- Structure Elucidation of Phomopsin A, a Novel Cyclic Hexapeptide Mycotoxin produced by Phomopsis leptostromiformis
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Phomopsin A, the main mycotoxin isolated from cultures of Phomopsis leptostromiformis and the cause of lupinosis disease in animals grazing infected lupins, is a cyclic hexapeptide containing 3-hydroxyisoleucine, 3,4-didehydrovaline, N-methyl-3-(3-chloro-4,5-dihydroxyphenyl)-3-hydroxyalanine, E-2,3-didehydroaspartic acid, E-2,3-didehydroisoleucine, and 3,4-didehydroproline; its 13C n.m.r. spectrum was completely assigned and the amino-acid sequence established unambiguously by extensive heteronuclear 13C- selective population inversion n.m.r. experiments.
- Culvenor, Claude C. J.,Cockrum, Peter A.,Edgar, John A.,Frahn, John L.,Gorst-Allman, Charles P.,et al.
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- Purification, characterization, and overexpression of psychrophilic and thermolabile malate dehydrogenase of a novel antarctic psychrotolerant, Flavobacterium frigidimaris KUC-1
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We purified the psychrophilic and thermolabile malate dehydrogenase to homogeneity from a novel psychrotolerant, Flavobacterium frigidimaris KUC-1, isolated from Antarctic seawater. The enzyme was a homotetramer with a molecular weight of about 123 k and that of the subunit was about 32 k. The enzyme required NAD(P)+ as a coenzyme and catalyzed the oxidation of L-malate and the reduction of oxalacetate specifically. The reaction proceeded through an ordered bi-bi mechanism. The enzyme was highly susceptible to heat treatment, and the half-life time at 40°C was estimated to be 3.0 min. The kcat/Km (μM-1·s-1) values for L-malate and NAD+ at 30°C were 289 and 2,790, respectively. The enzyme showed pro-R stereospecificity for hydrogen transfer at the C4 position of the nicotinamide moiety of the coenzyme. The enzyme contained 311 amino acid residues and much lower numbers of proline and arginine residues than other malate dehydrogenases.
- Oikawa, Tadao,Yamamoto, Noriko,Shimoke, Koji,Uesato, Shinichi,Ikeuchi, Toshihiko,Fujioka, Toru
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- Recombinant thermoactive phosphoenolpyruvate carboxylase (PEPC) from Thermosynechococcus elongatus and its coupling with mesophilic/thermophilic bacterial carbonic anhydrases (CAs) for the conversion of CO2 to oxaloacetate
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With the continuous increase of atmospheric CO2 in the last decades, efficient methods for carbon capture, sequestration, and utilization are urgently required. The possibility of converting CO2 into useful chemicals could be a good strategy to both decreasing the CO2 concentration and for achieving an efficient exploitation of this cheap carbon source. Recently, several single- and multi-enzyme systems for the catalytic conversion of CO2 mainly to bicarbonate have been implemented. In order to design and construct a catalytic system for the conversion of CO2 to organic molecules, we implemented an in vitro multienzyme system using mesophilic and thermophilic enzymes. The system, in fact, was constituted by a recombinant phosphoenolpyruvate carboxylase (PEPC) from the thermophilic cyanobacterium Thermosynechococcus elongatus, in combination with mesophilic/thermophilic bacterial carbonic anhydrases (CAs), for converting CO2 into oxaloacetate, a compound of potential utility in industrial processes. The catalytic procedure is in two steps: the conversion of CO2 into bicarbonate by CA, followed by the carboxylation of phosphoenolpyruvate with bicarbonate, catalyzed by PEPC, with formation of oxaloacetate (OAA). All tested CAs, belonging to α-, β-, and γ-CA classes, were able to increase OAA production compared to procedures when only PEPC was used. Interestingly, the efficiency of the CAs tested in OAA production was in good agreement with the kinetic parameters for the CO2 hydration reaction of these enzymes. This PEPC also revealed to be thermoactive and thermostable, and when coupled with the extremely thermostable CA from Sulphurhydrogenibium azorense (SazCA) the production of OAA was achieved even if the two enzymes were exposed to temperatures up to 60 °C, suggesting a possible role of the two coupled enzymes in biotechnological processes.
- Del Prete, Sonia,De Luca, Viviana,Capasso, Clemente,Supuran, Claudiu T.,Carginale, Vincenzo
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- Direct catalytic benzene hydroxylation under mild reaction conditions by using a monocationic μ-nitrido-bridged iron phthalocyanine dimer with 16 peripheral methyl groups
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Direct catalytic hydroxylation of benzene under mild reaction conditions proceeded efficiently in the presence of a monocationic μ-nitrido-bridged iron phthalocyanine dimer with 16 peripheral methyl groups in an acetonitrile solution with excess H2O2. Mechanistic studies suggested that the reaction was catalyzed by a high-valent iron-oxo species generated in situ. Moreover, the peripheral methyl groups of the catalyst were presumed to have enhanced the production rate of the iron-oxo species.
- Tanaka, Kentaro,Teoh, Chee-Ming,Toyoda, Yuka,Yamada, Yasuyuki
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supporting information
p. 955 - 958
(2022/02/07)
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- Bacterial flavoprotein monooxygenase YxeK salvages toxic S-(2-succino)-adducts via oxygenolytic C–S bond cleavage
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Thiol-containing nucleophiles such as cysteine react spontaneously with the citric acid cycle intermediate fumarate to form S-(2-succino)-adducts. In Bacillus subtilis, a salvaging pathway encoded by the yxe operon has recently been identified for the detoxification and exploitation of these compounds as sulfur sources. This route involves acetylation of S-(2-succino)cysteine to N-acetyl-2-succinocysteine, which is presumably converted to oxaloacetate and N-acetylcysteine, before a final deacetylation step affords cysteine. The critical oxidative cleavage of the C–S bond of N-acetyl-S-(2-succino)cysteine was proposed to depend on the predicted flavoprotein monooxygenase YxeK. Here, we characterize YxeK and verify its role in S-(2-succino)-adduct detoxification and sulfur metabolism. Detailed biochemical and mechanistic investigation of YxeK including 18O-isotope-labeling experiments, homology modeling, substrate specificity tests, site-directed mutagenesis, and (pre-)steady-state kinetics provides insight into the enzyme’s mechanism of action, which may involve a noncanonical flavin-N5-peroxide species for C–S bond oxygenolysis.
- Ellis, Holly R.,Kammerer, Bernd,Lagies, Simon,Matthews, Arne,Sch?nfelder, Julia,Schleicher, Erik,Stull, Frederick,Teufel, Robin
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- Interaction between Pyridoxal Hydrochloride and L-α-Asparagine in Comparison to L-α- and D-α-Aspartic Acids
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Abstract: The kinetics and mechanism of condensation of pyridoxal hydrochloride with L-α-asparagine, L?α- and D-α-aspartic acids are analyzed via UV spectroscopy and polarimetry. It is found that L?α?asparagine containing α-NH2 and γ-NH2/
- Pishchugin,Tuleberdiev
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- Two-Dimensional Tin Selenide (SnSe) Nanosheets Capable of Mimicking Key Dehydrogenases in Cellular Metabolism
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While dehydrogenases play crucial roles in tricarboxylic acid (TCA) cycle of cell metabolism, which are extensively explored for biomedical and chemical engineering uses, it is a big challenge to overcome the shortcomings (low stability and high costs) of recombinant dehydrogenases. Herein, it is shown that two-dimensional (2D) SnSe is capable of mimicking native dehydrogenases to efficiently catalyze hydrogen transfer from 1-(R)-2-(R′)-ethanol groups. In contrary to susceptible native dehydrogenases, lactic dehydrogenase (LDH) for instance, SnSe is extremely tolerant to reaction condition changes (pH, temperature, and organic solvents) and displays extraordinary reusable capability. Structure–activity analysis indicates that the single-atom structure, Sn vacancy, and hydrogen binding affinity of SnSe may be responsible for their catalytic activity. Overall, this is the first report of a 2D SnSe nanozyme to mimic key dehydrogenases in cell metabolism.
- Gao, Meng,Wang, Zhenzhen,Zheng, Huizhen,Wang, Li,Xu, Shujuan,Liu, Xi,Li, Wei,Pan, Yanxia,Wang, Weili,Cai, Xiaoming,Wu, Ren'an,Gao, Xingfa,Li, Ruibin
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supporting information
p. 3618 - 3623
(2020/02/13)
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- Catalytic oxidative dehydrogenation of malic acid to oxaloacetic acid
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Here we report the oxidative dehydrogenation of malic acid to oxaloacetic acid, a key precursor in the fabrication of amino acids, over Pt-Bi/C catalysts. Under optimized conditions, we discovered that OAA was selectively produced with up to 60% conversion (i.e. 60% yield). The recurrent unwanted decarboxylation of OAA to pyruvic acid was circumvented by successfully conducting the catalytic reaction at 25 °C. A comparison with the classical Fenton oxidation reaction is discussed.
- Drif, Asmaa,Pineda, Antonio,Morvan, Didier,Belliere-Baca, Virginie,De Oliveira Vigier, Karine,Jér?me, Fran?ois
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supporting information
p. 4604 - 4608
(2019/09/09)
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- Production of α-Ketoisocaproate and α-Keto-β-Methylvalerate by Engineered L-Amino Acid Deaminase
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This study aimed to develop an efficient enzymatic strategy for industrial production of α-ketoisocaproate (α-KIC) and α-keto-β-methylvalerate (α-KMV) from L-leucine and L-isoleucine, respectively. L-amino acid deaminase from Proteus mirabilis (PmLAAD) was heterologously expressed in E. coli BL21(DE3) and modified to increase its catalytic efficiency by engineering the PmLAAD substrate-binding cavity and entrance tunnel. Four essential residues (Q92, M440, T436, and W438) were identified from structural analysis and molecular dynamics simulations. Residue Q92 was mutated to alanine, and the volume of the binding cavity, enzyme activity, and the kcat/Km value of mutant PmLAAD Q92A increased to 994.2 ?3, 191.36 U mg?1, and 1.23 mM?1 min?1, respectively; consequently, the titer and conversion rate of α-KIC from L-leucine were 107.1 g L?1 and 98.1 %, respectively. For mutant PmLAADT436/W438A, the entrance tunnel, enzyme activity, and the kcat/Km value increased to 1.71 ?, 170.12 U mg?1, and 0.70 mM?1 min?1, respectively; consequently, the titer and conversion rate of α-KMV from L-isoleucine were 98.9 g L?1 and 99.7 %, respectively. Therefore, augmentation of the substrate-binding cavity and entrance tunnel of PmLAAD can facilitate efficient industrial synthesis of α-KIC and α-KMV.
- Yuan, Yuxiang,Song, Wei,Liu, Jia,Chen, Xiulai,Luo, Qiuling,Liu, Liming
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p. 2464 - 2472
(2019/05/10)
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- Silica Metal Oxide Vesicles Catalyze Comprehensive Prebiotic Chemistry
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It has recently been demonstrated that mineral self-assembled structures catalyzing prebiotic chemical reactions may form in natural waters derived from serpentinization, a geological process widespread in the early stages of Earth-like planets. We have s
- Mattia Bizzarri, Bruno,Botta, Lorenzo,Pérez-Valverde, Maritza Iveth,Saladino, Raffaele,Di Mauro, Ernesto,García-Ruiz, Juan Manuel
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p. 8126 - 8132
(2018/05/29)
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- Isolation and amino acid sequence of a dehydratase acting on D-erythro-3- hydroxyaspartate from Pseudomonas sp. N99, and its application in the production of optically active 3-hydroxyaspartate
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An enzyme catalyzing the ammonia-lyase reaction for the conversion of D-erythro-3-hydroxyaspartate to oxaloacetate was purified from the cell-free extract of a soil-isolated bacterium Pseudomonas sp. N99. The enzyme exhibited ammonia-lyase activity toward L-threo-3-hydroxyaspartate and D-erythro-3- hydroxyaspartate, but not toward other 3-hydroxyaspartate isomers. The deduced amino acid sequence of the enzyme, which belongs to the serine/ threonine dehydratase family, shows similarity to the sequence of L-threo-3-hydroxyaspartate ammonia- lyase (EC 4.3.1.16) from Pseudomonas sp. T62 (74%) and Saccharomyces cerevisiae (64%) and serine racemase from Schizosaccharomyces pombe (65%). These results suggest that the enzyme is similar to L-threo-3-hydroxyaspartate ammonia-lyase from Pseudomonas sp. T62, which does not act on D-erythro-3-hydroxyaspartate. We also then used the recombinant enzyme expressed in Escherichia coli to produce optically pure L-erythro-3-hydroxyaspartate and D-threo-3-hydroxyaspartate from the corresponding DL-racemic mixtures. The enzymatic resolution reported here is one of the simplest and the first enzymatic method that can be used for obtaining optically pure L-erythro-3-hydroxyaspartate.
- Nagano, Hiroyuki,Shibano, Kana,Matsumoto, Yu,Yokota, Atsushi,Wada, Masaru
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p. 1156 - 1164
(2017/05/29)
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- Meteorites as catalysts for prebiotic chemistry
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From outer space: Twelve meteorite specimens, representative of their major classes, catalyse the synthesis of nucleobases, carboxylic acids, aminoacids and low-molecular-weight compounds from formamide (see figure). Different chemical pathways are identified, the yields are high for a prebiotic process and the products come in rich and composite panels.
- Saladino, Raffaele,Botta, Giorgia,Delfino, Michela,Di Mauro, Ernesto
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p. 16916 - 16922
(2014/01/06)
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- Discovery and characterization of a thermostable D-lactate dehydrogenase from Lactobacillus jensenii through genome mining
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The demand on thermostable D-lactate dehydrogenases (d-LDH) has been increased for d-lactic acid production but thermostable d-DLHs with industrially applicable activity were not much explored. To identify a thermostable d-LDH, three d-LDHs from different Lactobacillus jensenii strains were screened by genome mining and then expressed in Escherichia coli. One of the three d-LDHs (d-LDH3) exhibited higher optimal reaction temperature (50 °C) than the others. The T5010 value of this thermostable d-LDH3 was 48.3 °C, much higher than the T5010 values of the others (42.7 and 42.9 °C) and that of a commercial D-lactate dehydrogenase (41.2 °C). The Tm values were 48.6, 45.7 and 55.7 °C for the three d-LDHs, respectively. In addition, kinetic parameter (k cat/Km) of d-LDH3 for pyruvate reduction was estimated to be almost 150 times higher than that for lactate oxidation at pH 8.0 and 25 °C, implying that D-lactate production from pyruvate is highly favored. These superior thermal and kinetic features would make the d-LDH3 characterized in this study a good candidate for the microbial production of D-lactate at high temperature from glucose if it is genetically introduced to lactate producing microbial.
- Jun, Chanha,Sa, Young Seung,Gu, Sol-A,Joo, Jeong Chan,Kim, Seil,Kim, Kyung-Jin,Kim, Yong Hwan
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p. 109 - 117
(2013/04/10)
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- Isolation, purification, and characterization of phenylpyruvate transaminating enzymes of Erwinia carotovora
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Enzymes of Erwinia carotovora that transaminate phenylpyruvate were isolated, purified, and characterized. Two aromatic aminotransferases (PAT1 and PAT2) and an aspartic aminotransferase (PAT3) were found. According to gel filtration, these enzymes have molecular weights of 76, 75, and 78 kDa. The enzymes consist of two identical subunits of molecular weights of 31.4, 31, and 36.5 kDa, respectively. The isoelectric points of PAT1, PAT2, and PAT3 were determined as 3.6, 3.9, and 4.7, respectively. The enzyme preparations considerably differ in substrate specificity. All three of the enzymes productively interacted with the following amino acids: L-aspartic acid, L-leucine (except PAT3), L-isoleucine (except PAT3), L-serine, L-methionine, L-cysteine, L-phenylalanine, L-tyrosine, and L-tryptophane. The aromatic aminotransferases display higher specificity to the aromatic amino acids and the leucine-isoleucine pair, whereas the aspartic aminotransferase displays higher specificity to L-aspartic acid and relatively low specificity to the aromatic amino acids. The aspartic aminotransferase does not use L-leucine or L-isoleucine as a substrate. PAT1, PAT2, and PAT3 show the highest activity at pH 8.9 and at 48, 53, and 58°C, respectively.
- Paloyan,Hambardzumyan,Halebyan
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scheme or table
p. 98 - 104
(2012/06/29)
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- Ruthenium(III) mediated oxidation of succinic acid by cerium(IV) in aqueous sulphuric acid medium - A kinetic and mechanistic approach
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The oxidation of succinic acid by cerium(IV) has been studied spectrophotometrically in aqueous sulphuric acid medium at 298 K at constant ionic strength of 1.6 mol dm-3. A minute amount of ruthenium(III) (10-6 mol dm-3) is sufficient to enhance the slow reaction between succinic acid and cerium(IV). The main reaction products are cerium(III) and oxaloacetic acid. The stoichiometry is 1 : 4, that is [suc. acid] : [CeIV] = 1:4. The reaction is first order In both cerium(IV) and ruthnium(III) concentrations. The order with respect to suc. acid concentration varies from first order to zero order, as the succinic acid concentration increases. Increase in sulphuric acid concentration decreases the reaction rate. The added sulphate and bisulpahte decreases the rate of reaction. The added product cerium(III) retards the reaction rate. The active species of oxidant and catalyst are Ce(SO4)2 and [Ru(H 2O)6]3+ respectively. Possible mechanism is proposed. The activation parameters were determined with respect to slow step and reaction constants involved have been determined.
- Rajeshwari,Savanur,Nandibewoor,Chimatadar
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experimental part
p. 295 - 308
(2011/08/05)
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- Oxidation of some α-hydroxy acids by tetraethylammonium chlorochromate: A kinetic and mechanistic study
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The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by tetraethylammonium chlorochromate (TEACC) in dimethylsulfoxide leads to the formation of corresponding oxoacids. The reaction is first order each in TEACC and hydroxy acids. Reaction is failed to induce the polymerization of acrylonitrile. The oxidation of α-deuteriomandelic acid shows the presence of a primary kinetic isotope effect (kH/kD = 5.63 at 298 K). The reaction does not exhibit the solvent isotope effect. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the following form: kobs = a + b[H+ ]. Oxidation of p-methylmandelic acid has been studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.
- Swami, Preeti,Yajurvedi,Mishra,Sharma, Pradeep K.
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experimental part
p. 50 - 55
(2010/04/06)
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- Micellar effect on the reaction of chromium(VI) oxidation of some representative α-hydroxy acids in the presence and absence of 2,2'-bipyridyl in aqueous acid media: A kinetic study
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The kinetics and mechanism of chromic acid oxidation of a-hydroxy acids in the presence and absence of 2,2'-bipyridyl in aqueous acid media have been studied at different temperatures by quenching technique under the conditions of [a-hydroxy acid] >> [Cr(VI)]T and [bpy]T >>[Cr(VI)]T. Under the kinetic conditions, the monomeric species of Cr(VI) has been found to be kinetically active in the absence of bpy while in the bpy-catalysed path, Cr(VI)-bpy complex is suggested as the active oxidant. In the bpy-catalysed path, Cr(VI)-bpy complex receives a nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a 2e-transfer redox decomposition leading to Cr(IV)-bpy complex and keto acid. Then the Cr(IV)-bpy complex participates in the oxidation of a-hydroxy acid in faster steps and ultimately is converted into the inert Cr(III)-bpy complex. In the uncatalysed path, Cr(VI)-substrate ester undergoes a redox decomposition through 2e-transfer at the rate determining step. The uncatalysed as well as the bpy-catalysed paths show first order dependence on both [α-hydroxy acid]T and [Cr(VI)]T. The bpy-catalysed path is first order in [bpy]T. In the presence of surfactants like N-cetylpyridinium chloride and sodium dodecyl sulfate, the reaction orders remain unchanged. The former has been found to retard both the uncatalysed and bpy-catalysed paths while the latter shows rate accelerating effect for both the paths. The observed micellar effects have been explained by considering hydrophobic and electrostatic interactions between the reactants and surfactants in terms of the proposed mechanism.
- Bayen, Ruhidas,Islam, Monirul,Das, Asim K.
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scheme or table
p. 1055 - 1061
(2010/03/05)
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- METHOD FOR SYNTHESIS OF KETO ACID OR AMINO ACID BY HYDRATION OF ACETHYLENE COMPOUND
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An object of the present invention is to provide a method for synthesis of keto acids by hydration of an acetylene compound (acetylene-carboxylic acids) under mild conditions free from harmful mercury catalysts and a method for synthesis of amino acids from acetylene-carboxylic acids in a single container (one-pot or tandem synthesis). In one embodiment of the method according to the present invention for synthesis of keto acids, acetylene-carboxylic acids is hydrated in the presence of a metal salt represented by General Formula (1), where M1 represents an element in Group VIII, IX, or X of the periodic table, and X1, X2, or X3 ligand represents halogen, H2O, or a solvent molecule, and k represents a valence of a cation species, and Y represents an anion species, and L represents a valence of the anion species, and each of K and L independently represents 1 or 2, and k × m = L × n.
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Page/Page column 17; 19
(2008/12/06)
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- Kinetics and mechanism of the oxidation of some α-hydroxy acids by 2,2′-bipyridinium chlorochromate
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The oxidation of glycolic, lactic, malic, and a few substituted mandelic acids by 2,2′-bipyridinium chlorochromate (BPCC) in dimethylsulphoxide leads to the formation of corresponding oxoacids. The reaction is first order each in BPCC and the hydroxy acids. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the form: kobs = a + b [H+]. The oxidation of α-deuteriomandelic acid exhibited a substantial primary kinetic isotope effect (kH/kd = 5.29 at 303 K). Oxidation of p-methylmandelic acid was studied in 19 different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.
- Kumbhat, Vinita,Sharma, Pradeep K.,Banerji, Kalyan K.
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p. 248 - 254
(2007/10/03)
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- Kinetics and mechanism of the oxidation of some α-hydroxy acids by quinolinium bromochromate
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The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by quinolinium bromochromate (QBC) in dimethylsulfoxide (DMSO) leads to the formation of the corresponding oxoacids. The reaction is first order each in QBC and the hydroxy acids. The reaction is catalyzed by the hydrogen ions. The hydrogen ion dependence has the form kobs = a + b [H +]. Oxidation of mandelic acid has been studied in different organic solvents. The solvent effect has been analyzed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.
- Sarswat, Sonu,Sharma, Vinita,Banerji, Kalyan K.
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p. 871 - 875
(2007/10/03)
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- Co-oxidation of malic acid and manganese(II) by chromium(VI) in the presence and absence of ionic surfactants
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The reaction of malic acid with dichromate studied in presence and absence of manganese(II) follows a second-order kinetics with respect to [malic acid] which shifts to first-order in presence of manganese(II). The catalytic effect of manganese(II) suggests that chromium(IV) is not formed as an intermediate. In the first-order reaction (in presence of manganese(II)), malic acid is oxidized to carbon dioxide and malonic acid. The effect of cationic and anionic surfactants was also investigated and it was found that cationic micelles catalyse the reaction while anionic micelles have no effect. The influence of different parameters such as [reactant], [surfactant], temperature and added salts was considered. For surfactant concentrations well above the ciritical micelle concentration, the rate constant-[surfactant] profiles can be interpreted in terms of distribution of both the reactants between water and the micelles, using the binding constants 121.2 and 22.5 mol-1 dm3 for chromium(VI) to CPB and CTAB, respectively. The catalytic effect of this reaction is greater for CPB than CTAB. This is the result of greater association of chromium(VI), not of a greater rate constant in the micelle.
- Kabir-ud-Din,Hartani, Khaled,Khan, Zaheer
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p. 2614 - 2624
(2007/10/03)
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- Kinetics and mechanism of the oxidation of α-hydroxy acids by tetrabutylammonium tribromide
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The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by tetrabutylammonium tribromide (TBATB) in 1:1 (v/v) acetic acid-water leads to the formation of corresponding oxoacids. The reaction is first order each in TBATB, and the hydroxy acid. Addition of tetrabutylammonium chloride does not affect the rate. Tribromide ion has been proposed as the reactive oxidizing species. The oxidation of α-deuteriomandelic acid shows the presence of a primary kinetic isotope effect (kH/kD = 5.50 at 303 K). The reaction does not exhibit any solvent isotope effect [k(H2O)/k(D2O) = 1.01]. The rate decreases with an increase in the amount of acetic acid in the solvent mixture. A mechanism involving hydride ion transfer to the oxidant is proposed.
- Baghmar,Sharma
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p. 311 - 315
(2007/10/03)
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- Cloning, sequencing, and expression of the gene encoding 4-hydroxy-4-methyl-2-oxoglutarate aldolase from Pseudomonas ochraceae NGJ1
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A DNA fragment that carried the gene (proA) encoding 4-hydroxy-4-methyl-2-oxoglutarate aldolase was cloned from the chromosomal DNA of Pseudomonas ochraceae NGJ1, and the coding region was assigned to the nucleotide sequence based on the N-terminal amino acid sequence of the enzyme purified from the organism. The proA gene was 684 bp long, corresponding to a protein of 227 amino acid residues with a calculated molecular mass of 24,067 Da. The genes encoding a putative transporter and a 4-oxalomesaconate hydratase were upstream, and a 3′-truncated gene encoding 2-pyrone-4,6-dicarboxylate lactonase was downstream from the proA gene in the same orientation on the DNA fragment. The proA gene product was overproduced in Escherichia coli and briefly purified to homogeneity from the crude extract by a two-step purification. The molecular and catalytic properties of the gene product were similar to those of the P. ochraceae enzyme.
- Maruyama, Kiyofumi,Miwa, Michiko,Tsujii, Nobuyuki,Nagai, Tomoyuki,Tomita, Naotaka,Harada, Toshiyuki,Sobajima, Hirobumi,Sugisaki, Hiroyuki
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p. 2701 - 2709
(2007/10/03)
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- Ruthenium-catalyzed oxidation of alkanes with tert-butyl hydroperoxide and peracetic acid
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The ruthenium-catalyzed oxidation of alkanes with tert-butyl hydroperoxide and peracetic acid gives the corresponding ketones and alcohols highly efficiently at room temperature. The former catalytic system, RuCl2(PPh3)3-t-BuOOH, is preferable to the oxidation of alkylated arenes to give aryl ketones. The latter system, Ru/C-CH3CO3H, is suitable especially for the synthesis of ketones and alcohols from alkanes. The ruthenium-catalyzed oxidation of cyclohexane with CH3CO3H in trifluoroacetic acid/CH2Cl2 at room temperature gave cyclohexyl trifluoroacetate and cyclohexanone with 90% conversion and 90% selectivity (85:15). The mechanistic study indicates that these catalytic oxidations of hydrocarbons involve oxo-ruthenium species as key intermediates.
- Murahashi,Komiya,Oda,Kuwabara,Naota
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p. 9186 - 9193
(2007/10/03)
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- Kinetics and mechanism of oxidation of some α-hydroxy acids by quinolinium fluorochromate
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The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by quinolinium fluorochromate (QFC) in dimethyl sulphoxide (DMSO) leads to the formation of corresponding oxoacids. The reaction is first order each in QFC and the hydroxy acids. The reaction is catalysed by the hydrogen ions. The hydrogen ion dependence has the form : k(obs) = a + b [H+]. Oxidation of p-methylmandelic acid has been studied in 19 different organic solvents. The solvent effect has been analysed by using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.
- Dave,Sharma,Banerji
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p. 728 - 733
(2007/10/03)
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- 13C, 15N, and 18O equilibrium isotope effects and fractionation factors
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A listing of 13C, 15N, and 18O equilibrium isotope effects and fractionation factors for atoms in specific positions is provided. Empirical factors that can be used to adjust these fractionation factors for more complex structures are presented and discussed. While much work needs to be done to determine equilibrium isotope effects for these heavy atoms, the values tabulated here should be useful to anyone working with isotope effects involving these atoms.
- Rishavy, Mark A.,Cleland
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p. 967 - 977
(2007/10/03)
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- Kinetics and mechanism of oxidation of α-amino acids by Fremy's radical in aqueous borate buffer medium
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Oxidation of α-amino acids viz., glycine, alanine, phenylalanine, valine, aspartic acid, serine and threonine by Fremy's radical (potassium nitrosodisulphonate, PNDS) in aqueous-borate buffer medium at pH 10.0 shows first order dependence each on [PNDS] and [α-amino acid]. Under the experimental conditions PNDS has been found to be quite stable. However, the little'self decomposition of PNDS found on standing for longer period has been prevented by the addition of sulphamate ion. Increase in ionic strength of the medium has no effect on the rate of oxidation. The mechanism proposed involves direct attack of PNDS on α-amino acid to give an α-amino acid radical. PNDS being a very good radical trap, efficiently reacts with α-amino acid radicals to give α-keto acid via easily hydrolysable α-imino acid. The order of reactivity has been found to be phenylalanine > alanine > serine > glycine > valine > threonine > aspartic acid.
- Kawle, Baloji,Thirupathi Rao,Adinarayana
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p. 667 - 670
(2007/10/03)
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- Kinetics and mechanism of oxidation of hydroxy acids by pyridinium hydrobromide perbromide
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The oxidation of glycollic, lactic, mandelic and malic acids by pyridinium hydrobromide perbromide (PHPB) in acetic acid-water mixture (3:7, v/v) leads to the formation of corresponding oxoacids.The reaction is first order each in PHPB and the hydroxy acid.Addition of pyridinium hydrobromide does not affect the rate indicating that PHPB itself is the reactive oxidizing species.The oxidation of α-deuteriomandelic acid shows the presence of a primary kinetic isotope effect (kH/kD=5.07).The reaction does not exhibit solvent isotope effect (k(H2O)/k(D2O)=1.01).The rate decreases with an increase in acetic acid content in the solvent mixture.A mechanism involving hydride ion transfer to the oxidant is proposed.
- Aparna, P,Kothari, Seema,Banerji, Kalyan K
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p. 1086 - 1088
(2007/10/02)
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- Oxidative Kinetics of Unsaturated Carboxylic Acids by Bromate in the Presence of Bromo-Complex Forming Metal Ions
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The kinetics and mechanism of oxidation of unsaturated carboxylic acids viz., acrylic, crotonic (trans), cinnamic, α-methyl and α-phenylcinnamic (trans), angelic, tiglic, vinylacetic and itaconic acids by acid bromate (unmixed by any competing or faster oxidation/addition by generated molecular bromine) in the presence of Tl(III)/Hg(II) are dealt.The reaction exhibits a first-order in , an order and accelerates with acidity of the medium.The reaction rate increases when deuterium replaces either α- or β-proton of substrate (kD/kH = 1.27).The factors governing the oxidative reaction rates are multifarious (electrostatic, electronic and steric effects), none alone can play a predominant role over a wide range of substrates.An attempt is made to propose a suitable mechanism which is consistent with the data concerning the reaction and also accounts satisfactorily the array of products that are obtained under various conditions.Tl(III) and Hg(II) behave only as bromo-complex forming metal ions and their effect on the bromate oxidation is displayed by their complex forming ability.
- Sanjeeva Reddy, Ch.
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p. 1009 - 1019
(2007/10/02)
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- RUTHENATE ION CATALYSED OXIDATION OF SODIUM MALATE AND SODIUM MANDELATE BY ALKALINE HEXACYANOFERRATE (III)
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The kinetics of oxidation of sodium malate and sodium mandelate by hexacyanoferrate (III) in aqueous alkaline medium catalised by ruthenate ion have been studied at constant ionic strength.The reaction shows first order dependence in ruthenate ion and zero order in hexacyanoferrate (III).The rate of reaction increases with increase in substrate concentration and shows Michaelis-Menton type of behaviour.The rate of reaction decreases with increase in hydroxide ion concentration.The observed data suggest that the oxidation proceeds via formation of a complex between substrate and ruthenate ion.A plausible mechanism, consistent with the experimental results, has been proposed.
- Gupta, K. C.,Kumar, Pradeed,Behari, K.
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p. 232 - 236
(2007/10/02)
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- Transformation of Citric Acid to Acetic Acid, Acetoin and Diacetyl by Wine Making Lactic Acid Bacteria
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A decrease in citric acid and increases in acetic acid, acetoin and diacetyl were found in the test red wine after inoculation of intact cells of Leuconostoc mesenteroides subsp. lactosum ATCC 27307, a malo-lactic bacterium, grown on the malate plus citrate-medium.Citric acid in the buffer solution was transformed to acetic acid, acetoin and diacetyl in the pH range of 2 to 6 after inoculation with intact cells of this bacterial species.It was concluded that citric acid in wine making involving malolactic fermentation, at first, was converted by citrate lyase to acetic and oxaloacetic acids, and the latter was successively transformed by decarboxylation to pyruvic acid which was subsequently converted to acetoin, diacetyl and acetic acid.Both the activities of citrate lyase and acetoin formation from pyruvic acid in the dialyzed cellfree extract were optimal at pH 6.0.Divalent cations such as Mn2+, Mg2+, Co2+ and Zn2+ activated the citrate lyase.The citrate lyase was completely inhibited by EDTA, Hg2+ and Ag2+.The acetoin formation from pyruvic acid was significantly stimulated by thiamine pyrophosphate and CoCl2, and inhibited by oxaloacetic acid.Specific activities of the citrate lyase and acetoin formation were considerably variable among the six strains of malo-lactic bacteria examined.Some activities of irreversible reduction of diacetyl to acetoin were found in the cell-free extracts of four of the malolactic bacteria strains and the optimal pH was 6.0 for this activity of Leu. mesenteroides.
- Shimazu, Yoshimi,Uehara, Mikio,Watanabe, Masazumi
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p. 2147 - 2158
(2007/10/02)
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- A Comparative Kinetic Study of Oxidation of Structurally Related Organic Substrates Viz. Succinic, Malic and Tartaric Acids and also of Glycerol with Cerium(IV) Sulphate in Sulphuric Acid Medium
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A comparative kinetic study of oxidation of structurally related organic substrates viz. succinic, malic and tartaric acids and also of glycerol with Cerium(VI) sulphate in sulphuric acid medium is carried out at 32.5 +/- 0.1 deg C and the course of the reaction is followed spectrophotometrically at 380 mμ.The order of the reaction with respect to succinic acid and glycerol is fractional and varying while the order in the case of the two hydroxy acids is unity.The reaction rate is inversely proportional to the and also separately 2->.The mechanism of the oxidation reaction with respect to hydroxy acid or glycerol is the prior formation of an activated complex (viz., 1:1 complex), the decomposition of which is the rate determining step.In the case of succinic acid the mechanism of oxidation is believed to take place through a free radical mechanism.Another important conclusion that can be drawn from this work is the synergestic effect of hydroxyl and carboxyl group in promoting the oxidation of hydroxy-carboxylic acids.While substrates with hydroxyl groups alone viz. glycerol and substrates with carboxyl groups alone, viz. succinic acid are less reactive, compounds containing both hydroxyl and carboxyl groups viz., malic and tartaric acids are much more easily oxidized.
- Rao, B. Madhava,Sastry, T. P.,Parekh, T. S.
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p. 906 - 919
(2007/10/02)
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