NMR applications of paramagnetic metals in aqueous solution

Paramagnetic metal complexes in aqueous solutions were used to demonstrate a range of NMR applications, including solvent signal suppression, control of nuclear spin relaxation times in high-field spectrometers with the use of an internal relaxation agent, a novel approach to the design of contrast agents for magnetic resonance imaging (MRI), and characterization of electron spin relaxation and ligand exchange through nuclear magnetic resonance dispersion (NMRD) measurements.; The 1H spin-lattice and spin-spin relaxation times of a diverse group of aqueous solutes, representing a variety of functional groups and biologically significant compounds, were measured in the presence of three coordinatively saturated paramagnetic complexes, Gd(TETA), Mn(DTPA) and Mn(Diamsar), to determine whether the paramagnetic metal complexes would be suitable as general relaxation agents for routine data collection in high-field NMR spectrometers. It was found that the paramagnetic metal complexes do not affect all the solute resonance signals uniformly, leading to the conclusion that these paramagnetic metal complexes have the potential to be exploited as molecular probes of the surface accessibility of other solute molecules.; Hexaaquochromium(III) was evaluated as a potential relaxation agent for the WATR (W&barbelow;ater A&barbelow;ttenuation by T&barbelow;ransverse R&barbelow;elaxation) method of solvent water suppression. It was found that the efficiency of hexaaquochromium(III) was strongly pH dependent, which may compromise its usefulness.; The hexafluoroferrate ion is unusually efficient as a solvent water 1H relaxation agent for a paramagnetic metal complex without any nominal first coordination sphere water molecules. Electron paramagnetic resonance (EPR) and NMR relaxation measurements were used to investigate the relaxation behavior of the hexafluoroferrate ion.; Paramagnetic metal complexes that are immobilized or in slowly rotating environments are able to provide useful information about the effects of chemical exchange and electron spin relaxation on the electron-nuclear dipole-dipole interaction. These effects are important for the design of highly efficient contrast agents for magnetic resonance imaging (MRI). Chelates of gadolinium(III) and manganese(II) were bound to a large serum protein, a protein gel, and ion-exchange resins and the temperature dependences of the NMRD profiles were used to extract information about the dynamics that are difficult to measure in freely rotating environments.