Contrasting Effects of a Rigid Core and an Alkyl Chain in nCB on the Phase Behavior of Lipid Bilayers
2016
Usuda, Hatsuho | Hishida, Mafumi | Yamamura, Yasuhisa | Saitō, Kazuya
Molecules incorporated into biomembranes often bear both a core and an alkyl chain in a single molecule (e.g., sterols). To clarify the effects of these two parts of a molecule, the phase behavior of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayer containing 4-n-alkyl-4′-cyanobiphenyl (nCB) (n = 0–8) was investigated. The trends of the main transition temperature (Tₘ) with respect to n and of the pretransition temperature (Tₚ) with respect to nCB content changed at n = 3. It was therefore suggested that the two parts of the molecule had opposing effects on the phase behavior of DPPC bilayers. The core appears to perturb molecular ordering in the gel phase and lowers Tₘ (like cholesterol), while alkyl chains appear to order the lipids in the gel phase and raise Tₘ (like n-alkanes). In addition, Tₘ exhibits the so-called odd–even effect based on the alkyl chain length of the minor component, nCB. Depending on the value of n, the variation in Tₚ was dependent on the additive content, although the pretransition was rarely observed at high contents.
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