Effect of surfactant structure on the mixed micelle formation of cationic gemini–zwitterionic phospholipid systems.

The micellization behavior of mixed zwitterionic/cationic solutions, that is, of zwitterionic phospholipid, 1, 2-dioctanoyl- sn -glycero-3-[phospho- L -serine] (sodium salt) (PL) and cationic gemini surfactants, alkanediyl-α,ω-bis(dimethylalkylammonium bromide (alkyl: 14 or 16 and alkane: butane, pentane or hexane) ( m - s - m ), have been studied by surface tension measurements. Various physicochemical properties, viz., critical micelle concentration (cmc), surface excess concentration ( Γ max ), minimum area per molecule ( A min ), interaction parameters ( β m , β σ ), and thermodynamic parameters such as standard Gibbs energy of micellization ( Δ G mic ° ), standard Gibbs energy of adsorption ( Δ G ads ° ), and excess free energy of mixing ( Δ G ex m ,   Δ G ex ° ), have been evaluated. The obtained results indicate that the mole fraction of PL in the mixed micelles, calculated on the basis of Rubingh's model, is different from stoichiometric mole fraction of PL ( α 1 ). The negative values of Δ G mic ° and Δ G ads ° show that the micelle formation and adsorption of surfactants at the air/solution interface is energetically favorable with the magnitude of Δ G ads ° greater than that of Δ G mic ° . The negative values of Δ G ex m and Δ G ex σ indicate better stability of the mixed systems. The insights presented herein on the gemini-phospholipid mixed micelle properties may find use towards their applications in the relevant areas of solubilization/drug delivery/etc. [ABSTRACT FROM AUTHOR]