Browsing by Subject "Rare earth metals"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Exploring new ligand environments for lanthanide coordination chemistry(2006) Moore, Jennifer Anne; Cowley, Alan H.Item Reactions and photochemistry of samarium(II) complexes(Texas Tech University, 2003-12) Knettle, Brian WesleyOver the previous twenty years, divalent lanthanide reagents have become reagents of choice for organic functional group transformations. Samarium diiodide has made a particularly impressive impact on the way synthetic chemists perform reductions, reductive couplings of multiple 7t-bonds, and coupling of alkyl halides to ;i-bonds. It has been shown that the rate of reduction and the reducing ability of samarium(II) complexes can be influenced by the coordinating ligands and solvent medium. The most common additive is HMPA, which accelerates many reactions, and can also alter the stereoselectivity of products. This is due to the electron donating ability of HMPA to the divalent cation (increasing the reducing power) and the increased steric bulk about the samarium reductant. The first portion of this research focused on the behavior of samarium(II) complexes towards imines. It was found that substitution of Sml2 (which does not mediate imine reductions) with SmBr2, Sm[N(SiMe3)2]2, or a mixture of Sml2-Et3N-H20 allowed for imine reduction. However, the study showed that profound differences in reactivity could be related to the choice of ligand. SmBr2 and Sm[N(Si(CH3)3)2]2 were both effective at reduction of ketimines to amines. Sm[N(Si(CH3)3)2]2 was also able to reductively couple certain aldimines in a stereoselective manner. The Sml2-Et3N-H20 mixture was found to be effective at coupling both aldimines and ketimines. It had been previously shown that illumination of Sml2 increased its reducing power. To further examine this phenomenon, photochemical quenching experiments were performed upon Sml2 solutions containing a quencher molecule. Experimental rate constants were calculated for quenching by the N-benzyl imine of acetophenone, styrene, 1-chlorobutane, 2-butanone, and 4-toludine, and were found to be in good agreement with theoretical rates derived from Marcus theory. This indicates that the electron transfer is an outer sphere process. Lastly, a spectroscopic study of several samarium(II) reagents was performed. Relative quantum yields for Sml2 and SmBr2 were found to be 0.13 and 0.011, respectively. Molar extinction coefficients were also found for these complexes and clearly showed that Sml2 is more efficient in the photon absorption process.Item Synthesis of lanthanide chelates for biomedical imaging(Texas Tech University, 2003-12) Goebel, Timothy Stephen O'GaraLanthanide chelates are a somewhat unique class of molecules that have proven to be useful in the biomedical field as contrast agents for disease detection. This is due to many factors including their extremely large Stokes' shift, generally around 300 nm, and millisecond fluorescent lifetimes. The ability of these molecules to produce fluorescence in the low or zero-background regime as well as low cytotoxicity makes this class of molecules excellent candidates for use as contrast agents for a wide variety of applications in biological settings. Here we present the simple preparation and spectroscopic characterization of a new Europium chelate contrast agent, based on the 1, 4, 7, 10-tctraazacyclododecane macrocycle (cyclen). Eu-QF(CTME) produces a bright pinkish red luminescence when excited with low photon fluxes of UV light, indicating its potential for use in the field of biomedical imaging as a fluorescent probe. To determine the efficacy of this molecule as a fluorescent probe for disease detection, both animal testing as well as testing in a human tissue culture system was preformed. The well documented DMBA-treated Golden Hamster Cheek pouch epithelial cancer model was employed with Eu-QF(CTME) used as a topical agent for the detection of diseased tissue. In this preliminary study, the agent was observed to associate with malignant lesions, as well as dysplastic tissue. This suggests that Eu-QF(CTME) could be used as a contrast agent to aid in identifying oral precancer and cancer lesions. The results from the cell uptake experiments demonstrates the potential of this molecule as a stain for cancer cells.