A new nonionic macrocyclic gadolinium(III) chelate as a potential magnetic-resonance-imaging contrast agent

Binuclear Gd3+ Complex of a 34-Membered Macrocycle with Six Carboxymethyl Arms: X-ray Structures, Formation Constants, NMR, EPR, and 1H NMR Relaxivities

“…The Gd−X distances in each coordination sphere are in the order Gd−N(amino) > Gd−O(water) ≥ Gd−O(amide) > Gd−O(carboxylate). This trend is the same as in [Gd(17dtpabn)(H 2 O)] 0 . The central metal ions in [Gd 2 (34dtpabn)(H 2 O) 2 ] 0 are located slightly out of the macrocyclic plane.…”

“…With respect to this plane, two neighboring carboxylate groups in half the metal chelate molecule are located on the same side as the metal ion to which they are coordinated, whereas the third coordinated carboxylate group is located on the opposite side. This up−up−down arrangement of the carboxylate arms with respect to the molecular plane of the macrocyclic ligand differs from the up−up−up arrangement in [Gd(17dtpabn)(H 2 O)] 0 ; the latter arrangement has been commonly reported for a number of mononuclear lanthanide complexes of polyazamacrocycles with three neighboring N -carboxymethyl arms, such as 1b , DO3A (1,4,7,10-tetraazacyclododecane- N,N ‘ ,N ‘ ‘ -triacetic acid), and DO3A derivatives. − ,− A molecular mechanics calculation performed on the binuclear Eu 3+ complex of 2a has shown that the up−down−up arrangement is stable compared with other arrangements in this complex . The same type of arrangement is formed in the uncoordinated ligand 2b , but its Gd 3+ complex has the up−up−down arrangement.…”

“…For this reason, a number of macrocyclic ligands with pendant carboxylate groups have been synthesized, and the structures of their Gd 3+ complexes have been studied extensively . A family of dioxopolyazamacrocycles with pendant carboxymethyl groups have been reported to be synthesized in a single step by reactions between ethylenediaminetetraacetic (edta) dianhydride or diethylenetriaminepentaacetic (dtpa) dianhydride and aliphatic diamines. − The dtpa-derived macrocycles are represented by the general formula 1 , which has three amino groups, two amide groups, and three pendant carboxylate groups. The planarity of the amide groups defines the rigidity of the macrocyclic rings, and the unique arrangement of the three types of donor groups results in novel coordination properties. − Reaction between an acid dianhydride and a diamine also gives a (2:2)-cyclization product in which two acid anhydride and two diamine units are linked by four amide groups. ,, A binuclear Eu 3+ complex with this type of dtpa-derived macrocycle 2a has been studied by luminescence spectroscopy and molecular mechanics .…”

Gadolinium(III) Chelates as MRI Contrast Agents: Structure, Dynamics, and Applications

“…As noted in the previous section, electronic relaxation can influence low field (<1 MHz) relaxivities; however, the similarity in relaxivity at 20 MHz for [Gd- Tables 20 and 21, relaxivities are collected for a variety of gadolinium(III) chelates. 23,28,[33][34][35]40,49,51,64,65,85,87,144,150,152,159,160,162,185,204,[225][226][227]231,239, Tweedle and co-workers 265 have shown that relaxivity per gadolinium(III) correlates well with molecular weight for a series of monomeric and multimeric gadolinium(III) chelates (Charts 17-19) and this is shown in Figure 38 (data in Table 21). For spheroidal molecules, increases in relaxivity increase approxi- mately with increasing molecular weight.…”

Structure, Dynamics, and Computational Studies of Lanthanide‐Based Contrast Agents

“…Unfortunately, the complexes of the lighter Ln 3+ ions were insoluble under conditions required for NMR, probably due to the formation of dimeric complexes, similar to those observed in the solid state for the Gd 3+ [182], La 3+ [219], and Y 3+ [182] complexes of this ligand. It should be noted that Ln 3+ complexes of similar 16-[187] and 17-membered [184] macrocycles (16-DTPA-PAM, 16-DTPA-HPAM, and 17-DTPA-BAM) crystallized as mononuclear complexes with a syn configuration of the amides. The Gd 3+ complex of a 34-membered macrocycle containing two DTPA units (DTPA-bn-DTPA-bn), however, was monomeric and showed coordination polyhedra with the amide functions in a cis configuration [190].…”