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New ‘chain mail’ material of interlocking molecules is tough, flexible and easy to make

University of California, Berkeley, chemists have created a new type of material from millions of identical, interlocking molecules that for the first time allows the synthesis of extensive 2D or 3D structures that are flexible, strong and resilient, like the chain mail that protected medieval knights.

The material, called an 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 linked rings. These structures served as the foundation for making molecular structures capable of moving, which are often referred to as molecular machines.

But the chemical synthesis of catenanes has remained laborious. Adding each additional ring to a catenane requires another round of chemical synthesis. In the 24 years since Sauvage created a two-ring catenane, chemists have achieved, at most, a mere 130 interwoven rings in quantities too small to see without an electron microscope.

The new type of catenane, produced in the laboratory of Omar Yaghi, UC Berkeley professor of chemistry, can be produced with an unlimited number of linked units in three dimensions. Because the individual units interlock mechanically and are not connected by chemical bonds, the structures can be flexed without breaking.

“We think that this has really important implications, not just in terms of making tough materials that don’t fracture, but also materials that would go into robotics and aerospace and armored suits and things like this,” said Yaghi, the James and Neeltje Tretter Chair Professor of Chemistry, co-director of the Kavli Energy NanoSciences Institute and the California Research Alliance by BASF, and chief scientist at UC Berkeley’s Bakar Institute of Digital Materials for the Planet.

Yaghi and his colleagues, including first author Tianqiong Ma, a UC Berkeley postdoctoral fellow, reported details of the chemical process this week in the journal Nature Synthesis.

Reticular chemistry
The leap forward in catenane production is possible using a type of chemistry that Yaghi invented more than 30 years ago: reticular chemistry. He describes it as “stitching molecular building blocks into crystalline, extended structures by strong bonds.”

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