title: Effects of Low Concentrations of Docosahexaenoic Acid on the Structure and Phase Behavior of Model Lipid Membranes.
abstract: In this paper we report an X-ray diffraction study on the phase behavior of binary lipid mixtures of 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (DHA-PE) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) at low concentrations below 5.0 mol% DHA-PE. Our results show that DHA-PE induces phase separation into a DHA rich liquid crystalline (Lα) phase and a DHA poor gel (Lβ') phase at overall DHA-PE concentrations as low as 0.1 mol%. In addition, we find that the structure of the Lβ' phase, from which the DHA-PE molecules are largely excluded, is modified in the phase-separated state at low DHA-PE concentrations, with a decrease in bilayer thickness of 1.34 nm for 0.1 mol% at room temperature, compared to pure DPPC bilayers. This result is contrary to that seen in similar studies on mono-unsaturated lipids where an increase in bilayer thickness is observed. The surprising effect of such low DHA-PE concentrations on membrane structure may be important in understanding the role of highly polyunsaturated lipids in biological membrane-based structures and similar artificial surfactant systems.
authors.affiliation: Bioengineering and Small Scale Technologies, School of Engineering, University of California, Merced, CA 95343, USA. clor@ucmerced.edu.
authors.forename: Chai
authors.initials: C
authors.lastname: Lor
authors.affiliation: Department of Physics, School of Natural Sciences, University of California, Merced, CA 95343, USA. lhirst@ucmerced.edu.
authors.forename: Linda S
authors.initials: LS
authors.lastname: Hirst
keywords: DHA; X-ray diffraction; gel phase; lipid bilayer