Synthesis, Characterization and Antibacterial Investigation of Mononuclear Copper (II) Complexes of Amine-phenolate Based Ligands

The antibacterial activities of two previously reported copper (II) coordination complexes [Cu(HL¹)Cl₂] and [Cu(HL²)Cl₂], and the two new complexes [Cu(HL³)Cl₂] and [Cu(HL⁴)Cl₂], where HL¹ is 2-(((pyridin-2-ylmethyl)amino)methyl)phenol, HL² is 2-((benzyl(pyridine-2-ylmethyl)amino)methyl)phenol, HL³ is 2-(((pyridin-2-ylethyl)amino)methyl)phenol and HL⁴ is 2-(((pyridin-2-ylmethyl)(quinolin-2-ylmethyl)-amino)methyl)phenol were investigated using agar well plate diffusion assay. The ligands were characterized using elemental analysis, IR, ¹H-NMR, ¹³C-NMR spectroscopy and thermal analysis. The corresponding copper (II) complexes of each ligand were synthesized and characterized using elemental analysis, FT-IR and UV-Visible spectroscopy, electronic spectra and magnetic moment measurements, and thermal analysis. Additionally, a thorough investigation of the copper complexes as potent drug candidates was performed using web-based software SwissADME to predict their physicochemical and pharmacokinetics properties. All copper complexes were stable to air and moisture and showed excellent stability up to 200 °C. Electronic spectra of all copper complexes in methanol consisted of single band at 14,490–15,260 cm⁻¹ depicting ligand field excitation (Cu (II) d–d band). Ligands were completely ineffective on gram positive bacteria; HL¹ and HL³ showed moderate to high activity at concentration range of 0.2–1 mg/ml. Copper complexes were found to exhibit moderate to high activity against bacteria as compared to the ligands. SwissADME analysis of all copper (II) complexes justified their candidature as potential candidate for pharmaceutical applications.