Browsing by Subject "Inorganic chemistry"

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Inorganic methods for ¹⁹F magnetic resonance-based biosensing
(2020-01-31) Xie, Da; Que, Emily
Fluorine magnetic resonance imaging (¹⁹F MRI) is a promising bioimaging technique due to the favorable magnetic resonance properties of the ¹⁹F nucleus and the lack of detectable biological background signal. One intriguing opportunity in ¹⁹F magnetic resonance molecular imaging is to design responsive agents that can serve as a readout of biological activity, including but not limited to the activity of enzymes, redox activity, the activity of ions, etc. Paramagnetic centers have the ability to enhance relaxation rates of nearby ¹⁹F nuclei through paramagnetic relaxation enhancement (PRE). Further, metals with anisotropic unpaired electrons can induce changes in ¹⁹F chemical shift through the pseudo-contact shift (PCS) effect. Paramagnetic agents are therefore well suited for this activity-based sensing as metal complexes can be designed to respond to specific biological activities and give a corresponding ¹⁹F response that results from changes in the metal complex structure and subsequently effect of PRE/PCS. In this thesis, we demonstrated the application of copper (Chapter 2-4) and nickel (Chapter 5-6) complexes as redox- and coordination-based sensors, respectively, for ¹⁹F magnetic resonance biosensing. Fluorinated CuATSM derivatives were prepared for sensing biological hypoxia due to its one-electron Cu²⁺/Cu⁺ redox well matched with cellular reduction potential under hypoxia and its fluorine MR signal effectively attenuated and restored between Cu²⁺ and Cu⁺ state. Prepared probes CuATSM-F₃ (Chapter 2), Cu4 (Chapter 3), and CuL₁ (Chapter 4) possessed an appropriate potential for hypoxia selectivity, and reduction to diamagnetic Cu⁺ complex and ligand dissociation to regenerate the ¹⁹F signal was demonstrated by NMR in cells grown under low O₂ tension. The successful employment of these Cu probes facilitates the translation to in vivo hypoxia sensing via ¹⁹F MR-based techniques. The development of Ni-based probes enables expansion of biosensing strategies and applications beyond biological redox. Proof-of-concept Ni probes based on dioxocyclam (Chapter 5) and side-bridged cyclam (Chapter 6) ligand framework exhibited the magnetic switching properties of the Ni²⁺ center in aqueous media and the potential to couple with ¹⁹F NMR/MRI to achieve sensing of pH, light irradiation and enzymatic activities in living biosystems.
Synthesis and post-synthetic modifications of novel carboxylated triphenylphosphine-based coordination polymers
(2014-05) Nuñez, Ana Julia; Humphrey, Simon M.; Freeman, Benny; Holliday, Bradley J; Mullins, Charles B; Sessler, Jonathan L
Over the last few decades, Porous Coordination Polymers (PCPs, a.k.a. MOFs) have been extensively studied for a number of applications due to their functional and structural versatility. Nonetheless, systematic studies that explore the structure-function relationship of frameworks decorated with different functional groups remain limited. In the present work, two families of coordination polymers that contain organophosphine building blocks have been synthesized and characterized. These materials contain a periodic array of P(III) Lewis base sites that are available for post-synthetic functionalization. PCM-10 is a porous coordination polymer based on Ca(II) and tris(p-carboxylated) triphenylphosphine. The material displayed a 3-dimensional surface, ideal for a series of post-synthetic modifications. The versatility of P(III)→P(V) chemistry allowed for decoration of the R₃P: sites of PCM-10 with different functional groups. Solid-state treatment of the framework with a variety of precursors, gave rise to a family of isostructural materials (ClAu-PCM-10, O=PCM-10 and (Me‒PCM-10)X; X = I⁻, F⁻, BF₄⁻ and PF₆⁻). These post-synthetic modifications directly affected the host-guest interactions, as demonstrated by comparative adsorption studied of CO₂, H₂ and other small molecules. For example, the phosphonium (Me-PCM-10)X composites displayed broad tunability of isosteric heats of CO₂ adsorption, depending on the counter-ion. Similarly, the ClAu-PCM-10 derivative resulted in selective adsorption of 1-hexene vs. n-hexane and displayed significantly increased H₂ uptake capacity, when compared to PCM-10. Ln-PCM-22 is a family of isostructural PCPs based on tris(p-carboxylated) triphenylphosphine and Ln(III) (Ln = Sm-Yb). Photoluminescence studies of Eu-PCM-22 and Tb-PCM-22 were used to elucidate certain aspects of the solid-state emissive properties of phosphine-based materials. In addition, a single-crystal-to-single-crystal post-synthetic oxidation of Tb-PCM-22 was achieved to yield the composite material Tb-O=PCM-22. This modification resulted in enhancement of the quantum efficiency, compared to that of the parent framework. These results will help further the understanding of PCMs and direct the upcoming synthesis and application of these materials.