Chlorido-containing ruthenium(II) and iridium(III) complexes as antimicrobial agents

Mallesh Pandrala, Fangfei LI, Marshall Feterl, Yanyan Mulyana, Jeffrey M. Warner, Lynne Wallace*, F. Richard Keene*, J. Grant Collins*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

67 Citations (Scopus)

Abstract

A series of polypyridyl-ruthenium(II) and -iridium(III) complexes that contain labile chlorido ligands, [{M(tpy)Cl}2{μ-bbn}]2/4+ {Cl-Mbbn; where M = Ru or Ir; tpy = 2,2′:6′,2′′-terpyridine; and bbn = bis[4(4′-methyl-2,2′-bipyridyl)]-1,n-alkane (n = 7, 12 or 16)} have been synthesised and their potential as antimicrobial agents examined. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of the series of metal complexes against four strains of bacteria – Gram positive Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), and Gram negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) – have been determined. All the ruthenium complexes were highly active and bactericidal. In particular, the Cl-Rubb12 complex showed excellent activity against all bacterial cell lines with MIC values of 1 μg mL−1 against the Gram positive bacteria and 2 and 8 μg mL−1 against E. coli and P. aeruginosa, respectively. The corresponding iridium(III) complexes also showed significant antimicrobial activity in terms of MIC values; however and surprisingly, the iridium complexes were bacteriostatic rather than bactericidal. The inert iridium(III) complex, [{Ir(phen)2}2{μ-bb12}]6+ {where phen = 1,10-phenanthroline) exhibited no antimicrobial activity, suggesting that it could not cross the bacterial membrane. The mononuclear model complex, [Ir(tpy)(Me2bpy)Cl]Cl2 (where Me2bpy = 4,4′-dimethyl-2,2′-bipyridine), was found to aquate very rapidly, with the pKa of the iridium-bound water in the corresponding aqua complex determined to be 6.0. This suggests the dinuclear complexes [Ir(tpy)Cl}2{μ-bbn}]4+ aquate and deprotonate rapidly and enter the bacterial cells as 4+ charged hydroxo species.
Original languageEnglish
Pages (from-to) 4686-4694
Number of pages9
JournalDalton Transactions
Volume42
Issue number13
DOIs
Publication statusPublished - 29 Jan 2013

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