Synthesis and Study of High-Spin Stable Organic Radicals for Electrical Conductors and Mannosamine Nitroxide for MRI Contrast Agents

In the first project, we describe the synthesis of an ambient stable high spin organic diradical 4 based on the Blatter moiety. The high-spin (S = 1) organic diradical 4, which consists of two Blatter radical moieties in a conjugated structure, exhibits a nearly exclusive population (88%) on triplet ground state at room temperature as a consequence of a large single-triplet energy gap (ΔEST = 0.5 kcal/mol). The target diradical molecule is synthesized over five steps with structural confirmation by single-crystal X-ray diffraction. The thermogravimetric analysis (TGA) shows the onset of decomposition at ~264 oC, indicating the diradical molecule has good thermal stability. The high spin organic molecules are not only purely organic magnets but also promising building blocks for emerging technologies. The diradical 4 crystal demonstrates good electrical conductivity. Also, the diradical can be evaporated under an ultra-high vacuum to form thin films, which are stable in ambient conditions for at least 18 h. In the second project, we describe the synthesis of a high-spin (S = 3/2) triBlatter triradical analogous to the diradical in the first project. The triradical was characterized by EPR, TGA, and UV-Vis near IR. Attempts to determine the ΔEDQ by EPR variable temperature measurement were performed. In the third project, we design and synthesize an organic radical MRI contrast agent. The structure of contrast agent is composed of a physiologically persistent nitroxide and a mannose sugar moiety. Taking advantage of the metabolic glycan labeling method, after the contrast agent was injected into mice, the nitroxides were expressed on the cell surface through metabolism, consequently changing the relativity of surrounding water molecules. Quantitative analysis of the in vivo NMR experiments and ex vivo EPR study were conducted. Advisor: Andrzej Rajca