The role of hydroperoxides in photo-oxidative degradation of cis-1,4-polybutadiene

Hydroperoxides undergo various types of homolytic reactions on exposure to u.v. radiation. Free radicals formed from the photodecomposition of the hydroperoxide group (OOH) are oxy (HO.) and peroxy (HOO.) radicals which participate in further reactions. In cis-1,4-polybutadiene, they may initiate free radical oxidations. Cleavage of alkoxy (RO.) radicals and crosslinking of polymer radicals through polymer peroxides in the presence of air in solid film nearly balance. Most polymer radicals produced in the absence of oxygen undergo cross-linking but form peroxy radicals (POO.) in its presence. This paper presents results on the photodecomposition of tert-butyl hydroperoxide, cumyl hydroperoxide and 2,5-dimethyl-2,5-dihydroperoxyhexane in cis-1,4-polybutadiene in film and in solution.     

Efficiency of energy transfer from γ-irradiated ammonium halides in aqueous iodide and nitrate solutions

It is well known that ammonium halide (NH₄X) crystals, on -exposure, store energy in the form of primary and secondary radiolytic products. Such crystals on dissolution in aqueous iodide and nitrate solutions result in oxidation of iodide and reduction of nitrate, respectively. The yields of iodine and nitrite are determined by chemical methods under varying conditions of the amount, dose and particle size of the irradiated ammonium halide salts. The maximum values of the efficiency of energy transfer for oxidation and reduction processes for ammonium halide salts correspond to 40% and 10%, respectively. At low doses, an empirical relation proposed between the percent efficiency of energy transfer and the absorbed dose is valid. The concentrations of inherent oxidizing and reducing species initially present are 7.0×10¹⁸ and 1.0×10¹⁸ per mol of ammonium halide, respectively.     

Some new results on Unsymmetric Successive Overrelaxation method

Summary The Unsymmetric Successive Overrelaxation (USSOR) iterative method is applied to the solution of the system of linear equationsA x=b, whereA is annxn nonsingular matrix. We find the values of the relaxation parameters and for which the USSOR iterative method converges. Then we characterize those matrices which are equimodular toA and for which the USSOR iterative method converges.     

Photo-degradation and photo-stabilisation of the two-phase system poly(vinyl chloride)-polybutadiene

The photo-oxidative degradation of poly(vinyl chloride) (PVC)/polybutadiene (PB) blends has been studied. After uv irradiation, photo-grafting of the PVC and PB phases was observed. Photolysis of PVC accelerates cis-trans isomerisation of PB. Both phases, PVC and PB, are photo-degraded according to free radical oxidation mechanisms. The rates of these processes can be decreased by the addition of metal chelates, such as commercially produced Cyasorb uv light absorber 1084 (2,2′-thiobis(4-t-octylphenolato)-n-butylamine nickel(II)) and Cyasorb uv light absorber 2548 (cobalt dicyclohexyldithiophosphinate).     

Feature of catalysis on bimetallic alloys Zr with V,Mo, and Fe in the reaction of methanol oxidation

Catalytic behaviors of bimetallic catalysts-alloys of zirconium with vanadium, molybdenum, and iron was investigated in the oxidative dehydrogenation of methanol. The conditions for the formation of the catalyst’s active surface were revealed. The conversion of methanol into formaldehyde, dimethyl ether, and dimethoxymethane on bimetallic catalysts was studied. The characterization of catalysts was performed by XRD, XPS, and SEM. It was shown that the activity of samples increases after О₂ + Н₂ treatment and was associated with segregation of the active components of alloys (V, Mo) on the surface of catalysts and realization of their optimal oxidation state under catalysis conditions.     

Application of Lipopeptide Biosurfactant Isolated from a Halophile: Bacillus tequilensis CH for Inhibition of Biofilm

Biosurfactants are amphiphilic molecules having hydrophobic and hydrophilic moieties produced by various microorganisms. These molecules trigger the reduction of surface tension or interfacial tension in liquids. A biosurfactant-producing halophile was isolated from Lake Chilika, a brackish water lake of Odisha, India (19°41′39″N, 85°18′24″E). The halophile was identified as Bacillus tequilensis CH by biochemical tests and 16S rRNA gene sequencing and assigned accession no. KC851857 by GenBank. The biosurfactant produced by B. tequilensis CH was partially characterized as a lipopeptide using thin-layer chromatography, Fourier transform infrared spectroscopy, and nuclear magnetic resonance techniques. The minimum effective concentration of a biosurfactant for inhibition of pathogenic biofilm (Escherichia coli and Streptococcus mutans) on hydrophilic and hydrophobic surfaces was found to be 50 μg ml^?1. This finding has potential for a variety of applications.     

Green synthesis of silver nanoparticle by <Emphasis Type="Italic">Penicillium purpurogenum</Emphasis> NPMF: the process and optimization

An eco-friendly microbial method for synthesis of silver colloid solution with antimicrobial activity is developed using a fungal strain of Penicillium purpurogenum NPMF. It is observed that increase in concentration of AgNO₃ increases the formation of silver nanoparticle. At 5 mM concentration highly populated polydispersed nanoparticles form. Furthermore, change in pH of the reaction mixture leads to change in shape and size of silver nanoparticles. At lower pH two peaks are observed in the absorption spectra showing polydispersity of nanoparticles. However, highly monodispersed spherical nanoparticles of 8–10 nm size form with 1 mM AgNO₃ concentration at pH 8. Antimicrobial activity of nanoparticles is demonstrated against pathogenic gram negative bacteria like Escherichia coli and Pseudomonas aeruginosa, and gram positive bacteria like Staphylococcus aureus. The antimicrobial activity of silver nanoparticles obtained at different initial pH show strong dependence on the surface area and shape of the nanoparticles.     

On the convergence of the symmetric successive overrelaxation method

The symmetric successive overrelaxation (SSOR) iterative method is applied to the solution of the system of linear equations $\text{A}\text{x}\text{=}\text{b}$, where A is an n×n nonsingular matrix. We give bounds for the spectral radius of the SSOR iterative matrix when A is an Hermitian positive definite matrix, and when A is a nonsingular M-matrix. Then, we discuss the convergence of the SSOR iterative method associated with a new splitting of the matrix A which extends the results of Varga and Buoni [1].     

Flowability and Mechanical and Thermal Properties of Nylon 6/Ethylene bis-Stearamide/Carboxylic Silica Composites

Nylon 6 (PA 6)/ethylene bis-stearamide (EBS)/SiO₂- carboxylic acid-functionalized silica nanoparticles (COOH) composites were prepared by in-situ polymerization of caprolactam. SiO₂-COOH was used to enhance the compatibility between SiO₂ and PA 6 matrix. For comparison, pure PA 6 and PA 6/EBS composites were also prepared via the same method. The PA 6/EBS/SiO₂-COOH composites with low content of EBS and SiO₂-COOH had greater melt-flow index (MFI) (the value of MFI increased by 50%–80%) than the pure PA 6. The results of mechanical properties showed almost no decrease in the tensile strength of PA 6/EBS/SiO₂-COOH composites, with the bending strength decreasing by 17%–21%. However, the Izod impact strength of the PA 6/EBS/SiO₂-COOH composites was greatly improved compared with pure PA 6, which indicated that the toughness of PA 6/EBS/SiO₂-COOH had been greatly improved. The morphology of Izod impacted fractured surfaces of PA 6/EBS/SiO₂-COOH was observed by scanning electron microscopy. The results revealed that the PA 6/EBS/SiO₂-COOH composites presented a typical ductile fracture behavior with large amounts of long and large strip-like cracks. When the content of SiO₂-COOH was 0.2 wt%, the SiO₂-COOH particles were uniformly dispersed over the entire body of the PA 6 matrix. The results from differential scanning calorimetry indicated that the melting point (T_m), degree of crystallinity (X_c), and crystallization temperatures (T_c) of PA 6/EBS/SiO₂-COOH composites were lower than the pure PA 6.     

Cholesterol and phospholipids in membranes: The hydrogen bonding problem

Cholesterol and phospholipids are major components of biological membranes. The role of cholesterol in membranes is not metabolic and is known to be a regulator of membrane fluidity which in turn regulates various biological phenomena. We have studied the nature of cholesterol and phospholipid interaction in artificial membranes using ¹³C NMR spectroscopy. This involved preparation of phospholipids specifically labeled with ¹³C in the ester carbonyl group. Though the chemical shift data did not provide very useful information the T₁ and T₂ measurements indicated that previously proposed H bonding between the ester carbonyl group and hydroxyl group of cholesterol seems unprobable.