Uranium may be good for something more than nuclear fireworks, according to new research that offers it a novel role: a catalyst for chemical reactions that could produce a new generation of pharmaceuticals and plastics.
“Uranium, undoubtedly, has really bad PR,” says Professor Steven Liddle of the University of Manchester, lead author of a paper on the research published in Nature Communications. “But to me it’s just an element of the periodic table. It’s about what you use it for.”
Liddle and his team have spent years studying the basic properties of uranium, looking to find applications for this misunderstood metal in the chemical industry.
Uranium belongs to a block of chemical elements known as the lanthanides and actinides, often drawn separately at the bottom of the periodic table. These heavy metals have some uses as catalysts in industrial chemistry, but they all tend to behave quite similarly, making them less interesting to chemists looking to develop new catalysts.
Typically, the most fertile elements of the periodic table for discovering catalysts are the transition metals. These metals, grouped around the centre of the periodic table, have electrons in configurations that make them very good at helping other molecules to break and form new bonds.
Now, Liddle and his team have shown that uranium can undergo two chemical processes which are usually associated with the transition metals, meaning that uranium may be able to access powerful new chemistry previously beyond its reach. The team achieved this change in the reactivity of uranium by attaching nitrogen-containing molecules to the metal, which modify its chemical behaviour.
The Manchester researchers have shown that uranium can undergo important processes called “oxidative addition” and “reductive elimination.” Oxidative addition occurs when a metal (M) inserts itself into the bond between two elements (such as carbon and oxygen, for example), turning a C–O bond into C–M–O molecule.
Reductive elimination is simply the reverse of oxidative elimination, where the metal is kicked out and two elements that were attached to the metal form a bond to each other.
This ability to break and form bonds, usually limited to the transition metals, can be harnessed by chemists to synthesise a wide variety of organic molecules, giving us access to better fuels, drugs, agrochemicals and plastics. The ability of uranium to access these chemical processes brings together the chemistry of the transition metals with that of the lanthanides and actinides, offering the possibility of a new type of hybrid catalyst which may have previously unseen properties.
This chemistry is still a long way from delivering new products to our shelves, but it does show that a huge wealth of untapped potential still lies within the humble elements of the periodic table, and that even the most unlikely elements might be key to the next scientific breakthrough.
Joel F. Hooper
Joel Hooper is a senior research fellow at Monash University, in Melbourne, Australia.
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