Carboxylates polydentate donors

The polydentate donor (201) contains six carboxylic acid groups and forms an anionic 1 1 complex with gadolinium, of formula [Gd(201)]3 .301... 

Numerous studies on the interactions of peptides and peptide-like ligands with vanadate have been reported.68,382 384>446>447 Some of these ligands coordinate through the carboxylate, the amine functionalities and the deprotonated amide nitrogen of the peptide bond,238,23 382 447 448 and some examples were described above in the section on polydentate ligands with two oxygen donor atoms. 

Further, some ligands contain groups with more than one heteroatom in principle capable of acting as a donor atom examples in the figure above are carboxylate (—COO ) and amido (—N —CO—). Coordination of both donors to the one metal ion may be forbidden by the shape of the ligand molecule, or else occurs under only special synthetic conditions. We shall explore polydentate ligands in more detail in Section 2.3. 

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