Molecular Dynamics Study of a Polymeric Reverse Osmosis Membrane
Edward Harder*, D. Eric Walters**, Yaroslav D. Bodnar+, Ron S. Faibish#,+, and Benoit Roux#,*
Department of Biochemistry and Molecular Biology, Center for Integrative Science, University of Chicago, Illinois, 60637
Chicago Medical School, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois, 60064
Nuclear Engineering Division, Argonne National Laboratory, Argonne, Illinois, 60439
In this paper, authors have presented an interesting molecular dynamics simulation of synthesizing polymeric reverse osmosis membrane. Though, chemical bond breaking and formation is not an automatic operation of an MD simulation, yet a heuristic approach has been presented which makes the bond formation and breaking processes possible in MD simulation.
Force field parameters for trimesoylchloride (TMC) and m-phenylenediamine (MPD) were built using generalized assisted model builder with energy refinement (AMBER) force field (GAFF). Partial charges on atoms and topology for the monomers were generated with ANTECHAMBER which is a part of AMBER package with AM1BCC partial charge method. The monomers and the partial charges on atoms are shown in figure 1. For simulation of water molecules, TIP3P water model was employed. The system consisted of 250 TMC and 250 MPD in simulation box with each side 61.3 Å and no water molecules were included in the initial assembly. After each 1000 steps of MD simulation, each side of box was reduced by 0.5 Å to get the target density of 1.3 g/cm3. CHARMM molecular simulation pacakge was used to run the simulation. The bond formation was carried out in steps. In first step, the amide links were formed between carbon of TMC and nitrogen of MPD with a distance criterion of 3.5 Å after 1 ps interval. In the next run, the distance criterion was changed to 6.5 Å and the membrane was formed in this way.
Amide bond order for individual monomers at each stage of simulation is shown in table 1. Finally, water flux simulation was carried out and a water box with the same x and y dimensions as those of membrane was constructed. The diffusion constant of water was found to be 5.1 x 10-5 cm2/s.
Reviewer: Aamir Alaud Din