gadoliniumion

Gadolinium ion (Gd3+) is the trivalent cation of gadolinium, a lanthanide with atomic number 64. In aqueous solution it is a hard, highly hydrated cation that forms coordination complexes with oxygen- and nitrogen-donor ligands, typically adopting a high coordination number (eight or nine) and a large hydration sphere.

In medicine, gadolinium is most widely encountered as gadolinium-based contrast agents (GBCAs). The Gd3+ ion is tightly bound by polyaminocarboxylate ligands such as DTPA or DOTA, reducing the risk of free gadolinium release. These chelates shorten T1 relaxation times, producing brighter signals on T1-weighted MRI images.

Safety: Free Gd3+ is toxic. In patients with severe kidney dysfunction, certain linear GBCAs have been linked to nephrogenic systemic fibrosis; macrocyclic chelates are more stable and associated with lower risk. Guidelines emphasize renal function assessment and using the lowest effective dose.

Occurrence and environment: Gadolinium occurs naturally only in trace amounts as a component of rare-earth minerals. Environmental release can occur via medical and industrial waste; concerns exist about gadolinium accumulation in aquatic systems, prompting monitoring and research into its fate and effects.

Chemistry: Gd3+ forms stable, kinetically inert chelates with ligands such as DTPA and DOTA; these complexes are designed for renal excretion. Gd3+ is paramagnetic with seven unpaired electrons, underlying the contrast effect in MRI.