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1.
Enantioselective Sulfoxidation Catalyzed by a Bisguanidinium Diphosphatobisperoxotungstate Ion Pair 下载免费PDF全文
Xinyi Ye Adhitya Mangala Putra Moeljadi Kek Foo Chin Prof. Dr. Hajime Hirao Dr. Lili Zong Prof. Dr. Choon‐Hong Tan 《Angewandte Chemie (International ed. in English)》2016,55(25):7101-7105
The first enantioselective tungstate‐catalyzed oxidation reaction is presented. High enantioselectivities were achieved for a variety of drug‐like phenyl and heterocyclic sulfides under mild conditions with H2O2, a cheap and environmentally friendly oxidant. Synthetic utility was demonstrated through the preparation of (S)‐Lansoprazole, a commercial proton‐pump inhibitor. The active ion‐pair catalyst was identified to be bisguanidinium diphosphatobisperoxotungstate using Raman spectroscopy and computational studies. 相似文献
2.
Kaarina Kekäläinen Henrikki Liimatainen Jouko Niinimäki 《Cellulose (London, England)》2014,21(5):3691-3700
Periodate–chlorite oxidized bleached hardwood kraft pulp fibre samples with six levels of charge densities ranging from 0.5 to 1.8 mmol/g were gradually disintegrated to microfibrils using a high-shear homogenizer. The disintegration kinetics and mechanisms were studied by a flow fractionation method, and the properties of the resulting particles were determined using low shear viscosity and transmittance measurements. The particles formed during the disintegration were visualized with a charge-coupled device camera and by field-emission scanning electron microscopy. The result showed that cellulose fibres with a low charge density disintegrated at a low rate and produced ragged fibres and bunches of microfibrils via bursting of the fibre walls, whereas those with a higher charge density broke down at a high rate and microfibrils were formed through swelling and the creation of balloon structures. A carboxyl content of 1.2 mmol/g was found to be the threshold value for the efficient formation of high aspect ratio microfibrils and also for the change in the disintegration mechanism in the high-shear homogenizer. 相似文献
3.
Enantioselective Synthesis of Quaternary Carbon Stereocenters: Addition of 3‐Substituted Oxindoles to Vinyl Sulfone Catalyzed by Pentanidiums 下载免费PDF全文
Dr. Lili Zong Shubo Du Kek Foo Chin Dr. Chao Wang Prof. Dr. Choon‐Hong Tan 《Angewandte Chemie (International ed. in English)》2015,54(32):9390-9393
A pentanidium‐catalyzed highly enantioselective conjugate addition of 3‐alkyloxindoles to phenyl vinyl sulfone has been demonstrated. This approach allows the construction of 3,3‐dialkyl‐substituted oxindole frameworks with high yield and excellent enantioselectivity (up to 99 %) under simple phase‐transfer conditions. A variety of oxindoles bearing all‐carbon quaternary stereogenic centers were obtained in the presence of 0.25 mol % pentanidium. Meanwhile, practicality was illustrated by a gram‐scale asymmetric synthesis of two 3,3‐dialkyl‐substituted oxindoles. The resulting adduct can be smoothly transformed to the natural product analogue in a short synthetic route. 相似文献
4.
Pekka Kekäläinen Mikko Voutilainen Antti Poteri Pirkko Hölttä Aimo Hautojärvi Jussi Timonen 《Transport in Porous Media》2011,87(1):125-149
A model transport system is considered in which a pulse of tracer molecules is advected along a flow channel with porous walls.
The advected tracer thus undergoes diffusion, matrix-diffusion, inside the walls, which affects the breakthrough curve of
the tracer. Analytical solutions in the form of series expansions are derived for a number of situations which include a finite
depth of the porous matrix, varying aperture of the flow channel, and longitudinal diffusion and Taylor dispersion of the
tracer in the flow channel. Novel expansions for the Laplace transforms of the concentration in the channel facilitated closed-form
expressions for the solutions. A rigorous result is also derived for the asymptotic form of the breakthrough curve for a finite
depth of the porous matrix, which is very different from that for an infinite matrix. A specific experimental system was created
for validation of matrix-diffusion modeling for a matrix of finite depth. A previously reported fracture-column experiment
was also modeled. In both cases model solutions gave excellent fits to the measured breakthrough curves with very consistent
values for the diffusion coefficients used as the fitting parameters. The matrix-diffusion modeling performed could thereby
be validated. 相似文献
5.
Numerical Algorithms - This paper presents a class of low memory quasi-Newton methods with standard backtracking line search for large-scale unconstrained minimization. The methods are derived by... 相似文献
6.
基于一维区域上的拟一致剖分,证明了线性元插值误差的最优下界估计.基于此并利用超收敛理论,我们得到了有限元离散误差的上、下界. 相似文献
7.
Mikko Voutilainen Paul Sardini Marja Siitari-Kauppi Pekka Kek?l?inen Vesa Aho Markko Myllys Jussi Timonen 《Transport in Porous Media》2013,96(2):319-336
Numerical time-domain-diffusion simulations were used for studying the diffusion behavior of tracer molecules in rock matrix with homogeneous and heterogeneous porosity. As the heterogeneous sample in these simulations, a 3D tomographic image of altered tonalite was used, in which the mineral components and the pores resolved by X-ray microtomography were represented by their respective intragranular porosities determined previously by the 14C-PMMA method. The apparent diffusion coefficient of a tracer in altered tonalite was determined experimentally, and was then used in the simulations. In the altered tonalite analyzed, inclusion of heterogeneity in the porosity increased the diffusion coefficient by 16 %. Altered and pristine feldspar was the main mineral component in the sample (72 %), and it also provided the dominant contribution to tracer diffusion, explaining alone 52 % of the diffusion coefficient. The large pores resolved by microtomography (6 %) and altered and pristine mica (22 %) gave an equal contribution to the diffusion coefficient. The simulation method applied was also validated by comparing the results to both an analytical and a numerical solution to the diffusion equation in a homogenous medium. In addition, the method was compared to discrete-time random-walk simulations in the case of randomly placed overlapping spheres. 相似文献
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9.
Kaarina Kekäläinen Henrikki Liimatainen Mirja Illikainen Thad C. Maloney Jouko Niinimäki 《Cellulose (London, England)》2014,21(3):1163-1174
The effect of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation on the structure of hornified fibres and their disintegration behaviour was studied by a method combining gradual disintegration of the fibre structure in an in-line homogenizer with a chromatographic separation technique. It was seen that hornification prior to TEMPO-mediated oxidation had a notable effect on the disintegration behaviour of bleached cellulose fibres in a high-shear homogenizer and on the properties of the resulting particles. Field-emission scanning electron microscopy imaging of the suspensions and viscosity and transmittance measurements revealed that never-dried oxidized fibres disintegrated into bunches of microfibrils and at higher charge densities into thinner and more individual microfibrils. These microfibrils were obtained from fibres through swelling and ballooning. The hornified fibres were mainly cut into shorter ones as the charge density increased. After reversing the hornification and allowing the fibres to swell further, however, microfibrils were also obtained from this source. The charge threshold for efficient microfibril production from never-dried fibres in the high-shear homogenizer used here was 0.7 mmol/g. 相似文献
10.
H. W. Meyer Ming Zhang U. Bismayer E. K. H. Salje C. Schmidt S. Kek 《Phase Transitions》2013,86(1-3):39-60
The thermal behaviour of natural titanite has been studied using infrared and Raman spectroscopy, linear birefringence and synchrotron X-ray diffraction. Natural single crystals from Rauris, Austria (Fe 1.8%. Al 3.8%) were investigated and two additional samples from the Smithonian Institute Washington (Fe 2.8%, Al 0.5% and Fe 8.8%, Al 13.9%) served for IR and birefringence measurements. The coupled substitution of Fe and Al for Ti and OH and F for O leads to the formation of long ranging defect fields which are assumed to account for an increased density of antiphase boundaries. Infrared absorption spectra show increased bandwidths with increasing defect concentration. The phase transition near 500 K is clearly seen in the IR spectra of samples with low defect concentrations but not for those with high defect densities. X-ray diffraction shows strong anisotropic diffuse scattering in the Rauris sample leading to the average symmetry A2/a at room-temperature. A second anomaly at ca. 850 K was found by X-ray diffraction techniques using synchrotron radiation and by a break in the temperature evolution of the IR spectra. 相似文献