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Issue 13, 2013
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Chlorido-containing ruthenium(ii) and iridium(iii) complexes as antimicrobial agents

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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.

Graphical abstract: Chlorido-containing ruthenium(ii) and iridium(iii) complexes as antimicrobial agents

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Article information


Submitted
21 Nov 2012
Accepted
21 Jan 2013
First published
29 Jan 2013

Dalton Trans., 2013,42, 4686-4694
Article type
Paper

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

M. Pandrala, F. Li, M. Feterl, Y. Mulyana, J. M. Warner, L. Wallace, F. R. Keene and J. G. Collins, Dalton Trans., 2013, 42, 4686
DOI: 10.1039/C3DT32775B

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