Quantification of Quercetin Using Glassy Carbon Electrodes Modified with Multiwalled Carbon Nanotubes Dispersed in Polyethylenimine and Polyacrylic Acid

This work reports the highly sensitive detection of quercetin using glassy carbon electrodes modified with multiwall carbon nanotubes (MWCNT) dispersed in polyethylenimine and poly(acrylic acid). The adsorptive stripping with square wave voltammetric transduction allowed the detection of 7.5 nM quercetin after 1.0 min accumulation at open circuit potential. The amperometric detection at 0.150 V is reported as an easier and simpler alternative to determine quercetin, with detection limits of 0.2 µM. The careful selection of the working conditions also made possible the detection of submicromolar levels of quercetin in the presence of excess of rutin. The proposed methodology was successfully used to quantify quercetin in onion samples.     

The kinetics of solid‐state reactions toward consensus—Part I: Uncertainties,failures, and successes of conventional methods

An account of conventional dynamic thermal analysis (TA) with respect to uncertainties, failures, successes, and limitations as applied to solid‐state (s‐s) processes is discussed. A review of some controversial aspects of TA is presented. The scope is to discuss in three parts the adequate understanding of TA and to open a controversy about the dynamic methods and about the necessity of stimulating a consensus between scientists for a better TA. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 343–353, 2001     

GPU computing for shallow water flow simulation based on finite volume schemes

This article is a review of the work that we are carrying out to efficiently simulate shallow water flows. In this paper, we focus on the efficient implementation of path-conservative Roe type high-order finite volume schemes to simulate shallow flows that are supposed to be governed by the one-layer or two-layer shallow water systems, formulated under the form of a conservation law with source terms. The implementation of the scheme is carried out on Graphics Processing Units (GPUs), thus achieving a substantial improvement of the speedup with respect to normal CPUs. Finally, some numerical experiments are presented.     

Multi‐commutated Flow‐through Multi‐optosensing: A Tool for Environmental Analysis

Abstract

Multi‐commutation, which refers to the use of solenoid valves to construct the flow network, has been widely used for providing automation in flow injection analysis. In this paper, the coupling of multi‐commutation and multi‐optosensing is developed for the analysis of two pesticides in environmental water samples, fuberidazole and o‐phenylphenol. In optosensing, the use of the solid support allows the discrimination between the analytes and other compounds that, if measuring in solution, would interfere in the analysis; in addition, the sensitivity needed when facing environmental samples is obtained. The two analytes are separated by using C₁₈ silica gel as solid support, taking into account their different kinetics of sorption/desorption when interacting with the solid support microbeads; the separation is performed in the same flow‐cell where the sensing detection is carried out (by using an additional amount of solid support in the cell itself above the irradiated microzone), so both separation and determination are integrated in the cell. The native fluorescence of fuberidazole and o‐phenylphenol was simultaneously measured at 314/356 and 250/345 nm, respectively. The detection limits obtained were 0.18 and 6.1 ng mL^?1 for fuberidazole and o‐phenylphenol respectively, with a sampling frequency of about 12 samples per hour. A recovery study was performed in waters obtained for wells and rivers, with satisfactory results.     

Symmetry Reduction in Symplectic and Poisson Geometry

We present a quick review of several reduction techniques for symplectic and Poisson manifolds using local and global symmetries compatible with these structures. Reduction based on the standard momentum map (symplectic or Marsden–Weinstein reduction) and on generalized distributions (the optimal momentum map and optimal reduction) is emphasized. Reduction of Poisson brackets is also discussed and it is shown how it defines induced Poisson structures on cosymplectic and coisotropic submanifolds.     

Bloch wave homogenization of a non-homogeneous Neumann problem

In this paper, we use the Bloch wave method to study the asymptotic behavior of the solution of the Laplace equation in a periodically perforated domain, under a non-homogeneous Neumann condition on the boundary of the holes, as the size of the holes goes to zero more rapidly than the domain period. This method allows to prove that, when the hole size exceeds a given threshold, the non-homogeneous boundary condition generates an additional term in the homogenized problem, commonly referred to as “the strange term” in the literature.     

DFT‐Aided Vibrational Circular Dichroism Spectroscopy Study of (−)‐S‐cotinine

The implementation of a strategy comprising the use of vibrational circular dichroism spectroscopy and DFT calculations allows determination of the solution‐state conformational distribution in (?)‐S‐cotinine, giving further proof of the extra conformer‐discriminating potential of this experimental technique, which may offer unique molecular fingerprints of subtly dissimilar molecular conformers of chiral samples. Natural bond orbital electronic structure calculations of the rotational barrier height between the two main conformers of the species indicate that hyperconjugative effects are the key force governing the conformational equilibrium. The negligible effect of the solvent’s polarity over both structure and conformational energy profile supports this result.     

Exo conformers of N‐(pyridin‐2‐yl)‐ and N‐(pyridin‐3‐yl)norbornene‐5,6‐dicarboximide crystals

Two isomeric pyridine‐substituted norbornenedicarboximide derivatives, namely N‐(pyridin‐2‐yl)‐exo‐norbornene‐5,6‐dicarboximide, (I), and N‐(pyridin‐3‐yl)‐exo‐norbornene‐5,6‐dicarboximide, (II), both C₁₄H₁₂N₂O₄, have been crystallized and their structures unequivocally determined by single‐crystal X‐ray diffraction. The molecules consist of norbornene moieties fused to a dicarboximide ring substituted at the N atom by either pyridin‐2‐yl or pyridin‐3‐yl in an anti configuration with respect to the double bond, thus affording exo isomers. In both compounds, the asymmetric unit consists of two independent molecules (Z′ = 2). In compound (I), the pyridine rings of the two independent molecules adopt different conformations, i.e. syn and anti, with respect to the methylene bridge. The intermolecular contacts of (I) are dominated by C—H...O interactions. In contrast, in compound (II), the pyridine rings of both molecules have an anti conformation and the two independent molecules are linked by carbonyl–carbonyl interactions, as well as by C—H...O and C—H...N contacts.