Synthesis, crystal structures, DFT studies, antibacterial assays and interaction assessments with biomolecules of new platinum(ii) complexes with adamantane derivatives†
Three platinum(II) complexes containing amantadine (atd), rimantadine (rtd) and memantine (mtn) as ligands were synthesized and characterized by chemical and spectroscopic methods. The crystal data revealed the coordination formula [PtCl2(ligand)(DMSO)] for the three complexes. The stability studies of the complexes by 1H nuclear magnetic resonance (NMR) spectroscopy revealed a ligand exchange of the DMSO ligand in the coordination sphere by deuterated DMSO-d6 used as solvent. The 195Pt NMR of the complexes confirmed the presence of one platinum species in solution and the chemical shifts are consistent with the coordination sphere observed in the crystallographic studies. Theoretical studies of complexes and ligands were also performed and combined with the experimental data to support the structural features of the synthesized compounds. The in vitro antibacterial activity assays showed that free ligands rimantadine and memantine were able to inhibit the growth of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa bacterial strains, while amantadine was inactive. Their respective Pt(II) complexes, on the other hand, showed to be more active over Gram-positive bacteria than the Gram-negative ones, with the platinum(II) memantine complex (Pt-mtn) being the most active one. Biophysical assays suggest that the Pt(II) complexes interact with CT-DNA and alter its B-form, as observed by CD spectroscopy. The interaction of the three complexes with bovine serum albumin was also evidenced by fluorescence spectroscopy, which revealed that the platinum(II) rimantadine complex (Pt-rtd) is the most reactive of this series.