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

Pandrala, Mallesh, Li, Fangfei, Feterl, Marshall, Mulyana, Yanyan, Warner, Jeffrey M., Wallace, Lynne, Keene, F. Richard, and Collins, J. Grant (2013) Chlorido-containing ruthenium(II) and iridium(III) complexes as antimicrobial agents. Dalton Transactions, 42 (13). pp. 4686-4694.

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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.

Item ID: 24799
Item Type: Article (Research - C1)
ISSN: 1477-9234
Funders: Australian Research Council (ARC)
Date Deposited: 01 Feb 2013 01:23
FoR Codes: 03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030201 Bioinorganic Chemistry @ 50%
03 CHEMICAL SCIENCES > 0302 Inorganic Chemistry > 030207 Transition Metal Chemistry @ 10%
06 BIOLOGICAL SCIENCES > 0605 Microbiology > 060599 Microbiology not elsewhere classified @ 40%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970103 Expanding Knowledge in the Chemical Sciences @ 60%
97 EXPANDING KNOWLEDGE > 970111 Expanding Knowledge in the Medical and Health Sciences @ 20%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 20%
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