Insights into the effect of combustion-generated carbon nanoparticles on biological membranes: a computer simulation study.

Classical molecular dynamics simulations of atomistic models of combustion-generated carbon nanoparticles and lipid bilayers have been performed to explore their possible structural, dynamical, and thermodynamic effects on biological membranes. The DREIDING generic force field is used for the carbonaceous nanoparticles of different morphologies, as produced from combustion sources, and the united atom model was employed for the dimyristoylphosphatidylcholine (DMPC) bilayer. It is observed that particle shape and structure have significant effects on solvation, mobility, adsorption, and permeation behavior of the particles. While combustion-generated carbon nanoparticles with an aspect ratio close to unity prefer to stay near the membrane center, precursors with other shapes mostly reside within the hydrocarbon tail region of the membrane. Carbon nanoparticles are not trapped in a local region even inside the membranes but move freely with a speed depending on their molecular weight. The adsorption of the particles on the surface of the biological membrane is comparable to thermal fluctuations because the weak segregation effect by water molecules is the main driving force to the adsorption behavior. The bigger the precursors are, the stronger they are bound to the membrane surface. The presence of combustion-generated nanoparticles inside the membrane perturbs local lipid density by pushing the neighboring lipid molecules away from the nanoparticles. This, coupled with thermal fluctuations, can induce an instantaneous membrane pore to allow water protrusion. From the umbrella sampling method, the potential of mean force for the permeation of carbona nanoparticles into the bilayer was also obtained. Surprisingly, elongated particles have a free energy barrier an order of magnitude smaller compared with more round ones. In addition, the round carbon nanoparticles showed strong hysteresis due to the local trapping of water molecules. Although the carbon soot precursors studied in this work are not the well-known carbon nanoparticles such as fullerenes or carbon nanotubes, the qualitative features of this study may be applicable to them as well.