526-98-7Relevant academic research and scientific papers
AuPt Alloy on TiO2: A Selective and Durable Catalyst for l-Sorbose Oxidation to 2-Keto-Gulonic Acid
Chan-Thaw, Carine E.,Chinchilla, Lidia E.,Campisi, Sebastian,Botton, Gianluigi A.,Prati, Laura,Dimitratos, Nikolaos,Villa, Alberto
, p. 4189 - 4194 (2015/12/30)
Pt nanoparticles were prepared by a sol immobilization route, deposited on supports with different acid/base properties (MgO, activated carbon, TiO2, Al2O3, H-Mordenite), and tested in the selective oxidation of sorbose to 2-keto-gulonic acid (2-KGUA), an important precursor for vitamin C. In general, as the basicity of the support increased, a higher catalytic activity occurred. However, in most cases, a strong deactivation was observed. The best selectivity to 2-KGUA was observed with acidic supports (TiO2 and H-Mordenite) that were able to minimize the formation of C1/C2 products. We also demonstrated that, by alloying Pt to Au, it is possible to enhance significantly the selectivity of Pt-based catalysts. Moreover, the AuPt catalyst, unlike monometallic Pt, showed good stability in recycling because of the prevention of metal leaching during the reaction.
2,5-Diketo-gluconic acid reductase from Corynebacterium glutamicum: Characterization of stability, catalytic properties and inhibition mechanism for use in vitamin C synthesis
Kaswurm, Vanja,Pacher, Claudia,Kulbe, Klaus Dieter,Ludwig, Roland
, p. 2012 - 2019 (2013/02/25)
2,5-Diketo-d-gluconic acid (2,5-DKG) reductase is an NADPH-dependent, monomeric aldo-keto reductase (AKR) which catalyzes the reduction of 2,5-DKG to 2-keto-l-gulonic acid (2-KLG) - the immediate precursor of vitamin C. The reaction catalyzed by 2,5-DKG reductase is attractive to bypass several chemical steps and produce vitamin C biocatalytically. In a screening of 22 bacterial strains, nine 2,5-DKG reductase producing bacterial strains were found. The gene of Corynebacterium glutamicum 2,5-DKG reductase was cloned and overexpressed in Escherichia coli. By batch fermentation 409 mg L-1 of 2,5-DKG reductase with a C-terminal His6-tag were obtained. The purified 2,5-DKG reductase was characterized in detail. The enzyme is most active in a pH range from 5.0 to 8.0 and its stability is high at temperatures below 35 °C. Catalytic constants for 2,5-DKG and NADPH were determined and a weak inhibition by the product 2-KLG was found. 2,5-DKG reductase activity is strongly inhibited by the common process ions Mg2+, Ca2+, SO43- and Cl-, which suggests that these should be avoided in the process. The inhibition mechanism for Cl- was elucidated. It is a competitive inhibitor with respect to NADPH and a noncompetitive inhibitior with respect to 2,5-DKG.
METHOD FOR EXTRACTING 2-KETONE-L-GULONIC ACID FROM A POLAR, PREFERABLY AQUEOUS SOLVENT
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Page/Page column 17, (2008/06/13)
The invention relates to a method for extracting 2-ketone-L-gulonic acids from a polar, preferably aqueous solvent, preferably from a solvent which contains a mixture of ascorbic acid and 2-ketone-L-gulonic acid, by means of liquid-liquid extraction with the aid of an extraction agent which contains a tertiary amine and a polar organic diluent. Preferably, the inventive method also comprises steps for retro-extracting the 2-ketone-L-gulonic acid and for returning the extraction agent. The invention also relates to a method for producing ascorbic acid from 2-ketone-L-gulonic acid and for isolating the thus produced ascorbic acid.
Platinum-containing hyper-cross-linked polystyrene as a modifier-free selective catalyst for L-sorbose oxidation
Sidorov,Volkov,Davankov,Tsyurupa,Valetsky,Bronstein,Karlinsey,Zwanziger,Matveeva,Sulman,Lakina,Wilder,Spontak
, p. 10502 - 10510 (2007/10/03)
Impregnation of hyper-cross-linked polystyrene (HPS) with tetrahydrofuran (THF) or methanol (ML) solutions containing platinic acid results in the formation of Pt(II) complexes within the nanocavities of HPS. Subsequent reduction of the complexes by Hsub
Regio- and stereo-selectivity in homogeneous catalytic hydrogenation of 2,5-diketo-D-threo-hexonic acid
Hamersak, Zdenko,Pavlovic, Nediljko,Delic, Vladimir,Sunjic, Vitomir
, p. 245 - 249 (2007/10/03)
2,5-Diketo-D-threo-hexonic acid (2,5-diketo-D-gluconic acid, 1), a crucial intermediate in the microbial production of L-threo-hex-2-enono-1,4-lactone (L-ascorbic acid, vitamin C), was isolated from the fermentation broth of bacterium Erwinia citreus ATCC 31623, and its regio- and stereo-selective hydrogenation, catalyzed by the water-soluble Ru(II) complex of tris(m-sulfophenyl)phosphine (TPPTS), was performed, The effect of hydrogen pressure, temperature, pH, and catalyst-to-substrate ratio on regio- and stereo-selectivity of the process was studied, at low pH, over 90% regioselectivity in favor of the reduction of the 5-keto group in 1 was achieved, affording L-xylo-2-hexulosonic acid (2-keto-L-gulonic acid, 2) as the main product. Maximal diastereoselectivity, i.e. ratio between 2 and 2-keto-n-gulonic acid (3) expressed as diastereomeric excess (d.e.%), amounted to ca. 50% and was not influenced by any of the above reaction parameters.
Platinum catalysts modified by adsorbed amines: A new method of enhancing rate and selectivity of L-sorbose oxidation
Broennimann,Bodnar,Aeschimann,Mallat,Baiker
, p. 720 - 729 (2007/10/03)
The Pt-catalyzed oxidation at C-1 of unprotected L-sorbose to 2-keto-L-gulonic acid, an intermediate in vitamin C synthesis, has been studied using molecular oxygen and neutral aqueous solution. The performance of Pt/alumina and Pt/C catalysts could be improved by addition of small quantities of tetraalkylammonium hydroxides, trialkyl-, triaryl-, and cycloaliphatic amines. The optimum modifier : Pts molar ratio is around 0.1, which corresponds to an amine : sorbose molar ratio of 1 : 1700. Rate enhancement (by a factor of up to 4.6) can be obtained when the pKa is around 10 or higher, and this correlation depends very little on the chemical structure of the amine. Rate acceleration is proposed to be connected with the hydration of the intermediate aldehyde (bifunctional catalysis). The influence of supported N-bases on the selectivity of Pt is a function of their chemical structure. The best results, 95% selectivity at 30% conversion and about 40% selectivity enhancement in the whole investigated conversion range, was obtained with Pt/C and hexamethylenetetramine. Electrochemical model studies revealed that hexamethylenetetramine is adsorbed on Pt and not oxidized during reaction. Molecular modeling suggests that the preferential oxidation at C-1 is due to complex formation by H-bonding between hexamethylenetetramine and sorbose. The adsorption of this complex on Pt results in a tilted position of the reactant in which only C-1 is exposed to oxidative dehydrogenation.
Localized Basification of Catalytic Surfaces enhances the Selective Oxidation of L-Sorbose over Supported Pt Catalysts modified with Tertiary Amines
Broennimann, C.,Mallat, T.,Baiker, A.
, p. 1377 - 1378 (2007/10/02)
Modification of supported Pt catalysts with strongly adsorbing tertiary amines is shown to be an efficient method to increase the reaction rate in the direct oxidation of L-sorbose to 2-keto-L-gulonic acid with molecular oxygen, and to increase the selectivity of the base-sensitive reaction.
Direct Oxidation of L-Sorbose to 2-Keto-L-gulonic Acid with Molecular Oxygen on Platinum- and Palladium-Based Catalysts
Broennimann, C.,Bodnar, Z.,Hug, P.,Mallat, T.,Baiker, A.
, p. 199 - 211 (2007/10/02)
The selective oxidation of the C1 hydroxyl group of L-sorbose to a carboxylic group without protection of the four other hydroxyl functions was investigated.The reactions were performed in slightly alkaline aqueous solutions with molecular oxygen over various alumina- and carbon-supported Pt and Pd catalysts.Optimum reaction conditions were 50 deg C, pH 7.3, and a catalyst:reactant ratio of 1:4 (wt/wt).The lower the pH and the temperature, the higher the selectivity toward 2-keto-L-gulonic acid.Catalyst deactivation was also found to increase with lower pH and temperature.A 5 wtpercent Pt/alumina catalyst showed the best catalytic performance (67percent selectivity at 58percent conversion).Promotion with Bi or Pb had a detrimental effect on selectivity for 2-keto-L-gulonic acid.Electrochemical measurements indicated that the reaction occurs in a rather narrow potential range, which corresponds to a moderate oxygen coverage of Pt or Pd.Four types of catalyst deactivation processes were identified, based on XPS and ICP-AES analysis and on the in situ determination of the oxidation state by monitoring the catalyst potential during reaction.A significant chemical poisoning of the active noble metal sites occurred during the initial, destructive adsorption of L-sorbose and during the oxidation reaction.The successive contamination of active sites resulted in overoxidation (too high oxygen coverage of Pt or Pd).The partially oxidized promoters and noble metals were corroded and dissolved in the presence of 2-keto-L-gulonic acid, resulting in an irreversible deactivation.
