Synthesis and characterization of new α,α′-diaminoalkane-bridged dicarbonyl(η5-cyclopentadienyl)ruthenium(II) complex salts: Antibacterial activity tests of η5-cyclopentadienyl dicarbonyl ruthenium(II) amine complexes

Abstract

Bacterial resistance to antimicrobial drugs is a significant threat to humans and requires urgent intervention. There is, therefore, a clear need for the development of new types of antibacterial agents. We have thus synthesized the α,α′-diaminoalkane-bridged diruthenium complex salts [Rp2NH2(CH2)nNH2]Y2 (Rp = CpRu(CO)2 where Cp = η5–C5H5; n = 2, 3, 4 and 6; Y=BF4 (1) or SO3CF3(2)) by the reaction of [RpNCCH3]Y and NH2(CH2)nNH2 (n = 2 (DAE) (3); n = 3 (DAP) (4); n = 4 (DAB) (5) and n = 6 (DAH) (6 (BF)4, 7 (SO3CF3)) at ambient temperature and pressure. These compounds are reported for the first time and have been fully characterized by infrared spectroscopy, 1H and 13C NMR spectroscopy, elemental analyses and melting points. The crystal structures of compounds 1 and 3 were obtained by single crystal X-ray crystallography. The two compounds crystallized in the monoclinic crystal system in the P21/n space group. Antimicrobial susceptibility tests were done for the new dinuclear complexes 3–7 as well as for mononuclear ruthenium complexes, [RpBA]BF4 (8), [RpMBA]BF4 (9), [RpMeOBA]BF4 (10) and [RpAMBN]BF4 (11) (BA=NH2CH2C6H5, MBA = NH2CH(CH3)C6H5, MeOBA = NH2CH2C6H4OCH3 and AMBN = NH2CH2C6H5) against selected drug-resistant and drug-susceptible Gram-positive and Gram-negative bacteria. Some of the dinuclear and mononuclear ruthenium complexes demonstrated good potential abilities to inhibit growth of the bacteria tested, with some showing better growth inhibition ability than well-known antibiotics such as ampicillin (AMP10). The ruthenium moiety CpRu(CO)2 triggered or enhanced the ability of the coordinated ligands to inhibit bacterial growth. In vitro cytotoxicity of the complexes 8 and 10 was investigated through cell viability evaluation using human colorectal cancer (Caco-2) cells and the non-cancerous human embryonic kidney (HEK293) cells.