Cadmium and silver complexes of a pyridine containing ligand: syntheses, structural studies, biological activity and docking studies†

The current study aimed to synthesize seven new metal coordination complexes (Q1–Q7) with potential biomedical applications. Novel mononuclear, polynuclear and mixed-ligand coordination compounds of the elements, cadmium(II) and silver(I) derived from a pyridine containing ligand (2,4,6-tris-(2-pyridyl)-1,3,5-triazine (TPT)) have been synthesized successfully with the general formulae [Cd(TPT)Cl₆]·H₂O and [Ag_x(TPT)_y(L)₂(ClO₄)](ClO₄)_z (x = 1,2,3, y = 1,2,3, L = PPh₃ or phen, z = 1,2). The structural features were fully characterized using various spectroscopic techniques, such as infrared, ultraviolet-visible spectroscopy, 1D and 2D-NMR (¹H, ¹³C, ³¹P, ¹H–¹H COSY and ¹H–¹³C HSQCAD), CHN analysis, molar conductance (Λ), thermogravimetric analysis (TGA), and powder X-ray diffraction analysis. The structure of complex Q6 was also confirmed by single-crystal X-ray analysis. The luminescence and electrochemical properties of complexes, in solution, have been studied. X-ray crystallographic determination of the [Ag(TPT)(PPh₃)₂]ClO₄·EtOH (Q6) complex shows that the Ag⁺ cation is bonded to one tridentate TPT ligand through NNN set of donor atoms and two triphenylphosphine ligands, giving the Ag⁺ a distorted trigonal bipyramidal geometry. X-ray powder diffraction analysis showed that metal complexes Q3, Q6 and Q7 display crystalline peaks. The complexes were evaluated for their in vitro antibacterial efficacy against various bacterial and fungal species. The in vitro efficacy against the MCF-7 human breast cancer cell line was assessed to determine the anticancer activities. The tri-nuclear silver complex Q3 shows great potential as a therapeutic candidate for treating breast cancer, since it exhibits a half-maximal inhibition concentration (IC₅₀) of 13.45 ± 0.9 μM. Molecular docking simulations were also carried out to evaluate the interaction strength and properties of the metal complexes with selected cancer and bacteria relevant proteins namely cyclin-dependent kinase 2 (CDK2), cyclin-dependent kinase 6 (CDK6), signal transducer and activator of transcription 3 (STAT3), and beta-lactamases from Escherichia coli and Staphylococcus aureus.