(316c) Quantification of Adsorption of Lanthanide-Binding Peptides at the Air-Water Interface Via Confocal Laser Scanning Microscopy

We seek to develop a green and efficient REE separation process that exploits peptide surfactants (PEPS) that selectively bind REEs in a binding loop and sequester them in the air-water interfaces of foam via a froth flotation process. Previous studies have shown that the bulk and interfacial selectivity of REEs binding to PEPS differ significantly and that the binding loop conformation changes subtly with different REEs. We hypothesize that the REE induced structural change confers differences in surface activity between different REE:PEPS complexes. To probe this concept, we incorporate the unnatural amino acid, acridon-2-ylalanine (Acd), into PEPS and image the air-water interface of PEPS solutions using confocal laser scanning microscopy (CLSM). By measuring the spatial intensity distribution of Acd fluorescence, we quantify the surface concentration of PEPS and REE:PEPS complexes. Additionally, the Acd fluorophore can sensitize the luminescence of Eu³⁺ captured by PEPS via FRET, thereby diminishing the Acd fluorescence intensity. Other REEs, when present in the binding loop, do not reduce Acd emission as significantly. Mixtures of a given REE with Eu³⁺ thus have intermediate Acd fluorescence, which allows ratiometric measurements of REE versus Eu³⁺ selectivity in the bulk and at the interface. With these tools, we measure the dynamics of adsorption of different REE:PEPS complexes and complement these measurements with parallel dynamic surface tension studies. We find that light REE:PEPS complexes adsorb to the air-water interface with faster kinetics than heavy REE:PEPS complexes. This difference in adsorption kinetics is consistent with the discrepancy between bulk and interfacial selectivity and can provide a basis for selective REE capture.