The journal of physical chemistry. B | 2019
Molecular Dynamics and Metadynamics Insights of 1,4-Dioxane Induced Structural Changes of Biomembrane Models.
1,4-dioxane is a cytotoxic B2 type human carcinogen, a serious water pollutant produced solely by industrial activity. The effect of 1,4-dioxane on phospholipid membrane models composed by DPPC and its branched isomer (IPPC) was investigated using MD simulations. Clear and polluted membranes were compared by membrane parameters such as APL, VPL, compressibility modulus, membrane thickness and orderliness of lipid tails. While neat systems significantly differ from each other, the presence of the pollutant has the same effect on both types of lipid membranes: high density of dioxane appears at the vicinity of ester groups which pushes away lipid headgroups from each other, leading to an overall change in lipid structure: APL and VPL grows, while the orderliness of lipid tails, membrane thickness and compressibility modulus decreases. Orientational preferences of water and dioxane molecules were also investigated and different membrane regions have been specified according to the stance of water molecules. Free energy profile for 1,4-dioxane penetration mechanism into DPPC membranes was carried out using metadynamics for two different concentrations of the pollutant (c1=7.51 g/dm3, c2=75.10 g/dm3), which showed that the higher the concentration is, the lower the free energy of penetration gets. Only a small free energy barrier was found in the headgroup region and accumulation of dioxane is thermodynamically unfavored in the middle of the bilayer. The penetration mechanism has been described in detail based on the orientational preference of 1,4-dioxane molecules and the free energy profiles.