Gadolinium complexes ligands

Kinetics of dissociation of one yttrium and seven gadolinium complexes of polyazaphosphinic acid ligands, 9 with the four CH2PO ... 

Both ligands are amides of DTPA and are obtained by treating the dianhydride of DTPA with the corresponding amine (methyl amine [15] and methoxyethylamine [16] respectively). These gadolinium complexes are freely soluble in water. As expected, the osmolality of the 0.5 molar solution of gadodiamide is lower (0.79 osmol/kg water) than that of the 0.5 molar solution of Gd-DTPA (gadopentetate) (Table 2) [17,18]. 

A second class of MRI contrast agents contains ligands that are derivatives of the macrocydic tetramine, 1.4.7.10-tetraazacyclododecane (cyclen). Gadoterate (Dotarem, Gd-DOTA, Scheme 3, formula 5) was the first macrocydic gadolinium complex which has entered the market. 

Neutral bis-and tris-gadolinium complexes of the oligomeric ligands have been obtained in the usual manner with gadolinium oxide and the corresponding dysprosium complexes by reaction with dysprosium oxide The latter might be useful as X-ray contrast agents. 

In this procedure the pentameglumine salt of the ligand DTPA was added to prevent any undesired release of the gadolinium ion from the chelate. Gadolinium-complex formulations normally contain a small amount of excess ligand either in its free or calcium-complexed form. As mentioned above, Pro-Hance (gadoteridol) contains calteridol, the calcium salt of the relatively weak calcium complex of the ligand for instance. 

In the case of a majority of ligands, the gadolinium complex is less stable than one would expect based on the simple electrostatic model. This has been known as the gadolinium break which cannot be explained in terms of steric hindrance since this anomaly is present even with ligands which offer no steric hindrance. 

Johnson, A.R., O Sullivan, B., and Raymond, K.N. (2000) Synthesis of a ligand based upon a new entry into the 3-hydroxy-N-alkyl-2(lH)-pyridinone ring system and thermodynamic evaluation of its gadolinium complex. Inorganic Chemistry, 39, 2652-2660. 

As the ligand phosphorescence is, in general, completely quenched at room temperature, for these coordination compounds , it is necessary to record the spectra at low temperature (77 K), otherwise the T states are deactivated by non-radiative processes. In this case, trivalent gadolinium complexes are generally used due to the intrinsic spectroscopic characteristics of the Gd + ion (Figure 2). 

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