Light sensitivity is no longer a problem for studying anti-microbial silver.

Japanese scientists have overcome decomposition problems to reveal why silver compounds are such good anti-microbial agents.

Since silver coins were used to disinfect water in ancient Greece, silver has been famed for its anti-microbial properties, finding application more recently in water purification on NASA space shuttles. It has even been used recently in wound dressings that release silver ions in low concentrations over time to promote healing whilst fighting infection.

It was thought that complexes containing just silver-oxygen and silver-nitrogen bonds have the most effective anti-microbial properties, but this has been difficult to study since their complexes tend to be light-sensitive.

Now scientists in Japan have prepared silver(I) complexes that are light-stable for a few hours at ambient temperature, allowing their full characterisation using a range of techniques. Their crystal structures have also been studied.

Kenji Nomiya and his team prepared six water-soluble chiral and achiral silver(I) complexes with camphanic acid ligands, containing oxygen atoms as donor atoms, and compared their anti-microbial activities. They concluded that the ligand exchangeability and the nature of the atom coordinated to the silver ion in the complex influences the anti-microbial activity displayed by the silver complex.

Monovalent silver ions interfere with biological processes in cells such as binding to DNA and deactivating enzymes, although silver complexes have also shown a wide range of anti-microbial activities against bacteria, yeast and mould.

Carolyn Ackers