ABSTRACT
The effect of water content on the static and dynamic properties of the deep eutectic solvent glyceline is studied using molecular dynamics (MD) simulations. Static properties are additionally calculated using the PC-SAFT equation of state. Force fields calibrated on water-free glyceline show predictive power for density and water activity over the entire composition range. In contrast, the PC-SAFT approach using pseudo one-component or two-component modelling strategies performed better for the density or the water activity, respectively. The MD simulations show that at low water content, the hydrogen-bond network between glycerol molecules as well as between glycerol and the cholinium cation is hardly affected by the water molecules while at higher water content, glycerol-glycerol hydrogen bonds are replaced by glycerol-water hydrogen bonds indicating the formation of an aqueous solution accompanied by a strong decrease of the shear viscosity. At the same time, the thermodynamic activity of water increases such that the MD simulations are able to guide the optimal composition with respect to requirements in biocatalytic applications such as low viscosity and low water activity. The combined application of PC-SAFT to efficiently predict static properties and molecular dynamics simulations to predict static and dynamic properties offers a powerful framework in solvent design applications.
ABSTRACT
Five molecular models for trimethylamine N-oxide (TMAO) to be used in conjunction with compatible models for liquid water are evaluated by comparison of molecular dynamics (MD) simulation results to experimental data as functions of TMAO molality. The experimental data comprise thermodynamic properties (density, apparent molar volume, and partial molar volume at infinite dilution), transport properties (self-diffusion and shear viscosity), structural properties (radial distribution functions and degree of hydrogen bonding), and dielectric properties (dielectric spectra and static permittivity). The thermodynamic and transport properties turned out to be useful in TMAO model discrimination while the influence of the water model and the TMAO-water interaction are effectively probed through the calculation of dielectric spectra.
