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101.
We show that we can unify the gravitational and internal gauge interactions in a high dimensional Riemann-Cartan spacetime in the spirit of Kaluza-Klein, if we identify some of the connection coefficients as Yang-Mills potentials and if the dynamics of the spacetime is governed by the Poincaré gauge theory of gravitation whose lagrangian contains curvature and torsion squared. 相似文献
102.
Four l-erythro-2-uloses were readily prepared from l-arabinose via a reaction sequence involving Fischer glycosidation, acetalization and oxidation. Bulky steric sensors at the anomeric center could enhance the stereoselectivity of the dioxirane epoxidation and one of the uloses performed with good enantioselectivity towards trans-stilbene (up to 90% ee). However, the catalysts decomposed during the epoxidation and the maximum chemical yield was only 13% under the basic conditions. Three l-threo-3-uloses could overcome the decomposition problem based on the electron withdrawing effect of the ester group(s) α to the ketone functionality. The best chemical yield was up to 93% using a ketone with two flanking ester groups. One of the improved uloses displayed moderate enantioselectivity towards trans-disubstituted and trisubstituted alkenes (40-68% ee). 相似文献
103.
Carmen W. Huie Edward S. Yeung 《Spectrochimica Acta Part B: Atomic Spectroscopy》1985,40(9):1255-1258
Spatial mapping of sodium dimers and sodium atoms produced in a laser-generated plume is reported. The distributions support a sputtering mechanism for atom production. 相似文献
104.
105.
Geert-Jan Boons Peter Grice Ray Leslie Steven V Ley Lam Lung Yeung 《Tetrahedron letters》1993,34(52):8523-8526
The reactivity of dispiroketal protected thioglycosides makes them useful new precursors for oligossaccharide synthesis as is illustrated by the preparation of a protected pentasaccharide unit common to the variant surface glycoprotein of Trypanosoma brucei. 相似文献
106.
107.
Capillary electrophoresis (CE) is a promising technique for assessment of free bilirubin and its interaction with albumin, as it requires only a small sample volume and provides a rapid and efficient separation of free bilirubin from its albumin-bound complex in a one-phase system. In order to maintain the equilibrium without dissociation of bilirubin from the albumin/bilirubin complex as in real clinical conditions, the coupling of CE with frontal analysis (FA) was investigated. A very large sample plug was introduced hydrodynamically into the capillary (36 cm length, 50 microm inner diameter) at 15 psi x s to develop the frontal conditions during CE separation. The working conditions for CE/FA separation of bilirubin and albumin were optimized as follows: +20 kV; running buffer, 10 mmol/L phosphate and 1 mmol/L ethylenediaminetetraacetic acid (EDTA), pH 7.4. The working range for bilirubin was found to vary from 5 to 206 micromol/L; precision with relative standard deviation (RSD) <2.0% for n = 3 and detection limit (signal to noise, S/N = 2) was 2 micromol/L. The residual binding capacity of a simulated cord blood serum for bilirubin was 26 mg/100 mL at pH 7.4. Bilirubin was shown to be displaced from albumin when aspirin was added. The free bilirubin concentration was found to increase to clinical significant concentrations from 11.9 to 21.1% when increasing aspirin was added in the range of 5-50 mg/100 mL, respectively. Thus, the investigation of aspirin displacement of bilirubin from albumin is clinically important and the CE/ FA method is a suitable procedure for this purpose. 相似文献
108.
Wong MS Xia PF Zhang XL Lo PK Cheng YK Yeung KT Guo X Shuang S 《The Journal of organic chemistry》2005,70(7):2816-2819
[reaction: see text] A facile and efficient protocol for the synthesis of oligophenylene OPP(n)-substituted calix[4]arenes (with n up to 4) via iodo-substituted oligoarylcalix[4]arenes has been developed. The cooperation effect of the proximate fluoroionophores in hexylsulfanyl end-capped OPP(n)-substituted calix[4]arene assemblies leads to metal ion binding enhancement. 相似文献
109.
A novel perfluorinated corrole, 2,3,7,8,12,13,17,18-octafluoro-5,10,15-tris(pentafluorophenyl)corrole, and its manganese(III) and oxomanganese(V) derivatives have been synthesized. The perfluorinated manganese corrolate exhibited excellent reactivity and stability in the catalytic oxidation of alkenes with iodosylbenzene. 相似文献
110.