Hansen approach versus COSMO-RS for predicting the solubility of an organic UV filter in cosmetic solvents

To widen the range of applications of solvents and particularly emerging sustainable solvents, tools are needed for the fast assessment of their solubilizing properties. Hansenʹs approach is the most popular one wherein solvents are described by 3 parameters corresponding to dispersion (δd), polar (δp) and hydrogen bonding (δh) interactions. The main methods to predict the values of Hansen solubility parameters are based on group contributions and thus fail in the description of complex molecules. Alternatively, the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) is a quantum chemical prediction model that considers molecules in their liquid state, allowing the estimation of a wide range of properties from the mere knowledge of the molecular structure, thus making a priori description of the solvent behavior. The performances of both methods are compared by investigating the solubilization of the UV-filter avobenzone in a series of cosmetic solvents. The coordinates (δd = 20.1 MPa½, δp = 9.5 MPa½, δh = 4.4 MPa½, R = 10.3 MPa½) of the Hansen solubility sphere of this key organic UV filter were experimentally determined, allowing the identification of its solvents and non-solvents in reasonable agreement with solubility values. The characterization of avobenzone thanks to the σ-profile of COSMO-RS provides reliable solubility predictions via the calculation of the chemical potential. In particular, the values predicted by this approach for very good solvents such as methylal and dimethyl isosorbide were found to be close to experimental values whereas they were outliers with the Hansen approach.