A kinetic study of D-glucose oxidation by bromine in aqueous solutions

The kinetics of the oxidation of D-glucose to D-gluconic acid by bromine in aqueous solution were studied using potentiometric techniques and theoretical considerations of complex bromine-bromide-pH equilibria. The pH has a strong influence on reaction rate. At pH < 8 the reaction is very slow, while in the pH range pH 8-9.5 the reaction is sufficiently fast and seems optimal for the reaction. The proposed active species at that pH region is hypobromous acid. At pH > 9.5, the reaction is further accelerated due to the formation of hypobromite. The proposed kinetics expression for gluconic acid formation, based on the determined kinetic parameters at pH 9.24, is of the form dc(GA)/dt = 160c(2)(G)c(o)(HOBr)c(o)(H(+)c(o)(Br)     

Anomeric selectivity in the synthesis of galloyl esters of d-glucose

The anomeric selectivity of the ester formation between d-glucopyranose and gallic acid was investigated under a variety of conditions. A new protocol was established that allows performing the reaction under conditions where mutarotation is very slow. Highly α- or β-selective transformations are possible when starting with α- or β-d-glucopyranose, respectively. Due to the kinetic anomeric effect, a high α-selectivity is more difficult to achieve than a high β-selectivity. The new methodology presented in this article was compared with established procedures for the synthesis of gallotannins. In addition to the advantages of a high yield and an easy purification protocol, the new procedure uniquely allowed for a highly selective synthesis of α-products.     

Synthesis and structural analysis of a series of d-glucose derivatives as low molecular weight gelators

Low molecular weight gelators are an interesting new type of compounds that are important in supramolecular chemistry and advanced materials. Previously, we had synthesized several acyl derivatives of methyl 4,6-O-benzylidene-α-d-glucopyranoside and found that a number of terminal acetylene-containing esters are good gelators. To understand the structure requirement of the acyl chains, we synthesized a series of analogs containing different functional groups including aryl, alkenyl, and halogen derivatives. X-ray crystal structures of a monoester and a diester derivative were also obtained to help understand the relationship between structure and gelation. For good gelation properties, the carboxyl derivatives should possess alkyl groups containing a terminal acetylene group and aryl derivatives.     

Polyamidoamine dendrimer as a spacer for the immobilization of glucose oxidase in capillary enzyme microreactor

Polyamidoamine dendrimer (PAMAM) is one of a number of dendritic polymers with precise molecular structure, highly geometric symmetry, and a large number of terminal groups. In this study, different generations of PAMAM (G0-G4) were introduced onto the inner wall of fused-silica capillaries by microwave irradiation and a new type of glucose oxidase (GOx) capillary enzyme microreactor was developed based on enzyme immobilization in the prepared PAMAM-grafted fused-silica capillaries. The optimal enzymolysis conditions for β-d-glucose in the microreactor were evaluated by capillary zone electrophoresis. In addition, the enzymolysis efficiencies of different generations of PAMAM-GOx capillary enzyme microreactor were compared. The results indicate that enzymolysis efficiency increased with increasing generations of PAMAM. The experimental results provide the possibility for the development and application of an online immobilized capillary enzyme microreactor.     

Efficient one-pot enzymatic synthesis of α-(1→4)-glucosidic disaccharides through a coupled reaction catalysed by Lactobacillus acidophilus NCFM maltose phosphorylase

Lactobacillus acidophilus NCFM maltose phosphorylase (LaMalP) of glycoside hydrolase family 65 catalysed enzymatic synthesis of α-(1→4)-glucosidic disaccharides from maltose and five monosaccharides in a coupled phosphorolysis/reverse phosphorolysis one-pot reaction. Thus phosphorolysis of maltose to β-glucose 1-phosphate circumvented addition of costly β-glucose 1-phosphate for reverse phosphorolysis with different monosaccharide acceptors, resulting in 91%, 89%, 88%, 86% and 84% yield of α-d-glucopyranosyl-(1→4)-N-acetyl-d-glucosaminopyranose [N-acetyl-maltosamine], α-d-glucopyranosyl-(1→4)-d-glucosaminopyranose [maltosamine], α-d-glucopyranosyl-(1→4)-d-mannopyranose, α-d-glucopyranosyl-(1→4)-l-fucopyranose and α-d-glucopyranosyl-(1→4)-d-xylopyranose, respectively, from 0.1 M maltose, 0.5 M N-acetyl glucosamine, 0.1 M glucosamine, 0.1 M mannose, 1 M l-fucose and 0.5 M xylose in 0.2 M phosphate-citrate pH 6.2. These current yields of 0.27-0.34 g of disaccharide products from 10 mL reaction mixtures are easy to scale up and moreover the strategy can be applied to large-scale production of other oligosaccharides from low-cost disaccharides as catalysed by phosphorylases with different substrate specificities.     

Melting behaviour of D-sucrose, D-glucose and D-fructose

The melting behaviour of d-sucrose, d-glucose and d-fructose was studied. The melting peaks were determined with DSC and the start of decomposition was studied with TG at different rates of heating. In addition, melting points were determined with a melting point apparatus. The samples were identified as d-sucrose, alpha-d-glucopyranose and beta-d-fructopyranose by powder diffraction measurements. There were differences in melting between the different samples of the same sugar and the rate of heating had a remarkable effect on the melting behaviour. For example, T(o), DeltaH(f) and T(i) (initial temperature of decomposition) at a 1 degrees Cmin(-1) rate of heating were 184.5 degrees C, 126.6Jg(-1) and 171.3 degrees C for d-sucrose, 146.5 degrees C, 185.4Jg(-1) and 152.0 degrees C for d-glucose and 112.7 degrees C, 154.1Jg(-1) and 113.9 degrees C for d-fructose. The same parameters at 10 degrees Cmin(-1) rate of heating were 188.9 degrees C, 134.4Jg(-1) and 189.2 degrees C for d-sucrose, 155.2 degrees C, 194.3Jg(-1) and 170.3 degrees C for d-glucose and 125.7 degrees C, 176.7Jg(-1) and 136.8 degrees C d-fructose. At slow rates of heating, there were substantial differences between the different samples of the same sugar. The melting point determination is a sensitive method for the characterization of crystal quality but it cannot be used alone for the identification of sugar samples in all cases. Therefore, the melting point method should be validated for different sugars.     

A facile synthesis of (1S,5R,6S)-5-azido-6-benzyloxycyclohex-2-en-1-ol

A facile and short synthesis of (1S,5R,6S)-5-azido-6-benzyloxycyclohex-2-en-1-ol (1) has been achieved in high yield starting from 4,5-epoxycyclohex-1-ene by using a catalytic asymmetric allylic oxidation reaction.     

Kinetic studies on the loss of water from α-d-glucose monohydrate

Although the dehydration of α-d-glucose monohydrate is an important aspect of several industrial processes, there is uncertainty with regard to the applicable rate law and other factors that affect dehydration. Therefore, the dehydration of three glucose monohydrate samples has been studied using isothermal gravimetric analysis. Dehydration follows a one-dimensional contraction (R1) rate law for the majority of kinetic runs, and an activation energy of 65.0 ± 3.9 kJ mol⁻¹ results when the rate constants are fitted to the Arrhenius equation. Fitting the rate constants to the Eyring equation results in values of 62.1 ± 3.7 kJ mol⁻¹ and −77.8 ± 4.7 J mol⁻¹ K⁻¹ for ΔH^‡ and ΔS^‡, respectively. The impedance effect on the loss of water vapor has also been investigated to determine the values for activation energy, enthalpy, and entropy for diffusion of water. The results obtained for the activation parameters are interpreted in terms of the absolute entropies of anhydrous glucose and the monohydrate.     

大鼠肌肉神经白介素纯化和生化特性及其与磷酸葡萄糖异位酶的关系

通过硫酸铵沉淀、DE_(52)层析、超滤和高压羟基磷灰石层析,从大鼠肌肉条件培养液中得到电泳纯的神经白介素(NLK)。未发现NLK的神经营养活性(维持鸡胚背根神经元存活和促进脊髓神经元突起伸展)及免疫活性(促进外周血单个核细胞产生免疫球蛋白),却有较强的6-磷酸葡萄糖异位酶(GPI)活性。SDS-PAGE测得亚基分子量为56kD;IEF示五条细而相距很近的带,PⅠ值分别为8.20,8.15,8.10,7.90,7.75。Western Blot证实,PAGE和IEF的五条带均可与抗GPI抗体结合,即五种同工酶形式;NLK与GPI的氨基酸组成相近,BrCN水解NLK和GPI得剖相同的肽谱。许多研究表明:NLK不作为一种神经营养因子,而可能是糖酵解酶,即6-磷酸葡萄糖异位酶。     

Regulation of the utilization of glucose and aromatic substrates in four strains of Pseudomonas putida

During the oxidation of various mixtures of glucose and aromatic substrates by four strains of Pseudomonas putida, diauxic growth was not observed. Strain A3.12 grew faster on benzoate than on glucose, whereas three other strains showed faster growth on glucose than on the aromatic test substrates. Growth rates on mixtures of glucose and aromatics were intermediate between those on the single substrates.The presence of glucose in media containing aromatic substrates accelerated in the bacteria the appearance of the ability to oxidize aromatic substrates. During growth of the organisms on binary mixtures of aromatics, simultaneous utilization of these compounds occurred, the utilization ratio depending on the quality of the compounds as carbon and energy sources. Addition of glucose to dual aromatic substrate media greatly increased the utilization ratio in favour of the better aromatic substrate.With decreasing concentration of glucose in relation to that of aromatic substrates, the rate of carbon assimilation from glucose increased. Enzymological and radiochemical studies demonstrated that even in the presence of an excess of aromatic substrates, glucose was exclusively catabolized via the 2-keto-3-deoxy-6-phosphogluconate pathway. In contrast, the rate of carbon assimilation from ¹⁴C-ring-labelled benzoate and anisate was unaffected by the presence of an excess of glucose.Abbreviations KDPG 2-keto-3-deoxy-6-phosphogluconate - PP pentose-phosphate - OD optical density