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Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is...
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Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...
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Engineering lanmodulin's selectivity for actinides over lanthanides by controlling solvent coordination and

Joseph A Mattocks1, Joseph A Cotruvo1, Gauthier J-P Deblonde2,3

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Researchers modified the lanmodulin (LanM) protein to enhance its selectivity for actinides over lanthanides. A key finding is that coordinated water molecules, not direct aspartate coordination, are crucial for LanM

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Area of Science:

  • Biochemistry and biophysics
  • Coordination chemistry
  • Radiochemistry

Background:

  • Developing selective chelators for lanthanides and actinides is critical for rare earths mining, nuclear waste management, and medicine.
  • Lanmodulin (LanM) is a highly selective protein chelator for f-elements, but its mechanism of action is not fully understood.
  • Achieving selectivity between actinides and lanthanides is a significant challenge in chelator design.

Purpose of the Study:

  • To investigate the role of the aspartate residue at the 9th position in LanM's metal-binding sites.
  • To understand how LanM achieves high affinity and selectivity for f-elements.
  • To explore strategies for improving LanM's actinide/lanthanide selectivity.

Main Methods:

  • Characterization of five LanM variants with substitutions at the 9th aspartate position (asparagine, histidine, alanine, methionine, selenomethionine).
  • Spectroscopic measurements using lanthanides (Nd3+, Eu3+) and actinides (Am3+, Cm3+).
  • Analysis of metal-coordinated water molecules and first-sphere/second-sphere interactions.

Main Results:

  • Metal-coordinated water molecules enhance LanM's affinity and pH-stability for f-elements, contrary to small chelator behavior.
  • The native aspartate residue hydrogen bonds to coordinated solvent rather than directly coordinating the metal.
  • The asparagine variant nearly doubled LanM's selectivity for actinides over lanthanides by tuning these interactions.

Conclusions:

  • Coordinated solvent plays an essential role in LanM's function for both physiological processes and separation applications.
  • LanM's preference for actinides over lanthanides can be significantly improved through targeted modifications.
  • Biomolecular scaffolds offer tunable interactions for developing advanced separation methods and bio-engineered chelators for medical isotopes.