I I 1 B g LOO -30.0 200 10.0 10 20 30 LO 50 100 200 300 400 T pC]-P bfml-Fig. 2. Effective hydrodynamic radius, R,. of DODAC-vesicles at I atrn determined by dynamic light scattering. Temperature-induced phase transition. Broken line: phase transition. 0 -0 DODAC vesicle, xx dirnyristoylphosphatidylcholine vesicle; A -A DODAC-vesicle containing I l"/o (w/w) cholesterol. R,=k,, TK2/(3xqT); k H = Boltzmann constant, r = ( l / r , ) = D K ' with K =(4nn/A)sin(8/2), r,=time constant, D=diffusion coefficient: A) temperature-induced phase transition at I bar, B) pressure-induced phase transition at 22 "C.(w/w) cholesterol reveal no changes in the radius of gyration, R,, sedimentation constant, $,,,,, or diffusion coefficient, D, upon changing temperature or pressure, but in the isopotential partial specific volume from @= 0.861 1 mL/g to 0.8541 mL/g. Moreover, DODAC vesicles containing 1 I% (w/w) cholesterol are more stable with respect to pH and passage of ions than those without cholesterol, and they reveal a considerably higher melting temperature ( T , =42 "C). The cholesterol is located close to the quaternary nitrogen.