(467a) Lanthanide Binding Tag Peptides for the Foam Fractionation of Rare Earth Elements

Solvent extraction is widely used for separation of rare earth elements trivalent cations (REEs or Ln³⁺) from an aqueous phase into an organic solvent. This process is energy intensive and environmentally unfriendly, requiring large volume of organic solvent and organo-phosphate surfactants. Here, we exploit the high affinity of a surface-active Lanthanide Binding Tag (LBT) peptide (LBT1, YIDTNNDGWYEGDELLA), that coordinates selectively with Ln3+ ions for its use in a bioinspired/eco-friendly extraction processes in which the complexed LBT1-Ln³⁺ peptide adsorbs to the air/aqueous interfaces of bubbles for foam recovery. To understand the surface activity and identify the bound cationic species at the air-water interface, we characterized the surface molecular adsorption and arrangement of LBT1 and the more surface active LBT1-LLA, which has three additional hydrophobic residues (-LLA) attached to the C-terminus of LBT1. For this, we measured the relaxation dynamic tension of the each LBT in the absence and presence of Tb3+ cations. X-ray reflectivity (XRR) and X-ray fluorescence near total reflection (XFNTR) measurements on the adsorbed layer were used to compute the surface concentration of the peptide and the Ln⁺³ cation, and the thickness of the interfacial layer. The addition of three hydrophobic residues to LBT1 increased the surface density of the peptide by three-fold. Additionally, the LBT1-LLA improved the adsorption of Tb3+ ions to the air-water interface up to approximately 30% over LBT1 peptides. The interfacial density of Tb-bound LBT1-LLA increased between 50% and 100% compared with the Tb-free, unbound LBT1-LLA. We also observed a four-fold increase in the surface coverage of LBT1 in the Tb-bound state over the Tb-free state. The enhancement in the surface activity of LBTs peptides is improved by the addition of hydrophobic residues appended to the C-terminus of the peptide. This improvement in the hydrophobicity of these biomolecules could be advantageous for a green, eco-friendly separation method of REEs.