Lanthanides europium

Europium(TTI) salts are typical lanthanide derivatives. Europium(ll) salts are pale yellow in colour and are strong reducing agents but stable in water. EuX2 are prepared from EuX -hEu (X=C1, Br, I) or EuFa + Ca EuCl2 forms a dihydrale. EUSO4 is prepared by electrolytic reduction of Eu(III) in sulphuric acid. Eu(II) is probably the most stable +2 stale of the lanthanides... 

Although rare-earth ions are mosdy trivalent, lanthanides can exist in the divalent or tetravalent state when the electronic configuration is close to the stable empty, half-fUed, or completely fiUed sheUs. Thus samarium, europium, thuUum, and ytterbium can exist as divalent cations in certain environments. On the other hand, tetravalent cerium, praseodymium, and terbium are found, even as oxides where trivalent and tetravalent states often coexist. The stabili2ation of the different valence states for particular rare earths is sometimes used for separation from the other trivalent lanthanides. The chemicals properties of the di- and tetravalent ions are significantly different. 

The uranium ore from Elliot Lake, Canada, contains yttrium and lanthanides (see Uranium and uranium compounds). In the Jiangxi province of the People s Repubhc of China a large reserve of a rare-earth-containing clay contains over 1,000,000 t of REO. This ore is characterized by having a low cerium content (<5%) but a high content in samarium, europium, terbium, and yttrium compared to the main base REO ores (Table 6). ... 

Europium (III) acetate (2H2O) [62667-64-5] M 383.1, pKj 8.31 (for aquo Eu " ). Recrystd several times from water [Ganapathy et al. J Am Chem Soc 108 3159 1986]. For europium shift reagents see lanthanide shift reagents in Chapter 4. 

The a—time curves for the vacuum decomposition at 593—693 K of lanthanum oxalate [1098] are sigmoid. Following a short induction period (E = 164 kJ mole-1), the inflexion point occurred at a 0.15 and the Prout—Tompkins equation [eqn. (9)] was applied (E = 133 kJ mole-1). Young [29] has suggested, however, that a more appropriate analysis is that exponential behaviour [eqn. (8)] is followed by obedience to the contracting volume equation [eqn. (7), n = 3]. Similar kinetic characteristics were found [1098] for several other lanthanide oxalates and the sequence of relative stabilities established was Gd > Sm > Nd > La > Pr > Ce. The behaviour of europium(III) oxalate [1100] is exceptional in that Eu3+ is readily reduced... 

The enantiomeric purity of optically active sulphoxides can be determined by chiral lanthanide shift reagents such as tris(3-trifluoroacetyl-ti-camphorato)europium(III) and tris(heptafluorobutyryl-d-camphorato)europium(III)218-219-221, the latter shown in Scheme 23. 

A closely related method does not require conversion of enantiomers to diastereomers but relies on the fact that (in principle, at least) enantiomers have different NMR spectra in a chiral solvent, or when mixed with a chiral molecule (in which case transient diastereomeric species may form). In such cases, the peaks may be separated enough to permit the proportions of enantiomers to be determined from their intensities. Another variation, which gives better results in many cases, is to use an achiral solvent but with the addition of a chiral lanthanide shift reagent such as tris[3-trifiuoroacetyl-Lanthanide shift reagents have the property of spreading NMR peaks of compounds with which they can form coordination compounds, for examples, alcohols, carbonyl compounds, amines, and so on. Chiral lanthanide shift reagents shift the peaks of the two enantiomers of many such compounds to different extents. 

Europium is the most reactive lanthanide metal, and may ignite on exposure to air if finely divided. 

This gives rise to dual valency state (+3 and +4) (23). As to the activity of lanthanide based catalysts we confirm a singular behavior that has been already reported by Chinese scientists (22) and that is summarized in Fig. 9. The activity of lanthanides in promoting the polymerization of butadiene and isoprene shows a large maximum centered on neodymium, the only exception being represented by samarium and europium that are not active, reasonably because they are reduced to bivalent state by aluminum alkyls, as pointed out by Tse-chuan and associates (22). 

Lanthanide-doped inverse photonic crystals have been reported.282 The lattices were prepared by infilling self-assembled polystyrene sphere templates with a mixture of zirconium alkoxide and europium at 450 °C, the polystyrene spheres were burnt out leaving hollow spheres of air, and the infilled material was converted to Zr02 Eu3+. The PL properties of the resulting photonic lattice were reported.282 The possibility of including phosphors into photonic lattices could lead to many... 

Until very recently, studies of the use of luminescent lanthanide complexes as biological probes concentrated on the use of terbium and europium complexes. These have emission lines in the visible region of the spectrum, and have long-lived (millisecond timescale) metal-centered emission. The first examples to be studied in detail were complexes of the Lehn cryptand (complexes (20) and (26) in Figure 7),48,50,88 whose luminescence properties have also been applied to bioassay (vide infra). In this case, the europium and terbium ions both have two water molecules... 

Assays based on luminescent lanthanide ions were developed initially in the 1970s, when instrumentation became available which could distinguish long-lived luminescence from a shortlived background. Leif and co-workers reported the first attempts to use lanthanide complexes (in this case europium complexes with 1,10-phenanthroline and 7-diketonates, i.e., [Eu(phen)(diketo-nate)3]) as tags for antibodies.107 These proved kinetically unstable in the pH regime required... 

A variation on the theme of conventional assay uses both lanthanide-labeled and biotin-labeled single strands to form split probes for sequence of target strands (Figure 12).120 When both of these bind to DNA, the complex binds (via the biotin residue) to a surface functionalized with streptavidin, immobilizing the europium and allowing assay to be carried out. This approach is already very sensitive to DNA sequence, since both sequences must match to permit immobilization of the lanthanide, but can be made even more sensitive by using PCR (the polymerase chain reaction) to enhance the concentration of DNA strands. In this way, initial concentrations corresponding to as few as four million molecules can be detected. This compares very favorably with radioimmunoassay detection limits. 

Lanthanide ions have been used as DEFRET acceptors in split probes for DNA sequence such as shown in Figure 15.137 When using europium and terbium complexes, the choice of chromo-phores is rather restricted, owing to the high-energy emissive states associated with these ions (vide supra). In this case, the donor chromophore is a salicylic acid unit appended to an... 

Lanthanides also have potential as DEFRET energy donors. Selvin et al. have reported the use of carbostyril-124 complexes (53) with europium and terbium as sensitizers for cyanine dyes (e.g., (54)) in a variety of immunoassays and DNA hybridization assays.138-140 The advantage of this is that the long lifetime of the lanthanide excited state means than it can transfer its excitation energy to the acceptor over a long distance (up to 100 A) sensitized emission from the acceptor, which occurs at a wavelength where there is minimal interference from residual lanthanide emission, is then measured. 

Traditionally, lanthanide-based assays have used ions which emit light in the visible region of the spectrum. Europium has been favored over other alternatives since it has a long luminescence... 

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