Europium resonance

Chemical isomer shifts for all four europium resonances have been measured in a number of compounds. The Eu values are given in Table 17 5. Comparison of pairs of values for two transitions should show a linear relationship. An early attempt to verify this for the Eu and Eu (97 and 103 keV) transitions in EU2O3, EUSO4, and Eu metal disclosed a large deviation [59], but this was later shown to be a result of impurity in the metal [62]. 

Spectral interferences in AAS arise mainly from overlap between the frequencies of a selected resonance line with lines emitted by some other element this arises because in practice a chosen line has in fact a finite bandwidth . Since in fact the line width of an absorption line is about 0.005 nm, only a few cases of spectral overlap between the emitted lines of a hollow cathode lamp and the absorption lines of metal atoms in flames have been reported. Table 21.3 includes some typical examples of spectral interferences which have been observed.47-50 However, most of these data relate to relatively minor resonance lines and the only interferences which occur with preferred resonance lines are with copper where europium at a concentration of about 150mgL 1 would interfere, and mercury where concentrations of cobalt higher than 200 mg L 1 would cause interference. 

A 100 MHz. proton magnetic resonance spectrum (chloroform d) of the amine in the presence of an equal amount of the chiral shift reagent, tris[3-(trifluoromethylhydroxymethylene)-d-camphorato]euro-pium(III)4 (submitters), or in the presence of an equal amount of tris[3-(heptafluoropropylhydroxymethylene)-d-camphorato]europium-(III) (checkers), revealed that the product contained no detectable enantiomeric isomer. 

When the proteins are in close proximity the Europium-cryptate emission can be absorbed by the acceptor (such as allophycocyanin [APC], or XL) which emits at a higher wavelength. When the two proteins are far apart, no fluorescence resonance energy transfer (FRET) occurs. 

In addition to the coupled-signal method just described, phosphorylated carbon signals can be detected by use of praseodymium chloride, which displaces a- and /8-carbon resonances of a,/8-D-mannose 6-phosphate and a-D-mannosyl phosphate downfield, with little effect on other resonances. Europium chloride has analogous properties, except that the displacements are upfield. With certain polysaccharides, such as the O-phosphonomannan of Hansenula capsulata (29), the sig-... 

Europium(III), and particularly ytterbium(III) shift reagents, induce downfield proton resonance shifts while the praseodymium(III) analogs cause upfield shifts. Lanthanide chelates of fluorinated /3-diketonates are more soluble in organic solvents, and they form more stable association complexes with donor molecules, than do LSRs with nonfluorinated ligands. Thus Eu(fod)3 is the preferred achiral LSR for weak nucleophiles89. 

A further example is the separation of the formyl proton resonance (at 24 ppm) of the enantiomers of 2-phenylpropanal in the presence of europium(III) tris[3-(heptafluorobutanoyl)-10-methylcamphorate] (Figure 7). 

Figure 8. Peak reversals of the proton resonances by inverting the chirality of the lanthanide shift reagent methyl 2-ehloropropanoatc (SIR 80 20) in the presence of europium(III) tris[3-(heptafluorobu-tanoyl)-( 1. S )-10-methylcamphoratc and the corresponding (I / )-enantiomer (90 MHz in chloroform-rf at 28 C)94.

These are the only type of interference that do not require the presence of analyte. For AAS the problem of spectral interference is not very severe, and line overlap interferences are negligible. This is because the resolution is provided by the lock and key effect. To give spectral interference the lines must not merely be within the bandpass of the monochromator, but actually overlap each other s spectral profile (i.e. be within 0.01 nm). West [Analyst 99, 886, (1974)] has reviewed all the reported (and a number of other) spectral interferences in AAS. Most of them concern lines which would never be used for a real analysis, and his conclusion is that the only real problem is in the analysis of copper heavily contaminated with europium The most commonly used copper resonance line is 324.754 nm (characteristic concentration 0.1 pg cm- ) and this is overlapped by the europium 324.753 nm line (characteristic concentration 75 pg cm- ). 

An alternate explanation of the emission intensities of terbium in the presence of other ions was given by Peterson and Bridenbaugh (54), that for europium was given by Axe and Weller (52). These authors point out that resonance exchange is a major factor in determining the emission intensities in these cases. This work has shed some doubt on the necessity of phonon-assisted transfer for the terbium and europium ions in the cases considered by Van Uitert and Iida. 

In samples of yttrium oxide codoped with europium and other trivalent rare-earth ions they correlated the 5D0->7F2 europium-emission intensities with the number of near resonances with a second ion. The permissable mismatch from a perfect resonance match was allowed to be 500 cm-1. The magnitude of the mismatch was chosen in such a way as to prohibit the inclusion of any phonon-assisted transfers. 

Figure 38 shows the result of this analysis. It is quite clear that a very good correlation exists between the europium-emission intensities and the number of resonances found. From this result Axe and Weller concluded that resonant-energy exchange is the likely mechanism by which the energy is transferred. 

The authors observe that other rare earths also quench terbium in the same solution. The quenching effects appear to correlate well with a resonance-exchange mechanism. This strongly points to the fact that the terbium-to-europium-transfer process is probably the same. Perhaps the most important aspect of this work is that it vividly shows that energy may migrate from one rare-earth ion to another without the necessity of a crystal or glass lattice. ... 

When the fluorescing atoms or molecules are placed inside such a microcavity, the fluorescence gets coupled to the MDR as an electromagnetic field. This results in alternatively enhancement or inhibition of the fluorescence depending on whether or not the fluorescence emission spectrally coincides with a cavity resonance. The effect of MDR on the radiative rate of chelated Europium ions [2] as well as the shortening of fluorescence lifetime of Rhodamine 6G due to the effect of MDR have been reported in microdroplets [3]. 

When 1 is added to a solution of a mixture of enantiomers, A and A, it associates differently with each of the two components to produce the diastereo-meric complexes A+ 1 and A 1. The nmr spectrum of the mixture then shows shift differences that are large compared to the uncomplexed enantiomers (because of the paramagnetic effect of the europium) and normally the resonances of the A+ 1 complex will be distinct from those of the A 1 complex. An example of the behavior to be expected is shown in the proton nmr spectrum (Figure 19-4) of the enantiomers of 1-phenylethanamine in the presence of 1. Although not all of the resonances are separated equally, the resolution is good for the resonances of nuclei closest to the metal atom and permits an estimate of the ratio of enantiomers as about 2 1 and the enantiomeric purity as 33%. 

Figure 5 Effect of increasing amounts of europium on the apparent absorbance from 1 mg l 1 copper at the two main copper resonance lines...

A homogeneous and sensitive HTRF binding assay was developed to allow prosecution of an HTS campaign for novel small molecule Hsp90 inhibitors. The HTRF assay was based on a non-radio-active resonance energy transfer between a donor label (europium chelate) and an acceptor label (allophycocyanin [APC]) brought into close proximity by a specific binding interaction. 

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