Oxicams: Computational thermochemical parameters and solubility

The following eight oxicam structures were studied using theoretical methods, (DFT), and the Gaussian 09 program in the gaseous and aqueous phases: 4-meloxicam, droxicam, isoxicam, lornoxicam, meloxicam, normeloxicam, piroxicam, and tenoxicam. More specifically, the thermodynamic parameters, polarizability, and dipole moments of each molecule were studied. Molecules with higher amounts of unsaturated bonds and phenyl groups in their structures show increased electron delocalization, thereby increasing the diffusion of the electron clouds. 4-meloxicam, isoxicam, meloxicam, piroxicam, and normeloxicam presented μ values that equaled 2.8965, 3.2664, 2.1138, 2.6692, and 3.9705 Debye, respectively, and all of them share a formation of hydrogen bridges and lower values due to the dispersion of their charges as demonstrated by an increase in polarizability values. Furthermore, we observed that with an increasing solvent dielectric constant, the dipole moment of the molecules under study, both of which do not form hydrogen bonds, also increases. These increments are mainly seen in protic solvents, followed by aprotic solvents from most to least ε.