Synthesis And Characterization Of Nanojars And Their Anion Binding Ability
Date of Award
Doctor of Philosophy
Gellert Mezei, Ph.D.
David Huffman, Ph.D.
Ramakrishna Guda, Ph.D.
Todd Barkman, Ph.D.
Anion recognition and encapsulation, anion selectivity, nanojars, self-assembly, supramolecular chemistry, synthetic receptors
Inorganic anions are an important class of inherently negatively charged species. Anions such as sulfate (SO42–) and phosphates (H2PO4–, HPO42–) are ubiquitous in nature and biological systems, whereas chromate (CrO42–) and arsenates (H2AsO4–, HAsO42–) are environmental pollutants. Because of the high interest in the sequestration of anions from aqueous media, different methods have been explored to bind anions. Among these, the use of noncovalent interactions to encapsulate anions by organic and metal-organic host molecules is particularly attractive, because the reversibility of binding allows for the easy recovery of the extracted anion and the recycling of the anion extracting agent.
Nanojars are a class of anion-encapsulating supramolecular coordination complexes that self-assemble from copper (Cu2+), hydroxide (HO–), and pyrazolate (pz = C3H3N2–) ions in the presence of anions with large hydration energy such as carbonate (CO32–) and sulfate. The selfassembled nanojars consist of three or four metallamacrocycles of the formula [(Cu(OH)(pz)]x (x = 6‒14, except 11) stacked in a jar-shaped structure that incarcerates an anion in the center. The incarcerated anion is held by a multitude of hydrogen bonds in a hydrophilic cavity surrounded by a hydrophobic periphery. The unique chemical structure of nanojars makes them an excellent class of compounds for studying anion binding and extraction; copper-pyrazole chemistry; crystal growth of large, self-assembled molecules; and supramolecular interactions in these assemblies.
In this dissertation research, nanojars incarcerating different anions, as well as their capped and expanded derivatives were synthesized and characterized in solution by electrosprayionization mass spectrometry (ESI-MS), 1H, 19F, 9Be, 31P nuclear magnetic resonance (NMR) and UV-vis spectroscopy, and in the solid state by single-crystal X-ray diffraction (XRD). The incarceration of anions by nanojars was applied to the extraction of environmentally relevant anions from water. Novel pyrazole derivatives containing charged groups at the 4-position and tethered pyrazoles of different tether lengths were synthesized and characterized by ESI-MS, 1H, 13C NMR, and XRD. The new pyrazoles were used to investigate the impact of the ligand structure on the anion selectivity and anion binding strength of nanojars. The effect of different counterions on the crystallization of nanojars was investigated, resulting in X-ray diffraction quality singlecrystals of previously uncrystallizable nanojars. The use of metals other than copper for the synthesis of nanojars was explored. The pyrazole ligand exchange and acid-induced anion exchange in nanojars were examined by ESI-MS using various pyrazole derivatives and different acids. The interaction of nanojars with biomolecules, including proteins, was also investigated using ESI-MS and UV-vis spectroscopy.
This research revealed interesting findings and discoveries about the chemistry of nanojars. Capped nanojars were found to be intermediates in the reversible, pH-dependent formation of nanojars. Expanded nanojars bind two carbonate ions instead of one, compared to the conventional nanojars. Rigidification of the nanojar’s outer shell by tethering pyrazole ligands led to anion selectivity of nanojars in the case of sulfate and carbonate. The first crystallographic characterization of non-covalently bound BeF42–, FPO32–, HPO32–, WO42– and SeO32– anions in supramolecular host-guest assemblies is provided.
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Al Isawi, Wisam Abdulabbas Flayyih, "Synthesis And Characterization Of Nanojars And Their Anion Binding Ability" (2022). Dissertations. 3872.