- Oxidation of some aldopentoses by chloramine-B in alkaline medium: a kinetic and mechanistic study
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The oxidation kinetics of D-xylose, D-ribose, and L-arabinose by chloramine-B (CAB) in alkaline medium at 35 deg C obey the rate law, rate = ->.Based on the results, a mechanism is suggested involving the anion of the β anomer of the pentose.The addition of reaction products, benzenesulphonamide and NaCl, had no effect on the rate of reaction whereas increase in the ionic strength and dielectric constant of the medium increased the rate.Proton-inventory studies were made in H2O-D2O mixtures.The rate of oxidation of pentoses follows the order: D-xylose > D-ribose > L-arabinose.Kinetic and thermodynamic parameters for the reaction were computed from the Arrhenius plots.The isokinetic temperature β = 416 K, which is much above the experimental temperature, suggests enthalpy-controlled reactions.
- Iyengar, Tirumala A.,Puttaswamy,Mahadevappa, Dandinasivara S.
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Read Online
- Selective Conversion of Various Monosaccharaides into Sugar Acids by Additive-Free Dehydrogenation in Water
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Abundant sugars of five and six carbon atoms are promising candidates for the production of valuable platform chemicals. Here, we describe the catalytic dehydrogenation of several pentoses and hexoses into their corresponding sugar acids with the concomitant formation of molecular hydrogen. This biomass transformation is promoted by highly active and selective catalysts based on iridium(III) complexes containing a triazolylidene (trz) as ligand. Monosaccharides are converted into sugar acids in an easy and sustainable manner using only catalyst and water, and in contrast to previously reported procedures, in the absence of any additive. The reaction is therefore very clean, and highly selective, which avoids the tedious purification and product separation. Mechanistic investigations using 1H NMR and UV-vis spectroscopies and ESI mass spectrometry (ESI-MS) indicate the formation of an unprecedented diiridium-hydride as dormant species that correspond to the catalyst resting state.
- Mollar-Cuni, Andres,Byrne, Joseph P.,Borja, Pilar,Vicent, Cristian,Albrecht, Martin,Mata, Jose A.
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p. 3746 - 3752
(2020/06/01)
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- Upgrading of Biomass Monosaccharides by Immobilized Glucose Dehydrogenase and Xylose Dehydrogenase
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Direct upgrading and separation of the monosaccharides from biomass liquors is an overlooked area. In this work we demonstrate enzymatic production of gluconic acid and xylonic acid from glucose and xylose present in pretreated birchwood liquor by glucose dehydrogenase (GDH, EC 1.1.1.47) and xylose dehydrogenase (XDH, EC 1.1.1.175), respectively. The biocatalytic conversions were compared using two different kinds of silica support materials (silica nanoparticles (nanoSiO2) and porous silica particles with hexagonal pores (SBA 15 silica) for enzyme immobilization. Upon immobilization, both enzymes showed significant improvement in their thermal stability and robustness at alkaline pH and exhibited over 50 % activity even at pH 10 and 60 °C on both immobilization matrices. When compared to free enzymes at 45 °C, GDH immobilized on nanoSiO2 and SBA silica displayed a 4.5 and 7.25 fold increase in half-life, respectively, whilst XDH immobilized on nanoSiO2 and SBA showed a 4.7 and 9.5 fold improvement in half-life, respectively. Additionally, after five reaction cycles both nanoSiO2GDH and nanoSiO2XDH retained more than 40 % activity and GDH and XDH immobilized on SBA silica maintained around 50 % of their initial activity resulting in about 1.5–1.6 fold increase in biocatalytic productivity compared to the free enzymes.
- Zdarta, Jakub,Pinelo, Manuel,Jesionowski, Teofil,Meyer, Anne S.
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p. 5164 - 5173
(2018/10/25)
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- Aerobic oxidation of xylose to xylaric acid in water over pt catalysts
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Energy-efficient catalytic conversion of biomass intermediates to functional chemicals can make bio-products viable. Herein, we report an efficient and low temperature aerobic oxidation of xylose to xylaric acid, a promising bio-based chemical for the production of glutaric acid, over commercial catalysts in water. Among several heterogeneous catalysts investigated, Pt/ C exhibits the best activity. Systematic variation of reaction parameters in the pH range of 2.5 to 10 suggests that the reaction is fast at higher temperatures but high C C scission of intermediate C5-oxidized products to low carbon carboxylic acids undermines xylaric acid selectivity. The C C cleavage is also high in basic solution. The oxidation at neutral pH and 60 8C achieves the highest xylaric acid yield (64 %). O2 pressure and Pt amount have significant influence on the reactivity. Decar-boxylation of short chain carboxylic acids results in formation of CO2, causing some carbon loss; however, such decarboxyla-tion is slow in the presence of xylose. The catalyst retained comparable activity, in terms of product selectivity, after five cycles with no sign of Pt leaching.
- Sadula, Sunitha,Saha, Basudeb
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p. 2124 - 2129
(2018/10/20)
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- Highly selective photocatalytic oxidation of biomass-derived chemicals to carboxyl compounds over Au/TiO2
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Highly selective transformation of biomass-derived chemicals into value-added chemicals is of great importance. In this work, selective photooxidation of various biomass-derived chemicals, including ethanol, glucose, xylose, 2-furaldehyde, 5-hydroxymethyl-2-furfural, and furfuralcohol to the corresponding carboxyl compounds was studied using atmospheric air as the oxidant at ambient temperature. It was found that the reactions could be carried out efficiently over Au nanoparticles (AuNPs) supported on TiO2 (AuNPs/TiO2) under both ultraviolet (UV) and visible light in Na2CO3 aqueous solution. Under the optimized conditions, the selectivities for desired products were higher than 95% for all the reactions. Detailed studies indicated that the surface plasmon resonance of AuNPs and the band-gap photoexcitation of TiO2 were responsible for visible-light-responding and UV-light-responding activities, respectively. Na2CO3 acted as the promoter for the visible-light-induced oxidation and the inhibitor of reactive oxygen species with strong oxidation power under UV light.
- Zhou, Baowen,Song, Jinliang,Zhang, Zhanrong,Jiang, Zhiwei,Zhang, Pei,Han, Buxing
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p. 1075 - 1081
(2017/03/17)
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- Expanding the reaction space of aldolases using hydroxypyruvate as a nucleophilic substrate
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Aldolases are key biocatalysts for stereoselective C-C bond formation allowing access to polyoxygenated chiral units through direct, efficient, and sustainable synthetic processes. The aldol reaction involving unprotected hydroxypyruvate and an aldehyde offers access to valuable polyhydroxy-α-keto acids. However, this undescribed aldolisation is highly challenging, especially regarding stereoselectivity. This reaction was explored using, as biocatalysts, a collection of aldolases selected from biodiversity. Several enzymes that belong to the same pyruvate aldolase Pfam family (PF03328) were found to produce the desired hexulosonic acids from hydroxypyruvate and d-glyceraldehyde with complementary stereoselectivities. One of them was selected for the proof of concept as a biocatalytic tool to prepare five (3S,4S) aldol adducts through an eco-friendly process.
- De Berardinis, Véronique,Guérard-Hélaine, Christine,Darii, Ekaterina,Bastard, Karine,Hélaine, Virgil,Mariage, Aline,Petit, Jean-Louis,Poupard, Nicolas,Sánchez-Moreno, Israel,Stam, Mark,Gefflaut, Thierry,Salanoubat, Marcel,Lemaire, Marielle
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p. 519 - 526
(2017/08/14)
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- Aqueous oxidation of sugars into sugar acids using hydrotalcite-supported gold nanoparticle catalyst under atmospheric molecular oxygen
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Hydrotalcite-supported gold nanoparticles show good activity as a heterogeneous catalyst for the oxidation of monosaccharides (xylose, ribose, galactose and mannose) and disaccharides (lactose and cellobiose) into the corresponding sugar acids under external base-free conditions in water solvent using atmospheric pressure of molecular oxygen. The produced sugar acids were thoroughly identified by 1H-, 13C-, and HMQC-NMR and ESI-FT-ICR MS spectroscopic techniques.
- Tomar, Ravi,Sharma, Jatin,Nishimura, Shun,Ebitani, Kohki
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supporting information
p. 843 - 845
(2016/07/16)
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- Solid base supported metal catalysts for the oxidation and hydrogenation of sugars
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Pt impregnated on γ-Al2O3 (acidic support) and hydrotalcite (basic support) catalysts were synthesized, characterized and used in the oxidation and hydrogenation reactions of C5 and C6 sugars. In the absence of homogeneous base, 83% yield for gluconic acid; an oxidation product of glucose can be achieved over Pt/hydrotalcite (HT) catalyst at 50 °C under atmospheric oxygen pressure. Similarly, 57% yield for xylonic acid, an oxidation product of xylose is also possible over Pt/HT catalyst. Hydrogenation of glucose conducted using Pt/γ-Al2O3 + HT catalytic system showed 68% sugar alcohols (sorbitol + mannitol) formation. The 82% yield for C5 sugar alcohols (xylitol + arabitol) was obtained by subjecting xylose to hydrogenation over Pt/γ-Al2O3 + HT at 60 °C. UV analysis helped to establish the fact that under alkaline conditions sugars prefer to remain in open chain form in the solution and thus exposes CHO group which further undergoes oxidation and hydrogenation reactions to yield acids and alcohols.
- Tathod, Anup,Kane, Tanushree,Sanil,Dhepe, Paresh L.
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- Solubilization, purification, and properties of membrane-bound D-glucono-δ-lactone hydrolase from Gluconobacter oxydans
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Membrane-bound glucono-δ-lactonase (MGL) was purified to homogeneity from the membrane fraction of Gluconobacter oxydans IFO 3244. After solubilization with 1 M CaCl2, MGL was purified in the presence of Ca2+ and detergent. A single
- Shinagawa, Emiko,Ano, Yoshitaka,Yakushi, Toshiharu,Adachi, Osao,Matsushita, Kazunobu
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body text
p. 241 - 244
(2009/06/20)
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- NOVEL REACTION WITH A GOLD CATALYST
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The invention relates to a process for the catalytic conversion of a carbohydrate, an alcohol, an aldehyde or a polyhydroxy compound in the presence of a catalyst containing gold in a solvent.
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Page/Page column 21-23
(2009/01/24)
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- Kinetics and mechanism of oxidation of some aldoses by hexacyanoferrate(III) ions in aqueous alkaline buffered medium
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Kinetics of oxidation of some aldoses like glucose, galactose, xylose and ribose by hexacyanoferrate(III) ions in aqueous alkaline buttered medium has been investigated. The kinetic results indicate the zero-order kinetics in hexacyanoferrate(III) and first-order in aldoses and OH-. The ionic strength of the medium has no influence on oxidation rate. Various activation parameters were also calculated at four different temperatures : 30, 35, 40 and 45°C. The corresponding acids were identified as the main oxidation products of the reaction. A suitable mechanism consistent with experimental findings has been proposed.
- Goel, Anjali,Shailja,Ruchi
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experimental part
p. 286 - 289
(2009/06/25)
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- HYDROGENATION PROCESS
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The invention relates to an improved process for the production of a sugar alcohol from the corresponding sugar through catalytic hydrogenation. Especially, the invention relates to a process for reducing the interference of sugar-derived aldonic acids in the hydrogenation process by adjusting the hydrogenation conditions so that the activity of the catalyst is maintained. In one embodiment of the invention, the process of the invention is carried out by adjusting the hydrogenation temperature by starting the hydrogenation at a lower temperature and then gradually rising the temperature to the final hydrogenation temperature. In another embodiment of the invention, the process of the invention is carried out by adding small-molecular monocarboxylic acids to the hydrogenation solution.
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Page/Page column 26-27
(2008/06/13)
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- Inhibition effect of {surfactant-substrate} aggregation on the rate of oxidation of reducing sugars by alkaline hexacyanoferrate(III)
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The effect of cationic (cetyltrimethylammonium bromide, CTAB), anionic (sodium lauryl sulfate, NaLS), and nonionic (Brij-35) surfactants on the rate of oxidation of some reducing sugars (xylose, glucose, and fructose) by alkaline hexacyanoferrate(III) has been studied in the temperature range from 35 to 50°C. The rate of oxidation is strongly inhibited in the presence of surfactant. The inhibition effect of surfactant on the rate of reaction has been observed below critical micelle concentration (CMC) of CTAB. In case of NaLS and Brij-35, the inhibition effect was above CMC, at which the surfactant abruptly associates to form micelle. The kinetic data have been accounted for by the combination of surfactant molecule(s) with a substrate molecule in case of CTAB and distribution of substrate into micellar and aqueous pseudophase in case of NaLS and Brij-35. The binding parameters (binding constants, partition coefficients, and free-energy transfer from water to micelle) in case of NaLS and Brij-35 have been evaluated with the help of Menger and Portnoy model reported for micellar inhibition.
- Shukla, Ratna,Upadhyay, Santosh K.
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p. 595 - 604
(2008/09/17)
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- Structure of a new ribitol teichoic acid-like O-polysaccharide of a serologically separate Proteus vulgaris strain, TG 276-1, classified into a new Proteus serogroup O53
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An unusual ribitol teichoic acid-like O-polysaccharide was isolated by mild acid degradation of the lipopolysaccharide from a previously non-classified Proteus vulgaris strain TG 276-1. Structural studies using chemical analyses and 2D 1H and 13C NMR spectroscopy showed that the polysaccharide is a zwitterionic polymer with a repeating unit containing 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (d-FucNAc4N) and two d-ribitol phosphate (d-Rib-ol-5-P) residues and having the following structure:{A figure is presented}where the non-glycosylated ribitol residue is randomly mono-O-acetylated. Based on the unique O-polysaccharide structure and the finding that the strain studied is serologically separate among Proteus bacteria, we propose to classify P. vulgaris strain TG 276-1 into a new Proteus serogroup, O53.
- Arbatsky, Nikolay P.,Kondakova, Anna N.,Senchenkova, Sof'ya N.,Siwinska, Malgorzata,Shashkov, Alexander S.,Zych, Krystyna,Knirel, Yuriy A.,Sidorczyk, Zygmunt
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p. 2061 - 2066
(2008/02/10)
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- Beneficiated water reducing compositions
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Exemplary compositions comprise at least one aldopentonic acid, such as xylonic acid; and further comprise a lignin, a lignosulfonic acid or its salt, an additional sugar acid such as a aldohexonic acid or salt, a conventional admixture (such as a polyacrylate superplasticizer, a corrosion inhibitor, a set retard, a set accelerator, etc.), or a mixture thereof. Exemplary methods for obtaining microbiologically or enzymatically converted sugar acids are also described herein.
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Page/Page column 8
(2008/06/13)
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- Kinetics and mechanism of oxidation of D-fructose and D-glucose by sodium salts of N-(chloro)-mono/di-substituted benzenesulfonamides in aqueous alkaline medium
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In an effort to introduce N-chloroarylsulfonamides of different oxidizing strengths, nine sodium salts of mono- and di-substituted N- chloroarylsulfonamides are employed as oxidants for studying the kinetics of oxidation of D-fructose and D-glucose in aqueous alkaline medium. The results are analyzed along with those by the sodium salts of N-chlorobenzenesulfonamide and N-chloro-4-methylbenzenesulfonamide. The reactions show first-order kinetics each in [oxidant], [Fru/Glu], and [OH-]. The rates slightly increase with increase in ionic strength of the medium. Further, the rate of oxidation of fructose is higher by 4 to 5 times than that of the glucose oxidation, by the same oxidant. Similarly, Ea values for glucose oxidations are higher by about 1.5 times the Ea values for fructose oxidations. The results have been explained by a plausible mechanism, and the related rate law deduced. The significant changes in the kinetics and thermodynamic data are observed with change of substituent in the benzene ring. It is because Cl + is the effective oxidizing species in the reactions of N-chloroarylsulfonamides. The oxidative strengths of the latter therefore depend on the ease with which Cl+ is released from them. The ease with which Cl+ is released from N-chloroarylsulfonamides depends on the electron density of the nitrogen atom of the sulfonamide group, which in turn depends on the nature of the substituent in the benzene ring. The following Hammett equations are valid for the oxidation of fructose and glucose, log kobs = -3.13 + 0.54 σ ρ and log kobs = -3.81 + 0.28 σ ρ, respectively. The enthalpies and entropies of activations for oxidations by all the N-chloroarylsulfonamides correlate well with isokinetic temperatures of 301 K and 299 K, for fructose and glucose oxidations, respectively. The effect of substitution in the oxidants on the Ea and log A for the oxidations is also considered.
- Gowda, B. Thimme,Damodara,Jyothi
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p. 572 - 582
(2007/10/03)
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- Microbial Synthesis of the Energetic Material Precursor 1,2,4-Butanetriol
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The lack of a route to precursor 1,2,4-butanetriol that is amenable to large-scale synthesis has impeded substitution of 1,2,4-butanetriol trinitrate for nitroglycerin. To identify an alternative to the current commercial synthesis of racemic D,L-1,2,4-butanetriol involving NaBH4 reduction of esterified D,L-malic acid, microbial syntheses of D- and L-1,2,4-butanetriol have been established. These microbial syntheses rely on the creation of biosynthetic pathways that do not exist in nature. Oxidation of D-xylose by Pseudomonas fragi provides D-xylonic acid in 70% yield. Escherichia coli DH5α/pWN6.186A then catalyzes the conversion of D-xylonic acid into D-1,2,4-butanetriol in 25% yield. P. fragi is also used to oxidize L-arabinose to a mixture of L-arabino-1,4-lactone and L-arabinonic acid in 54% overall yield. After hydrolysis of the lactone, L-arabinonic acid is converted to L-1,2,4-butanetriol in 35% yield using E. coli BL21(DE3)/pWN6.222A. As a catalytic route to 1,2,4-butanetriol, microbial synthesis avoids the high H2 pressures and elevated temperatures required by catalytic hydrogenation of malic acid. Copyright
- Niu, Wei,Molefe, Mapitso N.,Frost
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p. 12998 - 12999
(2007/10/03)
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- Ruthenium (III) catalysis of periodate oxidation of reducing sugars in aqueous alkaline medium
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The ruthenium (III) catalysis of periodate oxidation of D-ribose, D-sorbose and maltose in aqueous alkaline medium has been investigated. The reactions have been found to be zero order with respect to each reducing sugar and first order with respect to ruthenium (III). The linear dependence of the reaction rate at lower concentrations of periodate ion and hydroxide ion tends towards zero order at their higher concentrations. Positive effect of [Cl -] on the rate of reaction has also been observed. The observed kinetics with periodate ion, under the conditions [IO4 -]〉〉[Ru(III)]T suggests the formation of a 1:1 complex between Ru(III) and periodate in the rate controlling step, which subsequently interacts with reactive species of reducing sugar to give the final products, through a series of fast steps. The rate law is derived.
- Singh, Ashok Kumar,Gupta, Neena,Rahmani, Shahla,Singh, Vinod Kumar,Singh, Bharat
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p. 1871 - 1875
(2007/10/03)
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- Oxidation of threose-series, pentose and hexoses by N-arylbromosulphonamides in alkaline medium
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Kinetic studies of the oxidation of D-galactose, L-sorbose and D-xylose by bromamine-T (sodium-N-bromo-p-toluenesulphonamide or BAT) and bromamine-B (sodium-N-bromobenzene sulphonamide or BAB) in alkaline medium has been investigated at 303 K. The rate of the reaction is first order both with respect to oxidant and sugar, and second order with respect to [HO-]. The addition of the reaction product p-toluenesulphonamide (PTS) or benzenesulphonamide (BSA) and the variation of ionic strength of the medium have no effect on the rate. The rate decreases with the decrease in dielectric constant of the medium and values of dAB, the size of activated complex are calculated. Proton inventory studies in H2O · D2O mixtures suggest a single transition state. Product analysis for D-galactose, L-sorbose and D-xylose reveal that hexoses give mainly mixture of lyxonic and threonic acids with minor proportions of hexonic, xylonic and glyceric acids, whereas xylose yields a mixture of lyxonic, threonic and glyceric acids with minor amounts of xylonic and hexonic acids. From the results of kinetic studies, reaction stoichiometry and product analysis, a possible mechanism for the oxidation of threose-series sugars is suggested.
- Shashikala,Rangappa
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p. 1907 - 1914
(2007/10/03)
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- A novel mechanism for the oxidation of erythro-series pentoses and hexoses by N-arylbromosulphonamides in alkaline medium
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Kinetic studies of the oxidation of D-mannose, D-glucose, D-fructose, L-arabinose and D-ribose by bromamine-T (sodium N-bromo-p-toluenesulphonamide or BAT) and bromamine-B (sodium N-bromobenzenesulphonamide or BAB) in alkaline medium were investigated at 30°C. The rate of the reaction was first order both with respect to the oxidant and the sugar and second order with respect to [HO-]. The addition of the reaction product, p-toluenesulphonamide (PTS) or benzenesulphonamide (BSA), and the variation of ionic strength of the medium have no effect on the rate. The rate decreases with decrease in dielectric constant of the medium and values of dAB, the size of activated complex, were calculated. Proton inventory studies were made in H2O-D2O mixtures. The activation parameters of the reaction were computed from Arrhenius plots. HPLC and GLC-MS analysis of the products indicated that the sugars were oxidized to a mixture of aldonic acids consisting of arabinonic, ribonic, erythronic and glyceric acids. A general mechanism consistent with the observed results has been proposed.
- Shashikala,Rangappa
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p. 219 - 234
(2007/10/03)
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- Kinetics and mechanism of oxidation of hexoses by bromamine-T in alkaline medium
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The kinetics and mechanism of oxidation of D-glucose and D-mannose with bromamine-T in alkaline medium have been studied and the rate = κ[BAT][sugar][OH-]2, is observed. The rate of the reaction is influenced by a change in ionic strength of the medium and the dielectric effect is found to be positive. The latter enables the computation of dAB, the size of the activated complex. Proton inventory studies are made for the reactions in H2O-D2O mixtures. Activation parameters are calculated from the Arrhenius plots. The product analyses indicates that the sugars are oxidized to a mixture of aldonic acids, consisting of arabinonic, ribonic, erythronic and glyceric acids. A mechanism consistent with the observed kinetics has been proposed.
- Prashanth,Mantelingu,Murthy, A. S. Ananda,Anitha,Rangaswamy,Rangappa
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p. 241 - 245
(2007/10/03)
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- Reactivity of some sugars and sugar phosphates towards gold(III) in sodium acetate-acetic acid buffer medium
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The kinetics of the oxidation of some aldoses and aldose phosphates have been studied spectrophotometrically in sodium acetate-acetic acid buffer medium at different temperatures. The reactions are first order with respect to [Au(III)] and [substrate]. Both H+ and Cl- ions retard the reaction. The reactions appear to involve different gold(III) species, viz. AuCl4/-, AuCl3(OH2) and AuCl3(OH)-. The results are interpreted in terms of the probable intermediate formation of free radicals and Au(II). Aldoses react with gold(III) in the order: triose > tetrose > pentose > hexose. The sugar phosphates react with gold(III) at a faster rate than the parent sugars except glucose-1-phosphate, which reacts at slower rates than glucose. A tentative reaction mechanism leading to the formation of products has been suggested.
- Sen Gupta, Kalyan Kali,Pal, Biswajit,Begum, Bilkis Ara
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p. 115 - 123
(2007/10/03)
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- Kinetics and mechanism of the oxidation of some aldoses, amino sugars and methylated sugars by tris(pyridine-2-carboxylato)manganese(III) in weakly acidic medium
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The kinetics of oxidation of some aldoses, amino sugars and methylated sugars by tris(pyridine-2-carboxylato)manganese(III) have been studied spectrophotometrically in sodium picolinate -picolinic acid buffer medium. The reactions are first order with respect to both manganese(III) and sugar concentrations, but independent with respect to sodium picolinate - picolinic acid buffer medium. The mechanism for the reactions is discussed.
- Gupta, Kalyan Kali Sen,Begum, Bilkis Ara
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- Method for producing xylitol
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The invention relates to a method for producing xylitol from a material containing xylose and xylonic acid. According to the method, xylose and xylonic acid are separated from the material containing xylose and xylonic acid, whereafter the separated xylose and xylonic acid are reduced to xylitol, and the xylitol is recovered.
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- Oxidation of erythrose series sugars by sodium N-chlorobenzenesulphonamide in alkaline medium : A kinetic study
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The kinetics of oxidation of D-glucose, D-mannose, D-fructose, D-arabinose, and D-ribose, with sodium N-chlorobenzenesulphonamide (chloramine-B or CAB) in alkaline medium have been studied at 35°C and the rate law, rate = κ′ [CAB] [Sugar] [OH-]2 is observed. The rate of reaction is influenced by a change in ionic strength of the medium, and the dielectric effect is negative. The solvent isotope studies in D2O show that the rate is almost doubled in heavy water. HPLC and GLC-MS analyses of the products indicated that the erythrose-series sugars are oxidized to a mixture of aldonic acids consisting of arabinonic, ribonic, erythronic, and glyceric acids in varying proportions. Based on these data, a mechanism involving the aldoenolic anions of pentoses and keto-enolic anions of hexoses is suggested.
- Raghavendra,Rangappa,Mahadevappa,Channe Gowda
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p. 783 - 792
(2007/10/03)
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- Sodium N-Chlorobenzenesulfonamide as a Selective Oxidant for Hexosamines in Alkaline Medium: A Kinetic and Mechanistic Study
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Oxidation of D-mannosamine (1), D-glucosamine (2), and D-galctosamine (3) by sodium N-chlorobenzenesulfonamide or chloramine-B (CAB) at 313 K is followed by a shortening of carbon chain and obeys the rate law, rate = k[CAB][sugar][HO-]x, where x is less than unity. The products are arabinonic acid, ribonic acid, and erythronic acid for 1 and 2 with smaller amounts of glyceric and hexonic acids, while lyxonic and threonic acids are predominant in the oxidation of 3 with smaller amounts of glyceric and hexonic acids. Proton inventory studies made in a H2)O-D2)O mixture point toward a single transition state. In the proposed mechanism the alkoxy anion (S-) of the hexosamine formed in a base-catalyzed reaction at C-1 carbon is subjected to an electrophilic rate-limiting attack by Cl+ of the oxidant. The hexonic acid formed is decarboxylated with loss of ammonia to form the respective pentose, which is further converted into the corresponding pentonic acid. The breaking of the bond between C-1 and C-2 carbons in pentose yields tetronic acids. The thermodynamic parameters for sugar alkoxy anion formation and activation parameters for the rate-limiting step have been evaluated.
- Rangappa, Kanchugarakoppal S.,Raghavendra, Manikanahally P.,Mahadevappa, Dandinasivara S.,Channegowda, Doddegowda
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p. 531 - 536
(2007/10/03)
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- Kinetics and mechanism of oxidation of erythro-series pentoses and hexoses by N-chloro-p-toluenesulfonamide
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The kinetics and mechanism of oxidation of D-glucose, D-mannose, D- fructose, D-arabinose, and D-ribose with chloramine-T in alkaline medium were studied. The rate law, rate = k [Chloramine-T] [Sugar] [HO-]2, was observed. The rate of the reaction was influenced by a change in ionic strength of the medium, and the dielectric effect was found to be negative. The latter enabled the computation of d(AB), the size of the activated complex. The reaction rate was almost doubled in deuterium oxide. Activation energies were calculated from the Arrhenius plots. HPLC and GLC-MS analyses of the products indicated that the sugars were oxidized to a mixture of aldonic acids, consisting of arabinonic, ribonic, erythronic, and glyceric acids. Based on these data, a plausible mechanism involving the aldo-enolic anions of pentoses and keto-enolic anions of hexoses is suggested.
- Rangappa, Kanchugarakoppal S.,Raghavendra, Manikanahally P.,Mahadevappa, Dandinasivara S.,Gowda, D. Channe
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- Kinetics and mechanism of oxidation of D-mannosamine by sodium N-chloro-p-toluenesulphonamide in alkaline medium
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The kinetics of oxidation of D-mannosamine (S) to the aldonic acids by sodium N-chloro-p-toluenesulphonamide or chloramine-T (CAT) in the presence of alkali at 40°C follows the rate law d[CAT]/dt=k[CAT] [S] [HO-]x, where x2O)/k(H2O) was found to be 1.62. The mechanism assumes stepwise, the formation of sugar alkoxy anion, followed by a rate limiting complexation with oxidant resulting in the formation of the respective pentose through decarboxylation and deammation. The latter is oxidised to arabonic, ribonic, erythronic and glyceric acids. A mechanism involving the reaction of enolanion of sugar with the oxidant in the rate limiting step is proposed.
- Rangappa,Mahadevappa,Raghavendra
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p. 890 - 896
(2007/10/03)
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- Pd(II) inhibition during hexacyanoferrate (III) oxidation of sugars: a kinetic study
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An inhibition effect of PdCl2 on the rate of oxidation of sugars, by alkaline hexacyano-ferrate(III) has been observed. The order of reactions in hexacyanoferrate(III) and OH- is zero and unity, respectively, while that in sugars decreases from unity at higher sugar concentration. The kinetic data and spectrophotometric evidence support the formation of {PdII - (sugar)} and {PdII - sugar)2} complexes and their resistance to react with Fe(CN)63-.
- Bajpai,Shukla,Upadhyay
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p. 413 - 419
(2007/10/03)
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- Spectroscopic, crystallographic and computational studies of the formation and isomerization of cyclic acetals and ketals of pentonolactones
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The different reactivities of D-ribonolactone, L-arabinonolactone, D-xylonolactone, D-lyxonolactone and 2-deoxy-D-ribonolactone toward benzaldehyde and acetone in acidic media, were examined. The reactions involved complex equilibria and were investigated with extensive 13C NMR studies as well as X-ray crystallographic analysis of selected products. Molecular mechanics (MM2) and semiempirical (PM3 and AM1) calculations of some derivatives were carried out in order to facilitate structural and conformational assignments. The differences in reactivity observed for the reactions of D-pentono-1,4-lactones with benzaldehyde and acetone are rationalized in terms of their structural and conformational features.
- Han,Joullie,Fokin,Petasis
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p. 2535 - 2562
(2007/10/02)
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- Kinetics and mechanism of oxidation of monosaccharides by sodium-N-bromobenzenesulphonamide in alkaline medium
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Kinetic studies of the oxidation of D-fructose, D-glucose, D-galactose, D-mannose, D-xylose, D-ribose, D-lyxose and D-arabinose by bromamine-B (sodium-N-bromobenzene sulphonamide, BAB) have been carried out in alkaline medium at 30 deg.The reaction shows a zero order dependence on 0 and fractional orders in 0 and ->0.The rates tend to level off at higher 0 and ->0.Variation in ionic strength of the medium, and the addition of benzene sulphonamide, Cl- and Br- ions do not alter the rate while lowering the dielectric constant of the medium increases the rate slightly.Solvent isotope and proton-inventory studies have been made.Enolization rate coefficients and activation parameters for the rate limiting step have been determined from Michaelis-Menten type of plots.A probable scheme for the oxidation of monosaccharides through a common intermediate, 1,2-enediol has been proposed.
- Iyengar, T. Asha,Mahadevappa, D. S.
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p. 838 - 844
(2007/10/02)
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- Kinetics and Mechanism of Oxidation of Some Aldoses by Chromium Peroxydichromate in very Dilute Sulphuric Acid
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The oxidation of D-galactose, D-xylose and L-arabinose by chromium peroxydichromate has been studied in very dilute sulphuric acid (0.12-0.066 N).The reaction is of first order each in substrate, oxidant and sulphuric acid.HCrO4- ion appears to be the predominant oxidant.Neutral salts and Mn(II) have retarding effect on the reaction.A mechanism which is consistent with the observed rate laws and experimental facts has been proposed.
- Sharma, K.,Sharma, V. K.,Rai, R. C.
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p. 747 - 749
(2007/10/02)
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- CATALYTIC DEHYDROGENATION OF REDUCING SUGARS IN ALKALINE SOLUTION
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Aldoses in alkaline medium under the catalytic action of platinum of rhodium are converted into aldonic acids with high selectivity and with concomitant evolution of hydrogen gas.The dehydrogenation reaction has been studied for 25 different mono- and di-saccharides, and is generally applicable for reducing sugars.The influence of several reaction variables has been studied, leading to an adsorption model in which both the negatively charged O-1 and the close contact of H-1 with the catalyst surface are considered to be driving forces for the transfer of hydride from C-1 of the sugar to the catalyst.
- Wit, Gert de,Vlieger, Jan J. de,Dalen, Alida C. Kock-van,Heus, Roelf,Laroy, Rob,et al.
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p. 125 - 138
(2007/10/02)
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