Sustainable Catalysis: Efficient Chemistry Reduces Industrial and Pharmaceutical Waste for Economic and Environmental Gains
Illustration by Peter Allen.
The UN Climate Change Global Innovation Hub brilliantly — and essentially — envisions reimagining future communities so that fewer resources are needed by design. However, while we are building the blueprint for the future, there are also concrete steps we can take to mitigate environmental damage occurring right now because the climate crisis can’t wait. Some of these measures may even be necessary well into the future. For example, even in a healthier world, the demand for small-molecule drugs and medicines is unlikely to ever vanish, so we should continue optimizing the efficiency of the relevant chemical syntheses.
An emerging tool to realize such optimization is metal-organic layers (MOLs). MOLs can be thought of as molecular-scale K’Nex, that is, sets of junctions and linkers arranged to form scaffold-like extended structures. Specifically, they structure themselves as flat sheets of atoms to maximize their available surface area. Scientists then cover this surface area with catalysts, which are small molecules that accelerate and, in some cases, enable the chemical transformations used to synthesize other molecules such as drugs. Once finished, scientists mix the catalyst-covered MOLs into solutions that already contain the building blocks of drug molecules, and the MOL-catalyst structures begin assembling them. By taking the extra step of affixing their catalysts to MOLs, scientists can keep the catalyst molecules from accidentally bumping into each other in solution, a process that typically deactivates both colliding molecules. Thus, the isolated catalysts can continue transforming building blocks into products for much longer, sometimes hundreds of times as long as without MOL supports.
The efficiency of myriad processes has been improved with MOLs. Last year, they improved the efficiency of certain cross-coupling reactions by 200 times — even without MOL-based improvements, cross-coupling won the Nobel Prize in Chemistry in 2010. In February, MOLs contributed to the cheapest, most efficient ever synthesis of vesnarinone, a cardiac medicine. MOLs can even directly address the climate crisis — last year, researchers developed a MOL that realizes artificial photosynthesis an order of magnitude more efficiently than previously reported systems. Moreover, this MOL could generate useful fuels such as methane from its supply of carbon dioxide (the potent greenhouse gas) and water.
MOLs still suffer from limitations, such as the scale at which they can be produced and the high cost of some of the materials needed to build them. But as successes such as the vesnarinone synthesis make clear, they constitute a worthy topic of future investigation.