Enhanced water permeability across a physiological droplet interface bilayer doped with fullerenes

Abstract

We measure the water permeability across a physiological lipid bilayer produced by the droplet interface bilayer (DiB) technique. This lipid bilayer can be considered as physiologically relevant because it presents a lipidic composition close to human cell membranes. The measured water permeability coefficients across this lipid bilayer are reported as a function of the cholesterol concentration. It is found that the water permeability coefficients decreased with increasing cholesterol concentration, in agreement with the existing literature. And, consistently, the extracted corresponding activation energies increase with increasing cholesterol concentration in the lipid bilayer. Hence having demonstrated the robustness of the experimental system, we extend this study by exploring the influence of fullerenes on the water permeability of a physiological lipid bilayer. Interestingly, we observe a significant increase of the measured water permeability coefficients across this lipid bilayer for large fullerenes concentration. This enhanced permeability might be related to the conductive properties of fullerenes.

Fig. 1. (A) A DiB formed by two water droplets connected by a DOPC bilayer in squalene, and the associated contact angle θ. (B) Example of interfacial tension measurements of a water/oil–lipid mixture with the water pendant droplet method (blue square). The oil is squalene with a mixture of dissolved lipids (c ≈ 5 mg mL⁻¹), DOPC : DOPS : DOPE with 70 : 10 : 20 molar ratio and 40% cholesterol. In a second trace, plotted with red circles, is the same oil and lipid composition with 40 μg mL⁻¹ of fullerenes.

Fig. 2. (A) Time series of a DiB formed by 2 water droplets connected by a bilayer made of DOPC : DOPS : DOPE with 70 : 10 : 20 molar ratio and 40% cholesterol. The left droplet contains 100 mM of NaCl. At the start, the right droplet has a diameter equal to 0.6 mm. The timeframe between each picture is 303 s. The left droplet contains 100 mM of NaCl. (B) Fluorescent picture of a DiB, the fluorescent molecule Rho-DOPE is only visible in the oil phase. 40 μg mL⁻¹ of fullerene are also dissolved into the oily phase. No fluorescent molecules are visible in the droplets. (C) Image of the fluorescent bilayer observed with higher magnification. (D) Droplet shape analysis from the pictures in (A).

Fig. 3. (A) Arrhenius plot of the natural log of the permeability coefficient (P_f) versus the reciprocal of absolute temperature of membranes of DOPC : DOPS : DOPE (70 : 10 : 20 molar ratio) membranes, with different cholesterol concentrations: 0%, 20%, 40%. (B) Arrhenius plot of the natural log of the permeability coefficient (P_f) versus the reciprocal of absolute temperature of DOPC : DOPS : DOPE (70 : 10 : 20 molar ratio) membranes, with 40% cholesterol and doped with fullerenes at different concentrations.