Binding lanthanide ion

Figure 19-16 shows how Eu3+ can be incorporated into an immunoassay. A chelating group that binds lanthanide ions is attached to antibody 2 in Figure 19-13. While bound to the antibody, Eu3+ has weak luminescence. After all steps in Figure 19-13 have been completed, the pH of the solution is lowered in the presence of a soluble chelator that extracts Eu3+ into solution. Strong luminescence from the soluble metal ion is then easily detected by a time-resolved measurement.

An alternative approach is that adopted by Horrocks and co-workers, where the aromatic residues in metal-binding proteins are used as sensitizers. Since the distance between the metal and the donor is effectively fixed, this provides a rigid scaffold for the experiment, and the absence of a directly conjugated pathway between the metals means that Forster (through space) energy transfer can be assumed. The r-6 distance-dependence of this means that the extent of sensitized emission from the lanthanide ion provides information on the spatial relationship between the metal-ion binding site (lanthanide ions often bind at Ca2+ sites) and nearby aromatic residues. 58-60... 

Lanthanide ion catalysts, alcoholysis with, see Transition metal ion and Ln3+ catalysts, alcoholysis Laser flash photolysis (LFP), 170, 175-178 cyclodextrins (CD), binding dynamics of guests binding to, 215-216 DNA, binding dynamics of guests binding to, 193-194... 

Neilands, J. B. Naturally Occurring Non-porphyrin Iron Compounds. Vol. 1, pp. 59—108. Neilands, J. B. Evolution of Biological Iron Binding Centers. Vol. 11, pp. 145—170. Nieboer, E. The Lanthanide Ions as Structural Probes in Biological and Model Systems. Vol. 22, pp. 1-47. 

ILs are becoming useful solvenfs to investigate fhe specfroscopic behavior of both organic and inorganic lanthanide complexes in solution, especially of complexes with weakly binding ligands, which otherwise would be unable to compete with the solvent molecules for a binding site on the lanthanide ion [9]. 

The bipyridyl chromophore has been extensively used in lanthanide coordination chemistry. In addition to those based on the Lehn cryptand (see Section IV.B.4), a number of acyclic ligands have also employed this group. One such ligand is L17, which binds to lanthanide ions such that one face of the ligand is left open (Scheme 3) (60). As expected, luminescence is extremely weak in water and methanol, but stronger in acetonitrile ( = 0.30, 0.14 for europium and terbium, respectively). In addition, the nature of the counter ion can... 

A novel approach for determining metal-metal distances in proteins in solution was applied to thermolysin by Horrocks et al. (16), As mentioned earlier, thermolysin has four Ca2+ binding sites. Three of the four can be replaced by trivalent lanthanide ions. Tb3 + fluorescence is enhanced when Tb3+ is bound to the so-called 1 Ca2+ site of thermolysin. When Co2+ is added to the Zn2 + active site, the fluorescence of bound Tb3+ is quenched by... 

---