Synthesis and characterization of some Schiff-base-containing polyimides

The diamine, 4-aminophenyloxy-N-4-[(4-amiophenyloxy)benzylidene]aniline, was prepared via the nucleophilic substitution reaction and was polymerized with different dianhydrides either by one-step solution polymerization reaction or two-step procedure. The latter includes ring-opening polyaddition to give poly(amic acid), followed by cyclodehydration to polyimides. The inherent viscosity ranges from 0.61–0.79 dl/g. Some of the polymers were soluble in most of the organic solvents such as DMSO, DMF, DMAc, NMP, and m-cresol even at room temperature. The degradation temperature of the resultant polymers falls in the ranges from 240–500 °C in nitrogen with only 10% weight loss. Specific heat capacity at 200 °C ranges from 1.0929–2.6275 J g⁻¹ k⁻¹. The temperature at which the maximum degradation of the polymer occurs ranges from 600–630 °C. The glass transition temperature (Tg) values of the polyimides ranged from 185 to 272 °C. The activation energy and enthalpy of the polyimides ranged from 47.5–55.0 kJ/mole and 45.7–53.0 kJ/mole and the moisture absorption in the range of 0.23–0.72%.     

Pt–Ru electrocatalysts for fuel cells: a representative review

Three periods of Pt–Ru research are considered step-by-step: the initial period after discovery (1963–1970); observation and classification of basic tendencies (like the effects of composition, segregation, structural features on the activity; up to 1990); nanostructural studies and molecular level consideration of electrocatalytic phenomena in combination with advanced applied studies of materials, mechanistic, and applied aspects (after 1990). The main idea of this review is to balance various aspects of Pt–Ru electrochemistry related to material science and electrocatalysis as well as to remember the early basic results being of importance for future understanding of Pt–Ru functional properties. Dedicated to Professor Teresa Iwasita, as a token of her remarkable contribution to electrocatalysis.

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Ruthenium(III)-catalyzed and uncatalyzed kinetic studies on the oxidation of sulfanilic acid by chloramine-T in perchloric acid medium: a mechanistic approach

The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric acid medium. The reaction shows a first-order dependence on [CAT]_o and a non-linear dependence on both [SAA]_o and [HClO₄] for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to [Ru^III] is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated. The rate of the reaction increases in the D₂O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed reactions. The protonated conjugate acid (CH₃C₆H₄SO₂NH₂Cl⁺) is postulated as the reactive oxidizing species in both the cases.     

2-pyrrolidone - capped Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals

Water-soluble Mn₃O₄ nanocrystals have been prepared through thermal decomposition in a high temperature boiling solvent, 2-pyrrolidone. The final product was characterized with XRD, SEM, TEM, FTIR and Zeta Potential measurements. Average crystallite size was calculated as ∼15 nm using XRD peak broadening. TEM analysis revealed spherical nanoparticles with an average diameter of 14±0.4 nm. FTIR analysis indicated that 2-pyrrolidone coordinates with the Mn₃O₄ nanocrystals only via O from the carbonyl group, thus confining their growth and protecting their surfaces from interaction with neighboring particles.      

Palladium complexes with bis(diphenylphosphinomethyl)amino ligands and their application as catalysts for the Heck reaction

Aminomethylphosphine (P–C–N) type ligands, (Ph₂PCH₂)₂NR R = –(CH₂)₃Si(OEt₃)₃ or –CH₂CH₂OH, and their Pd(II) complexes have been synthesized. All the compounds were characterized by ¹H-, ³¹P-NMR, and elemental analysis. The complexes are proposed to have a square planar geometry. They were investigated as catalysts for the Heck reaction of aryl halides (I, Br, Cl) with methyl acrylate. Both complexes showed high activity to give methyl cinnamate in good yields, with the best turnover numbers found for [PdCl₂(Ph₂PCH₂)₂N(CH₂)₃Si(OEt)₃].     

Study on the electroreduction process of oxygen to superoxide ion by using acetylene black powder microelectrode

In this paper, the powder microelectrode technique was employed in studying the voltametric response of the O₂/₂⁻ couple, which demonstrated a nearly reversible redox process at an acetylene black powder microelectrode in N,N-dimethylformamide (DMF). A well-developed steady state current plateau for the electrochemical reduction of oxygen was obtained in this system. The electron transfer number (n) and heterogeneous electron transfer rate constant k _s were measured by steady-state voltametric response, and the results were 1.08, 3.4 × 10⁻³ cm s⁻¹, respectively. Additionally, the scavenging activity of O₂⁻ with biological antioxidant (ascorbic acid) was evaluated by cyclic voltammetry; IC₅₀ came to 5 × 10⁻⁴ mol/l. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1040–1044. The text was submitted by the authors in English.     

Voltammetric determination of malachite green in fish samples based on the enhancement effect of anionic surfactant

In this work, an electrochemical method for the determination of malachite green was developed on the basis of enhancement effect of an anionic surfactant: sodium dodecyl benzene sulfonate. It is found that the oxidation peak current of malachite green at carbon paste electrode significantly increases in the presence of low concentration of sodium dodecyl benzene sulfonate in pH 6.5 phosphate buffer, suggesting that sodium dodecyl benzene sulfonate shows obvious enhancement effect for the determination of malachite green. The experimental parameters, such as supporting electrolyte, kind of surfactant, concentration of sodium dodecyl benzene sulfonate and accumulation time, were optimized, and then a sensitive and convenient electrochemical method was proposed for the determination of malachite green. The oxidation peak current is proportional to the concentration of malachite green over the range from 8.0 × 10⁻⁹ to 5.0 × 10⁻⁷ mol l⁻¹, and the detection limit is 4.0 × 10⁻⁹ mol l⁻¹ after 5 min of accumulation. Finally, this new method was successfully employed to detect malachite green in fish samples. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1019–1024. The text was submitted by the authors in English.     

Thermal degradation of copolymers from vinyl acetate and vinyl alcohol

The thermal degradation of poly(vinyl acetate) (PVA), poly(vinyl alcohol) (PVAL), vinyl acetate-vinyl alcohol (VAVAL), vinyl acetate-vinyl-3,5-dinitrobenzoate (VAVDNB) and vinyl alcohol-3,5-dinitrobenzoate (VALVDNB) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal analysis indicates that PVA and PVAL are thermally more stable than VAVAL copolymers, being PVAL the most stable polymer. The presence of small amounts of vinyl-3,5-dinitrobenzoate (VDNB) in PVA or PVAL produces a marked decrease in the thermal stability of both homopolymers, being VALVDNB copolymers the less stable materials. The apparent activation energy of the degradative process was determined by the Kissinger and Flynn-Wall methods which agree well.     

Carboxyl groups in pre-treated regenerated cellulose fibres

The influence of peroxide bleaching and slack-mercerization on the amount of acidic groups in regenerated fibres (viscose, modal and lyocell) were studied. Conductometric titration was used to determine the total content of acidic carboxylic groups. Polyelectrolyte titration was used for surface and total charge determination, and to obtain information about the charge distribution and accessibilities of charged groups. Changes in fibre crystallinity to pre-treatment processes were characterized using iodine sorption (Schwertassek method) and correlated to treatments and the amount of carboxylic groups. For all three types of fibres the amount of accessible carboxyl groups was lowered by an increase in the degree of crystallinity. Bleaching with hydrogen peroxide causes some oxidative cellulose damage and, therefore, a larger amount of carboxyl groups (presumably formed at the end of cellulose chains). Slack-mercerization did not significantly change the total amount of acidic groups in the fibres, but their accessibility to cationic polyelectrolytes, in particular to polymers with high molecular weight was substantially lowered. Lidija Fras Zemljič, Zdenka Peršin, and Karin Stana Kleinschek are the members of the European Polysaccharide Network of Excellence (EPNOE).     

Synthesis and spectroscopic properties of furyl-phenyl-acrylates and naphthofurans and their interaction with ct-<Emphasis Type="Italic">DNA</Emphasis>

A series of novel substituted derivatives related to furyl-phenyl-acrylates and naphthofurans, was synthesized and characterized by UV/Vis and fluorescence spectroscopy. Acyclic compounds can undergo photochemical dehydrocyclization by visible light irradiation in order to obtain their cyclic derivatives. The interactions of the prepared compounds with calf thymus DNA was investigated by means of electronic absorption and fluorescence spectra. It is intriguing that addition of ct-DNA induced a fluorescence increase of acyclic derivatives, exactly the opposite of the strong fluorescence quenching observed for cyclic derivatives 10 and 12. Compound 11 showed decreasing fluorescence intensity for lower concentrations of ct-DNA, while increasing of fluorescence is observed for high excess of added ct-DNA. Correspondence: Grace Karminski-Zamola, Department of Organic Chemistry, Faculty of Chemical Engineering and Technology, University of Zagreb, Marulićev trg 20, HR-10000 Zagreb, Croatia.