PNNL

The Science

Peptoids are highly tunable biomimetic molecules capable of self-assembling into crystalline nanomaterials with complex 3D structures. These assemblies can mimic the active sites of metal-free enzymes, including carbonic anhydrases (CAs), to facilitate chemical reactions. CAs are used to convert carbon dioxide (CO₂) into bicarbonate in biological systems. Researchers incorporated imidazolyl ligands into peptoids and self-assembled the peptoids into crystalline nanosheets and nanotubes. The results demonstrate how the histidine-inspired groups organize in crystalline peptoid materials and how these materials can be used as metal-free CA mimics for enhanced CO₂ hydration and conversion into bicarbonate. The peptoids facilitated the formation of carbon-containing minerals in the presence of calcium ions.

The Impact

CAs effectively take CO₂ to bicarbonate and enhance carbonate precipitation by promoting both CO₂ hydration and the conversion of hydrated CO₂ into bicarbonate. Previous attempts at developing CA mimics have required the use of metal cofactors to generate sufficient function. This work establishes a strategy for creating metal-free, artificial enzymes through precise molecular design and supramolecular organization. The developed thermally and chemically stable peptoid assemblies offer a versatile platform for hydrolytic catalysis and CO₂ mineralization without metal cofactors.

Summary

CAs, enzymes that accelerate the conversion of CO₂ into bicarbonate, have inspired biomimetic approaches to turning CO₂ into carbonate minerals. However, the limited stability and high cost of natural CAs have hindered their practical application. Recently discovered metal-free CAs suggest that organized catalytic groups and hydrogen-bonding networks can enable catalysis without metal cofactors, providing inspiration for new artificial enzymes.

Researchers designed sequence-defined peptoids that self-assemble into crystalline nanosheets and nanotubes containing spatially organized, histidine-inspired catalytic groups. These assemblies catalyzed ester hydrolysis under physiological conditions and promoted CO₂ hydration and calcium carbonate formation while exhibiting high thermal and chemical stability. Mechanistic studies support general acid-base catalysis within the assembly microenvironment and suggest a role for cooperative proton transfer to adjacent solvated CO₂. Carbon-13 nuclear magnetic resonance measurements confirmed accelerated carbonate mineralization, with the presence of nanosheets eliminating the induction period before mineral formation. These findings establish a versatile platform for designing metal-free artificial enzymes and reveal how molecular organization can support catalytic activity and biomimetic mineralization.

Contact

Chun-Long Chen, Pacific Northwest National Laboratory, chunlong.chen@pnnl.gov

Funding

This work was mainly supported by the Department of Energy (DOE), Office of Science, Basic Energy Sciences program under award FWP 80124 at Pacific Northwest National Laboratory (PNNL). X-ray diffraction work was conducted at Beamline 8.3.1 at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory (LBNL). Beamline 8.3.1 at the ALS is operated by the University of California, San Francisco, with generous grants from the National Institutes of Health (R35 GM158447 for technology development and P30 GM124169 for beamline operations). The ALS (Berkeley, CA) is a national user facility operated by LBNL, under the Basic Energy Sciences program, on behalf of DOE, under contract number DE-AC02-05CH11231. PNNL is a multiprogram national laboratory operated for DOE by Battelle under contract DE-AC05-76RL01830. P.C. acknowledges generous start-up support from Kennesaw State University.