Thermodynamic Characterization of the Dimerization of an Anionic Perylene Bisimide Dye Using Molecular Simulation

Abstract

The thermodynamic signature of dimerization of an anionic di(glycyl) perylene bisimide derivative in aqueous solution is characterized using molecular dynamics simulations in explicit solvent with the aim of determining the impact of temperature, pressure, and solvent composition on the free energy of aggregation and its enthalpic and entropic contributions. The change in free energy varies only weakly with temperature independent of whether the solvent consists of pure water, an aqueous ethanol/water mixture, or an aqueous solution of sodium chloride. In agreement with experimental findings, the addition of ethanol weakens the interactions between the solute molecules, whereas the addition of sodium chloride leads to more stable aggregates. The temperature dependence of the potential of mean force can be accurately described using a simple expression derived from thermodynamic perturbation theory of first order. Molecular driving forces are discussed in terms of solute–solute and solute–solvent interactions.