Vesicles of mixtures of the bolaform amphiphile sodium di-n-decyl alpha,omega-eicosanyl bisphosphate and sodium di-n-decyl phosphate

Various properties of vesicles prepared from different ratios of the bolafo rm (bipolar) amphiphile disodium di-n-decyl alpha,omega-eicosanyl bisphosph ate (EBP) and the nonbolaform (monopolar) sodium di-n-decyl phosphate (DDP) have been studied. The colloidal stability decreased upon the increasing s odium di-n-decyl phosphate content. The main phase transitions, studied by fluorescence depolarization and differential scanning calorimetry, become l ess cooperative and occur at decreasing temperatures upon increasing sodium din-decyl phosphate content. The bolaform amphiphile was found to be membr ane spanning as indicated by the lamellar repeat spacing obtained by X-ray powder diffraction. Electron microscopic studies of the small vesicles prep ared from pure EBP revealed that addition of the fusogen Ca2+ caused format ion of tubules for the EBP. The tubules did not revert to vesicles upon add ition of the Ca2+ chelator EDTA, whereas mixed vesicles with 20-50 mol % DD P content showed enlarged vesicles after subsequent addition of Ca2+ and ED TA. A preliminary conclusion is that a substantial amount of nonbolaform am phiphiles must be present in a bolaform membrane to enable fusion to occur.