Electrochemical quartz crystal microbalance study of ion transport accompanying charging-discharging of poly(pyrrole) films

Electrochemical quartz crystal microbalance studies on poly(pyrrole) electrodes revealed a complex nature of the potential-dependent sorption of ionic substances. It is found that the relative contribution of anions and cations to the overall charge transport process depends upon several factors, such as the oxidation state of the polymer, the composition of the supporting electrolyte as well as on the film thickness. The phenomena observed are discussed in terms of morphological transformations arising as a result of interactions between the polymer and the mobile substances. Received: 21 August 1998 / Accepted: 21 October 1998     

Catalytic transfer hydrogenation of 2-butanone over oxide catalysts

Catalytic transfer hydrogenation of 2-butanone with 2-propanol was studied in gas phase over a series of oxides of different acid-base properties. Although the basic oxides (MgO, La₂O₃) gave high initial conversions, these oxides underwent deactivation during the reaction. This deactivation could be partially prevented by a previous treatment with chloroform of the oxide. The amphoteric oxides (TiO₂, ZrO₂, Al₂O₃) were also active in this reaction. Increasing the acidic character of the catalyst (Nb₂O₅, WO₃) led to a pronounced dehydration of 2-propanol. The results obtained over a series of rare earth oxides (La₂O₃, Sm₂O₃, Gd₂O₃, Dy₂O₃, Er₂O₃) revealed that beside the role of basic and acid sites a correlation seems to exist between the number of unpaired electrons of the metal ion and the catalytic activity, indicating the role of one electron donor sites.     

Comparative bioanalytical study of3H-deramciclane in dog plasma, using a gas chromatography-nitrogen-selective detection (GC-NPD), a new GC-radiochemical detection (GC-RD) and a liquid scintillation method

Summary A new, highly sensitive and selective gas chromatography method, using radiochemical detection (GC-DR) was developed for the selective determination of³H-labelled deramciclane and its N-desmethyl metabolite in dog plasma. Inter-day accuracy and precision, as well as system suitability of the GC-RD method was investigated during the method validation. The calibration curve was proved to be linear (r=0.9986) in a wide concentration range (13–1000 ngeqv mL⁻¹) The lower limit of quantitation (LLOQ) was 13.7 ngeqv mL⁻¹, and the limit of the detection (LOD) was 1 ngeqv mL⁻¹. Using this new GC-RD method, plasma levels of³H-labelled deramciclane and its metabolite were determined in dogs, after the administration of a single 10 mg kg⁻¹ oral dose. Pharmacokinetic curves and the calculated pharmacokinetic parameters were compared to those obtained using a previously elaborated gas chromatography-nitrogen selective detection method (GC-NPD) and to those obtained by measuring the plasma level of total radioactivity (liquid scintillation counting, LSC). Pharmacokinetic curves and the calculated pharmacokinetic parameters obtained with the two different gas chromatography detection methods (NPD and RD) showed good correlation. Comparison of these results to those acquired by total radioactivity measurement demonstrated that deramciclane was intensively metabolised. Moreover, the biological half-life (t ₁ ^2/β ) of the unknown metabolites proved to be more than a magnitude longer than the half-life of the parent compound or that of N-desmethyl metabolite. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997.     

An improved method for assay of vitamin C in fish feed and tissues

Summary A method was devised to assay four forms of vitamin C: L-ascorbic acid (AA), dehydroascorbic acid (DHA), ascorbate-2-mono- and polyphosphate (AMP, APP), as well as ascorbate-2-monosulphate (AMS), in sample series of different fish tissues and feed. Direct and indirect detection were combined. Sample extractions were carried out with 0.2 mol L⁻¹ sodium acetate buffer (pH 4.8) and extracts were deproteinized after different chemical or enzymatic reactions, with perchloric acid. The DHA was reduced to AA with dithioerythritol (DTE). Ascorbate oxidase enzyme was used for the detection of background and an acidic phosphatase enzyme for the hydrolysis of different phosphate esters. Ascorbate-2-sulphate was detected directly with help of coinjection of the compound. Chromatographic analysis was carried out with a single column isocratic reverse phase method. The mobile phase was an aqueous buffer of 0.04 M sodium-acetate, 0.05 mM EDTA, 0.5 mM tetrabutylammonium dihydrogen phosphate (TBA) adjusted to pH 3.76 with 85% H₃PO₄ and with 24 mL methanol added to 1000 mL. C-18 columns were used with 0.6 mL min⁻¹ flow rate at 23°C. The vitamin C forms were detected by UV absorption at 250 nm. The determination limit was 1.0–5.0 μg g⁻¹ in AA equivalent. The standard deviations were between 1–6% and depended on the concentrations of vitamin C forms and tissues. Recoveries were between 90–96% in samples. Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997     

Fundamental metal carbonyl equilibria: a quantitative infrared spectroscopic study of the equilibrium between dicobalt octacarbonyl and tetracobalt dodecacarbonyl under carbon monoxide pressure in hexane solution.

The equilibrium between Co₂(CO)₈ and Co₄(CO)₁₂ has been investigated in hexane solution in the temperature range 105–145°C under carbon monoxide pressure (6–14 bar). the data obtained by infrared analytical monitoring of the system in a high-pressure cell alow a reasonably precise extension of the calculated equilibrium concentration between —20 and 300°C. The thermo- dynamic parameters obtained for this system are: ΔH⁰ 29.5 ± 0.5 kcal mol^-1, ΔS⁰ 135 ± 3 cal mol^-1 K^-1. The stability regions of Co₂(CO)₈ and Co₄(CO)₁₂ in terms of p(CO) and temperature are discussed.     

Can a rate constant independent of sample size be obtained from the rate equation generally used in thermal analysis?

Some consequences of using the rate equation d/dt=k _t f() are shown on a simple example. It is demonstrated thatk _t usually depends on the sample size, and that it is usually incorrect to assume that if mass and heat transport effects are avoided both and d/dt — as functions of time — are independent of the initial mass. Rate equations should be based on real local quantities.     

Darstellung und eigenschaften von 124,2,4,6-thiatriazin-1-oxiden. zur struktur der hydrolyseprodukte von 1-arensulfonyl-imino-1λ4,2,4,6-thiatriazinen

Synthesis and structure of 4-phenoxy-H[1λ⁴,2,4,6]thiatriazino[4,3a]benzimidazole-2-oxide 5, 3-amino-4H[1λ⁴,2,4,6]thiatriazino[2,3-a]benzimidazole-1-oxide 6 and 3-amino-5-dimethylamino-2-tosyl-1λ⁴, 2,4,6-thiatriazine-1-oxide 7, obtained by hydrolysis of the corresponding arenesulfonyl imino compounds are discussed. The molecular and crystal structure of N-benzoyl-? tosyl-guanidine is presented.     

Synthesis,spectral, thermal and structural study of bis(2-bromobenzoato-O,O′)-bis(methyl-3-pyridylcarbamate-N)-zinc(II)

The new complex bis(2-bromobenzoato-O,O′)-bis(methyl-3-pyridylcarbamate-N)-zinc(II), [Zn(2-BrC₆H₄COO)₂mpc₂] (1), has been prepared and characterized by elemental analysis, IR spectroscopy, thermal analysis and single-crystal X-ray diffraction. The bonding between the ligands and the central atom was investigated by DFT studies. The theoretical infrared spectrum of 1 was compared with the experimental data. The complex proved to be thermally stable up to 165 °C. Volatile intermediate products of its thermal decomposition were identified by mass spectrometry. The coordination environment of the zinc atom consists of two nitrogen atoms of two methyl-3-pyridylcarbamate ligands and is chelated by four oxygen atoms of two 2-bromobenzoate ligands (ZnO₄N₂ – chromophore).     

Expedient and Diastereodivergent Assembly of Terpenoid Decalin Subunits having Quaternary Stereocenters through Organocatalytic Robinson Annulation of Nazarov Reagent

We report an expedient approach to highly functionalized cis‐ and trans‐decalines that could function as key structural subunits toward the synthesis of various classes of terpenoids. Key to the strategy is an organocatalyzed Robinson annulation reaction of the Nazarov reagent that affords chiral enone building blocks with high enantioselectivities. The quaternary carbon stereogenic center can direct the subsequent reactions and allow the rapid and diastereoconvergent assembly of complex decalines with contiguous stereocenters.