Ripple Phase in Mixed Model Membrane

Abstract

We have investigated by differential scanning calorimetry and radiowave dielectric spectroscopy, in the frequency range between 1kHz and 1MHz, the pretransition or ripple Pβ’ phase of aqueous suspensions of mixed phospholipid bilayers of DPPC and DPPE. Our results show that the endothermic peak associated with the pre transition, moves towards the main transition on increasing DPPE contents and disappears at an extrapolated concentration of 11% by weight. The observed anomalous hump in the low frequency dielectric response, associated with the pretransition, correspondingly shrinks and decreases by adding DPPE. These data suggest that DPPE decreases the mismatch between the chain packing volume and the head group area, and reduces the correlation length of the dipolar in-phase domain that, as previously suggested, is associated with the permittivity increment.