M. Soledade C.S. Santos

Partial molar volumes of linear hydrocarbons in methanol in the very dilute region. Intermolecular interactions. H-bond effects

Limiting partial molar volumes VB∞ for the linear hydrocarbons, C5, C6 , C7, C8 and C10 in methanol were determined with a vibrating tube densimeter at 24.994°C (ITS-90). VB∞ and bV were discussed in terms of solute–solvent and solute–solute molecular interactions, focusing on H-bond cleavage, hydrocarbon short-range correlations of molecular orbitals and conformational effects. VB∞ (HS)/VB (HS) values calculated according to Lees hard-sphere mixtures model are compared with experimental values. A discussion is presented and deviations are interpreted in terms of size, shape, packing densities and H-bond effects.

New Thermodynamics for Evaluating the Surface‐phase Enrichment in the Lower Surface Tension Component

Regarding the surface phase of liquid mixtures as a thermodynamic phase, ideal surface phases are designed so that at fixed bulk-phase composition, real and ideal surface phases have the same chemical composition and identical limiting slopes for the dependence of surface tension on mole fraction. Standard chemical potentials are introduced for surface phase components, and quasi-exact expressions are worked out to compute ideal surface tensions and surface-phase compositions of real liquid mixtures. Guidelines for choosing molecular models to estimate the molar surface area of pure constituents are given. Ideal and excess surface tensions are calculated by using literature data for aqueous ethanol solutions at 298 K. These results show treatment based on Butlers equations grossly overestimate predicted surface tensions, thus leading to lower ethanol content in the surface phase. These inaccuracies are ascribed to the use of molar surface areas in model equations that are too small.

Activity Coefficients in the Surface Phase of Liquid Mixtures

A novel equation for evaluating surface activity coefficients is obtained from a recent thermodynamic formalism describing the surface phase of liquid mixtures. The input quantities are the surface tension, bulk activity coefficients and pure constituent thermophysical properties. It is demonstrated thermodynamically that the order of magnitude of each component surface and bulk activity coefficients must be the same. This order is intrinsically associated with the sign of excess surface tension. Reliable activity coefficients of ethanol and water in the surface phase of their mixtures are computed and reported for the first time, by using literature data for the required input quantities. It is shown that the so-called transferring method for estimating surface activity coefficients is severely flawed, because it leads to contradictory values of predicted excess surface tensions depending on which component this prediction is based.

Palladium(II) extraction from concentrated chloride media: Reactions involving thioamide derivatives

ABSTRACT This work focuses on the detailed study of the palladium(II) extraction reactions by N-methyl-N-phenyl-octanthioamide (MPHTA) and N-methyl-N-cyclohexyl-octanthioamide (MCHTA) in toluene, since their ability to efficiently and selectively recover Pd(II) from a wide range of HCl concentrations is already known. Equilibrium data are presented and discussed, and further complemented by information depicted from UV–visible and NMR spectra. The determined apparent molar volumes show that MPHTA is monomeric, and MCHTA exhibits a slight tendency to aggregate. The Pd(II) extraction reactions by MPHTA and MCHTA are equivalent until 4.5 M HCl, passing through the formation of inner-sphere complexes with the metal ion.

Silver(I) complexation with tertiary amines in toluene

The extent of complexation between silver(I) nitrate and triethylamine and tri-n-butylamine in toluene solutions at 23 °C has been determined by infrared spectroscopy. Both amines produced a mixture of monoamine and diamine silver complexes, and the second stepwise formation constants (K2) are reported. Infrared and atomic absorption experiments on solutions saturated with silver nitrate also yielded formal values of the first formation constant (K1) and of the solubility product (Ks) of silver nitrate in toluene. The results showed that Et3N coordinates more strongly with silver(I) in toluene than does Bu3nN. The values of K1 in toluene were found to be 4–5 powers of ten higher than in protic and dipolar aprotic solvents, while the values of K2 were smaller. Structural and solvation reasons are given to explain these results.

Differential targeting of membrane lipid domains by caffeic acid and its ester derivatives

ABSTRACT Phenolic acids have been associated to a wide range of important health benefits underlain by a common molecular mechanism of action. Considering that significant membrane permeation is prevented by their hydrophilic character, we hypothesize that their main effects result from the interplay with cell membrane surface. This hypothesis was tested using the paradigmatic caffeic acid (CA) and two of its ester derivatives, rosmarinic (RA) and chlorogenic (CGA) acids, for which we predict, based on molecular dynamics simulations, a shallow location in phospholipid bilayers dependent on the protonation‐state. Using complementary experimental approaches, an interaction with the membrane was definitely revealed for the three compounds, with RA exhibiting the highest lipid bilayer partition, and the redox signals of membrane‐bound RA and CA being clearly detected. Cholesterol decreased the compounds bilayer partition, but not their ability to lower membrane dipole potential. In more complex membrane models containing also sphingomyelin, with liquid disordered (ld)/ liquid ordered (lo) phases coexistence, mimicking domains in the external leaflet of human plasma membrane, all compounds were able to affect nanodomains lateral organization. RA, and to a lesser extent CGA, decreased the size of lo domains. The most significant effect of CA was the possible formation of a rigid gel‐like phase, enriched in sphingomyelin. In addition, all phenolic acids decreased the order of lo domains. In sum, phenolic acid effects on the membrane are enhanced in cholesterol‐rich lo phases, which predominate in the outer leaflet of human cell membranes and are involved in many key cellular processes. Graphical abstract Figure. No caption available. HighlightsPhenolic acids interplay with membrane domains support diverse biological actions.Lipid bilayer partition depends on phenolic acid structure and membrane cholesterol.Redox signals of membrane‐bound rosmarinic and caffeic acids were clearly detected.Rosmarinic and chlorogenic acids disturb cholesterol‐enriched domains.Caffeic acid specifically targets sphingomyelin in membrane ordered domains.

Catalysed quaternization of coordinated triethylamine by ethyl iodide: further developments in the kinetic analysis

A new approach in the kinetic analysis of the joint homogeneous–heterogeneous catalysis of the quaternization of silver(I) coordinated triethylamine by ethyl iodide in toluene is presented. This complex competitive process was thoroughly scrutinized and the set of solution and surface rate equations were integrated under a novel perspective thus leading to the calculation of solution rate constants as well as guesstimates of the superficial quaternization rate. Testing the rate equations developed herein also required the performance of kinetic runs over a wider range of experimental conditions, than those previously reported.

The role of ethanol-water solvent mixtures in N719 sensitization of electrodeposited ZnO nanorods

Water plays an important role in N719 sensitization of ZnO films for application as photoanodes in DSC devices. The role of water content in ethanolic N719 sensitization solutions was examined resorting to N719-solvent interaction studies based on Kamlet-Taft solvatochromic parameters. Results show that as the water content increases, solvent’s HBA ability decreases, hindering dye aggregation in solution and increasing the fraction of dye carboxylic groups available for anchorage onto the charged ZnO surface. The impact of dye-dye-solvent equilibria in solution on ZnO nanorod films sensitization and device behavior was evaluated. Devices assembled with films sensitized in N719 solutions containing equal parts of ethanol and water showed a twofold increase in short-circuit current densities when compared to those sensitized in ethanol only, despite exhibiting significantly less stained films. Data indicate that the presence of water in the sensitization solution reduces the amount of dye aggregates in solution and on the ZnO surface.