A coarse-grained model for polyethylene glycol in bulk water and at a water/air interface

Abstract

Publisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. A coarse-grained model for polyethylene glycol (PEG) in water has been developed using a combination of the iterative Boltzmann inversion (IBI) methodology and a suitable coarse-grained water potential. The combined coarse-grained model is shown to be effective in reproducing the properties of single chains in bulk water and multiple chains across a series of chain lengths and concentrations, and is transferable to PEG chains at a water/air interface. Good agreement is achieved with both experiment and reference atomistic simulations in an explicit solvent. Simulations of a single chain in aqueous solution yield a molecular weight (M W )-radius of gyration (R g ) relation that compares favourably with the reported scaling law from experiment. Simulations of multiple chains across a wide concentration range show no concentration dependence of R g , in agreement with previous atomistic simulations. The model we develop is shown to be transferable between polymer in bulk water and at a water/air interface. For interfacial simulations, PEG chains are found to spontaneously migrate to the surface and adsorb to form a thin surface layer, which thickens with increasing surface concentration. The point at which the surface is fully saturated with polymer, and the polymer layer thicknesses obtained from simulations, are both in good agreement with experimental findings. At high surface concentrations, when the surface is fully saturated with polymer, ethylene oxide (EO) segments are found to extend into the water subphase as loop and tail conformations, with this extension increasing with further increases in the surface concentration.The coarse-grained model is noted to provide very large increases in simulation speed, with equilibration times of < 1000× the reference atomistic models. We also consider a number of different coarse-grained models for water in this study, showing that the CSJ model adopted in this work [Chiu et al., J. Chem. Theory Comput. 2010, 6, 851] is far superior for studying water at a water/air surface, than many of the previous coarse-grained models of water.

A coarse-grained model for polylactide: glass transition temperature and conformational properties

“…A set of CG potentials was derived by successively adjusting the different potential contributions in the order of their relative strengths, which are U stretch , U bend , U nonbonded , and U dihedral . Choosing this order is the most efficient way for obtaining CG potentials with the IBI technique since it has been shown from the previous works that the intramolecular degree of freedoms can be treated almost independently from intermolecular ones [22,36,37]. Figure 2 shows an excellent match of the bond-, angle-and dihedral angle distributions.…”

Easy creation of polymeric systems for molecular dynamics with Assemble!

“…Examples include the study of interactions of polymers with single-walled carbon nanotubes [3,4], the prediction of solubility of pharmaceutical compounds in polymeric carriers [5] and the study of structure and mechanics of glassy polymers [6]. Moreover, by exploiting coarse graining potentials, polymer simulation studies have been brought to a mesoscale level [7,8,9,10].…”

Multiscale approach for the construction of equilibrated all-atom models of a poly(ethylene glycol)-based hydrogel

“…Moreover, while previous molecular modeling studies have been reported for polymer hydrogels using all-atom models, [13][14][15][16][17][18] CG models, [19][20][21][22][23]28,31,33,[36][37][38][39][40] and lattice models, [24][25][26][27] each of these individual methods has its own unique limitations. As an approach to overcoming the limitations of each individual method, composite modeling schemes have been devised to bridge models at different levels in order to generate wellrelaxed atomistic models.…”

“…Numerical schemes have also been developed specifically for PEG-based systems; examples include studies of the conformation and hydrodynamics of PEG, 28 the interfacial properties of PEG surfactant/water, [30][31][32] PEG-contained proton exchange membranes, 22 PEG-lipid systems, 29 and the development of kinetic models to predict growth, cross-link density profiles, and the level of ligand incorporation for PEG hydrogels. 33 Molecular simulations have also been recently conducted to study the behavior of an individual peptide-polymer a) Electronic mail: latourr@clemson.edu conjugated chain to examine the influence of the polymer backbone on the conformation of a tethered peptide chain.…”

“…33 Molecular simulations have also been recently conducted to study the behavior of an individual peptide-polymer a) Electronic mail: latourr@clemson.edu conjugated chain to examine the influence of the polymer backbone on the conformation of a tethered peptide chain. 34,35 Most of the recent CG simulations [19][20][21][22][23]28,31,33,[36][37][38][39][40] for PEG-based systems have been carried out using the MARTINI CG force field method, 41,42 with the CG parameters developed by mapping from the results of atomic simulations based on class I force fields, such as CHARMM, 28,33 GROMACS, 36 and optimized potentials for liquid simulations. 37,38 In contrast, the all-atom polymer consistent force field (PCFF), [43][44][45][46] which is a class II force field, has been specifically parameterized for the simulation of synthetic polymeric materials, and may provide coverage of polymer functional groups that are not presently available in many of the class I force fields.…”