Enhancing 31P NMR relaxation rates with a kinetically inert gadolinium complex.

The kinetically stable heptadentate gadolinium complex Gd.pDO3A (1.Gd) demonstrates significant 31P nuclear magnetic resonance (NMR) relaxation enhancement of biologically relevant phosphate species; adenosine triphosphate (ATP), phosphocreatine (PCr) and inorganic phosphate. Gd.pDO3A (1.Gd) binds these species in fast exchange, enabling the relaxation of the bulk phosphate species in solution. This gives rise to 31P relaxation enhancements up to 250-fold higher than those observed for 31P relaxation enhancements with the commercial MRI contrast agent Gd.DOTA (DOTAREM), 2. Gd.pDO3A-like complexes may have potential applications as 31P magnetic resonance contrast agents, since shortening the T1 relaxation time of phosphate species would reduce the time needed to acquire 31P-MR spectra.