Gadolinium macrocyclic complexes

Figure 3 Single crystal X-ray diffraction structure of the gadolinium texaphyrin complex PCI-0101 (2) (bis-nitrate form) showing the planar nature of the basic monoanionic texaphyrin macrocycle and the four putative inner sphere coordination sites for water (occupied by two apical methanol molecules and a bidentate nitrate anion in this structure). The Gd(III) ion is nine-coordinate and lies 0.60 A out of the plane through the five nitrogen atoms of the macrocycle. Most hydrogen atoms have been omitted for clarity. Thermal ellipsoids have been scaled to the 30% probability level. Reproduced from [22] with permission. 1993 American Chemical Society...

Zhang X, Chang CA, Brittain HG, Garrison JM, Telser J, Tweedle MF. pH Dependence of relaxivities and hydration munbers of gadolinium(lII) complexes of macrocyclic amino carbox-ylates. Inorg Orem. 1992 31(26) 5597 5600. 

Lowe, M. P., Parker, D., Reany, O., Aime, S., Botta, M., Castellano, G., Gianolio, E., Pagliarin, R. pH-dependent modulation of relaxivity and luminescence in macrocyclic gadolinium and europium complexes based on reversible intramolecular sulfonamide ligation, J. Am. Chem. Soc. 123 (2001), 7601... 

Fig. 4.13. Structure of the dimetallic gadolinium complex with a ditopic macrocyclic Schiff base, [Gd2(L2 )(N03)4], Redrawn from I.A. Kahwa et al., J. Chem. Soc., Chem. Coramun. 1531, 1989.

Complexes, particularly of gadolinium, with a N4-donor macrocycle backbone that also supports carboxylate groups have assumed importance in the context of MRI contrast agents (Sections 5.5.2 and 5.5.3). 

As noted above, the porphyrins fail to form stable complexes with gadolinium(III) [13,74,98]. Since Gd(III) is inherently more paramagnetic than Mn(III), it is intrinsically more attractive for use in MRI contrast applications [6]. In view of this, the authors proposed that a larger porphyrin-like macrocycle, capable of coordinating gadolinium(III) in a stable, nonlabile manner, could prove useful as an... 

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

Keywords Lanthanide Sensor Sensitized luminescence Dipicolinate Macrocycle Ternary complex Bacterial spore Ancillary ligand Gadolinium break Catecholamine Salicylic acid Salicylurate. 

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