Evaluation of liquid chromatography–ion trap–time of flight hybrid mass spectrometry on the quantitative analysis for ginsenosides

It is ideal and desirable for a single instrument to meet the requirement of both qualitative and quantitative analysis of complicated components in pharmacokinetic research for herbal medicine. Liquid chromatography combined with hybrid ion trap and time‐of‐flight mass spectrometry (LCMS‐IT‐TOF) was recently confirmed as a very powerful tool for the qualitative analysis of both target and nontarget components in herbal medicines. The present study was designed to investigate the feasibility of LCMS‐IT‐TOF on quantitative analysis of ginsenosides in biological matrices. A simple liquid–liquid extraction procedure was followed by injection of the extracts onto a C₁₈ column with gradient elution and detection based on LCMS‐IT‐TOF system in negative scan mode. The developed method was validated with respect to the limit of quantification, linear dynamic range, precision, accuracy, matrix effects and stabilities. All the results suggested that the presently developed method was sufficiently sensitive and robust enough to simultaneously monitor 15 ginsenosides with diverse properties and a large range of concentration differences. Therefore, this method would be expected to be highly useful for comprehensive studies of ginsenosides in complicated matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Photoisomerization of a Maleonitrile‐Type Salen Schiff Base and Its Application in Fine‐Tuning Infinite Coordination Polymers

Strategically designed salen ligand 2,3‐bis[4‐(di‐p‐tolylamino)‐2‐hydroxybenzylideneamino]maleonitrile ( 1 ), which has pronounced excited‐state charge‐transfer properties, shows a previously unrecognized form of photoisomerization. On electronic excitation (denoted by an asterisk), 1Z *→ 1E isomerization takes place by rotation about the C2? C3 bond, which takes on single‐bond character due to the charge‐transfer reaction. The isomerization takes place nonadiabatically from the excited‐state ( 1Z ) to the ground‐state ( 1E ) potential‐energy surface in the singlet manifold; 1Z and 1E are neither thermally inconvertible at ambient temperature (25–30 °C), nor does photoinduced reverse 1E *→ 1Z (or 1Z *) isomerization occur. Isomers 1Z and 1E show very different coordination chemistry towards a Zn^II precursor. More prominent coordination chemistry is evidenced by a derivative of 1 bearing a carboxyl group, namely, N,N′‐dicyanoethenebis(salicylideneimine)dicarboxylic acid ( 2 ). Applying 2Z and its photoinduced isomer 2E as building blocks, we then demonstrate remarkable differences in morphology (sphere‐ and needlelike nanostructure, respectively) of their infinite coordination polymers with Zn^II.     

Synthesis of New Chiral Calix [4] crown Containing (R)‐Cysteine

Three new chiral heterocalix [4] crowns containing aza thio atoms bearing two chiral sites provided by (R)‐cysteine ester were synthesized. All new compounds were characterized by ¹H NMR, MS and elemental analysis.     

相对论性核–核碰撞中奇异夸克压低的约化

用含S夸克压低约化机制的事件产生器LUCIAE研究了相对论性核一核碰撞中青异增强现象,LUCIAE结果和相应的NA35实验数据符合得较好.结果还表明:s夸克压低约化在奇异产生物理中的作用要大于再散射.     

Stabilizer‐free dispersion copolymerization of maleic anhydride and vinyl acetate. I. Effects of principal factors on microspheres

A novel dispersion copolymerization of maleic anhydride (MAn) and vinyl acetate (VAc) without adding stabilizer is developed, which gives uniform copolymer microspheres with tunable sizes. Some principal factors affecting the microspheres, such as reaction time, monomer concentration and feed ratio, reaction media, and cosolvent, were investigated. It was found that the stabilizer‐free dispersion copolymerization of MAn and VAc is a rapid process, and the particle size grows in accordance with the evolution of polymerization. The chemical composition of the copolymer microspheres was characterized by FT‐IR and ¹³C NMR spectroscopies. Over a wide range of monomer concentrations, the microspheres can always be formed and stably dispersed, with uniform sizes ranging from 180 nm to 740 nm. The yield of copolymer microspheres reaches a maximum at 1:1 feed ratio of MAn to VAc, owing to the alternating copolymerization between the binary monomers by a known charge‐transfer‐complex mechanism. However, the diameter of microspheres drastically increases when MAn content is enhanced. Only some specific alkyl ester solvents, such as n‐butyl acetate, isobutyl acetate, n‐amyl acetate, are desirably fit for this unique stabilizer‐free dispersion polymerization. Furthermore, we found that when some acetone is added as a cosolvent, the copolymer microspheres can still be formed, with much larger diameters. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3760–3770, 2005     

Transverse distribution effects in beamstrahlung

Beamstrahlung is studied for bunches with densities that are transversely non-uniform. By treating an interesting special case analytically, one elicits the consequences of the new stationary phase conditions. Focusing effects are found to be relatively unimportant on the global radiated rate. Results are compared with the previously known case of uniform cylindrical bunches.     

Osmium Complexes with Tridentate 6‐Pyrazol‐3‐yl 2,2′‐Bipyridine Ligands: Coarse Tuning of Phosphorescence from the Red to the Near‐Infrared Region

We have prepared and characterized a series of osmium complexes [Os₂(CO)₄(fpbpy)₂] ( 1 ), [Os(CO)(fpbpy)₂] ( 2 ), and [Os(fpbpy)₂] ( 3 ) with tridentate 6‐pyrazol‐3‐yl 2,2′‐bipyridine chelating ligands. Upon the transformation of complex 2 into 3 through the elimination of the CO ligand, an extremely large change in the phosphorescence wavelength from 655 to 935 nm was observed. The results are rationalized qualitatively by the strong π‐accepting character of CO, which lowers the energy of the osmium d_π orbital, in combination with the lower degree of π conjugation in 2 owing to the absence of one possible pyridine‐binding site. As a result, the energy gap for both intraligand π–π* charge transfer (ILCT) and metal‐to‐ligand charge transfer (MLCT) is significantly greater in 2 . Firm support for this explanation was also provided by the time‐dependent DFT approach, the results of which led to the conclusion that the S₀→T₁ transition mainly involves MLCT between the osmium center and bipyridine in combination with pyrazolate‐to‐bipyridine ³π–π* ILCT. The relatively weak near‐infrared emission can be rationalized tentatively by the energy‐gap law, according to which the radiationless deactivation may be governed by certain low‐frequency motions with a high density of states. The information provided should allow the successful design of other emissive tridentate metal complexes, the physical properties of which could be significantly different from those of complexes with only a bidentate chromophore.