Metal Ion Sites Number, Composition, and Population Analysis

1 Metal Ion Sites Number, Composition, and Population Analysis 

Lanthanide ions have been used as substitutes for Ca and Zn° in proteins to obtain information on the number of metallic sites (by simple titration) and on their composition. This may of course be extended to any molecule or materials. One very useful transition in this respect is the highly forbidden and faint Eu ( Do Fo) transition which is best detected in excitation mode by analyzing the emission of the hypersensitive transition Do — Fa since both the emitting and end states are ncm-degenerate, its number of components indicates the number of different metal-ion sites. Moreover, the energy of this transition depends on the nephelauxetic effect generated by coordinated atoms and ions at 298 K  

When several metal ion sites are present in a compound, population analysis can be carried out in two main ways. For Eu , since the intensity of the MD transition Do — Fi is independent of the metal-ion environment, a spectral decomposition of the transition recorded under broad band excitation into its components measured imder selective laser excitation, followed by integration yields the population Pi of each site [31]. More generally, one can rely on lifetime measurement, since the luminescence decay will be a multi-exponential function which may be analyzed, for instance, with Origin , using the following equations  

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