Interfacial and fluorescence studies of mixed-micelle formation by 1,2-diheptanoyl- sn -glycero-3-phosphocholine with cationic surfactants

Abstract

Interfacial, γ, and fluorescence measurements have been performed to evaluate the synergism in mixed cationic and zwitterionic phospholipid systems, viz. dodecyltrimethylammonium bromide plus 1,2-diheptanoyl-sn-glycero-3-phosphocholine (DHPC), tetradecyltrimethylammonium bromide plus DHPC, and hexadecyltrimethylammonium bromide plus DHPC mixtures. From the γ data the maximum surface excess and minimum area per molecule were computed and it was found that the former decreases and the latter increases with the increase in the fraction of cationic component in the binary mixture. Application of regular solution theory demonstrated that strong synergistic interactions are present which increase with the increase in length of the hydrocarbon tail of the cationic surfactant component. These interactions were considerably less in the monolayers than in the mixed micelles. The aggregation number, N agg, of DHPC shows a significant decrease upon induction of the cationic component and vice versa. The decrease in N agg is explained on the basis of an increase in the total polarity of the mixed micelles.