Using Biomolecules to Separate Plutonium - 18393
Relying on the thermodynamics and the reaction kinetics of the metal-ligand bond is the traditional approach to selective separation of metals such as plutonium. An alternative is to use a biologically based separation that leverages multiple factors to sense, bind and transport metals in a series of steps. The protein serum transferrin (Tf) handles the regulation and transport of iron in the blood. Iron and a synergistic anion bind to Tf in one or both of Tf's two lobes (N-lobe and C-lobe). The conformation of Tf changes due to the lobes closing around the metals. The conformational change that occurs when a metal ion and synergistic anion bind to transferrin can trigger additional interactions with the transferrin receptor protein and the subsequent transport of the metal-transferrin complex into cells. Transferrin also is known to bind and transport plutonium into cells but this process is less efficient than iron transport because certain plutonium-transferrin complexes appear to be unable to trigger the same conformational change in transferrin as the iron-transferrin complex. We hypothesize that the synergistic anion is the cause of the different conformational changes that inhibit plutonium-transferrins from binding to the transferrin receptor protein. Using cerium as a non-radioactive surrogate for plutonium(IV), we have been able to synthesize cerium-transferrin complexes with only carbonate as the synergistic anion as a prelude to experiments with plutonium-transferrin complexes that can test our hypothesis. (authors)