Geometry and molecular arrangement of phosphatidylcholine-montmorillonite bioclays via classical molecular dynamics simulation

Abstract

Inspired by nature, a class of new perspective materials (here referred to as bioclays) can be prepared by combining clay minerals with charged bioorganic moieties. Here we present a comprehensive computational study of a phosphatidylcholine-montmorillonite bioclay composite by employing a series of classical molecular dynamics simulations. Our detailed analysis of the structure and energies of the resulting bioclays reveals that the phosphatidylcholine molecules bind to the montmorillonite surface through their zwitterionic heads, forming layers with the aliphatic tails stretched preferably parallel to the montmorillonite surface. The tails exhibit varying degrees of flexibility and disorder depending on their distance from the surface and density of the surface coverage. The observed detachment of naturally occurring Na+ cations caused by the presence of the phosphatidylcholine zwitterionic heads suggests that cation-exchange is very likely the driving mechanism for the phosphatidylcholine adsorption on montmorillonite. Once the first layer of phosphatidylcholine forms (corresponding to a complete surface saturation, estimated as 0.1 μg cm−2), more molecules can still be attached and stabilized by the mutual phosphatidylcholine intermolecular interactions.