Publication Nature Nanotechnology
Inspired by nature: Paints and coatings containing bactericidal agent nanoparticles combat marine fouling
Vanadium pentoxide nanoparticles mimic natural enzymes and inhibit surface build-up of algae and bacteria
Scientists at Johannes Gutenberg University in Mainz (Germany) and the Max Planck Institute for Chemistry in Mainz in collaboration with the Biocatalysis research group of the Van ‘t Hoff Institute for Molecular Sciences (University of Amsterdam) have discovered that tiny vanadium pentoxide nanowires can inhibit the growth of bacteria and algae on surfaces in contact with seawater. Their findings, published this week in Nature Nanotechnology, could lead to the development of new ‘antifouling’ coatings and paints for ship hulls. The new coatings are potentially less damaging to the environment than the ship coatings currently in use.
Marine fouling is the accumulation of organisms such as algae, mussels, and barnacles on ship hulls. It increases the fractional resistance, thus slowing the ship’s speed and increasing fuel consumption and CO2 emissions. This effect may to some extent be counteracted by using so-called antifouling paints, but conventional biocides incorporated in these paints are not very effective and can have adverse environmental consequences.
A new approach now taken by the team of scientists headed by Professor Dr. Wolfgang Tremel of the Institute of Inorganic Chemistry and Analytical Chemistry at Johannes Gutenberg University in Mainz (Germany) holds the promise of a more effective anti-fouling coating with less damage to the environment. It makes use of tiny vanadium pentoxide nanowires and is inspired by one of nature’s own defense mechanisms in which so-called vanadium haloperoxidase enzymes play a crucial role.
For the last 25 years Professor Ron Wever of the Van ‘t Hoff Institute for Molecular Sciences (HIMS) at the University of Amsterdam (UvA) has been studying these vanadium haloperoxidases and their role in the defense mechanism of certain brown and red algae. When the chemists at Mainz University discovered that vanadium pentoxide (V2O5) nanoparticles were able to mimic the activity of the vanadium haloperoxidase, Wever proposed to test the antibacterial and antifouling activity of these particles. Consequently this activity was investigated under both laboratory conditions and in natural seawater. Indeed, surfaces coated with paint containing the vanadium nanoparticles showed antibacterial and antifouling activity.
In brown and red algae vanadium haloperoxidase enzymes are able to oxidize bromide in the presence of hydrogen peroxide to hypobromous acid. The latter is highly toxic to many microorganisms, thus having a pronounced antibacterial effect. It also disturbs bacterial communications signals. The algae use it effectively to protect them against microbial attack and predators.
Wever established the reaction mechanism of the vanadium haloperoxidase enzymes and showed that vanadium oxide (VO43-) in the active site plays a prime role in their activity. He has been involved in projects to use the enzymes as natural antifouling agents, e.g. by including them in antifouling paints.
The research published in Nature Nanotechnology now shows that vanadium pentoxide nanowires can fulfill the same chemical role as the vanadium haloperoxidase enzymes. The required reactants for their activity are present in seawater. It already contains bromide ions, while small quantities of hydrogen peroxide are formed when seawater is exposed to sunlight. The figure illustrates the principle.
The vanadium oxide is particularly potent when it is present in the form of nanowires because then, due to the larger surface area, there is an enhanced catalytic effect. The use of vanadium nanowires has only very minimal consequences for the environment because the effect is restricted to micro-surfaces.
As shown by the research group headed by Dr. Klaus Peter Jochum of the Max Planck Institute for Chemistry in Mainz only very tiny amounts of vanadium migrate from the coating into seawater and will thus have no negative impact on the environment, also because seawater itself contains vanadium oxide.
According to the publication in Nature Nanotechnology, the vanadium pentoxide nanowires are considerably less toxic to marine life than are the tin- and copper-based active substances used in the commercially available products, due to their poor solubility and the fact that they are embedded in the ships’ coatings. Although more research is needed these findings may potentially lead to a new generation of antifouling paints that employ the natural defense mechanism used by marine organisms.
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Note: Ron Wever received a Valorisation Grant Phase 1 from STW entitled “Preventing biofim formation on membranes by immobilized vanadium chloroperoxidase”