The Experts below are selected from a list of 84 Experts worldwide ranked by ideXlab platform
Tyler R Josephson - One of the best experts on this subject based on the ideXlab platform.
-
cooperative catalysis by surface lewis acid silanol for selective fructose etherification on sn spp zeolite
ACS Catalysis, 2018Co-Authors: Tyler R Josephson, Robert F Dejaco, Swagata Pahari, Limin Ren, Qiang Guo, Michael Tsapatsis, Ilja J Siepmann, Dionisios G Vlachos, Stavros CaratzoulasAbstract:While Lewis-acid zeolites, such as Sn-Beta, catalyze glucose isomerization in an alcoholic medium, mesoporous Sn-SPP catalyzes both glucose isomerization to fructose and fructose etherification (formally ketalization) to ethyl Fructoside, enabling fructose yields in excess of the glucose/fructose equilibrium. Using periodic density functional theory calculations and force-field-based Monte Carlo simulations, the ketalization reaction mechanism and adsorption behavior were examined. The silanols on the Sn-SPP mesopore surface facilitate the ketalization reaction through hydrogen bonding interactions at the transition state, only possible via a Sn–O–Si−OH moiety, present in Sn-SPP but not in Sn-Beta. Fructose ketalization is favored over glucose acetalization due to differences in stability of the oxonium intermediates, which are stabilized by the Sn-SPP active site. The open site of hydrophobic Sn-Beta cannot perform these reactions because its active site does not contain an adjacent silanol of the right ...
-
Cooperative Catalysis by Surface Lewis Acid/Silanol for Selective Fructose Etherification on Sn-SPP Zeolite
2018Co-Authors: Tyler R Josephson, Robert F Dejaco, Swagata Pahari, Limin Ren, Qiang Guo, Michael Tsapatsis, Ilja J Siepmann, Dionisios G Vlachos, Stavros CaratzoulasAbstract:While Lewis-acid zeolites, such as Sn-Beta, catalyze glucose isomerization in an alcoholic medium, mesoporous Sn-SPP catalyzes both glucose isomerization to fructose and fructose etherification (formally ketalization) to ethyl Fructoside, enabling fructose yields in excess of the glucose/fructose equilibrium. Using periodic density functional theory calculations and force-field-based Monte Carlo simulations, the ketalization reaction mechanism and adsorption behavior were examined. The silanols on the Sn-SPP mesopore surface facilitate the ketalization reaction through hydrogen bonding interactions at the transition state, only possible via a Sn–O–Si−OH moiety, present in Sn-SPP but not in Sn-Beta. Fructose ketalization is favored over glucose acetalization due to differences in stability of the oxonium intermediates, which are stabilized by the Sn-SPP active site. The open site of hydrophobic Sn-Beta cannot perform these reactions because its active site does not contain an adjacent silanol of the right geometry. In addition to the more favorable activation barrier of the catalytic process, the adsorption at the catalytic site in Sn-SPP is also found to be more favorable than for Sn-Beta, in spite of competitive adsorption between fructose and ethanol in the ethanol-saturated zeolites
Sang-ki Rhee - One of the best experts on this subject based on the ideXlab platform.
-
molecular cloning of levan fructotransferase gene from arthrobacter ureafaciens k2032 and its expression in escherichia coli for the production of difructose dianhydride iv
Letters in Applied Microbiology, 2005Co-Authors: E K Jang, Ki Bang Song, K H Jang, S A Kang, Oh Suk Kwon, Sang-ki RheeAbstract:Aims: To clone and overexpress a novel levan fructotransferase gene lftA from Arthrobacter ureafaciens K2032. Methods and Results: The lftA gene, encoding a levan fructotransferase (LFTase) of 521 amino acids (aa) residues, was cloned from the genomic DNA of A. ureafaciens K2032, and overexpressed in Escherichia coli. The recombinant LFTase overexpressed in E. coli was then used to produce a difructose dianhydride (DFA IV) from levan. DFA IV crystals with 97% purity could be obtained from the reaction mixture in 83·7% yield by using a natural crystallization method. Conclusions: The lftA gene cloned from A. ureafaciens K2032 encode a novel levan fructotransferase which produces difructose dianhydride (DFA IV) from levan. Significance and Impact of the Study: Levan fructotransferase is a useful enzyme with great promise in the production of DFA IV and various Fructosides.
-
synthesis of methyl β d Fructoside catalyzed by levansucrase from rahnella aquatilis
Enzyme and Microbial Technology, 2000Co-Authors: Ki Bang Song, Sang-ki RheeAbstract:Abstract Methyl β-D-Fructoside(MF) was formed from sucrose and methanol by a transfructosylation reaction using recombinant levansucrase from Rahnella aquatilis . The increase in the yield of MF formation was achieved by increasing methanol concentration. The enzyme stability at higher concentrations of methanol was maintained by lowering the reaction temperature. The optimum temperature and sucrose concentration for MF formation was 10°C and 50 gL −1 respectively and the yield of MF was 70%.
-
Synthesis of methy1 beta-D-Fructoside catalyzed by levansucrase from Rahnella aquatilis
Elsevier, 2000Co-Authors: Min Gon Kim, Ki Bang Song, Chul Ho Kim, Jong Sik Lee, Sang-ki RheeAbstract:Methyl β-D-Fructoside(MF) was formed from sucrose and methanol by a transfructosylation reaction using recombinant levansucrase from Rahnella aquatilis. The increase in the yield of MF formation was achieved by increasing methanol concentration. The enzyme stability at higher concentrations of methanol was maintained by lowering the reaction temperature. The optimum temperature and sucrose concentration for MF formation was 10°C and 50 gL-1 respectively and the yield of MF was 70%.ope
-
Levan and fructosyl derivatives formation by a recombinant levansucrase from Rahnella aquatilis
Biotechnology Letters, 1998Co-Authors: Ki Bang Song, Bong Hyun Chung, Sang-ki RheeAbstract:Levan, fructo-oligosaccharides and fructosyl derivatives were formed from sucrose using recombinant levansucrase from Rahnella aquatilis. Levan formation was optimal at 30 °C resulting 57 % of the theoretical yield. The more suitable substrate concentration for levan formation was 200 g sucrose/L. Oligosaccharides was accumulated selectively at high substrate concentration. The increase of levan and oligosaccharides formation was not achieved by adding water-miscible organic solvents. Alkyl Fructosides were synthesized from various alcohols as fructosyl acceptors by R. aquatilis levansucrase. © Rapid Science Ltd. 1998
Anders Riisager - One of the best experts on this subject based on the ideXlab platform.
-
kinetic analysis of hexose conversion to methyl lactate by sn beta effects of substrate masking and of water
Catalysis Science & Technology, 2018Co-Authors: Irene Tosi, Anders Riisager, Esben Taarning, Pernille Rose Jensen, Sebastian MeierAbstract:Simple sugars show promise as substrates for the formation of fuels and chemicals using heterogeneous catalysts in alcoholic solvents. Sn-Beta is a particularly well-suited catalyst for the cleavage, isomerization and dehydration of sugars into more valuable chemicals. In order to understand these processes and save resources and time by optimising them, kinetic and mechanistic analyses are helpful. Herein, we study substrate entry into the Sn-Beta-catalysed methyl lactate process using abundant hexose substrates. NMR spectroscopy is applied to show that the formation of methyl lactate occurs in two kinetic regimes for fructose, glucose and sucrose. The majority of methyl lactate is not formed from the substrate directly, but from methyl Fructosides in a slow regime. At 160 °C, more than 40% of substrate carbon are masked (i.e. reversibly protected in situ) as methyl Fructosides within a few minutes when using hydrothermally synthesised Sn-Beta, while more than 60% methyl Fructosides can be produced within a few minutes using post-synthetically treated Sn-Beta. A significant fraction of the substrate is thus masked by rapid methyl Fructoside formation prior to subsequent slow release of fructose. This release is the rate-limiting step in the Sn-Beta-catalysed methyl lactate process, but it can be accelerated by the addition of small amounts of water at the expense of the maximum methyl lactate yield.
-
efficient isomerization of glucose to fructose over zeolites in consecutive reactions in alcohol and aqueous media
Journal of the American Chemical Society, 2013Co-Authors: Shunmugavel Saravanamurugan, Marta Paniagua, Juan A Melero, Anders RiisagerAbstract:Isomerization reactions of glucose were catalyzed by different types of commercial zeolites in methanol and water in two reaction steps. The most active catalyst was zeolite Y, which was found to be more active than the zeolites beta, ZSM-5, and mordenite. The novel reaction pathway involves glucose isomerization to fructose and subsequent reaction with methanol to form methyl Fructoside (step 1), followed by hydrolysis to re-form fructose after water addition (step 2). NMR analysis with 13C-labeled sugars confirmed this reaction pathway. Conversion of glucose for 1 h at 120 °C with H-USY (Si/Al = 6) gave a remarkable 55% yield of fructose after the second reaction step. A main advantage of applying alcohol media and a catalyst that combines Bronsted and Lewis acid sites is that glucose is isomerized to fructose at low temperatures, while direct conversion to industrially important chemicals like alkyl levulinates is viable at higher temperatures.
-
Efficient Isomerization of Glucose to Fructose over Zeolites in Consecutive Reactions in Alcohol and Aqueous Media
2013Co-Authors: Shunmugavel Saravanamurugan, Marta Paniagua, Juan A Melero, Anders RiisagerAbstract:Isomerization reactions of glucose were catalyzed by different types of commercial zeolites in methanol and water in two reaction steps. The most active catalyst was zeolite Y, which was found to be more active than the zeolites beta, ZSM-5, and mordenite. The novel reaction pathway involves glucose isomerization to fructose and subsequent reaction with methanol to form methyl Fructoside (step 1), followed by hydrolysis to re-form fructose after water addition (step 2). NMR analysis with 13C-labeled sugars confirmed this reaction pathway. Conversion of glucose for 1 h at 120 °C with H‑USY (Si/Al = 6) gave a remarkable 55% yield of fructose after the second reaction step. A main advantage of applying alcohol media and a catalyst that combines Brønsted and Lewis acid sites is that glucose is isomerized to fructose at low temperatures, while direct conversion to industrially important chemicals like alkyl levulinates is viable at higher temperatures
Stavros Caratzoulas - One of the best experts on this subject based on the ideXlab platform.
-
cooperative catalysis by surface lewis acid silanol for selective fructose etherification on sn spp zeolite
ACS Catalysis, 2018Co-Authors: Tyler R Josephson, Robert F Dejaco, Swagata Pahari, Limin Ren, Qiang Guo, Michael Tsapatsis, Ilja J Siepmann, Dionisios G Vlachos, Stavros CaratzoulasAbstract:While Lewis-acid zeolites, such as Sn-Beta, catalyze glucose isomerization in an alcoholic medium, mesoporous Sn-SPP catalyzes both glucose isomerization to fructose and fructose etherification (formally ketalization) to ethyl Fructoside, enabling fructose yields in excess of the glucose/fructose equilibrium. Using periodic density functional theory calculations and force-field-based Monte Carlo simulations, the ketalization reaction mechanism and adsorption behavior were examined. The silanols on the Sn-SPP mesopore surface facilitate the ketalization reaction through hydrogen bonding interactions at the transition state, only possible via a Sn–O–Si−OH moiety, present in Sn-SPP but not in Sn-Beta. Fructose ketalization is favored over glucose acetalization due to differences in stability of the oxonium intermediates, which are stabilized by the Sn-SPP active site. The open site of hydrophobic Sn-Beta cannot perform these reactions because its active site does not contain an adjacent silanol of the right ...
-
Cooperative Catalysis by Surface Lewis Acid/Silanol for Selective Fructose Etherification on Sn-SPP Zeolite
2018Co-Authors: Tyler R Josephson, Robert F Dejaco, Swagata Pahari, Limin Ren, Qiang Guo, Michael Tsapatsis, Ilja J Siepmann, Dionisios G Vlachos, Stavros CaratzoulasAbstract:While Lewis-acid zeolites, such as Sn-Beta, catalyze glucose isomerization in an alcoholic medium, mesoporous Sn-SPP catalyzes both glucose isomerization to fructose and fructose etherification (formally ketalization) to ethyl Fructoside, enabling fructose yields in excess of the glucose/fructose equilibrium. Using periodic density functional theory calculations and force-field-based Monte Carlo simulations, the ketalization reaction mechanism and adsorption behavior were examined. The silanols on the Sn-SPP mesopore surface facilitate the ketalization reaction through hydrogen bonding interactions at the transition state, only possible via a Sn–O–Si−OH moiety, present in Sn-SPP but not in Sn-Beta. Fructose ketalization is favored over glucose acetalization due to differences in stability of the oxonium intermediates, which are stabilized by the Sn-SPP active site. The open site of hydrophobic Sn-Beta cannot perform these reactions because its active site does not contain an adjacent silanol of the right geometry. In addition to the more favorable activation barrier of the catalytic process, the adsorption at the catalytic site in Sn-SPP is also found to be more favorable than for Sn-Beta, in spite of competitive adsorption between fructose and ethanol in the ethanol-saturated zeolites
Sheng Yuan - One of the best experts on this subject based on the ideXlab platform.
-
permeabilization of microbacterium oxylans shifts the conversion of puerarin from puerarin 7 o glucoside to puerarin 7 o Fructoside
Applied Microbiology and Biotechnology, 2010Co-Authors: Cigang Yu, Haidong Xu, Guodong Huang, Ting Chen, Nan Chai, Yin Ji, Siyuan Wang, Sheng YuanAbstract:The main product of the conversion of puerarin by unpermeabilized cells of bacterium Microbacterium oxydans CGMCC 1788 was puerarin-7-O-glucoside (241 ± 31.9 µM). Permeabilization with 40% ethanol could not increase conversion yield, whereas it resulted in change of main product; a previous trace product became a main product (213 ± 48.0 µM) which was identified as a novel puerarin-7-O-Fructoside by electrospray ionization time-of-flight MS, 13C NMR, 1H NMR, and GC-MS analysis of sugar composition, and puerarin-7-O-glucoside became a trace product (14.8 ± 5.4 µM). However, the extract from cells of M. oxydans CGMCC 1788 permeabilized with ethanol converted puerarin to form 113.9 ± 27.7 µM puerarin-7-O-glucoside and 187.8 ± 29.5 µM puerarin-7-O-Fructoside under the same conditions. When unpermeabilized intact cells were recovered and used repeatedly for the conversion of puerarin, with increase of reuse times, the yield of puerarin-7-O-glucoside gradually decreased, whereas the yield of puerarin-7-O-Fructoside increased gradually in the conversion mixture. The main product of the conversion of puerarin by the tenth recycled unpremerbilized cells was puerarin-7-O-Fructoside (288.4 ± 24.0 µM). Therefore, the change of permeability of cell membrane of bacterium M. oxydans CGMCC 1788 contributed to the change of conversion of the product’s composition.
