Date of Award
Chemistry and Biochemistry
Sandra S. Eaton, Ph.D.
Relaxation rates, Electron Spin-lattice
Pulsed and continuous wave electron spin resonance were used to characterize the relaxation rates of selected paramagnetic metals at 5 to 15 K or 80 K, measure the impact of these rapidly relaxing metals on the relaxation rates of nitroxide radicals in glassy mixtures and in discrete complexes, and characterize novel iron-sulfur proteins.
Spin echoes were observed at 5 to 7 K in 1:1 water:glycerol for Er(diethylenetriamine pentaacetic acid)2- (Er(DTPA)2-), Co(DTPA)3- and aquo Co2+ with relaxation times that are strongly temperature dependent. Deep proton modulation was present on spin echo decays (Ch. 3). For Gd3+ and Gd(DTPA)2- in 1:1 water:glycerol at 80 K T1 is 1.5 to 2 mus and T2 is about 0.5 mus. When Gd3+ is loaded into P22 viral capsids with local concentrations up to about 180 mM the relaxation rates at 80 K are dramatically increased (Ch. 6).
Relaxation rates for 0.2 mM nitroxide radical in mixtures with rapidly relaxing metal ions in 1:1 water:glycerol glasses were measured at temperatures between 20 and 200 K (Ch. 4). The enhancement of the relaxation rate of the nitroxide increases in the order Co2+ < Er3+ < Dy3+ < Tm3+. The maximum spin-lattice relaxation enhancement occurs at about 35 K for Dy3+, 40 K for Er3+, and 80 K for Co2+. Changes in T1 are a much larger fraction of the non-interacting values than for T2.
Complexes were prepared in which an ethylenediamine tetraacetic acid (EDTA) metal binding site was separated via linkers of varying lengths from a nitroxide radical. Energy minimization calculations found distances of 1.6, 2.4, and 3.4 nm between the metal binding and nitroxide N-O groups. The interaction between a paramagnetic metal bound to the EDTA and the nitroxide were characterized by measuring relaxation times and continuous wave power saturation.
The temperature dependence of the electron spin-lattice relaxation rates for iron-sulfur clusters from Pyruvate Formate Lyase- Activating Enzyme, hydrogenase and Mycofactin C protein were studied (Ch. 7). Compared to other iron-sulfur proteins the relaxation rates were relatively slow.
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Aggarwal, Priyanka, "Relaxation of Metals and Their Impact on Nitroxides" (2016). Electronic Theses and Dissertations. 1182.
Received from ProQuest