Development of Novel Ligand-Based Systems to Study the Chemical Properties of the Transactinides

John Despotopulos | 19-ERD-003

Project Overview

The periodic table is a living document that arranges elements into groups (columns) and periods (rows), whereby elements within the same group have similar chemical properties (homologs). Historically, when a transactinide (elements 104 to 118) was discovered, it was placed in the periodic table simply based on its proton number (Z). However, due to relativistic effects, which increase with Z2, these superheavy elements may not behave similarly to their direct homologs. The only way to know where they truly belong on the periodic table is by studying their chemical properties to compare them to the lighter elements of the same groups and surrounding groups.

The goal of this project was to develop the necessary infrastructure to study the aqueous phase chemistry of the heavy transactinides, specifically element 112 (copernicium, Cn) and element 114 (flerovium, Fl). The aqueous phase chemistry of these elements has never been studied due to the technical challenges associated with these experiments. Transactinides are produced at accelerators one atom at a time, with low production rates (≤ 1 atom/week) and short half-lives (≤ 30s), meaning chemical systems to study the properties of these elements must be robust, automated, and fast. Theoretical predictions show that elements heavier than Cn, particularly Fl, should have large deviations from their direct homologs, with flerovium potentially behaving more like mercury (Hg) or a noble gas (radon). Our group has synthesized molecules (thiacrown ether ligands) that specifically target the homologs of Cn (Hg) and Fl (lead and tin). Chemical systems for studying Cn have been developed with theoretical support from collaboration with the University of Chicago (Laura Gagliardi's research group). To facilitate on-line studies of the transactinides Cn and Fl, an automated microfluidic liquid–liquid extraction system was developed for chemical studies as well as an on-line liquid scintillation detection system for use in accelerator experiments. This LDRD has led to a deployable automated chemistry and detection system as well as chemistry based on novel thiacrown ethers for the first on-line study of Cn and Fl.

Mission Impact

This work supports the nuclear, chemical, and isotopic core competency, which is essential to Lawrence Livermore National Laboratory's stockpile stewardship mission, as well as its National Ignition Facility's, and Global Security's missions. Development of novel separation chemistry is critical for maintaining expertise and leadership in radiochemical methods, radiation counting, and studies of nuclear reactions. Automated chemistry can be adapted to post-detonation nuclear forensics, which requires rapid analysis of radioactive samples and high sample throughput. Material synthesis also has forensics applications; highly specific materials would enable field-deployable systems where small concentrations of analytes could be effectively isolated from interfering background products. Novel ligand synthesis, such as those presented here, also has applications for heavy-metal remediation in the environment. Therefore, both the synthesis of molecules and the development of automated systems may be applied to future national security challenges relevant to NNSA's missions.

Publications, Presentations, and Patents

Despotopulos, J. D., Kmak, K. N. 2021. "Rapid isolation of 197m,g-Hg from proton irradiated Au foils," J. Radioanal. Nucl. Chem. 327: 1349-1354.

Kmak, K. N., Despotopulos, J. D. 2021. "Extraction of gold, mercury and lead on CL resin in HCl." J. Radioanal. Nucl. Chem. (In Press)

Ferrier, M. G., Valdez, C. A., Singh, S. K., Hok, S., Ray, D., Gagliardi, L., Despotopulos, J. D. 2021. "Unsaturated sulfur crown ethers can extract Mercury(II) and show promise for future copernicium(II) studies: a combined experimental and computational study." Inorg. Chem. (Accepted)

Ferrier, M. G, Kmak, K. N., Kerlin, W. M., Valdez, C. A., Despotopulos, J. D. 2020. "Transactinide studies with sulfur macrocyclic extractant using mercury." J. Radioanal. Nucl. Chem. 326: 215-222.

Despotopulos, J. D., Gregorich, K. E., Ferrier, M. G., Kmak, K. N., Valdez, C. A., Kerlin, W. M, Saphon, H. 202. "Transactinide research at LLNL." PACIFICHEM 2021, December 16-21. (Invited)

Despotopulos, J. D., Valdez, C. A., Kmak, K. N 2020. Methods of isolating radioactive mercury and uses thereof. Patent U.S. Patent App. Serial No. 12/816,822.