Solute-solvent interactions on the keto-enol tautomerism of 2-nitrocyclohexanone in several organic solvents and room-temperature ionic liquids (RTILs) have been analyzed in terms of multiparameter equations. Permittivity and cohesive pressure values of the RTILs, unavailable by direct measurements, have been derived.

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We explore the effects of preparation protocol on the morphology and stability of aggregates from a poly(ethylene glycol-b-propylene sulfide-b-ethylene glycol) triblock copolymer, PEG44−PPS76−PEG44. Fluorescence spectra and excimer formation of the probe molecule pyrene elucidated the various stages of aggregate formation, and cryo-TEM yielded insight into aggregate morphology. When prepared by direct hydration of polymer films, an extraordinary variety of morphologies was formed, ranging from spherical micelles to wormlike micelles, Y-junctions, blackberry micelles, and vesicles. Aging produced more uniform structural ensembles, including wormlike micelles with undulations and eventually spherical micelles, indicating the nonequilibrium nature of the system as initially formed. On the contrary, preparation by dilution from organic solvent yielded only structures that were closer to equilibrium distributions.

An amphiphilic C60-derivative, AFE, characterized by the presence of the chiral fragment of L-acetyl carnitine in its hydrophilic appendage has been synthesized. In binary (THF/H2O) and ternary (THF/ MeOH/H2O) solutions, AFE exhibits a strong tendency to self-aggregation, provided that the Hildebrand polarity index, δ, of the solvent is higher than about 15. A stable aqueous solution of aggregated AFE was obtained. Partition experiments between n-octanol and water show that AFE cannot be spontaneously transferred from water into the organic solvent (and vice versa), although it is effectively "salted-out" by common electrolytes. Light scattering and reversed-phase liquid chromatography experiments carried out on the aqueous solution of AFE suggest for the aggregates an average diameter of 120 nm.

Membrane stability of extruded large unilamellar vesicles (LUV) formed by 1-palmitoyl-2oleoylphosphatidylcholine (POPC) containing fullerene C 60 or an amphiphilic fullerene derivative, 2-[2-(2-fulleropyrrolidin-1-ylethoxy)-ethoxy]-ethanol (FPE), has been investigated by spectrofluorimetrically monitoring the spontaneous release of entrapped carboxyfluorescein (CF). Under controlled conditions of temperature, osmolarity and pH, these guests increase the stability of the liposomal membrane as shown by the decrease in the rate of outflux of CF. The stability conferred to the POPC liposomes by C 60 and FPE has been compared with that conferred by the well-known stabilizing guest 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy-(polyethylene glycol)-2000] ammonium salt (PEG). The addition of amphiphilic molecules, such as non-ionic surfactants, which intercalate into the membrane bilayer, and of sucrose or NaCl, which induce a hyposmotic stress, has been extensively investigated in order to get information on how to modulate the release of entrapped CF. This information could hopefully be useful in the formulation of new drug delivery systems as well as for getting a deeper understanding of the mechanisms of the formation/enclosure of channels through the membrane. The viscosity and the micropolarity of the membrane have been measured fluorimetrically by using pyrene as the probe. An interesting increase of the gel-liquid crystal phase transition temperature has been observed for POPC liposomes hosting C 60 .

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in the press. failure of thiophenol itself to correlate with Taft c* parameter^,^ we have determined the thermodynamic acid dissociation constants, in water at 25 "C, for thiophenol, four &a-substituted thiophenols, and six para-substituted thiophenols. The substituents have been chosen as representative of a broad spectrum of substituent effects on reactivity. RESULTSIn determining acid dissociation constants the simplest expression is given by (1) and the pK, values so calculated would be the classical or concentration acidity constants. If ' pH ' in this expression is replaced by the thermodynamic

The equilibrium constant for the keto‐enol tautomerism of 3‐nitrobutan‐2‐one KT = [enol]/[ketone] has been measured in water as 4.57 × 10−3 (pKT = 2.34) by combining the rate constants for ketonisation of the enolate form and pKa of the ketone at 25 °C. The rates of ketonisation were measured by a rapid kinetic technique and the pKa was determined spectrophotometrically and potentiometrically as 5.15. A comparison with 2‐butanone and acetone shows a strong influence of the nitro group in enhancing the acidity of the substrate and in stabilizing the enol relative to the keto tautomer. By means of semiempirical AM1 calculations, good correlations were found between the atomic charge on the acidic hydrogens and the pKa (in water at 25 °C) of both tautomeric forms for a number of simple ketones whose pKas and pKTs are available in the literature. The agreement of experimental acidity constants of the enol, pKaEH, the ketone, pKaKH, and the tautomeric constant, pKT, with predicted values is satisfactory.