- One-Pot Preparation of d-Amino Acids Through Biocatalytic Deracemization Using Alanine Dehydrogenase and Ω-Transaminase
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d-Amino acids are pharmaceutically important building blocks, leading to a great deal of research efforts to develop cost-effective synthetic methods. Preparation of d-amino acids by deracemization has been conceptually attractive owing to facile synthesis of racemic amino acids by Strecker synthesis. Here, we demonstrated biocatalytic deracemization of aliphatic amino acids into d-enantiomers by running cascade reactions; (1) stereoinversion of l-amino acid to a d-form by amino acid dehydrogenase and ω-transaminase and (2) regeneration of NAD+ by NADH oxidase. Under the cascade reaction conditions containing 100?mM isopropylamine and 1?mM NAD+, complete deracemization of 100?mM dl-alanine was achieved after 24?h with 95% reaction yield of d-alanine (> 99% eeD, 52% isolation yield). Graphical Abstract: [Figure not available: see fulltext.].
- Han, Sang-Woo,Shin, Jong-Shik
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- Influence of silver on the glycerol electro-oxidation over AuAg/C catalysts in alkaline medium: A cyclic voltammetry and in situ FTIR spectroscopy study
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In the present work, we investigated the influence of silver on the glycerol electro-oxidation over carbon-supported AuAg catalysts by cyclic voltammetry and in situ FTIR spectroscopy. We observed that the presence of Ag in the bimetallic materials provided a more efficient catalyst in terms of the ability to electro-oxidize glycerol at relatively low potentials. On the other hand, the bimetallic catalysts were found to be less promising than the Au/C catalyst with respect to the reaction rate. Ag addition influenced the mechanism of glycerol electro-oxidation, favoring the C-C-C bond breaking, as evidenced by the selective formation of formic acid on the bimetallic catalysts. The impact of Ag on the glycerol electro-oxidation over AuAg/C may be driven by electronic modifications and Ag segregation on the catalysts surface.
- Gomes,Garcia,Gasparotto,De Souza,Ferreira,Pires,Tremiliosi-Filho
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- MECHANISTIC STUDY OF THE ALDOL CONDENSATION OCCURING IN THE ALKALINE SOLUTION OF 3-HYDROXY 2-OXO PROPRANOATE (Β HYDROXYPYRUVATE)
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With 3-bromo-2-oxopropanoate (β bromopyruvate) and its ethyl ester, the ionisation of the gemdiol of the hydrated form BrCH2-C(OH)2-COOR 1 initiates the elimination of the bromide anion yielding 3-hydroxy-2-oxopropanoate 2 (β-hydroxypyruvate).The mechanism of the reaction was investigated essentially by polarography in aqueous solution.In neutral ( and acid) media, the polarographic behaviour of 2 resembled that of other α-ketoacids: reduction at the mercury electrode yielded glycerate.In alkaline media, there was evidence of the carbanion enolate .3'.The overall rate constant was determined according to a kinetic law of the type: : found k = 1.56 min-1 in NaOH 0.5N at 25 deg.In the pH range 10.5 to 11.5, 3' existed in minor amounts and initiated a slow aldol codensation with the tautomer 3-oxo-2-hydroxypropanoate 4 (tartrone semialdehyde) according to a kinetic low of the type found at 25 deg., at pH 11.0.The aldol product was isolated as a sodium salt and its structure established by 13CNMR.
- Fleury, Daniele,Fleury, M. B.,Platzer, Nicole
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- Catalytic oxidation of crude glycerol using catalysts based on Au supported on carbonaceous materials
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Au catalysts supported on different carbon materials, such as graphite (G, 10 m2 g-1), ribbon-type carbon nanofibers (CNF-R, 109 m2 g-1), and carbon nanospheres (CNS, 3 m2 g-1), were prepared by the sol-gold method using tetrahydroxymethyl phosphonium chloride as the reducing agent. Different techniques were employed to characterize both the supports and the final Au catalysts: atomic absorption spectrometry, transmission electron microscopy, thermogravimetric analysis, X-ray diffraction, elemental analyses, N2 adsorption-desorption analysis, temperature-programmed reduction, and temperature-programmed decomposition. Au catalysts were tested in the liquid phase by selective oxidation of both commercial and crude glycerol, the latter obtained from the manufacture of biodiesel. Catalytic results obtained with commercial glycerol showed that the product distribution was dependent on the nature of the support and consequently on the Au particle size. The highest catalyst activity was achieved using highly crystalline carbon supports, supporting small-size (highly dispersed) Au particles. Accordingly the graphite-based catalyst exhibited higher catalytic activity than the CNF-R-based one. Catalytic results similar to those obtained with commercial glycerol were obtained when testing the stream resulting from a low cost neutralization procedure of the crude glycerol.
- Gil, Sonia,Marchena, Miriam,Fernández, Carmen María,Sánchez-Silva, Luz,Romero, Amaya,Valverde, José Luís
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- One-Pot Cascade Synthesis of (3S)-Hydroxyketones Catalyzed by Transketolase via Hydroxypyruvate Generated in Situ from d-Serine by d-Amino Acid Oxidase
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We described an efficient in situ generation of hydroxypyruvate from d-serine catalyzed by a d-amino acid oxidase from Rhodotorula gracilis. This strategy revealed an interesting alternative to the conventional chemical synthesis of hydroxypyruvate starting from toxic bromopyruvate or to the enzymatic transamination from l-serine requiring an additional substrate as amino acceptor. Hydroxypyruvate thus produced was used as donor substrate of transketolases from Escherichia coli or from Geobacillus stearothermophilus catalyzing the stereoselective formation of a carbon?carbon bond. The enzymatic cascade reaction was performed in one-pot in the presence of d-serine and appropriate aldehydes for the synthesis of valuable (3S)-hydroxyketones, which were obtained with high enantio- and diastereoselectivity and in good yield. The efficiency of the process was based on the irreversibility of both reactions allowing complete conversion of d-serine and aldehydes. (Figure presented.).
- L'enfant, Mélanie,Bruna, Felipe,Lorillière, Marion,Ocal, Nazim,Fessner, Wolf-Dieter,Pollegioni, Loredano,Charmantray, Franck,Hecquet, Laurence
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- Oxidation of reactive alcohols with hydrogen peroxide catalyzed by manganese complexes
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Two manganese-containing catalysts have been employed in the oxidation with hydrogen peroxide of two reactive alcohols (1-phenylethanol and glycerol): soluble catalyst [LMn(μ-O)3MnL](PF6)2 (1a) and heterogenized catalyst [LMn(μ-O)3MnL]2[SiW 12O40] (1b) (L is 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN). Oxidation of 1-phenylethanol catalyzed by 1a in acetonitrile solution proceeds at room temperature in the presence of a small amount of oxalic acid; the turnover number attains 15,000 after 3 h. It has been proposed on the basis of the kinetic study that an oxidizing species is a manganyl species containing fragment Mn=O rather that hydroxyl radical. This species reacts competitively with the alcohol, acetonitrile and hydrogen peroxide. In the case of 1b dependences of the initial rates of acetophenone accumulation on concentration of the alcohol and amount of 1b have plateau. Both homogeneous and heterogeneous catalysts are efficient in the oxidation of glycerol to produce dihydroxyacetone (DHA) as the main product. The oxidation catalyzed by 1a is one of the first examples of the glycerol oxidation by a catalytic homogeneous system. The yield of valuable products attained 45%. The oxidation of DHA in the absence of glycerol afforded mainly glycolic acid in yield 60% based on the starting DHA. The oxidation on 1b represents the first example of the glycerol transformation catalyzed by a heterogenized metal complex. Under certain conditions yields of products of deeper oxidation (glyceric, glycolic and hydroxypyruvic acids) are somewhat higher than the yield of dihydroxyacetone. Special experiments demonstrated that no leaching of active species occurs from catalyst 1b to the solution and that this catalyst can be re-used at least four times without substantial loss of activity.
- Shul'Pin, Georgiy B.,Kozlov, Yuriy N.,Shul'Pina, Lidia S.,Strelkova, Tatyana V.,Mandelli, Dalmo
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- Selective Oxidation of Glycerol to Glyceric Acid in Base-Free Aqueous Solution at Room Temperature Catalyzed by Platinum Supported on Carbon Activated with Potassium Hydroxide
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Pt supported on KOH-activated mesoporous carbon (K-AMC) was used to catalyze glycerol oxidation under base-free conditions at room temperature. To study the relationship between the carbon surface chemistry and the catalytic performance of the K-AMC-based Pt catalysts, different levels of surface oxygen functional groups (SOFGs) on the AMC supports were induced by thermal treatment at different temperatures under inert or H2 gas. A strong effect of the surface chemistry was observed on AMC-supported Pt catalysts for glycerol oxidation. The presence of carboxylic acid groups impedes the adsorption of glycerol, which leads to the reduction of catalytic activity, whereas the presence of high-desorption-temperature SOFGs, such as phenol, ether, and carbonyl/quinone groups, provide hydrophilicity to the carbon surface that improves the adsorption of glycerol molecules on Pt metal surface, which is beneficial for the catalytic activity.
- Tan, Hua,Tall, Omar E.,Liu, Zhaohui,Wei, Nini,Yapici, Tahir,Zhan, Tong,Hedhill, Mohamed Nejib,Han, Yu
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- Transketolase from Escherichia coli: A practical procedure for using the biocatalyst for asymmetric carbon-carbon bond synthesis
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A practical procedure is reported for the use of the enzyme transketolase, from Escherichia coli, for asymmetric carbon-carbon bond synthesis. The reactions with the biocatalyst are conveniently carried out, on a gram scale, in unbuffered aqueous media by employing a pH autotitrator. An improved large scale synthesis of hydroxypyruvate is also reported.
- Morris, K. Gail,Smith, Mark E.B.,Turner, Nicholas J.,Lilly, Malcolm D.,Mitra, Robin K.,Woodley, John M.
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- Mg-Al mixed oxides supported bimetallic au-pd nanoparticles with superior catalytic properties in aerobic oxidation of benzyl alcohol and glycerol
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Nano-sized Au and Pd catalysts are favorable for oxidations with molecular oxygen, and the preparation of this kind of nanoparticles with high catalytic activities is strongly desirable. We report a successful synthesis of bimetallic Au-Pd nanoparticles w
- Wang, Liang,Zhang, Wei,Zeng, Shangjing,Su, Dangsheng,Meng, Xiangju,Xiao, Fengshou
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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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- Role of the active site residues arginine-216 and arginine-237 in the substrate specificity of mammalian D-aspartate oxidase
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d-Aspartate oxidase (DDO) and d-amino acid oxidase (DAO) are flavin adenine dinucleotide-containing flavoproteins that catalyze the oxidative deamination of d-amino acids. Unlike DAO, which acts on several neutral and basic d-amino acids, DDO is highly specific for acidic d-amino acids. Based on molecular modeling and simulated annealing docking analyses, a recombinant mouse DDO carrying two substitutions (Arg-216 to Leu and Arg-237 to Tyr) was generated (R216L-R237Y variant). This variant and two previously constructed single-point mutants of mouse DDO (R216L and R237Y variants) were characterized to investigate the role of Arg-216 and Arg-237 in the substrate specificity of mouse DDO. The R216L-R237Y and R216L variants acquired a broad specificity for several neutral and basic d-amino acids, and showed a considerable decrease in activity against acidic d-amino acids. The R237Y variant, however, did not show any additional specificity for neutral or basic d-amino acids and its activity against acidic d-amino acids was greatly reduced. The kinetic properties of these variants indicated that the Arg-216 residue is important for the catalytic activity and substrate specificity of mouse DDO. However, Arg-237 is, apparently, only marginally involved in substrate recognition, but is important for catalytic activity. Notably, the substrate specificity of the R216L-R237Y variant differed significantly from that of the R216L variant, suggesting that Arg-237 has subsidiary effects on substrate specificity. Additional experiments using several DDO and DAO inhibitors also suggested the involvement of Arg-216 in the substrate specificity and catalytic activity of mouse DDO and that Arg-237 is possibly involved in substrate recognition by this enzyme. Collectively, these results indicate that Arg-216 and Arg-237 play crucial and subsidiary role(s), respectively, in the substrate specificity of mouse DDO.
- Katane, Masumi,Saitoh, Yasuaki,Maeda, Kazuhiro,Hanai, Toshihiko,Sekine, Masae,Furuchi, Takemitsu,Homma, Hiroshi
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- The pseudoalteromonas luteoviolacea L-amino acid oxidase with antimicrobial activity is a flavoenzyme
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The marine environment is a rich source of antimicrobial compounds with promising pharmaceutical and biotechnological applications. The Pseudoalteromonas genus harbors one of the highest proportions of bacterial species producing antimicrobial molecules. For decades, the presence of proteins with L-amino acid oxidase (LAAO) and antimicrobial activity in Pseudoalteromonas luteoviolacea has been known. Here, we present for the first time the identification, cloning, characterization and phylogenetic analysis of Pl-LAAO, the enzyme responsible for both LAAO and antimicrobial activity in P. luteoviolacea strain CPMOR-2. Pl-LAAO is a flavoprotein of a broad substrate range, in which the hydrogen peroxide generated in the LAAO reaction is responsible for the antimicrobial activity. So far, no protein with a sequence similarity to Pl-LAAO has been cloned or characterized, with this being the first report on a flavin adenine dinucleotide (FAD)-containing LAAO with antimicrobial activity from a marine microorganism. Our results revealed that 20.4% of the sequenced Pseudoalteromonas strains (specifically, 66.6% of P. luteoviolacea strains) contain Pl-laao similar genes, which constitutes a well-defined phylogenetic group. In summary, this work provides insights into the biological significance of antimicrobial LAAOs in the Pseudoalteromonas genus and shows an effective approach for the detection of novel LAAOs, whose study may be useful for biotechnological applications.
- Andreo-Vidal, Andrés,Sanchez-Amat, Antonio,Campillo-Brocal, Jonatan C.
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- The role of residues Arg169 and Arg220 in intersubunit interactions of yeast D-Amino acid oxidase
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D-Amino acid oxidase from the yeast Trigonopsis variabilis (EC 1.4.3.3, TvDAAO) exists as a dimer consisting of two identical subunits. The dimeric structure of the enzyme is stabilized by 12 (six pairs) hydrogen bonds, the residues Arg169 and Arg220 of each subunit being involved in eight hydrogen bonds. The Arg169Glu and Arg(169,220)Ala mutants of TvDAAO were prepared. Both mutant enzymes were expressed in E. coli cells as insoluble but catalytically active inclusion bodies. The introduction of amino acid substitutions at the intersubunit interface resulted in a change in the substrate specificity profile and a strong decrease in thermal stability.
- Cherskova,Khoronenkova,Tishkov
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- Efficient Enzymatic Preparation of13N-Labelled Amino Acids: Towards Multipurpose Synthetic Systems
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Nitrogen-13 can be efficiently produced in biomedical cyclotrons in different chemical forms, and its stable isotopes are present in the majority of biologically active molecules. Hence, it may constitute a convenient alternative to Fluorine-18 and Carbon-11 for the preparation of positron-emitter-labelled radiotracers; however, its short half-life demands for the development of simple, fast, and efficient synthetic processes. Herein, we report the one-pot, enzymatic and non-carrier-added synthesis of the13N-labelled amino acids l-[13N]alanine, [13N]glycine, and l-[13N]serine by using l-alanine dehydrogenase from Bacillus subtilis, an enzyme that catalyses the reductive amination of α-keto acids by using nicotinamide adenine dinucleotide (NADH) as the redox cofactor and ammonia as the amine source. The integration of both l-alanine dehydrogenase and formate dehydrogenase from Candida boidinii in the same reaction vessel to facilitate the in situ regeneration of NADH during the radiochemical synthesis of the amino acids allowed a 50-fold decrease in the concentration of the cofactor without compromising reaction yields. After optimization of the experimental conditions, radiochemical yields were sufficient to carry out in vivo imaging studies in small rodents.
- da Silva, Eunice S.,Gómez-Vallejo, Vanessa,Baz, Zuri?e,Llop, Jordi,López-Gallego, Fernando
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- Electrooxidation of glycerol on nickel and nickel alloy (Ni-Cu and Ni-Co) nanoparticles in alkaline media
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In the present study, nickel (Ni) and Ni alloy (Ni-Cu and Ni-Co) nanoparticles modified carbon-ceramic electrodes (Ni/CCE, Ni-Cu/CCE and Ni-Co/CCE) were prepared by an electrochemical process for the oxidation of glycerol. In order to obtain the surface and physicochemical information, the Ni/CCE, Ni-Cu/CCE and Ni-Co/CCE were investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and electrochemical techniques. Then, cyclic voltammetry and chronoamperometry were employed to characterize the electrocatalytic activity of the modified electrodes, Ni/CCE, Ni-Cu/CCE and Ni-Co/CCE, toward the oxidation of glycerol in 1.0 M NaOH solution. It was found that the Ni alloy nanoparticle modified electrodes are catalytically more active than the Ni/CCE, therefore, the alloying of the Ni with Cu and Co in the form of nanoparticles on the carbon-ceramic electrode, as a homemade substrate, greatly enhances the catalytic activity of the Ni-based electrocatalysts (as the non-platinum electrocatalysts) in glycerol oxidation.
- Habibi, Biuck,Delnavaz, Nasrin
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- Selective oxidation of glycerol over different shaped WO3 supported Pt NPs
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In this work, different shaped WO3 (rod-like, lamellar and cuboid) supported Pt catalysts were prepared in a facile routine and tested in the selective oxidation of glycerol in base-free aqueous solution. Characterizations indicated that rod-like WO3 supported Pt catalyst (Pt/R-WO3) possesses higher surface area because of the formation of vertical pore channels and highly exposed plane (100), the deposited Pt atoms combined strongly with the terminal [sbnd]W[dbnd]O in rod-like WO3. These properties promoted the adsorption, storage and surface diffusion of oxygen over Pt/R-WO3 which exhibited the excellent activity for the selective oxidation of glycerol. And the higher amount of acid sites on the surface of Pt/R-WO3 enhanced the selectivity of glyceric acid. The calculated turnover frequency of each Pt atom in Pt/R-WO3 reached 946 h–1 at 60 °C.
- Yang, Lihua,Jiang, Yuanyuan,Zhu, Zihui,Hou, Zhaoyin
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- SiO2-, Cu-, and Ni-supported Au nanoparticles for selective glycerol oxidation in the liquid phase
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We tested for the first time the efficiency of SiO2-, Cu-, and Ni-supported Au in deep glycerol oxidation in a diluted and viscous H2O2/H2O liquid phase. Acetic acid (AA), the C2 oxidate, was preferentially formed in such a system. High conversion (100%) and AA yields (90%) were observed for the sol-gel SiO2-supported Au in diluted solutions. Although with the increase of glycerol concentration in the viscous liquid phase these values decreased to ca. 40% (conversion) and 20% (AA yield), the addition of acetonitrile improved the AA yield to ca. 40%, while the surfactants were found to be capable of a many-fold enhancement of the catalyst activity at the room temperature highly viscous liquid phase. High performances were also observed for the bimetallic Au/Cu and Au/Ni catalysts obtained by nano-Au transfer; however, these catalysts were destroyed during the reaction by the Cu or Ni leaching effect.
- Kapkowski, Maciej,Bartczak, Piotr,Korzec, Mateusz,Sitko, Rafal,Szade, Jacek,Balin, Katarzyna,Lel?tko, Józef,Polanski, Jaroslaw
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- Effect of electron acceptors H2O2 and O2 on the generated reactive oxygen species 1O2 and OH in TiO2-catalyzed photocatalytic oxidation of glycerol
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The effect of the electron acceptors H2O2 and O2 on the type of generated reactive oxygen species (ROS), and glycerol conversion and product distribution in the TiO2-catalyzed photocatalytic oxidation of glycerol was studied at ambient conditions. In the absence of an electron acceptor, only HO radicals were generated by irradiated UV light and TiO2. However, in the presence of the two electron acceptors, both HO radical and 1O2 were produced by irradiated UV light and TiO2 in different concentrations that depended on the concentration of the electron acceptor. The use of H2O2 as an electron acceptor enhanced glycerol conversion more than O2. The type of generated value-added compounds depended on the concentration of the generated ROS.
- Jedsukontorn, Trin,Meeyoo, Vissanu,Saito, Nagahiro,Hunsom, Mali
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- Highly selective transformation of glycerol to dihydroxyacetone without using oxidants by a PtSb/C-catalyzed electrooxidation process
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We demonstrate an electrocatalytic reactor system for the partial oxidation of glycerol in an acidic solution to produce value-added chemicals, such as dihydroxyacetone (DHA), glyceraldehyde (GAD), glyceric acid (GLA), and glycolic acid (GCA). Under optimized conditions, the carbon-supported bimetallic PtSb (PtSb/C) catalyst was identified as a highly active catalyst for the selective oxidation of glycerol in the electrocatalytic reactor. The product selectivity can be strongly controlled as a function of the applied electrode potential and the catalyst surface composition. The main product from the electrocatalytic oxidation of glycerol was DHA, with a yield of 61.4% of DHA at a glycerol conversion of 90.3%, which can be achieved even without using any oxidants over the PtSb/C catalyst at 0.797 V (vs. SHE, standard hydrogen electrode). The electrocatalytic oxidation of biomass-derived glycerol represents a promising method of chemical transformation to produce value-added molecules.
- Lee, Seonhwa,Kim, Hyung Ju,Lim, Eun Ja,Kim, Youngmin,Noh, Yuseong,Huber, George W.,Kim, Won Bae
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- Mutant d-amino acid oxidase with higher catalytic efficiency toward d-amino acids with bulky side chains
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d-Amino acid oxidase from the yeast Trigonopsis variabilis (TvDAAO) is widely used in fine organic synthesis, including the preparation of unnatural l-amino acids and α-keto acids. The analysis of the three-dimensional structure of TvDAAO was carried out with the aim of producing the enzyme specific to d-amino acids with bulky side chains. The analysis revealed the residue Phe54 at the entrance to the active site, which controls the substrate access to this site. The residue Phe54 was replaced by residues Ala, Ser, and Tyr. The cultivation of recombinant E. coli strains expressing TvDAAO mutants showed that the mutein with the Phe54Ala substitution had very low stability. Thus, the inactivation of the enzyme occured within 10 min after the cell disruption. The Phe54Ser TvDAAO and Phe54Tyr TvDAAO mutants were obtained as homogeneous preparations, and their thermal stability and catalytic properties were investigated. The introduction of Phe54Ser and Phe54Tyr substitutions resulted in additional stabilization of the protein macromolecule compared to the wild-type TvDAAO. Thus, the half-inactivation time for the mutant enzymes at 54 C increased by a factor of 1.5 and 2, respectively. As in the case of wild-type TvDAAO, the thermal inactivation of the muteins proceeds via a two-step dissociative mechanism. The introduction of mutations led to a strong change in the substrate specificity profile. The mutants have no activity toward a series of d-amino acids (Phe54Ser TvDAAO toward d-Ala, d-Ser, d-Val, and d-Thr; Phe54Tyr TvDAAO toward d-Ser, d-Tyr, d-Thr, and d-Lys). The catalytic efficiency (the k cat/K M ratio) of the Phe54Ser TvDAAO mutant toward d-amino acids with bulky side chains (d-Lys, d-Asn, d-Phe, d-Tyr, d-Trp, and d-Leu) increased from 2.4 to 7.3 times.
- Komarova,Golubev,Khoronenkova,Tishkov
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- Enzymatic synthesis of 'natural-labeled' 6-deoxy-L-sorbose precursor of an important food flavor
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A biological route to natural 6-deoxy-L-sorbose is described. This method is based on the production of natural hydroxypyruvate and 4-deoxy-L-threose and their conversion into 6-deoxy-L-sorbose: hydroxypyruvate is obtained from L-serine by serine: glyoxylate aminotransferase catalysis, 4-deoxy-L-threose is obtained by microbial isomerization of 4-deoxy-L-erythrulose, this last being obtained from acetaldehyde (a naturally-available compound) and hydroxypyruvate by transketolase catalysis.
- Hecquet,Bolte,Demuynck
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- METHYLENEMALONIC ACID AND INTERMEDIATES, PROCESSES FOR THEIR PREPARATION AND ENGINEERED MICROORGANISMS
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The description relates to, inter alia, recombinant microorganisms, engineered metabolic pathways, chemical catalysts, and products produced through the use of the described methods and materials. The products produced include methylenemalonic acid and intermediates, as well as their salts and esters.
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- Microwave-assisted green oxidation of alcohols with hydrogen peroxide catalyzed by iron complexes with nitrogen ligands
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Oxidation of primary and secondary alcohols, including two diols and glycerol, with H2O2 was catalyzed by the iron(II) complexes [FeL3](OTf)2 (L = 2,2′-bipyridine, 2,2′-bipyrimidine, 1,10-phenanthroline and substituted derivatives) and [FeL2](OTf)2 (L = bis(2-pyridinylmethyl)amine, 2,6-di(2-pyridyl)pyridine). The reactions were performed in acetonitrile, water or mixed solvent (typically water/acetonitrile 4:1) in a microwawe reactor at low power. Effect of addition of a cocatalyst, which in some cases improved the yields of the catalytic reaction, was investigated by means of NMR and UV–Visible techniques.
- Cozzi, Irene Sofia,Crotti, Corrado,Farnetti, Erica
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- Effect of oxidants on photoelectrocatalytic decolourization using α-Fe2O3/TiO2/activated charcoal plate nanocomposite under visible light
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The present study is to investigate the effect of oxidants H2O2, S2O82-, BrO3-, ClO3- and IO4- with different concentrations on photoelectrocatalytic decolourization of Lanasol yellow 4G (LY4G) as a model contaminant using α-Fe2O3/TiO2/activated charcoal plate (ACP) nanocomposite under visible light. In this system, the decolourization efficiency increased with increasing BrO3-, ClO3- and IO4- doses but reached an optimum amount with H2O2 and S2O82- at 1 mM. Experimental data revealed that the decolourization rate of LY4G in all of the processes obeyed pseudo-first-order kinetics. Total organic carbon (TOC) results indicated that 21% and 100% of organic substrate were mineralized respectively after 80 min and 8 h. The gas chromatography-mass spectrometry (GC-MS) analysis was employed to identify the intermediate products. Also, a plausible degradation pathway was proposed. Finally, the real wastewater treatment was investigated by chemical oxygen demand (COD) measurements. This journal is
- Ayoubi-Feiz, Baharak,Aber, Soheil,Sheydaei, Mohsen
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p. 19368 - 19378
(2015/04/14)
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- Oxidation reactions catalyzed by osmium compounds. Part 4. Highly efficient oxidation of hydrocarbons and alcohols including glycerol by the H 2O2/Os3(CO)12/pyridine reagent
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Triosmium dodecacarbonyl cluster Os3(CO)12 catalyzes oxidation of linear (n-heptane) and cyclic alkanes (cyclohexane, cyclooctane, methylcyclohexane, cis- and trans-1,2-dimethylcyclohexanes) to the corresponding cycloalkyl hydroperoxides by hydrogen peroxide in acetonitrile solution. Addition of pyridine leads to the acceleration of the process. Turnover numbers in the case of cyclooctane attain 60 000 and turnover frequencies are up to 24 000 h-1. The alkyl hydroperoxide partly decomposes in the course of the reaction to afford cyclooctanone and cyclooctanol. Selectivity parameters obtained in oxidations of various linear and branched alkanes as well as kinetic features of the reaction indicated that the alkane oxidation occurs with the participation of hydroxyl radicals. A similar mechanism operates in transformation of benzene into phenol and styrene into benzaldehyde. The system also oxidizes 1-phenylethanol to acetophenone. Glycerol is oxidized to produce dihydroxyacetone, glycolic acid and hydroxypyruvic acid. The Royal Society of Chemistry 2013.
- Shul'pin, Georgiy B.,Kozlov, Yuriy N.,Shul'Pina, Lidia S.,Carvalho, Wagner A.,Mandelli, Dalmo
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p. 15065 - 15074
(2013/09/02)
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- PROCESS FOR STRAIGHTENING KERATIN FIBRES WITH A HEATING MEANS AND DENATURING AGENTS
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The invention relates to a process for straightening keratin fibres, comprising: (i) a step in which a straightening composition containing at least two denaturing agents is applied to the keratin fibres, (ii) a step in which the temperature of the keratin fibres is raised, using a heating means, to a temperature of between 110 and 250° C.
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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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- Effects of Gln102Arg and Cys97Gly mutations on the structural specificity and stereospecificity of the L-lactate dehydrogenase from Bacillus stearothermophilus
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The L-lactate dehydrogenase of Bacillus stearothermophilus (BSLDH) is a thermostable enzyme with considerable potential for applications in asymmetric synthesis. An understanding of the factors controlling its structural specificity and stereospecificity is therefore of interest. In this paper the effects of Gln102 → Arg and Cys97 → Gly mutations have been evaluated. In a survey of thirteen 2-keto acids, the Q102R mutation was found to reduce the activity of BSLDH toward the reduction of RCOCOOH substrates with small or hydrophilic R groups without affecting its activity toward those with larger, hydrophobic R substituents. In addition, the mutants have a high affinity for C3- and C4-2-keto dicarboxylates. The extent of fructose 1,6-diphosphate activation of the mutant enzymes was similar to its effect on wild-type BSLDH. The mutants also retained the synthetically desirable thermostability. As a probe of the commitment of BSLDH to L stereospecificity, the Q102R mutation was introduced to allow the new 102R site to compete with Arg171 for binding of the COO- groups of the RCOCOOH substrates, which would reverse the normal RCOCOOH orientation at the active site and thereby open up the possibility of the formation of a D-2-hydroxy acid in place of the natural L product. However, L stereospecificity in 2-keto acid reduction was strictly retained by the Q102R mutants. This was confirmed by preparative-scale reductions of pyruvate and phenylpyruvate to give the corresponding L-hydroxy acids in enantiomerically pure form and by comparison of the kinetics of oxidation of L- and D-lactate and L- and D-phenyl lactate. No evidence for substrate activity for the D enantiomers of either of these was seen with WT or mutant enzymes. Some catalysis of D-malate oxidation by both WT and mutant BSLDH was observed, but the L enantiomer was still preferred to approximately the same degree in both cases. That the inability of BSLDH and its 102R mutants to catalyze D-2-hydroxy acid oxidations was not simply due to the failure of the D enantiomers to bind at the active site was established by a comparison of competitive inhibition constants for the above L- and D-hydroxy acids. CD spectroscopy showed that the Gln102 → Arg mutations were not benign but induced significant structural perturbations. Electrostatic potential contours suggest that the structural changes are partly due to long-range interactions of the positive charge of the guanidinium group of Arg102 with several other residues that form an area of negative potential adjacent to the active site. The Cys97 → Gly mutation, while inadvertent, was of interest because of the potential specificity effects arising from its location adjacent to the hinge of the flexible 98-110 loop. However, its effects on BSLDH specificity were minor.
- Kallwass, Helmut K. W.,Luyten, Marcel A.,Parris, Wendy,Gold, Marvin,Kay, Cyril M.,Bryan Jones
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p. 4551 - 4557
(2007/10/02)
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- Polyfunctional (R)-2-Hydroxycarboxylic Acids by Reduction of 2-Oxo Acids with Hydrogen Gas or Formate and Resting Cells of Proteus vulgaris
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Various (R)-2-hydroxy acids such as (R)-2-hydroxy-3-enoic-, 3,5-dienoic-, 4-oxo-, (R,S)-3-hydroxy and some others were prepared on a scale up to 0.12 mol by biocatalytic reduction of the corresponding 2-oxo acids with P. vulgaris and hydrogen gas and/or formate as electron donors.With the exception of the 2-hydroxy-4-oxo acids it could be proved that the enantiomeric excess is >97 percent.For the 4-oxo derivatives this enantiomeric excess can be assumed.The yields of isolated products are high because they were isolated from rather small amounts of biocatalyst and low buffer concentrations.Product concentrations in the range of 0.1- 0.24 M were obtained.For 1 mmol of product formation in 15-20 h about 20-40 mg (dry weight) of P. vulgaris cells are necessary.
- Schummer, Anita,Yu, Hongtao,Simon, Helmut
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p. 9019 - 9034
(2007/10/02)
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- An Evaluation of the Substrate Specificity, and of Its Modification by Site-Directed Mutagenesis, of the Cloned L-Lactate Dehydrogenase from Bacillus stearothermophilus
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The L-lactate dehydrogenase of Bacillus stearothermophilus (BSLDH) is a stable, thermophilic oxidoreductase.It has been selected as a model of enzymes with considerable future promise in assymetric synthesis in that it has been cloned to ensure a plentiful and inexpensive supply and because of the potential for tailoring its specificity to accept unnatural substrate structures via the site-directed mutagenesis techniques of moleculer biology.In this study, the specificity of BSLDH toward representative α-keto acids possessing straight- and branched-chain alkyl,cycloalkyl, or aromatic side chains has been evaluated.The results show that substrates that are sterically bulky in the region of the α-keto group to be reduced are poorly accepted by the enzyme.Graphics analyses indicated that the low activities of these hindered substrates might be partly due to a bad interaction of the active site residue Gln102 with large or branched substituents adjacent to the α-keto group.Accordingly, Gln102 has been replaced by the smaller Asn residue by site-directed mutagenesis in an attempt to expand the active site volume available to receive substrates larger than the natural pyruvate.However, the kinetic data show that bulky α-keto acids are only marginally better accommodated by the Gln102 -> Asn mutant than by the wild-type enzyme.
- Luyten, Marcel A.,Bur, Daniel,Wynn, Hla,Parris, Wendy,Glod, Marvin,et al.
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p. 6800 - 6804
(2007/10/02)
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- Structure-Activity Studies with the αβ-Dihydroxyacid Dehydratase of Salmonella typhimurium
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(2RS,3RS)- and (2RS,3SR)-2,3-Dihydroxybutanoic acids, (2R,3R)-2,3-dihydroxy-3-methylpentanoic acid, (2RS)-2-ethyl-2,3-dihydroxypentanoic acid, (2RS,3RS)- and (2RS,3SR)-2,3-dihydroxy-3-methylhexanoic acids, and (2RS,3RS)- and (2RS,3SR)-2,3-dihydroxy-3-methylheptanoic acids were synthesised.These acids, as well as (RS)-2,3-dihydroxy-3-methylbutanoic acid and (RS)-glyceric acid were tested as substrates for the αβ-dihydroxyacid dehydratase of the isoleucine-valine biosynthetic pathway of Salmonella typhimurium.For acids having a propyl group at C-3, the activities were greatly reduced compared with those obtained for the natural substrates (2R,3R)-2,3-dihydroxy-3-methylpentanoic acid and (R)-2,3-dihydroxy-3-methylbutanoic acid .For acids having an n-butyl substituent at C-3, the activities were close to zero. (2RS,3SR)-2,3-Dihydroxybutanoic acid (threo isomer) underwent dehydration at a rate comparable with that of (2R,3R)-DHI, the natural substrate in the isoleucine pathway, whereas the (2RS,3RS)-acid (erythro-isomer) had much lower activity and (RS)-glyceric acid had even less activity.These results illustrate differences in the alkyl group requirements with respect to the areas of the binding site of the enzyme that accomodate the C-3 substituents.They also demonstrate the size limits of the alkyl groups that can be accomodated in substrate analogues.
- Armstrong, Frank B.,Lipscomb, Elizabeth L.,Crout, David H. G.,Morgan, Phillip J.
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p. 691 - 696
(2007/10/02)
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