Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

Travis S. Grimes; Colt R. Heathman; Santa Jansone-Popova; Alexander S. Ivanov; Santanu Roy; Vyacheslav S. Bryantsev; Peter R. Zalupski

doi:10.1021/acs.inorgchem.7b02792

Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

Travis S. Grimes, Colt R. Heathman, Santa Jansone-Popova, Alexander S. Ivanov, Santanu Roy, Vyacheslav S. Bryantsev, Peter R. Zalupski

Research output: Contribution to journal › Article › peer-review

26 Scopus citations

Abstract

The novel metal chelator N-2-(pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-PyM) was designed to replace a single oxygen-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) with a nitrogen-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen-bearing heterocyclic moiety. The Am³⁺, Cm³⁺, and Ln³⁺ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL_(aq) complexes at the same aqueous acidity. The denticity change observed for Eu³⁺ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL_(aq) complex is likely due to the protonation of an available carboxylate group because the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the curium complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from π-back-bonding interactions between singly occupied 5f orbitals of Am³⁺ and the pyridyl nitrogen. The differences between the stabilities of trivalent actinide chelates (Am³⁺, Cm³⁺) and trivalent lanthanide chelates (La³⁺-Lu³⁺) are observed in liquid-liquid extraction systems, yielding unprecedented 4f/5f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced nitrogen-donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N-(3-fluoro-2-pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-3-F-PyM) showed subdued 4f/5f differentiation due to the presence of this electron-withdrawing group.

Original language	English
Pages (from-to)	1373-1385
Number of pages	13
Journal	Inorganic Chemistry
Volume	57
Issue number	3
DOIs	https://doi.org/10.1021/acs.inorgchem.7b02792
State	Published - Feb 5 2018

Funding

The experimental work conducted by T.S.G., C.R.H., and P.R.Z. at the Idaho National Laboratory was supported by the U.S. Department of Energy, Office of Nuclear Energy, DOE Idaho Operations Office under Contract DE-AC07-05ID14517. The synthetic work by S.J.-P. and computational studies by A.S.I., S.R., and V.S.B. were supported by the Fuel Cycle Research and Development Program, Office of Nuclear Energy, U.S. Department of Energy. DFT calculations used resources of the National Energy Research Scientific Computing Center and the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, supported by the Office of Science of the U.S. Department of Energy under Contracts DE-AC02-05CH11231 and DE-AC05-00OR22725 respectively. The experimental work conducted by T.S.G., C.R.H., and P.R.Z. at the Idaho National Laboratory was supported by the U.S. Department of Energy, Office of Nuclear Energy, DOE Idaho Operations Office, under Contract DE-AC07-05ID14517. The synthetic work by S.J.-P. and computational studies by A.S.I., S.R., and V.S.B. were supported by the Fuel Cycle Research and Development Program, Office of Nuclear Energy, U.S. Department of Energy. DFT calculations used resources of the National Energy Research Scientific Computing Center and the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, supported by the Office of Science of the U.S. Department of Energy under Contracts DE-AC02-05CH11231 and DE-AC05-00OR22725, respectively.

Funders	Funder number
DOE Idaho Operations Office
Fuel Cycle Research and Development Program
U.S. Department of Energy	DE-AC07-05ID14517
Office of Science	DE-AC05-00OR22725, DE-AC02-05CH11231
Office of Nuclear Energy
Oak Ridge National Laboratory

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10.1021/acs.inorgchem.7b02792

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title = "Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants",

abstract = "The novel metal chelator N-2-(pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-PyM) was designed to replace a single oxygen-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) with a nitrogen-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen-bearing heterocyclic moiety. The Am3+, Cm3+, and Ln3+ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL(aq) complexes at the same aqueous acidity. The denticity change observed for Eu3+ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL(aq) complex is likely due to the protonation of an available carboxylate group because the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the curium complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from π-back-bonding interactions between singly occupied 5f orbitals of Am3+ and the pyridyl nitrogen. The differences between the stabilities of trivalent actinide chelates (Am3+, Cm3+) and trivalent lanthanide chelates (La3+-Lu3+) are observed in liquid-liquid extraction systems, yielding unprecedented 4f/5f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced nitrogen-donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N-(3-fluoro-2-pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-3-F-PyM) showed subdued 4f/5f differentiation due to the presence of this electron-withdrawing group.",

author = "Grimes, {Travis S.} and Heathman, {Colt R.} and Santa Jansone-Popova and Ivanov, {Alexander S.} and Santanu Roy and Bryantsev, {Vyacheslav S.} and Zalupski, {Peter R.}",

note = "Publisher Copyright: {\textcopyright} 2018 American Chemical Society.",

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doi = "10.1021/acs.inorgchem.7b02792",

language = "English",

volume = "57",

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T1 - Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

AU - Grimes, Travis S.

AU - Heathman, Colt R.

AU - Jansone-Popova, Santa

AU - Ivanov, Alexander S.

AU - Roy, Santanu

AU - Bryantsev, Vyacheslav S.

AU - Zalupski, Peter R.

PY - 2018/2/5

Y1 - 2018/2/5

N2 - The novel metal chelator N-2-(pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-PyM) was designed to replace a single oxygen-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) with a nitrogen-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen-bearing heterocyclic moiety. The Am3+, Cm3+, and Ln3+ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL(aq) complexes at the same aqueous acidity. The denticity change observed for Eu3+ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL(aq) complex is likely due to the protonation of an available carboxylate group because the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the curium complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from π-back-bonding interactions between singly occupied 5f orbitals of Am3+ and the pyridyl nitrogen. The differences between the stabilities of trivalent actinide chelates (Am3+, Cm3+) and trivalent lanthanide chelates (La3+-Lu3+) are observed in liquid-liquid extraction systems, yielding unprecedented 4f/5f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced nitrogen-donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N-(3-fluoro-2-pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-3-F-PyM) showed subdued 4f/5f differentiation due to the presence of this electron-withdrawing group.

AB - The novel metal chelator N-2-(pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-PyM) was designed to replace a single oxygen-donor acetate group of the well-known aminopolycarboxylate complexant diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid (DTPA) with a nitrogen-donor 2-pyridylmethyl. Potentiometric, spectroscopic, computational, and radioisotope distribution methods show distinct differences for the 4f and 5f coordination environments and enhanced actinide binding due to the nitrogen-bearing heterocyclic moiety. The Am3+, Cm3+, and Ln3+ complexation studies for DTTA-PyM reveal an enhanced preference, relative to DTPA, for trivalent actinide binding. Fluorescence studies indicate no changes to the octadentate coordination of trivalent curium, while evidence of heptadentate complexation of trivalent europium is found in mixtures containing EuHL(aq) complexes at the same aqueous acidity. The denticity change observed for Eu3+ suggests that complex protonation occurs on the pyridyl nitrogen. Formation of the CmHL(aq) complex is likely due to the protonation of an available carboxylate group because the carbonyl oxygen can maintain octadentate coordination through a rotation. The observed suppressed protonation of the pyridyl nitrogen in the curium complexes may be attributed to stronger trivalent actinide binding by DTTA-PyM. Density functional theory calculations indicate that added stabilization of the actinide complexes with DTTA-PyM may originate from π-back-bonding interactions between singly occupied 5f orbitals of Am3+ and the pyridyl nitrogen. The differences between the stabilities of trivalent actinide chelates (Am3+, Cm3+) and trivalent lanthanide chelates (La3+-Lu3+) are observed in liquid-liquid extraction systems, yielding unprecedented 4f/5f differentiation when using DTTA-PyM as an aqueous holdback reagent. In addition, the enhanced nitrogen-donor softness of the new DTTA-PyM chelator was perturbed by adding a fluorine onto the pyridine group. The comparative characterization of N-(3-fluoro-2-pyridylmethyl)diethylenetriamine-N,N′,N″,N″-tetraacetic acid (DTTA-3-F-PyM) showed subdued 4f/5f differentiation due to the presence of this electron-withdrawing group.

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Influence of a Heterocyclic Nitrogen-Donor Group on the Coordination of Trivalent Actinides and Lanthanides by Aminopolycarboxylate Complexants

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