Effect of Chain Length on the Partition Properties of Poly(ethylene oxide): Comparison between MARTINI Coarse-Grained and Atomistic Models

The MARTINI coarse-grained beads are parameterized to match the partition coefficients of several organic molecules in different solvents. Here, we test the method when modeling the partitioning properties of poly(ethylene oxide) between solvents of different polarities. We show that, among the existing models, the latest model developed by Lee and co-workers [ Lee , H. ; Pastor , R. W. J. Phys. Chem. B 2011 , 115 , 7830 - 7837 ] is the one that most successfully reproduces the hydration free energy of short oligomers, although it predicts highly negative solvation free energies in octanol and hexane. We develop a new CG model matching the solvation free energy of the monomer in different solvents and propose a simple method to select the Lennard-Jones parameters that reproduce the desired partition coefficients. The model correctly reproduces water/hexane partition properties for oligomers up to 10 monomers but still suffers from a transferability problem for larger molecular weight.