Microchip capillary electrophoresis with amperometric detection for rapid separation and detection of phenolic acids

A microchip capillary-electrophoresis protocol for rapid and effective measurements of food-related phenolic acids (including chlorogenic, gentisic, ferulic, and vanillic acids) is described. Relevant parameters of the chip separation and amperometric detection are examined and optimized. Under optimum conditions, the analytes could be separated and detected in a 15 mM borate buffer (pH 9.5, with 10% of methanol) within 300 s using a separation voltage of 2000 V and a detection voltage of +1.0 V. Linear calibration plots are observed for micromolar concentrations of the phenolic acid compounds. The negligible sample volumes used in the microchip procedure obviates surface fouling common to amperometric measurements of phenolic compounds. The new microchip protocol offers great promise for a wide range of food applications requiring fast measurements and negligible sample consumption. An application on a commercial red wine was performed with minimal sample preparation and promising results.     

An Elegant Synthesis of a New Class of 1‐(Substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxides by Microwave Irradiation

A simple and efficient one‐pot microwave‐assisted click formation of 1‐(substituted)‐1H‐1,2,3‐triazol‐4‐yl)methyl)diphenylphosphineoxide derivatives via Huisgen regioselective [3+2]‐cycloaddition of an in situ generated organic azides and diphenyl(prop‐2‐yn‐1‐yl)phosphine oxide in highly polar DMSO‐H₂O medium. This synthetic protocol is mild, requires shorter reaction time, and afforded products in excellent yields with high regioselectivity.     

Uniformity analysis in nanocrystalline silver thin films using fuzzy inference system

An automatic and efficient technique to analyze the uniformity of nanoscale images using wavelets, feature similarity index measure (FSIM) and fuzzy inference system is reported. It has been successfully tested on scanning electron micrographs of nanocrystalline silver thin films. Thin films are prepared using on‐axis and off‐axis pulse laser deposition (PLD) technique. It is found that the film prepared using on‐axis PLD is more uniformly distributed and has smoother texture compared with that of the off‐axis technique. In order to analyze the images quantitatively, they are transformed to the wavelet domain to extract the localized frequency variations and a uniformity measure is derived using a fuzzy inference system for quantitatively analyzing the uniformity of each image. The surface plot of the FSIM values of the image is found to be an efficient tool for nanoscientists to evaluate the smoothness of the thin film surfaces. This study is expected to help the nanoscientists to understand these nanostructures in detail. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermolytic investigations on nickel(II) complexes of 4‐N‐(4′‐antipyrylmethylidene)aminoantipyrine with various counterions

Phenomenological characteristics and kinetic and mechanistic aspects of the thermal decomposition of nitrate, chloride, bromide, and iodide complexes of nickel(II) with 4‐N‐(4′‐antipyrylmethylidene)aminoantipyrine have been studied using thermogravimetric (TG) and differential thermogravimetric (DTG) techniques. Kinetic parameters such as activation energy, preexponential factor, and entropy of activation were quantified. The rate‐controlling process in all stages of decomposition was found to be based on random nucleation with one nucleus on each particle according to the Mampel model. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 53–58, 2007     

COMPARE: A computer program for comparative analysis of EPR data for low-symmetry paramagnetic centers

A quantitative method has been proposed for comparative analysis of EPR (electron para-magnetic resonance) data for low-symmetry paramagnetic centers and a computer program, COMPARE, based on this method has been developed. Quantitative parametersS _A andS _D are introduced to describe the closeness of the orientation of any two-axis systems and the principal values of any two tensors, respectively. The method helps to identify the pairs of data sets, comprising the principal values as well as the orientations of the principal axes of the second-rank spin Hamiltonian terms, which may likely belong to the same physical center but have been ascribed to distinct centers. Other useful applications of the program COMPARE are briefly discussed.     

Polyimide-epoxy alloys prepared via micro-modification: Water sorption and diffusion

A novel polyimide-epoxy or PI-EP alloys are prepared by the modification of polyamic acid in the concentration range of 1.54×10⁻⁶ to 1.54×10⁻² mol/L. The methanol sorption for these alloys at 24 hrs and at equilibrium conditions are determined and the residual solvent in fully cyclized polyimides were calculated. The presence of the residual solvent is visualized in fully imidized polymer and a structure containing partly imidized amic acid moiety is proposed and their concentration (in percentage) is calculated. The water sorption for these alloys at 24 hrs and at equilibrium conditions and the values of the water diffusion coefficient are determined from absorption isotherms. The PI-EP alloys have shown comparatively lower water sorption and higher diffusion coefficient than the unmodified polyimide. The mechanistic aspects of water sorption and diffusion are discussed.     

A convenient preparation of 2-thioxo-4(3H)-quinazolinones

A simple method is described for the preparation of 3-aryl-2-thioxo-4(3H)-quinazolinones (4) by the reaction of anthranilic acids and ammonium or triethylammonium N-aryl-dithiocarbamates in ethanol. The method is also applicable to the preparation of 3-ethyl-2-thioxo-4(3H)-quinazolinone.     

Tunable solvation effects on the size-selective fractionation of metal nanoparticles in CO2 gas-expanded solvents

This paper presents an environmentally friendly, inexpensive, rapid, and efficient process for size-selective fractionation of polydisperse metal nanoparticle dispersions into multiple narrow size populations. The dispersibility of ligand-stabilized silver and gold nanoparticles is controlled by altering the ligand tails-solvent interaction (solvation) by the addition of carbon dioxide (CO2) gas as an antisolvent, thereby tailoring the bulk solvent strength. This is accomplished by adjusting the CO2 pressure over the liquid, resulting in a simple means to tune the nanoparticle precipitation by size. This study also details the influence of various factors on the size-separation process, such as the types of metal, ligand, and solvent, as well as the use of recursive fractionation and the time allowed for settling during each fractionation step. The pressure range required for the precipitation process is the same for both the silver and gold particles capped with dodecanethiol ligands. A change in ligand or solvent length has an effect on the interaction between the solvent and the ligand tails and therefore the pressure range required for precipitation. Stronger interactions between solvent and ligand tails require greater CO2 pressure to precipitate the particles. Temperature is another variable that impacts the dispersibility of the nanoparticles through changes in the density and the mole fraction of CO2 in the gas-expanded liquids. Recursive fractionation for a given system within a particular pressure range (solvent strength) further reduces the polydispersity of the fraction obtained within that pressure range. Specifically, this work utilizes the highly tunable solvent properties of organic/CO2 solvent mixtures to selectively size-separate dispersions of polydisperse nanoparticles (2 to 12 nm) into more monodisperse fractions (+/-2 nm). In addition to providing efficient separation of the particles, this process also allows all of the solvent and antisolvent to be recovered, thereby rendering it a green solvent process.     

Towards disposable lab-on-a-chip: poly(methylmethacrylate) microchip electrophoresis device with electrochemical detection

A fully disposable microanalytical device based on combination of poly(methylmethacrylate) (PMMA) capillary electrophoresis microchips and thick-film electrochemical detector strips is described. Variables influencing the separation efficiency and amperometric response, including separation voltage or detection potential are assessed and optimized. The versatility, simplicity and low-cost advantages of the new design are coupled to an attractive analytical performance, with good precision (relative standard deviation RSD = 1.68% for n = 10). Applicability for assays of mixtures of hydrazine, phenolic compounds, and catecholamines is demonstrated. Such coupling of low-cost PMMA-based microchips with thick-film electrochemical detectors holds great promise for mass production of single-use micrototal analytical systems.