Lanthanide ions luminescent probes

Horrocks WdeW Jr, Sudnick DR (1981) Lanthanide ion luminescence probes of the structure of biological macromolecules. Ace Chem Res 14 384-392... 

Horrocks WD Jr, CoUier WE. Lanthanide ion luminescence probes. Measurement of distance between intrinsic protein fluorophores and bound metal ions quantitation of energy transfer between tryptophan and terbiimi(lll) or europiimi(lII) in the caldiun-binding protein parvalbu-min. J Am Chem Soc. 1981 103(10) 2856-2862. 

The unique luminescent properties of rare earth metal clathrochelates have been used in the development of luminescent materials (luminophores and laser materials). The luminescence of these clathrochelates in solution makes their application as biological probes and concentrators of the luminescence (i.e., the antenna effect ) promising. These complexes can also serve as efficient molecular devices to convert UV light absorbed by the ligand to lanthanide ion luminescence in the visible region. Even in very dilute (10-5 mol l-i) solutions, the conversion of irradiated photons to luminescent ones has been observed to occur at a rate of approximately 1%. For rare earth metal aqua ions at the same concentration, the efficiency of conversion is equal to 4 x IQ- % [212, 390-392]. 

Horrocks, W. de W. Jr. Sudnick, D. R. Lanthanide ion probes of structure in biology. Laser-induced luminescence decay constants provide a direct measure of the number of metal-coordinated water molecules. J. Am. Chem. Soc. 1979,101(2), 334-340. 

The lifetime values of the luminescent probe in various solvents (either as a solvated ion or in a complexed form) are taken from the literature. However, considering the numerous publications available on lanthanide organic complexes (mostly of Eu(III)) that have been studied in water and in D2O or some other solvents, it is out of the scope of this work to cite them all. Only some studies, which lead to very general conclusions of interest for the discussions below, are presented. In some cases, experiments have been performed in mixtures of two solvents, in various proportions. When specified in the publications, the decays are said to be strictly monoexponential. 

In this section, lifetime values (and in few cases, data on emission spectra) are collected for a luminescent probe in a given solvent, to which variable amounts of supporting electrolytes have been added. To the best of our knowledge, such experiments have been performed only for aquo ions (never for complexes), in H2O or D2O, but in two cases. Although the term supporting electrolyte implies no chemical reactivity towards the probe, results involving chloride based electrolytes, for which a complexation process is sometimes evoked in the case of lanthanides, are also presented in this section. When discussed at all in the literature, decay spectra are said to be monoexponential. 

Circularly polarized luminescence (CPL) from chiral molecular systems is the emission analog of circular dichroism (CD) and as such reflects the chirality of the excited state in the same maimer as CD probes reflect the chirality of the ground state (Riehl and Muller, 2005). For lanthanide ions, laige CPL (and/or CD) signals are expected for f-f transitions obeying magnetic dipole selection rules, in particular A J = 0, 1 Eu(5Do —> 7Fi), Tb(5D4 7F4, 5D4 7F5), Dy(4F9/2 6Hn/2), Yb(2Fs/2 2F7/2) emissions are typical examples. Recent... 

The good encryption of lanthanide ions in DOTA-type molecules has also prompted the development of luminescent probes based on this structure, particularly by substituting DTMA, 1,4,7,10-tetrakis(methylcarbamoylmethyl)-1,4,7,10-tetraazacyclododecane. For instance, phenacyl and phenylphenacyl substituents have been grafted onto DTMA and the corresponding ligands, LI and L2 (Fig. 4.40) form stable 1 1 complexes in water with lanthanide ions (log/fi 12-13 at 295 K). The structure of [Tb(Ll)(H20)]3+ (Fig. 4.44) shows the ion well encapsulated into the cavity formed by the macrocyclic platform and... 

An important feature in the spectroscopic behavior is that of fluorescence or luminescence of certain lanthanide ions, notably Tb, Ho, and Eu. They are used commercially in oxide phosphors for television tubes and related devices. The luminescence of the Eu3+ ion can be used as a probe of its environment, giving... 

Applications of photophysics in biology and medicine are very extensive and only a few topics can be mentioned in this review. A survey of the use of lanthanide ions as luminescent probes of biomolecular structure and a general account of long distance electron transfer in proteins and model systems are very helpful. The methods applicable to the synthesis and activation of a number of photoactivable fluoroprobes have been described and photoactivation yields measured . 

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