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At least 19 recordsLinked to original sources
PubMed1989

Physical characterization of and ionophore-mediated europium(III) transport through unilamellar phosphatidylcholine vesicles. A laser-induced europium(III) luminescence spectroscopy study.

A continuation of the study of phospholipid bilayer vesicles as model membrane systems by laser-induced europium(III) luminescence spectroscopy is presented here (B.M. Cader and W. DeW. Horrocks, Jr, Biophys. Chem. 32 (1988) 97). This spectroscopic technique was used to characterize further the physical properties of small and large vesicles composed of dipalmitoylphosphatidylcholine and egg phosphatidylcholine, respectively. Unilamellar preparations were confirmed and internal aqueous volumes were calculated. The calcium-binding carboxylic ionophores, lasalocid A and A23187, were incorporated into the lipid bilayers of these vesicles for the purpose of modeling the mobile carrier mechanism of ion transport across cell membranes. Spectroscopic data implicate the presence of 1:1 and 1:2 europium(III)/lasalocid A complexes within the hydrophobic region, both capable of efficient transport and containing no water molecules in the inner sphere of europium(III). First-order rate constants for lasalocid A-mediated europium(III) transport were determined at 37 and 62 degrees C (0.018 and 0.11 min-1, respectively) using EGTA as a 'flag' to bind and detect the post-transported metal ion.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2004

Solvation of uranyl(II), europium(III) and europium(II) cations in "basic" room-temperature ionic liquids: a theoretical study.

We report a molecular dynamics study of the solvation of UO2(2+), Eu3+ and Eu2+ ions in two "basic" (Lewis acidity) room-temperature ionic liquids (IL) composed of the 1-ethyl-3-methylimidazolium cation (EMI+) and a mixture of AlCl4- and Cl- anions, in which the Cl-/AlCl4- ratio is about 1 and 3, respectively. The study reveals the importance of the [UO2Cl4]2- species, which spontaneously form during most simulations, and that the first solvation shell of europium is filled with Cl- and AlCl4- ions embedded in a cationic EMI+ shell. The stability of the [UO2Cl4]2- and [Eu(III)Cl6]3- complexes is supported by quantum mechanical calculations, according to which the uranyl and europium cations intrinsically prefer Cl- to the AlCl4- ion. In the gas phase, however, [Eu(III)Cl6]3- and [Eu(II)Cl6]4- complexes are predicted to be metastable and to lose two to three Cl- ions. This contrasts with the results of simulations of complexes in ILs, in which the "solvation" of the europium complexes increases with the number of coordinated chlorides, leading to an equilibrium between different chloro species. The behavior of the hydrated [Eu(OH2)8]3+ complex is considered in the basic liquids; the complex exchanges H2O molecules with Cl- ions to form mixed [EuCl3(OH2)4] and [EuCl4(OH2)3]- complexes. The results of the simulations allow us to better understand the microscopic nature and solvation of lanthanide and actinide complexes in "basic" ionic liquids.

Cations↗
PubMed2003

Determination of trace europium by use of the new fluorescence system europium-sparfloxacin-1,10-phenanthroline-sodium dodecyl sulfate.

A new lanthanide-sensitized luminescence system: europium-sparfloxacin-1,10-phenanthroline-sodium dodecyl sulfate has been discovered. The spectrofluorimetric properties of the system were studied. The effect of experimental conditions on the fluorescence intensity was defined. Under the optimum conditions, the fluorescence intensity of the system is a linear function of the concentration of europium in the range 5.0 x 10(-9) - 1.0 x 10(-6) mol L(-1) and the detection limit is 1.0 x 10(-10) mol L(-1). The system was used for the determination of trace amounts of europium in rare earth samples with satisfactory results.

Journal Article↗
PubMed2000

Comparative spectroscopic and electrochemical properties of bis(octakis(dodecylthio)naphthalocyaninato)europium(III) and bis(tetra-tert-butylnaphthalocyaninato)europium(III) complexes.

Bis(substituted-2,3-naphthalocyaninato)europium(III) complexes: bis(octakis(dodecylthio)-2,3-naphthalocyaninato)europium(III) (Eu[2,3-Nc(SC12H25)8]2, 1) and bis(tetra-tert-butyl-2,3- naphthalocyaninato)europium(III) (Eu[2,3-Nc(t-Bu)4]2, 2) have been synthesized by cyclic tetramerization of naphthalonitriles with Eu(acac)3.H2O in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing n-octanol. These compounds were characterized by UV-visible, magnetic circular dichroism (MCD), near-IR, IR, EPR, and mass spectroscopies. The absorption and MCD spectra of 1 showed splitting of the Q band, with peaks at 700 and 784 nm, red shifted from the Q band of 2 at 763 nm. The absorption and MCD spectral band deconvolution calculations of complex 1 gave two A terms in the Q-band region. The A terms are assigned to 2A2-->2E1 transitions. Cyclic voltammograms of 1 and 2 showed reversible oxidation couples at E1/2 = -0.28 V (for 2) and -0.25 V (for 1) vs ferrocenium/ferrocene (Fc+/Fc). The second oxidation exhibited a complicated behavior for both complexes. The reduction couples for 2 were observed at E1/2 = -0.61, -1.64, -1.97, and -2.42 V, and for 1 they were observed at E1/2 = -0.62, -1.60, -1.86, and -2.27 V vs Fc+/Fc. Spectral changes observed on chemical oxidation and reduction of the complexes are presented, and the behaviors of 1 and 2 are compared.

Journal Article↗
PubMed2004

Determination of rare earth impurities in high purity europium oxide by inductively coupled plasma-mass spectrometry and evaluation of concentration values for europium oxide standard material.

Direct determinations of 13 rare earth elements (La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Lu and Y) in high purity europium oxide by inductively coupled plasma mass spectrometry (ICP-MS) have been reported. The operating parameters of the instrument were optimized and the spectral interferences and the matrix effects were investigated. Using Ga or Rh as the internal standard can eliminate most of the matrix effects. The detection limits (3 sigma, n=10, integral time=1s) are 0.013-0.085 ng mL(-1) and the reproducibility (n=11) is 0.9-3%. The recoveries of spiking samples are 80-108%. Europium oxide standard material was made and its concentration values were evaluated by various techniques from 10 collaborating laboratories. By comparison of the results of ICP-MS with the results of other techniques, we have validated that ICP-MS is an accurate and reliable technique for analysis of ultratrace impurities in high purity rare earth matrix.

Europium↗
PubMed2003

Synthesis and luminescence studies of aryl substituted tetraamide complexes of europium(III): a new approach to pH responsive luminescent europium probes.

DOTA-tetraamide ligands having extended phenol or pyridine substituents have been synthesized. The (5)D(0) --> (7)F(J) deltaJ = 1 and 2 emission bands in the corresponding europium(III) complexes differ in their sensitivity to solution pH. This offers the potential for developing pH responsive probes for in vivo imaging that are independent of probe concentration.

Coloring Agents↗
PubMed1986

Interaction of europium(III) with phospholipid vesicles as monitored by laser-excited europium(III) luminescence.

The technique of laser-excited Eu(III) luminescence was applied to monitor Eu(III) binding to a variety of phospholipids. Eu(III) excitation spectra were similar with and without the presence of neutral phospholipids, while acidic phospholipids changed the spectrum in a concentration-dependent manner. Eu(III) appears to bind to the phosphate moiety with at least a 2:1 phospholipid:metal ion stoichiometry. Analysis of luminescence lifetimes reveals that only one or two waters of hydration are removed from Eu(III) by addition of neutral phospholipids, whereas acidic phospholipids and inorganic phosphate strip off all but one or two waters. Implications with regard to fusion and use of lanthanides as probes in membrane preparations are discussed.

Europium↗
PubMed2003

Europium luminescence of EF-hand helix-turn-helix chimeras: impact of pH and DNA-binding on europium coordination.

A series of Eu(III) metallopeptides, designed on the basis of the structural similarity of the helix-turn-helix and EF-hand motifs, have been studied by Eu(III) (7)F(0) --> (5)D(0) excitation spectroscopy. The impact of EF-hand ligand set differences on the hydration number and Eu(III) coordination environment are compared among the peptides. The conditional binding affinities were determined by Eu titration (P3, log K(a) = 6.0 +/- 0.4; P3W, log K(a) = 5.9 +/- 0.2; P5b, log K(a) = 5.3 +/- 0.1). Two similar coordination environments occur in each case, consistent with structural flexibility about the metal site. The coordination environments are consistent with 8- or 9-coordinate Eu(III), including six peptide-based ligands and two to three water molecules (P3, q = 1.9 +/- 0.2; P3W, q = 2.3 +/- 0.2; P4a, q = 1.9 +/- 0.3; P5b, q = 2.6 +/- 0.2). The Eu(III) (7)F(0) --> (5)D(0) excitation spectra are pH-dependent, as reported for several EF-hand proteins (oncomodulin, parvalbumin). A higher energy transition occurs at pH > 6, and has been assigned to deprotonation of coordinated water. The pK(a) leading to this new transition is dependent on Eu(III) Lewis acidity, which varies with the inner and outer sphere ligand set. The noncoordinating ninth position of the Eu-binding loop, which is poised to make second-sphere contacts to the coordinated water, stabilizes the deprotonated form of the coordinated solvent more effectively when it is Thr (P5b) than Asp (P3W). Upon DNA-binding by the metallopeptides, the pK(a) of the pH-dependent peak increases, but no new DNA-dependent transitions are observed. This indicates no DNA-based Eu(III) ligands are introduced, such as phosphate oxygen atoms of the DNA backbone. The hydration number decreases in the presence of DNA (P3W + DNA, q = 1.9 +/- 0.2; P5b + DNA, q = 1.7 +/- 0.2), indicating that DNA-binding by the metallopeptides organizes rather than compromises the Eu-binding site within the peptide.

DNA↗
PubMed2004

Europium(II) and ytterbium(II) cyclic organohydroborates: an europium(II) complex with an agostic interaction.

Lanthanide bis((cyclooctane-1,5-diyl)dihydroborate) complexes (THF)(4)Ln[(micro-H)(2)BC(8)H(14)](2) (Ln = Eu, 1; Yb, 2) were synthesized by a metathesis reaction between (THF)(x)()LnCl(2) and K[H(2)BC(8)H(14)] in THF in a 1:2 molar ratio. Attempts to prepare the monosubstituted lanthanide cyclic organohydroborates (THF)(x)LnCl[(micro-H)(2)BC(8)H(14)] were unsuccessful. On the basis of the molecular structure and IR spectrum of 1, there is an agostic interaction between Eu(II) and one of the alpha-C-H hydrogens from the [(micro-H)(2)BC(8)H(14)] unit. No such interaction was observed for 2. The coordinated THF in 1 and 2 can be removed under dynamic vacuum, but the solvent ligands remain bound to Yb when 2 is directly dissolved in Et(2)O or toluene. In strong Lewis basic solvents, such as pyridine or CH(3)CN, attack of the Yb-H-B bridge bonds results. Decomposition of 2 to the 9-BBN dimer in CD(2)Cl(2) was observed by (11)B and (1)H NMR spectroscopies. Compound 2 was reacted with 2 equiv of the hydride ion abstracting reagent B(C(6)F(5))(3) to afford the solvent-separated ion pair [Yb(THF)(6)][HB(C(6)F(5))(3)](2) (3). Complexes 1, 2, and 3 were characterized by single-crystal X-ray diffraction analysis. Crystal data: 1 is orthorhombic, Pna2(1), a = 21.975(1) A, b = 9.310(1) A, c = 16.816(1) A, Z = 4; 2 is triclinic, P1, a = 9.862(1) A, b = 10.227(1) A, c = 10.476(1) A, alpha = 69.87(1) degrees, beta = 76.63(1) degrees, gamma = 66.12(1) degrees, Z = 1; 3.Et(2)O is triclinic, P1, a = 13.708(1) A, b = 14.946(1) A, c = 17.177(1) A, alpha = 81.01(1) degrees, beta = 88.32(1) degrees, gamma = 88.54(1) degrees, Z = 2.

Journal Article↗
PubMed2005

Catalysis by methyltrioxorhenium(VII): reduction of hydronium ions by europium(II) and reduction of perchlorate ions by europium(II) and chromium(II).

The title reactions occur stepwise, the first and fastest being MeReO3 + Eu2+ --> Re(VI) + Eu3+ (k298 = 2.7 x 10(4) L mol(-1) s(-1)), followed by rapid reduction of Re(VI) by Eu2+ to MeReO2. The latter species is reduced by a third Eu2+ to Re(IV), a metastable species characterized by an intense charge transfer band, epsilon410 = 910 L mol(-1) cm(-1) at pH 1; the rate constant for its formation is 61.3 L mol(-1) s(-1), independent of [H+]. Yet another reduction step occurs, during which hydrogen is evolved at a rate v = k[Re(IV)][Eu2+][H+](-1), with k = 2.56 s(-1) at mu = 0.33 mol L(-1). The 410 nm Re(IV) species bears no ionic charge on the basis of the kinetic salt effect. We attribute hydrogen evolution to a reaction between H-ReVO and H3O+, where the hydrido complex arises from the unimolecular rearrangement of Re(III)-OH in a reaction that cannot be detected directly. Chromium(II) ions do not evolve H2, despite E(Cr) degrees approximately E(EU) degrees. We attribute this lack of reactivity to the Re(IV) intermediate being captured as [Re(IV)-O-Cr(III)]2+, with both metals having substitutionally inert d3 electronic configurations. Hydrogen evolution occurs in chloride or triflate media; with perchlorate present, MeReO2 reduces perchlorate to chloride, as reported previously [Abu-Omar, M. M.; Espenson, J. H. Inorg. Chem. 1995, 34, 6239-6240].

Journal Article↗
PubMed2004

A europium-151 Mössbauer spectral study of Eu(14)MnP(11), Eu(14)MnAs(11), and Eu(14)MnSb(11).

The europium-151 Mossbauer spectra of the Eu(14)MnP(11), Eu(14)MnAs(11), and Eu(14)MnSb(11) Zintl compounds, measured between 4.2 and 100 K, reveal europium(II) for all four crystallographically inequivalent europium sites in Eu(14)MnAs(11) and Eu(14)MnSb(11) and europium(II) and europium(III) for the three 32g and the 16f europium sites in Eu(14)MnP(11), respectively. Below the ordering temperatures of 52, 74, and 92 K, only very small hyperfine fields of 2-4 T are observed at the europium sites as a result of the polarization by the manganese magnetic moments. At 4.2 K, the europium(II) magnetic moments are ordered, and hyperfine fields of 24.4, 24.8, and 19.3 T are observed in Eu(14)MnP(11), Eu(14)MnAs(11), and Eu(14)MnSb(11), respectively, fields that are typical for magnetically ordered europium(II) ions. At 4.2 K the 16f europium(III) sites in Eu(14)MnP(11) experience a transferred hyperfine field of 33 T from the neighboring ordered europium(II) moments. Between its Curie temperature and 4.2 K, the europium-151 Mossbauer spectra of Eu(14)MnSb(11) reveal that the europium(II) moments order below ca. 13 K, i.e., below the second magnetic transition observed in magnetic measurements. Between their Curie temperatures and 4.2 K, the europium-151 Mossbauer spectra of Eu(14)MnP(11) and Eu(14)MnAs(11) are complex and have been analyzed with two models, models that give equivalently good fits. However, the second model in which the spectra are fit with a three-dimensional relaxation of the europium(II) and europium(III) hyperfine fields is preferred for its physical meaning and its reduced number of fitted parameters.

Journal Article↗
PubMed1988

Site-site interactions in EF-hand calcium-binding proteins. Laser-excited europium luminescence studies of 9-kDa calbindin, the pig intestinal calcium-binding protein.

Europium(III) binding to 9-kDa calbindin from pig intestines was studied by direct excitation of the 7Fo----5Do transition of the ion and by near-ultraviolet circular dichroic spectroscopy. Europium(III) binding is clearly biphasic. As with other lanthanides the C-terminal metal-binding site (site II) is filled first. The europium ion in this site gives an excitation spectrum with a single peak at 579.1 nm (peak 2). The occupation of the N-terminal site (site I) by europium gives excitation spectra that are pH-dependent and show a peak at 579.4 nm (peak 1a) at pH 5 which shifts to 578.7 nm (peak 1b) over the pH range 5-7. At pH 8.07 the fluorescence from europium in site I largely disappears because of weak binding, whereas that from site II is quenched by about 75% in spite of full occupancy of the site as shown by circular dichroic titration. There is a strong interaction between the two sites in spite of the very different affinities. The fluorescence from site II increases stoichiometrically with the addition not only of the first equivalent of europium, but also concomitantly with the fluorescence from site I upon addition of the second equivalent. Furthermore, when Eu1-calbindin is titrated with calcium the fluorescence at 579.1 nm is quenched by about 30% during the addition of one equivalent of calcium which fills site I. Subsequent titration with large excesses of calcium displaces europium from site II. The affinity of site II for europium is about 100 times that of calcium under these conditions.

Animals↗
PubMed2000

Reactivity of "Eu(OiPr)2" with phenols: formation of linear Eu3, square pyramidal Eu5, cubic Eu8, and capped cubic Eu9 polymetallic europium complexes.

The direct reaction of europium with 2-propanol and phenols has been investigated under a variety of conditions. The reaction of europium metal with 2,6-dimethylphenol and 2,6-diisopropylphenol in 2-propanol at reflux revealed that polymetallic europium complexes could be generated by this method. Hx[Eu8O6(OC6H3Me2-2,6)12(OiPr)8], 1, and H5[Eu5O5(OC6H3iPr2-2,6)6(NCCH3)8], 2, were isolated by recrystallization in the presence of hexanes and acetonitrile, respectively, and characterized by X-ray crystallography. Complex 1 has a cubic arrangement of europium ions with face-bridging mu 4-O donor atoms, edge-bridging mu-O(phenoxide/phenol) ligands, and terminal O(isopropoxide/2-propanol) ligands. Complex 2 is mixed valent and has a square pyramidal europium core with four Eu(II) ions at the basal positions and one Eu(III) ion at the apex. Since these reactions gave complicated mixtures of products from which 1 and 2 could only be obtained in low yields, direct reactions under less forcing reaction conditions were investigated. Europium reacts slowly at room temperature to form arene-soluble divalent [Eu(OiPr)2(THF)x]n, 3. Complex 3 reacts with 2,6-dimethylphenol to form the arene-insoluble complex (H[Eu(OC6H3Me2)2(OiPr)])n, 4. Recrystallization of 4 in the presence of THF results in the crystallographically characterizable divalent trimetallic complex [Eu(OC6H3Me2-2,6)2(THF)2]3, 5, which has an unusual linear metal geometry. In the presence of HOiPr at ambient conditions in the glovebox, crystals of 5 slowly convert to the mixed valent H10[Eu8O8(OC6H3Me2-2,6)10(OiPr)2(THF)6], 6, which was found to have a cubic arrangement of europium atoms similar to 1 by X-ray crystallography. Complex 4, upon heating under vacuum, followed by reaction with THF, forms the arene-soluble divalent complex H18([Eu9O8(OC6H3Me2-2,6)10(THF)7][Eu9O9(OC6H3Me2-2,6)10(THF)6]), 7, which contains two types of capped cubic arrangements of europium ions in the solid state.

Journal Article↗
PubMed1975

Europium as a fluorescent probe of transfer RNA structure.

The binding of europium(III) to Escherichia coli tRNA-fMet,Glu and to unfractionated E. coli tRNA has been investigated by using the 4-thiouridine sensitization of europium 5-Do yields 7-F1 emission and changes in the lifetime of the 5-Do state of europium reported earlier (J. M. Wolfson and D. R. Kearns (1974), J. Am. Chem. Soc. 96, 3653). Binding of the first 3-4 europium ions is independent and sequential, approximately 600 times stronger than the magnesium binding, and the binding sites are located near the 4-thiouridine residue found at position 8 in a number of E. coli tRNA. Competition experiments suggest the strong binding sites are the same for magnesium and europium. The europium binding properties of both unfractionated E. coli tRNA and purified tRNA-fMet are quite similar, indicating that the location of the strong binding sites and their binding constants are nearly the same for a large group of tRNA. The europium binding properties of native and denatured tRNA are quite different, however.

Binding Sites↗
PubMed1984

Europium as a label in time-resolved immunofluorometric assays.

A nonisotopic immunoassay has been developed based on a sensitive detection of europium (III) in water solution using time-resolved fluorometry. The europium label is bound to the antibody with EDTA derivatives, either diazophenyl-EDTA-Eu or isothiocyanatophenyl-EDTA-Eu. After the immunometric assay has been completed the europium is preferably dissociated from the antibody at low pH and measured by time-resolved fluorescence in a micellar solution containing Triton X-100, beta-diketone, and a Lewis base. The detergent solubilizes the chelating compounds in the solution and excludes water from the fluorescent ligand-europium complex. Europium concentrations as low as 5 X 10(-14)M were measured using a 1-s counting time. The sensitivity of the immunoassay of rabbit IgG used as a model system was 25 pg/ml (6 pg/assay).

Animals↗
PubMed1994

Time-resolved delayed luminescence image microscopy using an europium ion chelate complex.

Improvements and extended applications of time-resolved delayed luminescence imaging microscopy (TR-DLIM) in cell biology are described. The emission properties of europium ion complexed to a fluorescent chelating group capable of labeling proteins are exploited to provide high contrast images of biotin labeled ligands through detection of the delayed emission. The streptavidin-based macromolecular complex (SBMC) employs streptavidin cross-linked to thyroglobulin multiply labeled with the europium-fluorescent chelate. The fluorescent chelate is efficiently excited with 340-nm light, after which it sensitizes europium ion emission at 612 nm hundreds of microseconds later. The SBMC complex has a high quantum yield orders of magnitude higher than that of eosin, a commonly used delayed luminescent probe, and can be readily seen by the naked eye, even in specimens double-labeled with prompt fluorescent probes. Unlike triplet-state phosphorescent probes, sensitized europium ion emission is insensitive to photobleaching and quenching by molecular oxygen; these properties have been exploited to obtain delayed luminescence images of living cells in aerated medium thus complementing imaging studies using prompt fluorescent probes. Since TR-DLIM has the unique property of rejecting enormous signals that originate from scattered light, autofluorescence, and prompt fluorescence it has been possible to resolve double emission images of living amoeba cells containing an intensely stained lucifer yellow in pinocytosed vesicles and membrane surface-bound SBMC-labeled biotinylated concanavalin A. Images of fixed cells represented in terms of the time decay of the sensitized emission show the lifetime of the europium ion emission is sensitive to the environment in which it is found. Through the coupling of SBMC to streptavidin,a plethora of biotin-based tracer molecules are available for immunocytochemical studies.

Animals↗