Reaktive Polymere. II. Die Herstellung von Metallchelaten vernetzter Polymerer

The reaction of bivalent ions (Cu, Co, Zn, Ni) with ethylene diamine bounded to homogeneous crosslinked terpolymer glycidyl methacrylate-styrene-divinylbenzene or macroporous copolymer glycidyl methacrylate-ethyleneglycole dimethacrylate has been studied. The capacity of polymer sorbent, exchange ability and the kinetic of the reaction has been studied.     

The putative Saginaw impact structure,Michigan, Lake Huron,in the light of gravity aspects derived from recent EIGEN 6C4 gravity field model

The hypothetical impact structure in the Saginaw Bay (Michigan, USA, Lake Huron) has been tested by the gravity data derived from the recent gravity field model EIGEN 6C4 (expanded to degree and order 2190, with ground resolution of ~9?km). The following gravity field aspects were used: the gravity disturbances/anomalies, second derivatives of the disturbing potential (Marussi tensor), two of three gravity invariants, their specific ratio (known as 2D factor), the strike angles, and the virtual deformations. These gravity aspects are sensitive in various ways to the underground density contrasts. For the Saginaw Bay area, we confirm that we do not see any typical impact crater in terms of gravity disturbance or the radial second order derivative, possibly because of the thick layer of the ice located at the place and time of the impact. But the “combed” strike angles (one type of the gravity aspects we use) disclose a trace of high pressure to the SE/S/SW of the Bay and may be due to an impacting body. Thus, we provide circumstantial evidence of the Younger Dryas impact hypothesis.     

Analysis of the reaction mechanism and substrate specificity of haloalkane dehalogenases by sequential and structural comparisons

Haloalkane dehalogenases catalyse environmentally importantdehalogenation reactions. These microbial enzymes representobjects of interest for protein engineering studies, attemptingto improve their catalytic efficiency or broaden their substratespecificity towards environmental pollutants. This paper presentsthe results of a comparative study of haloalkane dehalogenasesoriginating from different organisms. Protein sequences andthe models of tertiary structures of haloalkane dehalogenaseswere compared to investigate the protein fold, reaction mechanismand substrate specificity of these enzymes. Haloalkane dehalogenasescontain the structural motifs of /ß-hydrolases and epoxidaseswithin their sequences. They contain a catalytic triad withtwo different topological arrangements. The presence of a structurallyconserved oxyanion hole suggests the two-step reaction mechanismpreviously described for haloalkane dehalogenase from Xanthobacterautotrophicus GJ10. The differences in substrate specificityof haloalkane dehalogenases originating from different speciesmight be related to the size and geometry of an active siteand its entrance and the efficiency of the transition stateand halide ion stabilization by active site residues. Structurallyconserved motifs identified within the sequences can be usedfor the design of specific primers for the experimental screeningof haloalkane dehalogenases. Those amino acids which were predictedto be functionally important represent possible targets forfuture site-directed mutagenesis experiments.     

Reactant partitioning in free-radical heterophase polymerization: The case of inverse microemulsion polymerization of acrylamide

Conversion curves have been determined at 60°C for the polymerization of acrylamide in percolating inverse microemulsions. Ammonium peroxo-disulphate (APS) and dibenzoyl peroxide (DBP) were used as initiators of free-radical polymerization in the presence or absence of potassium nitrosodisulphonate (Fremy's salt, FS). The percolation decreases the rate of polymerization of acrylamide initiated by APS. The polymerization is inhibited by FS. After an inhibition period, retardation of acrylamide polymerization is more pronounced in non-percolating microemulsions. No inhibition periods were observed for DBP-initiated polymerization of acrylamide. The percolation shortens the time interval of the ‘slow’ polymerization of acrylamide, but the rates of rapid acrylamide polymerization above 10% conversion are the same for percolating and for non-percolating inverse microemulsions. The polymer particle diameter is a function of acrylamide/water weight ratio and of [water]/[AOT] (AOT: bis(2-ethylhexyl)-sulphosuccinate sodium salt) molar ratio. No effect of the initiator's nature either in the presence or in the absence of FS was found. The results are interpreted on the basis of initiator and/or nitroxide radical partitioning between oil and water phases of the inverse microemulsion, and are discussed with respect to the mechanism of acrylamide polymerization and polymer particle formation proposed for non-percolating inverse microemulsions.     

Poly(methyl methacrylate) and polyacrylonitrile dispersions stabilized by gelatin

Methyl methacrylate was polymerized in an aqueous medium in the presence of gelatin using potassium persulfate as initiator. The dispersion mode of polymerization, when the monomer is completely miscible with water, was investigated and compared with an emulsion process, which proceeds at higher monomer concentration. Spherical and relatively uniform polymer particles were formed. Macroscopic precipitation of polymer is prevented by combination of the steric stabilization by grafted gelatin and of repulsive electrostatic interactions from the initiator residues attached to the particle surface. Static and dynamic light scattering have been used to determine the molar mass (molar mass of the whole dispersion particle, M_wD ～ 10⁸-10⁹ g mol^?1) and hydrodynamic radius (R_hD ～ 50-120 nm) of the particles. The number of particles per unit volume does not depend on overall monomer concentration, and it is higher, and therefore the particle size is smaller, than that observed for the soapless emulsion polymerization. The addition of gelatin may be thus used to modify the particle size. Acrylonitrile dispersions were prepared under similar conditions. Unlike methyl methacrylate, this monomer does not swell the polymer particles. While poly(methyl methacrylate) particles are spherical and relatively uniform, the polyacrylonitrile dispersions consist of polydisperse aggregates of tiny polymer particles.     

Influence of oxygen partial pressure and substrate temperature during vapour deposition on the structural properties of CdSe films

CdSe films prepared in vacuum by sublimation from the compound at oxygen partial pressures in the residual atmosphere from 2.8 × 10^?5 to 3.2 × 10^?4 Torr and at substrate temperatures of 295 and 523 K were subjected to X-ray structural analysis. The results obtained are analysed and discussed in terms of some structures different from those of CdSe, e.g. CdSeO₃ and CdSeO₃.SeO₂.     

Aldehyde functionalization of styrene polymers

Summary Two methods of the introduction of aldehyde group into polystyrene skeleton are described.     

Czech results at criticality dosimetry intercomparison 2002

Two criticality dosimetry systems were tested by Czech participants during the intercomparison held in Valduc, France, June 2002. The first consisted of the thermoluminescent detectors (TLDs) (Al-P glasses) and Si-diodes as passive neutron dosemeters. Second, it was studied to what extent the individual dosemeters used in the Czech routine personal dosimetry service can give a reliable estimation of criticality accident exposure. It was found that the first system furnishes quite reliable estimation of accidental doses. For routine individual dosimetry system, no important problems were encountered in the case of photon dosemeters (TLDs, film badge). For etched track detectors in contact with the 232Th or 235U-Al alloy, the track density saturation for the spark counting method limits the upper dose at approximately 1 Gy for neutrons with the energy >1 MeV.     

Double O,C,O-chelated diorganotin(IV) cation

The synthesis of double O,C,O-chelated diorganotin(IV) compound L₂SnBr₂ (1), where L is 2,6-(MeOCH₂)₂C₆H₃^?, the precursor for the synthesis of Sn ← O intramolecularly coordinated organotin(IV) cations is reported. Treatment of compound 1 with SnBr₄ yielded the double O,C,O-chelated diorganotin(IV) ionic pair [L₂SnBr]⁺ [SnBr₅·THF]^? (2). Both compounds 1 and 2 were characterized by ¹H, ¹³C, ¹¹⁹Sn NMR and molecular structure of compound 2 was established by X-ray diffraction.     

The carbonization of colloidal polyaniline nanoparticles to nitrogen‐containing carbon analogues

The carbonization of nanostructures afforded by conducting polymers represents a new route to the preparation of functional nanostructured carbons. The exposure of colloidal polyaniline particles stabilized with poly(N‐vinylpyrrolidone) or silica nanoparticles at 650 °C in inert atmosphere led, in both cases, to nitrogen‐containing carbonaceous materials with specific surface areas of 200 and 205 m² g^?1, respectively, and conductivities of 8.3 × 10^?7 and 1.9 × 10^?10 S cm^?1, respectively. The latter material contained 77 wt% of silica. The original particulate nanostructure of the samples was preserved after carbonization. The carbon‐to‐nitrogen atomic ratio was 7.2 and 7.9; the nitrogen content in the carbonized polyaniline–poly(N‐vinylpyrrolidone) particles was 10.8 wt%. Thermogravimetric analysis in air revealed their stability to be up to 500 °C. This is comparable with commercial multi‐wall carbon nanotubes, which have similar areas of application. The nitrogen‐containing carbons are potentially useful as supports for catalysts and in applications where carbon of higher hydrophilicity would be of benefit. Copyright © 2010 Society of Chemical Industry