Structural and Vibrational Study of Species Derived from Non-Steroidal Anti-inflammatory Agent Piroxicam Using DFT and Harmonic Force Fields Calculations

Abstract

In this investigation, structures of freebase or neutral, anionic, cationic and zwiterionic species of non-steroidal anti-inflammatory piroxicam agent have been optimised in gas phase and aqueous solution by using B3LYP/6-311++G** calculations in order to predict structural, electronic, topological and vibrational properties for all the species. The solvation energies follow the tendency: cation > anion > zwitterion > neutral. The neutral species presents low hydration and higher stabilities in both media. The frontier orbitals studies show that the reactivity increase according the following order: neutral < cation < anion < zwitterion, thus, the zwitterion is the most reactive species in both media. Very good concordances between experimental and theoretical 1H- and 13C-NMR, IR, Raman and ultraviolet spectra. Complete assignments of all the species and their scaled internal force constants are reported the scaled quantum mechanical force field (SQMFF) methodology.