Mn(II) complexes are of considerable interest as a source of novel MRI contrast agents. The solution speciation of these complexes as a function of pH, however, remains a considerable analytical challenge. 17O transverse relaxivities of D2O in solutions containing [Mn(H2O)6]2+, [Mn(EDTA)(H2O)]2-x, [Mn(DOTAM)]2+, [Mn(HxDOTA)]x-2, and related macrocyclic complexes have been investigated as a function of pH and temperature. Combined with speciation data from potentiometric titrations and pH dependent IR spectra, insight into the solution structures of several protonation states of the complexes have been obtained. Correlation of the data with 1H longitudinal relaxivities suggests that for some of the complexes in specific pH ranges, both water exchange and prototropic exchange contribute to the observed 1H relaxivities.

pH and temperature dependent 17O NMR relaxivities of Mn(II) complexes as a probe of solution speciation and water coordination

251st National Meeting (2016)

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