Poly(phenylenediamine) Dispersions

The formation and properties of poly(phenylenediamine) colloidal dispersions were investigated. Oxidative dispersion polymerization of 1,3-phenylenediamine dihydrochloride stabilized with poly(N-vinylpyrrolidone) was taken as a reference experiment. Conductivity, temperature, and acidity of the reaction mixture were recorded during the polymerization. Oxidations of all three phenylenediamine bases, of corresponding dihydrochlorides, and of dihydrochlorides in excess acid are compared. The effect of the nature of steric stabilizer on the course of polymerization was found to be marginal. Dispersion polymerization was observed to proceed faster than the precipitation one. Dynamic light scattering was used to assess particle sizes in poly(phenylenediamine) dispersions. The results are discussed in relation to an analogous polymerization of aniline leading to polyaniline dispersions. Copyright 2001 Academic Press.     

(1)H NMR and small-angle neutron scattering investigation of the structure and solubilization behavior of three-layer nanoparticles

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.     

Chemie der Seltenerdmetalle, 7. Mitt.: Tartratkomplexe des dreiwertigen Cers

Zusammenfassung Es wurde die systematische Untersuchung des Systems im sauren Bereich durchgeführt. Es wurden Stoffe der Zusammensetzung Ce₂(H₂ T)₃·6H₂O, Ce₂(H₂ T)₃·2H₂O, H[Ce(H₂ T)₂]·2H₂O isoliert^***. Diese wurden röntgenographisch untersucht und es wurde ihre thermische Analyse durchgeführt. Auf Grund von pH-Messungen wurden die Dissoziationskonstanten bestimmt.

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The systems were investigated in the acidic range. The compounds Ce₂(H₂ T)₃·6 H₂O, Ce₂(H₂ T)₃·2 H₂O and H[Ce(H₂ T)₂]·2 H₂O^*** were isolated. X-ray powder diagrams were taken, and a thermal analysis performed. The dissociation constants were determined, based upon pH-measurements.

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Mit 2 Abbildungen

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6. Mitt.:F. Bezina, J. Rosický undR. Pastorek, Acta Univ. Palack., im Druck.     

Capillary zone electrophoretic studies of interactions of some quaternary isoquinoline alkaloids with DNA constituents and DNA

Capillary zone electrophoresis was applied for the investigation of interactions of some quaternary isoquinoline alkaloids, namely sanguinarine, chelerythrine, berberine, and jatrorrhizine, with DNA constituents and with DNA. None of these alkaloids attach covalently to nucleotides or to the whole DNA under physiological conditions. The interaction with DNA constituents is a noncovalent complexation based on weak intermolecular forces. Electrostatic attraction participates in the interaction but other types of intermolecular forces are involved as well. Cations were identified as the most probable interacting forms of the alkaloids. The interaction with compounds derived from purine was always stronger than those derived from pyrimidine. All alkaloids behaved analogously and similarly to ethidium bromide, the classic DNA intercalator. Stability constants K (in l.mol(-1)) for sanguinarine and chelerythrine in phosphate buffer of pH 7.4 (I(S) = 30 mM) ranged from tens to hundreds.     

Axisymmetric free surface seepage

Summary Seepage through porous media in most instances is not a two-dimensional flow phenomenon. One such situation which is investigated herein is the flow from a pond with a bottom formed by the rotation of a curve consisting of a small segment being horizontal and the remainder being an arbitrary convex shaped curve. The approach used to solve this free surface axisymmetric seepage problem is an alternating iteration scheme in conjunction with the Baiocchi transformation and method. The problem is split into two overlapping regions, one in which the free surface is treated and the other in which the singularity is treated. This approach does not require moving meshes and allows a very general prescribed shape for the pond boundary. The numerical approach to the reformulated seepage problem is presented along with several numerical results and comparisons. Also presented is a proof of uniqueness of the solution for such problems provided we make a certain smoothness assumption for the free surface.The alternating iteration scheme is proved to converge provided existence and certain smoothness for the iterates and for their free surfaces are assumed. The iterates involved are solutions of certain complementarity systems. The existence and regularity of these solutions is not investigated in this paper.     

A mathematical model of the logical structure of chemistry. A bridge between theoretical and experimental chemistry and a general tool for computer-assisted molecular design

Summary A mathematical model of the logical structure of chemistry is suggested. The model is based on the phenomenon of convertibility between chemical species which is expressed by the so-called convertibility function . In the center of the model there is the potential energy (hyper)surface, PES. A heuristic modification of the general convertibility function is presented. Several algorithms have been developed for an analysis of PES which is described by paths, and for heuristic obtaining of PES paths. The notion ofK-barrier of conformational PES is introduced as well as an algorithm for its computation.     

Thermal degradation of polyaniline films prepared in solutions of strong and weak acids and in water - FTIR and Raman spectroscopic studies

Polyaniline (PANI) films were prepared in situ on silicon windows during the oxidation of aniline with ammonium peroxydisulfate in aqueous solutions of strong (0.1 M sulfuric) or weak (0.4 M acetic) acid or without any acid. In solutions of sulfuric acid, a granular PANI is produced, in solutions of weak acids or without any acid, PANI nanotubes are obtained. The thermal stability and structural variation of the corresponding films produced on silicon windows during treatment at 80 °C for three months were studied by FTIR and Raman spectroscopies. The morphology of the films is preserved during the degradation but the molecular structure changes. The results indicate that the spectral changes correspond to deprotonation, oxidation and chemical crosslinking reactions. The films of PANI salts loose their protonating acid. PANI bases are more stable than the salt forms during thermal ageing. The films obtained in water or in the presence of acetic acid are more stable than those prepared in solutions of sulfuric acid. The protonated structure is more prone to crosslinking reactions than deprotonated one. The molecular structure corresponding to the nanotubular morphology, which contains the crosslinked phenazine- and oxazine-like groups, is more stable than the molecular structure of the granular morphology.     

Free flow and capillary isoelectric focusing of bacteria from the tomatoes plant tissues

The means of the preconcentration and preseparation of selected species or pathovars of bacteria directly from the plant tissue suspension by free flow isoelectric focusing are introduced here. After the focusing, the resulting fraction of microorganisms, native or dynamically modified by the non-ionogenic tenside on the basis of pyrenebutanoate, was separated by capillary isoelectric focusing and/or cultivated and positively identified by gas chromatographic analysis of fatty acid methyl esters. Simultaneously, capillary isoelectric focusing with UV and fluorometric detection was used for the rapid estimation of unknown isoelectric points of the examined plant pathogenic species of genus Clavibacter, Xanthomonas and Pseudomonas prior to the preconcentration and preseparation. The microorganisms were of different origin, native and/or dynamically modified by the non-ionogenic tenside.