The secret is a type of nanoscale cage called a metal-organic framework and its purely organic counterpart, a covalent organic framework. They are like crystals built from Tinker Toys, with metal- or carbon-based hubs connected by rod-like molecules. What makes these crystals unlike any type of structure before is that they are mostly air, so they can trap molecules inside, where those molecules can react chemically with the cage or with others trapped nearby. These “shotgun marriages” may hold the key for producing liquid fuels from sunlight, or mopping up toxic chemicals in the environment, or learning more about the complex molecules essential to life.
Recently, Omar Yaghi, co-director of the Kavli Energy NanoSciences Institute, showed how to use these open frameworks to study molecules that are hard to isolate any other way, and to make strong textile-like woven structures chemically. To discuss this new chemistry and how it could transform fields as diverse as transportation, fuel production, electronics and medicine, The Kavli Foundation brought together three research leaders for a roundtable discussion.
The participants were:
- Omar M. Yaghi is a professor of chemistry at University of California, Berkeley, and co-director of the Kavli Energy NanoSciences Instituteand the California Research Alliance by BASF. He is considered the inventor of metal-organic frameworks and covalent organic frameworks. Between 2000 and 2010, he was the second most cited chemist in the world.
- Joseph Hupp is a professor of chemistry at Northwestern University and a Senior Scientist in the Materials Science Division at Argonne National Laboratory. His research group studies the application of MOFs to artificial photosynthesis, chemical separations, molecular sieves and fuel storage.
- Thomas Bein is the Chair of Physical Chemistry and a professor of nanoscience at Ludwig-Maximilians-Universität München in Germany. The Bein Research Group is investigating the use of MOFs and COFs in electronics, solar cells and targeted drug delivery.
The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.
THE KAVLI FOUNDATION: Professor Yaghi, what’s the advantage of this new way of doing chemistry using metal-organic frameworks (MOFs)?
OMAR YAGHI: If you think about how humans typically do chemistry, it usually involves some combination of high temperatures and high pressures, and it produces a lot of waste products in addition to the chemicals we want. This limits us to making fairly simple and small molecules.
Now compare that to nature. Biological systems conduct their reactions at room temperatures and pressures, and make the same molecule repeatedly and with no waste. And they often make molecules so large and complex, we are still trying to understand their structures.
For a long time, chemists had no way to make complex chemical structures the way nature does, so they usually wound up with a mess. Now, with these metal-organic frameworks, we have an easier way to do this, because they are essentially scaffolds. Like the framework of a skyscraper, they have a very precise, open, repeating structure. We can bind groups of chemicals onto them.
This lets us create something similar to the complex environments found in nature. An example of this is enzymes—proteins that trigger chemical reactions in living things. They only work if their shape matches the molecule they are designed to react with, and if their active site, where the reaction takes place, has the right molecules surrounding it. Change those molecules or its shape and it does something completely different. With framework crystals, we can create an environment similar to an enzyme’s, with a specific shape and a specific active site that initiates a reaction.
This is what the future of chemistry is really about—breaking and forming bonds in a selective way. Our work makes this possible because we can design the scaffold and modify it so that it acts very selectively.
In fact, in some ways we can go beyond what nature does. For example, we can create these structures that are more stable than their natural counterparts.]