexes within 64 s. The precision (relative standard deviation, RSD, n = 5) of migration time, peak area, and peak height for 2 mg·L,1 Hg(II) and 4 mg·L,1 MeHg(I) (as Hg) ranged from 0.7 to 0.9%, 2.1 to 2.9%, and 1.5 to 1.8%, respectively. The detection limit was 53 and 161 µg·L,1 (as Hg) for Hg(II) and MeHg(I), respectively. The recoveries of the spikes of mercury species in four locally collected water samples ranged from 92 to 108%. [source] Acute toxicity of heavy metals to acetate-utilizing mixed cultures of sulfate-reducing bacteria: EC100 and EC50ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2001Vivek P. Utgikar Abstract Acid mine drainage from abandoned mines and acid mine pit lakes is an important environmental concern and usually contains appreciable concentrations of heavy metals. Because sulfate-reducing bacteria (SRB) are involved in the treatment of acid mine drainage, knowledge of acute metal toxicity levels for SRB is essential for the proper functioning of the treatment system for acid mine drainage. Quantification of heavy metal toxicity to mixed cultures of SRB is complicated by the confounding effects of metal hydroxide and sulfide precipitation, biosorption, and complexation with the constituents of the reaction matrix. The objective of this paper was to demonstrate that measurements of dissolved metal concentrations could be used to determine the toxicity parameters for mixed cultures of sulfate-reducing bacteria. The effective concentration, 100% (EC100), the lowest initial dissolved metal concentrations at which no sulfate reduction is observed, and the effective concentration, 50% (EC50), the initial dissolved metal concentrations resulting in a 50% decrease in sulfate reduction, for copper and zinc were determined in the present study by means of nondestructive, rapid physical and chemical analytical techniques. The reaction medium used in the experiments was designed specifically (in terms of pH and chemical composition) to provide the nutrients necessary for the sulfidogenic activity of the SRB and to preclude chemical precipitation of the metals under investigation. The toxicity-mitigating effects of biosorption of dissolved metals were also quantified. Anaerobic Hungate tubes were set up (at least in triplicate) and monitored for sulfate-reduction activity. The onset of SRB activity was detected by the blackening of the reaction mixture because of formation of insoluble ferrous sulfide. The EC100 values were found to be 12 mg/L for copper and 20 mg/L for zinc. The dissolved metal concentration measurements were effective as the indicators of the effect of the heavy metals at concentrations below EC100. The 7-d EC50 values obtained from the difference between the dissolved metal concentrations for the control tubes (tubes not containing copper or zinc) and tubes containing metals were found to be 10.5 mg/L for copper and 16.5 mg/L for zinc. Measurements of the turbidity and pH, bacterial population estimations by means of a most-probable number technique, and metal recovery in the sulfide precipitate were found to have only a limited applicability in these determinations. [source] Synthesis and Functionalization of Germanium Triphenylcorrolate: The First Example of a Partially Brominated CorroleEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2007Sara Nardis Abstract Ge complexes of 5,10,15-triphenylcorrole were prepared in refluxing dry DMF using GeCl4 as the source of Ge. Chromatographic separation of the crude reaction mixture afforded the ,-oxo dimer 1 and the methoxy derivative 2a. The corresponding chloride 2b can be obtained by treatment of 1 or 2a with HCl. The reaction of 2a with Br2 in CHCl3/py afforded the hexabromo derivative 3 as the main product, giving the first indication of the regioselective substitution of pyrroles B and C on the corrole ring. The fully brominated open-chain tetrapyrrole 4 was also characterized as a reaction by-product. Different partially brominated Ge complexes 5 and 6 have been obtained by variation of reaction conditions, while the heptabromo derivative was obtained in a mixture with the corresponding fully brominated Gecorrole. Photophysical characterization of Ge corrolates confirmed the high fluorescence quantum yield of such complexes, and also led to the first observation of phosphorescence emissions from corrole complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] The Transient Titanocene(II): Direct Synthesis from Solvated Titanium(II) Chloride and Cyclopentadienylsodium and Ensuing Interception with Diphenylacetylene as 1,1-Bis(cyclopentadienyl)-2,3,4,5-tetraphenyltitanacyclopentadiene,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2007John J. Eisch Abstract For the first time the unstable titanocene(II) has been directly synthesized by the Wilkinson metallocene approach, namely the interaction of a THF-soluble form of titanium(II) chloride with two equivalents of cyclopentadienylsodium in THF solution at 0°,25 °C. Because of the transient existence of the titanocene(II) thereby obtained, it could only be chemically trapped in high yield as 1,1-bis(cyclopentadienyl)-2,3,4,5-tetraphenyltitanacyclopentadiene by two equivalents of diphenylacetylene, if the acetylene was added at 25 °C, without removal of the by-product LiCl and NaCl. If the addition of the acetylene was delayed, in order to filter off the LiCl and NaCl from the reaction mixture, then no trace of the titanacyclopentadiene derivative was found upon hydrolytic workup. Instead, a significant portion of the acetylene was found to have undergone hydrotitanation. This finding is clear evidence that the titanocene(II) had undergone a precedented rearrangement to a known dimer having the structure of a titanocene(III) hydride with a fulvalene bridge between the titanium centers. We suggest that the LiCl and NaCl present in the unfiltered reaction mixture form a dichloro complex with titanocene(II) and thereby retard its dimerizing rearrangement to the titanocene(III) hydride. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis, Characterization, and Electrochemical Properties of Dinuclear Complexes Assembled from Asymmetric CoIII Bis(dioximates) and Boronic AcidsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2005Renata Dreos Abstract Bis(methylphenylglyoximate)cobalt(III) complexes exist both as cis and trans isomers due to the asymmetry of the equatorial ligand, and, when the axial ligands are different, the trans isomer is chiral. The reaction of racemic trans -[CH3Co(mpgH)2py] (1) with either 3- or 4-pyridylboronic acid affords dimeric units arranged on a crystallographic symmetry center such that the pyridyl nitrogen of one moiety coordinates to the Co atom of the symmetry-related unit. In principle, three structurally different dimeric species (two homodimers and one heterodimer) can be obtained. Time-resolved 1H NMR spectra of a 1:1 mixture of racemic 1 and either 3- or 4-pyridylboronic acid in CDCl3/CD3OD show that the reaction does not converge toward a unique species in solution. Nevertheless, X-ray structures show that the heterochiral dimers are the only products that crystallize from the reaction mixture. The nature of the dioximate side groups does not affect the geometry of the dimeric arrangements assembled by 4-pyridylboronic acid ("molecular box"). On the contrary, the geometry of the species assembled by 3-pyridylboronic acid varies from the "molecular parallelogram" obtained from the bis(dimethylglyoximates) to the highly squeezed "molecular box" obtained from bis(methylphenylglyoximates). Cyclic voltammetry studies show that the metal centers in the dimeric species do not interact with each other and undergo a simultaneous redox process. However, depending on the geometry of the systems, the redox process involves a single four-electron reduction for 3 and 5 or two consecutive two-electron reduction steps for 4 and 6. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Micro-reactor for transesterification of plant seed oilsEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 5 2009Phattaraporn Kaewkool Abstract The fatty acid compositions of vegetable or other plant seed oils are generally determined by gas chromatography (GC). Methyl esters (the most volatile derivatives) are the preferred derivatives for GC analysis. Esters of higher alcohols are good for the separation of volatile and positional isomers. All the esters of the C1,C8 alcohols of vegetable oils were silmilarly prepared by passing the reaction mixture containing the desired alcohol, oil and tetrahydrofuran through the micro-reactor (a 3-mL dispossible syringe packed with 0.5,g of NaOH powder). The reaction products were acidified with acetic acid and the mixture was analyzed by high-performance size exclusion chromatography and GC. Transesterification was quantitative for primary alcohols, but an appreciable amount of free fatty acids was formed for secondary alcohols. Coriander seed oil was quantitatively esterified with 2-ethyl 1-hexanol with the micro-reactor in less than 1,min. Oleic and petroselinic acid 2-ethyl 1-hexyl esters are baseline separated on an Rtx-2330 capillary column (30,m×0.25,mm, 0.25,µm film thickness). [source] Simplification of separation of the reaction mixture after transesterification of vegetable oilEUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 4 2008Martin Hájek Abstract A heterogeneous reaction mixture is formed by transesterification of vegetable oils. The reaction mixture contains mainly methyl esters of higher fatty acids and glycerol. From this mixture, biodiesel is gained by spontaneous sedimentation in the gravitational field. The sedimentation can be considerably accelerated by controlled addition of water. It was found that addition of small amounts of water to the crude reaction mixture significantly affected the mixture, and substantial changes in the speed of the separation took place. Considerable differences in the composition and quality of the ester and glycerol phases occurred. The optical properties (transmittance and refractive indices) of the heterogeneous reaction mixture are changed after addition of water; this change can be observed spectrophotometrically. This method is applicable to all types of vegetable oils including waste frying oils. [source] Reusable, Polystyrene-Resin-Supported, Palladium-Catalyzed, Atom-Efficient Cross-Coupling Reaction of Aryl Halides with TriarylbismuthsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2010Wen-Jun Zhou Abstract A rapid, atom-efficient, cross-coupling reaction of triarylbismuths with aryl bromides or aryl iodides was reported, and the reaction involves the use of a catalytic amount of polystyrene-supported palladium in the presence of KF as base in DMSO at 105 °C in an open atmosphere. All three aryl groups of the triarylbismuths participated in the reaction and produced polyfunctional biaryls in excellent yields. The polymeric catalyst can be easily separated from the reaction mixture and reused more than 10 times without showing any obvious decrease in activity. [source] Improved Synthesis and Isolation of 2,- O -Methyladenosine: Effective and Scalable Enzymatic Separation of 2,/3,- O -Methyladenosine RegioisomersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2009Saúl Martínez-Montero Abstract An efficient separation of a mixture of 2,/3,- O -methyladenosine regioisomers (1 + 2; 1:1) has been developed by selective enzymatic acylation using immobilized Pseudomonas cepacia lipase (PSL-C) in combination with acetonoxime levulinate as acyl donor. The 3,-hydroxy group of 2,- O -methyladenosine (1) was acylated with high selectivity (ca. 70,%), whereas an equal amount of 3,- O -methyladenosine (2) in the same solution resulted in minor acylation of 5,-hydroxy group (ca. 8,%). The differential behavior of both regioisomers towards enzymatic acylation allowed to develop a separation protocol. Upon extraction of the acylated products, the 3,- O -methyladenosine was isolated in 81,% yield and 97,% purity from the aqueous layer. Hydrolysis of acylated products in organic layer furnished 2,- O -methyladenosine in 67,% yield and 99,% purity. The separation process was successfully applied to the crude reaction mixture of methylated products (ca. 3:1 of 1/2) on 5-g scale. We also report on the use of methyl p -toluenesulfonate as a safe reagent for 2,- O -methylation of adenosine.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Protonation of Diarylacetylenes in Superacid HSO3F and Their Oxidation in the HSO3F/PbO2 System: One-Pot Synthesis of Polysubstituted NaphthalenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2008Aleksander V. Vasilyev Abstract In the superacid HSO3F, diarylacetylenes bearing one electron-withdrawing group (NO2, CN, COMe, CO2Me) in each arene ring form stable ions, protonated at these groups. Oxidation of such diarylacetylenes in the HSO3F/PbO2 system at ,75 to ,50 °C over 2,2.5 h, followed by quenching of the reaction mixture with hydrochloric (or hydrobromic) acid at ,60 to 25 °C, resulted in the formation of (E,E)-1,4-dichloro (or dibromo)-1,2,3,4-tetraarylbuta-1,3-dienes. These butadienes spontaneously undergo electrocyclic transformation into polysubstituted naphthalenes at room temperature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Silica-Immobilized NHC,CuI Complex: An Efficient and Reusable Catalyst for A3 -Coupling (Aldehyde,Alkyne,Amine) under Solventless Reaction ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2008Min Wang Abstract A novel silica-immobilized NHC,CuI complex was developed and used as a highly efficient catalyst in the three-component coupling reactions of aldehydes, alkynes and amines (A3 -coupling). The reactions were applicable to aromatic and aliphatic aldehydes, alkynes and amines, and generated the corresponding propargylamines in good yields only in the presence of SiO2,NHC,CuI (2 mol-%) at room temp. under solvent-free reaction conditions. Moreover, the catalyst was quantitatively recovered from the reaction mixture by a simple filtration and reused for ten cycles with almost consistent activity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Phenylphosphoric Acid as a New Additive to Inhibit Olefin Isomerisation in Ruthenium-Catalysed Metathesis ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2007Nélida Gimeno Abstract A systematic study of the ruthenium-catalysed metathesis of alkenes containing hydrogen-bonding substituents (namely urea and thiourea groups) is presented. Under standard metathesis conditions, several of the substrates under study undergo alkene isomerisation instead of the targeted metathesis. However, in the course of these investigations it has been established that this unwanted isomerisation process can be suppressed by addition of phenylphosphoric acid to the reaction mixture. Some other potential isomerisation inhibitors (e.g. benzoic acid and salts of phosphoric acid) have been studied and their performance compared to that of phenylphosphoric acid. To extend the scope of phenylphosphoric acid, we also studied the metathesis of 1,3-diallylurea. Interestingly, not only did we observe the complete suppression of the isomerisation process, but also that it is possible to obtain instead of the ring-closing metathesis (RCM) product,ADMET oligomers resulting from the cross-metathesis of diallylurea at higher concentrations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Carbodiazenylation of Olefins by Radical Iodine Transfer and Addition to Arenediazonium SaltsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006Olga Blank Abstract Carbodiazenylation of olefins can be achieved with arenediazonium salts under reductive conditions. The method can be extended to aliphatic substituents when iodine compounds are present in the reaction mixture. Incorporation is achieved through a radical iodine transfer. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Evaluation of detergents for the soluble expression of ,-helical and ,-barrel-type integral membrane proteins by a preparative scale individual cell-free expression systemFEBS JOURNAL, Issue 23 2005Christian Klammt Cell-free expression has become a highly promising tool for the fast and efficient production of integral membrane proteins. The proteins can be produced as precipitates that solubilize in mild detergents usually without any prior denaturation sttif. Alternatively, membrane proteins can be synthesized in a soluble form by adding detergents to the cell-free system. However, the effects of a representative variety of detergents on the production, solubility and activity of a wider range of membrane proteins upon cell-free expression are currently unknown. We therefore analyzed the cell-free expression of three structurally very different membrane proteins, namely the bacterial ,-helical multidrug transporter, EmrE, the ,-barrel nucleoside transporter, Tsx, and the porcine vasopressin receptor of the eukaryotic superfamily of G-protein coupled receptors. All three membrane proteins could be produced in amounts of several mg per one ml of reaction mixture. In general, the detergent 1-myristoyl-2-hydroxy- sn -glycero-3-[phospho- rac -(1-glycerol)] was found to be most effective for the resolubilization of membrane protein precipitates, while long chain polyoxyethylene-alkyl-ethers proved to be most suitable for the soluble expression of all three types of membrane proteins. The yield of soluble expressed membrane protein remained relatively stable above a certain threshold concentration of the detergents. We report, for the first time, the high-level cell-free expression of a ,-barrel type membrane protein in a functional form. Structural and functional variations of the analyzed membrane proteins are evident that correspond with the mode of expression and that depend on the supplied detergent. [source] Chiral alcohol production by NADH-dependent phenylacetaldehyde reductase coupled with in situ regeneration of NADHFEBS JOURNAL, Issue 9 2002Nobuya Itoh Phenylacetaldehyde reductase (PAR) produced by styrene-assimilating Corynebacterium strain ST-10 was used to synthesize chiral alcohols. This enzyme with a broad substrate range reduced various prochiral aromatic ketones and ,-ketoesters to yield optically active secondary alcohols with an enantiomeric purity of more than 98% enantiomeric excess (e.e.). The Escherichia coli recombinant cells which expressed the par gene could efficiently produce important pharmaceutical intermediates; (R)-2-chloro-1-(3-chlorophenyl)ethanol (28 mg·mL,1) from m -chlorophenacyl chloride, ethyl (R)-4-chloro-3-hydroxy butanoate) (28 mg·mL,1) from ethyl 4-chloro-3-oxobutanoate and (S)- N-tert -butoxycarbonyl(Boc)-3-pyrrolidinol from N -Boc-3-pyrrolidinone (51 mg·mL,1), with more than 86% yields. The high yields were due to the fact that PAR could concomitantly reproduce NADH in the presence of 3,7% (v/v) 2-propanol in the reaction mixture. This biocatalytic process provided one of the best asymmetric reductions ever reported. [source] Phosphorylation of phosphodiesterase-5 by cyclic nucleotide-dependent protein kinase alters its catalytic and allosteric cGMP-binding activitiesFEBS JOURNAL, Issue 9 2000Jackie D. Corbin In addition to its cGMP-selective catalytic site, cGMP-binding cGMP-specific phosphodiesterase (PDE5) contains two allosteric cGMP-binding sites and at least one phosphorylation site (Ser92) on each subunit [Thomas, M.K., Francis, S.H. & Corbin, J.D. (1990) J. Biol. Chem.265, 14971,14978]. In the present study, prior incubation of recombinant bovine PDE5 with a phosphorylation reaction mixture [cGMP-dependent protein kinase (PKG) or catalytic subunit of cAMP-dependent protein kinase (PKA), MgATP, cGMP, 3-isobutyl-1-methylxanthine], shown earlier to produce Ser92 phosphorylation, caused a 50,70% increase in enzyme activity and also increased the affinity of cGMP binding to the allosteric cGMP-binding sites. Both effects were associated with increases in its phosphate content up to 0.6 mol per PDE5 subunit. Omission of any one of the preincubation components caused loss of stimulation of catalytic activity. Addition of the phosphorylation reaction mixture to a crude bovine lung extract, which contains PDE5, also produced a significant increase in cGMP PDE catalytic activity. The increase in recombinant PDE5 catalytic activity brought about by phosphorylation was time-dependent and was obtained with 0.2,0.5 ,m PKG subunit, which is approximately the cellular level of this enzyme in vascular smooth muscle. Significantly greater stimulation was observed using cGMP substrate concentrations below the Km value for PDE5, although stimulation was also seen at high cGMP concentrations. Considerably higher concentration of the catalytic subunit of PKA than of PKG was required for activation. There was no detectable difference between phosphorylated and unphosphorylated PDE5 in median inhibitory concentration for the PDE5 inhibitors, sildenafil, or zaprinast 3-isobutyl-1-methylxanthine. Phosphorylation reduced the cGMP concentration required for half-maximum binding to the allosteric cGMP-binding sites from 0.13 to 0.03 ,m. The mechanism by which phosphorylation of PDE5 by PKG could be involved in physiological negative-feedback regulation of cGMP levels is discussed. [source] Characterization of the PCR inhibitory effect of bile to optimize real-time PCR detection of Helicobacter speciesFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 2 2005Waleed Abu Al-Soud Abstract The inhibitory effect of human and porcine bile samples to detect Helicobacter DNA was studied by adding different concentrations of bile samples to PCR mixtures of six thermostable DNA polymerases containing cagA specific primers and Helicobacter pylori DNA. PCR products were amplified by using the Rotorgene system and SYBR Green I. Among the six DNA polymerases tested, rTth had the lowest sensitivity to bile inhibitors, whereas Taq and Tfl had the highest sensitivity. Bile proteins did not inhibit AmpliTaq DNA polymerase, whereas the fraction containing mainly bile acids and their salts inhibited the amplification capacity of AmpliTaq. Heating human bile at 98 °C and adding casein and formamide to the reaction mixture reduced the PCR inhibitory effect of bile. Therefore, a pre-PCR treatment based on dilution and heating of bile, adding casein and formamide to the reaction mixture of rTth DNA polymerase was found efficient to amplify DNA directly in bile. [source] Significant activity of a modified ribozyme with N7-deazaguanine at G10.1: the double-metal-ion mechanism of catalysis in reactions catalysed by hammerhead ribozymesGENES TO CELLS, Issue 8 2000Yuka Nakamatsu Background Several reports have appeared recently of experimental evidence for a double-metal-ion mechanism of catalysis in reactions catalysed by hammerhead ribozymes. In one case, hammerhead ribozyme-mediated cleavage was analysed as a function of the concentration of La3+ ions in the presence of a fixed concentration of Mg2+ ions so that the role of metal ions that are directly involved in the cleavage reaction could be monitored. The resultant bell-shaped curve for activation of cleavage was used to support the proposed double-metal-ion mechanism of catalysis. However, other studies have demonstrated that the binding of a metal ion (the most conserved P9 metal ion) to the pro-Rp oxygen (P9 oxygen) of the phosphate moiety of nucleotide A9 and to the N7 of nucleotide G10.1 is critical for efficient catalysis, despite the large distance (,20 Å) between the P9 metal ion and the labile phosphodiester group in the ground state. In fact, it was demonstrated that an added Cd2+ ion binds first to the pro-Rp phosphoryl P9 oxygen but not with the pro-Rp phosphoryl oxygen at the cleavage site. Results In earlier discussions, it was difficult to completely exclude the possibility that La3+ ions might have replaced the P9 metal ion and, as a result, created conditions represented by the bell-shaped curve. In order to clarify this situation, we examined a chemically synthesized hammerhead ribozyme (7-deaza-R34) that included a minimal modification, namely, an N7-deazaguanine residue in place of G10.1. We compared the kinetic properties of this ribozyme with those of the parental ribozyme (R34). Kinetic analysis revealed that, unlike the cases of added Cd2+ ions, the added La3+ ions did not replace the pre-existing P9 metal ion, and that the replacement of N7 by C7 at G10.1 reduced the catalytic activity to a limited extent. This result indicates that the binding of a Mg2+ ion to N7 at G10.1 is catalytically important but not indispensable. Most importantly, 7-deaza-R34 also yielded a bell-shaped curve upon addition of La3+ ions to the reaction mixture. Conclusions Since the data based on our experiments with 7-deaza-R34 are completely free from potential artefacts, due to the binding of a La3+ ion to N7 at G10.1, our results, that 7-deaza-R34 yielded a bell-shaped curve following the addition of La3+ ions to the Mg2+ -background reaction mixture, strongly supports the proposal that a double-metal-ion mechanism is operative in the cleavage reaction which is catalysed by hammerhead ribozymes. [source] Photochemical Reactions of Regioisomeric 2,2-Dimethyl-5,5-diphenyl- and 5,5-Dimethyl-2,2-diphenyl-Substituted Diazo Ketones of a Tetrahydrofuran SeriesHELVETICA CHIMICA ACTA, Issue 10 2009Ludmila Abstract The principal direction of conventional photolysis of the regioisomeric 2,2-dimethyl-5,5-diphenyl- and 5,5-dimethyl-2,2-diphenyl-substituted 4-diazodihydrofuran-3(2H)-ones 1a and 1b, respectively, is the Wolff rearrangement, while other photochemical processes, which are giving rise to the formation of CH-insertion, 1,2-alkyl- or -aryl-shifts, as well as H-atom-abstraction products occur to a much lower degree (Schemes,2 and 3). The ratio of similar reaction products from both regioisomers 1a and 1b is essentially independent of their structure, and a substantial effect of the relative position of the Ph and diazo group to each other on the yield of CH-insertion products does not occur. Based on stereochemical considerations, the Wolff rearrangement of diazodihydrofuran-3(2H)-ones apparently proceeds in a concerted manner, whereas the appearance in the reaction mixture of 1,2-shift and H-atom-abstraction products points to the parallel generation during photolysis of singlet and triplet carbenes (Schemes,4 and 5). [source] Promotion of the fenton reaction by Cu2+ ions: Evidence for intermediatesINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2006Mordechai L. Kremer The promotion of the Fenton reaction by Cu2+ ions has been investigated using a wide range of [Cu2+]. Both the disappearance of Fe2+ and the evolution of O2 were followed as a function of time by quenching the reaction mixture with o -phenanthroline or with excess Fe2 + ions, respectively. Two series of experiments were performed. In one series [H2O2] was 5 × 10,4 mol dm,3, and in the other [H2O2] was reduced to 5 × 10,5 mol dm ,3. By stopping the reaction with excess Fe2+ ions, significant differences in the measured absorbance in the two series were observed. In the higher [H2O2] range, the absorbance decreased monotonically in time, due to O2 formation during the reaction. In the lower range, an initial transient rise of the absorbance was observed, indicating the formation of spectroscopically distinct intermediates in the system. A mechanism involving the intermediates FeOCu4+ and FeOCu5+ has been set up. Rate constants of the mechanism have been determined. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 725,736, 2006 [source] Micelle-catalyzed reaction of ninhydrin with DL -valine in the absence and presence of organic solventsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2006Kabir-ud-Din Kinetics of the DL -valine-ninhydrin reaction has been studied spectrophotometrically under varying conditions of [CTAB], [ninhydrin], [DL -valine], pH, temperature, and %(v/v) organic solvents (solvents used: 1-propanol, methylcellosolve, acetonitrile, and dimethyl sulfoxide). Addition of CTAB and increase in the proportion of organic solvents, both showed catalyzing effect on the reaction. The effect of simultaneous presence of CTAB and DMSO in the reaction mixture has also been seen. The rate profiles obtained for solutions containing from 10% to 70% DMSO exhibited clear maxima that shifted progressively to higher concentrations of CTAB. The experimental results are explained in terms of specific solvent effects and the formation of stoichiometric hydrate DMSO · 2H2O and the inhibitory effect of DMSO on micelle formation. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 634,642, 2006 [source] Collagenous hydrolysates from untraditional sources of proteins.INTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 4 2001Reaction condition, the yield of enzymatic hydrolysis of short cattle tendons Synopsis The effect of reaction conditions on the yield of enzymatic hydrolysis of short cattle tendons was examined using statistical scheme of factorial experiments 24. The duration of enzymatic purification of the starting material and of purified material denaturation processes, the protease concentration in reaction mixture and hydrolysis time were considered to be the main sources of reaction yield variation. An attempt was made to find the conditions leading to maximal yield of collagen hydrolysate. Résumé On a étudié l'effet des conditions de réaction sur le rendement de l'hydrolyse enzymatique de tendons courts de bétail en utilisant un plan d'expériences statistique de factorielle 24. On a considéré que la durée de la purification enzymatique du produit de départ et des processus de dénaturation du matériau purifié, la concentration en protéase dans le mélange réactionnel et le temps d'hydrolyse étaient les paramètres majeurs de variation du rendement de réaction. On a effectué un essai de résolution des conditions conduisant au rendement maximal en hydrolysat de collagène. [source] Influence of pH, NaCl and pre-incubation on utilisation of surimi wash water in generation of antioxidative material by using the Maillard reactionINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 8 2010Chakree Thongraung Summary Maillard reaction products (MRPs) were generated from reaction mixtures of surimi wash water (SWW) with glucose or fructose (5%w/v) heated at 95 °C for 2,12 h. The effects of pH, NaCl and pre-incubation of SWW on the Maillard reaction and antioxidant capacity of MRPs were investigated. The antioxidative capacity of MRPs was determined by measuring free DPPH° radical scavenging activity and reducing power. The highest colour intensity (OD420) as well as antioxidative capacity was noted in the reaction mixture containing fructose at pH 9.0. The addition of NaCl (0.5,2.5%w/v) caused reduction in browning intensity but enhanced antioxidative capacity of the MRPs. Pre-incubation of SWW at 45 °C for 4 h decreased soluble protein but increased the Maillard reaction and antioxidative capacity of MRPs. A positive effect of salt or pre-incubation of SWW on the antioxidative capacity of MRPs was not associated with the soluble protein content in the reaction mixture. [source] Heterogeneously Catalyzed Oxidative Cyanation of Tertiary Amines with Sodium Cyanide/Hydrogen Peroxide using Polymer-Supported Iron(II) Phthalocyanines as CatalystADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010Sweety Singhal Abstract The first report on heterogeneously catalyzed oxidative cyanation of various tertiary amines to the corresponding ,-amino nitriles with high yields and selectivity by using hydrogen peroxide oxidant in presence of sodium cyanide and Fe(II) phthalocyanine supported on a polymer as catalyst is described. The present method has the added benefits of facile recovery of the catalyst from the reaction mixture and its subsequent use without further activation. Consistent catalytic activity with no metal leaching was observed during this course. [source] Synthesis and Application of Polymer-Supported Chiral Brønsted Acid OrganocatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Magnus Rueping Abstract A new methodology for the immobilization of chiral Brønsted acids has been developed. The resulting heterogeneous organocatalysts have been employed in multiple consecutive catalysis cycles in the asymmetric organocatalytic transfer hydrogenation. The new catalyst system can not only be easily recovered from the reaction mixture in a tea-bag approach but it can also be easily reused in several catalytic cycles without loss of reactivity and selectivity. [source] Kinetic Analysis of L -Carnosine Formation by ,-AminopeptidasesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Tobias Heck Abstract The ,,,-dipeptide L -carnosine occurs in high concentrations in long-lived innervated mammalian tissues and is widely sold as a food additive. On a large scale L -carnosine is produced by chemical synthesis procedures. We have established two aqueous enzymatic reaction systems for the preparation of L -carnosine using the dissolved bacterial ,-aminopeptidases DmpA from Ochrobactrum anthropi and BapA from Sphingosinicella xenopeptidilytica as catalysts and investigated the kinetics of the enzyme-catalyzed peptide couplings. DmpA catalyzed the formation of L -carnosine from C-terminally activated ,-alanine derivatives (acyl donor) and L -histidine (acyl acceptor) in an aqueous reaction mixture at pH,10 with high catalytic rates (Vmax=19.2,,mol,min,1 per mg of protein, kcat=12.9,s,1), whereas Vmax in the BapA-catalyzed coupling reaction remained below 1.4,,mol,min,1 per mg of protein (kcat=0.87,s,1). Although the equilibrium of this reaction lies on the side of the hydrolysis products, the reaction is under kinetic control and L -carnosine temporarily accumulated to concentrations that correspond to yields of more than 50% with respect to the employed acyl donor. However, competing nucleophiles caused unwanted hydrolysis and coupling reactions that led to decreased product yield and to formation of various peptidic by-products. The substitution of L -histidine for L -histidine methyl ester as acyl acceptor shifted the pKa of the amino functionality from 9.25 to 6.97, which caused a drastic reduction in the amount of coupling by-products in an aqueous reaction system at pH,8. [source] | |||||||||||||||||||||||||||||||||||||||||||