Browsing by Subject "Chelates"
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Item A study of the solvated chelates of scandium, thorium, and uranium with 8-quinolinol and 2-methyl-8-quinolinol(Texas Tech University, 1959-08) Van Tassel, James HenryNot availableItem Multi-disciplinary study of lanthanide chelates as multi-modal molecular imaging agents(Texas Tech University, 2004-05) Manning, Henry CharlesMolecular imaging is a powerful tool that has the ability to elucidate biochemical mechanisms and signal the early onset of disease. Lanthanide chelates represent a unique class of molecular imaging agents that can yield multi-modal signatures including long-lived fluorescence and magnetic resonance. The primary aim of this dissertation is to demonstrate the utility of Lanthanide chelate molecular imaging agents for contrast enhanced disease demarcation. Traditionally, Lanthanide chelate imaging agents have been non-targeted perfusion agents that distribute in-vivo based on charge and lipophilicity. It is shown here that the structural features of the chelate can be modified to facilitate tunable spectroscopic and biodistribution properties in-vivo. While our perfusion-based agents have demonstrated considerable utility, their principal limitation is specificity. For increased specificity, we synthesized a trifunctional Lanthanide chelate that possessed an antenna for metal sensitization, phosphonate acid pendant arms for chelation, and a carboxylate arm for conjugation to targeting moieties such as antibodies, peptides, or small molecule ligands. Recently, peripheral benzodiazepine receptor (PBR) overexpression has been reported in many types of disease. Small molecule ligands of the PBR, such as PK11195, have been shown to bind with high affinity and thus could be used as contrast agent targeting moieties. Therefore, we synthesized a structural analogue of PK11195 that facilitates C-terminal conjugation. This form was then coupled to the trifunctional Lanthanide chelate and complexed with Europium and Gadolinium (Ln-PK11195). With the Ln-PK11195 agent in hand, it was demonstrated that PBR overexpressing C6 glioma cells would actively uptake the agent and that Ln-PK11195 seemed to be localizing on the PBR. Additionally, multi-modal imaging (fluorescence and MR) was shown possible on a single group of cells incubated with a Eu-PKl 1195 and Gd- PK11195 cocktail. Next, we demonstrated PBR profiling on surgically resected human tissue samples using Eu-PKl 1195, indicating a possible use as a histopathology stain. Both cancerous and non-cancerous PBR expressing disease was labeled with the agent. Finally, we fully characterized the primary spectroscopic signatures of Ln- PK11195 (time-resolved fluorescence and MR) for sensitivity to pH. It was shown that Ln-PK11195 demonstrates adequate pH sensitivity to measure localized, intracellular pH in tissues.Item Spectroscopic evaluation of Tb(III) chelates for potential utility as diagnostic markers(Texas Tech University, 1998-05) Hubbard, Darren ScottLanthanide spectroscopy was exhaustively studied in the early 19th Century. It was quickly learned that the fluorescence of the molecules was superb; however, the absorption cross section of the molecule was low and interest in the molecules subsided. The interest in Lanthanides resurfaced in the 1980's when chelation of a lanthanide central ion into an organic cage solved the absorption problem. The most striking features of the Lanthanide chelates were the enormous Stoke's Shift and long luminescence lifetimes. These two features enabled the investigator to sensitively probe for the solute because the signal was spectrally and temporally shifted from background noise.Item Studies toward the development of an electronically switchable ion exchange system(2004) Johnson, Ashley Michelle; Holcombe, James A.Early studies toward the development of a chemical-free means of reclaiming metals from an ion exchange system were begun by exploring the option of controlling metal-ligand interactions electrochemically. Poly-L-cysteine (PLC), a soft acid cationic metal chelator, was explored as an option for an electroactive ligand for use as an electronically switchable ion exchange system. Initial studies were conducted by immobilizing PLC onto a glassy carbon electrode creating a modified electrode. The modified electrode was characterized using electrochemical techniques, atomic spectroscopy and molecular spectroscopy. Initial studies were conducted with poly-L-cysteine immobilized onto controlled pore glass and packed in a microcolumn for low pressure liquid chromatography experiments. Flow parameters, as well as the ability of poly-L-cysteine to act as a preconcentration agent, were established. Electrochemical methods, specifically cyclic voltammetry, were used to confirm polymer attachment and to estimate that near monolayer coverage on the glassy carbon electrode surface existed. Further studies examined the kinetics of electron transfer through the use of large amplitude potential steps to demonstrate consistency with other types of modified electrodes. The pKa of the polymer was determined to be between 7.5 and 8 by using surface charge density as a function of pH. The poly-L-cysteine modified electrode, as well as an electrode modified with cysteine monomers, was evaluated for its metal binding capabilities. Using Cd2+ as a target metal, optimal binding conditions were established. Binding experiments were repeated with Co2+, Cu2+, Ni2+ and Pb2+, as well as competitive binding studies comprised of binding in the presence of all five metals. Quantitative release of bound metals was achieved by repeatedly pulsing the potential from open circuit to a number of anodic potentials. Raman microscopy was used to probe the redox states of PLC, confirm the complexation of Cd2+ to the thiol groups of PLC and to establish an average formal reduction potential for PLC of -0.3 V vs. SHE. The possibility of multiple formal potentials was explored through the use of mathematical models based on the Nernst equation. The models suggest that many formal potentials do exist although the exact nature of the distribution could not be determined. As a plausible electronically switchable ion exchange option for heavy metal oxyanions, pyrrole was electropolymerized and investigated as a ligand for toxic chromate remediation. Polypyrrole, which bears a structural similarity to poly-L- histidine, a previously studied chromate chelator, was shown to have potential to both remediate and speciate Cr(VI) from Cr3+.Item Synthesis and characterization of lanthanide chelates for biomedical imaging(Texas Tech University, 2000-08) Griffin, John Michael MansfieldEarly detection is critical to the clinical outcome in the treatment of cancers (1-3). As an example, colon cancer accounts for 15% of all US cancer related deaths. Once these types of cancer reach metastatic activity there is only a 7% survival rate. In addition, only 37% percent of colon cancers are found early enough for moderate treatment (1). Oral cancer is another example of the necessity for early detection. Each year about 31,000 Americans develop oral cancer. Squamous cell carcinoma (SCC) accounts for 95%) of all malignant oral lesions with SCC having a survival rate of only 50%). Yet when this type of cancer is detected in its earliest stages then the survival rate becomes approximately 80% 4). However, current state-of-the-art detection means often miss early stage colon and oral SCC disease. These detection protocols employ white light endoscopy with gross visualization (5-6). Yet the visual cues for determination of disease state are small, especially the discrimination between non-malignant and dysplastic and pre-malignant lesions. Visual assessment of early lesions within the colon and oral cavities depends on many factors, including the experience of the clinician and his ability to identify the suspect lesions at an early stage of development, and selection of the suspect site that is to be biopsied. Clearly there is a significant need for the enhancement of detection of diseased tissue at its earliest stages to improve the clinical outcome.Item The chemistry of the solvated metal chelates of uranium (VI), thorium (IV), and scandium (III) with 8-quinolinol and substituted 8-quinolinols(Texas Tech University, 1963-05) Horton, Guy RobertNot availableItem Thermal Stability of Various Chelates that are Used in the Oilfield(2012-10-24) Sokhanvarian, KhatereAcid treatment, especially at high temperatures, is very challenging since HCl is really corrosive to the metal equipment. The use of HCl is associated with face dissolution, corrosion, and iron precipitation. Organic acids are weak and less corrosive than HCl but they have a limitation, which means that they can't be used at high concentrations. The next option would be chelating agents. Chelating agents are used in well stimulation, iron control during acidizing, and removal of inorganic scales. Chelates such as ethylenediaminetetraacetic acid (EDTA), N-(hydroxyethyl)-ethylenediaminetetraacetic acid (HEDTA), L- glutamic acid-N, N diacetic acid (GLDA), and nitrilotriacetic acid (NTA) are used in high-pressure/high-temperature oil and gas wells. GLDA is environmentally friendly, which makes it favorable. One of the concerns with these chelates is their thermal stability at high temperatures because if they degrade at high temperatures, they may lose their functionality. This study describes the thermal stability of these chelates, thermal degradation products, and some methods to improve their stability. The thermal stability is determined by measuring the concentration before and after heating using a complexo-metric titration utilizing FeCl? as a titrant. The degradation products are identified using Mass Spectrometry (MS). A series of experiments were run in the lab at varying temperatures (300 to 400?F) up to 12 hours, and the results shows chelates are not stable at temperatures greater than 350?F. Furthermore, chelates with two nitrogen atoms are more stable than those with one nitrogen atom. Iminodiacetic acid (IDA), acetic acid, and [alpha]-hydroxy acids are the decomposition products. There is a layer of black deposition after the chelates are heated, which is analyzed using Scanning Electron Microscope (SEM). Some coreflood tests are conducted using these degraded chelates to investigate the effect of these solid precipitates on the permeability of carbonate and sandstone cores. Increasing ionic strength and raising pH results in a higher thermal stability. Some salts such as, NH?Cl, KCl, Csformate, and NaBr are added to chelate solutions to enhance stability.Item Utilization of chelated copper and cupric sulfate by growing beef steers(Texas Tech University, 1998-05) Bowen, Corrie PNot available