Numerous technologies—with catalytic, therapeutic, and diagnostic applications—would benefit from improved chelation strategies for heavy alkaline earth elements: Ra2+, Ba2+, and Sr2+. Unfortunately, chelating these metals is challenging because of their large size and weak polarizing power. We found 18-crown-6-tetracarboxylic acid (H4COCO) bound Ra2+, Ba2+, and Sr2+ to form M(HxCOCO)x–2. Upon isolating radioactive 223Ra from its parent radionuclides (227Ac and 227Th), 223Ra2+ reacted with the fully deprotonated COCO4- chelator to generate Ra(COCO)2-(aq) (log KRa(COCO)2- = 5.97 ± 0.01), a rare example of a molecular radium complex. Comparative analyses with Sr2+ and Ba2+ congeners informed on what attributes engendered success in heavy alkaline earth complexation. Chelators with high negative charge [-4 for Ra(COCO)2-(aq)] and many donor atoms [≥11 in Ra(COCO)2-(aq)] provided a framework for stable complex formation. These conditions achieved steric saturation and overcame the weak polarization powers associated with these large dicationic metals.
Gilhula, James Connor, et al. "Advances in heavy alkaline earth chemistry provide insight into complexation of weakly polarizing Ra<sup>2+</sup>, Ba<sup>2+</sup>, and Sr<sup>2+</sup> cations." Science Advances, vol. 10, no. 1, Jan. 2024. https://doi.org/10.1126/sciadv.adj8765
Gilhula, James Connor, Xu, Lei, White, Jr., Frankie Don, et al., "Advances in heavy alkaline earth chemistry provide insight into complexation of weakly polarizing Ra<sup>2+</sup>, Ba<sup>2+</sup>, and Sr<sup>2+</sup> cations," Science Advances 10, no. 1 (2024), https://doi.org/10.1126/sciadv.adj8765
@article{osti_2283876,
author = {Gilhula, James Connor and Xu, Lei and White, Jr., Frankie Don and Adelman, Sara Linnae and Aldrich, Kelly Elise and Batista, Enrique Ricardo and Dan, David and Jones, Zachary Robert and Kozimor, Stosh Anthony and Mason, Harris E. and others},
title = {Advances in heavy alkaline earth chemistry provide insight into complexation of weakly polarizing Ra<sup>2+</sup>, Ba<sup>2+</sup>, and Sr<sup>2+</sup> cations},
annote = {Numerous technologies—with catalytic, therapeutic, and diagnostic applications—would benefit from improved chelation strategies for heavy alkaline earth elements: Ra2+, Ba2+, and Sr2+. Unfortunately, chelating these metals is challenging because of their large size and weak polarizing power. We found 18-crown-6-tetracarboxylic acid (H4COCO) bound Ra2+, Ba2+, and Sr2+ to form M(HxCOCO)x–2. Upon isolating radioactive 223Ra from its parent radionuclides (227Ac and 227Th), 223Ra2+ reacted with the fully deprotonated COCO4- chelator to generate Ra(COCO)2-(aq) (log KRa(COCO)2- = 5.97 ± 0.01), a rare example of a molecular radium complex. Comparative analyses with Sr2+ and Ba2+ congeners informed on what attributes engendered success in heavy alkaline earth complexation. Chelators with high negative charge [-4 for Ra(COCO)2-(aq)] and many donor atoms [≥11 in Ra(COCO)2-(aq)] provided a framework for stable complex formation. These conditions achieved steric saturation and overcame the weak polarization powers associated with these large dicationic metals.},
doi = {10.1126/sciadv.adj8765},
url = {https://www.osti.gov/biblio/2283876},
journal = {Science Advances},
issn = {ISSN 2375-2548},
number = {1},
volume = {10},
place = {United States},
publisher = {AAAS},
year = {2024},
month = {01}}
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Nuclear Physics (NP); USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program