Preparation,Characterisation, and Structure of N-Methylated Derivatives of 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol: Polyalcohols with Unusual Acidity

1,3,5-Trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (TDCI) and 1,3,5-trideoxy-1,3,5-tris(trimethylammonio)-cis-inositol (TTCI) were prepared by methylation of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (TACI). The ability of TDCI to form both intermolecular and intramolecular H-bonds, as demonstrated by X-ray diffraction, is probably responsible for the good solubility of TDCI in almost every common solvent. TTCI was found to be a polyol of unusual high acidity (pK₁ = 8.14 ± 0.02, pK₂ = 13.0 ± 0.2). This phenomenon could be explained by electrostatic interactions between the charged substituents of the cyclohexane residue.     

Über einen neuen aromatischen Kohlenwasserstoff C24H18 aus Erdölen

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Kinetik sehr schneller Methylquecksilber-Übertragungsreaktionen zwischen pyridinhaltigen Chelatliganden und dem Hydroxid-Ion

Kinetics of very fast Methylmercury-Transfer Reactions between Pyridine-containing Chelating Ligands and the Hydroxide Ion The kinetics of the reactions between methylmercury hydroxide and bipyridine, terpyridine, phenanthroline and pyridine-2-azo-4-dimethylaniline have been studied by means of the temperature jump relaxation method. These bi- and tridentate ligands form methylmercury chelates. Their formation is faster than the formation of the pyridine complex. The chelate complexes show an unusually high reactivity. Their reaction rates with hydroxide ions reach almost the diffusion controlled limit.     

Kinetics of Extremely Fast Ligand Exchange Reactions with Methylmercury(II)-complexes of 1-Methylpyridine-2-thione and 1-Methyl-quinaldine-4-thione: Rate-Equilibria Correlations

Methylmercury(II) transfer from two heterocyclic thiones to a wide variety of other ligands and the reverse reaction have been investigated by the temperature-jump method. The reactions are almost diffusion controlled, even when the free energy difference is negligible. The only exceptions are reactions to and from hydroxide. They are about hundred times slower than those with other ligands of comparable stability at zero free energy difference. This is in agreement with the behaviour of hydroxide in other methylmercury(II) exchange reactions. They follow an associative reaction mechanism. An empirical correlation of rate-and equilibrium-constants for atom transfer reactions is proposed. This equation shows some similarities to that of the Marcus type for atom transfer. However, the proposed equation not only describes reactions governed by an associative mechanism, but also those of dissociative type and cases between the two extremes.     

Einwirkung von Chlorschwefel auf Benzol

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Cobalt iron-oxide nanoparticle modified poly(methyl methacrylate) nanodielectrics

In this paper, we report the dielectric properties of composite systems (nanodielectrics) made of small amounts of mono dispersed magnetic nanoparticles embedded in a polymer matrix. It is observed from the transmission electron microscope images that the matrix polymeric material is confined in approximately 100 nm size cages between particle clusters. The particle clusters are composed of separated spherical particles which comprise unconnected networks in the matrix. The dielectric relaxation and breakdown characteristics of the matrix polymeric material are altered with the addition of nanometer size cobalt iron-oxide particles. The dielectric breakdown measurements performed at 77 K showed that these nanodielectrics are potentially useful as an electrical insulation material for cryogenic high voltage applications. Finally, structural and dielectric properties of nanocomposite dielectrics are discussed to present plausible reasons for the observed low effective dielectric permittivity values in the present and similar nanodielectric systems. It is concluded that polymeric nanoparticle composites would have low dielectric permittivity regardless of the permittivity of nanoparticles are when the particles are coordinated with a low dielectric permittivity surfactant.     

Colloidal synthesis of BaF2 nanoparticles and their application as fillers in polymer nanocomposites

Nanoparticles of pure and Eu-doped BaF₂ have been prepared through sol-gel colloidal synthesis. In addition, BaF₂-filled PMMA polymer nanocomposites were fabricated and dielectric properties were measured. The as-synthesized pure and Eu-doped BaF₂ nanoparticles were analyzed by both X-ray diffraction and transmission electron microscopy and consisted of crystalline BaF₂ particles with an average diameter of 13.6 nm with a standard deviation of about ±2.4 nm. The photoluminescence properties of the pure and Eu-doped (2%, 4% and 8%) nanoparticles showed characteristic emission of Eu³⁺ (⁵D₀→⁷F _J (J=1–4) transitions). We also measured significantly enhanced dielectric breakdown strength of up to 30% for BaF₂ nanocomposites over the unfilled PMMA polymer. This study thus offers some promise of sol-gel synthesis of nanocomposite dielectrics with great potential for use as electrical insulation materials in cryogenic high-voltage applications.