Biphosphinic ruthenium complexes as the promising antimicrobial agents

There is an urgent need for new antimicrobial compounds to combat the growing threat of widespread antibiotic resistance. Recently, metal complexes have been recognized as promising sources for new antibiotics since they exhibit unique modes of action such as ligand exchange or release, ROS generation, redox activation and catalytic generation of toxic species or depletion of essential substrates. In addition, it is known that gaseous nitric oxide exerts an antimicrobial effect. These observations led to the development of NO delivery systems that can harness the antimicrobial properties of this evanescent gas. Here, we investigate the antimicrobial activity of the ct-[RuCl(NO)(dppb)(4,4 '-Mebipy)](PF6)(2) nitrosyl complex along with its precursor cis-[RuCl2(dppb)(4,4 '-Mebipy)] complex. A series of antimicrobial activity studies using Gram(+) and Gram(-) bacteria were carried out with these compounds. Unfortunately, these ruthenium complexes did not show any activity against Gram(-) bacteria P. aeruginosa and E. coli, even at the highest concentration tested (500 mu g mL(-1)). Otherwise, both complexes showed promising antibacterial activity against Gram-positive bacterial strains of Staphylococcus aureus (ATCC25923, ATCC700698 and JKD6008) and Staphylococcus epidermidis (ATCC12228 and ATCC35984). However, the nitrosyl complex showed a greater antibiotic effect than its precursor, supporting the important role of NO in this process.