X-ray absorption spectroscopy of lanmodulin-derived peptides bound to rare earth elements

Area of Science:

• Materials Science
• Inorganic Chemistry
• Analytical Chemistry

Background:

• Sustainable rare earth element (REE) supply chains are vital for consumer, national security, and clean energy objectives.
• Current REE separation methods, like solvent extraction, are expensive and environmentally taxing.
• Developing selective aqueous-based ligands is essential for efficient and sustainable REE production.

Purpose of the Study:

• To investigate the relationship between ligand coordination structure and selectivity for individual REEs.
• To understand how different chelating ligands interact with lanthanide ions.
• To inform the design of novel ligands for improved REE separation.

Main Methods:

• Utilized X-ray absorption spectroscopy (XAS) to probe the local structure of lanthanide (Ln) ions (La, Ce, Pr, Nd).
• Employed a novel flow cell for collecting liquid-phase XAS spectra, mitigating bubble interference and beam damage.
• Analyzed X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) to discern structural differences.

Main Results:

• Observed distinct energy shifts, broadening, and intensity variations in XANES spectra across different Ln-ligand complexes.
• Identified differences in coordinating ligand distances and peak intensities in EXAFS spectra.
• Found subtle local coordination structure differences between lanthanide-lanmodulin EF-hand 1 peptide (LanM1) complexes compared to other ligands.

Conclusions:

• XAS provides valuable insights into the local coordination environment of lanthanide ions with aqueous ligands.
• Understanding these structures is key to designing more selective ligands for efficient REE separations.
• Further studies combining XANES, EXAFS, and modeling can enhance structural knowledge for sustainable REE production.