Formation of micelles and liposomes from carnitine amphiphiles

Esterification of the carboxy and/or the hydroxy groups of (R)-carnitine (3-hydroxy-4-trimethylammonium butanoate) produces interesting classes of (cationic or zwitterionic) surfactants whose CMC values are in general predictable from their molecular structure. In fact similar relationships between CMC and the number of carbon atoms, C-n, have been found for three classes of such surfactants. However the sensitivity of CMC to C-n for the diesters is considerably lower than that calculated from literature values for the monoesters (either in their cationic or zwitterionic forms). The CMC values for the diesters have been determined by tensiometric, conductimetric and spectrophotometric methods, both in pure water and in 0.154 M NaCl solutions, at 25 degreesC. In particular the tensiometric results provide evidence that double-chain diesters undergo self assembly into structures more complex than simple micelles if the two chains are of comparable length. EPR and electron microscopy experiments show that the aggregates spontaneously formed by these surfactants are a mixture of multilamellar vescicles. (C) 2000 Editions scientifiques et medicales Elsevier SAS.