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Exchange Reaction (exchange + reaction)
Kinds of Exchange Reaction Selected AbstractsSynthesis of Pb-Feldspar by Ion Exchange Reaction and Its ImplicationsACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2006LIU Rui Abstract, Feldspar and Pb(NO3)2 were mixed and reacted at T=380°C to synthesize Pb-feldspar. In the XRD (X-ray diffraction) pattern of the product, the d values (crystal lattice spacing) of the five peaks are 0.654, 0.342, 0.332, 0.327 and 0.257 nm. The XPS analysis results show that the binding energy of Pb 4f7/2 in the feldspar was between 137.81,138.03 eV. Pb2+ can replace alkali and alkali earth cations in the feldspar structure through ion exchange reaction to form Pb-feldspar. [source] Stereoselective Functionalization of ,-Iodo-,,,-Unsaturated Ketones via an Iodine,Copper Exchange Reaction.CHEMINFORM, Issue 36 2006Xiaoyin Yang 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] ChemInform Abstract: Selective Halogen,Magnesium Exchange Reaction via Organomagnesium Ate Complex.CHEMINFORM, Issue 41 2001Atsushi Inoue Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: The Tellurium,Lithium Exchange Reaction: Selective Functionalization of Electron-Deficient Heteroaromatics.CHEMINFORM, Issue 31 2001Osamu Sugimoto Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Hydrogen/Deuterium Exchange Reactions of Olefins with Deuterium Oxide Mediated by the Carbonylchlorohydrido- tris(triphenylphosphine)ruthenium(II) ComplexADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2010Sunny Kai San Tse Abstract The catalytic properties of several ruthenium, osmium and rhodium hydride complexes for hydrogen/deuterium (H/D) exchange between olefins and deuterium oxide (D2O) were investigated. The most effective catalytic precursor was found to be the carbonylchlorohydridotris(triphenylphosphine)ruthenium(II) complex. Through H/D exchange between metal hydride and D2O, and reversible olefin insertion into an RuH(D) bond, protons attached to olefinic carbons and alkyl chains of olefins can all undergo H/D exchange with D2O. The catalytic reactions can be used to deuterate both terminal and internal olefins, for example, styrene, stilbene and cyclooctene. [source] Regioselective Palladium(0)-Catalyzed Cross-Coupling Reactions and Metal-Halide Exchange Reactions of Tetrabromothiophene: Optimization, Scope and LimitationsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009ng Thanh Tùng Abstract The Suzuki reaction of tetrabromothiophene with arylboronic acids provides a regioselective approach to various 5-aryl-2,3,4-tribromothiophenes, symmetrical 2,5-diaryl-3,4-dibromothiophenes, and tetraarylthiophenes. Unsymmetrical 2,5-diaryl-3,4-dibromothiophenes are prepared by Suzuki reaction of 5-aryl-2,3,4-tribromothiophenes. Tetraarylthiophenes containing two different types of aryl groups are obtained by Suzuki reactions of 2,5-diaryl-3,4-dibromothiophenes. During the optimization of the conditions of each individual reaction, the solvent, the catalyst and the temperature play an important role. In several cases, classical conditions [use of tetrakis(triphenylphosphane)palladium(0), Pd(PPh3)4, as the catalyst] gave excellent yields. The yields of those transformations which failed or proceeded sluggishly could be significantly improved by application of a new biarylmonophosphine ligand developed by Buchwald and co-workers. Regioselective metal-halide exchange reactions of tetrabromothiophene provide a convenient approach to various 2,5-disubstituted 3,4-dibromothiophenes. 5-Alkyl-2-trimethylsilyl-3,4-dibromothiophenes could be prepared in one pot by sequential addition of trimethylchlorosilane and alkyl bromides. The reaction of tetrabromothiophene with methyl chloroformate and subsequent Suzuki reactions afforded 3,4-diaryl-2,5-bis(methoxycarbonyl)thiophenes. [source] Phosphatidylinositol Synthase of Tetrahymena: Inositol Isomers as Substrates in Phosphatidylinositol Biosynthesis and Headgroup Exchange ReactionsTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2007BRIDGET M. RIGGS ABSTRACT. Phosphatidylinositol (PtdIns) synthase in microsomal fractions derived from Tetrahymena vorax was studied to determine its activity requirements. The suitability of inositol isomers as substrates for the synthase and in headgroup exchange reactions also was investigated. Tetrahymena PtdIn synthase activity was optimum in the presence of 2 mM MgCl2 plus 2 mM MnCl2, a pH of 7.8, and a temperature of 30°C. The enzyme retained approximately 80% of its activity after incubation at 70°C for 10 min. PtdIns headgroup exchange activity was maximal in the presence of cytidine monophosphate. By following either the accumulation of radiolabeled reaction products or the loss of radiolabel from precursors, each of the inositol isomers tested appeared to serve as substrates for both the PtdIns synthase and PtdIns:inositol phosphatidyl transferase activities. In each case, myo -inositol and scyllo -inositol were the preferred substrates. The data suggest two routes for the formation of phosphatidyl-non- myo -inositols in Tetrahymena and the potential for the production of novel, non- myo -inositol-containing second messengers. [source] ChemInform Abstract: Integrated Micro Flow Synthesis Based on Sequential Br,Li Exchange Reactions of p-, m-, and o-Dibromobenzenes.CHEMINFORM, Issue 15 2008Aiichiro Nagaki 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 of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Ion Exchange Reactions of NaSbO3 and Morphotropic Series MSbO3.CHEMINFORM, Issue 10 2007Vladimir Babkenovich Nalbandyan 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] Successive Iodine,Magnesium or ,Copper Exchange Reactions for the Selective Functionalization of Polyhalogenated Aromatics.CHEMINFORM, Issue 31 2003Xiaoyin Yang Abstract For Abstract see ChemInform Abstract in Full Text. [source] One-Pot Chemoselective Functionalization of Arylsilanes via Cascade Metal,Metal Exchange Reactions.CHEMINFORM, Issue 44 2002Eike Hupe Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and reactivity of some diselenasila cycles containing an annelated dicarba- closo -dodecaborane(12) unitAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 1 2010Bernd Wrackmeyer Abstract The use of 1,2-diselenolato-1,2-dicarba- closo -dodecaborane(12) dianions [1,2-(1,2-C2B10H10)Se2]2, prepared in situ as the dilithium salt may lead to irreproducible results. This is shown by the straightforward synthesis of silanes using the purified and isolated dianions, in contrast with previous less successful attempts. Thus, the reactions of the dianions with dichlorosilanes afford the five-membered diselenasila cycles containing the SiMe2 or the SiPh2 units, and with 1,2-dichloro-tetramethyldisilane the six-membered cycle containing the Si2Me4 unit. The latter was studied by X-ray diffraction, and all products were characterized by multinuclear magnetic resonance (1H, 13C, 29Si, 77Se NMR) in solution. Novel isotope effects were detected in 13C and 77Se NMR spectra. Exchange reactions of the five- and six-membered diselanasila cycles with chlorosilanes were studied. Copyright © 2009 John Wiley & Sons, Ltd. [source] Peroxotungstates and Their Citrate and Tartrate DerivativesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2006Shu-Ya Hou Abstract The reaction of potassium tungstate with the biologically relevant ligands citric and tartaric acid, in the presence of hydrogen peroxide, was investigated to discover the effect of pH variation on the product pattern. The reaction with citric acid led to the formation of the dimer K5[WO(O2)2(Hcit)H(Hcit)(O2)2OW]·6H2O (1; H4cit = citric acid) due to carboxyl-carboxylic acid hydrogen bonding in the pH range 2,5; this complex can also be obtained by an exchange reaction between the oxo ligands of the dimeric hydrogencitrate tungstate K4[W2O5(Hcit)2]·4H2O (6) and H2O2. Interestingly, a novel dimeric peroxotungstate K3[W2O3(O2)4(OH)]·H2O (2), without the coordination of citrate ligands, was isolated in the pH range 7,9, as confirmed by 17O NMR solution studies. The reaction of potassium tungstate with (R,R)-tartaric acid afforded the tartratoperoxotungstate K4[W2O2(O2)4{(R,R)-tart}]·3H2O [3; H4tart = (R,R)-tartaric acid] in the pH range 1,3. The dimeric peroxotungstate K2[W2O3(O2)4(H2O)2]·2H2O (4) was found to react with citric or tartaric acid at pH 2,5 or 2,3, respectively, to give species 1 and 3. Evidence that 1 exists as a dimer in solution is presented. The three complexes were characterized by elemental analysis, IR and NMR spectroscopy, and X-ray structural analyses. The formation of these complexes is dictated by pH, and the thermal stabilities of 1 and 3 vary with the coordinated ligands. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Enzymatic fatty acid exchange in glycero-phospholipids,EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 10 2003Patrick Adlercreutz Abstract Lipases can be used to exchange fatty acids in the sn -1 position of glycerophospholipids and phospholipase A2 is useful for the corresponding exchange reaction in the sn -2 position. In both cases, the exchange can be done in a one-step acidolysis process or in a two-step process. In the latter case, the original fatty acid in the desired position is removed by enzymatic hydrolysis or alcoholysis and after isolation of the resulting lysophospholipid, the new fatty acid is introduced, using the same enzyme, in an esterification reaction. Several synthesis examples from the literature are reviewed. Incorporation of a new fatty acid into the sn -1 position is more favourable than incorporation into the sn -2 position because of the magnitudes of the equilibrium constants of the reactions and because lipases can be used at much lower water activity than phospholipase A2. With the consecutive use of both enzymes highly pure products with defined fatty acids in both positions can be obtained. [source] Modeling of tRNA-assisted mechanism of Arg activation based on a structure of Arg-tRNA synthetase, tRNA, and an ATP analog (ANP)FEBS JOURNAL, Issue 17 2009Michiko Konno The ATP,pyrophosphate exchange reaction catalyzed by Arg-tRNA, Gln-tRNA and Glu-tRNA synthetases requires the assistance of the cognate tRNA. tRNA also assists Arg-tRNA synthetase in catalyzing the pyrophosphorolysis of synthetic Arg-AMP at low pH. The mechanism by which the 3,-end A76, and in particular its hydroxyl group, of the cognate tRNA is involved with the exchange reaction catalyzed by those enzymes has yet to be established. We determined a crystal structure of a complex of Arg-tRNA synthetase from Pyrococcus horikoshii, tRNAArgCCU and an ATP analog with Rfactor = 0.213 (Rfree = 0.253) at 2.0 Å resolution. On the basis of newly obtained structural information about the position of ATP bound on the enzyme, we constructed a structural model for a mechanism in which the formation of a hydrogen bond between the 2,-OH group of A76 of tRNA and the carboxyl group of Arg induces both formation of Arg-AMP (Arg + ATP , Arg-AMP + pyrophosphate) and pyrophosphorolysis of Arg-AMP (Arg-AMP + pyrophosphate , Arg + ATP) at low pH. Furthermore, we obtained a structural model of the molecular mechanism for the Arg-tRNA synthetase-catalyzed deacylation of Arg-tRNA (Arg-tRNA + AMP , Arg-AMP + tRNA at high pH), in which the deacylation of aminoacyl-tRNA bound on Arg-tRNA synthetase and Glu-tRNA synthetase is catalyzed by a quite similar mechanism, whereby the proton-donating group (,NH,C+(NH2)2 or ,COOH) of Arg and Glu assists the aminoacyl transfer from the 2,-OH group of tRNA to the phosphate group of AMP at high pH. [source] A novel stereoselective synthesis of (2Z)-2-arylsulfanylallylic alcohols by tin,lithium exchange of (E)-,-stannylvinyl sulfidesHETEROATOM CHEMISTRY, Issue 6 2008Yaping Xu Tin,lithium exchange reaction of (E)-,-stannylvinyl sulfides 1 with n -butyllithium gave (Z)-,-arylsulfanylvinyllithiums 2, which reacted with aldehydes or ketones 3 to afford stereoselectively (2Z)-2-arylsulfanylallylic alcohols 4 in good to high yields. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:639,643, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20487 [source] Unsymmetrical ,-diimine nickel (II) complex with rigid bicyclic ring ligand: Synthesis, characterization, and ethylene polymerization in the presence of AlEt2ClJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Ting Li Abstract Unsymmetrical ,-diimine ligand 1 was successfully synthesized via condensation of trimethylaluminum (TMA) metalated 2-methyl-6-isopropyl-aniline with rigid bicyclic aliphatic diketone camphorquinone. Syn- and anti-stereoisomers were detected by 13C NMR in the condensation product. The corresponding ,-diimine nickel (II) complex 1 was prepared from the exchange reaction of (DME)NiBr2 with the ligand 1, and displayed high activity for ethylene polymerization in the presence of diethylaluminum chloride (AlEt2Cl). The resultant polymers were confirmed by gel permeation chromatography and 13C NMR characterization to be broad molecular weight distribution polyethylene with various branches, and high degree of branching, even at low polymerization temperature ,10°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Interactions of the "piano-stool" [ruthenium(II) (,6 -arene)(en)CL]+ complexes with water and nucleobases; ab initio and DFT studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2009k Futera Abstract Piano stool ruthenium complexes of the composition [Ru(II)(,6 -arene)(en)Cl]+/2+ (en = ethylenediamine) represent an emerging class of cisplatin-analogue anticancer drug candidates. In this study, we use computational quantum chemistry to characterize the structure, stability and reactivity of these compounds. All these structures were optimized at DFT(B3LYP)/6-31G(d) level and their single point properties were determined by the MP2/6-31++G(2df,2pd) method. Thermodynamic parameters and rate constants were determined for the aquation process, as a replacement of the initial chloro ligand by water and subsequent exchange reaction of aqua ligand by nucleobases. The computations were carried out at several levels of DFT and ab initio theories (B3LYP, MP2 and CCSD) utilizing a range of bases sets (from 6-31G(d) to aug-cc-pVQZ). Excellent agreement with experimental results for aquation process was obtained at the CCSD level and reasonable match was achieved also with the B3LYP/6-31++G(2df,2pd) method. This level was used also for nucleobase-water exchange reaction where a smaller rate constant for guanine exchange was found in comparison with adenine. Although adenine follows a simple replacement mechanism, guanine complex passes by a two-step mechanism. At first, Ru-O6(G) adduct is formed, which is transformed through a chelate TS2 to the Ru-N7(G) final complex. In case of guanine, the exchange reaction is more favorable thermodynamically (releasing in total by about 8 kcal/mol) but according to our results, the rate constant for guanine substitution is slightly smaller than the analogous constant in adenine case when reaction course from local minimum is considered. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Preparation and reactions of pyridinyl telluridesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2001Manabu Shilai Tellurium-metal exchange reaction of n -butyl 2-pyridinyl telluride derivatives with n -butyllithium or dilithium dimethylcyanocuprate proceeded smoothly to give the corresponding 2-pyridinylmetal derivatives, which are important intermediates for functionalization of pyridines. [source] Synthesis of 2-[(2-chloro-2,-[18F]fluoroethyl)amino]-2H-1,3,2-oxazaphosphorinane-2-oxide (18F-fluorocyclophosphamide), a potential tracer for breast tumor prognostic imaging with PETJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 9 2005Goran Lacan Abstract A fluorine-18 labeled analog of the widely used chemotherapeutic agent cyclophosphamide was synthesized as a tracer for prognostic imaging with positron emission tomography. 2-[(2-Chloro-2,-[18F]fluoroethyl)amino]-2H-1,3,2-oxazaphosphorinane-2-oxide (18F-fluorocyclophosphamide), was prepared by direct halogen exchange reaction from the parent cyclophosphamide. In small-scale syntheses, radiochemical yields of up to 4.9% and specific activities of 960 Ci/mmol were achieved in a total synthesis time of 60,75 min. The [18F]-labeled cyclophosphamide analog with radioactive purity >99% and chemical purity >96% was suitable for in vivo (microPET imaging) and ex vivo studies of a murine model of human breast tumors. Copyright © 2005 John Wiley & Sons, Ltd. [source] Fast and efficient tritium labelling of the nonsteroidal anti-inflammatory drugs naproxen, tolmetin, and zomepiracJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 8 2005Steen K. Johansen Abstract Fast and efficient tritium labelling of the nonsteroidal anti-inflammatory drugs naproxen, tolmetin and zomepirac is reported. Naproxen along with its (R)-enantiomer were labelled by catalytic tritium,halogen exchange of the corresponding 5-bromo derivatives providing [3H]naproxen with a specific activity of 25.4 Ci/mmol. Tolmetin and zomepirac were labelled by the hydrogen isotope exchange reaction using Crabtree's catalyst. This provided [3H]tolmetin and [3H]zomepirac with specific activities of 80.8 and 64.3 Ci/mmol, respectively. All compounds were obtained in high radiochemical purity (>98%). Copyright © 2005 John Wiley & Sons, Ltd. [source] A general method for the fluorine-18 labelling of fluoroquinolone antibioticsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 8 2003Oliver Langer Abstract Fluoroquinolones are an important class of antibiotic agents with a broad spectrum of antibacterial activity. Labelling of fluoroquinolones with fluorine-18 is of interest for the performance of pharmacokinetic measurements and the visualization of bacterial infections in humans with positron emission tomography. A two-step radiosynthetic pathway to prepare fluorine-18-labelled ciprofloxacin (1-cyclopropyl-6-[18F]fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-quinoline-3-carboxylic acid) has previously been developed. In the present work this approach was applied to the preparation of the structurally related compounds [18F]norfloxacin (1-ethyl-6-[18F]fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-quinoline-3-carboxylic acid) and [18F]pefloxacin (1-ethyl-6-[18F]fluoro-1,4-dihydro-7-(4-methyl-1-piperazinyl)-4-oxo-quinoline-3-carboxylic acid). The first step of the radiosynthesis consisted of a 18F for 19F exchange reaction on a 7-chloro-substituted precursor molecule, followed by coupling reactions with the amines piperazine or 1-methylpiperazine. Starting from 51,58 GBq of [18F]fluoride 1.9,2.0 GBq of [18F]norfloxacin or [18F]pefloxacin, ready for intravenous injection, could be obtained in a synthesis time of 130 min (3.5,3.8% overall radiochemical yield). Moreover, the preparation of [18F]levofloxacin ((-)-(S)-9-[18F]fluoro-2,3-dihydro-3-methyl-10-(4-methyl-1-piperazinyl)-7-oxo-7H-pyrido[1,2,3-de]-1,4-benzoxazine-6-carboxylicacid) was attempted but failed to afford the desired product in practical amounts. Copyright © 2003 John Wiley & Sons, Ltd. [source] Synthesis of tritium labelled zaleplonJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 11 2002V.P. Shevchenko Abstract The reaction conditions for the incorporation of tritium into zaleplon have been investigated. The methods studied were the catalytic isotope exchange reaction with tritium gas and catalytic isotope exchange reaction with tritiated water. The results showed that the latter method was the method of choice giving a compound with a higher specific activity and a better yield. Copyright © 2002 John Wiley & Sons, Ltd. [source] Ion chemistry in germane/fluorocompounds gaseous mixtures: a mass spectrometric and theoretical studyJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 10 2008Paola Antoniotti Abstract The ion,molecule reactions occurring in GeH4/NF3, GeH4/SF6, and GeH4/SiF4 gaseous mixtures have been investigated by ion trap mass spectrometry and ab initio calculations. While the NFx+ (x = 1,3) react with GeH4 mainly by the exothermic charge transfer, the open-shell Ge+ and GeH2+ undergo the efficient F-atom abstraction from NF3 and form GeF+ and FGeH2+ as the only ionic products. The mechanisms of these two processes are quite similar and involve the formation of the fluorine-coordinated complexes GeFNF2+ and H2GeFNF2+, their subsequent crossing to the significantly more stable isomers FGeNF2+ and FGeH2NF2+, and the eventual dissociation of these ions into GeF+ (or FGeH2+) and NF2. The closed-shell GeH+ and GeH3+ are instead much less reactive towards NF3, and the only observed process is the less efficient formation of GeF+ from GeH+. The theoretical investigation of this unusual H/F exchange reaction suggests the involvement of vibrationally-hot GeH+. Passing from NF3 to SF6 and SiF4, the average strength of the MF bond increases from 70 to 79 and 142 kcal mol,1, and in fact the only process observed by reacting GeHn+ (n = 0,3) with SF6 and SiF4 is the little efficient F-atom abstraction from SF6 by Ge+. Irrespective of the experimental conditions, we did not observe any ionic product of GeN, GeS, or GeSi connectivity. This is in line with the previously observed exclusive formation of GeF+ from the reaction between Ge+ and CF compounds such as CH3F. Additionally observed processes include in particular the conceivable formation of the elusive thiohypofluorous acid FSH from the reaction between SF+ and GeH4. Copyright © 2008 John Wiley & Sons, Ltd. [source] Characterizing closely spaced, complex disulfide bond patterns in peptides and proteins by liquid chromatography/electrospray ionization tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 1 2002Ten-Yang Yen Abstract Identifying the Cys residues involved in disulfide linkages of peptides and proteins that contain complex disulfide bond patterns is a significant analytical challenge. This is especially true when the Cys residues involved in the disulfide bonds are closely spaced in the primary sequence. Peptides and proteins that contain free Cys residues located near disulfide bonds present the additional problem of disulfide shuffling via the thiol,disulfide exchange reaction. In this paper, we report a convenient method to identify complex disulfide patterns in peptides and proteins using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) in combination with partial reduction by tris(2-carboxyethyl)phosphine (TCEP). The method was validated using well-characterized peptides and proteins including endothelin, insulin, ,-conotoxin SI and immunoglobulin G (IgG2a, mouse). Peptide or protein digests were treated with TCEP in the presence of an alkylation reagent, maleimide-biotin (M-biotin) or N -ethylmaleimide (NEM), followed by complete reduction with dithiothreitol and alkylation by iodoacetamide (IAM). Subsequently, peptides that contained alkylated Cys were analyzed by capillary LC/ESI-MS/MS to determine which Cys residues were modified with M-biotin/NEM or IAM. The presence of the alkylating reagent (M-biotin or NEM) during TCEP reduction was found to minimize the occurrence of the thiol,disulfide exchange reaction. A critical feature of the method is the stepwise reduction of the disulfide bonds and the orderly, sequential use of specific alkylating reagents. Copyright © 2001 John Wiley & Sons, Ltd. [source] A new formulation of garnet,clinopyroxene geothermometer based on accumulation and statistical analysis of a large experimental data setJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2009D. NAKAMURAArticle first published online: 13 JUL 200 Abstract Published experimental data including garnet and clinopyroxene as run products were used to develop a new formulation of the garnet,clinopyroxene geothermometer based on 333 garnet,clinopyroxene pairs. Only experiments with graphite capsules were selected because of difficulty in estimating the Fe3+ content of clinopyroxene. For the calibration, a published subregular-solution model was adopted to express the non-ideality of garnet. The magnitude of the Fe,Mg excess interaction parameter for clinopyroxene (WFeMgCpx), and differences in enthalpy and entropy of the Fe,Mg exchange reaction were regressed from the accumulated experimental data set. As a result, a markedly negative value was obtained for the Fe,Mg excess interaction parameter of clinopyroxene (WFeMgCpx = , 3843 J mol,1). The pressure correction is simply treated as linear, and the difference in volume of the Fe,Mg exchange reaction was calculated from a published thermodynamic data set and fixed to be ,120.72 (J kbar,1 mol,1). The regressed and obtained thermometer formulation is as follows: where T = temperature, P = pressure (kbar), A = 0.5 Xgrs (Xprp , Xalm , Xsps), B = 0.5 Xgrs (Xprp , Xalm + Xsps), C = 0.5 (Xgrs + Xsps) (Xprp , Xalm), Xprp = Mg/(Fe2+ + Mn + Mg + Ca)Grt, Xalm = Fe/(Fe2+ + Mn + Mg + Ca)Grt, Xsps = Mn/(Fe2+ + Mn + Mg + Ca)Grt, Xgrs = Ca/(Fe2+ + Mn + Mg + Ca)Grt, XMgCpx = Mg/(Al + Fetotal + Mg)Cpx, XFeCpx = Fe2+/(Al + Fetotal + Mg)Cpx, KD = (Fe2+/Mg)Grt/(Fe2+/Mg)Cpx, Grt = garnet, Cpx = clinopyroxene. A test of this new formulation to the accumulated data gave results that are concordant with the experimental temperatures over the whole range of the experimental temperatures (800,1820 °C), with a standard deviation (1 sigma) of 74 °C. Previous formulations of the thermometer are inconsistent with the accumulated data set; they underestimate temperatures by about 100 °C at >1300 °C and overestimate by 100,200 °C at <1300 °C. In addition, they tend to overestimate temperatures for high-Ca garnet (Xgrs , 0.30,0.50). This new formulation has been tested against previous formulations of the thermometer by application to natural eclogites. This gave temperatures some 20,100 °C lower than previous formulations. [source] Prograde P,T path of medium-pressure granulite facies calc-silicate rocks, Higo metamorphic terrane, central Kyushu, JapanJOURNAL OF METAMORPHIC GEOLOGY, Issue 2 2009K. MAKI Abstract This paper reports an occurrence of medium-pressure granulite facies calc-silicate rocks intercalated with pelitic gneisses in the Higo metamorphic terrane, central Kyushu, Japan, which is classified as a low- P/high- T (andalusite-sillimanite type) metamorphic belt. Three equilibrium stages are recognized in the calc-silicate rock based on reaction textures: M1 stage characterized by an assemblage of porphyroblastic garnet + coarse-grained clinopyroxene + plagioclase included in the clinopyroxene; M2 stage by two kinds of breakdown products of garnet, one is plagioclase + coronitic clinopyroxene within garnet and the other is plagioclase + vermicular clinopyroxene surrounding garnet; and M3 stage by amphibole replacing clinopyroxene. The key assemblage in the calc-silicate rock common to M1 and M2 stages is Grt + Cpx + Pl ± Qtz, which constrains the pressure and temperature (P,T) conditions for these stages by Fe,Mg exchange reaction and the two univariant net-transfer reactions: 2Grs + Alm + 3Qtz = 3Hd + 3An or 2Grs + Prp + 3Qtz = 3Di + 3An. The P,T conditions for M1 and M2 stages were estimated to be about 8.4 ± 1.9 kbar and 680 ± 122 °C, and 6.7 ± 1.9 to 8.9 ± 2.2 kbar and 700 ± 130 to 820 ± 160 °C, respectively. Estimates are consistent with an isobaric heating P,T path. The high peak temperature conditions at normal crustal depths and the prograde isobaric heating path probably require heat advection due to melt migration during the high- T metamorphism. [source] A novel approach to enhancing cellular glutathione levelsJOURNAL OF NEUROCHEMISTRY, Issue 3 2008Pamela Maher Abstract GSH and GSH-associated metabolism provide the major line of defense for the protection of cells from oxidative and other forms of toxic stress. Of the three amino acids that comprise GSH, cysteine is limiting for GSH synthesis. As extracellularly cysteine is readily oxidized to form cystine, cystine transport mechanisms are essential to provide cells with cysteine. Cystine uptake is mediated by system xc,, a Na+ -independent cystine/glutamate antiporter. Inhibition of system xc, by millimolar concentrations of glutamate, a pathway termed oxidative glutamate toxicity, results in GSH depletion and nerve cell death. Recently, we described a series of compounds derived from the conjugation of epicatechin (EC) with cysteine and cysteine derivatives that protected nerve cells in culture from oxidative glutamate toxicity by maintaining GSH levels. In this study, we characterize an additional EC conjugate, cysteamine-EC, that is 5- to 10-fold more potent than the earlier conjugates. In addition, we show that these EC conjugates maintain GSH levels by enhancing the uptake of cystine into cells through induction of a disulfide exchange reaction, thereby uncoupling the uptake from system xc,. Thus, these novel EC conjugates have the potential to enhance GSH synthesis under a wide variety of forms of toxic stress. [source] Synthesis of magnetic, reactive, and thermoresponsive Fe3O4 nanoparticles via surface-initiated RAFT copolymerization of N -isopropylacrylamide and acroleinJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2010Zhong-Peng Xiao Abstract A reversible addition-fragmentation chain transfer (RAFT) agent was directly anchored onto Fe3O4 nanoparticles in a simple procedure using a ligand exchange reaction of S -1-dodecyl- S,-(,,,,-dimethyl-,,-acetic acid)trithiocarbonate with oleic acid initially present on the surface of pristine Fe3O4 nanoparticles. The RAFT agent-functionalized Fe3O4 nanoparticles were then used for the surface-initiated RAFT copolymerization of N -isopropylacrylamide and acrolein to fabricate structurally well-defined hybrid nanoparticles with reactive and thermoresponsive poly(N -isopropylacrylamide- co -acrolein) shell and magnetic Fe3O4 core. Evidence of a well-controlled surface-initiated RAFT copolymerization was gained from a linear increase of number-average molecular weight with overall monomer conversions and relatively narrow molecular weight distributions of the copolymers grown from the nanoparticles. The resulting novel magnetic, reactive, and thermoresponsive core-shell nanoparticles exhibited temperature-trigged magnetic separation behavior and high ability to immobilize model protein BSA. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 542,550, 2010 [source] Synthesis and properties of poly(carbonate-urethane) consisting of alternating carbonate and urethane moietiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2006Bungo Ochiai Abstract Poly(carbonate-urethane) consisting of alternating carbonate and urethane moieties (poly(HC-MDI)) was prepared by polyaddition of 4,4,-diphenylmethane diisocyanate (MDI) and a monocarbonate diol bis(3-hydroxypropyl)carbonate (HC), prepared by hydrolysis of a six-membered spiroorthocarbonate 1,5,7,11-tetraoxa-spiro[5.5]undecane. The polyaddition proceeds without concomitant side reactions including carbonate exchange reaction and affords the desired poly(carbonate-urethane). The hydrolysis and thermal behaviors of poly(HC-MDI) were compared with those of the analogous polyurethane carrying no carbonate structure (poly(ND-MDI)) prepared from MDI and 1,9-nonanediol (ND). Although the glass transition behaviors are almost identical, poly(HC-MDI) is less crystalline than poly(ND-MDI). Poly(HC-MDI) is more susceptible to hydrolysis than poly(ND-MDI) probably due to the higher polarity and the lower crystallinity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2802,2808, 2006 [source] | ||||||||||||||||||||||||||||||||||||||||