Determination of zearalenone and its metabolites in urine samples by liquid chromatography with electrochemical detection using a carbon nanotube-modified electrode

A simple and sensitive method for the separation and determination of zearalenone (ZON) and its secondary metabolites, namely beta-zearalenol (beta-ZAL), beta-zearalanol (beta-ZOL), alpha-zearalenol (alpha-ZAL), alpha-zearalanol (alpha-ZOL) and zearalanone (ZAN) in urine (human, bovine and swine) samples is proposed. The method comprises previous clean-up and pre-concentration on C(18) adsorption cartridges of the analytes followed by liquid chromatographic separation and direct electrochemical detection at +0.85mV using a carbon nanotube-modified glassy carbon electrode (CNT-GCE). This method allows the determination of beta-ZAL, beta-ZOL, alpha-ZAL, alpha-ZOL, ZAN and ZON in a linear range between 5 and 50ngmL(-1), with relative standard deviation values lower than 6.9% (intra-day) and 7.1% (inter-day), in all cases. Detection limits ranging between 1.3ngmL(-1) (beta-ZOL, alpha-ZAL, alpha-ZOL) and 1.4ngmL(-1) (beta-ZAL, ZAN, ZON) were achieved. The usefulness of the proposed method was demonstrated by the analysis of spiked and natural samples of human, bovine and swine urine samples.     

MCE‐electrochemical detection for following interactions of ssDNA and dsDNA with methylene blue

The interaction between the organic dye, methylene blue and DNA has been studied by MCE with electrochemical detection. Interaction produces two different signals, one corresponding to free methylene blue and other, for the complex methylene blue–DNA. The hybridization between a ssDNA and a complementary sequence, specific to the severe acute respiratory syndrome virus, has been performed and studied in a thermoplastic olefin polymer of amorphous structure CE‐microchip with an end‐channel gold wire detector. Moreover, studies with a longer dsDNA, an expression vector involved in the transitory or stable expression in mammals cells, pFLAG‐CMV4, has also been performed.     

Solvent effects on the three-photon absorption cross-section of a highly conjugated fluorene derivative

Herein, we report the study of the three-photon absorption cross-section dependence on solvents parameters for a highly conjugated organic dye, 2,2'-(4,4'-(1E,1'E)-2,2'-(9,9-didecyl-9H-fluorene-2,7-diyl) bis(ethene-2,1-diyl)bis(4,1-phenylene))dibenzo[d]thiazole (A-pi-pi-pi-A). The three-photon absorption cross-section was measured for this organic dye in solution in four different solvents with polarity function, Deltaf between 0.162 and 0.247. The experiments show how the solvent's reorientation of the electrons and polarity contribute to the 3PA cross-section. Multiphoton-absorption experiments of A-pi-pi-pi-A in all four different solvents were performed with a tunable OPG pumped by a 25 picosecond Nd-YAG laser.     

The impact of the pi-electron conjugation length on the three-photon absorption cross section of fluorene derivatives

The three-photon absorption cross sections of three different fluorene derivatives, with extended pi-electron conjugation lengths was experimentally measured and compared with shorter pi-electron conjugation length analogs. The effect of the conjugation length on the three-photon absorption cross section sigma(3) (') of this family of molecules has been elucidated. It is demonstrated that sigma(3) (') of the asymmetric compound D-pi-pi-pi-A is 6.6 times larger than its shorter configuration D-pi-A, while for the symmetric compounds D-pi-pi-pi-D and A-pi-pi-pi-A a two-fold enhancement was found relative to their shorter conjugation length analogs. Measurements of the three-photon excitation of these compounds in THF solution (10(-3)M) were accomplished with a tunable optical pulse generation pumped by a 25 ps Nd-YAG laser.     

Amperometric detector designs for capillary electrophoresis microchips

Electrochemical (EC) detection is a sensitive and miniaturisable detection mode for capillary electrophoresis (CE) microchips. Detection cell design is very important in order to ensure electrical isolation from the high separation voltage. Amperometric detectors with different designs have been developed for coupling EC detection to CE-microchips. Different working electrode alignment: in-channel or end-channel has been tested in conjunction with several materials: gold, platinum or carbon. The end-channel detector was based on a platinum or gold wire manually aligned at the exit of the separation channel. Thick- (screen-printed carbon electrode) and thin-film (sputtered gold film) electrodes have also been employed with this configuration, but with a different design that allowed the rapid replacement of the electrode. The in-channel detector was based on a gold film within the separation channel. A gold-based dual electrode detector, which combined for the first time in- and end-channel detection, has been also tested. These amperometric detectors have been evaluated in combination to poly(methylmethacrylate) (PMMA) and Topas (thermoplastic olefin polymer of amorphous structure) CE-microchips. Topas is a new and promising cyclic olefin copolymer with high chemical resistance. Relevant parameters of the polymer microchip separation such as precision, efficiency or resolution and amperometric detection were studied with the different detector designs using p-aminophenol and L-ascorbic acid as model analytes in Tris-based buffer pH 9.0.     

A finite-strain constitutive theory for electro-active polymer composites via homogenization

This paper presents a homogenization framework for electro-elastic composite materials at finite strains. The framework is used to develop constitutive models for electro-active composites consisting of initially aligned, rigid dielectric particles distributed periodically in a dielectric elastomeric matrix. For this purpose, a novel strategy is proposed to partially decouple the mechanical and electrostatic effects in the composite. Thus, the effective electro-elastic energy of the composite is written in terms of a purely mechanical component together with a purely electrostatic component, this last one dependent on the macroscopic deformation via appropriate kinematic variables, such as the particle displacements and rotations, and the change in size and shape of the appropriate unit cell. The results show that the macroscopic stress includes contributions due to the changes in the effective dielectric permittivity of the composite with the deformation. For the special case of a periodic distribution of electrically isotropic, spherical particles, the extra stresses are due to changes with the deformation in the unit cell shape and size, and are of order volume fraction squared, while the corresponding extra stresses for the case of aligned, ellipsoidal particles can be of order volume fraction, when changes are induced by the deformation in the orientation of the particles.     

An investigation of strong backflow events at the interface of air–water systems using large-eddy simulation

A large-eddy simulation of a counter-current gas–liquid flow is performed. At the flat interface where the different fluids meet, continuity of momentum and momentum fluxes are enforced following the work of Lombardi et al. [Direct numerical simulation of near-interface turbulence in coupled gas-liquid flow. Phys Fluids. 1996;8(6):1643–1665]. The increase in vertical vorticity fluctuations near the interface increases mixing, reducing the thickness of the inner region of the boundary layer. Such increase reduces shear while allowing for more frequent backflow motions in the inner region, being this phenomenon stronger on water. Due to the higher inertia of water these backflow motions are ultimately responsible for the streaky structure of shear stresses seen along the interface. The present study shows that such bimodality in the streamwise velocities is also seen in the angle distribution of vorticity relative to the interface, where such angles are linked to the presence of interface-connected and quasi-streamwise vortex cores. Finally, it is shown that backflow events on the interface shear stresses correlate with coupled ‘strong’ ejections in the near interface region despite the disparagingly different near-interface streamwise velocity distributions on the near interface boundary layers.     

Fourier transform infrared and Raman spectra. Semi empirical AM1 and PM3; MP2/DZV and DFT/B3LYP-6-31G(d) ab initio calculations for dimethylterephthalate (DMT)

Fourier transform infrared and Raman spectra of dimethylterephthalate (DMT), as microcrystalline powder, have been investigated. The vibrational spectra were calculated using the AM1 and PM3 semi empirical procedures, and the M?ller-Plesset (MP2/DZV), and the Becke-Lee, Yang and Parr gradient-corrected correlation functional: B3LYP/6-31G(d) ab initio calculations. On this basis, and assisted with the FT-IR and Raman spectra of the terephthalic acid, an assignment of the vibrational spectra of dimethylterephthalate was proposed. In the calculations, remarkable differences concerning the assignments of the vibrational spectra were noted between the AM1 and PM3 methods. Also, the ab initio procedure shows differences in interpreting the spectra compared with the semi empiric procedures, and among themselves. Calculated geometrical parameters were compared with the experimental values of dimethylterephthalate, diethylterephthalate and terephthalic acid.     

Fourier transform infrared and raman spectra, vibrational assignment and ab initio calculations of terephthalic acid and related compounds

The Fourier transform infrared and Raman spectra of solid terephthalic acid, p-C6H4(COOH)2, have been recorded, and the Fourier transform Raman spectra for the terephthalate anion were measured. The wavenumbers for the band positions have been calculated in order to assign them. Moller-Plesset (MP2) and Density functional theory (DFT) calculations have been carried out with Huzinaga-Dunning basis sets (DZV). Also, a normal coordinate analysis through the Wilson-El'yashevich method was performed. The differences between the calculated ab initio spectra and the spectra of the solid phase have been interpreted with respect to the different C(2h) and C(i) local symmetry in the gas and in the solid phase, respectively, and considering also the formation of long-chains of terephthalic acid in the solid phase. In spite to the absence of experimental data for the cis conformation, calculations have been carried out and structural parameters and infrared intensities have been evaluated for the trans and cis conformations of terephthalic acid.