Programmable synthetic materials

Art molecules could one day form the information unit of a new type of computer as the basis for programmable substances. The information would be encoded in the spatial arrangement of the individual atoms – similar to how the sequence of base pairs determines the information content of DNA, as sequences of zeros and which form the memory of computers.

Researchers from the University of California, Berkeley, and Ruhr-Universität Bochum (RUB) have taken a step toward this vision. They showed that atomic probe tomography can be used to read a complex spatial arrangement of metal ions in multivariate metal-organic frameworks.

Metal-organic frames (MOFs) are crystalline porous networks of multi-metal nodes connected by organic units to form a well-defined structure. To encode information with a sequence of metals, it is essential to read the metal arrangement first. However, reading the scheme was very challenging. Recently, the interest in characterizing metal sequences has been growing because of the extensive information that such multivariate structures could provide.

Fundamentally, there was no method to read the metal sequence in MOFs. In the present study, the research team successfully performed using atomic probe tomography (APT), in which Bochum-based materials scientist Tong Li is an expert. The researchers chose MOF-74, made by the Yaghi group in 2005, as the object of interest. They design the MOFs with mixed combinations of cobalt, cadmium, lead, and manganese, and then decrypt their spatial structure with APT.

Li, professor and head of the research group Atomic-Scale Characterization at the Institute for Materials at RUB, describes the method together with Dr. Zhe Ji and Professor Omar Yaghi of UC Berkeley in the journal Science, published online on August 7, 2020.

Just as sophisticated as biology

In the future, MOFs could form the basis of programmable chemical molecules: for example, an MOF could be programmed to introduce an active pharmaceutical ingredient into the body to target infected cells and then break down the active ingredient into harmless substances if it once did not. more is needed. Or MOFs can be programmed to release different medications at different times.

“This is very powerful because you basically code the behavior of molecules that leave the pores,” Yaghi said.

They could also be used to capture CO₂ and at the same time convert the CO₂ in a useful raw material for the chemical industry.

“In the long run, such structures with programmed atomic sequences could completely change our way of thinking about material synthesis,” the authors write. “The synthetic world could reach a whole new level of precision and sophistication previously reserved for biology.”