Modulation of Magnetic Properties in Magnetic Resonance Imaging Contrast Agents and Molecular Magnetic Materials

This dissertation focuses on fundamental research in two areas of magnetism, the technologically advanced field of magnetic resonance imaging (MRI) and the nascent discipline of molecular magnetic materials. Contrast agents for MRI based on the gadolinium(III) ion were designed and studied to gain insight into the parameters that may be modulated to control contrast agent efficacy. Two parameters in particular, the inner-sphere coordination environment and the electronic relaxation of the gadolinium(III) ion, were examined. Investigations into the electronic relaxation of the gadolinium(III) ion led to insights that were applied to the synthesis and evaluation of a low dimensional magnetic material based on ruthenium(III) and nickel(II) ions. Manipulation of the gadolinium(III) coordination sphere provided the basis for an MRI contrast agent designed to be sensitive to the oncologically relevant enzyme beta-glucuronidase. This agent functions by restricting water access to the inner-sphere coordination sites of the gadolinium(III) ion. The design, synthesis, magnetic properties and biochemistry of the agent are described in detail. The agent displays good enzyme kinetics and complicated coordination equilibria with water and carbonate ion. A second approach to modulating contrast agent efficacy consisted of varying the electronic relaxation time of the gadolinium(III) ion. Towards this goal, ligand frameworks were designed and synthesized to influence the relaxation time of the gadolinium(III) ion via remote redox activity. Structural characterization and in vitro assays of these ligand-metal constructs indicated more robust ligands were required for complex stability. Initial steps toward a ligand that fulfills these requirements proved successful. The structural data from the electronic relaxation studies led to the synthesis of a one-dimensional coordination polymer comprised of chelated ruthenium(III) and nickel(II) ions bridged by cyanide ligands. The compound was studied by X-ray crystallography and its magnetic properties indicated that the ions were ferromagnetically coupled.