An analogue of the oxygen-carrying molecule in blood, which contains vanadium rather than iron, could be a promising drug lead, according to its designers. 

Vanadium compounds have promising medicinal properties, including anticancer, antiviral and insulin-mimetic activity, says Jonathan Sessler at the University of Texas at Austin, US. Now Sessler and colleagues have made a new vanadium-based compound that incorporates an expanded porphyrin, similar to the iron-porphyrin complex found in haemoglobin. 

Expanded porphyrins are mimics of naturally occurring porphyrins - large cyclic structures that can bind metal ions. Chemists have previously enlarged porphyrin rings to allow them to hold larger metal atoms.

But Sessler has now shown that, by subtly rearranging their structure, the expanded rings can also coordinate very small metals like vanadium. The ion at the centre of the complex is attached to two oxygen atoms, making a dioxovanadium core. The complex relies on two different types of chemical bond, hydrogen bonding and covalent bonding, to hold it together, which is extremely rare, said Sessler.

Zeev Gross, an expert in metalloporphyrins and bioinorganic chemistry at Technion - Israel Institute of Technology, Haifa, said, 'this research demonstrates that expanded porphyrins have a large degree of structural freedom and can thus act as near-ideal ligands for a wide range of very different metal ions.' 

The next challenge in this work will be to develop analogues that are suitable for biomedical study, said Sessler. 'Nevertheless, the promise that such new drug leads hold justifies the challenge,' he said.

James Mitchell Crow