Chain-length dependence of lipid bilayer properties near the liquid crystal to gel phase transition

Abstract

The temperature dependence of the mean orientational order parameter in the vicinity of the liquid crystal to gel phase transition is obtained from the first moment M1 of deuterium nuclear magnetic resonance spectra for bilayers of chain perdeuterated phosphatidylcholines with acyl chains of 12, 14, 16, and 18 carbons. The data clearly show an increasing temperature dependence of the orientational order parameter in the vicinity of the transition, with the effect becoming more pronounced with decreasing chain length. Assuming a linear relationship between the mean orientational order parameter and the extension of the acyl chain, estimates of the change in area of the membrane at the transition are shown to be consistent with those obtained from other measurements. It is shown that the transition may be modeled in terms of a Landau expansion of the free energy involving a small number of phenomenological parameters. From this it is shown that the behavior of these systems in the temperature range of interest is, in large part, controlled by the close proximity of a spinodal to the transition temperature.

Lipid Internal Dynamics Probed in Nanodiscs

“…Figure 5 depicts a schematic overview of the lipid‐phase order for both nanodiscs and liposomes. We found that the response of lipid dynamics to a temperature change crossing T m deviates in nanodiscs (Figure 5 C and D) from the classical picture found in liposomes in this study (Figure 5 A and B) and that reported in the literature 6, 33. Specifically, we observed that DMPC molecules in liposomes were in the gel phase below 20 °C and adopted a tilted position with respect to the bilayer normal,26, 42 with very tight packing (Figure 5 A).…”

“…Herein, we have compared the lipid dynamics in liposomes and nanodiscs below,a t, and above their gel-to-fluid-phase transition temperature, T m .F igure 5d epicts as chematic overview of the lipid-phase order for both nanodiscsa nd liposomes.Wefound that the response of lipid dynamics to at emperaturec hange crossing T m deviates in nanodiscs ( Figure 5C and D) from the classical picture found in liposomes in this study ( Figure 5A andB )a nd that reported in the literature. [6,33] Specifically,w eo bserved that DMPC molecules in liposomes were in the gel phase below 20 8Ca nd adopted at ilted position with respect to the bilayer normal, [26,42] with very tight packing ( Figure 5A). Lipids in nanodiscs, however,s till undergo axially symmetric motions with respect to the membrane normal; this indicates that even significantly below the phase transition temperature am ixture of fluid and gel-likep hases are present( Figure 5C).…”

Chain length dependence of anomalous swelling in multilamellar lipid vesicles

“…This model is supported by experimental evidence of an anomalous decrease in the elastic modulus close to the main transition [8]. The pseudocriticality of the main transition of multilamellar vesicles of phosphocholines with saturated fatty acid chains has been established through a variety of experiments and computer simulations [9][10][11][12][13][14], and it has also been shown using computer simulations and NMR a e-mail: stine@ruc.dk b e-mail: dorthe@ruc.dk that the pseudocritical behaviour is enhanced with decreasing chain length of the lipids [13,14]. A consequence of the bending renormalization model is therefore that the anomaly should increase with decreasing chain length.…”

“…In this study we instead follow the strategy of experimentally varying a parameter in one of the models, namely the proximity of the main transition temperature to a spinodal point. That is the system is approaching a critical point on the gel/liquid crystal coexistence curve as the lipid chain length is decreased, the lateral density fluctuations thus 88 The European Physical Journal E increasing [13,14]. We compare our experimental results with the predictions of the model of critical unbinding of the bilayers.…”

Cover Feature: Lipid Internal Dynamics Probed in Nanodiscs (ChemPhysChem 19/2017)

“…[6,33] Specifically,w eo bserved that DMPC molecules in liposomes were in the gel phase below 20 8Ca nd adopted at ilted position with respect to the bilayer normal, [26,42] with very tight packing ( Figure 5A). Lipids in nanodiscs, however,s till undergo axially symmetric motions with respect to the membrane normal; this indicates that even significantly below the phase transition temperature am ixture of fluid and gel-likep hases are present( Figure 5C).…”