Thermodynamic Analysis of Chain-Melting Transition Temperatures for Monounsaturated Phospholipid Membranes: Dependence on cis-Monoenoic Double Bond Position

Abstract

Unsaturated phospholipid is the membrane component that is essential to the dynamic environment needed for biomembrane function. The dependence of the chain-melting transition temperature, T(t), of phospholipid bilayer membranes on the position, n(u), of the cis double bond in the glycerophospholipid sn-2 chain can be described by an expression of the form T(t) = T(t)(c)(1 + h'(c)|n(u) - n(c)|)/(1 + s'(c)|n(u) - n(c)|), where n(c) is the chain position of the double bond corresponding to the minimum transition temperature, T(t)(c), for constant diacyl lipid chain lengths. This implies that the incremental transition enthalpy (and entropy) contributed by the sn-2 chain is greater for whichever of the chain segments, above or below the double-bond position, is the longer. The critical position, n(c), of the double bond is offset from the center of the sn-2 chain by an approximately constant amount, deltan(c) approximately 1. 5 C-atom units. The dependence of the parameters T(t)(c), h'(c), and s'(c) on sn-1 and sn-2 chain lengths can be interpreted consistently when allowance is made for the chain packing mismatch between the sn-1 and sn-2 chains. The length of the sn-2 chain is reduced by approximately 0.8 C-atom units by the cis double bond, in addition to a shortening by approximately 1.3 C-atom units by the bent configuration at the C-2 position. Based on this analysis, a general thermodynamic expression is proposed for the dependence of the chain-melting transition temperature on the position of the cis double bond and on the sn-1 and sn-2 chain lengths. The above treatment is restricted mostly to double-bond positions close to the center of the sn-2 chain. For double bonds positioned closer to the carboxyl or terminal methyl ends of the sn-2 chain, the effects on transition enthalpy can be considerably larger. They may be interpreted by the same formalism, but with different characteristic parameters, h'(c) and s'(c), such that the shorter of the chain segments makes a considerably smaller contribution to the calorimetric properties of the chain-melting transition.

Interplay of Unsaturated Phospholipids and Cholesterol in Membranes: Effect of the Double-Bond Position

“…When the double-bond position is moved from the middle of the chain toward the lipid head group, the average area per PC is reduced as well, but now the reduction is substantially smaller, ;0.007 nm 2 , close to the margin of error (60.003 nm 2 ). Nonetheless, it is clear that A PC has a maximum when the double bond resides in the middle of an acyl chain, in line with experiments (18) indicating that the main transition temperature is smallest when the double bond is located in the middle of the chain. Comparison with experimental values shows good agreement: Petrache et al (42) obtained an average area per lipid of 0.66 nm 2 at 338 K for a DSPC bilayer (0.670 nm 2 in our simulations), and x-ray data for a fully hydrated DOPC bilayer provides a range of 0.721-0.725 nm 2 for the area per lipid (43-46) (0.731 nm 2 6 0.003 nm 2 in our simulations).…”

“…Those studies showed that ordering within a membrane was weakest when the double bond was located in the middle of an acyl chain. For comparison, other experiments have shown (18) that the main transition temperature of single-component lipid bilayers with monounsaturated acyl chains has a minimum when the double bond resides in the middle of the hydrocarbon chain, indicating that membrane order is minimized under those conditions. Both simulations and experiments therefore support the view that by favoring monounsaturated acyl chains with a double bond in the middle of a chain, nature promotes membrane fluidity.…”

Sugar‐based tertiary amino gemini surfactants with a vesicle‐to‐micelle transition in the endosomal pH range mediate efficient transfection in vitro

“…Unfortunately, time did not allow measurement of γ vs. pH curves for compound 9 (oleyl analogue). However, it has been observed [49,50] that amphiphiles with unsaturated alkyl tails have analogous aggregation behaviour to saturated compounds containing 2–4 fewer methylene units. We therefore expect the pH c of compound 9 to lie within the endosomal range.…”

Mammalian phospholipid homeostasis: Homeoviscous adaptation deconstructed by lipidomic data driven modelling

“…The position of the cis unsaturation and branching in the chain has an effect on the T m value as does the individual headgroup i.e. phosphatidylethanolamine (PE) or phosphatidylcholine (PC) (Cevc, 1991;Marsh, 2013Marsh, , 1999, however the introduction of a single unsaturation into a saturated chain causes one of the biggest changes to T m and membrane order. Thus the ratio sats/unsats accounts for the major structural contribution of each individual compositional lipid species to the mixed membrane order parameter.…”