Swellable Model POPC/POPG/DHPC Membrane with a Lamellar Long-Range Order*

A physiological relevant biomimetic model membrane is of great necessity for the structural characterization of membrane protein. This presentation will report a small-angle neutron scattering (SANS) result on two lipid bicellar series composed of 1-palmitoyl-2-oleoyl-\textit{sn}-glycero-3-phosphocholine(POPC)/1,2-dihexanoyl-\textit{sn}-glycero-3-phosphocholine (DHPC) and POPC/DHPC/1-palmitoyl-2-oleoyl-\textit{sn}-glycero-3-phospho-(1'-\textit{rac}-glycerol) (POPG). Instead of the multi-lamellae vesicle (MLV) structure observed in zwitterionic POPC/DHPC mixture, the perforated lamellae (PL) structure is found in POPC/POPG/DHPC upon addition of small amount of charged lipid, POPG {\{}R=[POPG]/([POPC]+[POPG])=0.01{\}}. The PL phase exists from 10 to 60 degree C and the interlamellar spacing (d-spacing) varies from 12.9 to 49.0 nm as the lipid concentration changes from 25 to 7.5{\%} wt where the lamellae still indicate long-range order. The effect of temperature and charge density (R) on structural variation will be discussed in this presentation.