Chemists at the University of California, Berkeley, have created a new type of material from millions of identical, interlocking molecules that allows for the first time to synthesize large-scale two- or three-dimensional structures that are flexible, strong, and resilient, like the chain mail that protected medieval knights.
The substance, called infinite catenane, can be synthesized in a single chemical step.
French chemist Jean-Pierre Sauvage shared the 2016 Nobel Prize in Chemistry for synthesizing the first catenane – two connected rings. These structures served as the basis for making moving molecular structures, which are often referred to as molecular machines.
But the chemical synthesis of catenans has been daunting. Adding each additional ring to catenane requires another round of chemical synthesis. In the 24 years since Sauvage created the bicyclic catinan, chemists have achieved, at most, a mere 130 interlocking rings in amounts too small to see without an electron microscope.
Produced in the lab of Omar Yaghi, a UC Berkeley professor of chemistry, the new type of catenane can be produced with an unlimited number of bonded units in three dimensions. Because the individual units are mechanically interlocked and not connected by chemical bonds, the structures can be bent without breaking.
“We think this has really important implications, not only in terms of making solid materials that don’t break, but also materials that can go into robotics and aerospace and armored suits and things like that,” said Yaghi, James and Neilty. Tretter Chair Professor of Chemistry, Co-Director of the Kavli Energy NanoSciences Institute and California Research Alliance by BASF, and Senior Scientist at the Baccarat Institute for Digital Materials for the Planet at UC Berkeley.
Yaghi and colleagues, including first author Tianqiong Ma and a postdoctoral fellow at the University of California, Berkeley, detail the chemical process this week in the journal Nature. Synthesis of nature.
The leap forward in β-catenin production is possible using a type of chemistry Yaghi invented more than 30 years ago: retinal chemistry. He describes it as “the stitching of molecular building blocks into crystalline structures extended by strong bonds.”
Using this technique, he made inexpensive porous materials—metal-organic frameworks (MOFs) and covalent organic frameworks (COFs)—that have proven useful for capturing, storing, and separating gases such as carbon dioxide, hydrogen, and water vapor. More than 100,000 types of MOFs have been manufactured so far.
To make MOFs, it is only necessary to assemble the right hybrid molecules—metal groups connected by an organic bond—and mix them in solution so that they bond to form a rigid, highly porous three-dimensional network. Chemical groups within the framework are chosen to bind and release certain molecules – depending on the temperature – and to reject others.
One of the MOFs Yaghi created could draw water from even the driest air and then release it when heated, allowing water to be captured in deserts.
To make catenans, Yaghi and What synthesized a molecule with a junction between two identical halves, covalently bonded by a copper atom. The structure, which they call catena-COF, is reminiscent of a threaded arm arm with a copper atom where they cross. When mixed, these molecules bond to form a porous 3D network of interlocking building blocks. The building blocks, a type of polyhedral molecule called adamantane, essentially lock together their six arms to form an extended framework.
“What’s new here is that the building blocks have these crossings, and because of the crossings, you get interlocking systems that have interesting, flexible, and flexible properties,” Yaghi said. “They’re programmed to work together in one step. That’s the power of retinal chemistry. Instead of building one unit at a time to create a larger structure, you can actually program them so that they come together and grow on their own.”
The molecule with the cross can be changed chemically so that the final catenane reacts with certain compounds. Yaghi calls these substances (∞) catenanes, using the infinity symbol.
“I think this is the first step toward making materials that can flex and that can stiffen in response to stimuli, such as a certain movement,” he said. “So, in certain directions, it can be very flexible, and in certain other directions, it can get stiff, just because of the way the structure is built.”
He noted that while these catenins stretch in three directions on a microscopic level, they can be made thin enough for two-dimensional uses, such as in clothing. Recently, some scientists reported that they created MOFs and COFs by 3D printing, so it may be possible to 3D print catenans as well, such as woven fabric.
“Traditionally, this entanglement has been made through a laborious, multi-step process of creating molecules with only one, two, or three entangled rings, or polyhedra. But to make materials that have amazing properties, such as toughness and elasticity, you need millions and millions of these entanglements.” . “The traditional way of making it just doesn’t cut it. Retinal chemistry comes with a building block approach and finds a way to do it in one step. That’s really the strength of this report.”
The work was supported in part by the King Abdulaziz City for Science and Technology and the Defense Advanced Research Projects Agency (DARPA, HR001-119-S-0048). The researchers used Lawrence Berkeley National Laboratory’s Advanced Light Source Resources (DOE DE-AC02-05CH11231).