Physicochemical studies on proton transfer reaction between methyl[5-(propylthio)-1H-benzoimidazole-2-yl]carbamate (albendazole, ABZ) with 2,4,6- trinitrophenol (picric acid, PA) in chloroform

Abstract

In this study, a new proton transfer complex between albendazole drug (ABZ), methyl [5-(propylthio)-1H-benzoimidazole-2-yl]carbamate and picric acid (PA) has been synthesized and characterized in chloroform and solid state by different physicochemical methods. In chloroform, the proton transfer complex exhibited an absorption maxima at 409 nm. In addition, the complex was formed in a 1:1 molecular composition. The formation constant, spectroscopic physical parameters and enthalpy of formation confirmed that, the formed complex has high stability. The solid-state complex was also found in a 1:1 stoichiometric ratio from elemental analysis and was isolated as yellow crystals. Changes in vibrational mode wavenumbers and chemical shifts in infrared and 1H NMR spectra were found in comparison with the reactants, confirming the complex formation. Furthermore, TG/DTA analysis provided information about changes in material properties as a function of temperature. Density functional theory (DFT) at B3LYP/6-31G (d,p) level of the theory was employed to support the experimental results. The optimized structures of reactants and the new complex, their geometrical parameters, reactivity parameters, molecular electrostatic potential maps (MEP) and natural atomic charges from natural bond orbital (NBO) analysis were calculated. It has been concluded from the investigated computational analysis that the presence of many hydrogen bonds in the formed complex beside charge transfer interaction are certainly responsible for its high stability. Time-dependent functional theory (TD-DFT) at the same was applied to explain the origin of the recorded electronic transition in chloroform. A good consistency was found between experimental and theoretical results.