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Equilibrium constants for the proton transfer reaction between pyridines and trifluoroacetic acid were measured in room-temperature ionic liquids (ILs) of different cation-anion compositions. The experimental equilibrium constants for ion-pair formation were corrected according to the Fuoss equation. The calculated equilibrium constants for the formation of free ions were taken as a quantitative measure of the base strength in IL solutions and compared with the relative constants in water. The effect of IL composition is discussed for a series of fixed IL anions and fixed IL cations. Finally, the sensitivity of the proton transfer reaction to the electronic effects of the substituent groups on the pyridine ring was quantified by applying the Hammett equation. A more marked levelling effect on the base strength was observed in ILs than in water. The Hammett reaction constants were ρ then correlated with solvent parameters according to a multi-parametric analysis, which showed that both specific hydrogen-bond donor/acceptor and nonspecific interactions play an important role, with α and permittivity being the main parameters affecting the ability of the IL to differentiate the strength of the base. [ABSTRACT FROM AUTHOR]

We have developed a simple artificialphotoresponsive ion-gatingdevice by inserting molecular switches in the membrane of liposomes.A controlled and directed proton transport across the bilayer membranecan lower the internal pH of the liposomes from neutral to around4 under combined light and chemical stimulation. [ABSTRACT FROM AUTHOR]

The mechanism of base catalyzed keto-enol interconversion of aqueous 2-phenylacetylthiophene has been investigated by a joint application of experimental and computational approaches. Primarily we have focused our attention on the water-enolate proton transfer representing the rate determining step of the reaction. Computational results, in good agreement with experimental data demonstrate the crucial role exerted by the solvent. In particular, beyond the bulk catalytic effect an explicit assistance of solvent molecules allows the reaction to increase its efficiency. A combination on Molecular Dynamics simulations and Perturbed Matrix Method calculations also highlight the subtle balance between energetic and entropic effects which characterize the mechanistic scenario. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]