Electrocatalytic Oxidation of Some Carbohydrates by Nickel/Poly(o‐Aminophenol) Modified Carbon Paste Electrode

This study investigates the electrocatalytic oxidation of glucose and some other carbohydrates on nickel/poly(o‐aminophenol) modified carbon paste electrode as an enzyme free electrode in alkaline solution. Poly(o‐aminophenol) was prepared by electropolymerization using a carbon paste electrode bulk modified with o‐aminophenol and continuous cyclic voltammetry in HClO₄ solution. Then Ni(II) ions were incorporated to electrode by immersion of the polymeric modified electrode having amine group in 1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode; a good redox behavior of Ni(OH)₂/NiOOH couple at the surface of electrode can be observed, the capability of this modified electrode for catalytic oxidation of glucose and other carbohydrates was demonstrated. The amount of α and surface coverage (Γ*) of the redox species and catalytic chemical reaction rate constant (k) for each carbohydrate were calculated. Also, the electrocatalytic oxidation peak currents of all tested carbohydrates exhibit a good linear dependence on concentration and their quantification can be done easily.     

Determination of the exchange current in the SOFC composite cathode

To evaluate the exchange current I _o of the oxygen electrode reaction at the O₂ strontium-doped lanthanum manganite (LSM)/yttria stabilized zirconia (YSZ) composite/YSZ interface, the variation of the current I vs overvoltage η is measured at low cathodic and anodic polarizations (−50 to 30 mV). A linear behavior is observed within this potential domain with a unique slope. Taking into account of the dissociative adsorption of the oxygen molecule on the LSM electrocatalyst surface and the charge transferred at the triple-phase boundary, the exchange current is evaluated to 2.93 mA in air at 747 °C.     

PDE aspects of Aubry-Mather theory for quasiconvex Hamiltonians

We propose a PDE approach to the Aubry-Mather theory using viscosity solutions. This allows to treat Hamiltonians (on the flat torus ) just coercive, continuous and quasiconvex, for which a Hamiltonian flow cannot necessarily be defined. The analysis is focused on the family of Hamilton-Jacobi equations with a real parameter, and in particular on the unique equation of the family, corresponding to the so-called critical value a = c, for which there is a viscosity solution on . We define generalized projected Aubry and Mather sets and recover several properties of these sets holding for regular Hamiltonians.Received: 23 November 2003, Accepted: 3 March 2004, Published online: 12 May 2004     

On the proximinality of the unit ball of proximinal subspaces in Banach spaces: A counterexample

A known, and easy to establish, fact in Best Approximation Theory is that, if the unit ball of a subspace of a Banach space is proximinal in , then itself is proximinal in . We are concerned in this article with the reverse implication, as the knowledge of whether the unit ball is proximinal or not is useful in obtaining information about other problems. We show, by constructing a counterexample, that the answer is negative in general.

     

Bases d'ouverts réguliers et formule de Poisson pour l'équation de la chaleur

Summary Nous donnons une formule de Poisson pour certains polyèdres. Nous résolvons ainsi le problème de Dirichlet pour l'équation de la chaleur dans ces domaines.

     

Palladium-catalyzed carbonylative annulation of o-alkynylphenols: syntheses of 2-substituted-3-aroyl-benzo[b]furans

We report here a general synthetic methodology for palladium-catalyzed carbonylative annulation of o-alkynylphenol to construct 2-substituted-3-aroyl-benzo[b]furan. On the basis of the results, this methodology could be applied to a wider selection of iodide substrates to generate desired products. In accordance with mechanistic studies, this process involves coordination of cationic and less hindered acyl palladium complexes with o-alkynylphenols to create a desired cascade triad (coordination, nucleophilic addition, and reductive elimination). Consistent with this mechanism, addition of 1 equiv of AgBF(4) to palladium catalyst Pd(Ph(3)P)(4) generates an ideal candidate for this unique transformation.     

Block based embedding of encrypted watermarks using singular value decomposition

Watermarking is a solution to the problem of copyright protection of multimedia documents over the Internet. This paper presents a block based watermarking scheme using the singular value decomposition (SVD) algorithm to embed encrypted watermarks into digital images. The paper compares between the traditional method of Liu and the proposed method for embedding encrypted watermarks. Also, a permutation based encryption algorithm and a diffusion based encryption algorithm are compared as the watermark encryption algorithms. Experimental results show that the proposed method is superior to the traditional method of Liu for embedding encrypted watermarks and extracting them efficiently under attacks. Results also show that it is preferred to use permutation based encryption algorithms than diffusion based encryption algorithms for watermark encryption due to their lower sensitivity to attacks.     

Supramolecular Study on the Interaction Between Ofloxacin and Methyl β-Cyclodextrin by Fluorescence Spectroscopy and its Analytical Application

The supramolecular interaction of ofloxacin (Oflo) and methyl β-cyclodextrin (Mβ-CD) has been examined by UV–vis, IR and fluorescence spectroscopy. The formation of inclusion complex has been confirmed based on the changes of the spectral properties. The results showed that Mβ-CD reacted with Oflo to form an inclusion complex. The Oflo and Mβ-CD complex formed a host-guest complex in 1:1 stoichiometry and inclusion constant (K?=?7.8?×?10^?3 L mol^?1) was ascertained by the typical double reciprocal plots. Furthermore, the thermodynamic parameters (?H°, ?S° and ?G°) associated with the inclusion process were also determined. In addition, solid inclusion complex was synthesized. Based on the significant enhancement of the fluorescence intensity of Oflo produced through complex formation, a simple, accurate, rapid and highly sensitive spectrofluorometric method for the determination of Oflo in pharmaceutical formulation was developed. The measurement of relative fluorescence intensity was carried out at 497 nm with excitation at 296 nm. The factors affecting the inclusion complex formation were studied and optimized. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9995) were in the concentration range of 50–350 ng/mL for spectrofluorimetry. The limit of detection (LOD) was 11.5 ng/mL. The proposed method was successfully applied to the analysis of Oflo in pharmaceutical preparation.     

Photochromism and Photoisomerization in Some 2,3,4,4,5,6-Hexasubstituted 4H-Thiopyrans

Photochromism and photoisomerization reactions of some new 2,3,4,4,5,6-hexasubstituted 4H-thiopyrans are described.     

The Synthesis and Characterization of 2-Amino-3-methylpyridinium Dihydrogenmonophosphate: (C6H9N2)H2PO4

A new crystal of 2-amino-3-methylpyridinium dihydrogenmonophosphate has been prepared and characterized by X-ray crystallography, thermal analysis, and impedance and NMR spectroscopies. This compound crystallizes in the triclinic space group P with a = 7.343(2) Å, b = 7.987(2) Å, c = 8.116(4) Å, α = 77,62(3)°, β = 77,74(3)°, γ = 87,03(2)°, V = 454.3 (3)ų, and Z = 2. The crystal structure was solved and refined to R = 0.030 with 1602 independent reflections. The atomic arrangement can be described as (H₂PO₄ ^?)_n polymeric chains anchoring the 2-amino-3-methylpyridinium cations through short hydrogen bonds. All ring atoms of the organic entity are coplanar. The exocyclic N atom is an electron receiving center, which is consistent with features of imino resonance evidenced by bond lengths and angles. Solid state ³¹P, ¹³C, and ¹⁵N CP-MAS-NMR spectroscopies are in agreement with the X-ray structure. Ab initio calculations allow the attribution of carbons and nitrogen to the independent crystallographic sites.