Dynamic and structural properties of polymerized phosphatidylcholine vesicle membranes

The phase transition, fluidity, and polarity properties of polymerized and nonpolymerized vesicle membranes derived from 1-palmitoyl-2-[12(methacryloyloxy)dodecanoyl]-L-α-phosphatidylcholine (1), bis[12-(methacryloyloxy)dodecanoyl] -L-α-phosphatidylcholine (2), and 1,2-dipalmitoyl[N-2-(methacryloyloxy)ethyl]-DL-α-phosphatidylcholine (3) have been examined by means of differential scanning calorimetry and by the spin-labeling technique. Above 5 °C aqueous multilamellar dispersions of 1, 2, and 3 show a broad-phase transition, no phase change, and a sharp transition, respectively. Polymerization of the group causes a decrease in membrane fluidity in each case and an increase in the temperature of the gross phase change for 1 and 3. Membrane fluidity in copolymerized vesicles of 1 and 2 decreases linearly with the mole fraction of 2 used. The polarity gradient in membranes of 3 is small; polarity gradients in membranes of 1 and 2 are large. Polymerization no noticeable effect on these gradients. Fluidity gradients are also present in membranes of 1, 2, and 3 above 20 °C. Polymerization alters the fluidity gradients in a manner which is comparable to lowering the temperature; it also reduces the ability of each membrane to bind [^(15)N]perdeuteriotempone. These results are compared directly with the dynamic and structural properties found in conventional liposomes derived from dipalmitoylphosphatidylcholine and egg yolk phosphatidylcholine.