Use of molecular dynamics simulations to estimate the solubility of menadione in supercritical CO2 using Chrastil's model

- A force field for menadione was developed to represent the system menadione in CO2.
- NVT simulations were performed in order to understand menadione-CO2 interaction.
- MD simulation was used to estimate the parameters k and ΔH of the Chrastil equation.
- A steric effect by the methyl group affects the interaction menadione-CO2.
- Menadione association was observed in the binary system.

The binary system of menadione in explicit supercritical carbon dioxide (SC-CO2) was studied using molecular dynamics (MD) simulations, with the objective to understand the nature of interactions between menadione and SC-CO2 at different temperatures and pressures in order to complement experimental solubility measurements. A force field was developed for menadione and tested by comparing computed and experimental monoclinic crystal structures at 283 K and 0.01 MPa. Lattice parameters obtained from anisotropic isothermal-isobaric MD simulations agreed reasonably well with experimental values, with an average absolute relative deviation (AARD%) less than 7%. A previously validated force field for SC-CO2 was used, and simple mixing rules were used to describe cross interactions. Canonical ensemble MD simulations were used to estimate the association number for CO2 about menadione and the enthalpy required to form a SC-CO2 solvate complex with menadione as a function of temperature and CO2 density. Spatial distribution functions were computed to better understand the nature of the molecular-level interactions between menadione and SC-CO2 as well as between associating menadione molecules. This work is the first part of a study that uses MD simulations as the main tool to represent a binary system. The MD methodologies of this work will be applied to represent our future studies of menadione derivatives in SC-CO2.