De-novo protein crystals as mesoporous functional materials for critical element separations

NON-TECHNICAL SUMMARY: Many elements play essential roles in the advancement of technology. Critical elements, including rare earth metals, are vital for electronics, renewable energy, and advanced materials. However, the stable supply of these elements remains a challenge due to the limitations of the current extraction and separation methods that are high-cost, polluting, and/or geographically constrained. Nature has evolved sophisticated metal-binding peptides (MBPs) that selectively recognize and bind certain ions and molecules, which show great promise as a new modality for critical element separation. In practice, these MBPs need to be immobilized in a porous scaffold to facilitate the adsorption of targeted elements and promote the recycling of MBPs. The goal of this project is to study and develop a new class of immobilization substrates, namely mesoporous protein crystals, for critical element separation. Protein crystals show several appealing properties for MBP immobilization, including appropriate pore size and distribution, structural stability, and low toxicity, but they are limited by a low propensity of crystal nucleation. In this project, computationally designed protein crystals will be used to study the nucleation and growth behaviors of protein crystals. The structure-property relationship of protein crystals will be systemically characterized. The team will further evaluate immobilization strategies to maximize the density of MBPs in crystals while maintaining a sufficient porosity for ion diffusion. The capability of immobilized MBPs in sequestering critical elements will be evaluated and compared to the free MBPs. The success of the project will create a new MBP immobilization platform for efficient and selective critical element separation. The platform can be generalized to immobilize other materials for broader applications. Additionally, the project will provide valuable training and education opportunities to graduate, undergraduate, and high-school students by developing educational modules on advanced biomaterials for energy and sustainability. TECHNICAL SUMMARY: This project aims to obtain a comprehensive understanding of protein crystals as immobilization substrates for critical element separation. The team will combine protein engineering and rational design to tune the assembly of protein crystals and unravel factors that impact the crystal nucleation and growth. Batch crystallization will be exploited for the scalable synthesis of protein crystals and their physicochemical properties in varied structures and binding affinity will be systemically investigated. The team will explore immobilization strategies that can maximize the gravimetric ratio of guest MBP proteins in the crystalline scaffold while maintaining stable immobilization without gradual loss of MBPs over time. The immobilization platform will be examined by immobilizing Lanmodulin (LanM), a protein derived from nature for selective sequestration of rare earth elements (REEs). The capability of LanM-crystal complexes in binding REEs and their selectivity over other bivalent and trivalent cations will be evaluated. The team will further test the performance of immobilized LanM in practical REE extraction scenarios, such as extraction from simulated low-grade leachate using fixed-bed columns packed with LanM-crystal complexes. The new immobilization platform will address the scalability, cost, and stability issues of protein-based adsorbents that traditionally hinder their deployment. The success of this project will also offer a secure and resilient critical elements supply chain essential to economic prosperity and national defense. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.