Biomembranes of cells are mainly composed of phospholipid bilayers, including various kinds of small organic molecules. To understand widely the effects of these small molecules on a phospholipid bilayer, systematization of the effects is desired with focusing on the molecular structures of the additive molecules. Cholesterol is well known to disturb the molecular ordering of a lipid bilayer in the gel (Lβ' and Pβ') phases, resulting in softening of the bilayer and lowering of the transition temperature between Pβ' and Lα' phases. On the other hand, in the present study, we found n-alkane makes the molecular arrangement more ordered in the Lβ' phase, resulting in rigidification of the bilayer and raise of the transition temperature. Bulky core-like molecules such as cholesterol and the molecules with a linear and flexible chain contrastingly affect the bilayers due to the contrary effects on the ordering of acyl chains in the bilayer. Indeed, cis-stilbene, the bulkier molecule, disturbs the acyl chains more largely than the trans-isomer, lowering the transition temperature more drastically. When a core part and an alkyl chain coexist in a molecule like nCB, the effects of these parts compete each other. The effect of a whole molecule changes depending on the length of an alkyl chain.
Keywords:Phospholipid bilayer, additive molecules, Membrane elasticity, Phase behavior
Publication Date: 2017-04-25