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Electron paramagnetic resonance spectroscopy is a versatile tool for probing structural information about systems with unpaired electrons, in particular, biological systems with metal centres or chemically attached spin labels. This work uses a variety of electron paramagnetic resonance techniques to investigate the ability to measure distances between two spins (radical and metal), as well as characterise the local environment. Distance measurements are used to probe the mechanism of translocation across a membrane, where a change in distance is observed upon ATP cycling, indicating channel movement of the SecYEG:SecA complex. Furthermore, to expand the scope of distance measurements for more complex, cysteine-rich systems, spin labelling regimes are developed and optimised on the test protein myoglobin. Specifically, next generation maleimide spin labels are demonstrated to label and selectively cleave. Myoglobin is further exploited to successfully introduce the unnatural amino acid, dehydroalanine, for selective and orthogonal labelling. The development of the labelling and measurement strategy for the gadolinium-based spin label, [Gd.sTPATCN]-SL, is also shown, where the narrow central transition of the label allows a long phase memory time and increased DEER modulation depth, to give increased measurement sensitivity. In addition, gadolinium(III) distances are used to characterise the binding site of a peptide system for the application of magnetic resonance imaging. The optimisation of measuring inter-gadolinium(III) distances between 2-5 nm at both Q- and W-band is also demonstrated in the corresponding peptide ruler series. The additional benefit of the peptide to act as a metal ruler is further investigated using copper(II), where hyperfine spectroscopy is utilised to successfully confirm the nature of the binding site as all oxygen binding.

The antiferromagnetic coupling between a rare-earth (RE) and a tran- sition metal (TM) ferromagnet can be exploited to engineer normal state and superconducting functional devices. RE/TM ferromagnetic multi- layers were previously used as spin-mixers to generate spin-triplet su- percurrents. This was possible due to magnetic inhomogeneity present in the devices, however the precise nature of the inhomogeneity was not understood. Here we present a comprehensive study of the Ni/Gd/Ni system using a powerful element-specific measurement technique: x-ray magnetic circular dichroism. In order to analyse the experimental results we present a novel model based on the Stoner-Wohlfarth model, which shows that significant inhomogeneity exists at the Ni/Gd interfaces due to the competition between the exchange energies within the system and the Zeeman energy of the applied magnetic field. The experiment and model together provide a complete overview of the Ni/Gd/Ni system due to the breadth of temperatures and thicknesses studied. The knowledge gained from this work is then applied to designing and test- ing new spin valves based on the intrinsic inhomogeneity at the RE/TM interface, and both Ni/Gd- and Gd/Ho-based devices show reversible magnetic switching behaviour which alters the superconducting critical temperature.

31P magnetic resonance has yet to realise its clinical potential principally due to the relatively low sensitivity of the 31P nucleus. While 31P-MRS can uniquely provide vital information regarding in vivo phosphorus metabolism, the long acquisition times required are incompatible with observing dynamic changes in phosphorus speciation (e.g. monitoring ATP/phosphocreatine ratios in real time). This thesis reports how heptadentate Gd.DO3A derivatives can be used to enhance 31P relaxivity reducing T1 values by more than an order of magnitude per millimolar Gd. This enables shorter repetition times markedly improving the signal to noise ratio (SNR) per unit time. These complexes bind in fast exchange with phosphate species, while linear commercial Gd complexes were found to demonstrate competitive binding of ATP to Gd. Structural modifications of the DO3A complex were found to alter the affinity for specific phosphate species, as monitored by luminescence spectroscopy of the europium complexes, and also influenced the relaxivity of the Gd complex. In vivo, the phosphate species of interest reside intracellularly and therefore cellular uptake of these complexes was investigated, using fluorescence microscopy on luminescent complexes and NMR diffusion methods for the gadolinium complexes themselves. The complexes were found to remain extracellular or display endosomal uptake. These results indicate that these systems have clear potential as extracellular 31P contrast agents. Alternative approaches will be required to achieve intracellular 31P contrast.

The high-pressure behaviour of the lanthanide series of metals has been the subject of study since the work of Percy Bridgman in the 1940s. Differences in said behaviour between the different lanthanide metals are attributed to the increasing occupation of the 4f electron shell as Z increases. Upon compression, or as Z decreases, the trivalent lanthanides (La to Lu, excluding Eu and Yb) undergo a common phase transformation sequence through various close packed structures: hcp → Sm-type (the structure adopted by samarium at ambient conditions) → dhcp → fcc → distorted fcc (d-fcc). Upon further compression, the lanthanide metals experience a first order transition to a "volume collapsed" phase. Many studies have focused on the low-Z members of the series, since the various phase transitions occur at much lower pressure where it is comparatively easy to collect high quality data. By contrast, the other members of the series have received comparability little attention, and there are even fewer reports of the structural behaviour of the lanthanide metals at high pressure and high temperature. This thesis contains the results of angle-dispersive x-ray powder diffraction experiments at high pressure and high temperature of the various members of the lanthanide metals. Ce has been the subject of many previous studies, but a systematic x-ray diffraction study of the fcc/d-fcc phase boundary has never been attempted. Furthermore, the location in P-T space of the high temperature fcc/bct/d-fcc triple point has only been inferred, due to the lack of data on the fcc/bct phase boundary at high temperature. The high-pressure high-temperature phase diagram of Ce is presented and discussed. La is unique amongst the lanthanide metals due to its empty 4f shell at ambient conditions. Despite this, La undergoes the common lanthanide transformation sequence up to the d-fcc phase, after which it undergoes a re-entrant transition back to the fcc phase at 60 GPa. The diffraction peaks of d-fcc La are shown in this thesis to undergo changes in intensity upon compression, indicating a transformation to the oI 16 structure found in Pr. La is one of the few elements whose behaviour has been unknown above 100 GPa, and results of La's structural behaviour upon compression to 280 GPa are presented and discussed. At 76 GPa, La begins a transition from the fcc phase to a new phase with the bct structure. Finally, the d-fcc→fcc re-entrant phase transition has been determined at various temperatures, and the d-fcc stability region has been mapped out. Finally, x-ray diffraction experiments were performed on Gd up to 100 GPa and ~700 K, to determine the structure of the d-fcc phase and the "volume collapsed" phase. While d-fcc Gd does not undergo pressure-induced changes similar to its low Z brethren, the d-fcc Gd remains stable up to 41 GPa at 700 K, putting a constraint on the d-fcc stability region. The data collected on Gd's "volume collapsed" phase cannot be fitted to the currently accepted mC4 structure. This has implications for our understanding of the lanthanide series as a whole, since most of of the heavier members, and some of the lighter lanthanides, are reported to adopt the mC4 structure.

Anisotropic magnetic materials have been proposed over the past twenty years or so as candidates for high density storage, so-called Single-Molecule Magnets (SMMs). These may in future be used to store data at the level of an individual molecule. Separately, isotropic materials may be harnessed for their large magnetocaloric effect which enables them to be used as refrigerants. This can potentially replace the increasingly rare and therefore expensive 3He and 4He currently employed either separately or in 3He-4He dilution refrigerators. This thesis examines the use of lanthanide(III) ions for these applications, by detailing the synthesis, characterisation and performance of three new classes of zero-dimensional compounds, {LnIII2}, {LnIII2ZnII4} and {LnIII7}. These are assessed by several techniques including SQUID magnetometry, heat capacity measurements luminescence spectroscopy, Electron Paramagnetic Resonance and ab initio calculations. In doing so we extended the use of a tripodal ligand widely employed in 3d chemistry to 4f ions, and found only the second 3d-4f phosphonate SMM. Investigating several members of a known three-dimensional lanthanide(III) polymer, {LnIII}n, showed the isotropic gadolinium(III) analogue is one of the very best of all known magnetic refrigerants in the low-temperature regime.

Magnetic resonance imaging (MRI) is a powerful technique for disease diagnosis, but extending this technology to applications in molecular imaging has been challenging due to lack of safe and effective contrast agents with required sensitivity and specificity. To address this need, we have developed a new generation of protein-based contrast agents (ProCA32) that exhibit high relaxivity, high metal selectivity, and low toxicity. Here we report development and application of biomarker targeted contrast agents such as ProCA32.Collagen, ProCA32.CXCR4, and ProCA32.CXCL12 to image Collagen I, CXCR4, and CXCL12, which are molecular biomarkers overexpressed with chronic diseases. The collagen-targeted agent, ProCA32.Collagen, exhibits strong collagen I affinity and high relaxivities, enabling early-stage detection of liver fibrosis with a 7-fold increase in contrast-to-noise ratio (CNR) in mouse models. In addition, ProCA32.Collagen detects primary liver and pancreatic tumors and liver metastasis from uveal melanoma (UM), colon cancer, and pancreatic cancer. We further demonstrate that ProCA32.Collagen detects small liver cancer (sHCC) and premalignant nodules in several mouse models with different liver backgrounds, including steatosis and fibrosis. In addition, ProCA32.Collagen can detect fibrotic regions in the hearts of Ischemia-Reperfusion and Myocardial Infarction mouse models, and can monitor the treatment by PKM1/PKM2 during cardiovascular MRI imaging. We also report the development of Gd3+/Mn2+-ProCA32.CXCL12 and Gd3+-ProCA32.CXCR4 to detect liver fibrosis and cancer with multi-color imaging. Overall, the development of ProCA32.Collagen, ProCA32.CXCR4, and ProCA32.CXCL12, and their successful preclinical applications using7T MRI scanner, represent a promising approach to early detection and accurate diagnosis of primary/metastatic liver cancers, and other cancers such as pancreas cancer, as well as heart fibrosis, with high sensitivity and specificity. These agents have broad applications in both early detection and probing heterogeneous changes in the microenvironment upon disease progression, which may help to determine the most effective treatment for patients.

To improve chances of survival and response to treatment for life-threatening chronic diseases like cancer, detection of the early disease state is essential. MRI is the most beneficial imaging modality but due to the low sensitivity of current contrast agents, its capability for diagnosis is limited. Dr. Jenny Yang’s group has developed a novel protein-based MRI contrast agent with collagen- and HER2-targeting moieties, hProCA32.collagen1 and hProCA32.HER2, exhibiting high relaxivity, and improved sensitivity and specificity. The focus of this thesis is the optimization of hProCA32 purification by the addition of a refolding step, pH adjustment, and pre-loading of Gd3+, to yield ~90% monomer of a pure hProCA32.collagen1. The purified hProCA32.collagen1 was found to exhibit good collagen-binding affinity (1.8 µM) and high relaxivity (30.4 mM-1s-1 and 43.0 mM-1s-1 for r1 and r2) thereby suggesting that the MRI contrast agent may be useful to diagnose cancers at an early stage.

As a chronic disease, deaths caused by cancer are estimated to increase to 11.5 million by 2030. Patient response to treatment and chances of survival improves significantly when cancer is diagnosed at an early stage. MRI is a superior imaging modality but is limited due to the low relaxation rates of current contrast agent. Dr. Jenny Yang’s lab engineered a protein-based MRI contrast agent with high relaxation rates. hProca32.collagen contains two cysteine residues and must be refolded to form intra-strand disulfide bonds, which is necessary for its activity. In this thesis, the purification and refolding of hProca32 were optimized to yield a pure protein that is approximately 80% monomer. Various formulation conditions are reported, which allow hProca32.collagen to have a good collagen-binding affinity (1.3 µM). It exhibits good relaxivity values (30 and 42 mM-1s-1 for r1 and r2, respectively), which are 10-fold greater than clinically available contrast agents.

Gold nanoparticles (GNPs) have become a pivotal platform for the delivery of pharmaceutical and diagnostic agents as well as for general therapeutic purposes. Despite their potential for use in biomedicine, their interaction with serum proteins is crucial as it could change their biological profile due to the formation of a protein corona, which can affect their delivery to target tissues in the body. Grafting the GNPs with polyethylene glycol (PEG) is widely used in research to decrease opsonization of the particles by serum proteins and decrease the uptake by the reticuloendothelial system. Here in this dissertation, we have developed a library of 4 and 10 nm GNPs conjugated with a gadolinium chelate as MRI contrast agent, cancer-targeting aptamer AS1411 (CRO aptamer was used as control), and with or without polyethylene glycol (PEG) of different molecular weights (Mw: 1, 2, and 5 kDa). We have quantified the amount of proteins that adsorbed on the surface of PEGylated and non-PEGylated GNPs after incubation in human serum proteins. Additionally, we have quantified the uptake of nanoparticles with and without protein corona by the human breast cancer cell line MDA-MB-231 and the murine monocyte/macrophage cell line RAW 264.7. Furthermore, we have investigated the in vivo biodistribution of GNPs using the murine model of 4T1 mammary carcinoma in BALB/c female mice. The in vitro results showed that PEG failed to decrease protein adsorption and the cellular uptake by macrophage cells was contingent on the different configurations of the aptamers and the length of PEG chain. While in vivo biodistribution showed that PEG increased the uptake by tumor cells for some GNPs, it did not decrease the uptake of GNPs by macrophage-rich organs.

Abstract: The ultimate goal of this thesis research was to design, fabricate, and characterize an integrated nanotheranostics platform for activatable doxorubicin delivery and simultaneous MRI- radiosensitization for synergistic cancer therapy, targeting breast cancer treatment. As shown in the diagram, once these nanocomplexes enter into tumour sites through the EPR (enhanced permeability and retention) effect, an external radiation source can be applied with extreme precision to activate the cleavage of the mPGA shells (the outer fluorescent blue layer in the diagram). This exposes the positively charged Gd:Mn-Dox cores which are readily adsorbed by the negatively charged cancer cell membrane and internalized through endocytosis. The acidic environment within endosomes then triggers the dissociation of the Gd:Mn-Dox nanocomplexes contained within them, and resulting release of doxorubicin and gadolinium for simultaneous real time MRI-radiosensitization and synergistic therapy. Gadolinium, as one of lanthanide metal elements, has been well investigated and its chelates are commonly used as T1 contrast agents for clinical magnetic resonance imaging (MRI). Anthracycline antibiotics, such as the cancer chemotherapeutic drug doxorubicin, can form complexes with transition metals. Gadolinium and doxorubicin drug-metal complexes were selected for study, and were fabricated as nanostructures through a simple one-step homogeneous precipitation method. They were designed for acidic environment-triggered doxorubicin and gadolinium release. A partially modified poly-glutamic acid polymer (which was esterified to prevent the polymer material from undergoing auto-hydrolysis) was used to coat the surface of the harvested spherical Gd:Mn-Dox nanocomplexes. This surface coating was designed to be radiation activatable and biocompatible. The first nanostructures synthesized in this thesis were Gd(OH)3 and Gd(OH)3:Mn crystalline nanorods, and rod-shaped crystalline Gd(OH)3:Mn-Dox nanocomplexes with a 7.85wt% drug loading capacity of doxorubicin. The longitudinal dimension of these nanorods and nanocomplexes ranged from 200 nm to 400 nm. Next, the reaction process was modified to successfully produce spherical amorphous Gd:Mn and Gd:Mn-Dox nanocomplexes with a higher doxorubicin loading capacity (10.1wt%). The diameter of these nanospheres could be tuned within the range of 100 nm to 500 nm by using different quantities of glycerol in the reaction process. Both the rod-shaped and spherical nanocomplexes were demonstrated to undergo dissociation and release of doxorubicin and gadolinium in acidic environments. The amorphous spherical nanocomplexes had a shorter release time relative to the crystalline rod-shaped nanocomplexes. Confocal and TEM micrographs demonstrated that the synthesized nanocomplexes were actively taken up via endocytosis by human breast cancer cells. A radiation-activated radiosensitization effect, as well as dose-dependent trends in the percentage of apoptotic cells, were measured in the nanocomplex-treated cancer cells in vitro. MRI traceability of this nanotheranostics platform was demonstrated both in vitro and in vivo, using clinical MRI and PET-MRI. These nanocomplexes were well tolerated in rats at the highest tested dose of 240 mg/kg administered intravenously, with negligible histological changes observed. The in vivo biodistribution of these intravenously injected nanocomplexes was observed to be mainly in the liver, lungs and spleen. Overall, a novel and smart doxorubicin-loaded gadolinium-based amorphous cancer nanotheranostic system was developed with a very simple and environmentally-friendly fabrication process. This system demonstrated the capability to deliver gadolinium and doxorubicin for theranostic MRI-radiosensitization and doxorubicin chemotherapy. This proposed nanotheranostics platform represents an increasing trend in cancer nanotheranostics towards the research and development of novel and much more effective drug delivery platforms which pave the way for individualized cancer medicine. This thesis work has explored the feasibility of fabricating a new amorphous-phase gadolinium-based drug/metal theranostic nanocomplex doped with manganese through an environmentally friendly process. The research performed in this thesis takes advantage of the fact that doxorubicin drug molecules can form drug-metal complexes with gadolinium and manganese ions, allowing one to avoid incorporating other complex chelating materials. This work also uses a “smart” radiation-activable strategy for theranostic cargo delivery. This new design of a nanotheranostic solution paves the way for new clinical workflows where real-time MRI-guided synergistic therapy can be carried out during treatment. This work also inspired the consideration of other suitable drugs that may be studied using a similar work flow to extend their potential applications into theranostics and brought about new insights regarding the fabrication of theranostic nanoplatforms.

Pancreatic ductal adenocarcinoma (PDAC) is a debilitating disease with abnormally high mortality and morbidity. The incidence of PDAC continues to grow and substantial improvements in PDAC management have not dramatically improved patient survival. Early detection of PDAC lesions improve survival in conjunction with available therapies but is not possible with current imaging techniques. PDAC tumors consist of a substantial extracellular matrix (ECM), which is integral to PDAC biology and molecularly distinct from normal tissue ECM. The oncomarker extradomain B fibronectin (EDB-FN) is expressed only in malignant tissue ECM and presents an opportunity to use molecular imaging techniques to improve the imaging of PDAC. Magnetic resonance imaging (MRI) is a clinically accepted imaging modality for solid tumors, owing to its high soft tissue contrast and high spatial resolution, making it a strong candidate for further research.This research focuses on the development of molecular imaging probes, primarily in MRI to enable molecular magnetic resonance imaging (MRMI). To accomplish this, we utilize an EDB-FN binding peptide named ZD2 to target gadolinium-based MRMI contrast agents to the tumor ECM. We show that ZD2 enables tumor-specific accumulation of contrast agents in several models of primary PDAC as well as PDAC metastasis. We also demonstrated the superiority of ZD2 targeted MRMI contrast agents to nontargeted MRI contrast agents in clinical use. We further demonstrate the clinical translatability of EDB-FN MRMI by analyzing the expression of EDB-FN in patient samples of primary and metastatic PDAC, as well as premalignant lesions. In doing so, we have generated foundational work that establishes EDB-FN MRMI as a tool to improve PDAC diagnosis.

Liver metastases are often observed with primary cancers, including uveal melanoma (UM), breast, ovarian, and colon cancer. Chemokine receptor 4 (CXCR4) is one of the major chemokine receptors that overexpressed by cancers due to its role in tumor growth, migration, and progression. Organs such as the liver, bone, and brain have an intrinsically high concentration of CXCR4 ligand, C-X-C motif chemokine ligand 12 (CXCL12). As a result, CXCR4 is also often expressed at metastases in these organs. There is an unmet medical need for noninvasively early detecting, staging, and monitoring the prognosis of liver cancers and metastases as well as probing tumor microenvironment for target therapy and drug. In this dissertation, we first report the elevated expression of CXCR4 in the UM patients’ liver metastases and metastatic UM mouse models and validate its role as an imaging biomarker for liver metastases. We then report our achievement in the development of a CXCR4-targeted MRI contrast agent, ProCA32.CXCR4, for sensitive detection of UM liver metastases using MRI. ProCA32.CXCR4 exhibits high relaxivities (r1 = 30.9 mM-1 s-1, r2 = 43.2 mM-1 s-1, 1.5 T; r1 = 23.5 mM-1 s-1, r2 = 98.6 mM-1 s-1, 7.0 T), strong CXCR4 binding affinity (Kd = 1.1 ± 0.2 µM), and the capability of CXCR4 molecular imaging in both metastatic and intrahepatic xenotransplantation UM mouse models. ProCA32.CXCR4 enables robust detection of UM metastases as small as 0.1 mm2 in the liver. CXCR4 receptor blockage experiment proved the specific binding of ProCA32.CXCR4 to CXCR4. In addition, the application of ProCA32.CXCR4 in primary liver cancer detection and treatment effect monitoring are tested in hepatocellular carcinoma (HCC) mouse model. Except for gadolinium, we explored the possibility of manganese-based protein contrast agent and proved manganese-based ProCA exhibits high relaxivity and strong gadolinium binding affinity. We further designed and characterized ProCA32.RGD for integrin avb3 molecular imaging to reveal the tumor microenvironment. ProCA32.RGD targeted imaging was achieved in a 4T1 breast cancer mouse model. Further development of the biomarker targeted imaging agents is expected to have strong translation potential for early detection, surveillance, and treatment stratification of cancer and related diseases.

Trimetallic nitride endohedral fullerenes (TNT-EMF) have been recognized for their multifunctional capabilities in biomedical applications. Functionalized gadolinium-loaded fullerenes attracted much attention as a potential new nanoplatform for next-generation magnetic resonance imaging (MRI) contrast agents, given their inherent higher 1H relaxivity than most commercial contrast agents. The fullerene cage is an extraordinarily stable species which makes it extremely unlikely to break and release the toxic Gd metal ions into the bioenvironment. In addition, radiolabeled metals could be encapsulated in this robust carbon cage to deliver therapeutic irradiation. In this dissertation, we aim to develop a series of functionalized TNT-EMFs for MRI detection of various pathological conditions, such as brain cancer, chronic osteomyelitis, and gastrointestinal (GI) tract. As a general introduction, Chapter 1 briefly introduces recent progress in developing metallofullerenes for next-generation biomedical applications. Of special interest are MRI contrast agents. Other potential biomedical applications, toxicity, stability and biodistribution of metallofullerenes are also discussed. Finally, the challenges and future outlook of using fullerene in biomedical and diagnosis applications are summarized at the end of this chapter. The large carbon surface area is ideally suited for multiple exo-functionalization approaches to modify the hydrophobic fullerene cage for a more hydrophilic bio-environment. Additionally, peptides and other agents are readily covalently attached to this nanoprobe for targeting applications. Chapter 2 presents the functionalized metallofullerenes conjugated with interleukin-13 peptide exhibits enhanced targeting of U-251 glioblastoma multiforme (GBM) cell lines and can be effectively delivered intravenously in an orthotopic GBM mouse model. Chapter 3 shows, with the specific targeting moiety, the functionalized metallofullerenes can be applied as a non-invasive imaging approach to detect and differentiate chronic post-traumatic osteomyelitis from aseptic inflammation. Fullerene is a powerful antioxidant due to delocalization of the π-electrons over the carbon cage, which can readily react with free radicals and subsequently delivers a cascade of downstream possessions in numerous biomedical applications. Chapter 4 investigates the antioxidative and anti-inflammatory properties of functionalized Gd3N@C80. This nanoplatform would hold great promise as a novel class of theranostic agent in combating oxidative stress and resolving inflammation, given their inherent MRI applications. In chapter 5, Gd3N@C80 is modified with polyethylene glycol (PEG) for working as MRI contrast agents for GI tract. The high molecular weight can prevent any appreciable absorption through the skin or mucosal tissue, and offer considerable advantages for localized agents in the GI tract. Besides the excellent contrast capability, the PEGylated-Gd3N@C80 exhibits outstanding radical scavenging ability, which can potentially eliminate the reactive oxygen species in GI tract. The biodistribution result suggests this nanoplatform can be worked as the potential contrast agent for GI tract at least for 6 hours. A novel amphiphilic Gd3N@C80 derivative is discussed in Chapter 6. It has been noticed for a long time the functionalization Gd3N@C80 contrast agents have higher relaxivity at lower concentrations. The explanation for the concentration dependency is not fully understood. In this work, the amphiphilic Gd3N@C80 derivative is used as the model to investigate the relationship between the relaxivity and concentration of the Gd-based fullerenes. Click chemistry has been extensively used in functionalization due to the high efficiency and technical simplicity of the reaction. Appendix A describes a new type of Sc3N@C80 derivative conducted by employing the click reaction. The structure of Sc3N@C80-alkynyl and Sc3N@C80- alkynyl-benzyl azide are characterized by NMR, MALDI-TOF, UV-Vis, and HPLC. The high yield of the click reaction can provide access to various derivatives which have great potential for application in medical and materials science. The functionalization and characterizations of Ho3N@C80 derivatives are reported in Appendix B. The contrast ability of Ho3N@C80 is directly compared with Gd3N@C80. The Ho-based fullerenes can be performed as the radiotherapeutic agents; the leaching study is performed to test the stability of carbon cage after irradiation. Appendix C briefly shows a new method to develop Gd3N@C80 based targeting platform, which can be used as the probe for chronic post-traumatic osteomyelitis.

It is now well established that over 80\% of the matter in our Universe is comprised of a non-luminous substance known as dark matter. By far the most popular dark matter candidate is the weakly interacting massive particle (WIMP). Attempting to discover the nature of WIMP dark matter through direct detection has been a central activity of experimental physics for at least the last 20 years. To date, no conclusive signal consistent with WIMP interactions has been observed.The LZ (LUX-ZEPLIN) experiment is a second generation direct dark matter detector under construction one mile underground in the Davis Laboratory of the Sanford Underground Research Facility (SURF) in Lead, South Dakota, USA. LZ will use a 7 tonne central liquid xenon target, arranged in a dual-phase time projection chamber (TPC), to seek evidence for nuclear recoils from a hypothesized galactic flux of WIMPs. Two active detector elements will surround the TPC: a layer of liquid xenon, the xenon skin, optimized to detect $\gamma$'s, and the outer detector (OD), optimized to detect neutrons. Together, these detectors will tag backgrounds to the sought-after WIMP signal and characterize the background environment around LZ.The OD is comprised of acrylic tanks filled with 17.3 tonnes of LAB-based gadolinium-loaded liquid scintillator (GdLS) that will surround the central cryostat of LZ in a near-hermetic fashion. Its primary function will be to tag neutron single-scatter events in the liquid xenon which could mimic a WIMP dark matter signal. I summarize simulation studies of the OD expected performance as a neutron veto and expected light collection.The rate of single background pulses in the OD is also discussed. The three primary sources of rate in the OD are identified as: LZ detector components, $\gamma$-rays from the Davis Laboratory walls, and the radioimpurities in the GdLS. The radioimpurities in the GdLS are particularly troublesome because the OD is sensitive to both the $\alpha$ and $\beta$/$\gamma$ decays of these isotopes. To meet the requirements for the OD, the radioimpurity levels in the GdLS must be kept below $\lesssim0.07$ mBq/kg. This background level corresponds to a rate of $\approx50$ Hz above an energy threshold of 100 keV.I report on the design and performance of the ``Screener", a small liquid scintillator detector consisting of $\approx23$ kg of the GdLS to be used in the OD. The Screener was operated in the ultra-low-background environment of the former LUX water shield in the Davis Laboratory at SURF for radioassay of the GdLS. Careful selection of detector materials and use of ultra-low-background PMTs allows the measurement of a variety of radioimpurities. The $^{14}\textrm{C}$/$^{12}\textrm{C}$ ratio in the scintillator is measured to be $(2.83\pm0.06\textrm{(stat.)}\pm0.01\textrm{(sys.)}) \times 10^{-17}$. Use of pulse shape discrimination allows the concentration of isotopes throughout the $^{238}\textrm{U}$, $^{235}\textrm{U}$, and $^{232}\textrm{Th}$ chains to be measured by fitting the collected spectra from $\alpha$ and $\beta$ events. It is found that equilibrium is broken in the $^{238}\textrm{U}$ and $^{232}\textrm{Th}$ chains and that a significant portion of the contamination in the GdLS results from decays in the $^{227}\textrm{Ac}$ subchain of the $^{235}\textrm{U}$ series.Predictions for the singles rate in the OD are presented. The rate from radioimpurities above 100 keV in the GdLS is estimated to be $97.5\pm6.3$ Hz, with $65.0\pm1.4$ Hz resulting from $\alpha$-decays.

Pyroprocessing is an electrochemical method that is capable of separating uranium (U) and minor actinides from LiCl-KCl eutectic salt where used nuclear fuel (UNF) is dissolved. During the process, fission products including rare earth metals (RE) continually accumulate in the salt and eventually affecting uranium recovery efficiency. To reduce the salt waste after uranium and minor actinides recovery, electrolysis is performed to drawdown rare earth materials from molten salt to restore salt initial state. Present research focus on the development of RE fundamental physical properties in LiCl-KCl eutectic salt. These properties includes apparent potential, activity coefficient, diffusion coefficient and exchange current density. Additional properties including charge transfer coefficient and reaction rate constant are calculated during the analysis. La, Nd and Gd are three RE that we are particularly interested in due to the high ratio of these elements in UNF (La, Nd), the well-studied properties in dilute solution to provide a base for comparison, and the highest standard potential among all RE (Gd). Fundamental properties of La, Nd, Gd in LiCl-KCl eutectic salt are studied at a temperature ranging from 723 K to 823 K and RE concentration ranging from 1 wt% to 9 wt%. These properties are studied by electroanalytical methods including Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), Tafel method, Chronocoulummetry (CC) and Chronopoentiometry (CP). BET model that considers the RE adsorption on the electrode is developed for diffusion coefficient analysis. Electrode kinetic model is developed to account for mass transfer effect during the analysis of exchange current density. Correlations of diffusion coefficient, apparent potential, exchange current density with temperature and concentration are developed. These fundamental data are integrated with a electrolysis model to predict the electrolysis process for RE drawdown from LiCl-KCl salt. The model considers both the diffusion in electrolyte and Faraday process on the electrode surface and a surface layer is introduced to account for the fact that diffusion current is not necessarily equal to the current due to the Butler-Volmer equation. The model is validated by chronoamperometry and chronopotentiometry.

Electron paramagnetic resonance (EPR) in combination with site-directed spin labeling (SDSL) is a powerful tool for elucidating the structure, organization, and dynamics of biomolecules in native-like environments. With EPR and SDSL, we can site-specically label pairs of sites in a biomolecule and accurately measure the distance, or distribution of distances, between them on length scales ranging from Angstroms to several nanometers. Of particular interest are membrane proteins and higher-order membrane protein complexes, which have historically resisted traditional biophysical characterization techniques. EPR as a means to measure protein structure becomes even more powerful at high fields and using Gd(III) spin labels, which together provide much improved sensitivity. This work expands on the capabilities of high-field continuous-wave (CW) EPR for distance measurement with spin labels based on Gd(III) complexes. First, we investigate a model system of and show that CW EPR with Gd(III) labels allows for distance measurements in the range of at least 1.2 - 3.4 nm at cryogenic temperatures. We additionally show that distance measurements are possible up to room temperature. Next, we investigate the zero-field splitting - a property of great importance for determining the EPR lineshape of high-spin systems - for a variety of different Gd(III) complexes. Combining EPR spectra measured at 35 GHz, 95 GHz, and 240 GHz, we compare literature models for the broadly distributed second-order ZFS parameters D and E. We test these results against a superposition model for predicting the magnitude of the ZFS based on knowledge of the structure of a Gd(III) complex, which can potentially be useful for designing new Gd(III) complexes tailored for use as spin labels with high-field EPR. Finally, we apply high-field CW EPR with Gd(III) spin labels to the study of proteorhodopsin (PR), a transmembrane protein that functions as a light-driven proton pump for marine bacteria. Inter-PR CW EPR distance measurements in the range of ~1.5 - 3 nm are used to elucidate the functionally relevant oligomeric structure of PR, demonstrating the usefulness of this technique in targeting complex oligomeric systems. Finally, we present the development of methods which will allow CW EPR with Gd(III) to be used as a probe of protein dynamics, by measuring at a distance change induced by motions of the E-F loop region of PR upon light activation.