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141.
Acyl Migration Kinetics of Vegetable Oil 1,2-Diacylglycerols 总被引:1,自引:0,他引:1
Joseph A. Laszlo David L. Compton Karl E. Vermillion 《Journal of the American Oil Chemists' Society》2008,85(4):307-312
The acyl migration kinetics of long-chain 1,2-diacylglycerol (1,2-DAG) to form 1,3-diacylglycerol (1,3-DAG) over the temperature
range of 25–80 °C were examined using 1H-NMR spectroscopy. Lipase-catalyzed ethanolysis of high-oleic sunflower oil, followed by a series of solvent extraction steps,
generated high purity 1,2-DAG (0.93 mol fraction of the DAG content). The 1,2-DAG mole fraction of 0.32 at equilibrium was
found to be insensitive to temperature, indicating that long-chain acyl group migration is neither endothermic nor exothermic.
Determination of the temperature-dependent, first-order reaction kinetic parameters revealed a 1,2-DAG half life (t
1/2) of 3,425 h and 15.8 h at 25 and 80 °C, respectively. A comparison of 1,2-DAG with 2-monoacylglycerol indicated that there
is no difference between the two in the potential energy state (ΔG
‡) of their respective transitions states or cyclic intermediates.
Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard
of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may
be suitable. 相似文献
142.
One of the most promising technologies for the production of hydrogen is the use of a Palladium Membrane in order to separate hydrogen from a gas mixture coming from the allothermal biomass gasification process. At the TU München, an innovative allothermal gasifier called Biomass Heat Pipe Reformer (BioHPR) has been developed. This gasifier produces a hydrogen rich gas which can be further used for energy production. A Palladium Membrane can be installed in the gasifier in order to gain pure hydrogen from this gas mixture. This gas can be then used in applications which demand high purified hydrogen like for example Polymer Electrolyte Membrane Fuel Cells (PEMFC). The present paper describes the aforementioned gasification technology combined with a palladium filter and investigates the results from the simulation of these systems. 相似文献
143.
Mi Jung Kim Mi Suk Jeong Yang Kim Karl Seff 《Microporous and mesoporous materials》1999,30(2-3):233-241
The crystal structures of fully dehydrated Sr46–X [Sr46Si100Al92O384; a=25.214(7) Å] and of its ammonia sorption complex, Sr46–X·102NH3 [Sr46Si100Al92O384·102NH3; a=25.127(7) Å], have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd
at 21(1)°C. The Sr46–X crystal was prepared by ion exchange in a flowing stream of aqueous 0.05 M Sr(ClO4)2 for 5 days followed by dehydration at 360°C and 2×10−6 Torr for 2 days. To prepare the ammonia sorption complex, another dehydrated Sr46–X crystal was exposed to 230 Torr of zeolitically dried ammonia gas for 1 h followed by evacuation for 12 h at 21(1)°C and 5×10−4 Torr. The structures were refined to the final error indices, R1=0.043 and Rw=0.039 with 466 reflections, and R1=0.049 and Rw=0.044 with 382 reflections, for which I>3σ(I). In dehydrated Sr46–X, all Sr2+ ions are located at two crystallographic sites. 16 Sr2+ ions are at the centers of the double six-rings, filling that site (site I, Sr–O=2.592(6) Å). The remaining 30 Sr2+ ions are in the supercage (site II); each extends 0.56 Å into the supercage from the plane of its three nearest oxygen atoms (Sr–O=2.469(6) Å). In the structure of Sr46–X·102NH3, the Sr2+ ions are located at three crystallographic sites: 12 are found at site I [Sr–O=2.652(10) Å]; four in the sodalite units (site I′) each coordinated to three framework oxygen atoms at 2.654(9) Å and also to three ammonia molecules at 2.76(8) Å. The remaining 30 Sr2+ ions lie at site II. Each extends 1.12 Å into the supercage where it coordinates to three framework oxygen atoms at 2.584(7) Å and also to three ammonia molecules at 2.774(24) Å. 相似文献
144.
Catalytic distillation experiments were carried out in a 100 mm diameter column for the removal of dilute acetic acid from water. The column was installed with a novel internal composed of alternating a dualflow tray and a catalyst basket. Amberlyst 15 was used as a catalyst to accelerate the esterification of acetic acid with methanol. The effects of various operating parameters on the acid removal were investigated. For the feed which contains 2.5 to 9.9 wt% of acetic acid in water, more than 50 wt% of acetic acid can be recovered as methyl acetate in the 1.5 meter high test column. 相似文献
145.
Removal of acetic acid from water by catalytic distillation. Part 2: Modeling and simulation studies
A simulation program has been established by incorporating basic models for reaction kinetics, vapor–liquid equilibrium and mass transfer into Aspen Plus (Aspen Technology Inc., 1996) to simulate the catalytic distillation process for the removal of dilute acetic acid from water. The simulated concentration profiles agree well with those measured under various operating conditions. 相似文献
146.
Marianne Wittrup Larsen Dr. Dorota F. Zielinska Mats Martinelle Dr. Aurelio Hidalgo Dr. Lars Juhl Jensen Prof. Uwe T. Bornscheuer Prof. Karl Hult Prof. 《Chembiochem : a European journal of chemical biology》2010,11(6):796-801
A water tunnel in Candida antarctica lipase B that provides the active site with substrate water is hypothesized. A small, focused library created in order to prevent water from entering the active site through the tunnel was screened for increased transacylation over hydrolysis activity. A single mutant, S47L, in which the inner part of the tunnel was blocked, catalysed the transacylation of vinyl butyrate to 20 mM butanol 14 times faster than hydrolysis. The single mutant Q46A, which has a more open outer end of the tunnel, showed an increased hydrolysis rate and a decreased hydrolysis to transacylation ratio compared to the wild‐type lipase. Mutants with a blocked tunnel could be very useful in applications in which hydrolysis is unwanted, such as the acylation of highly hydrophilic compounds in the presence of water. 相似文献
147.
Hazem Khalil Hans‐Jürgen Gläsel Karl Köhler Ferdinand Hardinghaus Michael R. Buchmeiser 《大分子材料与工程》2010,295(3):276-282
Acrylate‐based nanocomposite coatings prepared from uniformly sized, nanoscaled inorganic, i.e., BaSO4‐ and CaF2‐ as well as organometallic, i.e., Al‐maleate‐derived nanoparticles were prepared applying photochemical curing. Excellent mechanical and thermal stability as well as high optical transparency was achieved as compared to standard SiO2‐based coatings. The performance of CaF2‐based nanocomposites could be further enhanced by addition of nanocorundum. A comprehensive data set on surface and Martens hardness, the penetration depths, glass transition temperatures, and UV–Vis transparency of the final coatings is presented.
148.
Ingrid M le Roux Karl le Roux W Scott Comulada Erin M Greco Katherine A Desmond Nokwanele Mbewu Mary Jane Rotheram-Borus 《Nutrition journal》2010,9(1):56
Background
Child and infant malnourishment is a significant and growing problem in the developing world. Malnourished children are at high risk for negative health outcomes over their lifespans. Philani, a paraprofessional home visiting program, was developed to improve childhood nourishment. The objective of this study is to evaluate whether the Philani program can rehabilitate malnourished children in a timely manner. 相似文献149.
In the cheese industry, the concentration of milk using ultrafiltration for continuous soft and fresh cheese production is standard technology. The object of the work presented here was to produce a semi-hard cheese of quality and composition comparable to that of traditionally made cheese from highly concentrated microfiltered milk retentate. Two different membrane systems were tested for the production of high viscous milk retentate with high dry matter content. For milk containing 3.2% fat and skim milk, a concentration factor of 6.6 and 9.1 respectively was obtained using the MF/UF/UF pilot plant fitted with cassette modules. Milk containing 3.2% fat was concentrated in batches by a factor of 5.7 in the pilot plant using a ceramic membrane. Using minimal curd separation, a semi-hard one day old cheese with a dry matter of 533 g/kg, moisture on a fat-free basis (MFFB) of 626 g/kg and fat on a dry basis (FDB) value of 478 g/kg was made from the milk retentate produced with the ceramic module. The ripened cheese fulfilled the legal requirements of a traditionally produced semi-hard cheese with superb sensory qualities. Using the MF/UF/UF plant, a dry matter of 495 g/kg (MFFB 669 g/kg, FDB 493 g/kg) was achieved in a semi-hard cheese made from skim milk retentate. Our results suggest that by using a larger spacer distance in the last loop of the MF/UF/UF plant, combined with new hybrid technologies, semi-hard cheese production from full concentrate milk will soon become possible. 相似文献
150.
We have shown that autoxidized polyphenolic nutraceuticals oxidize H2S to polysulfides and thiosulfate and this may convey their cytoprotective effects. Polyphenol reactivity is largely attributed to the B ring, which is usually a form of hydroxyquinone (HQ). Here, we examine the effects of HQs on sulfur metabolism using H2S- and polysulfide-specific fluorophores (AzMC and SSP4, respectively) and thiosulfate sensitive silver nanoparticles (AgNP). In buffer, 1,4-dihydroxybenzene (1,4-DB), 1,4-benzoquinone (1,4-BQ), pyrogallol (PG) and gallic acid (GA) oxidized H2S to polysulfides and thiosulfate, whereas 1,2-DB, 1,3-DB, 1,2-dihydroxy,3,4-benzoquinone and shikimic acid did not. In addition, 1,4-DB, 1,4-BQ, PG and GA also increased polysulfide production in HEK293 cells. In buffer, H2S oxidation by 1,4-DB was oxygen-dependent, partially inhibited by tempol and trolox, and absorbance spectra were consistent with redox cycling between HQ autoxidation and H2S-mediated reduction. Neither 1,2-DB, 1,3-DB, 1,4-DB nor 1,4-BQ reduced polysulfides to H2S in either 21% or 0% oxygen. Epinephrine and norepinephrine also oxidized H2S to polysulfides and thiosulfate; dopamine and tyrosine were ineffective. Polyphenones were also examined, but only 2,5-dihydroxy- and 2,3,4-trihydroxybenzophenones oxidized H2S. These results show that H2S is readily oxidized by specific hydroxyquinones and quinones, most likely through the formation of a semiquinone radical intermediate derived from either reaction of oxygen with the reduced quinones, or from direct reaction between H2S and quinones. We propose that polysulfide production by these reactions contributes to the health-promoting benefits of polyphenolic nutraceuticals. 相似文献