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Project ID: ICA3-CT-2002-10016
Financiado con arreglo a: FP5-INCO 2
País: Spain

Destruction of E. coli and E. Faecalis in homogeneous water phase using Ru (II) complexes as singlet oxygen photosensitizers

Recent advances on water disinfection treatments propose singlet oxygen, a reactive oxygen species, as a bactericidal species which can be generated photocatalytically with solar light in aqueous solution and also in heterogeneous phase. Singlet oxygen can therefore be used as an alternative to other typical chemical reagents employed in water disinfection treatment. Its electrophilic character, energy excess (ca. 95 kJ mol 1) and high bimolecular rate constants with biomolecules such as proteins (6 x 107 M 1s 1) and lipids (1 x 105 M 1s 1) makes singlet oxygen a promising bactericidal agent vs. water borne microorganisms.

Our research group has developed a new family of singlet oxygen photosensitizers based on polyazaheterocyclic Ru(II) complexes with different structural features. They display singlet oxygen production quantum yields in the 0.2 - 1 range in homogeneous phase and those containing the 4,7-diphenyl-1,10-phenanthroline ligand or its derivatives show very efficient generation of singlet oxygen.
We have carried out experiments with aqueous samples containing E. coli or E. faecalis in the presence of RDP2+ [tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II)] or RSD4 [tris(4,7-diphenylsulfonate-1,10-phenanthrolinyl)ruthenate(II)] photosensitizers, in the dark or under Vis irradiation. No toxic effects were observed for E. coli or E. faecalis after 5 h incubation in the dark with RSD4 10 6 M or with RDP2+ 5 x 10 9 M (due to its very low solybility in water). On the other hand, under Vis irradiation, no disinfection was observed for E. coli or E. faecalis after 4 h irradiation with RSD4 5 x 10 9 M, while a decrease of 5 orders of magnitude in bacteria concentration was observed in the case of RDP2+ photosensitizer. Disinfection assays in homogeneous phase were also performed using suspensions of E. coli in water with RDP2+ or RSD4 at concentrations up to 5.0 x 10 8 M. Significant disinfection (two orders of magnitude decrease in viable bacteria concentration) were obtained after 6 hours irradiation in the presence of the cationic photosensitizer. With the anionic photosensitiser, using the same experimental conditions, low disinfection (ca. 15% decrease in the viable bacteria concentration) has been observed.

No efficient disinfection was observed with RSD4 photosensitizer in homogeneous phase while it was clearly observed with RDP2+ (even at nanomolar concentration due to its scarce water solubility). This result can be explained if the anionic character of biological membranes and also of RSD4 photosensitizer is taken into account, which limits the interaction between the microorganism and the sensitizer molecules. On the other hand, the cationic photosensitizer RDP2+ interacts electrostatically with the anionic membrane of the microorganism, leading to efficient inactivation.

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Reported by

UCM (Universidad Complutense de Madrid)
Department of Organic Chemistry, Faculty of Chemistry Av Complutense s/n
28040 MADRID
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