Conductance in homomorphous solvents: Tetrabutylammonium salts and alkali picrates in butyrolactone-sulfolane mixtures

Conductance measurements are reported for LiPi, NaPi, KPi, RbPi, CsPi, Bu₄NPi, Bu₄NBr, Bu₄NClO₄, Bu₄NNO₃, and Bu₄NBBu₄ at 25°C in -butyrolactone-sulfolane mixtures. In these mixtures of solvents that are practically homomorphous, isodielectic and with comparable dipole moments, the ion pair association and ionic mobilities of large ions conform to the expectations of the primitive model. Electrolytes containing lithium or sodium ions show anomalies indicating that other factors besides shape, dipole moment, and polarizability of the solvent molecules are involved in the association and transport processes of these ions.     

Effect of dose rate of gamma irradiation on biochemical quality and browning of mushrooms Agaricus bisporus

In order to enhance the shelf-life of edible mature mushrooms Agaricus bisporus, 2 kGy ionising treatments were applied at two different dose rates: 4.5 kGy/h (I⁻) and 32 kGy/h (I⁺). Both I⁺ and I⁻ showed 2 and 4 days shelf-life enhancement compared to the control (C). Before day 9, no significant difference (p>0.05) in L^* value was detected in irradiated mushrooms. However, after day 9, the highest observed L^* value (whiteness) was obtained for the mushrooms irradiated in I⁻. Analyses of phenolic compounds revealed that mushrooms in I⁻ contained more phenols than I⁺ and C, the latter containing the lower level of phenols. The polyphenol oxidase (PPO) activities of irradiated mushrooms, analysed via catechol oxidase and dopa oxidase substrates, resulted in being significantly lowered (p0.05) compared to C, with a further decrease in I⁺. Analyses of the enzymes indicated that PPO activity was lower in I⁺, contrasting with its lower phenol concentration. Ionising treatments also increased significantly (p0.05) the phenylalanine ammonia-lyase (PAL) activity. The observation of mushrooms cellular membranes, by electronic microscopy, revealed a better preserved integrity in I⁻ than in I⁺. It is thus assumed that the browning effect observed in I⁺ was caused by both the decompartimentation of vacuolar phenol and by the entry of molecular oxygen into the cell cytoplasm. The synergetic effect of the residual active PPO and the molecular oxygen, in contact with the phenols, allowed an increased oxidation rate and, therefore, a more pronounced browning in I⁺ than in I⁻.     

Conductivity of lithium perfluorononanoate in water-poly(vinyl pyrrolidone) solutions

Conductivity measurements, focused on the counterion binding of lithium perfluorononanoate (LiPFN) micelles in pure water and in the presence of poly(vinyl pyrrolidone) (PVP), have been carried out. An abrupt decrease of the conductance of the LiPFN in pure water, due to the self aggregation of anions and to dynamic linkage of cations on the micellar surface, has been found. Analysis of the conductometric data indicates that about 50% of the stoichiometric concentration of Li⁺ interacts with the head groups of the perfluorinated anions involved in micellar assembly. Conductometric data of LiPFN-water-PVP systems reveals a favorable influence of the PVP on the micellization process modulated by the concentration and by the molecular weight of the polymer. Analysis of these data shows that in presence of PVP the degree of binding of lithium ion to the micellar assemblies linked to the polymer is smaller than in pure water. By increasing the amount of surfactant in solution up to the concentration where the polymer becomes saturated by LiPFN micelles, the binding of lithium ion in the system becomes slightly greater than that observed in LiPFN-water system. This finding can be interpreted in terms of additional binding of lithium ion to the polymer chains. Conductivity measurements carried out on LiClO₄ and KClO₄ in water + PVP support this interpretation.