Size Dependent Thermodynamic Properties of DPPC Liposome

_{The thermodynamic properties of DPPC liposomes were investigated as a function of liposome size using a combination of dynamic light scattering (DLS) and differential scanning calorimetry (DSC). During the melting transition of the liposome its bilayer thickness decreases. By assuming the volume of bilayer is conserved a noticeable increase of diameter during the phase transition is observed. Liposomes with nominal diameters ranging from 200 to 30 nm were prepared by passing lipid solutions through pole sizes of varying diameter. DLS was used to measure liposome size and the variation of liposome size with temperature. Analysis of DLS yielded the lipid thermal expansion coefficient, the gel-liquid transition temperature, the lipid bilayer thickness jump at the transition, and the thermal width of the transition. The transition width could be used, through the Van’t Hoff equation, to yield the transition enthalpy. DSC measurements yielded the transition enthalpy and transition temperature. The accuracy of each technique will be discussed as well as the systematics of the variation of liposome properties with size.}