Mixed micelle formation between amino acid-based surfactants and phospholipids

Amino acid-based gemini surfactant (C8Cys)2 and single-chain surfactant C8Cys form mixed micelles with the phospholipids DHPC and DMPC, as a result of the interplay between electrostatic forces and packing constraints. [Display omitted] ► Mixed micelle formation was observed for dimeric or monomeric cysteine surfactants and phospholipids. ► Mixed micelles were the result of the interplay between electrostatic forces and packing constraints. ► Phospholipid-surfactant interactions were synergistic and dependent on the type of phospholipid and surfactant hydrophobicity. The mixed micelle formation in aqueous solutions between an anionic gemini surfactant derived from the amino acid cystine (C 8Cys) 2, and the phospholipids 1,2-diheptanoyl- sn-glycero-3-phosphocholine (DHPC, a micelle-forming phospholipid) and 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC, a vesicle-forming phospholipid) has been studied by conductivity and the results compared with the ones obtained for the mixed systems with the single-chain surfactant derived from cysteine, C 8Cys. Phospholipid-surfactant interactions were found to be synergistic in nature and dependent on the type of phospholipid and on surfactant hydrophobicity. Regular solution theory was used to analyse the gemini surfactant–DHPC binary mixtures and the interaction parameter, β 12, has been evaluated, as well as mixed micelle composition. The results have been interpreted in terms of the interplay between reduction of the electrostatic repulsions among the ionic head groups of the surfactants and steric hindrances arising from incorporation of the zwitterionic phospholipids in the mixed micelles.