Synthesis, structural, spectral and antimicrobial activity studies of copper-nalidixic acid complex with 1,10-phenanthroline: DFT and molecular docking.

The mix-ligand coordination compound, [Cu(Nal)(Phen)(HO)].(Phen).ClO.(HO) (Nal= Monoanion of nalidixic acid and Phen = 1,10- Phenanthroline), was investigated by focusing on its supramolecular architecture. Structural properties of the complex were characterized by XRD, spectroscopic methods and elemental analysis. The complex has crystallized in the triclinic crystal system and P-1 space group. In the structure where the Cu (II) ion is in the center of symmetry, nalidixate anion and water molecule coordinated to Cu (II) metal through oxygen atoms while phen coordinated through nitrogen atoms. The monomer units are connected by hydrogen bonds to form supramolecular structures. The ground state molecular structure of the complex was optimized using DFT/B3LYP/LANL2DZ method, and compared with experimental X-ray geometry. The FT-IR study of the complex was carried out in the middle IR region focusing on the characteristic vibrations of the free ligands and the complex. Scaled calculated vibrational frequencies are compared with experimental values. The magnetic properties of the complex were investigated by electron paramagnetic resonance (EPR) spectroscopy. Further ultra-violet (UV)-visible spectral analysis was also performed to understand optical properties. The experimental UV-Vis data were associated with the calculated frontier molecular orbitals HOMO/LUMO and, molecular electrostatic potentials (MEP) are also investigated. Biological study of the complex against Bacillus subtilis, Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Candida albicans showed very strong antibacterial activity with MIC values ranging from 128 μg/ml to 1 μg/ml concentration. The optimized complex is docked to the DNA Gyrase (3LPX) and gyrase tip IIA topoisomerase (3UC1).

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