Synthesis, spectroscopy, density functional theory study and biological activity of [Cu(phen)(L-arg)Cl]Cl·2.5H₂O

Copper complexes are known for a range of biological properties that include anticancer, antimicrobial, and superoxide dismutase-like activities. In this work, we describe the synthesis of [Cu(phen)(L-arg)Cl]Cl·2.5H₂O crystal, formed by the complexation of the metallic ion copper(II) with organic ligands - 1,10-phenanthroline (phen) and L-arginine (L-arg) -, by slow solvent evaporation. The crystal was characterized by advanced spectroscopic and structural techniques, such as Powder X-ray Diffraction (PXRD), Fourier Transform - Infrared (FT-IR) and Raman Spectroscopy. Density functional theory (DFT) calculations were also carried out the first time for [Cu(phen)(L-arg)Cl]⁺ complex, considering vacuum conditions and the solvation effects in water and in methanol, showing a greater stability of the complex in water. The intramolecular IR and Raman modes were determined from the DFT calculations, while time-dependent DFT calculations supported the study of electronic transitions. Solvation effects on calculated IR and Raman spectra were also evaluated, and spectral changes were identified. Initial analyses of the interaction between the complex and double-stranded deoxyribonucleic acid (DNA) were performed, showing ability to interact via hydrogen bonds with a binding affinity of -8.0 kcal/mol. The anticancer activity of the synthesized crystal was tested on prostate (PC-3) and promyelocytic (HL-60) cancer cell lines, revealing cytotoxicity in both lines at 1.4 and 1.7 µM, respectively. The antibacterial activity of the crystal was also tested on Gram-positive (Staphylococcus aureus, Enterococcus faecalis, Streptococcus pneumoniae, Streptococcus mutans) and Gram-negative (Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa) bacterial strains, achieving satisfactory inhibition at the concentration of 50 µg/mL. The biological results suggest a high potential of [Cu(phen)(L-arg)Cl]Cl·2.5H₂O to be exploited as a chemotherapeutic drug for the treatment of prostate cancer and leukemia, and also as antibacterial drug candidate.