Synthesis, crystal structure, lipophilicity, antioxidant activity, binding interactions, and antibacterial activity against methicillin-resistant Staphylococcus aureus of a Ni(ii) Schiff base complex: combined theoretical and experimental approaches

Abstract

Herein, we report the synthesis, crystal structure, and antibacterial activity of a new Ni(II) complex derived from the N, O donor (E)-2,4-dibromo-6-(2-(1-phenylethylimino) ethyl) phenol ligand. Both the ligand and the complex were characterized by employing FT-IR, UV-Visible, and fluorescence spectroscopy as well as single-crystal X-ray diffraction studies. The crystallographic results reveal that the complex crystalizes in the monoclinic unit cell with the space group C2, and the coordination environment around the Ni centre consists of NiN₂O₂ donor sites exhibiting a highly distorted tetrahedral geometry. The oxidative assay of DPPH (α,α-diphenyl-β-picrylhydrazyl) was used for evaluating the radical scavenging activity or antioxidant properties of the complex in terms of IC50 values (50% inhibition); it was observed that the complex showed reasonable antioxidant activities with ascorbic acid (AA) as the standard. Detailed interaction studies with calf thymus (CT) DNA and bovine serum albumin (BSA) were performed through various spectroscopic and theoretical approaches and indicated that the complex has promising binding capability with both the systems. Comprehensive biological studies were performed and showed that the complex exhibits notable antibacterial activity against Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) by interfering with its cell wall integrity. Microscopic imaging confirmed cellular abnormalities, such as alterations in the cell shape, size, and quantity. Molecular docking analyses also provided insights into the activities of the complex. In contrast, the complex displayed minimal growth inhibition properties against Gram-negative Klebsiella pneumoniae (KP) even at higher complex concentration, indicating that the specific inhibition activity of the complex is only against Gram-positive MRSA. Moreover, based on optical density readings, the results demonstrated that the complex exhibited effective antibacterial activity against MRSA with an MIC value between 34 and 36 μg ml⁻¹, whereas the MIC value of standard cefoxitin is >70 μg ml⁻¹. Thus, our complex demonstrated better antibacterial activity than the conventional antibiotic.