Coordination Chemistry, Antibacterial Screening, and In Silico ADME Study of Mononuclear NiII and CuII Complexes of Asymmetric Schiff Base of Streptomycin and Aniline

Abstract

Two novel metal complexes, that is, Ni (StmAn)2(4) and Cu (StmAn)2(5), were synthesized from unsymmetrical Schiff base ligand StmAn (3). The ligand was prepared by refluxing streptomycin (2) and aniline (1). They were characterized by elemental microanalysis, conductivity measurements, and spectroscopic techniques such as 1H NMR, FT-IR, ESI-mass, and electronic absorption spectral study. Interestingly, the study revealed metal coordination through azomethine nitrogen and N-atom of NH-CH3 of N-methyl-L-glucosamine unit of streptomycin. The electronic absorption spectral study supported an octahedral geometry for complex 4 and a tetrahedral geometry for complex 5. Particle size calculation by Scherrer’s formula indicated their nanocrystalline nature. The geometry optimization of the complexes was achieved by running an MM2 job in Gaussian supported Cs-ChemOffice ultra-12.0.1 and ArgusLab 4.0.1 version software. Based on SwissADME predictions, a theoretical drug profile was generated by analyzing absorption, distribution, metabolism, excretion, and toxicity (ADMET) scores of the compounds. They were screened for in vitro antibacterial activity study against four clinical pathogens such as E. coli, S. pneumoniae, P. vulgaris, and S. aureus. Minimum inhibitory concentration (MIC) study demonstrated greater inhibitory potency of complex (4) (0.024 g/L) for S. aureus relative to ligand (3) and complex (5). Studies show that metal complexes are more toxic to bacteria.

Schiff Bases and Their Metal Complexes: Synthesis, Structural Characteristics and Applications

“…The Schiff bases' great affinity for chelation towards inner and non-inner transition metal ions is employed to produce stable complexes. Unsymmetrical ligands do not have a rotation or mirror axis of symmetry and bind to a metal ion with two groups, and symmetrical ligands have [52,53]. It has been argued that unsymmetrical Schiff base ligands are superior to their symmetrical counterparts due to their ability to more accurately predict the geometry of metal ion binding sites in biological systems that contain metal ions and their ability to more easily combine natural and synthetic structural components (Figure 6).…”