Phase quilibria in the system dimyristoylphosphatidyl choline/ N-hexadecyl- N, N, N,-trimethylammoniumbromide/water at 30°C. Swelling behaviour of the lamellar phase with different electrolyte solutions

Abstract

The phase equilibria of a swelling amphiphile, dimyristoylphosphatidylcholine (DMPC) and a cationic soap, cetyltrimethylammoniumbromide (CTAB) has been investigated in water at 30°C. The swelling of the lamellar phase of DMPC in water increases dramatically in the presènce of a few mol% of CTAB. Maximum swelling of the lamellar phase in water is obtained when the lamellar phase is in equilibrium with aqueous solution whose concentration of CTAB is less than the critical micell concentration (cmc). Vesicles are easily formed by the lamellar phase in this region. When the cme of CTAB is exceeded, DMPC is solubilized in micelles. The solubilizing capacity corresponds to about 1 mol of DMPC per 3 mol of CTAB. The phase behaviour of DMPC and CTAB in water is very similar to the corresponding equilibria for amphiphite compounds with shorter hydrocarbon chains. The swelling of DMPC and CTAB is influenced by the presence of electrolytes in the water phase. Due to electrostatic effects the swelling of the lamellar phase is lower in electrolyte solutions than in pure water.