Analysis of natural antioxidants by capillary electromigration methods

In this work, an exhaustive survey of capillary electromigration methods used to analyze natural antioxidants is presented together with some discussion of the use of these substances use as functional foods. This review provides an updated and exhaustive overview of the separation and identification by capillary electrophoresis of natural compounds with antioxidant activity found in natural matrices and/or foods. The compounds concerned are catechins, isoflavones, anthocyanins, phenolic acids, vitamins, as well as other less common natural substances that have shown antioxidant activity.     

Polymerization of styrene oxide by nitronium tetrafluoroborate

The polymerization of styrene oxide by nitronium tetrafluoroborate in nitromethane and methylene chloride at 5, 20, and 50°C is investigated. GPC analyses of the products combined with isocyanate method show that both cyclic and linear oligomers are formed. In CH₃NO₂ the cyclic dimer and trimer are 2-benzyl-4-phenyl-1,3-dioxolane and 1,3,5-tribenzyl-trioxane, respectively. In CH₂Cl₂ 2,5-diphenyldioxane is isolated. In nitromethane, mainly isomerized structures with acetal linkage are produced, while in methylene chloride isomerization does not proceed. By NMR and IR spectra the presence of C?O and OH end groups in the linear oligomers is shown. There are indications that oligomers are formed both directly from the monomer and by degradation of the polymer.     

Determination of impurities and counterions of pharmaceuticals by capillary electromigration methods

The review presents a survey of recent applications of high‐performance capillary electromigration methods—capillary zone electrophoresis, nonaqueous capillary electrophoresis, capillary isotachophoresis, micellar electrokinetic chromatography, microemulsion electrokinetic chromatography and capillary electrochromatography—for the determination of impurities of pharmaceuticals, including chiral impurities, for the period 2007–2013. In addition, due to the missing evaluation of the determination of counterions of pharmaceuticals by capillary electromigration methods in the last 20 years, the publications dealing with this topic since 1995 are included in this review. General aspects of both these types of applications of capillary electromigration methods in pharmaceutical analysis are discussed, and detailed experimental conditions used for determination of various chemical impurities and counterions of many particular drugs are described.     

Chiral analysis of pollutants and their metabolites by capillary electromigration methods

Chiral separation of enantiomers is one of the most challenging tasks for any analytical technique including CE. Since the first report in 1985 showing the great possibilities of CE for the separation of chiral compounds, the amount of publications concerning this topic has quickly increased. Although chiral electromigration methods have mainly been used for enantioseparation of drugs and pharmaceuticals, they have also been applied to analyze chiral pollutants. This article intends to provide an updated overview, including works published till January 2005, on the principal applications of CE to the chiral analysis of pollutants and their metabolites, with special emphasis on articles published in the last 10 years. The main advantages and drawbacks regarding the use of CE for chiral separation of pollutants are addressed including some discussion on the foreseen trends of electromigration procedures applied to chiral analysis of contaminants.     

气相色谱法同时测定苯乙烯催化氧化反应液中的苯乙烯、环氧苯乙烷和苯甲醛

建立了同时测定苯乙烯催化氧化反应液中的苯乙烯、环氧苯乙烷和苯甲醛的气相色谱分析方法。该法以正庚烷为内标物,在DB-1毛细管色谱柱上进行分离,氢火焰离子化检测器。方法的回收率98%~101.5%,相对标准偏差小于2.0%。     

Physico-chemical characterization and photocatalytic activity of zinc oxide prepared by various methods

Zinc oxide was prepared by different methods by varying precipitating agents, the source of the salt precursors and the microwave irradiation time and was characterized by XRD, BET-surface area, surface acidity and crystallite sizes. The photocatalytic reactions were carried out under solar radiation in batch reactors towards oxidation of 4-nitrophenol and reduction of Cr(VI) by varying different parameters such as irradiation time, pH of the solution, catalyst amount and substrate concentration and the activities were correlated with the physico-chemical parameters. Zinc oxide samples prepared by microwave irradiation and calcined at 300 degrees C exhibit highest surface area, acid sites and lowest crystallite sizes and show highest activity towards photocatalytic reactions.     

High reaction activity of nitrogen-doped carbon nanotubes toward the electrooxidation of nitric oxide

Carbon nanotubes doped with N (NCNTs) enable 1.5 times faster electron-transfer kinetics for the oxidation of NO compared to pristine carbon nanotubes (CNTs), which may be due to the low adsorption energy for a NO on pyridinic NCNT(5,5) allowing NO to lose electrons readily and facilitate the following oxidation to nitrate.     

毛细管电泳电迁移扩散的定量研究

电迁移扩散是毛细管电泳中影响区带展宽的重要冈素之一。本文利用毛细管电泳电导检测装置对电迁移扩散进行了定量研究,提出一种评价电迁移扩散的方法。在该方法中引入一种描述电迁移扩散的物理量,它可通过几个易测的实验参数来计算。它不仅考虑到电迁移进样的歧视效应,而且考虑到样品浓度对电迁移扩散的影响。采用毛细管电泳中常用的两种缓冲液(磷酸和甲酸-组氨酸)对该方法进行了实验验证,结果表明它与理论预测符合良好。     

The polymerization of styrene oxide by the triisobutylaluminum–water system

Styrene oxide has been polymerized by the triisobutylaluminum–water catalyst system. Kinetic studies of the effects of varying the monomer, triisobutylaluminum, and water concentrations in benzene solutions have been made. Styrene oxide was consumed in two reactions: an initial fast one producing trimer and a slower reaction forming higher molecular weight polymer.     

A resonance Raman investigation on the interaction of styrene and 4-methyl styrene oligomers on sulphated titanium oxide

In order to understand the nature of the interaction that gives rise to the yellow-orange colour observed when styrene or 4-methyl styrene are put in contact with sulphated TiO2, the resonance Raman spectra of such systems, including deuterated styrene (ring-deuterated d5 and perdeuterated d8) and allylbenzene were investigated. In all cases a substantial enhancement of the ring v(CC) stretching mode was observed. A charge transfer process involving a transition from the ring pi-electrons to the empty d-pi orbitals of titanium was ascribed responsible for the absorption in the visible. Two types of resonance Raman spectra were observed depending on the excitation wavelength, which can be explained by the presence of two kinds of oligomers, saturated and unsaturated, on the surface of the oxide with the former giving rise to a Raman enhancement at a higher excitation energy.     

Recent advances in the application of capillary electromigration methods for food analysis

This review covers the application of capillary electromigration methods to analyze foods and food components, including amino acids, biogenic amines, peptides, proteins, DNAs, carbohydrates, phenols, polyphenols, pigments, toxins, pesticides, vitamins, additives, small organic and inorganic ions, chiral compounds, and other compounds in foods, as well as those applications of CE for monitoring food interactions and food processing. The use of microchips as well as other foreseen trends in food analysis by CE are discussed. Papers that were published during the period June 2005-March 2007 are included following the previous review by Cifuentes (Electrophoresis 2006, 27, 283-303).     

Recent advances in the application of capillary electromigration methods for food analysis

This article reviews the latest developments in the application of capillary electromigration methods for the analysis of foods and food components. Nowadays, methods based on CE techniques are becoming widely used in food analytical and research laboratories. This review covers the application of CE to analyze amino acids, biogenic amines, peptides, proteins, DNAs, carbohydrates, phenols, polyphenols, pigments, toxins, pesticides, vitamins, additives, small organic and inorganic ions, chiral compounds, and other compounds in foods, as well as to investigate food interactions and food processing. The use of microchips as well as other foreseen trends in CE analysis of foods is discussed. Papers that were published during the period June 2002-June 2005 are included following the previous review by Frazier and Papadopoulou (Electrophoresis 2003, 24, 4095-4105).     

Oligomerization of styrene over molybdenum oxide on silica-alumina catalyst

Styrene was found to yield saturated and unsaturated linear oligomers in the presence of a surface-supported catalyst, molybdenum oxide on silica-alumina. The reaction rates, the structure, and the molecular weight distribution of the products were found to be controlled by the choice of the solvent. Higher-molecular-weight fractions were favored in isooctane, whereas low-molecular-weight oligomers were preferred in dioxane. The reaction followed first-order kinetics with respect to the monomer. End-group analysis suggests a probable cationic mechanism. Approximate transfer constants K_trK_p were deduced from product distribution data. The behavior of the surface-supported catalyst was compared with other cationic catalyst systems.     

Colorimetric glutathione assay based on the peroxidase-like activity of a nanocomposite consisting of platinum nanoparticles and graphene oxide

Microchimica Acta - This work describes a colorimetric glutathione (GSH) assay that is taking advantage of (a) the peroxidase-like activity of a nanocomposite prepared from platinum nanoparticles...     

Mechanism of the reaction of styrene oxide with phosphonate-carbanions

Assignment of absolute configuration to the trans-2-phenylcyclopropane -carboxylic acid reveals that the reaction between optically active styrene oxide and phosphonate-carbanions proceeds with inversion at the asymmetric centre.     

椰壳炭磺酸催化环氧苯乙烷的醇解反应

利用椰壳制备的固体炭磺酸催化环氧苯乙烷的醇开环反应.考察了椰壳炭磺酸催化剂用量,溶剂对产率的影响.比较了椰壳炭磺酸与磺酸树脂、对甲苯磺酸和硫酸氢钠等传统磺酸型催化剂在该反应中的催化性能.结果表明,椰壳炭磺酸是一种绿色高效的固体酸催化剂.     

环氧乙烷与苯乙烯两亲性聚合物的合成

Graft eopolymer eontaining poly(ethylene oxide)side chains on a polystyrene backbone were acrylamided. The amide groups in the copolymers were ionized by using potassium naphthalene, and grafting was achieved by utilizing the amide anions as initiator sites for the polymerization of ethylene oxide at 70℃. The graft copolymers was characterized with respect to molecule weight and composition using NMR, IR, GPC, and DSC. GPC result from the graft copolymer sample suggested a narrow size distribution.     

DFT study of the glutathione peroxidase-like activity of phenylselenol incorporating solvent-assisted proton exchange

Modeling of the glutathione peroxidase-like activity of phenylselenol has been accomplished using density-functional theory and solvent-assisted proton exchange (SAPE). SAPE is a modeling technique intended to mimic solvent participation in proton transfer associated with chemical reaction. Within this method, explicit water molecules incorporated into the gas-phase model allow relay of a proton through the water molecules from the site of protonation in the reactant to that in the product. The activation barriers obtained by SAPE for the three steps of the GPx-like mechanism of PhSeH fall within the limits expected for a catalytic system at physiological temperatures (DeltaG(1)++ = 19.1 kcal/mol; DeltaG(2)++= 6.6 kcal/mol; G(3)++ = 21.7 kcal/mol) and are significantly lower than studies which require direct proton transfer. The size of the SAPE network is also considered for the model of the reduction of the selenenic acid, step 2 of the GPx-like cycle. Use of a four-water network better accommodates the reaction pathway and reduces the activation barrier by 5 kcal/mol over the two-water model.     

Sensing behavior of BN nanosheet toward nitrous oxide: A DFT study

In order to develop a sensor for the detection of toxic N₂O molecules, the interaction of pristine and Aldoped BN nanosheets with an N₂O molecule was investigated using density functional theory calculations. It was found that unlike the pristine sheet, the Al-doped sheet can effectively interact with the N₂O molecule so that its electronic properties and conductivity are dramatically changed. Webelieve that replacing a B atom of the BN sheet with an Al atom may be a good strategy for improving the sensitivity of these nanosheets toward N₂O, which cannot be trapped and detected by the pristine sheet.     

A study of the polymerization of styrene initiated by K-THF-GIC system

In this paper, the polymerization of styrene initiated by potassium (K)-tetrahydrofuran (THF)-graphite intercalation compound (GIC) (K-THF-GIC) was studied. The mechanism of the polymerization was determined to be anionic polymerization according to its characteristics. The effect of the concentration of the initiator and monomer was studied. It was found that the polymerization mainly occurred on the surface and edge of the intercalated graphite. It was also shown that the polarity of solvent has little effect on the polymerization yield in this system.