Molecular structure simulation of (E)-2-(butan-2-ylidene) hydrazinecarbothioamide using the DFT approach, and antioxidant potential assessment of its complexes

Abstract

The molecular structure of (E)-2-(butan-2-ylidene)hydrazinecarbothiomide (2-butanone thiosemicarbazone) was validated by density functional theory (DFT) calculations. The characterization of the ligand was done using various spectroscopic techniques. Four transition metal complexes were prepared with the ligand and their antioxidant activity was tested. Molecular docking studies of the complexes were also performed against nicotinamide adenine dinucleotide phosphate (NADPH) and myeloperoxidase (MPO). Structure validation of the ligand was done in Gaussian 09 software. The geometry optimization was done at B3LYP/6-31G++(d,p) level. The 1H and 13C NMR chemical shifts, FT-IR vibrations and UV–visible transitions were validated with the help of theoretical calculations. The frontier molecular orbital analysis, molecular electrostatic potential (MEP) and global reactivity descriptors were calculated to predict the stability of the molecule. Non-linear optical (NLO) properties were assessed and compared with urea. Natural bond orbital (NBO) analysis was done to predict the stability of the ligand resulting from hyper conjugative interactions and electron delocalization. Molecular docking studies of the complexes were performed with iGEMDOCK 2.1 and AutoDock 4.2.6.Antioxidant potential was assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH) Assay. 1H and 13C correlation coefficients (R2) were 0.9964 and 0.9974 respectively. In case of FT-IR, the correlation coefficient (R2) was 0.9984. [Fe(C5H11N3S)2(SO4)] possessed maximum antioxidant potential followed by [Cu(C5H11N3S)2(SO4)]. Molecular docking findings suggested that the Fe complex released the minimum binding energy. Computational structure validation is an important aspect in finding a lead moiety. The theoretical spectral findings correlated well with the experimental findings in the present study. The metal complexes showed appreciable antioxidant potential as predicted by the computational and experimental findings. The ligand possessed better NLO properties than urea.