Bending elasticity of saturated and monounsaturated phospholipid membranes studied by the neutron spin echo technique

Abstract

We have used neutron spin echo (NSE) spectroscopy to study the effect of bilayer thickness and monounsaturation (existence of a single double bond on one of the aliphatic chains) on the physical properties of unilamellar vesicles. The bending elasticity of saturated and monounsaturated phospholipid bilayers made of phospholipids with alkyl chain length ranging from 14 to 20 carbons was investigated. The bending elasticity κ(c) of phosphatidylcholines (PCs) in the liquid crystalline (L(α)) phase ranges from 0.38 × 10(-19) J for 1,2-dimyristoyl-sn-glycero-3-phosphocholine to 0.64 × 10(-19) J for 1,2-dieicosenoyl-sn-glycero-3-phosphocholine. It was confirmed that, contrary to the strong effect on the main transition temperature, the monounsaturation has a limited influence on the bending elasticity of lipid bilayers. In addition, when the area modulus K(A) varies little with chain unsaturation or length, the elastic ratios (κ(c)/K(A))(1/2) of saturated and monounsaturated phospholipid bilayers varies linearly with lipid hydrophobic thickness d which agrees well with the theory of ideal fluid membranes.

Adsorbed liposome deformation studied with quartz crystal microbalance

“…27,35 For instance, Tristam-Nagle et al 27 give κ ∼ 10 × 10 −19 J for the gel phase of DMPC, which is similar to the value obtained for DPPC in the same phase, as shown in Figure 4(a). 26 Third, we show in Figure 4(b) that the size of DMPC liposomes in solution (not adsorbed to a surface) increases with temperature.…”

“…The temperature dependence of the bending modulus in the P β phase has been reported by several investigators for DPPC and for DMPC. 26,29,35,36 The DPPC data illustrate this trend best; therefore, we compare our results with these data. The absolute values of the bending moduli in the gel phase vary, however: the values reported by Dimova et al 36 for DMPC reach ∼25-35 × 10 −19 J at ∼19…”

“…This is consistent with what we expect based on the CryoTEM results ( Figure 2). Second, in Figure 4(a), the equivalent film thickness h is plotted as a function of temperature together with the bilayer bending modulus for DPPC measured by Lee et al 26 and for DMPC measured by Yi et al 35 There is a clear correspondence between the behavior of the equivalent thickness and the bending modulus as a function of temperature: below the main transition temperature, when the lipid is in the P β phase, the bending modulus increases with decreasing temperature. 26,29,35,36 There is a corresponding increase in the equivalent thickness extracted from the QCM data.…”

“…Second, in Figure 4(a), the equivalent film thickness h is plotted as a function of temperature together with the bilayer bending modulus for DPPC measured by Lee et al 26 and for DMPC measured by Yi et al 35 There is a clear correspondence between the behavior of the equivalent thickness and the bending modulus as a function of temperature: below the main transition temperature, when the lipid is in the P β phase, the bending modulus increases with decreasing temperature. 26,29,35,36 There is a corresponding increase in the equivalent thickness extracted from the QCM data. Identifying the equivalent thickness with the height of the adsorbed liposomes, we explain the observed correspondence in terms of the effect of the bending modulus on the adsorbed liposome deformation: higher bending modulus (stiffer liposomes) leads to smaller deformation and larger equivalent thickness.…”

Lipid Bilayers and Membrane Dynamics: Insight into Thickness Fluctuations

“…However, the diffusion constant for such a large object (vesicle radius % 50 nm) of roughly 10 À12 m 2 =s, estimated from the Stokes-Einstein equation, is outside the NSE window. Thus, the theory of Zilman and Granek for the bending motion of a single membrane [29] should be applicable here and, as shown in previous studies of ULVs [30,31], À should scale as q 3 . As was the case for the previously studied surfactant system [17][18][19], the data for the fluid phase (above T m ) of the lipid systems shown in Figs.…”