Graduate Studies, UNL

 

Dissertations and Doctoral Documents from University of Nebraska-Lincoln, 2023–

First Advisor

Andrzej Rajca

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Chemistry

Date of this Version

2025

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy (Ph.D.)

Major: Chemistry

Under the supervision of Professor

Lincoln, Nebraska, December 2025

Comments

Copyright 2025, the author. Used by permission

Abstract

The first part of this dissertation focuses on the design, synthesis, and characterization of a thermally robust S =1/2 phototetrazolinyl monoradical and the development of synthetic methodologies for a high-spin (S = 1) phototetrazolinyl diradical. Electrochemical studies of the phototetrazolium cation (precursor to the monoradical) revealed a remarkably narrow electrochemical band gap (Ecell ≈ 0.82 V), suggesting promising electrical conductivity. Thermal analysis of the monoradical demonstrated excellent stability, with the onset of decomposition at 232 °C. Building on the excellent thermal stability and promising properties for electrical conductivity of the monoradical, we developed two condensation-based synthetic routes that provide viable pathways to a high-spin phototetrazolinyl diradical.

In the second part of this dissertation, we discuss the design, synthesis, and characterization of a quartet ground state (S = 3/2) triBlatter triradical with three Blatter radical centers. The synthesis, purification, and recrystallization of the triBlatter triradical were performed and optimized. The resulting triradical was examined using solid-state EPR spectroscopy and electrochemical studies to investigate its magnetic and electronic properties.

In the final chapter, we report the design, synthesis, and characterization of two conjugates of metabolic organic radical contrast agents (mORCAs) developed for magnetic resonance imaging (MRI). The design of the mORCAs constitutes a sterically shielded gem-diethyl nitroxide radical conjugated to a D-mannosamine sugar backbone. These mORCAs can be utilized for direct metabolic glycan labeling, bypassing the need for two-step bioorthogonal reactions followed by metabolic glycan engineering.

In Vivo MRI experiments in mice demonstrated that the paramagnetic nitroxide radical contrast agents shortened the T1 and T2 times in the kidney and the brain by up to ~10% after 3 days. Ex vivo experiments showed that the contrast agents were immobilized and primarily localized in mouse tissues in the kidney, lung, liver, heart, and blood.

Advisor: Andrzej Rajca

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