Structural ordering of lipid bilayers induced by surfactant molecules with small hydrophilic head group

<p>A series of 100 ns-long molecular dynamics calculations for binary bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 33 mol% ethylene-glycol-ethers () were performed under the isothermal–isobaric condition ( K and atm) to investigate systematically changes in physico-chemical properties of the binary bilayer depending on the length of the hydrophilic head group and the hydrophobic tail. Remarkable differences were observed in membrane properties between the bilayers mixed with surfactants with a large hydrophilic head group and a small hydrophilic head group. In the former, the binary bilayers extended laterally with more disorder in lateral arrangement of the lipid molecules and more disordered acyl tail conformation of the DMPC molecules in the binary bilayers than those in pure DMPC bilayer. In the latter, the bilayers shrunk laterally with more order in lateral arrangement of the lipids and more ordered DMPC acyl tail conformation. The molecular mechanism of these changes in membrane properties is discussed on the basis of two-dimensional radial distribution functions of the lipid mass centres, radius of gyration of lipids and void distribution in membranes. The umbrella effect of phosphocholine head groups was investigated.