Perfluorooctanoic acid rigidifies a model lipid membrane

We report a combined dynamic light scattering and neutron spin-echo (NSE) study on vesicles composed of the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine under the influence of varying amounts of perfluorooctanoic acid. We study local lipid bilayer undulations using NSE on time scales up to 200 ns. Similar to the effect evoked by cholesterol, we attribute the observed lipid bilayer stiffening to a condensing effect of the perfluorinated compound on the membrane.

Figure 1

Relaxation rate ${\Gamma }_d$ vs $q^2$ for vesicles composed of DMPC and DMPC/PFOA (5 mol %). Linear fits yield the vesicle center-of-mass diffusion constant D.

Figure 2

(a) Normalized intermediate scattering function $S(q,t)/S\left(q\right)$ for DMPC (30 ${}^{\circ }$C) at $\lambda =10$ Å. Single-exponential fits yield the relaxation rates ${\Gamma }_f\left(q\right)$; (b) the effective diffusion constant $D_f^{\mathrm{eff}}\left(q\right)={\Gamma }_f\left(q\right)/q^2$ exhibits a $q$ dependence, indicating further dynamics.

Figure 3

Normalized intermediate scattering functions $S(q,t)/S\left(q\right)$ for DMPC (30 ${}^{\circ }$C): (a) $q$ range covered at $\lambda =17$ Å. (b) Combined fit according to Eq. (2); single contributions are indicated by dotted lines.

Figure 4

Bilayer undulations: (a) Relaxation rate ${\Gamma }_u$ vs $q^3$, for DMPC and DMPC/PFOA. Linear fits yield the concentration-dependent bilayer bending rigidity $\kappa$ shown in (b).