Lanthanide Binding Peptide Surfactants at Air-Aqueous Interfaces for Interfacial Separation of Rare Earth Elements

08 May 2024, Version 2


We are developing an all-aqueous, bio-inspired approach using peptides as surfactants that selectively bind rare earth element (REE) cations and adsorb at the air/water interface to enable green capture and separation. REEs are essential components in modern electronic devices and clean energy technologies which must be separated from feedstocks of aqueous mixtures. Their selective capture is particularly challenging owing to their similarity in size and charge. Lanthanide binding tags (LBTs) are amphiphilic peptide sequences based on the binding loop in the evolutionarily conserved EF-hand metal binding motif. We study LBTs optimized for coordination to Tb$^{3+}$ using a suite of experimental methods including luminescence spectroscopy, surface tensiometry, x-ray reflectivity and x-ray fluorescence near total reflection, and find that these LBTs capture Tb$^{3+}$ in bulk and adsorb at the interface. Molecular dynamics show that the binding pocket remains intact upon adsorption. We find that, if the net negative charge on the peptide results in a negatively charged complex, excess cations are recruited to the interface by non-selective Coulombic interactions that compromise selective REE capture. If, however, the net negative charge on the binding loop is -3, resulting in a neutral complex, a 1:1 surface ratio of cation to peptide is achieved. We demonstrate selective interfacial extraction from an equimolar mixture of Tb$^{3+}$ and La$^{3+}$, validating an LBT-mediated interfacial separation of REEs.


Rare Earth Elements

Supplementary materials

Supplementary Information
Supplementary figures and tables. Equations used for the calculations of parameters reported in the main manuscript.


Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.