Hydration behavior of protic ionic pair of methyl ammonium formate: A comparative molecular dynamics simulation study with their conjugate neutral forms

The structure and dynamics of methylammonium formate (MAF), methylamine (MA) and formic acid (FOR) in aqueous solution were investigated by employing classical molecular dynamics simulations. We explored the fundamental difference between charged and their corresponding conjugate neutral forms towards interactions with water molecules. Structural properties were investigated by calculating radial distribution functions, spatial distribution functions, and combined distribution functions. These properties reveal that water molecules approach the solutes in a specific direction. The hydrogen bonds formed by ionic species are stronger as compared to the neutral molecules. MA interacts through its nitrogen atom mainly whereas MAM interacts through its acidic hydrogen atoms. Dynamic properties were investigated by continuous and forward hydrogen bond lifetimes of all possible pairs as well as residence times calculated from respective autocorrelation functions. Dynamics become slow in ionic environments and profound differences in dynamics are found in case of concentrated solutions as compared to dilute solutions. © 2019 Elsevier B.V