Computational investigation of molecular structures, spectroscopic properties, cholinesterase inhibition and antibacterial activities of triazole Schiff bases endowed metal chelates

The aim of this project was to introduce novel bioactive compounds through the design and synthesis of two mono-Schiff bases, 4- [(5-amino-1H-1,2,4-triazol-3-yl)imino]methylbenzene-1,3-diol (L-1) and 2-[(5-amino-1H-1,2,4-triazol-3-yl)imino]methyl}-6-methoxyphenol (L-2) and one bis-Schiffbase, 2,2'-{1H-1,2,4-triazole-3,5-diylbis [nitrilomethylylidene]}bis(6-methoxyphenol) (L-3) together with their complexes of transition metals [VO(IV), Cr(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II)]. The molecular structures of as-synthesized Schiff bases were explicitly confirmed by physical, spectral, analytical and computational studies. Quantum chemical calculations based on density functional theory (DFT) were performed at B3LYP/6-311+G(d.p) level to explore the optimized geometrical structures, molecular electrostatic potential (MEP), Mulliken atomic charges (MAC) and frontier molecular orbital (FMO) analysis of the as-synthesized ligands. The FMO energy gaps were rationalized to be 0.162, 0.158 and 0.138 eV for ligands (L-1), (L-2) and (L-3), respectively which can efficiently polarize their chemical structures. As-synthesized metal complexes have good agreement with their purposed structures with octahedral geometry except vanadium complexes, which have square pyramidal geometry. As-synthesized compounds were also evaluated through thermogravimetry and fluorescence analysis. Additionally, the compounds were also scrutinized for antibacterial activity against five bacterial strains (Halomonas halophila, Chromohalobacter israelensis, Escherichia coli, Chromohalobacter salexigens and Halomonas salina) and enzyme inhibition bioassay against butyrylcholinesterase (BChE) and acetylcholinesterase (AChE). The results showed that the complexes (15) and (1) were the most active inhibitors of BChE and AChE enzymes with 94.60% and 90.90% activity, respectively. Moreover, all the compounds also exhibited significant antibacterial activity. It has been found that the metal complexes displayed more biological activity in contrary to parent ligands as a result of chelation. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The aim of this study was to design and synthesize novel bioactive compounds, with the results showing that the synthesized metal complexes exhibited higher activity in enzyme inhibition and antibacterial effects compared to the parent ligands.