Abstract
Charge transfer (CT) complexes have great scientific importance because they include wide applications in different fields, one of the most essential of these applications is to determine the activity of pharmacological compounds. CT complexes between the donor piroxicam and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and chloranilic acid (ChA) as electron acceptors have been studied and characterized both experimentally and theoretically. Herewith we aimed to determine the stability of the expected structure of the formed piroxicam complexes for the first time. Several analytical tools (FTIR, NMR, mass spectrometry, UV-Visible spectroscopy and conductometric analysis) were applied to characterize these complexes. The stoichiometry of the examined complexes was assessed using Job's method and Benesi-Hildebrand equation, and a molar ratio of 1:1 between the donor and acceptors were resulted from these complexes. The physical parameters of the formed CT-complexes were determined by calculations of formation constant, molar absorptivity, oscillator strength, dipole moment, ionization potential, CT energy, resonance energy, dissociation energy, and standard free energy of complexation. In addition, the UV-Vis spectra and CT transition properties of these complexes were computationally determined with DFT and TD-DFT methods. The results confirmed that these complexes are CT complexes. The current study shows that the complexes formed are stable and can be used for the determination of piroxicam in pharmaceutical form.