Atomic level imaging of artificial proteins

Science

Scientists have created thin, paper-like crystalline sheets using a synthetic protein-like molecule called a polypeptoid. These nanosheets are only one molecule thick, the molecules being arranged in a very specific way. Scientists take images of these nanosheets using electron microscopes under cryogenic conditions. Until recently, these images were blurry due to the small number of electrons that can pass through the leaves without causing damage. In this study, the researchers used algorithms based on machine learning to process approximately 500,000 independent images. The result is the first clear, real image of individual atoms in a flexible synthetic material.

The impact

Synthetic polymers are essential for many products we take for granted. These range from plastic furniture to the fuselages of modern airplanes. They are also at the heart of devices such as fuel cells and rechargeable batteries. These devices are becoming increasingly important in the emerging clean energy landscape. All the important properties of synthetic polymers depend on the arrangement of their atoms. The ability of scientists to position individual atoms in polymeric materials will improve our understanding of the bottlenecks that limit the performance of synthetic polymers. This research also marks an important step in all nanosciences.

Summary

For the first time, scientists have revealed the atomic structural details of a flexible synthetic material. Peptoid diblock copolymers consist of two different protein-like chains that are linked together. These materials were designed to fit closely together to form highly organized crystalline sheets in water. The individual molecules and their relative orientations within the nanosheets were directly observed by cryogenic transmission electron microscopy (cryo-TEM), revealing atomic details in positional space inaccessible by conventional scattering techniques. The ultra-cold temperature used to quickly freeze the nanosheets effectively locked the molecules in place. Imaging the sample under cryogenic conditions prevented energetic electrons from destroying the structure. To better protect soft materials from the electron beam, the researchers used fewer electrons per image. The images obtained under these conditions were processed using sophisticated mathematical tools and machine learning algorithms to produce high resolution images of the structure at the atomic scale.

The combined precision synthesis of peptoid polymers, atomic imaging of cryo-MET, and computer modeling have helped scientists understand polymer structures at the atomic level. Researchers are now able to make modifications at the atomic level to design targeted molecules. This paves the way for the rational engineering of sophisticated functions in flexible materials through systematic control of their chemical structure. The research was conducted in part at two Department of Energy user facilities, the Molecular Foundry and the Advanced Light Source.

Funding

This work was funded by the Department of Energy Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division. The work of the Molecular Foundry and the Advanced Light Source at the Lawrence Berkeley National Laboratory was supported by user projects at these user facilities, supported by the Department of Energy Office of Science, Office of Basic Energy Sciences. The micrographs shown here were obtained at the Donner cryo-MET facility at the Lawrence Berkeley National Lab and the Berkeley Bay region cryo-MET facility at UC Berkeley.

Source:

Journal reference:

Xuan, S., et al. (2021) Atomic-level engineering and imaging of polypeptoid crystal lattices. PNAS. doi.org/10.1073/pnas.1909992116.


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