On the diffusion of ketoprofen and ibuprofen in water: An experimental and theoretical approach

In view of its importance for the development of dispersion and distribution models in the environment and also for the design of removal methods from wastewaters, the mobility and solute-solvent interaction in aqueous solutions of two non-steroidal anti-inflammatory drugs (ketoprofen and ibuprofen) were studied by measuring mutual diffusion coefficients of each pharmaceutical in water at infinitesimal concentration as a function of temperature, using the Taylor dispersion method. Intra-diffusion coefficients of the same solutes in water at the same temperature range were also calculated by Molecular Dynamics simulations. The analysis of the simulation trajectories allowed the study of the structure of the solvent molecules around the solute and their mutual interaction, which was also addressed by quantum mechanical (DFT) calculations. Ibuprofen presents a higher mutual diffusion coefficient in water than ketoprofen and molecular dynamics simulations are able to predict the experimental values for two solutes. Besides the solute molecular weight and molecular dimensions, the diffusion coefficients of these two pharmaceuticals are influenced by the solute-solvent interactions, which seem to be stronger in the case of ketoprofen. The solvation free energy obtained via DFT calculations confirms that hypothesis