Metal mimics

German scientists have made progress in the quest to mimic the activity of catechol oxidase, the copper-containing enzyme found in fungi, bacteria and plants.

Although catechol oxidase contains copper, manganese (Mn) can also be useful to study synthetic systems and understand the naturally-occurring processes.

By making ligands based around a disubstituted 2-anilino-4,6-di-tert-butylphenol group, Phalguni Chaudhuri and his team were able to make seven di- and mono-nuclear radical-containing Mn(iv) compounds. They then looked at the compounds’ catecholase activity.

The electrochemical behaviour of the systems revealed that oxidation and reduction took place at the ligands rather than the metal.

Chaudhuri claims that the Mn(iv)-radical complexes catalyse the oxidation of 3,5-di-tert-butylcatechol with molecular oxygen to give a corresponding quinone molecule. They suggest the radicals have an ’on-off’ mechanism that happens without any redox-participation from the central Mn atoms and that the Mn complexes are better catalysts than their corresponding copper complexes.

This work could open the way for other enzyme-mimics being developed that contain metals other than copper.

Carolyn Ackers