Date of this Version
Olankitwanit, A. Syntheses of Aminyl Diradicals and Nitroxide Tetra- and Octaradicals. Ph.D. Dissertation, University of Nebraska – Lincoln, Lincoln, NE, Oct 2014.
This dissertation comprises of two main research projects: aminyl diradicals and calixarene nitroxide tetra- and octaradicals. The design, multi-step synthesis and characterization, including NMR, EPR spectroscopy, magnetic measurements and X-ray crystallography of precursors and target compounds will be discussed.
Aminyl radicals, nitrogen-centered radicals, are typically short-lived and considered as reactive intermediates. Because of their unique magnetic properties, aminyls are attractive building blocks for high-spin di-and polyradicals. The challenge is in the design and synthesis of aminyls with increased stability. In this chapter, we have prepared triplet (S = 1) ground state aminyl diradicals, which are derivatives of aza-m-xylylene diradicals. Triplet (S = 1) ground state these aminyl diradicals are predicted to possess singlet-triplet energy gap, DEST » 10 - 14 kcal mol-1. Kinetics experiments for these aminyl diradicals are carried out in solution of 2-methyltetrahydrofuran at room temperature with the half-life measured in minutes.
Nitroxides are one of the most studied stable radicals in chemistry and in other related fields because of their stability. To explore potential of nitroxides as paramagnetic contrast agents for magnetic resonance imaging (MRI), we designed and synthesized 1,3-alternate calixarenes nitroxide tetraradical and octaradical. Attachment of nitroxides on a rigid, well-defined framework such as calixarene locked in 1,3-alternate conformation allow for study of the exchange coupling through bond and through space. In this chapter, 1,3-alternate calixarenes with phenylene spacers connecting mononitroxides and high-spin (S =1) dinitroxides on the upper rim providing calixarene nitroxide tetraradicals and octaradicals, respectively, are synthesized and characterized by 1H NMR and EPR spectroscopy. With the desire in biological applications, calixarene nitroxide tetraradical and octaradical with hexaethylene glycol methyl ether (HEG) are also synthesized and characterized.
Advisor: Andrzej Rajca