Charge-transfer complexes of hypoglycemic sulfonamide with π-acceptors: Experimental and DFT-TDDFT studies

Abstract

Charge-transfer interactions (CT) between the electron donor gliclazide (GLC) and the π-acceptors 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tetracyanoethylene (TCNE) were studied in a chloroform solution and in the solid state. The CT complexes were discussed in terms of formation constants (KCT), molar extinction coefficients (εCT), standard reaction quantities (ΔG°, ΔH°, and ΔS°), oscillator strength (f), transition dipole moment (μEN), and ionization potential (Ip). The limits of detection (LOD) and limits of quantification (LOQ) have also been reported. The stoichiometry of these complexes was found to be in a 1:1 M ratio. The formed solid CT complexes were also synthesized and characterized using electronic methods, FT-IR, 1H and 13C NMR spectroscopy. Thermogravimetric analysis techniques (TGA/DTA) and differential scanning calorimetry (DSC) were used to determine the thermal stability of the synthesized CT complex. The kinetic parameters (ΔG*, ΔH*, and ΔS*) were calculated from thermal decomposition data using the Coats-Redfern method. Moreover, density functional theory (DFT) studies are discussed for the charge transfer complex GLC-TCNE, using the B3LYP with 6–311++G (d, p) basis set. The harmonic vibrational frequencies were calculated, and the scaled values have been compared with experimental FT-IR spectra. The calculated 1H and 13C NMR chemical shifts using the GIAO method showed good correlations with the experimental data. The theoretical UV–visible spectrum of the compound and the electronic properties, such as HOMO and LUMO energies, were performed using the time-dependent (TD-DFT) approach with CAM-B3LYP, employing the 6–311++G (d, p) basis set, and good agreement with the theoretical and experimental UV–visible data was found.