Predicting adsorption of organic chemicals at the air-water interface

The sorption capacity of the air-water interface for organic chemicals can easily be much larger than the bulk water or bulk air phase of small water droplets or air bubbles in water, respectively. Therefore, adsorption constants must be known in addition to the bulk air/water partition constants to assess the transport capacity of such small droplets or bubbles. Here the quantum-chemical-based software COSMOtherm is tested for its ability to predict air-water adsorption constants for a diverse set of more than 200 organic compounds. To this end, the free energies of adsorption that are received as model output are converted into adsorption constants based on a reference state of adsorption that is derived here. This approach can be shown to predict adsorption constants with a root-mean-square error of 0.6 log units for K values ranging over seven orders of magnitude. In addition, the model's ability to predict enthalpies of adsorption is demonstrated.