Microscopic Structure and Solubility Predictions of Multifunctional Solids in Supercritical Carbon Dioxide: A Molecular Simulation Study

Abstract

Molecular dynamics simulations were employed to both estimate the solubility of nonelectrolyte solids, such as acetanilide, acetaminophen, phenacetin, methylparaben, and lidocaine, in supercritical carbon dioxide and understand the underlying molecular-level driving forces. The solubility calculations involve the estimation of the solute's limiting activity coefficient, which may be computed using conventional staged free-energy calculations. For the case of lidocaine, wherein the infinite dilution approximation is not appropriate, we demonstrate how the activity coefficient at finite concentrations may be estimated without additional effort using the dilute solution approximation and how this may be used to further understand the solvation process. Combining with experimental pure-solid properties, namely, the normal melting point and enthalpy of fusion, solubilities were estimated. The results are in good quantitative agreement with available experimental data, suggesting that molecular simulations may be a powerful tool for understanding supercritical processes and the design of carbon dioxide-philic molecular systems. Structural analyses were performed to shed light on the microscopic details of the solvation of different functional groups by carbon dioxide and the observed solubility trends.

Application of MOSCED To Predict Limiting Activity Coefficients, Hydration Free Energies, Henry’s Constants, Octanol/Water Partition Coefficients, and Isobaric Azeotropic Vapor–Liquid Equilibrium

“…In the context of classical molecular simulation free energy calculations, we have shown previously that the solvation free energy of a solute (component 2, Δ G 2 solv ), or equivalently the residual chemical potential at infinite dilution, may be related to the limiting (or infinite dilution) activity coefficient of the solute as ,− where f 2 0 is the pure liquid fugacity of the solute. The pure liquid fugacity may be related to the solute “self”-solvation free energy (Δ G 2 self ) as At low pressures we may assume the vapor phase in equilibrium with the liquid phase at T is an ideal gas (such that the fugacity coefficient is unity) and the Poynting correction is negligible such that f 2 L ≈ p 2 sat , where p 2 sat is the (pure component) liquid saturation pressure .…”

Thermodynamic Analysis ofn-Hexane–Ethanol Binary Mixtures Using the Kirkwood–Buff Theory

“…Molecular simulations have proven to be a powerful tool for understanding the microscopic mechanisms underlying various physical phenomena − and for predicting several properties such as volumetric, , dynamical, − rheological, − thermodynamic, , and so on. However, a complete thermodynamic analysis of systems equilibrated using either molecular dynamics (MD) or Monte Carlo (MC) simulations is not a simple task.…”

Assessment of the SM12, SM8, and SMD Solvation Models for Predicting Limiting Activity Coefficients at 298.15 K

“…The solvation free energy in this context is defined as taking a solute from a non-interacting ideal gas state to solution at the same molecular density (or concentration). We have shown previously that the solvation free energy is readily related to the limiting activity coefficient (γ ∞ i,j ) as [24,[37][38][39][40][41][42]:…”