Characterization and stability of catanionic vesicles formed by pseudo-tetraalkyl surfactant mixtures

Abstract

The phase behavior of an ad hoc synthesized surfactant, sodium 8-hexadecylsulfate (8-SHS), and its mixtures with didecyldimethylammonium bromide (DiDAB) in water is reported. We dealt with dilute concentration regimes, at a total surfactant content of <30 mmol kg(-1) where vesicular aggregates may be formed. The high synergistic behavior of such catanionic mixtures is concomitant with strongly negative interaction parameters, β (≈-18 kBT), significant gain in the free energy of association, ΔGagg, and much lower association concentration compared to the pure surfactants. Vesicle size and ζ-potential depend on the mixture composition. Hydrodynamic diameters increase by progressive addition of oppositely charged surfactants to the one in excess. Counter-intuitively, the ζ-potential becomes more negative at DiDAB molar fractions close to 0.2. The same holds in the reverse case, the ζ-potential becomes more positive after small additions of 8-SHS; anyhow, the effect is more significant in anionic-rich mixtures. This phenomenon was explained by assuming a significant release of counterions and an asymmetric distribution of the two surfactants in the inner and outer vesicle leaflets. The equimolar mixtures form a cubic phase rather than the expected lamellar one. The effect of NaBr concentration on the stability of catanionic vesicles was also investigated. At high NaBr concentrations, all systems are destabilized. For DiDAB-rich vesicles, flocculation is observed, while for 8-SHS-rich ones, lamellar domains are formed at the bottom of the samples. The role played by NaBr depends on whether it is added before or after mixing the surfactants. In particular, preformed catanionic vesicles show a great kinetic stability towards addition of NaBr compared to those obtained by other procedures.

Biocompatible Catanionic Vesicles from Arginine-Based Surfactants: A New Strategy to Tune the Antimicrobial Activity and Cytotoxicity of Vesicular Systems

“…The cmc values of the pure surfactants were found to be in good agreement with the literature values [ 25 , 29 ]. Due to their more hydrophobic character, the cmc of the cationic gemini surfactant C 3 (CA) 2 and the double chain surfactant 8-SH was lower than that of LAM and sodium laurate.…”

“…The PdI values indicate that both 8.2LM and 2.8LM contained a monodisperse population of small vesicles with a mean D h of 121 nm and 190 nm, respectively. The DLS results were supported by visual observations, as the 8.2LM and 2.8LM dispersions were bluish in color, which is typical of catanionic vesicles sized in the visible wavelength range ( Table 3 , Figure 5 a) [ 25 ]. At an equimolar ratio, the mixed solution became very turbid and the surfactant mixture was prone to precipitate.…”

“…Water from a Milli-Q Millipore system (Millipore, Burlington, MA, USA) was used to prepare aqueous solutions. Sodium dodecanoate and myristate were from Sigma (San Luis, MO, USA), while the other surfactants used to prepare the catanionic mixtures (LAM, C 3 (CA) 2 and 8-SH) were prepared in our laboratory following procedures already described [ 24 , 25 ]. Briefly, the gemini surfactant C 3 (CA) 2 was obtained with a purity of 99% by chemical condensation of the previously protected single N α-decyl- l -arginine to the propanediamine in presence of an activating agent.…”

Green Catanionic Gemini Surfactant–Lichenysin Mixture: Improved Surface, Antimicrobial, and Physiological Properties

“…10 Recently it has been demonstrated that catanionic mixtures may also have improved biological properties, attributed to synergistic effects, compared with those of the individual components. 11 In a previous study, the catanionic mixture of lichenysin and an arginine-based surfactant showed synergistic antimicrobial activity. 12 These results prompted us to explore new catanionic mixtures (lichenysin plus arginine-based surfactants) in order to define the molecular requirements in their chemical structures for synergistic antimicrobial activity, and to characterise their mode of action and physicochemical and physiological properties.…”

Catanionic vesicles and DNA complexes: a strategy towards novel gene delivery systems

“…The purity of the nal product was checked by 1 H, 13 C NMR and elemental analysis; it resulted to be above 99%. 12 Water was bi-distilled using a Milli-Q four-bowl system. The phase behaviour of the two surfactants has been investigated previously.…”