A swollen gel phase of DPPC aqueous solution with small amount of ethanol observed at moderate pressure and temperature

In order to clarify effects of pressure on phospholipids, small-angle neutron scattering and X-ray scattering experiments on an aqueous solution of dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) with small amount of ethanol were carried out. At moderate temperature and pressure (41 ≤ T ≤ 60°C and 10 ≤ P ≤ 80 MPa), among a fluid lamellar (L_α) phase, a ripple gel (P_α′) phase and an interdigitated gel (L_βI) phase, we have found a new phase with a single peak at around Q = 0.06 Å⁻¹. This phase was characterized to be a swollen gel phase from the data analysis. The kinetics of the phase transition to the L_βI phase was investigated, and the relaxation was much slower than the transition to the other bilayer structures.