Archaebacterial lipid models: highly salt-tolerant membranes from 1,2-diphytanylglycero-3-phosphocholine.

1,2-Di(3RS,7R,11R-phytanyl)-sn-glycero-3-phosphocholine and its glycerol epimers were synthesized as model lipids of archaebacterial halophiles. These amphiphiles, upon sonication of aqueous suspensions, gave rise to small unilamellar vesicles (SUV) of 300-800 A in diameter and about 80 A in the membrane thickness. The liposomes were very stable for at least a month even in a highly concentrated suspension or 5 M aqueous NaCl. The vesicles could retain Na+ and Cl- ions as well as 5(6)-carboxyfluorescein in the aqueous interior at temperature as high as 70 degrees C. The liposomes of ordinary diester lipids such as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and egg-yolk lecithin were less stable and more permeable than those of the diphytanyl lipids.