Protein Complex Shows Promise for Berkelium Separation

Berkelium (Bk) is a highly radioactive constituent of nuclear waste. The ability to separate it from elements that can be recycled as nuclear fuel would be desirable for reducing the volume of waste that must be stored. In theory, Bk differs from other heavy metals by taking on an extra positive charge (a +IV oxidation state as opposed to +III) when bound to a particular synthetic organic molecule—a “chelate” that binds a central metal atom like a claw. This difference in the Bk oxidation state could help scientists develop better methods for handling and purifying nuclear materials, but experimental confirmation had been lacking. In this work, numerous approaches, including liquid chromatography, mass spectrometry, and computational simulations, determined that the Bk in the chelate complex is indeed Bk(IV).

One way to use this fact to separate Bk from other actinides is via the protein siderocalin. It recognizes and binds actinide(III)–chelate complexes, which are negatively charged, but not neutral Bk(IV) complexes. To gain greater insight into how siderocalin interacts with such complexes, the researchers performed x-ray crystallography at Beamline 5.0.2 on californium (Cf)–chelate—siderocalin complexes. Until recently, there was little to no structural data on Bk or Cf. These experiments allowed the researchers to extract a great deal of data out of much smaller material quantities, which is not only safer, but more efficient for these rare and radioactive materials. Combined with theoretical predictions, the data add significant insight to the field and may lead to innovative Bk separation and purification processes.