POLYMORPHIC PHASE-BEHAVIOR OF FLUOROCARBON DOUBLE-CHAIN PHOSPHOCHOLINES DERIVED FROM DIAMINOPROPANOL, SERINE AND ETHANOLAMINE AND LONG-TERMSHELF STABILITY OF THEIR LIPOSOMES

This paper describes the morphological characterization, by freeze-fra cture electron microscopy, and the thermotropic phase behavior, by dif ferential scanning calorimetry, of aqueous dispersions of various fluo rocarbon/fluorocarbon or mixed fluorocarbon/hydrocarbon double-chain 2 ,3- or 1,3-diamidopropano-, diamidoserino- or amidoethyl-phosphocholin es (PC). These fluorinated PCs form lamellar phases and liposomes, as their ester or ether glycerol-based analogs. The effects on the thermo dynamic parameters associated with these lamellar phases of several st ructural elements-chemical junction (secondary CONHR or tertiary CONRR ), connecting unit (diamino-propanol, serine or ethanolamine), number and length of the perfluoroalkylated chains, length of the fluorinated tail and hydrocarbon-are discussed. These data are compared with thos e reported for fluorocarbon or hydrocarbon glycerophosphocholines and hydrocarbon diamidophosphocholines, and for sphingomyelins. Most of th e liposomes formed from the fluorinated amido-connected PCs display a remarkable long-term shelf stability: they can be thermally sterilized and stored at room temperature for several months without any signifi cant modification of their size and size distribution. (C) 1997 Elsevi er Science Ireland Ltd.