Influence of Lipid Composition on the Insertion Process of Glyphosate into Membranes: A Thermodynamic Study

In this work, molecular dynamics simulations were applied to investigate the influence of lipid composition of the model membrane on the insertion of glyphosate (in its charged state, GLYP^2-). The profiles of free energy, entropy and enthalpy were obtained through umbrella sampling calculations, for lipid bilayers composed by only 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC), only 1,2-dipalmitoyl-sn-glycerol-3-phosphoserine (DPPS) or a symmetric binary mixture of DPPC and DPPS. In general, the location, the values of minima and maxima of the free energy, and the trend of free energy profiles are influenced by the lipid composition of the lipid bilayer. The driving force in the glyphosate insertion process depends on the lipid composition of the membrane model. If the lipid bilayer is composed solely of DPPS or DPPC, GLYP^2- insertion is driven by a favorable enthalpic change. However, if the membrane is composed of a mixture of both lipids, this process is driven by a favorable entropic change. In the lipid bilayer containing DPPS, the glyphosate was found to penetrate hydrated and coordinated with Na⁺ ions, in contrast to the pure zwitterionic lipid bilayer which penetrated only hydrated. This effect is independent of the concentration of sodium ions present in the bulk solution.