Probing the binding of Tb(III) and Eu(III) to the hammerhead ribozyme using luminescence spectroscopy

BACKGROUND: Divalent metal ions serve as structural as well as catalytic cofactors in the hammerhead ribozyme reaction. The natural cofactor in these reactions is Mg(II), but its spectroscopic silence makes it difficult to study. We previously showed that a single Tb(III) ion inhibits the hammerhead ribozyme by site-specific competition for a Mg(II) ion and therefore can be used as a spectroscopic probe for the Mg(II) it replaces. RESULTS: Lanthanide luminescence spectroscopy was used to study the coordination environment around Tb(III) and Eu(III) ions bound to the structurally well-characterized site on the hammerhead ribozyme. Sensitized emission and direct excitation experiments show that a single lanthanide ion binds to the ribozyme under these conditions and that three waters of hydration are displaced from the Tb(III) upon binding the RNA. Furthermore, we show that these techniques allow the comparison of binding affinities for a series of ions to this site. The binding affinities for ions at the G5 site correlates linearly with the function Z(2)/r of the aqua ion (where Z is the charge and r is the radius of the ion). CONCLUSIONS: This study compares the crystallographic nature of the G5 metal-binding site with solution measurements and gives a clearer picture of the coordination environment of this ion. These results provide one of the best characterized metal-binding sites from a ribozyme, so we use this information to compare the RNA site with that of typical metalloproteins.     

Probing metal binding in the 8-17 DNAzyme by TbIII luminescence spectroscopy

Metal-dependent cleavage activities of the 8-17 DNAzyme were found to be inhibited by Tb(III) ions, and the apparent inhibition constant in the presence of 100 microM of Zn(II) was measured to be 3.3+/-0.3 microM. The apparent inhibition constants increased linearly with increasing Zn(II) concentration, and the inhibition effect could be fully rescued with addition of active metal ions, indicating that Tb(III) is a competitive inhibitor and that the effect is completely reversible. The sensitized Tb(III) luminescence at 543 nm was dramatically enhanced when Tb(III) was added to the DNAzyme-substrate complex. With an inactive DNAzyme in which the GT wobble pair was replaced with a GC Watson-Crick base pair, the luminescence enhancement was slightly decreased. In addition, when the DNAzyme strand was replaced with a complete complementary strand to the substrate, no significant luminescence enhancement was observed. These observations suggest that Tb(III) may bind to an unpaired region of the DNAzyme, with the GT wobble pair playing a role. Luminescence lifetime measurements in D(2)O and H(2)O suggested that Tb(III) bound to DNAzyme is coordinated by 6.7+/-0.2 water molecules and two or three functional groups from the DNAzyme. Divalent metal ions competed for the Tb(III) binding site(s) in the order Co(II)>Zn(II)>Mn(II)>Pb(II)>Ca(II) approximately Mg(II). This order closely follows the order of DNAzyme activity, with the exception of Pb(II). These results indicate that Pb(II), the most active metal ion, competes for Tb(III) binding differently from other metal ions such as Zn(II), suggesting that Pb(II) may bind to a different site from that for the other metal ions including Zn(II) and Tb(III).     

Spectrophotometric determination of the stability constant of the Eu(III)-murexide complex

The values of the stability constants of the Ca(II) and lanthanide(III) complexes of murexide reported in the literature were determined without proper correction for binding of buffer ions to the metal ion. The constants are best determined without a buffer present. Accurate values of conditional stability constants for the Eu(III)—murexide complex (relative standard deviation better than 3%), of the differential molar absorptivity of the Eu(III)—murexide complex with respect to murexide at 480 nm (relative standard deviation better than 0.5%) and of the molar absorptivity of murexide at 520 and at 506 nm (precision better than 0.4%) at pH 5.0 and 6.5 at 15, 25 and 35° are reported. The accuracy and precision of the concentration of metal ion solution determined by using these conditional stability constants are discussed.     

Functionalized gold nanoparticles as phosphorescent nanomaterials and sensors

Ligand-capped gold nanoparticles were synthesized by capping monothiol derivatives of 2,2'-dipyridyl onto the surface of Au nanoparticles (Au-BT). The average size of the metal core is around 4 nm, with a shell of approximately 340 bipyridine ligands around the Au nanoparticle. The high local concentration of the chelating ligands ( approximately 5 M) around the Au nanoparticle makes these particles excellent ion sponges, and their complexation with Eu(III)/Tb(III) ions yields phosphorescent nanomaterials. Absorption spectral studies confirm a 1:3 complexation between Eu(III)/Tb(III) ions and bipyridines, functionalized on the surface of Au nanoparticles. The red-emitting Au-BT:Eu(III) complex exhibits a long lifetime of 0.36 ms with six line-like emission peaks, whereas the green-emitting Au-BT:Tb(III) complex exhibits a lifetime of 0.7 ms with four line-like emission peaks. These phosphorescent nanomaterials, designed by linking BT:Eu(III) complexes to Au nanoparticles, were further utilized as sensors for metal cations. A dramatic decrease in the luminescence was observed upon addition of alkaline earth metal ions (Ca(2+), Mg(2+)) and transition metal ions (Cu(2+), Zn(2+), Ni(2+)), resulting from an isomorphous substitution of Eu(III) ions, whereas the luminescence intensity was not influenced by the addition of Na(+) and K(+) ions. Direct interaction of bipyridine-capped Au nanoparticles with Cu(2+) ions brings the nanohybrid systems closer, leading to the formation of three-dimensional superstructures. Strong interparticle plasmon interactions were observed in these closely spaced Au nanoparticles.     

Heterodinuclear cryptates [EuML(dmf)](ClO(4))(2)(M=Ca,Cd, Ni,Zn): tuning the luminescence of europium(III) through the selection of the second metal ion

Four heterodinuclear cryptates [EuML(dmf)](ClO(4))(2) (M=Ca, Cd, Ni, Zn) were synthesized by a two-step method (L denotes deprotonated anionic cryptand synthesized by condensation of tris(2-aminoethyl)amine with 2,6-diformyl-4-chlorophenol). The ES-MS spectra of the four cryptates and the crystal structure of [EuNiL(dmf)](ClO(4))(2) x MeCN confirm that a strict dinuclear Eu(III)-M(II) entity exits in the cryptates. The cyclic voltammetry and luminescence spectral investigations indicate that the introduction of second metal ions into the mononuclear Eu(III) cryptate result in a negative shift of the redox potential of Eu(III) and a change in luminescence intensity of Eu(III). The cryptate [EuML(dmf)](ClO(4))(2) was shown to quench the emission of Eu(III) when M=Ni and to enhance the emission of Eu(III) when M=Ca, Cd, and Zn in the sequence: mononuclear相似文献   

Structural elucidation of the binding and inhibitory properties of lanthanide (III) ions at the 3'-5' exonucleolytic active site of the Klenow fragment

BACKGROUND: Biochemical and biophysical experiments have shown that two catalytically essential divalent metal ions (termed 'A' and 'B') bind to the 3'-5' exonuclease active site of the Klenow fragment (KF) of Escherichia coli DNA polymerase I. X-ray crystallographic studies have established the normal positions in the KF 3'-5' exonuclease (KF exo) active site of the two cations and the single-stranded DNA substrate. Lanthanide (III) luminescence studies have demonstrated, however, that only a single europium (III) ion (Eu3+) binds to the KF exo active site. Furthermore, Eu3+ does not support catalysis by KF exo or several other two-metal-ion phosphoryl-transfer enzymes. RESULTS: A crystal structure of KF complexed with both Eu3+ and substrate single-stranded oligodeoxynucleotide shows that a lone Eu3+ is bound near to metal-ion site A. Comparison of this structure to a relevant native structure reveals that the bound Eu3+ causes a number of changes to the KF exo active site. The scissile phosphate of the substrate is displaced from its normal position by about 1 A when Eu3+ is bound and the presence of Eu3+ in the active site precludes the binding of the essential metal ion B. CONCLUSIONS: The substantial, lanthanide-induced differences in metal-ion and substrate binding to KF exo account for the inhibition of this enzyme by Eu3+. These changes also explain the inability of KF exo to bind more than one cation in the presence of lanthanides. The mechanistic similarity between KF exo and other two-metal-ion phosphoryl-transfer enzymes suggests that the principles of lanthanide (III) ion binding and inhibition ascertained from this study will probably apply to most members of this class of enzymes.     

Calix[4]azacrowns as novel molecular scaffolds for the generation of visible and near-infrared lanthanide luminescence

Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximately 5-6 and log beta(12) approximately 10. The structural changes of the ligands upon La(III) complexation were probed by 1H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely, fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III) luminescence was weak (Phi(lum) 相似文献   

Lanthanide(III) Complexes of Cyclen Triacetates and Triamides Bearing Tertiary Amide-Linked Antennae

The coordination compounds of the trivalent lanthanide ions (Ln(III)) have unique photophysical properties. Ln(III) excitation is usually performed through a light-harvesting antenna. To enable Ln(III)-based emitters to reach their full potential, an understanding of how complex structure affects sensitization and quenching processes is necessary. Here, the role of the linker between the antenna and the metal binding fragment was studied. Four macrocyclic ligands carrying coumarin 2 or 4-methoxymethylcarbostyril sensitizing antennae linked to an octadentate macrocyclic ligand binding site were synthesized. Complexation with Ln(III) (Ln = La, Sm, Eu, Gd, Tb, Yb and Lu) yielded species with overall −1, 0, or +2 and +3-charge. Paramagnetic ¹H NMR spectroscopy indicated subtle differences between the coumarin- and carbostyril-carrying Eu(III) and Yb(III) complexes. Cyclic voltammetry showed that the effect of the linker on the Eu(III)/Eu(II) apparent reduction potential was dependent on the electronic properties of the N-substituent. The Eu(III), Tb(III) and Sm(III) complexes were all luminescent. Coumarin-sensitized complexes were poorly emissive; photoinduced electron transfer was not a major quenching pathway in these species. These results show that seemingly similar emitters can undergo very different photophysical processes, and highlight the crucial role the linker can play.     

A comparison of sensitized Ln(III) emission using pyridine- and pyrazine-2,6-dicarboxylates

The synthesis, X-ray structure, solution stability, and photophysical properties of Eu(III) complexes with pyrazine-2,6-dicarboxylic acid (H(2)PYZ) are reported, and compared to structurally analogous complexes with pyridine-2,6-dicarboxylic acid (H(2)DPA). The [Eu(PYZ)(3)](3-) complex demonstrates highly efficient metal-centered Eu(III) luminescence in the solid state (Φ(total) ～ 60.9%). In aqueous solution, moderate stability is retained at pH 7.4 (pEu ～ 10.5), although hydrolysis of the complex anion becomes competitive below mM concentrations, and the observed luminescence intensity from the Eu(III) metal ion is reduced as a result. A complete evaluation of the thermodynamic solution stability has allowed the observed differences in the solution behaviour luminescence properties of these complexes to be rationalized. An analysis of their luminescence behaviour in the solid state has also allowed a direct comparison of the sensitisation behaviour for these isostructural compounds.     

Structures and luminescent properties of two heterotrimetallic Ln(III)–Sr(II)–K(I) complexes

Eu(III)–Sr(II)–K(I) and Tb(III)–Sr(II)–K(I) heterotrimetallic metal-organic frameworks with 2,4,6-pyridinetricarboxylic acid have been synthesized under hydrothermal conditions. The complexes are isomorphic and both in triclinic space group P-1. The ligands bond with three metal ions with two coordination modes. One connects seven metal ions and the other connects eight metal ions. IR spectra, thermal analysis, and photoluminescent properties have been studied. The results display strong characteristic emissions of Eu(III) or Tb(III) ions with excitation of ultraviolet radiation.     

Chiroptical spectra of a series of tetrakis((+)-3-heptafluorobutylyrylcamphorato)lanthanide(III) with an encapsulated alkali metal ion: circularly polarized luminescence and absolute chiral structures for the Eu(III) and Sm(III) complexes

The luminescence and circularly polarized luminescence (CPL) spectra of M(I)[Eu((+)-hfbc)(4)] show a similar behavior to the exciton CD in the intraligand π-π* transitions when the alkali metal ions and solvents are manipulated. There is a difference in susceptibility in solvation toward the alkali metal ions but not toward the Eu(III) ion, as in the case of axially symmetric DOTA-type compounds. The remarkable CPL in the 4f-4f transitions provide much more information on the stereospecific formation of chiral Eu(III) complexes, since CPL spectroscopy is limited to luminescent species and reflects selectively toward helicity of the local structural environment around the lanthanide(III). While in comparison, exciton CD reveals the chiral structural information from the helical arrangement of the four bladed chelates. Of special importance, the observation of the highest CPL activities measured to date for lanthanide(III)-containing compounds (i.e., Eu and Sm) in solution supports the theory that the chirality of lanthanide(III) in the excited state corresponds to that in the ground state, which was derived from the exciton CD.     

Columinescence effect in macromolecular complexes of Eu(III) and Tb(III)

The effect of Y(III) and Gd(III) coactivator ions on the intensity of Eu(III) and Tb(III) luminescence in monomer and polymer mixed-metal complexes was studied. Isomorphic replacement of Eu(III) and Tb(III) ions by Y(III) and Gd(III) ions in macromolecular complexes led to sensitization of Eu(III) and Tb(III) ion luminescence. A mechanism of columinescence was suggested. It involves a charge transfer and the ligand orbitals and the vacant orbitals of Eu(III) and Tb(III) ions and coactivators.     

Immobilized tris(hydroxymethyl)aminomethane as a scaffold for ion-selective ligands: the auxiliary group effect on metal ion binding at the phosphate ligand

The metal ion affinities of a ligand in a polymer-supported reagent can be enhanced by the presence of a proximate group capable of hydrogen bonding. A new polymer-supported reagent has been synthesized by immobilizing tris(hydroxymethyl)aminomethane (Tris) onto cross-linked poly(vinylbenzyl chloride) and then phosphorylating the -OH moieties. The -NH- acts as the auxiliary group to increase the extent of complexation by the phosphate ligand. Additionally, Tris acts as a scaffold, wherein the phosphate ligands are in a known stereochemical arrangement. The Tris resin is mono-, di-, and triphosphorylated, depending on the concentration of the phosphorylating agent. The highest metal ion affinities are found with the resin having a phosphorus-to-nitrogen ratio of 2.36, consistent with one-third of the ligands being triphosphorylated and the remainder being diphosphorylated. The unphosphorylated Tris and phosphonate diester resins have no ionic affinities under the same conditions. Trivalent ions (Fe(III), Al(III), La(III), Eu(III), Lu(III)) are preferred over divalent ions (Pb(II), Cd(II), Cu(II), Zn(II)) from solutions at pH 2. The distribution coefficients of the divalent ions correlate with the Misono softness parameters, indicating that the polarizability of the phosphoryl oxygen is important to binding of the metal ions. The mechanism of complexation is probed with Fe(III) in 0.01-5 M HNO3 and HCl. The high affinities are ascribed to activation of the P=O ligand toward metal ion binding by the N-H moieties acting as auxiliary groups, coupled with intraligand cooperation among the phosphate moieties at a given site. FTIR spectra show that the P=O band at 1261 cm-1 shifts as a function of the extent of hydrogen bonding. Binding at the P=O requires a balance between activation by hydrogen bonding and availability of the lone pair electrons to the metal ions.     

Europium(III)-chelates embedded in nanoparticles are protected from interfering compounds present in assay media

Lanthanide chelates are excellent labels in ligand binding assays due to their long lifetime fluorescence, which enables efficient background reduction using time-resolved measurement. In separation-free homogeneous assays, however, some compounds in the sample may cause quenching of the lanthanide fluorescence and extra steps are required before these samples can be measured. In this study we have evaluated whether europium chelates packed inside a polystyrene nanoparticle are better protected from the environment than individual Eu(III)-chelates, and do these particles have higher tolerance against known interfering compounds (bivalent metal ions and variation of pH). We also tested whether metal ions had any effect on a fluorescence resonance energy transfer (FRET) based detection of a bioaffinity binding reaction. The presence of metal ions or variation of pH did not affect the fluorescence of the Eu(III)-chelate dyed nanoparticles, while significant decrease of the fluorescence was detected with a 9-dentate Eu(III)-chelate. Metal ions also decreased the fluorescence lifetime of the 9-dentate Eu(III)-chelate from 0.960 to 0.050 ms. Coloured metal ions caused a minor decrease in sensitised emission generated by FRET when Eu(III)-chelate dyed nanoparticles were used as donor labels. The decreased signal was due to the absorption of the sensitised emission by the coloured metal ions, since the metal ions had no effect on the lifetime of the sensitised emission. Thus the Eu(III)-chelate dyed nanoparticles are preferred labels in homogeneous bioaffinity assays, when interfering compounds are known to be present.     

High luminescence quantum yields and long luminescence lifetime from Eu(III) complex containing two crystal water based on a new beta-diketonate ligand

New members of family of Eu(III) complex based on the thenoylacetophenone have been synthesized and characterized. The compounds were found for high metal luminescence quantum yields and long luminescence lifetime, especially for compound with two crystal water, corresponding with other compounds containing two crystal water. The result is attributed to high molar absorption coefficients of the Eu(III) complex according to UV-vis and emission spectra. The high molar absorption coefficients balance quenching effect from OH oscillators of water contained in compound.     

Catalytic activities of polymer‐supported metal complexes in oxidation of phenol and epoxidation of cyclohexene

The metal complexes of N, N′‐bis (o‐hydroxy acetophenone) propylene diamine (HPPn) Schiff base were supported on cross‐linked polystyrene beads. The complexation of iron(III), copper(II), and zinc(II) ions on polymer‐anchored HPPn Schiff base was 83.4, 85.7, and 84.5 wt%, respectively, whereas the complexation of these metal ions on unsupported HPPn Schiff base was 82.3, 84.5, and 83.9 wt%. The iron(III) complexes of HPPn Schiff base were octahedral in geometry, whereas copper(II) and zinc(II) ions complexes were square planar and tetrahedral. Complexation of metal ions increased the thermal stability of HPPn Schiff base. Catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in the presence of hydrogen peroxide. The polymer‐supported HPPn Schiff base complexes of iron(III) ions showed 73.0 wt% conversion of phenol and 90.6 wt% conversion of cyclohexene at a molar ratio of 1:1:1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 63.8 wt% conversion for phenol and 83.2 wt% conversion for cyclohexene. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 93.1 and 98.3 wt%, respectively with supported HPPn Schiff base complexes of iron(III) ions but was lower with HPPn Schiff base complexes of copper(II) and zinc(II) ions. Activation energy for the epoxidation of cyclohexene and phenol conversion with unsupported HPPn Schiff base complexes of iron(III) ions was 16.6 kJ mol^?1 and 21.2 kJ mol^?1, respectively, but was lower with supported complexes of iron(III) ions. Copyright © 2007 John Wiley & Sons, Ltd.     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Polymer supported catalysts for oxidation of phenol and cyclohexene using hydrogen peroxide as oxidant

Polymer supported transition metal complexes of N,N′-bis (o-hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by anchoring its amino derivative Schiff base (AHPHZ) on cross-linked (6 wt%) polymer beads and then loading iron(III), copper(II) and zinc(II) ions in methanol. The loading of HPHZ Schiff base on polymer beads was 3.436 mmol g⁻¹ and efficiency of complexation of polymer anchored HPHZ Schiff base for iron(III), copper(II) and zinc(II) ions was 83.21, 83.40 and 83.17%, respectively. The efficiency of complexation of unsupported HPHZ Schiff base for these metal ions was lower than polymer supported HPHZ Schiff base. The structural information obtained by spectral, magnetic and elemental analysis has suggested octahedral and square planar geometry for iron(III) and copper(II) ions complexes, respectively, with paramagnetic behavior, but zinc(II) ions complexes were tetrahedral in shape with diamagnetic behavior. The complexation with metal ions has increased thermal stability of polymer anchored HPHZ Schiff base. The catalytic activity of unsupported and polymer supported HPHZ Schiff base complexes of metal ions was evaluated by studying the oxidation of phenol (Ph) and epoxidation of cyclohexene (CH). The polymer supported metal complexes showed better catalytic activity than unsupported metal complexes. The catalytic activity of metal complexes was optimum at a molar ratio of 1:1:1 of substrate to oxidant and catalyst. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) in oxidation of phenol and epoxidation of cyclohexene was better with polymer supported metal complexes in comparison to unsupported metal complexes. The energy of activation for oxidation of phenol (22.8 kJ mol⁻¹) and epoxidation of cyclohexene (8.9 kJ mol⁻¹) was lowest with polymer supported complexes of iron(III) ions than polymer supported Schiff base complexes of copper(II) and zinc(II) ions.     

Polyols as scaffolds in the development of ion-selective polymer-supported reagents: the effect of auxiliary groups on the mechanism of metal ion complexation

In developing ion-selective polymer-supported reagents, the inherent affinity of a given ligand for a targeted metal ion is found to be affected by auxiliary groups on a scaffold. A series of polyols (ethylene glycol, glycerol, tris(hydroxymethyl)ethane, pentaerythritol, and pentaerythritol triethoxylate) are immobilized onto cross-linked poly(vinylbenzyl chloride), then monophosphorylated. The pentaerythritol, glycerol, and pentaerythritol triethoxylate polymers have the highest affinities for both trivalent and divalent ions. The distribution coefficients of divalent ions (Pb(II), Cd(II), Cu(II), Ni(II), and Zn(II)) correlate with the Misono softness parameter, reflecting a single-site interaction between the metal ion and the phosphoryl oxygen. The distribution coefficients for trivalent ions are in the order Fe(III) < Al(III) < Y(III) less, approximately < La(III) approximately Eu(III) approximately Lu(III). For example, the phosphorylated pentaerythritol polymer has distribution coefficients (also reported as percent complexed) for Fe of 68.4 (75.3%); for Al of 182 (88.5%); and for the rare earth ions Y, Lu, Eu, and La of 374 (94.4%), 1390 (98.4%), 1690 (98.4%), and 708 (96.9%), respectively, from solutions at pH 2.0. The opposite trend (i.e., Fe(III) > Al(III) > (rare earths)) correlates with their hardness, acidity, electron affinity, electronegativity, and formation constants with soluble complexants, including tributyl phosphate. A binding mechanism is proposed wherein the polymer initially has the auxiliary -OH groups hydrogen-bonded to the phosphate ligand; then, binding to the polarizable phosphoryl oxygen with the divalent ions dominates, while the trivalent ions are drawn closer to the phosphoryl oxygen because of their greater charge and, once closer, bind in a multisite interaction with both the phosphate and -OH groups.     

Simultaneous spectrophotometric determination of atrazine and cyanazine by chemometric methods

Three novel ligands containing pyridine-2,6-dicarboxylic acid unit, trans-4 -(4'-methoxystyryl) pyridine-2,6-dicarboxylic acid, trans-4-(4'-(dimethylamino)styryl)pyridine-2,6-dicarboxylic acid, and trans-4-(4'-(diphenylamino)styryl)pyridine-2,6-dicarboxylic acid were synthesized and their complexes with Eu(III), Tb(III) ions were successfully prepared. The ligands and the corresponding metal complexes were characterized by means of MS, elemental analysis, IR, (1)H NMR and TG-DTA. The luminescence spectra of Eu(III) and Tb(III) complexes in solid state were studied. The strong luminescence emitting peaks at 615 nm for Eu(III) and 545 nm for Tb(III) can be observed. The applications in cell imaging of the europium and terbium complexes were investigated.