The boron-catalyzed polymerization of dimethylsulfoxonium methylide. A living polymethylene synthesis

Trialkyl and aryl organoboranes catalyze the polymerization of dimethylsulfoxonium methylide (1). The product of the polymerization is a tris-polymethylene organoborane. Oxidation affords linear telechelic alpha-hydroxy polymethylene. The polymer molecular weight was found to be directly proportional to the stoichiometric ratio of ylide/borane, and polydispersities as low as 1.01-1.03 have been realized. Although oligomeric polymethylene has been the most frequent synthetic target of this method, polymeric star organoboranes with molecular weights of 1.5 million have been produced. The average turnover frequency at 120 degrees C in 1,2,4,5-tetrachlorobenzene/toluene is estimated at >6 x 10(6) g of polymethylene (mol boron)(-1) h(-1). The mechanism of the polyhomologation reaction involves initial formation of a zwitterionic organoborane.ylide complex which breaks down in a rate-limiting 1,2-alkyl group migration with concomitant expulsion of a molecule of DMSO. The reaction was found to be first order in the borane catalyst and zero order in ylide. DMSO does not interfere with the reaction. The temperature dependence of the reaction rate yielded the following activation energy parameters (toluene, DeltaH(++) = 23.2 kcal/mol, DeltaS(++) = 12.6 cal deg/mol, DeltaG(++) = 19.5 kcal/mol; THF, DeltaH(++) = 26.5 kcal/mol, DeltaS(++) = 21.5 cal deg/mol, DeltaG(++) = 20.1 kcal/mol).     

SiH2Cl2: ab initio anharmonic force field, dipole moments, and infrared vibrational transitions

The vibrational spectra of SiH2Cl2 have been recorded in the 1000-13,000 cm(-1) region, utilizing the Fourier-transform spectroscopy and Fourier-transform intracavity laser absorption spectroscopy. Totally 61 band centers and intensities are derived from the infrared spectra. An ab initio quartic force field is obtained by applying the second-order Moller-Plesset perturbation theory and correlation-consistent polarized valence triplet-zeta basis sets [J. Chem. Phys. 90, 1007 (1989); 98, 1358 (1993)]. Most observed bands are assigned by the vibration analysis based on the second-order perturbation theory. Reduced-dimensional ab initio dipole moment functions (two dimensional and three dimensional) have also been calculated to investigate the absolute band intensities of the SiH2 chromophore. The calculated values agree reasonably with the observed ones.     

Theoretical studies on vibrational spectra of some halides of Group IIB elements

The vibrational spectra of Group IIB elements halides MX2 and their dimers M2X4 (M=Zn(II), Cd(II) and Hg(II); X=F, Cl, Br and I) have been systematically investigated by ab initio RHF and B3LYP methods with LanL2MB, LanL2DZ and SDD basis sets. The optimized geometries, calculated vibrational frequencies are evaluated via comparison with the experimental data. The vibrational frequencies, calculated by these methods with different basis sets, are compared to each other too. The best results can be obtained by RHF/SDD method, with this method, the deviations for MX2 and Hg2X4 are <7%. Some vibrational frequencies of M2X4 that have not been experimentally reported are also predicted.     

Filter-based microfluidic device as a platform for immunofluorescent assay of microbial cells

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.     

快原子轰击质谱及其在金属有机配合物研究中的应用

本文介绍FAB质谱的原理、功能和优点。综述了FAB机理,讨论了影响FAB谱的因素。归纳了FAB法在金属有机配合物研究中的应用。     

Multiplicative posets

A functionf from the posetP to the posetQ is a strict morphism if for allx, y P withx we havef(x). If there is such a strict morphism fromP toQ we writeP Q, otherwise we writeP Q. We say a posetM is multiplicative if for any posetsP, Q withP M andQ M we haveP ×Q M. (Here (p ₁,q ₁)<(p ₂,q ₂) if and only ifp ₁<p ₂ andq ₁<q ₂.) This paper proves that well-founded trees with height are multiplicative posets.This research was supported in part by NSERC Grant #69-1325.     

A note on Littlewood-Paley inequality for arbitrary intervals in\mathbb{R}^{n*}

Using the extension of Journé's covering lemma to higher dimensional spaces due to J. Pipher and our observation, we present a simple proof of the boundedness of the Littlewood-Paley operator Δ in for 2≤p<∞ and n≥3. The project Supported by NSFC.