Date of Award

8-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Committee Member

Brian Powell, Committee Chair

Committee Member

Modi Wetzler

Committee Member

Bill Pennington

Committee Member

Shiou-Jyh Hwu

Committee Member

Lindsay Shuller-Nickles

Abstract

The wide use of the f-elements, including nuclear weapons, nuclear energy and radiopharmaceuticals, has led to the growing unwanted accumulation of the lanthanides and actinides in the environment. The removal of these metals requires the design of highly selective ligands that take advantage of their complex chemistry (wide degree of covalency and high coordination numbers). Additionally, the environments these metals are typically being removed from involve a complicated mixture of other metals and strong counterions. Ligand design for the f-elements requires high selectivity and the formation of stable complexes in a wide range of environments. Ethylene diamine tetraacetic acid (EDTA) is one of the most well-known and widely utilized ligands in coordination chemistry, and hydroxamate-containing ligands are some of the most common in biological chemistry, suggesting a natural combination of EDTA-like backbones with hydroxamate arms. Specifically, the increase from the hexadentate EDTA to the decadentate hydroxamate analog would address the larger coordination numbers of the f-elements. EDTA, however, is too small even for Fe(III), leaving a coordinated water on the Fe, and is far too small for Ln/An(III) ions. Consequently, I synthesized a hydroxamate EDTA analog where the arms are longer by one carbon (ethylenediamine tetrapropionyl hydroxamic acid, EDTPHA). Potentiometric titrations of EDTPHA with La(III), Eu(III), and Lu(III), and a comparison with a synthetic all-carboxylate analog (EDTP) reveal that EDTPHA is powerful ligand for lanthanides competitive with EDTA. During the course of the work I developed a new protecting group for use in hydroxamate synthesis, and the straightforward synthesis of the EDTPHA ligand (utilizing highly pure aza-Michael chemistry) enables future work with additional ligands including EDTA-like ligands as well as siderophore-like peptide ligands to optimize their selectivity for f-element chemistry.

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