How lipid hydration and temperature affect the structure of DC-Chol–DOPE/DNA lipoplexes

Effect of lipid hydration on the structure of lamellar lipoplexes made of the cationic lipid 3-[N-(N,N-dimethylaminoethane)-carbamoyl]cholesterol (DC-Chol), the neutral ‘helper’ lipid dioleoylphosphatidylethanolamine (DOPE) and calf-thymus DNA was investigated by synchrotron small angle X-ray diffraction (SAXD). Here, we show that lipid hydration is the key factor regulating the equilibrium structure of lipoplexes. Thermotropic behavior was also investigated between 5 and 65 °C. Both the membrane thickness and the water layer thickness were found to decrease linearly as a function of temperature while the one dimensional DNA rod lattice between lipid bilayers was found to enlarge. Structural results were interpreted in terms of recently proposed theoretical models.