Sustainable\nProtein Conjugates as a Soluble Capture\nand Release System for Lanthanides

We describe an innovative method for lanthanide harvest\nand recovery\nusing a semisynthetic protein as a soluble capture and release system.\nUp to nine equivalents of the lanthanide-binding ligand diethylenetriaminepentaacetic\nacid were conjugated to myoglobin, a renewable protein readily obtained\nfrom plants, resulting in a protein conjugate (MbD). MbD was characterized\nby mass spectrometry and electrophoresis. Competitive binding assays\nconfirmed MbD shows strong binding to Eu<sup>III</sup>, similar to\nthat of nonconjugated diethylenetriaminepentaacetic acid. Importantly,\nMbD enables efficient capture of Eu<sup>III</sup> through liquid extraction\nand size-exclusion filtration, followed by irreversible release of\nEu<sup>III</sup> with a simple buffer exchange to phosphate-buffered\nsaline, yielding EuPO<sub>4</sub> as a precipitate that can be harvested\nand separated readily from the soluble protein MbD for recycling.\nRecyclability studies for MbD showed over 80% efficiency for Eu<sup>III</sup> capture after three cycles, validating the sustainable\nnature of MbD. As a proof of concept, MbD achieved over 90% lanthanide\ncapture from coal fly ash leachate, demonstrating its practical application\nin extracting lanthanides from a complex mixture of many different\nmetals. The soluble protein system provides distinct advantages compared\nto more traditional methods involving ligands bound to solid support\nthat require harsh acids, rather than phosphate buffer, to achieve\nlanthanide release. Furthermore, MbD adheres to green chemistry principles\nby enabling recyclability of the conjugate with minimal loss of efficiency.