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 enzymes, including the carbonic anhydrases (CAs) that convert carbon dioxide (CO₂) into bicarbonate. By incorporating specific ligands into self-assembling peptoids and coordinating them with metal cations, researchers synthesized crystalline CA mimic peptoid nanosheets and nanotubes. The peptoid assemblies exhibited catalytic activity toward CO₂ hydration and conversion to bicarbonate and then carbonate, facilitating the formation of carbon-containing minerals in the presence of calcium ions.

The Impact

CAs are so effective for CO₂ sequestration due to their high catalytic performance in converting CO₂ to HCO₃^- for carbonate precipitation because they promote both CO₂ hydration and the conversion of hydrated CO₂ to bicarbonate. Previous attempts at synthesizing CA mimics have been unable to match their overall reactivity. This work reports the first example of CA mimics that can catalyze both necessary steps. The insights learned from both the experimental and computational work offer essential guidance for the future design of high-performance CA mimics suitable for applications in converting CO₂ and developing artificial enzymes with higher stability than those found in nature for the development of advanced bio-inspired hybrid materials. 

Summary

CO₂ is an industrial waste product that is found throughout the atmosphere. To contain CO₂, researchers have explored biomimetic approaches to carbonation using CAs. CAs have shown considerable promise for CO₂ sequestration due to their catalytic performance converting CO₂ to HCO₃^-. However, the use of natural CAs has been limited due to their intrinsic low stability and high cost. 

By designing and assembling peptoids with specific metal-ligand coordination, researchers developed crystalline peptoid assemblies with tunable surface chemistries and microenvironments for promoted hydration and sequestration of CO₂. These peptoid catalysts are highly stable and retain their catalytic activity after multiple cycles at elevated temperatures. The assemblies promoted conversion of CO₂ all the way to carbonate, which can then react with metals in the environment to form solid carbonate minerals. The experimental findings were further corroborated with molecular dynamics simulations, which highlight the critical roles of the peptoid–Zn²⁺ binding energy and active site microenvironment on the catalytic performance of the peptoid-based CA mimics. This study paves a path for designing highly efficient CA mimics with high programmability and flexibility as well as enhancing scientific understanding of catalytic CO₂ hydration and sequestration processes. Further investigation of peptoid-based catalysts will be crucial for developing artificial enzymes capable of rivaling natural CA activity while retaining the necessary thermal and chemical stabilities for practical applications.

Contact

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

Funding

This work was supported by the Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division, Biomolecular Materials program, FWP80124. BSH and MDB performed and analyzed molecular dynamics simulations supported under FWP77876. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a Department of Energy Office of Science user facility located at Lawrence Berkeley National Laboratory (LBNL), operated under Contract No. DE-AC02-05CH11231 using NERSC award BES-ERCAP0023738. XRD work was conducted at the Advanced Light Source of LBNL, which was supported by the Office of Science (No. DE-AC02-05CH11231).