- Titania-supported gold nanoparticles as efficient catalysts for the oxidation of cellobiose to organic acids in aqueous medium
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Titania-supported gold nanoparticles were prepared by using the deposition-precipitation method, followed by reduction under a hydrogen flow. The catalytic activity of these as-prepared catalysts was explored in the oxidation of cellobiose to gluconic acid with molecular oxygen, and the properties of these catalysts were examined by using XRD, TEM, temperature-programmed desorption of NH3, energy-dispersive X-ray spectroscopy, UV/Vis, and X-ray photoemission spectroscopy (XPS). The catalyst sample reduced at high temperature demonstrated an excellent catalytic activity in the oxidation of cellobiose. The characterization results revealed the strong metal-support interaction between the gold nanoparticles and titania support. Hydrogen reduction at higher temperatures (usually >600C) plays a vital role in affording a unique interface between gold nanoparticles and titania support surfaces, which thus improves the catalytic activity of gold/titania by fine-tuning both the electronic and structural properties of the gold nanoparticles and titania support.
- Amaniampong, Prince N.,Li, Kaixin,Jia, Xinli,Wang, Bo,Borgna, Armando,Yang, Yanhui
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Read Online
- Product Control and Insight into Conversion of C6 Aldose Toward C2, C4 and C6 Alditols in One-Pot Retro-Aldol Condensation and Hydrogenation Processes
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Alcohols have a wide range of applicability, and their functions vary with the carbon numbers. C6 and C4 alditols are alternative of sweetener, as well as significant pharmaceutical and chemical intermediates, which are mainly obtained through the fermentation of microorganism currently. Similarly, as a bulk chemical, C2 alditol plays a decisive role in chemical synthesis. However, among them, few works have been focused on the chemical production of C4 alditol yet due to its difficult accumulation. In this paper, under a static and semi-flowing procedure, we have achieved the product control during the conversion of C6 aldose toward C6 alditol, C4 alditol and C2 alditol, respectively. About C4 alditol yield of 20 % and C4 plus C6 alditols yield of 60 % are acquired in the one-pot conversion via a cascade retro-aldol condensation and hydrogenation process. Furthermore, in the semi-flowing condition, the yield of ethylene glycol is up to 73 % thanks to its low instantaneous concentration.
- Gao, Lou,Hou, Wenrong,Hui, Yingshuang,Tang, Yi,Zhan, Yulu,Zhang, Yahong
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p. 560 - 566
(2021/06/25)
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- PROCESS FOR PREPARING ALKYLENE GLYCOL MIXTURE FROM A CARBOHYDRATE SOURCE WITH DECREASED SELECTIVITY FOR POLYOL SIDE PRODUCTS
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The invention relates to a process for preparing a mixture of alkylene glycols (e.g. ethylene glycol and/or propylene glycol) from a carbohydrate source by catalytic conversion with hydrogen. More specifically, the catalytic hydrogenolysis process of the invention has a decreased selectivity for larger polyols like sorbitol and erythritol, which larger polyols are obtained generally as a side product in catalytic hydrogenolysis, when viewed in comparison to the selectivity for small alkylene glycols (like ethylene glycol and propylene glycol). This is achieved by ensuring the carbohydrate feed is rich in sucrose.
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Page/Page column 7-9
(2021/08/27)
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- Selective and Scalable Synthesis of Sugar Alcohols by Homogeneous Asymmetric Hydrogenation of Unprotected Ketoses
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Sugar alcohols are of great importance for the food industry and are promising building blocks for bio-based polymers. Industrially, they are produced by heterogeneous hydrogenation of sugars with H2, usually with none to low stereoselectivities. Now, we present a homogeneous system based on commercially available components, which not only increases the overall yield, but also allows a wide range of unprotected ketoses to be diastereoselectively hydrogenated. Furthermore, the system is reliable on a multi-gram scale allowing sugar alcohols to be isolated in large quantities at high atom economy.
- Tindall, Daniel J.,Mader, Steffen,Kindler, Alois,Rominger, Frank,Hashmi, A. Stephen K.,Schaub, Thomas
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supporting information
p. 721 - 725
(2020/10/19)
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- START-UP PROCESS FOR THE PRODUCTION OF GLYCOLS
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The invention provides a start-up method for a process for the preparation of glycols from a starting material comprising one or more saccharides in the presence of hydrogen and a catalyst system comprising one or more retro-aldol catalysts comprising tungsten and one or more catalytic species suitable for hydrogenation in a reactor, said method comprising introducing the one or more retro-aldol catalysts to the reactor whilst also in the presence of one or more agents suitable to suppress tungsten precipitation.
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Paragraph 0056-0057
(2020/05/07)
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- Boron oxide modified bifunctional Cu/Al2O3 catalysts for the selective hydrogenolysis of glucose to 1,2-propanediol
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A series of B2O3 modified Cu/Al2O3 catalysts were prepared for the hydrogenolysis of glucose. The catalysts were fully characterized by BET, ICP, N2O adsorptive decomposition, XRD, SEM, TG, H2-TPR, CO-FTIR, XPS, and NH3-TPD. The strong interaction between B2O3 and CuO could promote the dispersion of copper and inhibit the reduction of CuO, creating a proper mol ratio of Cuδ+/Cu0 for the hydrogenolysis of glucose to oxygen-containing chemicals. Furthermore, the doping of B2O3 also introduced more acid sites onto the CuB/Al2O3 catalysts, which is favorable for the cleavage of hydroxyl through dehydration. Therefore, the selective hydrogenolysis of glucose to 1,2-propanediol was dependent on the contribution of Cuδ+, Cu0, and acid sites. The catalytic activity and 1,2-propanediol selectivity were improved significantly by doping B2O3 into Cu/Al2O3. Among the catalysts, 1CuB/Al2O3 showed the highest selectivity for 1,2-propanediol, with the value of 49.5% at 96.6% conversion of glucose.
- Liu, Chengwei,Shang, Yaning,Wang, Shen,Liu, Xin,Wang, Xianzhou,Gui, Jianzhou,Zhang, Chenghua,Zhu, Yulei,Li, Yongwang
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- Effect of Cu addition to carbon-supported Ru catalysts on hydrogenation of alginic acid into sugar alcohols
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The objective of this study was to investigate the effect of Cu addition to carbon supported Ru catalysts on the hydrogenation of macroalgae-derived alginic acid into sugar alcohols, mainly sorbitol and mannitol. Both geometric and electronic effects were determined based on results of H2-TPR, H2- or CO-chemisorption, and XPS analyses after Cu was added to Ru. The addition of Cu to Ru caused blocking of active Ru surface and electron transfer between Ru and Cu. The intimate interaction between Ru and Cu formed RuCu bimetallic clusters which expedited hydrogen spillover from Ru to Cu. The highest yield of target sugar alcohols of 47.4% was obtained when 5 wt% of Ru and 1 wt% of Cu supported on nitric acid-treated activated carbon reacted at 180 °C for 2 h. The RuCu bimetallic catalyst exhibited deactivation upon repeated reactions due to the carbon deposition on the catalyst.
- Ban, Chunghyeon,Yang, Seungdo,Kim, Hyungjoo,Kim, Do Heui
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- Crystal structure of yeast xylose reductase in complex with a novel NADP-DTT adduct provides insights into substrate recognition and catalysis
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Aldose reductases (ARs) belonging to the aldo-keto reductase (AKR) superfamily catalyze the conversion of carbonyl substrates into their respective alcohols. Here we report the crystal structures of the yeast Debaryomyces nepalensis xylose reductase (DnXR, AKR2B10) in the apo form and as a ternary complex with a novel NADP-DTT adduct. Xylose reductase, a key enzyme in the conversion of xylose to xylitol, has several industrial applications. The enzyme displayed the highest catalytic efficiency for l-threose (138 ± 7 mm?1·s?1) followed by d-erythrose (30 ± 3 mm?1·s?1). The crystal structure of the complex reveals a covalent linkage between the C4N atom of the nicotinamide ring of the cosubstrate and the S1 sulfur atom of DTT and provides the first structural evidence for a protein mediated NADP–low-molecular-mass thiol adduct. We hypothesize that the formation of the adduct is facilitated by an in-crystallo Michael addition of the DTT thiolate to the specific conformation of bound NADPH in the active site of DnXR. The interactions between DTT, a four-carbon sugar alcohol analog, and the enzyme are representative of a near-cognate product ternary complex and provide significant insights into the structural basis of aldose binding and specificity and the catalytic mechanism of ARs. Database: Structural data are available in the PDB under the accession numbers 5ZCI and 5ZCM.
- Paidimuddala, Bhaskar,Mohapatra, Samar B.,Gummadi, Sathyanarayana N.,Manoj, Narayanan
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p. 4445 - 4464
(2018/10/24)
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- Structure of an entangled heteropolysaccharide from Pholidota chinensis Lindl and its antioxidant and anti-cancer properties
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A major polysaccharide PCP-I was isolated and purified from Pholidota chinensis Lindl. The physicochemical and structural properties of PCP-I were studied using high-performance size-exclusion chromatography (HPSEC), gas chromatography (GC), Fourier transform infrared spectroscopy (FTIR), periodate oxidation-smith degradation, methylation-GC–MS analysis, nuclear magnetic resonance (NMR) spectroscopy and transmission electron microscopy (TEM) analysis. PCP-I was homogeneous with molecular weight (Mw) of 249 kDa and composed of xylose and fucose at a molar ratio of 2.45:1. The repeating structural units of PCP-I were →3)-α-D-Xylp-(1→ and →4)-α-L-Fucp-(1→ the terminal fractions were T-D-GalAp, and TEM further revealed that PCP-I was the entangled microstructure which was composed of four non-branched single chains. Compared with Vitamin C (Vc) and 5 fluorine urine (5-Fu), PCP-I showed scavenging effects of superoxide (EC50 = 1.09 mg/mL) and hydroxyl (EC50 = 0.11 mg/mL) radicals equivalent to Vc, and PCP-I (IC50 = 69.54 μg/mL) also exhibited good anti-proliferation capability for human colon cancer cell line caco-2.
- Luo, Dianhui,Wang, Zhaojing,Li, Zhiming,Yu, Xiao-qiang
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p. 921 - 928
(2018/02/27)
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- Isolation, purification, characterization and antioxidant activity of polysaccharides from the stem barks of Acanthopanax leucorrhizus
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A novel water-soluble polysaccharide (named ALP-1) was successfully isolated from the stem barks of Acanthopanax leucorrhizus by hot-water extraction, and further purified by Cellulose DEAE-52 and Sephadex G-100 chromatography. The structure of ALP-1 was characterized by HPLC, HPGPC, partial acid hydrolysis, periodate oxidation, Smith degradation, methylation, together with UV, IR and NMR spectral analysis. The antioxidant activities also were evaluated in vitro. Structural analysis revealed that ALP-1 was a homogeneous galactan with the average molecular weight of 169 kDa, composed of galactose, glucose, mannose and arabinose in a molar ratio of 6.1:2.1:1.1:1.0, owning a backbone structure of 1,6-linked α-D-Galp residues with some branches of α-D-Manp-(1 → 3)-α-L-Araf residues at O-3 and α-D-Galp residues at O-4 of 1,6-linked α-D-Galp. Antioxidant assay showed that ALP-1 exhibited strong DPPH[rad] and HO[rad] scavenging activities, as well as ferric-reducing antioxidant power. These results provide a scientific basis for the further use of polysaccharides from A. leucorrhizus.
- Hu, Hao-Bin,Liang, Hai-Peng,Li, Hai-Ming,Yuan, Run-Nan,Sun, Jiao,Zhang, La-La,Han, Ming-Hu,Wu, Yun
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p. 359 - 367
(2018/05/29)
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- Ordered Mesoporous NiCeAl Containing Catalysts for Hydrogenolysis of Sorbitol to Glycols
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Cellulose-derived sorbitol is emerging as a feasible and renewable feedstock for the production of value-added chemicals. Highly active and stable catalyst is essential for sorbitol hydrogenolysis. Ordered mesoporous M–xNiyCeAl catalysts with different loadings of nickel and cerium species were successfully synthesized via one-pot evaporation-induced self-assembly strategy (EISA) and their catalytic performance were tested in the hydrogenolysis of sorbitol. The physical chemical properties for the catalysts were characterized by XRD, N2 physisorption, H2-TPR, H2 impulse chemisorption, ICP and TEM techniques. The results showed that the ordered mesopores with uniform pore sizes can be obtained and the Ni nanoparticles around 6 nm in size were homogeneously dispersed in the mesopore channels. A little amount of cerium species introduced would be beneficial to their textural properties resulting in higher Ni dispersion, metal area and smaller size of Ni nanoparticles. The M–10Ni2CeAl catalyst with Ni and Ce loading of 10.9 and 6.3 wt % shows better catalytic performance than other catalysts, and the yield of 1,2-PG and EG can reach 56.9% at 493 K and 6 MPa pressure for 8 h after repeating reactions for 12 times without obvious deterioration of physical and chemical properties. Ordered mesoporous M–NiCeAl catalysts are active and stable in sorbitol hydrogenolysis.
- Zhou, Zhiwei,Zhang, Jiaqi,Qin, Juan,Li, Dong,Wu, Wenliang
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p. 456 - 465
(2018/03/21)
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- Hydrolytic hydrogenation of chitin to amino sugar alcohol
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Chitin is the second most abundant biomass and characteristically contains nitrogen atoms in its monomer units. These favourable features promote chitin to be a potential resource for renewable organonitrogen compounds. 2-Acetamido-2-deoxysorbitol (ADS) is an attractive target in the derivatives of chitin, but the conversion of chitin to ADS has not been reported so far. In this work, we demonstrate the catalytic conversion of chitin to ADS using mechanocatalysis in the presence of H2SO4 and subsequent hydrolytic hydrogenation by H2SO4 and Ru/TiO2 without any purification process. Our study clarified that the yield of ADS is strongly influenced by the reaction temperature and pH. The hydrolysis favourably proceeds at high temperature and low pH (2.0), but the hydrogenation needs a low temperature and a specific pH of 3-4 to achieve high selectivity. Specifically, in the hydrogenation step, an acid causes various side-reactions of amide and hemiacetal groups especially in the presence of a Ru catalyst, whereas even a small amount of base drastically accelerates the retro-aldol reaction to form erythritol and N-acetylethanolamine. Therefore, a one-pot but two-step reaction is necessary to optimise both the hydrolysis and hydrogenation steps and maximise the overall yield of ADS up to 52%.
- Kobayashi, Hirokazu,Techikawara, Kota,Fukuoka, Atsushi
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p. 3350 - 3356
(2017/07/28)
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- Xylitol Hydrogenolysis over Ruthenium-Based Catalysts: Effect of Alkaline Promoters and Basic Oxide-Modified Catalysts
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The aqueous-phase hydrogenolysis of xylitol into glycols over Ru/C was performed in the presence and absence of a wide range of concentrations of Ca(OH)2 to investigate the reaction pathway. Without base, epimerization and cascade decarbonylation were the predominant reactions with high selectivities to C5 and C4 alditols and light alkanes at full conversion. Glycol production was obtained by the addition of Ca(OH)2 to promote the retro-aldol reaction. It competed with reactions without base and became the main reaction for a OH?/ xylitol molar ratio Rmol(OH/xylitol) of 0.13, and high selectivities to glycols (56 %) and glycerol (16 %) were observed. However, lactate was a byproduct at up to 27 % with a high base amount (Rmol(OH/xylitol)=0.68). Bifunctional Ru/metal oxide/C catalysts (metal: Zn, Sn, Mn, Sr, W) were synthesized and were able to cleave the C?C bond into glycols without a base promoter. The 3.1 wt %Ru/MnO(4.5 %)/C catalyst was the most active (220 h?1) with reasonable selectivity to glycols (22 %) and glycerol (10 %) and a low production of lactate (1 %). Nevertheless, metal oxide leaching of the catalyst was observed likely because of the production of traces of lactate.
- Rivière, Maxime,Perret, Noémie,Cabiac, Amandine,Delcroix, Damien,Pinel, Catherine,Besson, Michèle
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p. 2145 - 2159
(2017/06/28)
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- Hormonemate Derivatives from Dothiora sp., an Endophytic Fungus
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A search for cytotoxic agents from cultures of the endophytic fungus Dothiora sp., isolated from the endemic plant Launaea arborescens, led to the isolation of six new compounds structurally related to hormonemate, with moderate cytotoxic activity against different cancer cell lines. By using a bioassay-guided fractionation approach, hormonemates A-D (1-4), hormonemate (5), and hormonemates E (6) and F (7) were obtained from the acetone extract of this fungus. Their structures were determined using a combination of HRMS, ESI-qTOF-MS/MS, 1D and 2D NMR experiments, and chemical degradation. The cytotoxic activities of these compounds were evaluated by microdilution colorimetric assays against human breast adenocarcinoma (MCF-7), human liver cancer cells (HepG2), and pancreatic cancer cells (MiaPaca_2). Most of the compounds displayed cytotoxic activity against this panel.
- Pérez-Bonilla, Mercedes,González-Menéndez, Víctor,Pérez-Victoria, Ignacio,De Pedro, Nuria,Martín, Jesús,Molero-Mesa, Joaquín,Casares-Porcel, Manuel,González-Tejero, María Reyes,Vicente, Francisca,Genilloud, Olga,Tormo, José R.,Reyes, Fernando
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p. 845 - 853
(2017/05/05)
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- Influence of the Surface Chemistry of Multiwalled Carbon Nanotubes on the Selective Conversion of Cellulose into Sorbitol
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Carbon nanotubes (CNT) were submitted to liquid-phase chemical treatments using HNO3 and subsequently to gas-phase thermal treatments to incorporate different sets of oxygenated groups on the surface. The modified CNT were used as supports for 0.4 wt % Ru in the direct conversion of ball-milled cellulose to sorbitol and high conversions were reached after 3 h at 205 °C. Ru supported on the original CNT, although less active, was the most selective catalyst for the one-pot process (70 % sorbitol selectivity after 2 h). Unlike the one-pot process, the support acidity greatly promoted the rate of cellulose hydrolysis (35 % increase after 2 h) and the glucose selectivity (12 % increase after 2 h). The rate of glucose hydrogenation was almost not affected by the support modification. However, the catalyst acidity improved the sorbitol selectivity from glucose. The support acidity was a central factor for the one-pot conversion of cellulose, as well as for the individual hydrolysis and hydrogenation steps, and the original CNT supported Ru catalyst was the most efficient and selective catalyst for the direct conversion of cellulose to sorbitol.
- Ribeiro, Lucília S.,Delgado, Juan J.,de Melo órf?o, José J.,Ribeiro Pereira, M. Fernando
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p. 888 - 896
(2017/03/13)
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- Influence of the functional groups of multiwalled carbon nanotubes on performance of Ru catalysts in sorbitol hydrogenolysis to glycols
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Different functional groups (i.e. [sbnd]NH2, [sbnd]COOH, [sbnd]OH and nitrogen-doping) modified CNTs (denoted as AMCN, CMCN, HMCN and NMCN, respectively) supported ruthenium catalysts (Ru/AMCN, Ru/CMCN, Ru/HMCN and Ru/NMCN) were prepared by incipient wetness impregnation method. They were fully characterized by XRD, TG, Raman, XPS, TPD and TEM to elucidate the relationship between the physical property and their catalytic performance. TEM results shown that Ru particles were well dispersed on the surface for all the samples with the size of 1.48–1.99 nm. The effects of functional groups of carbon nanotubes (CNTs), nitrogen doping and base additive types on activity and selectivity of ethylene glycol (EG) and propylene glycol (1,2-PD) were investigated. In addition, the activity and final products distribution were much influenced by the properties of functional groups on CNTs and the type of metal cation of the base promoters, which probably participated in the reaction for accelerating a retro-aldol reaction for C[sbnd]C cleavage. Among the catalysts, Ru supported on AMCN exhibited the best catalytic activities and glycols selectivities than on MCN, CMCN, HMCN and NMCN.
- Guo, Xingcui,Dong, Huihuan,Li, Bin,Dong, Linlin,Mu, Xindong,Chen, Xiufang
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- Kinetic insight into the effect of the catalytic functions on selective conversion of cellulose to polyols on carbon-supported WO3 and Ru catalysts
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Efficient conversion of cellulose, the most abundant biomass on Earth, to chemicals in high yields remains a formidable challenge. Here, we report the marked change in the distribution of polyol products in the cellulose reaction on Ru/C and WO3/C, strongly depending on the competitive reactions of the glucose intermediate. WO3 crystallites not only promote, as a solid acid, the efficient hydrolysis of cellulose to glucose, but also catalyze the selective cleavage of the C-C bonds in glucose and other C6 sugar intermediates, leading to the formation of ethylene glycol and propylene glycol, in competition with the sugar hydrogenation to the corresponding C6 polyols (e.g. sorbitol) on Ru/C. The basic C support, behaving similar to other solid bases (i.e. MgO), catalyzes the isomerization of glucose into fructose, leading to the favored formation of propylene glycol instead of ethylene glycol. Such strong dependence of the product distribution on the catalytic functions is clarified by the kinetic analysis of the three competitive reactions of glucose, including its hydrogenation, isomerization and C-C bond cleavage. Importantly, such kinetic analysis can predict the maximum selectivity ratio of propylene glycol to ethylene glycol, which is 2.5, for example, at 478 K under the reaction conditions in this work, corresponding to a maximum yield of propylene glycol of ~71%. These understandings shed new insights into the selective conversion of cellulose, which provides guidance for the rational design of catalyst functions and tuning of reaction parameters towards the controllable synthesis of specific products from cellulose.
- Liu, Yue,Liu, Haichao
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- Effect of WOx on Bifunctional Pd-WOx/Al2O3 Catalysts for the Selective Hydrogenolysis of Glucose to 1,2-Propanediol
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A series of Pd-WOx/Al2O3 catalysts with different contents of WOx were prepared by stepwise incipient wetness impregnations. The influence of WOx on the physicochemical properties of Pd-WOx/Al2O3 catalysts, as well as their catalytic performance for the hydrogenolysis of glucose to 1,2-propanediol (1,2-PDO), was investigated. At low surface W density (0.3-2.1 W nm-2), distorted isolated WOx and oligomeric WOx are present on the Pd-WOx/Al2O3 catalysts. Furthermore, isolated WO4 are the dominating species on the Pd-WOx(5%)/Al2O3 catalyst. When the W density increased to 3.1 W nm-2, polymeric WOx species are dominant on the Pd-WOx(30%)/Al2O3 catalyst. The Pd surface area decreased while the acid amount increased with increasing W density. Furthermore, increased Lewis acid sites are provided by isolated WO4 and oligomeric WOx species whereas increased Bronsted acid sites exist on polymeric WOx species. Lewis acid sites promote glucose isomerization to fructose, which is an intermediate in glucose hydrogenolysis to 1,2-PDO. Metal sites catalyze C=O hydrogenation and C-C hydrogenolysis, which avoid the coke formation on catalysts. 1,2-PDO selectivity is dependent on the synergy of Lewis acid and metal sites; however, Bronsted acid sites have no contribution to the 1,2-PDO production. Typically, the Pd-WOx(5%)/Al2O3 catalyst possessing the optimal balance of Lewis acid and the metal site shows a 1,2-PDO selectivity of 60.8% at a glucose conversion of 92.2% and has a lifetime of over 200 h.
- Liu, Chengwei,Zhang, Chenghua,Sun, Sikai,Liu, Kangkai,Hao, Shunli,Xu, Jian,Zhu, Yulei,Li, Yongwang
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p. 4612 - 4623
(2015/08/18)
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- Selective terminal C-C scission of C5-carbohydrates
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The selective catalytic production of C4-tetritols (erythritol and threitol) from C5-sugars is an attractive route for the conversion of non-digestible sugars to C4-building blocks from agro residues. Here we show that an unprecedented high selectivity of 20-25% C4-tertritols can be achieved under mild conditions (138 °C, 6 bar H2, and 24 h) in the aqueous conversion of xylose over a 5 wt% Ru/C catalyst. A mechanistic study revealed that the dominant reaction mechanism for C5-sugar conversion involves a formal decarbonylation step leading to the initial formation of the desired C4-tetritols. Subsequently the formed C4-tetritols undergo further terminal C-C scissions to glycerol and ethylene glycol. Remarkably, potentially competing reactions like internal C-C chain scission (fragmentation) or hydrodeoxygenation (HDO) do not occur to any significant extent under the applied conditions.
- Van Der Klis, Frits,Gootjes, Linda,Van Haveren, Jacco,Van Es, Daan S.,Bitter, Johannes H.
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p. 3900 - 3909
(2015/07/15)
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- Structure of Galactomannan from Seeds of Crotalaria alata
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A galactomannan of MW 540 kDa was isolated from seeds of Crotalaria alata. Chemical and spectral (PMR and 13C NMR) methods established that the main chain of the galactomannan consisted of β-1,4-mannan with α-1,6-D-galactopyranose side chains.
- Kodiralieva,Shashkov,Rakhmanberdyeva
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p. 405 - 408
(2015/06/16)
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- Catalytic oxidation of cellobiose over TiO2 supported gold-based bimetallic nanoparticles
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A series of Au-M (M = Cu, Co, Ru and Pd) bimetallic catalysts were supported on TiO2via a deposition-precipitation (DP) method, using urea as a precipitating agent. The resulting catalysts were employed in the catalytic oxidation of cellobiose to gluconic acid and the properties of these catalysts were carefully examined using various characterization techniques. Cu-Au/TiO2 and Ru-Au/TiO2 catalysts demonstrated excellent catalytic activities in the oxidation of cellobiose to gluconic acid, though with contrasting reaction mechanisms. Complete conversion of cellobiose (100%) with a gluconic acid selectivity of 88.5% at 145 °C within 3 h was observed for reactions performed over Cu-Au/TiO2; whereas, a conversion of 98.3% with a gluconic acid selectivity of 86. 9% at 145°C within 9 h was observed for reactions performed over Ru-Au/TiO2. A reaction pathway was proposed based on the distribution of reaction products and kinetic data. It is suggested that cellobiose is converted to cellobionic acid (4-O-beta-d-glucopyranosyl-d-gluconic acid) and then gluconic acid is formed through the cleavage of the β-1,4 glycosidic bond in cellobionic acid over Cu-Au/TiO2 catalysts. On the other hand, for reactions over the Ru-Au/TiO2 catalyst, glucose was observed as the reaction intermediate and gluconic acid was formed as a result of glucose oxidation. For reactions over Co-Au/TiO2 and Pd-Au/TiO2 catalysts, fructose was observed as the reaction intermediate, along with small amounts of glucose. Co and Pd remarkably promoted the successive retro-aldol condensation reactions of fructose to glycolic acid, instead of the selective oxidation to gluconic acid. This journal is
- Amaniampong, Prince Nana,Jia, Xinli,Wang, Bo,Mushrif, Samir H.,Borgna, Armando,Yang, Yanhui
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p. 2393 - 2405
(2015/04/14)
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- From microcrystalline cellulose to hard- and softwood-based feedstocks: Their hydrogenolysis to polyols over a highly efficient ruthenium-tungsten catalyst
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The utilization of cellulose and its integration in a biorefinery concept is essential even in the near future due to the growing global shortage of crude oil. Here, we report the catalyzed one-pot hydrogenolysis of cellulosic materials to valuable bio-derived molecules, especially polyols (e.g. ethylene glycol). We demonstrate how a very promising bifunctional catalyst, Ru/W/AC, converted not only 100% of microcrystalline cellulose to polyols in repeated experiments with a maximum yield of 84% and an ethylene glycol productivity of 3.7 g (gcatalyst h)-1, but also pine-, birch-, and eucalyptus-derived materials. Moreover, we systematically investigated the problem of catalyst stability with time by studying the changes in both the catalyst structure and the liquid phase, which have often been overlooked when biomass is converted to fuels and chemicals. Control of the active sites for the conversion of cellulosic feedstocks coupled with reaction engineering and strategies to prevent catalyst deactivation, is a prerequisite to understanding how high yields of platform chemicals can be achieved.
- Fabi?ovicová, Katarína,Lucas, Martin,Claus, Peter
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p. 3075 - 3083
(2015/05/27)
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- Conversion of sugars to ethylene glycol with nickel tungsten carbide in a fed-batch reactor: High productivity and reaction network elucidation
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Bifunctional nickel tungsten carbide catalysis was used for the conversion of aqueous sugar solutions into short-chain polyols such as ethylene glycol. It is shown that very concentrated sugar solutions, viz. up to 0.2 kg L -1, can be converted without loss of ethylene glycol selectivity by gradually feeding the sugar solution. Detailed investigation of the reaction network shows that, under the applied reaction conditions, glucose is converted via a retro-aldol reaction into glycol aldehyde, which is further transformed into ethylene glycol by hydrogenation. The main byproducts are sorbitol, erythritol, glycerol and 1,2-propanediol. They are formed through a series of unwanted side reactions including hydrogenation, isomerisation, hydrogenolysis and dehydration. Hydrogenolysis of sorbitol is only a minor source of ethylene glycol. To assess the relevance of the fed-batch system in biomass conversions, both the influence of the catalyst composition and the reactor setup parameters like temperature, pressure and glucose addition rate were optimized, culminating in ethylene glycol yields up to 66% and separately, volume productivities of nearly 300 gEG L-1 h-1.
- Ooms, Roselinde,Dusselier, Michiel,Geboers, Jan A.,Op De Beeck, Beau,Verhaeven, Rick,Gobechiya, Elena,Martens, Johan A.,Redl, Andreas,Sels, Bert F.
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p. 695 - 707
(2014/02/14)
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- Direct conversion of cellulose into acetol on bimetallic Ni-SnO x/Al2O3 catalysts
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The direct conversion of cellulose into acetol was studied on SnO x-modified Ni/Al2O3 catalysts with different Sn/Ni atomic ratios in the range of 0-2.0. The selectivity to acetol strongly depended on the Sn/Ni ratios, which reached the highest value of 53.9% at the ratio of 0.5, compared at similar cellulose conversions (~20%). On Ni-SnOx/Al2O3 (Sn/Ni = 0.5), cellulose, glucose and fructose converted to acetol in high yields of approximately 35%, 53% and 73%, respectively, at 210 °C and 6 MPa H2. The effects of the Sn/Ni ratios on the acetol selectivity appear to be related to their effects on the hydrogenation activity of the Ni-SnOx/Al2O3 catalysts that decreased with increase of the Sn/Ni ratios, and to the relative rate between the hydrogenation of C6 sugar intermediates (e.g. glucose and fructose) and their degradation intermediates (e.g. glyceraldeyde and dihydroxyacetone) involved in the cellulose reaction on the Ni particles and the isomerization of glucose to fructose and their CC bond cleavage by retro-aldol condensation on the SnOx domains. Comparison of SnO x with CeOx, ZnOx and AlOx supported on Al2O3 with different basicity suggested that the larger concentration of stronger basic sites on SnOx facilitated the isomerizaiton of glucose to fructose and its subsequent CC bond cleavage. These results and their understanding provide guidance for improving the acetol production from cellulose by tuning the catalytic functions required for the involved reactions of hydrogenation on the metal surfaces, and isomerization and CC bond cleavage on the basic sites.
- Deng, Tianyin,Liu, Haichao
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- Catalytic conversion of cellulose to ethylene glycol over a low-cost binary catalyst of Raney Ni and tungstic acid
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Following our previous report on the selective transformation of cellulose to ethylene glycol (EG) over a binary catalyst composed of tungstic acid and Ru/C, we herein report a new lowcost but more effective binary catalyst by using Raney nickel in place of Ru/C (Raney Ni+H2WO4). In addition to tungstic acid, other W compounds were also investigated in combination with Raney Ni. The results showed that the EG yield depended on the W compound: H4SiW12O40H3PW 12O40WO3H2WO4, but all the investigated W compounds were selective towards EG. Moreover, both WO 3 and H2WO4 were dissolved partially under the reaction conditions and transformed into HxWO3 which is the genuinely active species for the C-C bond breakage of cellulose. This result further confirmed that the reaction that involves the selective breakage of the C-C bonds of cellulose with W species is homogenous. Among various binary catalysts, the combination of Raney Ni and H2WO4 gave the highest yield of EG (65 %), which could be attributed to the high activity of Raney Ni for hydrogenation and its inertness for the further degradation of EG. Moreover, Raney Ni+H2WO4 showed good reusability; it could be reused at least 17 times without any decay in the EG yield, which shows its great potential for industrial applications.
- Tai, Zhijun,Zhang, Junying,Wang, Aiqin,Pang, Jifeng,Zheng, Mingyuan,Zhang, Tao
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p. 652 - 658
(2013/07/27)
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- Asymmetric organocatalytic formation of protected and unprotected tetroses under potentially prebiotic conditions
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Esters of proteinogenic amino acids efficiently catalyse the formation of erythrose and threose under potentially prebiotic conditions in the highest yields and enantioselectivities yet reported. Remarkably while esters of (l)-proline yield (l)-tetroses, esters of (l)-leucine, (l)-alanine and (l)-valine generate (d)-tetroses, offering the potential to account for the link between natural (l)-amino acids and natural (d)-sugars. The effect of pH and NaCl on the yields and enantioselectivities was also investigated and was shown to be significant, with the optimal enantioselectivities occurring at pH 7.
- Burroughs, Laurence,Clarke, Paul A.,Forintos, Henrietta,Gilks, James A. R.,Hayes, Christopher J.,Vale, Matthew E.,Wade, William,Zbytniewski, Myriam
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experimental part
p. 1565 - 1570
(2012/04/05)
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- COMPOSITIONS CONTAINING SUCRALOSE AND APPLICATION THEREOF
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Novel utilization of sucralose which is a high intense sweetener. Compositions containing sucralose including: sweetening compositions having excellent sweetness qualities based on the characteristics of sucralose; foods with a masked unpleasant smell and unpleasant taste; performance food compositions (viscous food compositions, gel food compositions, emulsified food compositions); foods with improved flavors; preservatives and foods with improved quality of taste; and flavor compositions with improved flavors. Novel utilization of sucralose as a sweetener improver, a masking agent for unpleasant smell/unpleasant taste, a flavor improver, a function improver (viscosity, gelling properties, emulsification properties), a taste characteristic improver, and a flavor improver/enhancer.
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- Probing the ruthenium-catalyzed higher polyol hydrogenolysis reaction through the use of stereoisomers
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Nine polyol stereoisomers ranging from three to six carbons in length were reacted under hydrogenolysis conditions (205-240°C, 100 bar H2) over a Ru-C catalyst to better understand the reaction mechanism. Previous reports have postulated the retro-aldol mechanism as the main pathway leading to C-C scission. However, the retro-aldol mechanism was insufficient in explaining the product distribution of tetritols from pentitols, while the decarbonylation mechanism could explain the selectivity results of terminal C-C scission. Retro-aldol scission of internal C-C bonds was confirmed to occur by the tetritol product distribution from hexitols. Therefore, the presence or role of 3-keto and 4-keto intermediates had a negligible effect on the C-C hydrogenolysis of polyols when compared to aldehyde intermediates. The reaction rates of the polyols depended on the configuration of the polyol stereoisomers. The reactivity of the stereoisomers was correlated to the presence of erythro sequences of hydroxyl groups and was independent of the carbon chain length. The Royal Society of Chemistry.
- Deutsch, Keenan L.,Lahr, Daniel G.,Shanks, Brent H.
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p. 1635 - 1642
(2013/02/23)
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- Nitrone formation in phosphate buffer and aqueous solutions: Novel chemistry inspired by a natural product
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Nitrones are formed from the reaction of aspergillusol A (1) and a ketone/aldehyde in phosphate buffer and aqueous solutions with pH ranges of 6.8-8.6, resembling physiological conditions. The reaction of 1 with 1-substituted cyclohexanones gave the (1′S,2′R)-isomer, diastereoselectively.
- Pansanit, Acharavadee,Ingavat, Nattha,Aree, Thammarat,Mahidol, Chulabhorn,Ruchirawat, Somsak,Kittakoop, Prasat
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supporting information; experimental part
p. 2129 - 2131
(2012/07/14)
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- Hydrogenolysis of sorbitol over Ni and Pt loaded on NaY
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The hydrogenolysis of sorbitol (15% aqueous solution) was carried out at 60 bar pressure at 220 °C in a stirred batch reactor using Ni-NaY (2, 4, 6 wt.% Ni) with and without added Pt(1 wt.%). 1,2-Propanediol was the major product over Ni-NaY and glycerol was the main product over Pt(1 wt.%)-NaY. The addition of 1 wt.% Pt to the Ni-catalysts had only a marginal effect on conversion and selectivity of the catalysts. Addition of Ca(OH)2 as the promoter to both Ni and Pt catalysts increased the conversion significantly without any significant effect on selectivity.
- Banu,Sivasanker,Sankaranarayanan,Venuvanalingam
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experimental part
p. 673 - 677
(2012/01/12)
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- Heteropoly acids as efficient acid catalysts in the one-step conversion of cellulose to sugar alcohols
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Cellulose and even spruce can be converted efficiently into valuable platform chemicals via combined hydrolysis and hydrogenation in the aqueous phase. Thereby, heteropoly acids together with supported ruthenium catalysts show not only high activity but also remarkable selectivity to sugar alcohols reaching up to 81% yield of C4 to C6 sugar alcohols in only 7 h at 160 °C.
- Palkovits, Regina,Tajvidi, Kameh,Ruppert, Agnieszka M.,Procelewska, Joanna
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supporting information; experimental part
p. 576 - 578
(2011/03/17)
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- Properties and tissue distribution of a novel aldo-keto reductase encoding in a rat gene (Akr1b10)
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A recent rat genomic sequencing predicts a gene Akr1b10 that encodes a protein with 83% sequence similarity to human aldo-keto reductase (AKR) 1B10. In this study, we isolated the cDNA for the rat AKR1B10 (R1B10) from rat brain, and examined the enzymatic properties of the recombinant protein. R1B10 utilized NADPH as the preferable coenzyme, and reduced various aldehydes (including cytotoxic 4-hydroxy-2-hexenal and 4-hydroxy- and 4-oxo-2-nonenals) and α-dicarbonyl compounds (such as methylglyoxal and 3-deoxyglucosone), showing low Km values of 0.8-6.1μM and 3.7-67μM, respectively. The enzyme also reduced glyceraldehyde and tetroses (Km=96-390μM), although hexoses and pentoses were inactive and poor substrates, respectively. Among the substrates, 4-oxo-2-nonenal was most efficiently reduced into 4-oxo-2-nonenol, and its cytotoxicity against bovine endothelial cells was decreased by the overexpression of R1B10. R1B10 showed low sensitivity to aldose reductase inhibitors, and was activated to approximately two folds by valproic acid, and alicyclic and aromatic carboxylic acids. The mRNA for R1B10 was expressed highly in rat brain and heart, and at low levels in other rat tissues and skin fibroblasts. The results suggest that R1B10 functions as a defense system against oxidative stress and glycation in rat tissues.
- Endo, Satoshi,Matsunaga, Toshiyuki,Kuragano, Tsukasa,Ohno, Satoshi,Kitade, Yukio,Tajima, Kazuo,El-Kabbani, Ossama,Hara, Akira
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experimental part
p. 230 - 237
(2011/10/30)
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- Fabaceae polysaccharides. III. Galactomannan from astragalus cicer seeds
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Seeds of Astragalus cicer L. (Fabaceae) afforded a galactomannan (5.90% yield of seed mass) of molecular weight 1064 kDa, solutions of which had high viscosity [η] 925.5 mL/g and optical activity [α]D +71.9°. The galactomannan consisted of galactose and mannose units in a 1:1.39 ratio. Physicochemical methods established that the main chain of the polysaccharide consisted of 1,4-β-D-mannopyranose units substituted at 72% of the C-6 positions by single α-D-galactopyranose units. The content of variously substituted galactose mannobiose units Man-Man, (Gal)Man-Man/Man- Man(Gal) and (Gal)Man-Man(Gal) in the galactomannan were 18.7, 19.8, and 61.5%, respectively.
- Olennikov,Rokhin
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experimental part
p. 165 - 168
(2010/10/21)
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- Efficient asymmetric organocatalytic formation of erythrose and threose under aqueous conditions
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Esters of proteinogenic amino acids efficiently catalyse the formation of erythrose and threose under aqueous conditions in the highest yields and enantioselectivities yet reported. Remarkably while esters of (l)-proline yield (l)-carbohydrates, esters of (l)-leucine and (l)-alanine generate (d)-carbohydrates, offering the potential to account for the prebiotic link between natural (l)-amino acids and natural (d)-sugars.
- Burroughs, Laurence,Vale, Matthew E.,Gilks, James A. R.,Forintos, Henrietta,Hayes, Christopher J.,Clarke, Paul A.
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supporting information; experimental part
p. 4776 - 4778
(2010/09/05)
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- Hydrogenolysis of cellulose combining mineral acids and hydrogenation catalysts
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A catalytic system capable of reaching high performance in the hydrogenolysis of cellulose at low reaction temperature and short reaction times has been developed. Therefore, supported noble metal catalysts based on Pt, Pd and Ru have been combined with dilute mineral acids. A broad variable set in terms of type of noble metal, type of acid, acid concentration and reaction time could be evaluated based on chemical interpretation and supported by a Design of Experiment (DoE) approach. The variables significantly influenced conversion of cellulose, product range and selectivity towards sugar alcohol formation. Thus, at 160 °C, above 60% yield in sugars and sugar alcohols with 84% selectivity at a cellulose conversion of 72% could be reached. Besides, glycerol, propylene glycol, ethylene glycol and methanol were formed as additional valuable by-products leading to an overall carbon utilization above 89%. Furthermore, the concept was successfully transferred to real feedstocks in the form of spruce reaching close to 60% conversion in only one hour reaction time.
- Palkovits, Regina,Tajvidi, Kameh,Procelewska, Joanna,Rinaldi, Roberto,Ruppert, Agnieszka
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scheme or table
p. 972 - 978
(2010/08/19)
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- Selective bifunctional catalytic conversion of cellulose over reshaped Ni particles at the tip of carbon nanofibers
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Access to cellulose: Carbon nanofibers grown over Ni supported on γ-Al2O3 act as efficient catalysts for the one-pot conversion of cellulose to sugar alcohols, owing to the enhanced accessibility of the water-insoluble substrate towards the active catalytic sites. The new catalyst design concept yields unprecedented results for selective cellulose conversion using inexpensive Ni catalysts.
- Van de Vyver, Stijn,Geboers, Jan,Dusselier, Michiel,Schepers, Hans,Vosch, Tom,Zhang, Liang,Van Tendeloo, Gustaaf,Jacobs, Pierre A.,Sels, Bert F.
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scheme or table
p. 698 - 701
(2011/12/21)
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- A novel (1 → 4)-α-d-glucan isolated from the fruits of Opuntia ficus indica (L.) Miller
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A water-soluble polysaccharide (PS-1) was isolated from the fruits of Opuntia ficus indica (L.) Miller by hot water extraction, anion-exchange and gel-permeation chromatography (yield 167.5 mg/kg raw fruit; [α] D16 1 + 192° (c 1.0, H2O); total neutral sugar content 96.60% w/w; weight-average molecular weight (M w) ~360 kDa). Structural characterisation was performed by monosaccharide analysis and linkage analysis (methylation analysis, periodate oxidation and Smith degradation) on full and partial acid hydrolysates, followed by alditol acetylation, and product quantification by GC/GC-MS. Spectroscopic analysis (FT-IR and 1H/13C NMR) was also performed. Polysaccharide PS-1 was found to be an α-d-glucan with a (1 → 4)-linked α-d-Glcp backbone, with (1 → 6)-linked (1 → 4)-α-d-Glcp side chains, side chains being short in length with no additional branching, and a minimum branching of ~1 in every 9-11 backbone units. The distribution of side chains lengths and corresponding branching density requires further investigation.
- Ishurd, Omar,Zgheel, Faraj,Elghazoun, Mohamed,Elmabruk, Mohamed,Kermagi, Adel,Kennedy, John F.,Knill, Charles J.
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experimental part
p. 848 - 853
(2011/12/15)
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- Chemical properties and antiulcerogenic activity of a galactomannoglucan from Syagrus oleracea
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A galactomannoglucan (GMG) with an estimated weight-average molar mass of 415,000. g/mol was obtained from an aqueous extract of the mesocarp of fruits of Syagrus oleracea (Mart.) Becc. by fractionation by Sephacryl S-300 HR and Sephadex G-25. Chemical and spectroscopic studies indicated that GMG has a chain of (1 → 4)-linked β-d-mannopyranosyl residues attached to an initial chain of (1 → 3)-linked β-d-galactopyranosyl residues and a terminal chain of (1 → 4)-linked α-d-glucopyranosyl residues which comprised galactose, mannose and glucose in the molar ratio of 30:33:37. Results of the present study indicated that the polysaccharide GMG of S. oleracea significantly inhibited gastric lesions induced by ethanol, showing a gastroprotective property.
- da Silva, Bernadete Pereira,Parente, José Paz
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experimental part
p. 1076 - 1080
(2011/12/03)
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- Transition metal-tungsten bimetallic catalysts for the conversion of cellulose into ethylene glycol
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Tungsten-based bimetallic catalysts (W M(8,9,10); where M(8,9,10) is Ni, Pd, Pt, Ir, Ru, or Rh) are found to be highly active and selective for the formation of ethylene glycol from cellulose. The cooperation between C-C cracking reactions over metallic tungsten and the hydrogenation of unsaturated intermediates over the transition metals M(8,9,10) results in a particularly high selectivity towards ethylene glycol, up to 75%.
- Zheng, Ming-Yuan,Wang, Ai-Qin,Ji, Na,Pang, Ji-Feng,Wang, Xiao-Dong,Zhang, Tao
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experimental part
p. 63 - 66
(2011/02/21)
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- Aspergillusol A, an α-glucosidase inhibitor from the marine-derived fungus Aspergillus aculeatus
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A new tyrosine-derived metabolite, aspergillusol A (4), was isolated on a gram scale, together with a methyl ester of 4-hydroxyphenylpyruvic acid oxime (5) and secalonic acid A, from the marine-derived fungus Aspergillus aculeatus CRI323-04. The tetraol in 4 was identified as erythritol by comparison of the 1H NMR spectrum of its benzoylated derivative with those of benzoylated erythritol (7) and D-threitol (8), as well as by cellulose-based chiral HPLC analysis. Aspergillusol A (4) selectively inhibited α-glucosidase from the yeast Saccharomyces cerevisiae, but it was inactive toward the α-glucosidase from the bacterium Bacillus stearothermophilus.
- Ingavat, Nattha,Dobereiner, Jeffrey,Wiyakrutta, Suthep,Mahidol, Chulabhorn,Ruchirawat, Somsak,Kittakoop, Prasat
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experimental part
p. 2049 - 2052
(2010/06/13)
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- Direct catalytic conversion of cellulose into ethylene glycol using nickel-promoted tungsten carbide catalysts
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Nickel saves dimes: The expense of using precious-metal catalysts is avoided in the high-yielding conversion of cellulose to ethylene glycol (see picture; AC = activated carbon). This process occurs in up to 29% yield over a tungsten carbide catalyst, and in up to 61% yield when the catalyst is promoted with a small amount of nickel. An attractive feature of this reaction is the low yields of other polyols with respect to ethylene glycol. (Figure Presented)
- Ji, Na,Zhang, Tao,Zheng, Mingyuan,Wang, Aiqin,Wang, Hui,Wang, Xiaodong,Chen, Jingguang G.
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supporting information; experimental part
p. 8510 - 8513
(2009/05/15)
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- Cellulose conversion into polyols catalyzed by reversibly formed acids and supported ruthenium clusters in hot water
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(Chemical Equation Presented) A green approach to efficient conversion of cellulose into hexitols and other lighter alcohols through two steps is reported. In this process, cellulose is hydrolyzed to glucose by acids formed reversibly in situ from hot water, and the glucose is hydrogenated on Ru/C. Understanding of the green aqueous catalytic systems should lead to more efficient conversion of cellulose into fuels and chemicals.
- Luo, Chen,Wang, Shuai,Liu, Haichao
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p. 7636 - 7639
(2008/09/18)
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- Rhodium-catalyzed decarbonylation of aldoses
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(Chemical Equation Presented) A catalytic procedure is described for decarbonylation of unprotected aldoses to afford alditols with one less carbon atom. The reaction is performed with the rhodium complex Rh(dppp)2Cl in a refluxing diglyme-DMA solution. A slightly improved catalyst turnover is observed when a catalytic amount of pyridine is added. Under these conditions most hexoses and pentoses undergo decarbonylation into the corresponding pentitols and tetrols in isolated yields around 70%. The reaction has been applied as the key transformation in a five-step synthesis of L-threose from D-glucose.
- Monrad, Rune Nygaard,Madsen, Robert
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p. 9782 - 9785
(2008/03/17)
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- Prebiotic carbohydrate synthesis: Zinc-proline catalyzes direct aqueous aldol reactions of α-hydroxy aldehydes and ketones
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Zn-proline catalyzed aldolisation of glycoladehyde gave mainly tetroses whereas in the cross-aldolisation of glycoladehyde and rac-glyceraldehyde, pentoses accounted for 60% of the sugars formed with 20% of ribose. The Royal Society of Chemistry 2005.
- Kofoed, Jacob,Reymond, Jean-Louis,Darbre, Tamis
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p. 1850 - 1855
(2007/10/03)
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- Glycosidase inhibitors and methods of synthesizing same
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A method for synthesizing Salacinol, its stereoisomers, and analogues, homologues and other derivatives thereof potentially useful as glycolsidase inhibitors. The compounds of the invention may have the general formula (I) or (II): The synthetic schemes c
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- Multiple Forms of Xylose Reductase in Candida intermedia: Comparison of Their Functional Properties Using Quantitative Structure-Activity Relationships, Steady-State Kinetic Analysis, and pH Studies
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The xylose-fermenting yeast Candida intermedia produces two isoforms of xylose reductase: one is NADPH-dependent (monospecific xylose reductase; msXR), and another is shown here to prefer NADH ≈4-fold over NADPH (dual specific xylose reductase; dsXR). To compare the functional properties of the isozymes, a steady-state kinetic analysis for the reaction D-xylose + NAD(P)H + H + ? xylitol + NAD(P)+ was carried out and specificity constants (kcat/Kaldehyde) were measured for the reduction of a series of aldehydes differing in side-chain size as well as hydrogen-bonding capabilities with the substrate binding pocket of the enzyme. dsXR binds NAD(P)+ (KiNAD+ = 70 μM; KiNADP+ = 55 μM) weakly and NADH (Ki = 8 μM) about as tightly as NADPH (Ki = 14 μM). msXR shows uniform binding of NADPH and NADP + (KiNADP+ ≈ KiNADPH = 20 μM). A quantitative structure-activity relationship analysis was carried out by correlating logarithmic kcat/Kaldehyde values for dsXR with corresponding logarithmic kcat/Kaldehyde values for msXR. This correlation is linear with a slope of ≈1 (r2 = 0.912), indicating that no isozyme-related pattern of substrate specificity prevails and aldehyde-binding modes are identical in both XR forms. Binary complexes of dsXR-NADH and msXR-NADPH show the same macroscopic pK of ≈9.0-9.5, above which the activity is lost in both enzymes. A lower pK of 7.4 is seen for dsXR-NADPH. Specificity for NADH and greater binding affinity for NAD(P)H than NAD(P)+ are thus the main features of enzymic function that distinguish dsXR from msXR.
- Nidetzky, Bernd,Brueggler, Kaspar,Kratzer, Regina,Mayr, Peter
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p. 7930 - 7935
(2007/10/03)
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- Polyol polymers, meso-erythritol polymers and their aliphatic acid esters and aliphatic ethers
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A polyol polymer having a greater number of hydroxy groups, an aliphatic acid ester of a polyol polymer having a greater number of hydroxy groups, and an aliphatic ether of a polyol polymer having a greater number of hydroxy groups are provided. A polymer obtained by polymerizing a polyol containing meso-erythritol, and an aliphatic acid ester and an aliphatic ether of the polymer are provided.
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- Catalytic hydrogenation of arabinonic acid and lactones to arabitol
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Aqueous solutions (20 wt%) of arabinonic acid in equilibrium with arabinonolactones were hydrogenated on ruthenium catalysts at 100°C or lower temperatures in a batch reactor. The highest selectivity to arabitol was 98.9% at 98% conversion, with a reaction rate of 73 mmol h-1 gRu-1 at 80°C. Reaction modeling was achieved by a detailed kinetic analysis of reaction data under various reaction conditions. The conversion of substrate follows a rate equation established with the Horiuti-Polanyi mechanism. The selectivity was higher on small particles supported on carbon supports because of an electron-donating effect of the support on the ruthenium particles, which decreases the rate of dehydroxylation reactions leading to unwanted deoxy products. The most important factor enhancing the selectivity was the presence of anthraquinone-2-sulfonate (A2S), which decreased the formation of deoxy products. With an optimum amount of A2S the selectivity at 100°C was improved from 93.6 to 96.7%. The molecule acted as a permanent surface modifier since the catalyst was recycled with the same selectivity without further addition of A2S. The molecule could act as an electron-donating surface ligand decreasing the rate of dehydroxylation reactions.
- Fabre, Lionel,Gallezot, Pierre,Perrard, Alain
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p. 247 - 254
(2007/10/03)
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- Experimental studies on complex oscillations in a Mn2+-catalyzed acidic bromate-glucose reaction
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Under batch-reactor conditions, the BrO3--glucose-Mn2+-H2SO 4 system exhibits several types of oscillations, depending on the concentrations of the reactants. In certain cases, dual-frequency oscillat
- Li,Wang
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p. 1817 - 1821
(2007/10/03)
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- Alkylation of partially protected xylofuranoses and tetritols with (2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoroheptyl)-oxirane and the stability of protecting acetal groups towards Lewis acid-type catalyst
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1,2-O-Isopropylidene-3-O-methyl-α-D-xylofuranose (2), 1,2-O-isopropylidene-α-D-xylofuranose (3), 2,4-O-ethylidene-D-erythritol (4) and 1,3-O-ethylidene-D-threitol (5) were alkylated with racemic (2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoroheptyl)oxirane (1) using boron trifluoride diethyl etherate as a catalyst. The desired mono- or disubstituted polyfluoroalkyl derivatives 6-11 were isolated only in low to medium yields. The fluoroalkylation was accompanied with disproportional distributions of the protecting acetal/ketal groups and polymerization of saccharides. Therefore the stability of 3, 4, 5, 5-O-acetyl-1,2-O-isopropylidene-α-D-xylofuranose (14) and 1,2-O-isopropylidene-α-D-glucofuranose (15) in the presence of a catalytic amount of boron trifluoride diethyl etherate was investigated in various solvents. A mechanism explaining the effect of the catalyst has been proposed.
- Kefurt, Karel,Moravcova, Jitka,Bambasova, Sarka,Buchalova, Katerina,Vymetalikova, Barbora,Kefurtova, Zdenka,Stanek, Jan,Paleta, Oldrich
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p. 1665 - 1681
(2007/10/03)
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