Electrochemically inactive organic substance influence on peak height in anodic stripping voltammetry

A simplified method was proposed for calculation of changes of peak height (i) vs. deposition time (t_e) in the presence of a surfactant acting only at the deposition stage. The simplification was based on the assumption that the deposition current has a constant value until time t₁ when it decreases abruptly to a lower level. Hence the dependency of the peak height on the deposition time can be written:i=β₀t₁+β₁(t_e?t₁) Limiting cases were discussed: t₁→0 and β₁→1 leading to three types of i vs. t_e relation. The experimental evaluation was carried out for Pb(II), Cu(II) and Cd(II) in the presence of various polyethyleneglycols. All three types of curves were obtained in the experiments, as well as some which did not fit the simplified theory.     

Evaluation of loop and pump injection systems in preparative liquid chromatography

The usefulness of pump or loop injectors in preparative liquid chromatography was evaluated. The concentration distribution of samples flowing through a UV detector cell, directly connected to the injector, was recorded at various flow velocities, at various diameters of loop tubing, and using various methods of injection [injection with sample volumes equal to a fraction or total loop volume, etc.]. The most advantageous methods were found to be either use of a loop injector to inject only a fraction of its total volume or use of a pump. Both of these methods ensure a almost rectangular concentration distribution.     

Chemically binding Eu^3＋ onto CdS semiconductor nanoparticle surface

Europium ions were chemically bound to CdS nanoparticles surface by diethylenetri-aminepentaacetate (DTPA, 1) in a two-step synthetic route. First 1 was applied to chelate with cadmium on the surface of cadmium-rich CdS nanoparticles and act as a capping agent. Further, the purified 1-capped particles were used to bind with Eu~3 . The purified and redispersed particles were characterized by photoluminescence spectroscopy, TEM and SEM. It was observed that Eu~3 on the nanoparticle surface significantly increased the band gap emission and decreased the surface emission intensity of the CdS nanoparticles.     

Synthesis of Functionalized (2-Thienylcarbonyl)thiazoles and 4-(2-Thienyl)pyridines by Reaction of (2-Thienylcarbonyl)thioacetanilides and their Enamine Derivatives

The condensation of two molecules of 2-(2-thienylcarbonyl)thioacetanilides catalyzed by piperidine yielded thiazole derivatives as confirmed by X-ray crystal structure analysis. The reaction of malononitrile with 3-morpholino-3-(2-thienyl)acrylic acid thioanilides furnished 6-amino-1-aryl-4-(2-thienyl)-1,2-dihydro-2-thioxopyridine-5-carbonitriles. A similar reaction of malononitrile with 3-morpholino-3-(2-thienyl)acrylic acid anilides provided 2-oxopyridine-5-carbonitriles.     

Reaction of β‐cyano esters with hydrazine hydrate. Unexpected formation of dipyrrolo[1,2‐b:1′,2′‐e][1,2,4,5]tetrazine,a novel ring system

Some intermediates and by‐products of the title reaction, known to yield 6‐hydrazinopyridazine‐3‐one derivatives, were isolated or detected when the amount of hydrazine hydrate used to react with two model β‐cyano esters was reduced to less than two equivalents. N'‐(1‐amino‐4‐hydrazino‐4‐oxo‐2‐phenylbutyli‐dene)‐4‐hydrazino‐4‐oxo‐2‐phenylbutanehydrazonamide and 3,3,8,8‐tetramethyl‐2,3,7,8‐tetrahydro‐1H,6H‐dipyrrolo[1,2‐b:1′,2′‐e][1,2,4,5]tetrazine‐1,6‐dione were isolated as the terminal products of side‐reactions; they were unreactive to hydrazine. The latter compound is a derivative of a novel ring system. Mechanism of the reaction was proposed.     

Synthesis, characterisation and speciation studies of heterobimetallic pyridinehydroxamate-bridged Pt(II)/M(II) complexes (M = Cu, Ni, Zn). Crystal structure of a novel heterobimetallic 3-pyridinehydroxamate-bridged Pt(II)/Cu(II) wave-like coordination polymer

The reaction of cis-[Pt(NH3)2(3-pyhaH)2]2+ (3-pyhaH = 3-pyridinehydroxamic acid) and cis-[Pt(NH3)2(4-pyhaH)2]2+ (4-pyhaH = 4-pyridinehydroxamic acid) with Cu(II), Ni(II) or Zn(II) in aqueous solution affords novel heterobimetallic pyridinehydroxamate-bridged complexes, {cis-[Pt(NH3)2(mu-3-pyha)M(mu-3-pyha)].SO4.xH2O}n and {cis-[Pt(NH3)2(mu-4-pyha)M(mu-4-pyha)].SO4.xH2O}n respectively. The crystal and molecular structure of one of these, {cis-[Pt(NH3)2(mu-3-pyha)Cu(mu-3-pyha)]SO4.8H2O}n 3a, has been determined and was found to be a novel heterobimetallic wave-like coordination polymer, the structure of which contains interlinked pyridinehydroxamate-bridged repeating units of Pt(II) and Cu(II) ions in slightly distorted square-planar N4 and O4 coordination environments respectively and extensive hydrogen-bonding through the Pt ammines and the deprotonated hydroxamate O and via the O of the SO4(2-) counterions and the H(N) of the hydroxamate moiety. Spectrophotometric and speciation studies on the other heterobimetallic systems confirm that very similar species are being formed in solution and based on elemental analysis and spectroscopic results analogous complexes are formed in the solid-state. In this paper, we report the first examples of coordination polymers incorporating both Pt(II)/Cu(II), Pt(II)/Ni(II) and Pt(II)/Zn(II) and containing pyridinehydroxamic acids as bridging scaffolds.     

Adsorption at the liquid/liquid interface in mixed systems with hydrophobic extractants and modifiers 1. Study of equilibrium interfacial tension at the hydrocarbon/water interface in binary mixed systems

Equilibrium interfacial tension at the liquid/liquid interfaces for two chelating metal ion extractants, 2-hydroxy-5-nonylacetophenone oxime (HNAF) and 1-phenyldecane-1,3-dion (beta-diketone), two solvating extractants, trioctylphosphine oxide (TOPO) and tributyl phosphate (TBP), and a modifier, decanol, were obtained with a drop volume tensiometer. Moreover, four equimolar binary mixtures of extractant/extractant and extractant/modifier type were considered. The composition of the mixed adsorbed monolayer and the molecular interaction parameters beta were determined by the Rosen equation. It was found that in all the studied systems coadsorption exists; however, synergism in the reduction of interfacial tension was not observed. The obtained results indicate that in the case of three mixtures considered the composition of a mixed monolayer at the hydrocarbon/water interface was quite different from that in the bulk organic phase. Only for the TOPO/beta-diketone mixture were the compositions at the interface and in the bulk organic phase similar. The obtained results indicate that it is impossible to predict the composition of a mixed monolayer by taking into account the interfacial activity of individual components of the mixture. In some cases the compound shows lower interfacial activity (smaller efficiency and effectiveness of adsorption) and occupies a dominant position at the interface, regardless of the type of hydrocarbon used as the organic diluent.     

über 4-Alkylamino-bzw. 4-Arylamino-5,6-dihydro-2(1H)-pyridinthione

Heating 1-alkyl- or 1-aryldihydro-6-methyl-2(1H)-pyrimidinethiones5, 6 in an inert medium causes rearrangement to 4-alkylamino-(4-arylamino-)-5,6-dihydro-2(1H)-pyridinethiones11, 12, probably via the methylene form29, by thermal heterolysis of the N₁/C₂ bond and exchange of the alkylamino (arylamino) group 1 through the carbon atom of the methylene group 6. The aminodihydropyridinethiones11, which can be regarded as cyclic derivatives of 3-aminothiocrotonamide, react with bistrichlorophenylmalonate under diacylation, and with formaldehyde and primary amines to yield aminodialkylation products of the enamine system, tetrahydro-4-hydroxy-7,7-dimethyl-5-thioxopyrido[4,3-b]pyridine-2(1H)-ones13, 14 and hexahydro-7,7-dimethylpyrido[4,3-d]pyrimidine-5(6H)-thiones18, 19, 21 respectively. H₂O₂ converts11 to the corresponding 4-aminodihydro-2(1H)-pyridones22, which can be reconverted into11 with P₄S₁₀.11 reacts with alkyl halides to 2-alkylthiodihydropyridines23, 24, 25. The mechanism of the methylpyrimidine-pyridine rearrangement is discussed.     

Autoassociates and tautomerism of 2-oxo-5-halogenopyrimidines: theoretical and experimental investigations

Theoretical calculations (on a semi-empirical level) of energy and geometry of the autoassociates of two tautomeric forms of 2-oxo-5X-pyrimidines (X = H, Cl, Br) are presented. On the basis of the calculated energies of autoassociates it is possible to explain the enol—keto tautomeric transition between the gas phase and condensed phases. We propose a double-proton transfer reaction as a possible mechanism for the tautomeric transition.

Infrared absorption spectra of 2-oxo-5X-pyrimidines in the v(NH …) and v(C=O) regions in solid phases and in low-temperature argon matrices are also presented and discussed. Comparison of IR spectra and results of the theoretical calculations with known crystallographic structures of 2-oxo-5X-pyrimidines (X = H, F, Cl) lead to the conclusion that the crystal structure of the 5-bromo derivative should be similar to that of the 5-chloro derivative.     

15N-NMR study of activated enamines. Structural dependence of δ (15N) and nJ(N,H) in primary,secondary and tertiary enamino-ketones,esters and amides

The pulse sequence INEPT was used to obtain proton-coupled ¹⁵N-NMR spectra in natural isotope abundance for enamines substituted in 2-position with electron-with-drawing groups. The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N-alkyl substitution, double-bond configuration, H-bonding, N-lone-pair delocalization within the conjugated system, and steric effects. It is concluded that ¹⁵N chemical shifts are a sensitive probe for local structural modifications at the N-atom and conformational changes in a remote part of a conjugated molecule, while one-bond N,H-coupling essentially reflects N-hybridization and subtle local geometric distortions. Stereospecific three-bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)-isomers in all investigated compounds, whereas two-bond coupling to olefinic protons (²J(N,H) = 0.5 to 5 Hz) is observed in (E)-isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the C? N bond.