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951.
Highly enantioselective copper(I)-fesulphos-catalyzed 1,3-dipolar cycloaddition of azomethine ylides
Cabrera S Gómez Arrayás R Carretero JC 《Journal of the American Chemical Society》2005,127(47):16394-16395
The catalyst system formed by Cu(CH3CN)4ClO4 and the planar chiral P,S-ligand Fesulphos behaves as a very efficient chiral Lewis acid in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides. This catalyst shows a remarkable reactivity at low catalyst loading (0.5-3 mol %), affording in good yields the endo adducts with exceptional levels of enantioselectivity (up to >99% ee). This catalytic asymmetric procedure has a broad structural scope with regard to both azomethine and dipolarophile substitution. The first examples of catalytic asymmetric 1,3-dipolar cycloaddition with ketimine-derived azomethines are reported. 相似文献
952.
Rodríguez Flores J Berzas Nevado JJ Durán Merás I Rodríguez Gómez MJ 《Journal of separation science》2005,28(7):658-664
A capillary zone electrophoresis (CZE) method using a fused-silica capillary (60.2 cm x 75 microm ID) was investigated for the determination of triamterene (TRI), methotrexate (MTX), and creatinine (CREA) in human urine. The separation was performed using a hydrodynamic injection time of 7 s (0.5 psi), a voltage of 25 kV, a capillary temperature of 30 degrees C, and 40 mM phosphoric acid adjusted to pH 2.25 by addition of triethanolamine as separation electrolyte. Under these conditions, analysis takes about 15 min. A linear response over the 0.5-15.0 mg L(-1) concentration range was found for TRI and MTX, and 0.5-80.0 mg L(-1) for CREA. Dilution of the sample (water:urine, 1:1 for TRI and MTX, and 1:25 for CREA determination) was the only step necessary prior to analysis by electrophoresis. The developed method is easy, rapid, and sensitive and has been applied to determine triamterene,methotrexate, and creatinine in urine samples with satisfactory results. 相似文献
953.
Filter-based microfluidic device as a platform for immunofluorescent assay of microbial cells 总被引:5,自引:0,他引:5
A filter-based microfluidic device was combined with immunofluorescent labeling as a platform to rapidly detect microbial cells. The coin-sized device consisted of micro-chambers, micro-channels and filter weirs (gap = 1-2 microm), and was demonstrated to effectively trap and concentrate microbial cells (i.e., Cryptosporidium parvum and Giardia lamblia), which were larger in size than the weir gap. After sample injection, a staining solution containing fluorescently-labeled antibodies was continuously provided into the device (flow rate = 20 microl min(-1)) to flush the microbial cells toward the weirs and to accelerate the fluorescent labeling reaction. Using a staining solution that was 10 to 100 times more dilute than the recommended concentration used in a conventional glass method, those target cells with a fluorescent signal-to-noise ratio of 12 could be microscopically observed at single-cell level within 2 to 5 min prior to secondary washing. 相似文献
954.
Juan M. Kok Kevin C. Lim Brian W. Skelton Allan H. White 《Journal of Cluster Science》2004,15(3):377-386
The structural characterizations of some copper(I) halide (CuX) adducts with norbornadiene (nbd) are recorded. CuCl : nbd (1:1)4 (a redetermination), (2:1)2(|), are systems both based around Cu4Cl4 cubane-type cluster arrays. CuBr : nbd (7:3)(|)( 0.5 MeOH), a complex polymer with 3-symmetry, is believed to be the complex previously described as an adduct of 2:1 stoichiometry. Attempts to obtain an iodide counterpart have resulted in the definition of an ephemeral adduct CuI : MeCN (3:2)(|). 0.5 C7H8 in which, remarkably, the nbd is uncoordinated; the complex is a polymer, related to the [AgX(quinoline)](|) (X = Cl, Br) saddle polymer. 相似文献
955.
We computed the free energy of solvation for a series of ions and neutral molecules using two different continuum approaches. First, we used the AM1–SM1 technique, where the AM1 Fock matrix is modified to include a generalized Born contribution. Second, we applied the DelPhi approach, where the electrostatic component of the free energy of solvation is evaluated by resolving the Poisson–Boltzman equation by a finite difference method. Both methods appear equally reliable for ionic systems. For neutral compounds, AM1–SM1 performs better than DelPhi; however, the differences become less pronounced for compounds with larger free energies of solvation. In parallel, both methods were applied to study the influence of the solvation process in the overall drug receptor interaction for a series of closely related ligands for the D1 dopamine receptor. An inverse linear relationship was found between the free energy of solvation and the logarithm of the affinity of the ligands; nevertheless, electrostatic properties are likely to modulate affinity as well. © 1993 John Wiley & Sons, Inc. 相似文献
956.
Summary We consider the Cauchy problem for the generalized porous medium equation ut=(u) where u=u(x, t), xRn and t>0, and the initial datum u(x, 0) is assumed to be nonnegative, integrable mid to nave compact support. The nonlinearity (u) is a C1 function defined for uO which grows like a power of u. Our assumptions generalize the porous medium case, (u)=um, m>1, and also include the equation of the Marshak waves. This problem has finite speed of propagation. We estimate the rate of growth of the support of the solution with precise estimates for t 0 and t. Our main result deals with the regularity of the solutions. We show that after a certain time t0 the pressure, defined by v=(u), with (u)=(u)/u and (0)=0, is a Lipschitz-continuous function of x and t and the interface is a Lipschitz-continuous surface in RN+1; the solution u is Hölder continuous for all times t> 0.Both authors partially supported by CAICYT, Project 2805-83. The second author also supported by USA-Spain Joint Research Grant CCB-8402023. 相似文献
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