Sun, Biyun, Southam, Hannah M., Butler, Jonathan A., Poole, Robert K., Burgun, Alexandre, Tarzia, Andrew, Keene, F. Richard, and Collins, J. Grant (2018) Synthesis, isomerisation and biological properties of mononuclear ruthenium complexes containing the bis[4(4'-methyl-2,2'-bipyridyl)]-1,7-heptane ligand. Dalton Transactions, 47. pp. 2422-2434.

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Abstract

A series of mononuclear ruthenium(II) complexes containing the tetradentate ligand bis[4(4'-methyl-2,2'-bipyridyl)]-1,7-heptane have been synthesised and their biological properties examined. In the synthesis of the [Ru(phen')(bb7)]2+ complexes (where phen' = 1,10-phenanthroline and its 5-nitro-, 4,7 dimethyl and 3,4,7,8-tetramethyl- derivatives), both the symmetric cis-α and non symmetric cis-β isomers were formed. However, upon standing for a number of days (or more quickly under harsh conditions) the cis-β isomer converted to the more thermodynamically stable cis-α isomer. The minimum inhibitory concentrations (MIC) and the minimum bactericidal concentrations (MBC) of the ruthenium(II) complexes were determined against six strains of bacteria: Gram positive Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA); and the Gram-negative Escherichia coli (E. coli) strains MG1655, APEC, UPEC and Pseudomonas aeruginosa (P. aeruginosa). The results showed that the [Ru(5-NO2phen)(bb7)]2+ complex had little or no activity against any of the bacterial strains. By contrast, for the other cis-α-[Ru(phen')(bb7)]2+ complexes, the antimicrobial activity increased with the degree of methylation. In particular, the cis-α-[Ru(Me4phen)(bb7)]2+ complex showed excellent and uniform MIC activity against all bacteria. By contrast, the MBC values for the cis-α [Ru(Me4phen)(bb7)]2+ complex varied considerably across the bacteria and even within S. aureus and E. coli strains. In order to gain an understanding of the relative antimicrobial activities, the DNA-binding affinity, cellular accumulation and water–octanol partition coefficients (log P) of the ruthenium complexes were determined. Interestingly, all the [Ru(phen')(bb7)]2+ complexes exhibited stronger DNA binding affinity (Ka ≈ 1 × 107 M−1) than the well-known DNA intercalating complex [Ru(phen)2(dppz)]2+ (where dppz = dipyrido[3,2-a:2',3'- c]phenazine).

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