Force field parametrization of hydrogenoxalate and oxalate anions with scaled charges.

Models of the hydrogenoxalate (bioxalate, charge -1) and oxalate (charge -2) anions were developed for classical molecular dynamics (CMD) simulations and parametrized against ab initio molecular dynamics (AIMD) data from our previous study (Kroutil et al. (2016) J Mol Model 22:210). The interactions of the anions with water were described using charges scaled according to the electronic continuum correction approach with rescaling of nonbonded parameters (ECCR), and those descriptions of anion interactions were found to agree well with relevant AIMD and experimental results. The models with full RESP charges showed excessively strong electrostatic interactions between the solute and water molecules, leading to an overstructured solvation shell around the anions and thus to a diffusion coefficient that was much too low. The effect of charge scaling was more evident for the oxalate dianion than for the hydrogenoxalate anion. Our work provides CMD models for ions of oxalic acid and extends previous studies that showed the importance of ECCR for modeling divalent ions and ions of organic compounds. Graphical abstract The radial distribution function between a water oxygen (Ow) and an oxygen of the oxalate dianion (Ox) significantly improved when scaled charges were applied to the anion.