Determination of trace amounts of silver with a chemically modified carbon paste electrode

A method for the determination of trace amounts of silver with a chemically modified carbon paste electrode is described. The modified electrode is prepared by simply mixing a chelating resin (a polythioether backbone and dioxymonosulphur polyethylene polyimines in the side-chain polymer) with graphite powder and Nujol oil. By immersing the electrode in a silver sample solution (pH = 6.5–7.5), silver can be adsorbed on the electrode surface and then determined by voltammetry in a separate blank solution. The response depends on the concentration of silver and the preconcentration time. For a preconcentration time of 5 min, the detection limit is about 3 × 10^?10 M and the linear range is from 5 × 10^?10 to 1 × 10^?7 M with a relative standard deviation of 4%. Many common metal ions have no or little effect on the determination of silver. The recommended procedure was applied to the determination of trace amounts of silver in waste water.     

大孔交联甲基丙烯酸缩水甘油酯共聚物的合成及其结构性能研究(Ⅰ)

甲基丙烯酸缩水甘油酯（GMA）为单体，三烯丙基氰尿酸酯（TAC）为交联剂，在致孔剂甲苯、正庚烷存在下，用悬浮聚合法制得一系列大孔共聚物（GT）。测定了共聚物的孔结构性能，讨论了不同交联剂及致孔剂用量和配比对共聚物结构的影响，并初步讨论了特大孔共聚物的形成机理。     

Highly efficient aza-Baylis-Hillman reaction of N-tosylated imines with MVK, acrolein, and phenyl acrylate or alpha-naphthyl acrylate: Lewis base effects and a convenient method to synthesize alpha,beta-unsaturated beta-amino carbonyl compounds

This paper describes several highly efficient aza-Baylis-Hillman reactions of N-tosylated imines with MVK, acrolein, and phenyl acrylate or alpha-naphthyl acrylate in the presence of a Lewis base. In most cases, the reaction can be completed within 1 h using the appropriate Lewis base catalyst. An efficient method to synthesize beta-amino ketones, aldehydes and esters in high yields and short reaction time has been developed.     

Highly efficient, one-step macrocyclizations assisted by the folding and preorganization of precursor oligomers

Highly efficient, one-step macrocyclizations leading to the formation of macrocyclic hexa(aramides) in high yields (69-82%) are described. The one-step macrocyclizations were facilitated by the preorganization or folding of the backbones of uncyclized precursors in the course of macrocyclization. The preorganization of backbones was achieved by the presence of localized three-centered hydrogen bonds that were adopted in the design of a class of closely related, backbone-rigidified foldamers. The macrocyclization involved reactions between diacid chloride 1 and diamine 2. The crude reaction mixtures and products were conveniently examined by mass spectrometric method (MALDI-TOF). Compared to most traditional one-step macrocyclizations that usually require high dilution conditions and often lead to very low overall yields of the desired products, cyclic hexamers 3 were obtained as the overwhelmingly major product under a variety of reaction conditions, suggesting the generality of this approach.     

DRY METHOD SYNTHESIS OF PURE SILICEOUS FORM OF ZEOLITE ZSM-35

IntroductionZeoliteZSM-35isclassifiedasfcrricritc(FER)t\pc.x'hicllalsoincludesZSM-ZI.ZSM-38andFER.Zeolitesofthist}'pcha\lcrclatit'CI}UlldiscrinlinablcXRDpattcnlswhichindicatetheirsinlilarit\'illst,u.tu,.,I11.Thehighsiliceousfonllsofthesezeolitesarcgcllcra…     

Morphology and electric conductivity of cross-linked polyethylene–carbon black blends prepared by gelation/ crystallization from solutions

 Ultra-high-molecular-weight polyethylene (UHMWPE) – carbon black (CB) blends were prepared by gelation/ crystallization from PE dilute solutions containing CB particles. The UHMWPE/CB composition chosen were 1/0.15, 1/0.25, 1/0.5, 1/0.75, 1/1, 1/3, 1/5, and 1/9, etc. The cross-linking of PE chains was performed by chemical reaction of dicumyl-peroxide at 160 ^°C. X-ray diffraction patterns indicate that the crystallinity of PE within the blends decreased drastically through the chemical reaction at high temperature. The sample preparation method by gelation/crystallization provided the UHMWPE–CB system with various CB contents up to 90% and the conductivities for the resultant specimens were in the range from 10^-9 to 1 Ω^-1 cm^-1 corresponding to the electric conductivity range of semiconductors. The blends assured thermal stability of electric conductivity by cross-linking of PE chains, although the mechanical property such as the storage and loss moduli were very sensitive to temperature. The conductivity of the blends with CB content ≥20% were almost independent of temperature up to 220 ^°C and the values in the heating and cooling processes were almost the same. On the other hand, for the UHMWPE–CB blends with 13% CB content corresponding to the critical one, temperature dependence of electric resistivity showed positive temperature coefficient (PTC) effect. The PTC intensities for non-cross-linked and cross-linked materials were lower than that of the corresponding low-molecular-weight-polyethylene (LMWPE)–CB blend but the maximum peak appeared at 160 ^°C which is higher than the peak temperature of LMWPE–CB blend. Received: 10 December 1997 Accepted: 9 April 1998     

Synergistic effects in mixed gas chromatographic stationary phases containing hepatkis(2.3.6-tri-O-pentyl)-β-cyclodextrin and AgNO3 or TINO3 in the separation of xylene isomers

Summary The gas chromatographic separation of xylene isomers using special mixed stationary phases consisting of heptakis(2.3.6-tri-O-pentyl)-β-CD-AgNO₃, heptakis (2.3.6-tri-O-pentyl)-β-CD-TINO₃ or bentone-34-AgNO₃ is investigated. The first two have positive synergistic effects for the separation of m, and p-xylene isomers, but negative synergistic effects for the m, and oisomers. The separation effects depend on temperature, mixing ratio and how mixing is accomplished.     

化学模式识别技术评价中药厚朴质量的研究

本文对不同产地和市售的二十四种厚朴药材及饮片的萃取液进行了高效液相色谱、气相色谱及紫外光谱分析;对所得数据用主成分分析进行分类,概括出不同样品化学成分的异同,认为大叶木兰可做为厚朴的代用品,而在陕西安康购得的样品不应做厚朴使用,后者经生药学鉴定为厚朴伪品凹叶木兰。化学模式识别技术可为寻找药材的代用品、评价中药质量及鉴定伪劣药材提供依据。     

Surprising selectivity in the transformation of dimethoxy azaindoles

Transformation of 4,7-dimethoxy-6-azaindole into 4-hydroxy-7-methoxy-6-azaindole or 7-hydroxy-4-methoxy-6-azaindole can be readily controlled by careful selection of a reagent. Treatment with concentrated HCl results in hydrolysis at the 4-position exclusively, while TMS-I provides demethylation at the 7-position only. Products were unambiguously identified by single crystal X-ray crystallography.     

Template-synthesized LiCoO2, LiMn2O4, and LiNi0.8 Co0.2 O2 nanotubes as the cathode materials of lithium ion batteries

The first point of this work is to synthesize LiCoO2, LiNi0.8 Co0.2 O2, and LiMn2O4 nanotubes with the template of porous anodic aluminum oxide by thermal decomposition of sol-gel precursors. The as-synthesized materials were open-ended nanotubes with uniform shape and size based on the analysis of scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. An "in situ reaction from nanoparticle to nanotube" mechanism was discussed for the formation process of the nanotubes. The second point of this paper is to investigate the electrochemical properties of the as-synthesized nanotubes for the cathode materials of lithium ion batteries. It was found that the nanotube electrodes exhibited better reversibility and higher discharge capacities than that of their nanocrystalline counterparts. The reason for the improved electrochemical performance of the nanotube electrodes was also interpreted.