Surface speciation of Eu3+ adsorbed on kaolinite by time-resolved laser fluorescence spectroscopy (TRLFS) and parallel factor analysis (PARAFAC)

Time-resolved laser fluorescence spectroscopy (TRLFS) is an effective speciation technique for fluorescent metal ions and can be further extended by the parallel factor analysis (PARAFAC). The adsorption of Eu(3+) on kaolinite as well as gibbsite as a reference mineral was investigated by TRLFS together with batch adsorption measurements. The PAFAFAC modeling provided the fluorescence spectra, decay lifetimes, and relative intensity profiles of three Eu(3+) surface complexes with kaolinite; an outer-sphere (factor A) complex and two inner-sphere (factors B and C) complexes. Their intensity profiles qualitatively explained the measured adsorption of Eu(3+). Based on the TRLFS results in varied H(2)O/D(2)O media, it was shown that the outer-sphere complex exhibited more rapid fluorescence decay than Eu(3+) aquo ion, because of the energy transfer to the surface. Factor B was an inner-sphere complex, which became dominant at relatively high pH, high salt concentration and low Eu(3+) concentration. Its spectrum and lifetime were similar to those of Eu(3+) adsorbed on gibbsite, suggesting its occurrence on the edge face of the gibbsite layer of kaolinite. From the comparison with the spectra and lifetimes of crystalline or aqueous Eu(OH)(3), factor C was considered as a poly-nuclear surface complex of Eu(3+) formed at relatively high Eu(3+) concentration.     

Europium complexation by an aquatic fulvic acid - effects of competing ions

Effects of competing ions, Fe (2+)Fe (3+) and Al(3+), on Eu(3+) complexation with an aquatic fulvic acid (FA), have been investigated using an ion exchange technique. The influence of different concentrations (10(-6), 10(-4) M) of the competing ions on the distribution coefficient for Eu was measured, and the overall complex formation function, beta(ov), was resolved for the Eu systems with Fe and Al. All systems showed pH-dependent beta(ov)-functions. The presence of 10(-4) M concentration of competing ion reduced the resolved complex formation function (logbeta(ov)) for Eu complexation with fulvic acid by 0.6 and 0.4 log units at pH 5 for Fe and Al, respectively. this indicates that Fe has a more perturbing effect on Eu-FA complexation than Al. In similar competition studies Sr and Eu were found not to perturb each others complexation with fulvic acid, suggesting therefore that the two metals probably bind to different sites on the fulvic acid molecule.     

Eu(3+)-mediated polymerization of benzenetetracarboxylic acid studied by spectroscopy, temperature-dependent calorimetry, and density functional theory

Thermodynamic parameters for the complexation of Eu(3+) with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerizable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 μM Eu(3+), <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60 °C. At elevated concentrations (>500 μM Eu(3+) and BTC) a temperature-dependent polymerization was observed, where BTC monomers are linked via coordinating shared Eu(3+) ions. The two methods lead to comparable thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol(-1); ΔS = 152 ± 5/130 ± 5 J mol(-1) K(-1); TRLFS/ITC) in the absence of polymerization. With the onset of polymerization, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly chelating coordination with two carboxylate groups in the monomeric complex and monodentate binding of a single carboxylate group in the polymeric complex of the polycarboxylate with Eu(3+). The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerization as a crucial factor in determining the effect of humic acids on the mobility of heavy metals in the environment.     

Electrochemically controllable emission and coloration by using europium(III) complex and viologen derivatives

We have demonstrated electroswitchable emission and coloration using a novel composite material containing luminescent europium(III) complex Eu(hfa)(3)(H(2)O)(2) and diheptyl viologen HV(2+). The photoluminescence of the Eu(III) complex was controlled by the electrochemical coloration of HV(2+)via intermolecular energy transfer mechanisms.     

Synthesis, characterization and luminescent properties of new highly luminescent organic ligand and complexes of trivalent rare earth

A novel ligand with two carboxylic groups has been synthesized. The composition and structure of the ligand were characterized by IR, (1)H NMR and MS spectrometry. The highly luminescent intensity complexes were prepared with the ligand and phen. The IR, solid state (13)C NMR and fluorescent spectra of the complex were studied. IR absorption spectra indicate that the ligand is coordinated to the Eu(3+) ion, and chemical bonds are formed between Eu(3+) ion and nitrogen atoms of phen. The fluorescent spectra illustrate that the complex has an excellent luminescence, indicating the ligand favors energy transfer to the emitting energy level of Eu(3+). The influences of pH and reaction solvent on the fluorescence intensity of the complex were also discussed.     

A single red InGaN-based light-emitting diode with a europium (III) ternary complex as mono-phosphor

A novel europium (III) ternary complex, Eu(TPBDTFA)(3)Phen, was designed and synthesized. Photoluminescence measurements show that the energy absorbed by the organic ligands was efficiently transferred to the central Eu(3+) ions, and the complex exhibits strongly red emission due to the (5)D(0)-(7)F(j) transitions of Eu(3+) ions with appropriate CIE (Commission Internationale de l'Eclairage, International Commission on Illumination) chromaticity coordinates (x=0.66, y=0.33) under 310-420 nm light excitation. The luminescence quantum yield for the Eu(3+) complex is 0.18. Thermogravimetric analysis (TGA) confirms a high thermal stability of the complex with a decomposition temperature of 341 degrees C. All the characteristics indicate that the Eu(3+) complex is a highly efficient red phosphor suitable to be excited by near UV light. An intense red-emitting LED was fabricated by combining the mono-phosphor Eu(TPBDTFA)(3)Phen with a approximately 395 nm emitting InGaN chip.     

Studies on the extraction and separation of lanthanide ions with a synergistic extraction system combined with 1,4,10,13-tetrathia-7,16-diazacyclooctadecane and lauric acid

1,4,10,13-Tetrathia-7,16-diazacyclooctadecane (ATCO) and its binary extraction system containing lauric acid were studied extensively as extractants of lanthanide (M(3+)=La(3+), Ce(3+), Pr(3+), Nd(3+), Sm(3+), Eu(3+) and Gd(3+)) in 1,2-dichloroethane solution. The percentage extraction of Ce(3+) and Eu(3+) by ATCO were only measured to be less than 5% during a pH range 5.5-7.0 in NCS(-), ClO(4)(-) and PF(6)(-) mediums respectively, which indicates that ATCO alone has very low extractability to lanthanide, due to the bad fit of metal ions in its cavity. However, when lauric acid was added to the ATCO organic phase, because of forming rare earth adduct, the percentage extraction for lanthanide until Gd(3+) was enhanced in the binary system in comparison with that did not adopt the lauric acid within the pH range 6-7. The extraction species and extraction equilibrium constants logK(ex) were found to be CeLA(3)3HA, -8.5, EuLA(3)HA, -6.7, and GdLA(2)NO(3)2HA, -1.8, respectively. The separation factor between Eu(3+) and Ce(3+) was found to be 2.5, however, poor selectivity for lanthanide was observed. From Gd(3+) to Er(3+) and Lu(3+), the synergistic effect of the binary extraction system decreases with increasing atomic number. For gadolinium, the synergistic effect becomes much weaker than that of Ce(3+) and Eu(3+), no synergistic effect existed for erbium and lutetium. Thermodynamic data for synergistic solvent extraction are also reported in this paper. The order of organic phase stability constants of the extraction species is Sm (5.8)>Pr (5.7)>Eu (5.6)>Ce (5.3)>La (5.2)>Gd (2.8).     

The binding of strontium and europium by an aquatic fulvic acid--ion exchange distribution and ultrafiltration studies

The complexation of an aquatic fulvic acid, FA, with Sr(2+) and Eu(3+) was studied at 0.10 and O1.O1M NaClO(4) using trace levels of metal ([Sr(2+)] = 10(-9)M and [Eu(3+)] = 10(-11)M) and a constant FA concentration (0.12 g/l) by an ultrafiltration technique (UF) and an ion exchange distribution method (IEDS). The overall complex formation function, beta(OV) for the two metals was calculated and its dependence on pH, ionic strength and method was investigated. The absolute value of log beta(OV), the pH dependence and the influence of the ionic strength on the complexation differed depending on the metal ion and experimental technique employed. By considering the functional group heterogeneity of the FA molecule, it was possible to predict the most predominantly bound site (keto-enol) and resolve the complex formation function for this site and EU(3+) (IEDS: 9.43 +/- 0.29 l/eq at 0.10M and 10.58 +/- 0.72 l/eq at 0.01M; UF: 7.19 +/- 1.51 l/eq at 0.01M and 6.88 +/- 0.91 l/eq at 0.01M). The results are discussed in the light of possible intrinsic problems of the two experimental methods.     

Synthesis, potentiometric, kinetic, and NMR Studies of 1,4,7,10-tetraazacyclododecane-1,7-bis(acetic acid)-4,10-bis(methylenephosphonic acid) (DO2A2P) and its complexes with Ca(II), Cu(II), Zn(II) and lanthanide(III) ions

A cyclen-based ligand containing trans-acetate and trans-methylenephosphonate pendant groups, H 6DO2A2P, was synthesized and its protonation constants (12.6, 11.43, 5.95, 6.15, 2.88, and 2.77) were determined by pH-potentiometry and (1)H NMR spectroscopy. The first two protonations were shown to occur at the two macrocyclic ring N-CH 2-PO 3 (2-) nitrogens while the third and fourth protonations occur at the two phosphonate groups. In parallel with protonation of the two -PO 3 (2-) groups, the protons from the NH (+)-CH 2-PO 3 (2-) are transferred to the N-CH 2-COO (-) nitrogens. The stability constants of the Ca (2+), Cu (2+), and Zn (2+) (ML, MHL, MH 2L, and M 2L) complexes were determined by direct pH-potentiometry. Lanthanide(III) ions (Ln (3+)) form similar species, but the formation of complexes is slow; so, "out-of-cell" pH-potentiometry (La (3+), Eu (3+), Gd (3+), Y (3+)) and competitive spectrophotometry with Cu(II) ion (Lu (3+)) were used to determine the stability constants. By comparing the log K ML values with those of the corresponding DOTA (H 4DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and DOTP (H 8DOTP = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetramethylenephosphonic acid) complexes, the order DOTA < DO2A2P < DOTP was found for all the metal ion complexes examined here with the exception of the Ca (2+) complexes, for which the order is reversed. The relaxivity of Gd(DO2A2P) decreases between pH 2 and 7 but remains constant in the pH range of 7 < pH < 12 ( r 1 = 3.6 mM (-1) s (-1)). The linewiths of the (17)O NMR signals of water in the absence and presence of Gd(DO2A2P) (at pH = 3.45 and 8.5) between 274 and 350 K are practically the same, characteristic of a q = 0 complex. Detailed kinetic studies of the Ce (3+) and Gd (3+) complexes with DO2A2P showed that complex formation is slow and involves a high stability diprotonated intermediate Ln(H 2DO2A2P)*. Rearrangement of the diprotonated intermediate into the final complex is an OH (-) assisted process but, unlike formation of Ln(DOTA) complexes, rearrangement of Ln(H 2DO2A2P)* also takes place spontaneously likely as a result of transfer of one of the protons from a ring nitrogen to a phosphonate group. The order of the OH (-) assisted formation rates of complexes is DOTA > DO2A2P > DOTP while the order of the proton assisted dissociation rates of the Gd (3+) complexes is reversed, DOTP > DO2A2P > DOTA. (1)H and (13)C NMR spectra of Eu(DO2A2P) and Lu(DO2A2P) were assigned using two-dimensional correlation spectroscopy (2D COSY), heteronuclear multiple quantum coherence (HMQC), heteronuclear chemical shift correlation (HETCOR), and exchange spectroscopy (EXSY) NMR methods. Two sets of (1)H NMR signals were observed for Eu(DO2A2P) characteristic of the presence of two coordination isomers in solution, a twisted square antiprism (TSAP) and a square antiprism (SAP), in the ratio of ~93% and ~7%, respectively. Line shape analysis of the (1)H NMR spectra of Lu(DO2A2P) gave lower activation parameters compared to La(DOTP) for interconversion between coordination isomers. This indicates that the Ln(DO2A2P) complexes are less rigid probably due to the different size and spatial requirements of the carboxylate and phosphonate groups.     

Preparation and photoluminescence of a novel beta-diketone ligand containing electro-transporting group and its europium(III) ternary complex

A novel beta-diketone with an electro-transporting oxadiazole group, 1-(4'-(5-(4-methylphenyl)-1,3,4-oxadiazol-2-yl)biphenyl-4-yl)-4,4,4-trifluorobutane-1,3-dione (MPBDTFA), was prepared with high yield. With this synthesized ligand as the first ligand and 1,10-phenanthroline (Phen) as the secondary ligand, a new europium(III) ternary complex, Eu(MPBDTFA)(3)Phen, was synthesized. The new beta-diketone and its europium(III) ternary complex were characteristized by elemental analysis, thermo-gravimetric analysis, IR and UV-visible spectroscopies. Photoluminescence measurements indicated that the energy absorbed by the organic ligands was efficiently transfered to the central Eu(3+) ions, and the complex showed intensely and characteristically red emissions due to the (5)D(0)-->(7)F(j) transitions of the central Eu(3+) ions. With an electro-transporting group in molecule and highly thermal stability, the synthesized Eu(III) ternary complex is expected as a red-emitting candidate material for fabrication of organic light-emitting diodes (OLEDs).     

Na2EuAs2S5, NaEuAsS4, and Na4Eu(AsS4)2: controlling the valency of arsenic in polysulfide fluxes

The reactivity of europium with As species in Lewis basic alkali-metal polysulfide fluxes was investigated along with compound formation and the As(3+)/As(5+) interplay vis-à-vis changes in the flux basicity. The compound Na(2)EuAs(2)S(5) containing trivalent As(3+) is stabilized from an arsenic-rich polysulfide flux. It crystallizes in the monoclinic centrosymmetric space group P2(1)/c. Na(2)EuAs(2)S(5) has [As(2)S(5)](4-) units, built of corner sharing AsS(3) pyramids, which are coordinated to Eu(2+) ions to give a two-dimensional (2D) layered structure. A sodium polysulfide flux with comparatively less arsenic led to the As(5+) containing compounds NaEuAsS(4) (orthorhombic, Ama2) and Na(4)Eu(AsS(4))(2) (triclinic, P1) depending on Na(2)S/S ratio. The NaEuAsS(4) and Na(4)Eu(AsS(4))(2) have a three-dimensional (3D) structure built of [AsS(4)](3-) tetrahedra coordinated to Eu(2+) ions. All compounds are semiconductors with optical energy gaps of ～2 eV.     

Spectrofluorimetric determination of superoxide dismutase using a Europium-tetracycline probe

Superoxide dismutase (SOD) can enhance the characteristic fluorescence of europium in europium (Eu(3+))-tetracycline (TC) system. According to this, a new spectrofluorimetric determination of SOD was developed. Under the optimum conditions, Eu(3+)-TC formed a ternary complex in close proximity with SOD and then intra-molecular energy transfer from TC-SOD complex to Eu(3+), which resulted in the enhancement of characteristic peak of Eu(3+) at 612 nm. The enhanced fluorescence intensity is in proportion to the concentration of SOD, and the linear range was 0.0553-38.71 microg mL(-1) with the limit of detection of 5.53 ng mL(-1). The developed method was practical, simple, sensitive and relatively free from interference coexisting substances and has been successfully applied to the determination of SOD in the plant and blood samples. The mechanism of fluorescence enhancement between Eu(3+)-TC complex and SOD was also studied.     

Isophthalato-based 2D coordination polymers of Eu(III), Gd(III), and Tb(III): enhancement of the terbium-centered luminescence through thiophene derivatization

We present here the first examples of lanthanide ion complexes with only isophthalic acid or thiophenylisophthalic acid ligands. The complexes of isophthalic acid with Eu(3+) (1) and Tb(3+) (2) and the moderately soluble complexes of 5-thiophen-3-ylisophthalate with Eu(3+) (3), Gd(3+) (4), and Tb(3+) (5) were isolated as single crystals through gel crystallization. X-ray diffraction studies confirm the cross-linking structure of these complexes, which, in case of the thiophenyl derivatives, results in low solubility in common solvents. The two-dimensional isophthalato complex of Eu(3+) (1) crystallizes in the C2/c space group, with a = 22.154(4), b = 12.649(3), and c = 15.921(3) A, beta = 112.34(3) degrees, and V = 4126.7(14) A(3), while the one-dimensional Tb(3+) complex of the same ligand, 2, crystallizes in the space group P2(1)/c with a = 11.921(2), b = 10.838(2), and c = 17.499(4) A, beta = 92.44(3) degrees, and V = 2258.9(8) A(3). The thiophenylisophthalato complexes of Eu(3+) (3) and Gd(3+) (4) are two-dimensional and crystallize in the P2/n space group with parameters for 3 of a = 14.139(3), b = 10.684(2), and c = 15.138(3) A, beta = 102.51(3) degrees, and V = 2232.3(8) A(3) and parameters for 4 of a = 14.1195(13), b = 10.6594(10), and c = 15.1149(14) A, beta = 102.529(2) degrees, and V = 2220.7(4) A(3), while the Tb(3+) complex, 5, also two-dimensional, crystallizes in the P space group with a = 11.051(2), b = 14.528(3), and c = 15.041(3) A, alpha = 77.63(3), beta = 87.86(3), and gamma = 83.51(3) degrees, and V = 2343.48 A(3). All complexes of Eu(3+) and Tb(3+) luminesce in aqueous solution, and the luminescence lifetimes and quantum yields are 123.8 +/- 7.4, 0.14% (1), 475.1 +/- 14.5, 3.58% (3), 129.3 +/- 3.5, 0.19% (4), and 213.9 +/- 2.2 micros, 7.46% (5).     

一种新型Eu3+ 和Zn2+ 双金属杂核配合物的结构与发光性质

合成了一种新型双金属杂核配合物Eu(TTA)3Zn(Salen).H2O(Salen=双水杨醛缩乙二胺,TTA=2-噻吩甲酰三氟丙酮),并对其进行了结构和荧光性能表征.配合物的晶体属于三斜晶系,Pī空间群.中心Eu(Ⅲ)离子与六个TTA分子的氧原子和Salen分子的两个酚氧原子配位,形成8配位的扭曲四方反棱柱构型.Zn(Ⅱ)离子与Salen分子中的两个酚氧原子和两个氮原子以及一个水分子配位,形成五配位的扭曲的四方锥构型.配合物Eu(TTA)3Zn(Salen).H2O的发光量子效率(18.0%)较配合物Eu(TTA)3.2H2O(12.5%)发光量子效率有明显提高,说明第二配体Zn(Salen).H2O对中心离子有较强的敏化发光作用.     

The thermal stabilities of luminescence and microstructures of Eu2+-doped KBaPO4 and NaSrPO4 with β-K2SO4 type structure

Eu(2+)-doped monophosphates NaSrPO(4) and KBaPO(4) with the β-K(2)SO(4) structure were synthesized using the conventional high temperature solid state reaction. The X-ray powder diffraction, photoluminescence excitation, and emission spectra and decay curves were measured. The phosphors can be efficiently excited by UV-visible light from 220 to 430 nm to realize emission in the visible range. The natures of the Eu(2+) emission, e.g., the chromaticity coordinates, the Stokes shifts, and the luminescence absolute quantum efficiencies, were reported. The luminescence quenching temperatures and the thermal activation energies for NaSrPO(4):Eu(2+) and KBaPO(4):Eu(2+) were obtained from the temperature dependent (10-435 K) luminescence intensities and decay curves. KBaPO(4):Eu(2+) presents only one emission center; however, Eu(2+) ions have a "disordered environment" in NaSrPO(4) lattices. The relationship between the luminescence thermal stabilities and the crystal structures was discussed. The crystallographic occupations of rare earth ions doped in these hosts were analyzed by the site-selective emission spectra and the excitation spectra of Eu(3+) ions in the (7)F(0)→(5)D(0) transitions using a pulsed, tunable, and narrow-band dye laser. In KBaPO(4), the Eu(3+) ions could be distributed in the host with a high "ordered state" in only one site in the lattices. However, the multiple site structure of Eu(3+) ions with highly disordered distributions in NaSrPO(4) lattices was suggested.     

Luminescent lanthanide complexes of a bis-bipyridine-phosphine-oxide ligand as tools for anion detection

The Gd(3+), Tb(3+), and Eu(3+) complexes of a bis-bipyridine-phenylphosphine oxide ligand PhP(O)(bipy)(2) 1 (bipy for 6-methylene-6'-methyl-2,2'-bipyridine) have been synthesized. In acetonitrile solutions at room temperature, the Tb(3+) and Eu(3+) complexes show a metal-centered luminescence, indicative of an efficient energy transfer from the two bipy subunits to the Ln center. The photophysical properties drastically depend on the nature of the anions present in solution. In particular, addition of 2 equiv of nitrate anions to a solution containing the [Ln.1](OTf-)(3) leads to an 11-fold increase of the luminescence intensity for the Eu(3+) and a 7-fold increase for the Tb(3+) complexes. Similar effects are provided with Cl-, F-, and CH(3)COO- anions. UV-vis titration experiments were used to determine association constants for binding of, respectively, one, two, and three anions. Stepwise anion addition has also been investigated on the molecular level using quantum mechanical (QM) calculations for the Eu complexes. These calculations reproduce the experimental findings, especially if solvent molecule addition is taken into account. The X-ray crystal structure of the nitrate salt of the Tb complex, as well as QM calculation of a similar Eu complex, demonstrates the coordination of three nitrate anions in a bidentate mode and the step-by-step relegation of the bipy subunits in the second coordination sphere. These features give valuable insights into the mechanism of the overall light amplification process.     

A Cl- anion-responsive luminescent Eu3+ complex with a chiral tripod: ligand substituent effects on ternary complex stoichiometry and anion sensing selectivity

A new series of N3,O-mixed donor tripods was prepared for luminescent Eu3+ complexes, in which the soft quinoline nitrogen, tertiary amine nitrogen, and hard amide oxygen donors were cooperatively involved. The mixed donor tripods formed more stable 1 : 1 complexes with Eu(NO3)3, La(NO3)3 and Tb(NO3)3 than the corresponding N4 donor tripods, and their Eu3+ complexes particularly exhibited anion-responsive luminescence properties. NMR, UV, and luminescence spectroscopic characterizations revealed that -CH3 substitution on the tripod skeleton remarkably altered the preferred stoichiometry of the "tripod-Eu3+-anion" ternary complex and gave anion-dependent europium luminescence. Although the disubstituted tripod preferred to form non-luminescent 2 : 1 (tripod : Eu3+) complexes with Eu(NO3)3 and other salts, it formed a luminescent 1 : 1 complex with EuCl3. Thus, this type of tripod offered Cl- anion-selective luminescence enhancement that was easily observed by the naked eye.     

Luminescent ruthenium(II) bipyridine-calix[4]arene complexes as receptors for lanthanide cations

The synthesis and photophysical properties of novel luminescent ruthenium(II) bipyridyl complexes containing one, two, or six lower rim acid-amide-modified calix[4]arene moieties covalently linked to the bipyridine groups are reported which are designed to coordinate and sense luminescent lanthanide ions. All the Ru-calixarene complexes synthesized in this work are able to coordinate Nd(3+), Eu(3+), and Tb(3+) ions with formation of adducts of variable stoichiometry. The absorbance changes allow the evaluation of association constants whose magnitudes depend on the nature of the complexes as well as on the nature of the lanthanide cation. Lanthanide cation complex formation affects the ruthenium luminescence which is strongly quenched by Nd(3+) ion, moderately quenched by the Eu(3+) ion, and poorly or moderately increased by the Tb(3+) ion. In the case of Nd(3+), the excitation spectra show that (i) the quenching of the Ru luminescence occurs via energy transfer and (ii) the electronic energy of the excited calixarene is not transferred to the Ru(bpy)(3) but to the neodymium cation. In the case of Tb(3+), the adduct's formation leads to an increase of the emission intensities and lifetimes. The reason for this behavior was ascribed to the electric field created around the Ru calix[4]arene complexes by the Tb(3+) ions by comparison with the Gd(3+) ion, which behaves identically and can affect ruthenium luminescence only by its charge. However, especially for compounds 1 and 3, it cannot be excluded that some contribution comes from the decrease of vibrational motions (and nonradiative processes) due to the rigidification of the structure upon Tb(3+) complexation. In the case of Eu(3+), compounds 1, 2, and 4 were quenched by the lanthanide addition but the quenching of the ruthenium luminescence is not accompanied by europium-sensitized emission which suggests that an electron-transfer mechanism is responsible for the quenching. On the contrary, compound 3 exhibits enhanced emission upon addition of Eu(3+) (as nitrate salt); it is suggested that the lack of quenching in the [3.2Eu(3+)] adduct is due to kinetic reasons because the electron-transfer quenching process is thermodynamically allowed.     

Highly sensitive spectrofluorimetric determination of trace amounts NADP using Europium ion-doxycycline complex probe

A new spectrofluorimetric method was developed for determination of trace amount of Coenzyme II (NADP). Using europium ion-doxycycline (DC) as a fluorescent probe, in the buffer solution of pH 8.44, NADP can remarkably enhance the fluorescence intensity of the Eu(3+)-DC complex at lambda=612 nm and the enhanced fluorescence intensity is in proportion to the concentration of NADP. Optimum conditions for the determination of NADP were also investigated. The dynamic range for the determination of NADP is 3.3 x 10(-7) to 6.1 x 10(-6) mol l(-1) with detection limit of 6.8 x 10(-8) mol l(-1). This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of NADP in synthetic water samples and in serum samples. Moreover, the enhancement mechanisms of the fluorescence intensity in the Eu(3+)-DC system and the Eu(3+)-DC-NADP system have been also discussed.     

Kinetics of the Formation of Macrocyclic Polyaminocarboxylate Ligand Complexes: A Laser-Excited Luminescence Study of the Eu(3+)-dtpa-dien System

Excitation spectroscopy of the (7)F(0) --> (5)D(0) transition of Eu(3+) is used to detect and characterize a kinetic intermediate in the formation of a complex between Eu(3+) and the macrocyclic ligand dtpa-dien (1,4,7-tris(carboxymethyl)-9,17-dioxo-1,4,7,10,13,16-hexaazacyclooctadecane). Both the long-lived intermediate and the final product, [Eu(Hdtpa-dien)(H(2)O)](+), are formed immediately upon mixing the components, as evidenced by separate peaks in the excitation spectrum. The transformation of the intermediate to the final product, monitored by excitation spectroscopy, occurs by both proton-assisted and non-proton-assisted pathways. It is proposed that the intermediate represents a "blind alley" in the pathway to a final nine-coordinate tricapped trigonal prismatic product. The intermediate with an "up, down, up" configuration of carboxylate arms must undergo some decoordination to form the final complex. Molecular mechanics calculations and excited state lifetimes suggest that the intermediate is eight-coordinate with one coordinated water molecule. The stability constant of the final complex is found to be log K = 14.11 +/- 0.05.