Solvent effect on the solubility and absorption spectra of meloxicam: experimental and theoretical calculations

The solubility and absorption spectra of meloxicam (MLX) in 18 pure solvents were determined. In addition, molecular modelling calculations were performed. MLX presents the lowest solubility in water and the highest in dioxane. The results indicate that the polarity/polarisability of the solvent, and the Hildebrand’s solubility parameter, have a greater influence on its solubility. The MLX absorption spectra show that a redshift occurs when the solvent polarity increases. By applying Kamlet-Taft and Catalán methods it has been suggested that the solvent polarisability is the most important solvent´s parameter in the solvatochromism of MLX. The electronic transitions were determined using the TD-DFT methodology with the B3LYP, PBE0 and LC-wPBE functional. The best results were obtained with PBE0. Also, it was determined that the main MOs responsible for the electronic transition are HOMO → LUMO with a ππ* character with a significant intraligand charge transfer from the thiazole to the oxycam group.