José L. López-Fontán

Mixed micelles of n-alkyltrimethylammonium bromides: influence of alkyl chain length

The influence of chain length on the composition of micelles in a binary mixture of n-hexyltrimethylammonium bromide and n-octyl-, n-decyl-, n-dodecyl-, n-tetradecyl- and n-hexadecyltrimethylammonium bromides has been determined from an analysis of the variation of the critical micelle concentration (determined by conductivity techniques) as a function of solution composition. Using the theoretical treatment of Motomura, the composition of each compound in mixed micelles was evaluated. The nonideality of mixing was expressed in terms of the molecular interaction parameter β, obtained with the Holland and Rubingh theory. The molecular thermodynamic model of Puvvada and Blanckschtein was used to study the nonideal behaviour of the mixtures.

The self-association of acebutolol: Conductometry and light scattering

The association characteristics of an amphiphilic beta-blocker drug, acebutolol hydrochloride, in aqueous solution containing high concentrations of electrolyte and at different temperatures have been examined by static and dynamic light scattering and electrical conductivity. Time averaged light scattering measurements on aqueous solutions of acebutolol at 298.15 K in the presence of added electrolyte (0.4–1.0 mol kg−1 NaCl) have shown discontinuities which reflect the appearance of aggregates. The critical micelle concentration, aggregation numbers, effective micelle charges, and degree of micellar ionization were calculated. Dynamic light scattering has shown an increase in micellar size with increase in concentration of added electrolyte. Data have been interpreted using the DLVO theory to quantify the interaction between the drug aggregates and the colloidal stability. Critical micelle concentrations in water have been calculated from conductivity measurements over the temperature range 288.15–313.15...

The surfactant characteristics of short-chain lecithins analyzed through lecithin-lecithin and lecithin-biopolymer interactions

The micellar behaviour of the binary mixed systems dihexanoylphosphatidylcholine (diC6PC)/diheptanoylphosphatidylcholine (diC7PC), diC7PC/dioctanoylphosphatidylcholine (diC8PC) and diC6PC/ diC8PC has been studied. Critical micelle concentrations of the mixtures were quantitatively estimated from surface tension measurements versus solution composition plots. The micellar composition in the micelles was determined by the Motomura thermodynamic model. The nature and the strength of the interaction between two surfactants in the mixture were estimated by calculating the values of their β 12 M parameter from Holland and Rubingh’s treatment. DiC6PC and diC7PC mix ideally with an interaction parameter near zero. DiC7PC/ diC8PC and diC6PC/diC8PC show nonideality for about 75 and 40% diC8PC in the mixture, respectively. The nonideality has been attributed to differences in the acyl chain length, the size of the micelles formed by pure components and the composition of mixed micelles. Zeta potential and microcalorimetric measurements were used to investigate the effect of diC8PC on human serum albumin. The results revealed that the interaction is hydrophobically driven and depends on lecithin concentration.