Analysis of acyclovir by high performance capillary electrophoresis with on-column amperometric detection

The separation of acyclovir (ACV) by high performance capillary electrophoresis (HPCE) with on-column amperometric detection using alpha-amino-5-mercapto-3,4-dithiazole (AMD) as internal standard is described. The calibration line was linear in the range of 0.5-20 mg/L of ACV. The detection limit was 0.15 mg/L of ACV. Its recovery ranged from 98 to 101% with relative standard deviations (RSDs) from 1.9 to 3.2% (n = 5). This method was successfully used for determining ACV in some pharmaceuticals and human urine. Comparable results with HPCE with ultraviolet (UV) detection and amperometric detection were obtained.     

A semi-rigid bis(imidazolyl) ligand for the construction of nanoscopic supramolecules. From the molecular rectangle to the 1D coordination polymer

Reaction of the semi-rigid ligand 2,4-bis(1-imidazolylmethyl)-mesitylene (m-bimms) with CdCl₂ afforded a boat-like molecular rectangle [Cd(m-bimms)Cl₂]₂ · 1/2H₂O (1), with the orientation of the two imidazolyl arms of the ligand in syn-conformation and bridging chloride ions bisecting the macrocycle. Weak Cl· · ·H—C interations further extended the dimers into 1D infinite chains with nanoscopic channels. An analogous reaction with Cd(NO₃)₂ gave a 1D coordination polymer [Cd(m-bimms)₂(NO₃)₂]_n · 2nH₂O (2) composed of nanoscopic metallamacrocycles, where the two imidazolyl arms adopt an anti-conformation. Different anions result in different ligand conformations and thus determine the varied molecular architectures.     

Chiral separation of anticholinergic drug enantiomers in nonaqueous capillary electrophoresis

Nonaqueous capillary electrophoretic (NACE) method for the separation of nine structurally similar chiral anticholinergic drugs was developed. The eight drug enantiomers were separated on baseline within 18 min using 20mM phosphoric acid and 10 mM NaOH, containing 10 mM heptakis(2,3-dimethyl-6-sulfato)-4beta-cyclodextrin (HDMS-beta-CD) in methanol. The results were compared with those obtained in the high performance liquid chromatography system.     

Topology evolution and gelation mechanism of agarose gel

Kinetics as well as the evolution of the agarose gel topology is discussed, and the agarose gelation mechanism is identified. Aqueous high melting (HM) agarose solution (0.5% w/v) is used as the model system. It is found that the gelation process can be clearly divided into three stages: induction stage, gelation stage, and pseudoequilibrium stage. The induction stage of the gelation mechanism is identified using an advanced rheological expansion system (ARES, Rheometric Scientific). When a quench rate as large as 30 deg C/min is applied, gelation seems to occur through a nucleation and growth mechanism with a well-defined induction time (time required for the formation of the critical nuclei which enable further growth). The relationship between the induction time and the driving force which is determined by the final setting temperature follows the 3D nucleation model. A schematic representation of the three stages of the gelation mechanism is given based on turbidity and rheological measurements. Aggregation of agarose chains is promoted in the polymer-rich phase and this effect is evident from the increasing mass/length ratio of the fiber bundles upon gelation. Continuously increasing pore size during gelation may be attributed to the coagulation of the local polymer-rich phase in order to achieve the global minimum of the free energy of the gelling system. The gel pore size determined using turbidity measurements has been verified by electrophoretic mobility measurements.     

Bridged bis-pyridinylimino dinickel(II) complexes: Syntheses, characterization, ethylene oligomerization and polymerization

A series of bridged bis(pyridinylimino) ligands were efficiently synthesized through the condensation reaction of 4,4′-methylene-bis(2,6-disubstituted aniline) with 2-pyridinecarboxaldehyde or 2-benzoylpyridine. They reacted with (DME)NiBr₂ to form dinuclear Ni(II) complexes. All resultant compounds were characterized by elemental analysis, IR spectra as well as the single-crystal X-ray diffraction to confirm the structures of ligands and complexes. Activated with methylaluminoxane (MAO), these nickel complexes showed considerably good activities for ethylene oligomerization and polymerization. Their catalytic activities and the properties of PEs obtained were depended on the arched environment of ligand and reaction conditions.     

Preparation of Ce-Zr-O solid solution

A single phase solid solution of Ce-Zr-O can be made by using NH₄HCO₃ solution as precipitating agent. The influence of preparation conditions, such as pH, Zr⁴⁺/(CO₃ ^2-+HCO₃ ^-) and Ce³⁺/Zr⁴⁺ ratio on the formation of the solid solution were investigated. The results show that a single phase Ce-Zr-O solid solution can be formed only under a narrow window of preparation conditions, indicating that some compounds are formed in the precipitating process. The compound may contain Ce³⁺, Zr⁴⁺, CO₃ ^2-, HCO^3-, and OH^-. The solid solution so prepared can be described as Ce_0.37Zr_0.63O₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study on pyrolysis kinetics of walnut shell

Slow pyrolysis of walnut shell which is a cheap and abundantly available solid waste was carried out using thermogravimetric analysis. The effects of raw material heating rate on the pyrolysis properties and kinetic parameters were investigated. A two-step consecutive reaction model were used to simulate the pyrolysis process. The kinetic parameters were established by using the pattern search method. Comparison between experimental data and the model prediction indicated that the two-step consecutive reaction model can better describe the slow pyrolysis of walnut shell as the formation of an intermediate during the pyrolysis process was taken into account.     

含氮宾或卡宾的金属羰基簇合物的结构化学研究——Ⅰ.H_2Fe_3(N-C_6H_5)(CO)_9和Fe_3(N-C_6H_5)(μ_3-CO)(CO)_9的合成和结构

含氮宾的两个三核羰基铁簇合物是由[Et_3NH][HFe_3(CO)_(11)]与C_6H_5NCO在苯中反应获得。应用四园衍射仪测定了H_2Fe_3(N-C_6H_5)(CO)_9(Ⅰ)和Fe_3(N-C_6H_5)(μ_3-CO)(CO)_9(Ⅱ)的晶体结构。晶体数据为:C_(15)H_7NO_9Fe_3(Ⅰ),空间群P2_1/a,a=18.343(2),b=9.072(1),c=11.451(1)(?),β=102.03(1)°,V=1863.7(?)~3,Z=4,D_c=2.143g/cm~3;C_(16)H_5NO_(10)Fe_3(Ⅱ),空间群P2_1/c,a=8.634(1),b=13.026(1),c=17.642(2)(?),β=97.68(1)°,V=1966.3(?)~3,Z=4,D_c=1.820g/cm结构系用直接法解出,最后R_(Ⅰ)因子为0.033,R_(Ⅱ)因子为0.027。测定结果表明,(Ⅰ)和(Ⅱ)分子均具有C_s对称性,且三个Fe原子共面,呈近似等边三角形结构。(Ⅰ)中面桥N原子以不对称方式与三个Fe原子成键;(Ⅱ)中面桥羰基以不对称方式与三个Fe原子键连。Fe-N和Fe-C键长分别在1.896-1.938(?)和2.006-2.110(?)之间。