We report on the mechanism of a series of ZnII-activated magnetic resonance contrast agents that modulate the access of water to a paramagnetic GdIII ion to create an increase in relaxivity upon binding of ZnII. In the absence and presence of ZnII, the coordination at the GdIII center is modulated by appended Zn II binding groups. These groups were systematically varied to optimize the change in coordination upon ZnII binding. We observe that at least one appended aminoacetate must be present as a coordinating group to bind GdIII and effectively inhibit access of water. At least two binding groups are required to efficiently bind ZnII, creating an unsaturated complex and allowing access of water. 13C isotopic labeling of the acetate binding groups for NMR spectroscopy provides evidence of a change in the metal coordination of these groups upon the addition of Zn II supporting our proposed mechanism of activation as presented.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry