Micellar behavior of short chains phospholipids binary mixture in an aqueous Tmedium: interfacial and fluorescence study

The mixed micellar behavior of short chain zwitterionic phospholipids 1,2-dioctanoyl-snglycero-3-phosphocholine (DOPC) and 1,2-diheptanoyl-sn-glycero- 3-phosphocholine (DHPC) have been studied at the air-water interface and in the aqueous bulk phase via interfacial tension and pyrene fluorescence (I1\I3) intensity measurements, respectively. The critical micellar concentration (cmc) and the thermodynamic parameters such as the free energy of micellization have been evaluated. The interfacial study reveals that a mixed monolayer is formed at the air-water interface by the adsorption of both of the phospholipids. This has been confirmed by evaluating interfacial parameters; the maximum surface excess (max) or the minimum area per molecule (Amin) of those monomers. Their mixing behaviors have also been expressed in terms of the regular solution interaction parameter, , in the mixed micelle. The parameters are not significantly different from each other, and very close to zero; in other words they are consistent with ideal behavior. The equilibrium distribution of components between the micelle and the aqueous bulk was evaluated by Motomuraʹs formulation. The micellar mole fraction evaluated from regular solution theory and Motomuraʹs formulation also lies close to that corresponding to ideal behavior.