Octadentate cyclen

A series of rare earth complexes with cyclen derivatives fitted pendant arms exhibit effective sensing abilities in water. Fig. 15 illustrates the crystal stracture of the 27-Eu + complex with an octadentate cyclen, in which one water molecule occupies the ninth coordination site (Zucchi et al., 2001). The lifetime and NMR measurements confirmed that only one water molecule is located in the first coordination sphere even in aqueous solution. In contrast, hep-tadentate cyclen 28 leaves two vacant sites on the rare earth center, andbidentate guest anions are expected to occupy the two adjacent coordination sites. Therefore, cyclen derivatives can be used to control the number of anion binding sites. 

Fig. 15. Rare earth complexes with octadentate cyclen 27 and heptadentate cyclen 28. Redrawn, with permission,...

Neutral N-derivatized octadentate ligands based on cyclen (1,4,7,10-tetraazacy-clododecane) form tripositive cationic complexes with the trivalent lanthanides [116-124]. The N-substituted tetraamide derivatives have proven useful in understanding the relationship between the solution structure of the Ln3+ complex and its water exchange rate, a critical issue in attaining optimal relaxation efficiency of CA s [125-131]. 

Incorporation of (111) into a kinetically stable complex suitable for attachment to an antibody calls for an octadentate ligand, and so pendant-arm cyclen derivatives are appropriate. In particular, two or three antigen-binding fragments of an antibody (Fabs) have been attached to the di- or trimaleimide ligands 80-82 (Scheme 8) (90, 91)... 

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