COMPETITIVE INTERACTIONS IN NEGATIVELY CHARGED LIPOSOME-POLYCATION-POLYANION TERNARY-SYSTEMS

This paper involves small unilamellar liposomes (SULs) of phosphatidyl choline (PC) imparted with a negative charge via the incorporation of cardiolipin (CL2-), a lipid with a double-negative charge. Such liposo mes in water strongly adsorb polycations such as CP(2) (a 93/7 copolym er of N-ethyl-4-vinylpyridium bromide and 4-vinylpyridine) or CP(2,16) (a 83/3/14 copolymer of N-ethyl-4-vinylpyridinium bromide, N-cetyl-4- vinylpyridinium bromide, and 4-vinylpyridine). Neither CP(2) nor CP(2, 16) disrupts the integrity of the PC-CL2- liposome despite the tight b inding. Addition of NaCl is able to totally dissociate CP(2) from the negative SULs, whereas CP(2,16) is only partially dissociated even at high salt concentrations. Thus, only 3% long-chain pendant groups on t he polycation is sufficient to immobilize the polycation onto the nega tive surface of SULs. Similarly, poly(acrylic acid) (PAA) in its anion ic state will remove CP(2) from the liposome surface to form a CP(2)-P AA complex. CP(2,16), on the other hand, is more resistant to removal. Evidence is provided that the CP(2,16) associates with PAA but noneth eless remains on the surface of the liposome. Thus, a liposome-CP(2,16 )-PAA ternary complex is created. This work makes heavy use of photon correlation spectroscopy, conductometry, electrophoretic mobility, and fluorescent labeling of the liposomes.