Microwave-assisted conversion of lignin into aromatic compounds

Low-power (≤10 W) microwave radiation considerably reduces the initial temperature in the catalytic hydrocracking of lignin as compared to conventional thermal heating. The microwave-assisted catalytic transformation of lignin at 260-290°C under atmospheric pressure afforded in high yield C₆-C₁₀ aromatic and aliphatic hydrocarbons in addition to methoxyphenols and alkylated methoxyphenols. A correlation has been found between the activity of the catalyst (1% Pt/C) and the size of platinum metal particles.     

Coupled HPLC-capillary GC – state of the art and outlook

HPLC fractions involving eluents of low to intermediate polarity can be introduced into capillary GC using the retention gap technique. Partial or complete solvent evaporation during sample introduction reduces the length of, or almost eliminates, the zone in the column inlet (retention gap) flooded by the introduced liquid, allowing introduction of larger HPLC fractions and/or use of shorter retention gaps. The corresponding techniques are reviewed. The retention gap technique is poorly suited for water-containing HPLC eluents (reversed phase HPLC) and fails completely if HPLC eluents contain, e.g., buffer salts. Various techniques for extracting such HPLC eluents are considered, preference being given to extraction into GC stationary phases from where solutes are thermally desorbed into the GC separation column. Limiting factors are diffusion of solutes within the liquid phase to be extracted and retention power of the extraction tubes.     

Microwave-assisted synthesis of phthalocyanine-porphyrin complex and its photoelectric conversion properties

A soluble phthalocyanine-porphyrin complex (Lu(TBPor)Pc) has been rapidly synthesized from a lutetium porphyrin (Lu(TBPor)OAc) and a metal-free phthalocyanine (H₂(TBPc)) under microwave irradiation. Its photoelectric conversion properties have also been investigated. The experimental results reveal that Lu(TBPor)Pc exhibits better photoelectric conversion effect than Lu(TBPor)OAc, H₂(TBPc), and Lu(TBPor)OAc/H₂(TBPc) blend. Furthermore, we have also introduced a n-type photoconductor (N,N′-bis(1,5-dimethylhexyl)-3,4:9,10-perylenebis(dicarboximide)(PDHEP)) and TiO₂ into Lu(TBPor)Pc photoelectric cell to fabricate a SnO₂/Lu(TBPor)Pc + PDHEP + TiO₂/Al photoelectric cell, exhibiting the largest short-circuit photocurrent (691.3μA/cm²) among all of lab-made cells under illumination of white light (1.2 mW/cm²).     

State of the art of shear driven chromatography. Advantages and limitations

The present paper reports on the experimental difficulties encountered when trying to realize the full potential of shear-driven chromatography in nanochannels. While it theoretically offers the possibility to yield over 10,000 plates per centimetre in a few seconds, the practical realization of this potential requires a detector miniaturisation that is carried to the extreme combined with very high sampling rates. In the present study, a charge coupled device camera and a photomultiplier tube combined with pinhole were tested as detector. Despite the fact that the photomultiplier tube could offer a higher sampling rate and a better sensitivity, the charge coupled device turned out to be better suited for the current set-up because of inevitable problems with the stray-light transported through the glass channel wall. The chemistry of the separation surface was additionally studied getting more homogenous coating, thus higher separation efficiency. Having also carried out a number of mechanical improvements, it is now possible to measure separations at a distance of 8mm downstream from the injection point. This is four times further downstream than ever before while realizing a four components mixture separation in less than 1.5s, with a plate generation velocity of about 2000-7000 plates per second depending on the sample.     

Microwave-assisted synthesis of ethynylarylboronates for the construction of boronic acid-based fluorescent sensors for carbohydrates

A reliable and operationally simple procedure for the synthesis of 2,2-dimethylpropane-1,3-diyl ethynylaryl boronates 4 was developed. The key step is microwave-facilitated selective formation of 2,2-dimethylpropane-1,3-diyl trimethylsilylethynylaryl boronates by Sonogashira reaction from the corresponding bromides. The use of microwave was found to significantly improve the reaction yield and shorten the reaction time. The 2,2-dimethylpropane-1,3-diyl ethynylaryl boronates 4 prepared can be used in the construction of diboronic acid libraries through [2+3] Huisgen cycloaddition for carbohydrate fluorescent sensor development.     

Modelling rheology and free energy of entangled polymers. State of the art

Significant progress made in recent times on the basic molecular theory of Doi and Edwards for entangled polymers is briefly reviewed. In particular we present a recent version of the theory that is entirely described by a set of differential equations, and is therefore especially useful for simulations of complex flows as encountered in polymer processing. The model also provides an expression for the excess free energy that can be of use to predict the onset of flow-induced crystallisation.     

Electrochemical disinfection – State of the art and tendencies

Electrochemical disinfection has gained increasing interest in many sectors of social and industrial life. The reason is the growing need to disinfect the air, water, and special surfaces of different nature such as drinking water, wastewater, pool water, and other water qualities or surfaces. New research studies are reported and discussed. A stronger orientation on engineering aspects is intended. Following tendencies can be identified - research on complex liquid systems, implementation of risks consideration seen from by-product formation, and better cooperation between researchers and industry oriented to improve cell design and disinfection technology. Partially, reaction kinetics is studied and discussed at higher levels of likelihood. Furthermore, it can be found that more and more research papers deal with hybrid technologies to create novelty, to use synergistic effects and to meet the demands of real system treatment under practical conditions. A major focus can be identified for wastewater treatment/disinfection emphasizing electrocoagulation and electro-photocatalysis.     

Microwave-assisted conversion of aromatic heterocyclic nitriles to various heterocyclic molecules

Abstract

Dihydroimidazole (3a-c), dihydrooxazole (3d-f), benzoxazole (5a-c), benzothiazole (5d-f) and oxazolopyridine (7a-c) derivatives have been synthesized by condensation of various heterocyclic aromatic nitriles with diamine, aminoalcohal, aminophenol, aminothiophenol, and 3-aminopyridine-2-ol, respectively, under microwave irradiation and under solvent free conditions. This catalyst free and solvent free approach provided heterocyclic compounds in quantitative yields. Time taken for the condensation to occur is < 20 min.     

State of the art of coherent forward scattering spectroscopy

Summary Magneto-optic rotation produced by the Faraday or the Voigt configuration has been employed to determine trace elements in an atomic vapour under the name of coherent forward scattering spectroscopy (CFS). Theoretically and experimentally, at low atomic density, the forward scattering radiation intensity is proportional to the square of the atomic density. Therefore, highly sensitive detection can be expected. However, from the opposite point of view, CFS signal drops very rapidly with the concentration near the detection limit, and CFS degrades sensitivity when it is utilized to detect atomic species at low concentration. The alleviation of this unattractive feature and that of small dynamic range were attempted by the experimental set-up of the Voigt configuration: a transverse magnetic field of 10 kOe around a graphite furnace with Rochon prisms as polarizer and analyzer. Then the analytical applications of CFS for the determination of trace elements in several metals following simple sample dissolving procedure were carried out. One of the advantage of the CFS: capability of simultaneous multielement analysis with simpler instrumentation could be ascertained using a xenon lamp as a radiation source.

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Stand der Spektroskopie durch kohärente Vorwärtsstreuung

Zusammenfassung Magneto-optische Rotation, beobachtet in Faraday- oder Voigt-Konfiguration, wurde unter dem Namen kohärente Vorwärtsstreuung (CFS) benutzt, um Spurenelemente in atomarem Dampf zu bestimmen. Bei niedrigen Atomdichten ist die vorwärtsgestreute Intensität, theoretisch und experimentell, proportional dem Quadrat der Atomzahldichte. Daher kann eine hohe Empfindlichkeit erwartet werden. Vom entgegengesetzten Standpunkt aus gesehen fällt jedoch das CFS-Signal zu Konzentrationen nahe der Nachweisgrenze hin rasch ab, was für den Nachweis von Atomen bei niedrigen Konzentrationen nachteilig ist. Es wurde versucht, diese ungünstige Eigenschaft sowie den kleinen dynamischen Bereich durch den experimentellen Aufbau der Voigt-Konfiguration zu verbessern: ein transversales Magnetfeld, in dem sich der Graphitrohrofen befindet, mit Rochon-Prismen als Polarisator und Analysator. Damit wurde die CFS für die Bestimmung von Spurenelementen in mehreren Metallen nach einfachem Lösen der Probe angewandt. Einer der Vorteile der CFS ist die Möglichkeit der simultanen Multielementanalyse mit einfacher instrumenteller Ausrüstung mit Hilfe einer Xenonlampe als Strahlungsquelle.

     

Calibration-Free Laser-Induced Breakdown Spectroscopy: State of the art

The aim of this paper is offering a critical review of Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS), the approach of multi-elemental quantitative analysis of LIBS spectra, based on the measurement of line intensities and plasma properties (plasma electron density and temperature) and on the assumption of a Boltzmann population of excited levels, which does not require the use of calibration curves or matrix-matched standards. The first part of this review focuses on the applications of the CF-LIBS method. Quantitative results reported in the literature, obtained in the analysis of various materials and in a wide range of experimental conditions, are summarized, with a special emphasis on the departure from nominal composition values. The second part is a discussion of the simplifying assumptions which lie at the basis of the CF-LIBS algorithm (stoichiometric ablation and complete atomization, thermal equilibrium, homogeneous plasma, thin radiation, detection of all elements). The inspection of the literature suggests that the CF-LIBS method is more accurate in analyzing metallic alloys rather than dielectrics. However, the full exploitation of the method seems to be still far to come, especially for the lack of a complete characterization of the effects of experimental constraints. However, some general directions can be suggested to help the analyst in designing LIBS measurements in a way which is more suited for CF-LIBS analysis.     

State of the art and limitations of quantitative polymerase chain reaction

Consequential to the implementation of European Commission (EC) Regulation 1139/98, EC Regulation 49/2000, and EC Regulation 50/2000 has been the need to measure accurately the levels of the genetically modified (GM) species Roundup Ready Soya and Bt 176 Maize that are present in food. Analytical methods to detect and quantitate these transgenic species have received much attention particularly with respect to the deminimus threshold of 1% for their presence in materials derived from non-GM identity-preserved (IP) supplies. The relative advantages and limitations of threshold analysis by double-competitive polymerase chain reaction (PCR) and quantitative real-time PCR are discussed in their application to the quantitative analysis of processed foods. Consideration is also given to other factors involved in the analyses that affect the performance of quantitative procedures, and to the many uncertainties involved in the precision of a reported analytical result.     

混合色谱填料的研究进展

随着科学技术的发展,人们需要分离分析的样品越来越复杂,尤其是多肽、蛋白质类生物样品的复杂性使得单一模式色谱难以满足分离分析的要求。混合模式色谱因其独特的分离性能,可以在一次分离中获得与多维色谱相当的分离效果,而且可以避免多维色谱系统结构复杂、流动相兼容性差、分析时间长等问题,成为近年来的研究热点之一。混合模式色谱的研究重点是色谱固定相的设计与开发。混合模式色谱固定相包括反相/离子交换混合固定相、反相/亲水混合固定相、亲水/离子交换混合固定相、两性离子交换混合固定相及三相混合固定相。本文综述了近年来混合模式色谱填料的研究及应用进展,并对混合模式色谱及固定相的发展前景进行了展望。     

金属卤化物促进糖类催化转化制备5-羟甲基糠醛

研究了碱金属卤化物对AlCl₃催化葡萄糖转化制备5-羟甲基糠醛（HMF）的促进作用. 结果表明,NaF对反应有显著抑制作用,而NaI和NaBr对反应有显著促进作用,而且NaI比NaBr的促进效果更明显. 在N,N-二甲基乙酰胺（DMAC）中,以NaI为添加剂,130 ℃反应15 min,AlCl₃催化葡萄糖转化制备HMF,葡萄糖转化率由71%提高到86%,HMF收率由36%提高到62%. AlCl₃-NaI-DMAC体系也可用于果糖、甘露糖等单糖,蔗糖、麦芽糖、纤维二糖等二糖,以及菊粉等多糖的转化. 以蔗糖为原料,HMF收率可达63%.     

Microwave-assisted conversion of N-substituted oxazolidin-2,4-diones into α-hydroxyamides

N-Substituted oxazolidin-2,4-diones have been synthesized in a novel one-pot reaction by reacting cyanohydrins stepwise with 1,1′-carbonyldiimidazole and primary amines followed by acidic hydrolysis of the intermediate 4-imino-oxazolidin-2-ones. Their microwave-assisted conversion into α-hydroxyamides was accomplished by treatment with catalytic amounts of sodium methoxide in methanol.     

Highly efficient and N-bromosuccinimide-mediated conversion of carbohydrates to 5-hydroxymethylfurfural under mild conditions

Highly efficient and selective conversion of different carbohydrates to 5-hydroxymethylfurfural (HMF) has been successfully performed with N-bromosuccinimide (NBS) as a promoter. In the presence of single NBS, a 64.2 % yield of HMF from fructose was obtained in N-methylpyrrolidone for 2 h. The effects of time, temperature and reaction media are discussed. It was concluded that the preliminary bromination of substrate could improve the generation of HMF compared to the direct dehydration process. Moreover, the HMF yield could be elevated to 79.6 and 82.3 % when FeCl₃ and SnCl₄ were used as the additives, respectively. Furthermore, the addition of CrCl₃ facilitated the conversion pathway from glucose, sucrose, inulin, or cellulose to HMF. A 57.3, 68.2, 62.4, or 6.1 % yield of HMF was, respectively, obtained in the presence of CrCl₃ and NBS under mild conditions, which will therefore generate a promising application strategy for biomass transformation.