Lanthanide complexes crystal structure, amino acids

While studies on the crystal structures of Ln-amino acid complexes offer a clear picture of how the lanthanide... 

The angular and distance information provided by the lanthanide induced shift has found widespread application from the determination of solution structures of Ln chelates [18,19] to gaining structural information on proteins, nucleotides and amino acids [19], More recently anion binding to coordinatively unsaturated lanthanide complexes has been effectively signalled as the observed lanthanide induced shift has been directly correlated to the nature of the donor atom in the axial position [8,20,21], It is the polarisability of the axial donor that ranks the second order crystal field coefficient, B02, and hence determines the magnitude of the observed shift. Values of the mean shift of the four most-shifted axial protons of the 12-Nq ring for [Yb.la]3+ are collated in Table 2. 

In view of the structural and functional relationship between amino acids and polyaminopolycarboxylic acids, the coordination of some lanthanide ions (La, Pr, Er) with ethylenediaminetetraacetate (EDTA) has also been examined under much higher pH conditions. The formation of lanthanide-hydroxo complexes formulated as K2R(0H)EDTA 4H20 was reported as early as in 1955 (Djordjevic and Vuletic, 1980), but it is not until recent studies that the first crystal structure of a lanthanide-EDTA hydroxo species was reported. Efforts in this field were also stimulated by the recognition that the R(OH2)s array present in previously known mononuclear EDTA complexes is dimensionally close to the R(/is-0H)3 fragment of [R4(/i3-OH)4] + clusters and by the desire to understand the mechanism of formation of the clusters. A proposal for the latter is outlined in Figure 90. 

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