Catanionic vesicles formed with arginine-based surfactants and 1,2-dipalmitoyl-sn-glycero-3-phosphate monosodium salt

We report on mixing an anionic diacyl phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphate monosodium salt, DPPA) with either monoacyl and diacyl arginine-based surfactants. These mixtures are part of the rich family of pseudo-triple-chain and pseudo-tetra-chain catanionic mixtures, respectively. Vesicle size and zeta-potential were measured at several mixing ratios. Additional information on counterion binding, vesicle size, and integrity was obtained from ion selective electrode and Cryo-TEM measurements. Addition of positively charged surfactants to DPPA results in an increase of vesicle size. However, zeta-potential shows different trends, depending on whether water or acid media are used as solvent. In the latter, zeta-potential values progressively approach 0 upon addition of amino acid based surfactants. In water, surprisingly, zeta-potential values become more negative. The results are discussed in terms of modifications in counterion binding and vesicle size.