NOPR Collection:

Do silylenes show ambiphilicity?:A theoretical study

1997-12-01T00:00:00Z

Title: Do silylenes show ambiphilicity?:A theoretical study Authors: Prasad, B V; Kaur, D; Uppal, P Abstract: Ab initio calculations show that silylenes can show lewis acidic behaviour. The complexation between silylenes and lewis bases proceeds without energy barrier. The resultant silylene-lewis base complexes show nucleophilicity. The larger the stabilization between silylene and lewis base, the larger is the nucleophilicity of the resultant complex. Silylenes can show nucleophilicity only after their electrophilicity gets satisfied. Page(s): 1013-1017

Dynamic instability and non-equilibrium patterns during the growth of E.coli

1997-12-01T00:00:00Z

Title: Dynamic instability and non-equilibrium patterns during the growth of E.coli Authors: Das, Ishwar; Kumar, Anuj; Singh, U K Abstract: The diffusion controlled growth morphology and kinetics of E.coli colonies under different experimental conditions, have been studied. Fractal dimension is calculated by box counting method and found to be 1.55 ± 0.03. A transition from Eden-like to smooth spreading colony patterns was observed. Influence of vitamins, H₂O₂, antibiotics and Bacillus subtillis on growth behaviour has been studied. Burst morphologies in E.coli and phthalic acid are observed similar to diffused growth in hepatocellular carcinoma and black sea fan. Vitamin C and vitamin B complex showed stimulatory effect to some extent while oxytetracyclin and H₂O₂ inhibited the growth of the microorganism. E coli and Bacillus subtilis, grow independently when cocultivated on the same plate. Page(s): 1018-1022

Electrochemistry and catalytic chemistry of ruthenium-substituted Keggin type heteropolytungstates in the presence of nitrite ion

1997-12-01T00:00:00Z

Title: Electrochemistry and catalytic chemistry of ruthenium-substituted Keggin type heteropolytungstates in the presence of nitrite ion Authors: Sun, Wenliang; Xie, Yan; Liu, Huizhang; Kong, Jilie; Jin, Songlin; Xie, Gaoyang; Deng, Jiaqi Abstract: The electrochemical behaviour of ruthenium-substituted Keggin type heteropolytungstates, [H₂ORu¹¹¹XW₁₁O₃₉]^n- (X=B, n=6; X=Si, Ge, n=S; X=P, n=4), have been investigated in acetonitrile and aqueous solutions. In acetonitrile solutions, these ruthenium- based heteropolyanions exhibit two-step one-electron reduction processes, just like their corresponding unsubstituted parent compounds. These redox waves are ascribed to the W(VI®V) processes of the heteropolytungstate framework. The slope of a plot of formal redox potentials against the ionic charge is evaluated. In acid buffer solutions (PH 2.0~6.0). all these anions exhibit one pair of reversible, one- electron redox peaks. This pair is assigned to the Ru(I1I) center. These ruthenium-substituted heteropolyanions are shown to be excellent catalysts for the electroreduction of nitrite ion. The unsubstituted parent and lacunary anions show no catalytic activity. The rate constants of the catalytic reaction at differen pH values are measured. For the case of [H₂ORu¹¹¹SiW ₁₁O₃₉)^5-, the maximum rate constant of the catalytic reaction is obtained at pH 3.0, K_obsd = 4.2 x10³ M^-1s^-1. The catalytic mechanism involves the rapid formation of a nitrosyl complex with the Ru(II) form of the catalyst, which seems to depend on the electron configuration of Ru(II) and the inorganic structure of the ruthenium-substituted polyoxotungstates. The dependence of the redox potentials of the Ru(III)/Ru(II) couple on the identity of the central heteroatoms is also explored. Page(s): 1023-1030

Physicochemical studies of the hexadecylpyridinium bromide micellar system in the presence of various concentrations of sodium bromide using a surfactant-selective electrode

1997-12-01T00:00:00Z

Title: Physicochemical studies of the hexadecylpyridinium bromide micellar system in the presence of various concentrations of sodium bromide using a surfactant-selective electrode Authors: Shamsipur, Mojtaba; Alizadeh, Naader; Gharibi, Hossein Abstract: A membrane electrode selective to hexadecylammonium bromide has been used to study the micellization of the surfactant in the presence of varying amounts of sodium bromide at 27°C. It is found that there is an inverse relationship between the amount of NaBr added and the critical micelle concentration and the degree of counter-ion dissociation of the system studied. The aggregation number of the micelles formed has been determined and found to increase with the concentration of NaBr added. Some evidence for the formation of dimer forms of the surfactant prior to the micelle formation is found at higher concentrations of the electrolyte. Page(s): 1031-1036