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61.
Substituted 3-hydroxy-delta-lactones (3HLs) are valuable intermediates in the synthesis of pharmaceuticals and other biologically active natural products. Herein we report the first example of the catalytic carbonylation of substituted homoglycidols to 3HLs using HCo(CO)4. Upon optimization of the catalyst and reaction conditions, a functionally diverse set of 3HLs was prepared. Mechanistic insight was gained by observation of the carbonylation reaction using in situ IR spectroscopy, and we propose a mechanism that is consistent with previously studied epoxide carbonylation systems. 相似文献
62.
Rezaei F Joh LD Kashima H Reddy AP VanderGheynst JS 《Applied biochemistry and biotechnology》2011,164(6):793-803
Solid-state fermentation has been widely used for enzyme production. However, secreted enzymes often bind to the solid substrate
preventing their detection and recovery. A series of screening studies was performed to examine the role of extraction buffer
composition including NaCl, ethylene glycol, sodium acetate buffer, and Tween 80, on xylanase and cellulase recovery from
switchgrass. Our results indicated that the selection of an extraction buffer is highly dependent on the nature and source
of the enzyme being extracted. While a buffer containing 50 mM sodium acetate at pH 5 was found to have a positive effect
on the recovery of commercial fungal-derived cellulase and xylanase amended to switchgrass, the same buffer had a significant
negative effect on enzyme extraction from solid fermentation samples colonized by the bacterium Acidothermus cellulolyticus. Xylanase activity was more affected by components in the extraction buffers compared to cellulase. This study demonstrated
that extraction followed by diafiltration is important for assessing enzyme recovery from solid fermentation samples. Reduction
in activity due to compounds present in the switchgrass extracts is reversible when the compounds are removed via diafiltration. 相似文献
63.
The limiting factors of second-order methods for large-scale semidefinite optimization are the storage and factorization of
the Newton matrix. For a particular algorithm based on the modified barrier method, we propose to use iterative solvers instead
of the routinely used direct factorization techniques. The preconditioned conjugate gradient method proves to be a viable
alternative for problems with a large number of variables and modest size of the constrained matrix. We further propose to
avoid explicit calculation of the Newton matrix either by an implicit scheme in the matrix–vector product or using a finite-difference
formula. This leads to huge savings in memory requirements and, for certain problems, to further speed-up of the algorithm.
Dedicated to the memory of Jos Sturm. 相似文献
64.
This work presents a model and simulation results for the friction detachment of a finite sized interface, following previous results on the phenomenon by Ben-David and Fineberg, namely “experiments demonstrating that the ratio of shear to normal force needed to move contacting bodies can, instead, vary systematically with controllable changes in the external loading configuration”. In particular, we extend a previous one-dimensional simulation model by Bar-Sinai with colleagues to a quasi 2D model to allow for a tilting of one of the contacting blocks. While Bar-Sinai with colleagues postulate that the presence of “slow fronts” of detachment (an order of magnitude lower than the usual Rayleigh fronts as in crack propagation) is due to a strengthening term in the friction law, which is not always measured in unlubricated contacts, we find slow fronts also with a purely weakening law. 相似文献
65.
When treated as an effective three-body problem in the framework of a simple field-theory model, the NNπ system acquires, in addition to the disconnected subsystem interactions usually considered, a new type of disconnected driving term, possible only for non-conserved particles such as the π. These terms pose a disconnectedness problem more intricate than that solved by Faddeev's equations or their known modifications for connected three-body forces. The solution of this problem in terms of a set of connected-kernel integral equations is presented. 相似文献
66.
Rudolf Ochs W. Fresenius P. Saccardi Weber J. M. Kolthoff H. Hamer H. Röttger E. Schowalter E. Spaeth A. Gompf J. Gerum G. Metge A. Röhrig L. Fresenius G. de Astis A. Bornträger H. Astruc Radet M. Martini A. Nourrisson L. Roos A. Kling A. Lassieur M. François Ch. Lormand J. Dubaquié P. Chauvet J. L. Chelle G. Filaudeau Bonis H. Boßelmannn F. Mach M. Fischler C. von der Heide Joh Pinnow D. Fonzes-Diakon L. Semichon K. Kroemer R. Meissner A. Widmer O. Kalberer L. Minder Th. v. Fellenberg G. Chancel P. Balavoine X. Roques C. Lagneau von der Heide 《Analytical and bioanalytical chemistry》1926,68(12):469-480
67.
Structure Redetermination and Magnetic Studies on Mn2SnS4 The crystal structure of Mn2SnS4 was redetermined by single crystal and powder X-ray studies. It has a deficient NaCl superstructure crystallizing in the orthorhombic space group Cmmm proposed by Wintenberger and Jumas in 1980 (Z = 2, a = 740.7(1), b = 1047.5(1) and c = 366.7(2) pm, Rf = 1.4% for 266 unique reflections with I > 0σ1). Some additional reflections, which are not compatible with this cell, can be refined assuming formation of twinned trilling crystals. Mn2SnS4 undergoes antiferromagnetic ordering below 160 K. The effective magnetic moment μeff of Mn2+ is 5.92 B.M. The IR and Raman spectra display 5 and 3 bands in the range 150–320 cm?1, respectively. 相似文献
68.
Yasuhi Joh Heimei Yuki Shunsuke Murahashi 《Journal of polymer science. Part A, Polymer chemistry》1970,8(11):3311-3328
The effect of polymerization conditions such as aging time of the catalyst, polymerization temperature, polymerization time, monomer concentration, and catalyst concentration on the polymerization of isobutyl vinyl ether was intensively studied by using the VCI3·LiCl–Al(i-Bu)3 system at an Al(i-Bu)/VCl3·LiCl ratio of 6 at which the cationic polymerization by VCl3·LiCl is sufficiently depressed. About 10 min aging of the catalyst in the presence of monomer yields a fairly stable catalytie system. The optimum polymerization temperature is around 30°C. The conversion increased with increasing monomer concentration, whereas the stereospecificity of polymerization decreased. Unexpectedly, the conversion decreased as total catalyst concentration increased. This phenomenon is explained by considering the deactivation of catalytic sites by the excess of Al(i-Bu)3. A reasonable mechanism from kinetic considerations is that two molecules of Al(i-Bu)3 deactivate the catalytic site in an equilibrium reaction. This deactivation is understandable by considering that the coordination of two molecules of Al(i-Bu)3 will occupy all the coordination positions of vanadium, so that there is no room for coordination of monomer coming to the catalytic site. 相似文献
69.
Iva Matolínová Viktor Johánek Josef Mysliveček Kevin C. Prince Tomáš Skála Michal Škoda Nataliya Tsud Mykhailo Vorokhta Vladimír Matolín 《Surface and interface analysis : SIA》2011,43(10):1325-1331
Methanol adsorption on ion‐sputtered Pt(111) surface exhibiting high concentration of vacancy islands and on (2 × 1)Pt(110) single crystal were investigated by means of photoelectron spectroscopy (PES) and thermal desorption spectroscopy. The measurements showed that methanol adsorbed at low temperature on sputtered Pt(111) and on (2 × 1)Pt(110) surfaces decomposed upon heating. The PES data of methanol adsorption were compared to the data of CO adsorbed on the same Pt single crystal surfaces. In the case of the sputtered Pt(111) surface, the dehydrogenation of HxCO intermediates is followed by the CO bond breakage. On the (2 × 1)Pt(110) surface, carbon monoxide, as product of methanol decomposition, desorbed molecularly without appearance of any traces of atomic carbon. By comparing both platinum surfaces we conclude that methanol decomposition occurs at higher temperature on sputtered Pt(111) than on (2 × 1)Pt(110). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献