Effects of Fullerenes on Phospholipid Membranes: A Langmuir Monolayer Study

We investigate two‐component Langmuir monolayers of dipalmitoylphosphatidylcholine (DPPC)/C60 by recording surface pressure/area (π/A) and surface potential/area (ΔV/A) isotherms and by direct Brewster angle microscopy (BAM) imaging. Atomic force microscopy (AFM) is employed to study morphologies of the mixed monolayers transferred to a solid substrate by the Langmuir–Blodgett technique. C60 is shown to have little influence on isotherms of the DPPC/C60 monolayers even at a molar fraction as high as XC60=0.3. The elastic modulus (Cₛ- 1 ) versus π curves of the DPPC/C60 monolayers almost overlay each other, as well as that of pure DPPC, that is, the elasticities of pure DPPC monolayers and DPPC/C60 monolayers are remarkably similar. AFM studies reveal that fullerene flocs form at low surface pressures (π≤15 mN m−1), are gradually disaggregated and dispersed in the DPPC monolayer with increasing surface pressure up to 35 mN m−1, and are then progressively squeezed out to form protruded islands as the surface pressure increases up to 65 mN m−1. Our work provides experimental support to the computational result that C60 can dissolve in lipid bilayers without significantly compromising their mechanical properties, a finding which has important implications for the toxicity and development of drug vehicles from fullerene materials.