Development of zirconium and potassium perchlorate igniter for AP/HTPB composite propellant base bleed grain

Journal of Thermal Analysis and Calorimetry - For effective and reliable ignition of ammonium perchlorate and hydroxyl-terminated polybutadiene (AP/HTPB) solid composite propellant base bleed (BB)...     

Effect of ring substitution on synthesis of benzimidazolium salts and their silver(I) complexes: characterization,electrochemical studies and evaluation of anticancer potential

Transition Metal Chemistry - A series of bidendate 5,6-dimethyl benzimidazolium-based N-heterocyclic carbene (NHC) proligands and their silver complexes were synthesized. The synthetic approaches...     

Preparation of cadmium selenide-polyolefin composites from functional phosphine oxides and ruthenium-based metathesis

Cadmium selenide nanoparticles, prepared by known methods, were stabilized with functional phosphine oxide 1, then used to support the polymerization of cyclic olefins radially outward from the surface by ruthenium-catalyzed ring-opening metathesis polymerization (ROMP). The conversion of compound 1 into the new metathesis catalyst 3 by carbene exchange and the subsequent polymerization of cyclic olefins were observed spectroscopically by (1)H NMR to afford for example CdSe-polycyclooctene composite 6. Transmission electron micrographs on thin films of these composites showed good nanoparticle dispersion. This is in stark contrast to the substantial nanoparticle aggregation observed when similar polymerizations were performed in the presence of conventional TOPO-covered nanoparticles. The methods reported here to prepare composite product 6 are applicable to other cyclic olefins, and suggest that this chemistry will be useful for incorporating CdSe nanoparticles into a wide variety of polymer matrices.     

Ion exchangers as catalysts. II. Catalytic decomposition of hydrogen peroxide with resin-ethylenediamine-copper(II) complex ions

Summary The slow decomposition of H₂O₂ in the presence of Dowex-50 W resin in the form of an ethylenediaminecopper(II) complex ion in water is accompanied by an induction period. The reaction is first order with respect to [H₂O₂] and the rate constant (perg of dry resin) was deduced. Autocatalytic behaviour was found for the H₂O₂ decomposition with 2% crosslinked divinylbenzene. The induction period disappeared and the reaction rate increased when the decomposition was carried out with a resin in the form of a peroxo-copper complex, which proves that the formation of an intermediate (active species) retards the reaction rate. The precursor of the active species, formed during the induction period, was not the amine-copper(II) complex ion but a product of the latter with H₂O₂. It proved impossible to carry out the decomposition in acid or buffer solutions, in which the resin is regenerated.     

Nanoparticle assembly at fluid interfaces: structure and dynamics

The self-assembly of nanoparticles at fluid interfaces, driven by the reduction in interfacial energy, was investigated. With spherical, tri-n-octyl-phosphine-oxide covered cadmium selenide (CdSe) nanoparticles (1-8 nm), thermal fluctuations compete with the interfacial segregation giving rise to a size-dependent self-assembly of the particles. The structure of the nanoparticle assembly was studied using electron microscopy, atomic force microscopy, and X-ray scattering in situ, which indicate that the particles form a densely packed monolayer. The energetics of the adsorption of nanoparticles onto the interface was revealed by time-dependent fluorescence studies on a mixture of two different sized nanoparticles at the interface. The dynamics of the nanoparticles at the fluid interface, probed using fluorescence photobleaching methods, suggests a liquid-like behavior. The results have implications in the design of hierarchical self-assemblies of nanoparticles for the one-step fabrication of devices on multiple length scales.     

Theoretical studies on tautomerism of imidazole-2-selenone

The tautomerism of all possible forms of imidazole selenone (ISe1–ISe6), induced by proton transfer was studied theoretically in different environments including gas phase, continuum solvent, and microhydrated environment with one explicit water molecule. The calculations were performed at the MP2 and CAM-B3LYP levels of theory, separately. It was found that the imidazole selenone, in the form of ISe3, is the most stable isomer in both gas phase and solvent. The activation energy for conversion of ISe3 to imidazole selenol (ISe6), as the second stable form, is 41.72 and 43.0 kcal/mol in the gas phase and water, respectively. The infrared spectral frequencies as well as the vibrational frequency shifts were reported and assigned to their corresponding vibrational modes. In addition, the variation of dipole moments and charges on the atoms with change of solvent was studied. The energies of HOMO, LUMO, and HOMO–LUMO gap were calculated in both gas phase and solvent. Specific solvent effects with addition of water molecule near the electrophilic centers of tautomers and the transition states of proton transfer, assisted by water molecule, were investigated. It was found that the water molecule can form different hydrogen bonds with the molecule. Aggregation of the isomers with water molecule does not change the order of stability of isomers, but proton transfer reaction assisted by a water molecule needs less energy than when the proton shifts through the intramolecular process.     

A green and efficient procedure for one-pot synthesis of xanthenes and acridines using silica boron–sulfuric acid nanoparticles (SBSANs) as a solid Lewis-protic acid

Silica boron–sulfuric acid nanoparticles (SBSANs) as a solid Lewis-protic acid have been found to be an efficient heterogeneous catalyst in the synthesis of xanthene and acridine derivatives. The SBSAN-catalyzed reaction between carbonyl compound (aldehyde/ketone/ethyl orthoformate) and 5,5-dimethyl-1,3-cyclohexanedione (dimedone) for synthesis of xanthene derivatives is performed under mild conditions with the excellent isolated yield. Also, we can apply a broad scope of carbonyl compounds and amines for efficient synthesis of various acridine derivatives in the presence of SBSAN catalyst. In these multicomponent approaches the SBSAN catalyst can be reused for several times without any treatment in its catalytic activity.     

Kinetics of heterogeneous decomposition of hydrogen peroxide

The kinetics of the decomposition of hydrogen peroxide was studied in aqueous medium in the temperature range 25–40°C in the presence of Wofatit KPS-resin in the form of Cu(II)-ammine complex ions. The rate constant was deduced at various degrees of resin cross-linkage and different concentrations of hydrogen peroxide. The order of the decomposition reaction varied from first order to half order, i.e., the order of the reaction decreased with increasing the concentration of H₂O₂. The decomposition process was found to be a catalytic reaction which was controlled by the chemical reaction of H₂O₂ molecules with the active species inside the resin particles. The mechanism of the reaction can be summarized by the equation in which the subsequent reactions of the probable active complex are discussed.