Microwave‐improved polymerization of ϵ‐caprolactone initiated by carboxylic acids

The ring‐opening polymerization of ε‐caprolactone (ε‐CL), initiated by carboxylic acids such as benzoic acid and chlorinated acetic acids under microwave irradiation, was investigated; with this method, no metal catalyst was necessary. The product was characterized as poly(ε‐caprolactone) (PCL) by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, and gel permeation chromatography. The polymerization was significantly improved under microwave irradiation. The weight‐average molecular weight (M_w) of PCL reached 44,800 g/mol, with a polydispersity index [weight‐average molecular weight/number‐average molecular weight (M_w/M_n)] of 1.6, when a mixture of ε‐CL and benzoic acid (25/1 molar ratio) was irradiated at 680 W for 240 min, whereas PCL with M_w = 12,100 and M_w/M_n = 4.2 was obtained from the same mixture by a conventional heating method at 210 °C for 240 min. A degradation of the resultant PCL was observed during microwave polymerization with chlorinated acetic acids as initiators, and this induced a decrease in M_w of PCL. However, the degradation was hindered by benzoic acid at low concentrations. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 13–21, 2003     

酸糖蛋白手性柱分离6种手性化合物

通过考察缓冲液种类、浓度及其pH值对对映体在手性柱上的保留和分离行为的影响,以及流动相中加入不同种类、不同浓度的不带电荷的有机溶剂乙腈、甲醇、正丙醇、异丙醇、流动相流速和柱温对对映体分离能力的影响,优化了含碳手性中心的碱性药物苯丙哌林、酸性化合物MT-A5及MT-酸和含硫手性中心的质子泵抑制剂奥美拉唑、泮托拉唑、雷贝拉唑对映体分离条件,最佳手性分离条件为:苯丙哌林,0.05 mol/L磷酸二氢铵缓冲液(pH 3.0)-乙腈(95∶5,V/V)为流动相,流速为0.7 mL/m in,柱温为20℃;MT-A5及MT-酸,流动相为0.01 mol/L醋酸铵缓冲液(pH 5.0)-乙腈(74∶26,V/V),流速为0.9 mL/m in,柱温为20℃;泮托拉唑,流动相为10 mmol/L醋酸铵缓冲液(pH 5.5)-乙腈(93∶7,V/V),流速为0.9 mL/m in;柱温为20℃;奥美拉唑和雷贝拉唑,流动相为0.01 mol/L醋酸铵缓冲液(pH 3.0)-乙腈(95∶5,V/V),流速为0.7 mL/m in,柱温为20℃。实现了应用高效液相色谱法在α1-酸糖蛋白手性柱上对上述化合物的对映体分离,并成功用于手性药物合成中的对映体过量百分率的测定。     

A microspectroscopic study of the electronic homogeneity of ordered and disordered Sr2FeMoO6

Disordered Sr₂FeMoO₆ shows a drastic reduction in saturation magnetization compared to highly ordered samples, moreover magnetization as a function of the temperature for different disordered samples shows qualitatively different behaviours. We investigate the origin of such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish that e_xtensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples, is responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with composition fluctuations of the type Sr₂Fe_1+x Mo_1-x O₆ with Fe-rich (x > 0) and Mo-rich (x < 0) regions. Dedicated to Prof J Gopalakrishnan on his 62nd birthday.     

The role of variable surface charge and surface complexation in the adsorption of humic acid on magnetite

The ionic strength dependence of humic acid (HA) adsorption on magnetite (Fe₃O₄) was investigated at pH 5, 8 and 9, where variable charged magnetite is positive, neutral and negative, respectively. The adsorption studies revealed that HA has high affinity to magnetite surface especially at lower pH, where interacting partners have opposite charges. However, in spite of electrostatic repulsion at pH 9 notable amounts of humate are adsorbed. Increasing ionic strength enhances HA adsorption at each pH due to charge screening. The dominant interaction is probably a ligand-exchange reaction, nevertheless the Coulombic contribution to the organic matter accumulation on oxide surface is also significant under acidic condition. The results from size exclusion chromatography demonstrate that the smaller size HA fractions enriched with functional groups are adsorbed preferentially on the surface of magnetite at pH 8 in dilute NaCl solution.     

An efficient palladium catalyzed synthesis of 2-arylbenzothiazoles

A novel and convergent palladium catalyzed synthesis of 2-arylbenzothiazoles has been investigated. The key step in the synthesis is a Suzuki biaryl coupling of 2-bromobenzothiazole with aryl boronic acids to provide a variety of 2-arylbenzothiazole derivatives in good yield. The synthetic utility of this methodology is demonstrated by the synthesis of 2-(4-aminophenyl)-6-methoxybenzothiazole, a PET probe precursor for the in vivo imaging of Alzheimer's disease.     

副品红共振光散射法测定脱氧核糖核酸

本文基于脱氧核糖核酸 (DNA)对有机染料副品红的共振光散射的增强效应 ,拟定了一种测定DNA的共振光散射法。在pH =0 5～ 1 5范围内 ,有机染料副品红于 35 5nm处的共振光散射强度被DNA强烈增强 ,且增强程度与DNA浓度呈线性关系 ,线性范围为 0 10～ 15 μg·mL- 1 ,检出限可达 36ng·mL- 1 。该方法简便、快速、具有较高的灵敏度和准确度 ,且线性范围较宽。将该方法用于混合样品中DNA的测定 ,结果令人满意。     

Formation of Supersonic Zones and Local Separation Zones in Transonic Steady-State Flow Past Surface Roughness in the Free Interaction Regime

Within the framework of free interaction theory numerical methods are used to investigate the occurrence of supersonic zones with shocks in the outer inviscid region for flow past roughness in the lower viscous sublayer, with and without the formation of local separation zones.     

Mg,Si和S同位素链的壳反常

采用考虑轴向形变的相对论平均场理论,以双中子、双质子分离能隙δ_2n/δ_2p作为壳封闭的特征,分析了Mg,Si和S同位素链的壳封闭和壳反常,发现Mg同位素链在N=12,16处,Si同位素链在N=14,S同位素链在N?=16处出现明显的壳封闭结构,Si同位素链在N=28处壳层结构并没有消失.Mg,Si和S同位素链在N=20处壳效应并不太明显.     

Dual Problems and Separation of Sets: Lagrange and Fenchel Duality

An extremum problem is embedded in a parametric scheme which contains, as a particular case, the classic perturbation function. The introduction of the image of the embedded problem allows one to derive a generalized duality and, in particular, Lagrangian and Fenchel duality.