Poly(vinyl alcohol) oligomer in dilute aqueous solution: a comparative molecular dynamics simulation study.

Molecular dynamics (MD) simulations of a poly(vinyl alcohol), PVA, oligomer in very diluted aqueous solution have been carried out, at the 2-fold aim to investigate structural and dynamical features of this system and to comparatively test the robustness of G45A3 and G45A4 GROMOS force fields in modeling PVA in aqueous environment. An atactic PVA chain of 30 repeating units in water at concentration of 3% (w/w) has been simulated at 293, 303, and 323 K. The trajectory analysis has focused on the temperature influence on chain size, conformational properties and intramolecular hydrogen bonding of PVA. The PVA-water interaction and the polymer induced modifications of water properties have been also investigated. Simulation results have been compared with available experimental data on PVA aqueous solutions, in order to evaluate the reliability of these force fields in the MD simulation of PVA-based systems in aqueous environment. Findings obtained from the simulations with the G45A4 force field have shown a better agreement with experimental results and have highlighted peculiar structural and dynamical characteristics of PVA in dilute aqueous solution. In particular, the simulation has shown a heterogeneity in the overall chain structure, not affected by temperature, and the absence of intrachain hydrogen bonds between nonadjacent residues. The trajectory analysis has revealed that the polymer influence on water structure and dynamics involves about six water molecules per PVA residue.