Direct detection of¹⁷O in [Gd(DOTA)]-by NMR spectroscopy

The ¹⁷O NMR spectrum of the non-coordinated carboxyl oxygen in the Gd^III-DOTA (DOTA = tetraazacyclododecanetetraacetic acid) complex has been observed experimentally. Its line width is essentially unaffected by paramagnetic relaxation due to gadolinium, and is only affected by the quadrupole pathway. The results are supported by the relevant parameters (hyperfine and quadrupole coupling constants) calculated by relativistic DFT methods. This finding opens up new avenues for investigating the structure and reactivity of paramagnetic Gd^III complexes used as contrast agents in magnetic resonance imaging.