Increased water presence in phospholipid fluid bilayers upon addition of lysolipids

In spite of the numerous studies dealing with the interaction between lipid membranes and surfactants at subsolubilizing membrane concentrations, quantifying detailed bilayer structure, as for instance pore formation, on phospholipid bilayers upon addition of single chain lipids continues to be a challenge. Herein, we analyze the effects of lysophosphatidylcholine (18: 1 LPC or lysolipid) on soybean phosphatidylcholine (SPC) extruded liposomes, where vesicles containing additional LPC exhibit approximately a 10% reduction in size as indicated by dynamic light scattering experiments. Most importantly, we benefit from the non perturbing nature of small-angle neutron scattering (SANS) measurements to determine the degree of water incorporation presumably through the surfactant stabilized pores along the fluid bilayers. Model-free analysis of SANS curves reveals that the membrane part of the pure SPC vesicles contain 3.3% v of water. As the lysolipid is added to the dispersion, the volume fraction of water counted into the lipid membrane (flipo D2O) increases to 15–20%. Finally, assuming flipo D2O to be equivalent to the volume fraction of pores within the bilayers we estimate the pore size and density.