Coordination behavior of sulfamethazine drug towards Ru(III) and Pt(II) ions: Synthesis, spectral, DFT, magnetic, electrochemical and biological activity studies

Ru(III) and Pt(II) complexes of sulfamethazine drug have been synthesized as antibacterial agents, aiming to enhance the biological activity of sulfamethazine drug against resistance development of some organisms and to throw more light about the debatable coordination behavior of sulfamethazine, and their structures were elucidated by several experimental and theoretical tools. Sulfamethazine acts as a bidentate ligand through sulfonamidic (N15) and pyrimidic (N23) nitrogen atoms. AC magnetic susceptibility measurements of RuIII complex showed anti-ferromagnetic behavior in 80–212 K with a Néel temperature at 128 K. Electrochemical studies revealed that –NH2 and –SO2 groups remain intact in complex formation. Antibacterial activity and structural activity relationship (SAR) showed that activity decreases with complex formation due to increase the energy of lowest unoccupied molecular orbital (ELUMO), dipole moment, and charge on sulfonamidic nitrogen (N15) as a result of formation of covalent M-sulfonamidic bond, which in turn suppress the activity.

Sulfamethazine is coordinated to RuIII ion through pyrimidic (N23) and sulfonamidic (N15) nitrogen atoms forming a distorted octahedral geometry.Figure optionsDownload as PowerPoint slideHighlights
► RuIII complex showed anti-ferromagnetic behavior with a Néel temperature at 128 K.
► The poor antibacterial activity of complexes is attributed to formation of covalent M-sulfonamidic bond.
► Electrochemical studies proved that –NH2 and –SO2 groups remain intact in complexes.
► Sulfamethazine interacts with metal ions through pyrimidic and sulfonamidic N atoms.
► High populations of 4d (RuIII) are in agreement with ligand to dRu electron transfer.