Metallosurfactants as Carbon Monoxide-Releasing Molecules

The dark side of carbon monoxide (CO) as a very toxic gas has a complementary bright side as a natural gasotransmitter. CO is endogenously produced in mammals and its biological activity comprises, for example, the regulation of the vascular system and cell metabolism. These and other effects have stimulated its study as exogenous drug, an effort that collides with a high wall: its administration. To circumvent the problem of dosage by inhalation several CO-releasing molecules (CORMs) have been synthesized, most of them based on metal–carbonyl complexes. These molecules can be administered in aqueous medium and release CO by the action of biological components or due to external stimuli. Some of these CORMs have been conjugated to biomolecules and/or incorporated into drug-delivery systems to improve their release on a given target site. A combined strategy is constituted by the carbonylic metallosurfactants, which, somehow, share the two previous approaches. On the one hand, their structure mimics that of natural polar lipids containing a hydrophilic domain and a hydrophobic region, which includes the non-polar metal carbonyl. On the other hand, they aggregate – alone or with other molecules, like phospholipids – forming several supramolecular structures that become efficient drug-delivery systems, since they exhibit CO-releasing properties and show interaction with cells.