Determining the cytotoxicity of catanionic surfactant mixtures on HeLa cells.

The cytotoxicity of commonly used synthetic surfactants and catanionic mixtures of those was evaluated using MTT on HeLa cells. The 50% inhibition concentration (IC(50)) for MTT reduction was calculated. The effect on chain length increase and inclusion of polyoxyethylene groups on the toxicity was tested on single surfactant systems. A general trend of increasing toxicity with increasing chain length and the presence of polyoxyethylene groups was observed. The measured IC(50) values of catanionic systems lie between those of participating surfactants. The increase in toxicity as the cationic surfactant is added to the anionic one is however not linear. A steep decrease of the IC(50) values (and therefore increase in the toxic properties) is observed immediately already at low concentrations of the cationic surfactants. This behavior is analogous to the enzyme activity in catanionic microemulsions.

Spontaneous formation of bilayers and vesicles in mixtures of single-chain alkyl carboxylates: effect of pH and aging and cytotoxicity studies.

We report the observation of bilayer fragments, some of which close to form vesicles, over a large range of pH at room temperature from mixtures of single-chain biocompatible commercially available nontoxic alkyl carboxylic surfactants after neutralization with HCl. The pH at which the morphological transitions occur is varied only by changing the ratio between two surfactants: the alkyloligoethyleneoxide carboxylate and sodium laurate. The effect of aging of the mixed surfactant systems in the pH region desired for dermatologic application (4.5 < pH < 7) is also studied. Finally, we show results of cytotoxicity studies on the surfactant mixtures.

Blastulae aggregates: new intermediate structures in the micelle-to-vesicle transition of catanionic systems.

A new type of intermediate structure was found in the salt-induced micelle-to-vesicle transition in a catanionic system composed of sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) in aqueous solution with an excess of anionic surfactant. The appearance of symmetrically shaped hollow structures, which we named blastulae vesicles, is presented.

Specific alkali cation effects in the transition from micelles to vesicles through salt addition.

The transition of ionic micelles to vesicles with added salts is explored in this paper. The catanionic surfactant solution was comprised of sodium dodecylsulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) with an excess of SDS. The micellar size increased with concentration for all salts. No anion specificity was found, probably because of the excess of SDS. However, when the cation of the added salt was varied, large differences were observed in the hydrodynamic radii of the aggregates. A classification of the cations according to their ability to increase the measured hydrodynamic radii follows a Hofmeister series. The change in aggregate size can be explained by modified counterion binding and dehydration of the surfactant headgroups.