Thermal and Surface Analytical Study of Flame Retarded Polyolefins I. Interaction of Additives and Structure Formation

Pentaerythritol may react with tetraethoxy-silane and ammonium-polyphosphate in flame retarded polyolefins and an interfacial layer can be formed around the ammonium-polyphosphate particles. It is advantageous to study such systems using methods of thermal and surface analysis together. This revised version was published online in August 2006 with corrections to the Cover Date.     

Solution-state NMR spectroscopy of famotidine revisited: spectral assignment, protonation sites, and their structural consequences

Multinuclear one (1D-) and two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopic investigations of famotidine, the most potent and widely used histamine H₂-receptor antagonist, were carried out in dimethyl sulfoxide-d₆ (DMSO-d₆) and water. Previous NMR assignments were either incomplete or full assignment was based only on 1D spectra and quantum-chemical calculations. Our work revealed several literature misassignments of the ¹H, ¹³C, and ¹⁵N NMR signals and clarified the acid–base properties of the compound at the site-specific level. The erroneous assignment of Baranska et al. (J. Mol. Struct. 2001, 563) probably originates from an incorrect hypothesis about the major conformation of famotidine in DMSO-d₆. A folded conformation similar to that observed in the solid-state was also assumed in solution, stabilized by an intramolecular hydrogen bond involving one of the sulphonamide NH₂ protons and the thiazole nitrogen. Our detailed 1D and 2D NMR experiments enabled complete ab initio ¹H, ¹³C, and ¹⁵N assignments and disproved the existence of the sulphonamide NH hydrogen bond in the major conformer. Rather, the molecule is predominantly present in an extended conformation in DMSO-d₆. The aqueous acid–base properties of famotidine were studied by 1D ¹H- and 2D ¹H/¹³C heteronuclear multiple-bond correlation (HMBC) NMR-pH titrations. The experiments identified its basic centers including a new protonation step at highly acidic conditions, which was also confirmed by titrations and quantum-chemical calculations on a model compound, 2-[4-(sulfanylmethyl)-1,3-thiazol-2-yl]guanidine. Famotidine is now proved to have four protonation steps in the following basicity order: the sulfonamidate anion protonates at pH = 11.3, followed by the protonation of the guanidine group at pH = 6.8, whereas, in strong acidic solutions, two overlapping protonation processes occur involving the amidine and thiazole moieties.     

Displacement processes on hydrophilic/hydrophobic surfaces in 1-propanol-water mixtures

Selective adsorption of 1-propanol-water mixtures was investigated on adsorbents of various surface character. The enthalpy of displacement of 1-propanol by water was studied on graphitized PRINTEX-80, K-60 silicagel, and n-alkylammonium vermiculites. The free enthalpy and entropy isotherms of displacement were derived. The adsorption between the silicate layers of hydrophobic vermiculites was followed by x-ray measurements, and thermodynamic functions were calculated for the structural changes in the adsorption layers. Formation of alcohol-water clusters on the surfaces plays an important role.     

Studies of thermally stimulated current in polypropylene/calcium carbonate/surfactant systems

Thermally stimulated polarization (TSP) and depolarization (TSD) experiments have been performed with two grades of polypropylene and some respective CaCO₃-filled composites containing small amounts of nonionic surfactant (0–2 wt%). The effects of electrode blocking, electrode materials on the thermally stimulated currents, and reproducibility of the measurements have been studied. The effect of water vapor adsorbed from the ambient air on the AC dielectric properties and on the thermally stimulated polarization behavior has been determined.The addition of either CaCO₃ or surfactant to PP decreases the intensity of the _c depolarization current peak in the pre-melting region, while the presence of both components increases the current. Partial discharges are present in poly propylene/CaCO₃ composites under high voltages if neither water vapor nor a coherent surfactant layer is present at the matrix/filler interface.A short literature survey is presented on the TSC studies of polyolefins and their composites, and various mechanisms responsible for the observed changes are discussed, including interfacial polarization, trap redistribution through nucleation, and oriented adsorption.     

Vergleichende Untersuchungen zur katalytischen Aktivität von Nickel und kristallinen Nickelboriden sowie RANEY-Nickel und borhaltigem RANEY-Nickel: Hydrierungs- und Dehydrierungsreaktionen,elektrochemische Methanoloxydation

The catalytic activation of the decomposition of gaseous formic acid with nickel powder and crystalline nickel borides is compared. Only after treatment with NH₃-solution the activity of the nickel borides has the same order as that of nickel powder. Ni₃B is the best of the catalysts used. The crystalline nickel borides cannot catalyze the anodic oxydation of methanol in alcaline solution at 80°C. — Nickel catalysts containing Boron can be prepared by the RANEY method from nickel boride and aluminum. These catalysts have the same activity as normal RANEY nickel with respect to the hydrogenation of the C?C? bond in crotonic acid; they are more active with respect to the C?O? bond of acetone. Methanol can be oxydised fastly in alcaline solution at 80°C on electrodes containing RANEY nickel. RANEY nickel containing boron is still better.