Solid extraction of caffeine and theophylline from green tea by molecular imprinted polymers

This paper involves a feasibility study on using molecular imprinted polymers as the sorbent materials in solid phase extraction for caffeine and theophylline from green tea. Two kinds of MIPs, with caffeine-theophylline mixture and pentoxifylline-theophylline mixture as the templates respectively, MAA as the monomer, EDMA as the crosslinker and ATBN as the initiator, were applied to this purpose. Mixture solution of caffeine and theophylline (1 Μg/ ml in acetonitrile) was applied to the solid extraction cartridges following a load, wash and elute procedure with acetonitrile, methanol, methanol-acetic acid (90/10, v/v) as the solvents, respectively. This solid phase extraction protocol was applied for extraction of caffeine and theophylline from green tea. Comparison between the results obtained with the MIPs cartridges and a traditional C₁₈ reversed-phase cartridge was made. It showed that the MIP-based sorbent on the solid phase extraction was comparable with that of C₁₈ material. HPLC analysis using a C₁₈ column (5 Μm, 250× 4.6 mm from Rstech corporation), methanol: water (60 :40, v/v) as the mobile phase at a flow rate of 0.6 ml/min was applied for the quantitative determination.     

Epoxidation of propylene by using [π-C5H5NC16H33]3[PW4O16] as catalyst and with hydrogen peroxide generated by 2-ethylanthrahydroquinone and molecular oxygen

The epoxidation of propylene catalyzed by a reaction-controlled phase transfer catalyst [π-C₅H₅NC₁₆H₃₃]₃[PW₄O₁₆] is investigated. The H₂O₂ is generated by the oxidation of 2-ethylanthrahydroquinone (EAHQ) with molecular oxygen in the organic solvent. Under mild conditions, the selectivity for propylene oxide, based on propylene, is 95%, and the yield, based on 2-ethylanthrahydroquinone, is 85%. During the epoxidation, the catalytic system is homogeneous. However, after the H₂O₂ is used up, the catalyst can be recovered as a precipitate and can be reused. After the epoxidation reaction, 2-ethylanthraquinone can be regenerated to 2-ethylanthrahydroquinone by catalytic hydrogenation, and no coproduct is produced.     

Broadband dielectric spectroscopy of nanostructured maleated polypropylene/polycarbonate blends prepared by in situ polymerization and compatibilization

The miscibility and molecular dynamics of nanostructured maleated polypropylene (mPP)/polycarbonate (PC) blends prepared by in situ polymerization of macrocyclic carbonates with polypropylene modified with 0.5 wt% of maleic anhydride-reactive groups were investigated over a wide range of frequencies (10⁻²-0.5 × 10⁷ Hz) at different constant temperatures using broadband dielectric spectroscopy and scanning transmission electron microscope (STEM). The molecular dynamics of the glass relaxation process of the blend (α-relaxation process) appeared at a lower temperature range compared with that of the pure PC. This shift in the molecular relaxation process is attributed to the partial miscibility of the two polymer components in the blends as previously confirmed by the morphology via STEM. Nanoscale morphologies with average domain diameters as small as 50 nm were obtained for the different blend compositions studied. The STEM photographs show that the graft mPP-g-PC prefers to locate at the interfaces as previously reported. The relaxation spectrum of pure PC and mPP/PC blends was resolved into α- and β-relaxation processes using the Havriliak-Negami equation and ionic conductivity. The dielectric relaxation parameters, such as relaxation peak broadness, maximum frequency, f_max, and dielectric strength, Δ? (for the α- and β-relaxation processes), were found to be blend composition dependent. The kinetics of the α-relaxation processes of the blends were well described by Vogel-Fulcher-Tammann (VFT) equation. The local process of PC was resolved into two relaxation processes β₁ and β₂, associated with the carbonyl groups' motion and the combined motions of carbonyl and phenylene groups, respectively. Only β₂ shifted to lower frequency in the blend while β₁ was relatively not affected by blending. The electric modulus of the blends was used to get a sufficient resolution of the different relaxation processes in the samples, i.e., α-, β-relaxation processes, ionic conductivity, and interfacial polarization. In addition, the blending method used was found to increase the d.c. conductivity without affecting the charge carrier transport mechanism, making it possible to develop novel polymer blends with tunable dielectric properties and morphology from existing polymers.     

Continuous Levels‐of‐Detail and Visual Abstraction for Seamless Molecular Visualization

Molecular visualization is often challenged with rendering of large molecular structures in real time. We introduce a novel approach that enables us to show even large protein complexes. Our method is based on the level‐of‐detail concept, where we exploit three different abstractions combined in one visualization. Firstly, molecular surface abstraction exploits three different surfaces, solvent‐excluded surface (SES), Gaussian kernels and van der Waals spheres, combined as one surface by linear interpolation. Secondly, we introduce three shading abstraction levels and a method for creating seamless transitions between these representations. The SES representation with full shading and added contours stands in focus while on the other side a sphere representation of a cluster of atoms with constant shading and without contours provide the context. Thirdly, we propose a hierarchical abstraction based on a set of clusters formed on molecular atoms. All three abstraction models are driven by one importance function classifying the scene into the near‐, mid‐ and far‐field. Moreover, we introduce a methodology to render the entire molecule directly using the A‐buffer technique, which further improves the performance. The rendering performance is evaluated on series of molecules of varying atom counts.     

A molecular dynamics simulation study on the crystallization of 22,8-polyurethane

By means of the molecular dynamics (MD) simulation, the crystallization mechanism of 22,8-polyurethane which contains hydrogen-bond units is investigated and the results show that the crystallization process at a fixed temperature can be characterized by three stages: (1) The extended chain collapses to a globular random coil; (2) The random coil reorganizes into an ordered lamellar structure; (3) Accompanied with the segments clustering due to the hydrogen-bond formation, the lamellar develops with local defects. Two kinds of hydrogen-bond, which are formed between NH group and CO group (N-H?OC), and between NH group and urethane alkoxy oxygen (N-H?O), respectively, are found to play an important role in the crystallization process of 22,8-polyurethane. Furthermore, the effect of temperature on the crystallization is also studied by selecting three temperatures 200, 300 and 400 K. The lower the crystal temperature is, the slower the crystallization rate is and the stronger the hydrogen-bonding interactions are presented. This is in harmony with the experimental results.     

PPTA／尼龙1010分子复合材料流变行为的研究

本文采用共沉淀法制备了聚对苯二甲酰对苯二胺(PPTA)/尼龙1010分子复合材料。测定了PPTA/尼龙1010分子复合材料的流变行为,发现PPTA使尼龙1010的表观熔体粘度变大,且PPTA/尼龙1010分子复合材料的表观熔体粘度对温度的敏感性不象尼龙1010那样突出。     

High-performance dispersant of coal–water slurry synthesized from wheat straw alkali lignin

Environmental concerns have stimulated interest in utilizing plant-derived materials in various industrial fields. The main objective of the present study was to synthesize a new type of high-performance lignin series dispersant of coal–water slurry (CWS) from wheat straw alkali lignin (WAL), and determine the affecting factors in the reaction and the application performance for CWS preparation. The experimental results showed that the inherent viscosity and the sulfonic group content of the modified wheat straw alkali lignin (MSL) are the key factors affecting its dispersing effect for CWS. In the reaction, the reactant mass concentration and the sulfonating agent amount were changed to obtain the MSL with different inherent viscosities and sulfonic group contents, and the MSL with intermediate inherent viscosity (6.0 ml/g) and higher sulfonic group content (1.80 mmol g^− 1) was found to have excellent dispersing effect for CWS. The MSL obtained from optimized process was used as dispersant for CWS preparation, the studies of the properties of CWS showed that MSL has similar dispersing effect with naphtalenesulfonate–formaldehyde condensate, and far better dispersing effect than lignosulphonate. Recently this kind of new dispersant has been applied in several power plants in China.     

Molecular sieve properties obtained by cracking of methane on activated carbon fibers

Molecular sieve properties of activated carbon fibers modified by cracking treatment with methane are studied herein. The effect of methane treatment on the porous texture of the samples has been studied while varying temperature and time. These materials have been evaluated for their selectivity during CO₂ and CH₄ separation; their uptakes have been compared with non-treated activated carbon fibers (studied previously), which were considered suitable to be used as molecular sieves. Kinetics of CO₂ and CH₄ uptake have also been investigated in this research. The treatment produced materials exhibiting fast kinetics and high selectivity during CO₂ and CH₄ separation; at the same time however, the CO₂ uptake capacity was diminished.     

ATOMISTIC MOLECULAR DYNAMICS SIMULATIONS OF GAS DIFFUSION AND SOLUBILITY IN RUBBERY AMORPHOUS HYDROCARBON POLYMERS

Diffusion coefficients D of H 2 , He, O 2 , N 2 , and CO 2 in different rubbery amorphous polymeric matrices were estimated by atomistic molecular dynamics simulations at 298 K using the Einstein relationship, and compared with the relevant experimental values, where available. The simulated diffusion coefficients D of all the gases in all polymers considered almost regularly decreased with increasing molecular gas volumes and increasing polymer glass transition temperature. Further, solubility coefficients and heats of solution were obtained for all gases from Grand Canonical Monte Carlo simulations, which were also used to calculate sorption isotherms. In general, there is a good agreement between experimental and simulated values of diffusion and solubility coefficients for all gases considered.     

丙烯酰胺与2-丙烯酰胺基-2-甲基丙磺酸反相乳液聚合的研究

采用Span-80为乳化剂，白油为分散介质，（NH4）2S2O8-Na2SO3为引发剂，研究了丙烯酰胺（AM）与2-丙烯酰胺基-2-甲基丙磺酸（AMPS）的反相乳液共聚反应，合成出了高相对分子质量的共聚物。讨论了引发剂用量、乳化剂用量、水油比、单体浓度等因素对共聚物相对分子质量的影响。引发剂用量为单体质量的0．2‰，乳化剂为油相的6．7％，水油比为1：1．5，单体浓度为37．5％时可获得高相对分子质量的共聚物，且聚合反应平稳易控制。