Thermodynamic study of Eu(III) complexation by pyridine monocarboxylates

The thermodynamic parameters (log K, ΔG, ΔH and ΔS) of complexation of Eu(III), a chemical analogue of trivalent actinides, with pyridine monocarboxylates, namely, picolinic acid (pyridine-2-carboxylic acid), nicotinic acid (pyridine-3-carboxylic acid), isonicotinic acid (pyridine-4-carboxylic acid) have been studied at 1.0 M ionic strength adjusted by NaClO₄ and 298 K by potentiometry, fluorescence spectroscopy and calorimetry. The potentiometric results revealed formation of four complexes, ML_i (i = 1–4) in case of picolinate whereas only ML complexes in case of nicotinate and isonicotinate. The log K_ML for Eu(III) picolinate complex is higher than that for complexes of Eu(III) with the other two acids. The complexation reaction between Eu(III) and picolinate was found to be exothermic due to chelate formation via pyridyl nitrogen. In case of complexation of Eu(III) with nicotinate and isonicotinate, the enthalpy changes are similar as in the case of simple mono carboxylates and are positive. Life time measurements by time resolved fluorescence spectroscopy, for the decay of ⁵D₀ state of Eu(III) also indicated the formation of ML₄ with picolinate and formation of ML only with the other two acids. The experimental observations on the stability and binding mode of the complexes are corroborated by theoretical calculations using the TURBOMOLE software. The detail analysis of calculated charge values of the free ligands and the complexes indicates that charge polarization is more in the isonicotinate than in nicotinate upon complexation.     

Determination of fluoroquinolone antibiotics through the fluorescent response of Eu(III) based nanoparticles fabricated by layer-by-layer technique

The present work introduces the determination of fluoroquinolone antibiotics (FQs) in aqueous solutions through the fluorescent response of Eu(TTA)₃ and [Eu(TTA)₃1] (TTA⁻ and 1 are thenoyltrifluoroacetonate and phosphine oxide derivative) complexes encapsulated into the polyelectrolyte capsules fabricated through layer-by-layer deposition of poly(sodium 4-styrenesulfonate) (PSS) and polyethyleneimine (PEI). The variation of luminescent core, polyelectrolyte deposition and concentration conditions reveals two modes of fluorescent response on FQs of diverse structure namely the sensitization and quenching of Eu(III) centered luminescence. The obtained regularities reveal the ternary complex formation and the ligand exchange occurring at the interface of polyelectrolyte coated [Eu(TTA)₃1] based colloids as the reasons of the diverse fluorescent response of Eu(III) centered luminescence on FQs. The factors affecting the fluorescent response have been revealed, which are: the content of luminescent core, the mode of polyelectrolyte deposition, concentration and structure of FQs. The discrimination of moxifloxacin and lomefloxacin from levofloxacin, ofloxacin, difloxacin, perfloxacin through the quenching of Eu(III) luminescence in PSS-[Eu(TTA)₃1] colloids has been revealed.     

Thermal investigation and infrared evolved gas analysis of light lanthanide(III) complexes with pyridine-3,5-dicarboxylic acid

The characterisation of light lanthanide(III) complexes with pyridine-3,5-dicarboxylic acid of the formula Ln₂pdc₃·nH₂O where Ln denotes lanthanides from La to Gd, pdc = C₇H₅NO₄²⁻; n = 6 for Ce(III), n = 7 for Pr(III) and Sm(III), n = 8 for La and n = 13 for Nd(III), Eu(III) and Gd(III) was performed by the thermal analysis TG-DTA and the simultaneous infrared evolved gas analysis TG-FTIR. Heating of the crystalline complexes resulted in the dehydration process at first. Next, dehydrated compounds decompose releasing of CO₂, CO, CH₄ and hydrocarbons. Free pyridine molecules were detected only in the gaseous products of lanthanum(III) complex decomposition.     

Synthesis and photovoltaic properties of new europium complex Eu（DBM）3（CPyBM）

A new europium（Ⅲ） complex, tris（dibertzoylmethanate）{ 1-[9-hexyl-9-carbazole]-2-（2-pyridyl）-bertzimidazole}europium（Ⅲ） [Eu（DBM）a（CPyBM）] was synthesized and used as an electron-acceptor and electron-transport layer in organic photovoltaic （PV） device. Power conversion efficiency achieved from the device was 1.04% under illumination with 365 nm UV light at 1.6 mW/cm^2. Compared with the previous reported devices based on Eu（Ⅲ） complexes, the PV performances were improved. The working mechanism of the organic PV device was discussed.     

Light-induced spin crossover in Fe(II)-based complexes: The full photocycle unraveled by ultrafast optical and X-ray spectroscopies

The light-induced spin and structure changes upon excitation of the singlet metal-to-ligand charge transfer (¹MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([Fe^II(bpy)₃]²⁺) by a combination of ultrafast optical and X-ray spectroscopies. Polychromatic femtosecond fluorescence up-conversion, transient absorption studies in the 290–600 nm region and femtosecond X-ray absorption spectroscopy allow us to retrieve the entire photocycle upon excitation of the ¹MLCT state from the singlet low-spin ground state (¹GS) as the following sequence: ^1,3MLCT → ⁵T → ¹GS, which does not involve intermediate singlet and triplet ligand-field states. The population time of the HS state is found to be ～150 fs, leaving it in a vibrationally hot state that relaxes in 2–3 ps, before decaying to the ground state in 650 ps. We also determine the structure of the high-spin quintet excited state by picosecond X-ray absorption spectroscopy at the K-edge of Fe. We argue that given the many common electronic (ordering of electronic states) and structural (Fe–N bond elongation in the high-spin state, Fe–N mode frequencies, etc.) similarities between all Fe(II)-polypyridine complexes, the results on the electronic relaxation processes reported in the case of [Fe^II(bpy)₃]²⁺ are of general validity to the entire family of Fe(II)-polypyridine complexes.     

Crystal Structure and Luminescence of [Eu(TTA)3·DAF]·0.5C7H8 Complex Excited by Visible Light

The non‐ionic europium(III) complex [Eu(TTA)₃·DAF]·0.5C₇H₈ (TTA = 2‐thenoytrifluoroacetonate, DAF = 4, 5‐diazafluoren‐9‐one) was synthesized. The structural determination has been carried out. DAF coordination induces the both excitation spectra in the solid state and solution having a red shift and sensitizes Eu³⁺ luminescence under visible light excitation.     

Photophysical properties of clozapine and determination of its concentration by using Eu(III)–dipicolinic acid complex as photo probe

Clozapine drug is photo-stable under irradiation of light for a long time, so we can store it in difficult and hot conditions. In addition the activity of clozapine is inhibited of the absorption spectra in the presence of glucose and enhanced in the presence of iron(III). We succeeded in detecting the concentration of clozapine in the range 1–60 × 10^?9 M using Eu(III)–dipicolinic acid complex as photo probe type and using Stern–Völmer equation to determine the Stern–Völmer constant, critical radius and the mechanism of quenching of luminescence of Eu(III)–dipicolinic acid complex is found to be of dipolar–dipolar interaction.     

Temporal evolution study of the plasma induced by CO2 pulsed laser on targets of titanium oxides

This paper reports studies on time-resolved laser induced breakdown spectroscopy (LIBS) of plasmas induced by IR nanosecond laser pulses on the titanium oxides TiO and TiO₂ (anatase). LIBS excitation was performed using a CO₂ laser. The laser-induced plasma was found strongly ionized yielding Ti⁺, O⁺, Ti^2 +, O^2 +, Ti^3 +, and Ti^4 + species and rich in neutral titanium and oxygen atoms. The temporal behavior of specific emission lines of Ti, Ti⁺, Ti^2 + and Ti^3 + was characterized. The results show a faster decay of Ti^3 + and Ti^2 + ionic species than that of Ti⁺ and neutral Ti atoms. Spectroscopic diagnostics were used to determine the time-resolved electron density and excitation temperatures. Laser irradiation of TiO₂-anatase induces on the surface sample the polymorphic transformation to TiO₂-rutile. The dependence on fluence and number of irradiation pulses of this transformation was studied by micro-Raman spectroscopy.     

Cyclometallated ruthenium(III) complexes: Synthesis,structure and properties

Reactions of Schiff bases (H₂apahR) derived from acetophenone and acid hydrazides, triethylamine and [Ru(PPh₃)₃Cl₂] (1:2:1 mole ratio) in methanol provide cyclometallated ruthenium(III) complexes of formula trans-[Ru(apahR)(PPh₃)₂Cl] in 74–81% yields. The complexes have been characterized by elemental analysis, magnetic susceptibility, spectroscopic (infrared, electronic and EPR) and electrochemical measurements. X-ray crystal structures of two representative complexes have been determined. In each complex, the metal centre is in distorted octahedral CNOClP₂ coordination sphere assembled by the C,N,O-donor meridionally spanning apahR^2?, the chloride and the two mutually trans-oriented PPh₃ molecules. All the complexes are one-electron paramagnetic (μ_eff. = 1.85–1.98 μ_B) and display rhombic EPR spectra in frozen (120 K) dichloromethane-toluene (1:1) solution. Electronic spectra of the complexes display several absorptions within 470–270 nm due to ligand-to-metal charge transfer and ligand centred transitions. The complexes are redox active and display a Ru(III) → Ru(II) reduction and a Ru(III) → Ru(IV) oxidation in the potential ranges ?0.66 to ?0.70 V and 0.75 to 0.80 V (vs. Ag/AgCl), respectively.     

An oxazoline derivatized Pybox ligand for Eu(III) and Tb(III) sensitization

A new Tb(III) dimer with an oxazoline-derivatized pyridine ligand, dimethyl-2,2′-(pyridine-2,6-diyl)bis(4,5-dihydrooxazole-4-carboxylate), has been isolated. This complex is highly luminescent and crystallizes in the triclinic P-1 space group with parameters a = 9.6167(2) Å, b = 11.6786(2) Å, c = 12.7548(3) Å, α = 70.026(1)°, β = 83.219(1)°, γ = 81.973(1)° and V = 1329.31(51)ų. Solution speciation studies showed the formation of monomeric species with 1:1 and 2:1 ligand-to-metal ion stoichiometries with log β₁₁ = 3.66 ± 0.41 and log β₂₁ = 6.16 ± 0.37 for Eu(III) and log β₁₁ = 3.56 ± 0.41 and log β₂₁ = 6.21 ± 0.38 for Tb(III). The quantum yields of emission Φ and luminescence lifetimes τ of solutions with 2:1 stoichiometry were 26.4 ± 0.5% and 1.47 ± 0.06 ms for Eu(III) and 41.0 ± 1.3% and 1.87 ± 0.06 ms for Tb(III).     

Luminescence Investigations on Eu(III) Thenoyltrifluoroacetonate Complexes with Amide Ligands

The influence of amide ligands on the photoluminescent behavior of tris(thenoyltrifluoroacetonate)- europium(III) in the solid state is reported. Elemental analysis showed that these compounds have the following formulas [Eu(TTA)₃·(ANL)₂] and [Eu(TTA)₃·PZA], where ANL = acetanilide and PZA = pyrazinamide. The photoluminescence spectra of the complexes recorded in the range 420-720 nm at 77 K show narrow bands arising from the ⁵D₀ → ⁷F _J transitions (where J = 0-4), under excitation at 394 nm. Based on the emission spectra and luminescence decay curves the intensity parameters (Ω_λ), lifetime (τ) and emission quantum efficiency (η) were determined. The Ω₂ values indicate that the Eu³⁺ion in these complexes is in a highly polarizable chemical environment. The higher value of η (60%) obtained for the complex with the ANL ligand, in comparison with the complex with the PZA ligand (30%), indicates a more efficient deactivation of the Eu³⁺ion in the [Eu(TTA)₃·PZA] complex.     

Luminescence of Eu(DBM)3Phen-doped in azobenzene-containing copolymers—Effects of absorption overlapping of two components

Poly(N-isopropylacrylamide)-b-poly{6-[4-(4-methylphenyl-azo)phenoxy]hexylmethacrylate} (PNIPAM₃₂-b-PAzoMM₈) and poly(N-isopropylacrylamide)-b-poly{6-[methyl(4-nitrophenyldiazenyl)phenyl]aminohexylmethacrylate} (PNIPAM₃₂-b-PAzoNO₁₀) were prepared by reversible addition–fragmentation chain transfer (RAFT) radical polymerization. The optical properties of Eu(DBM)₃Phen (Eu, Europium; DBM, dibenzoylmethide; Phen, 1,10-phenanthroline)-doped azobenzene-containing copolymer vesicle solutions were studied by UV–vis and fluorescence spectroscopy. When the electronic transition bands of azobenzene and Eu(DBM)₃Phen overlapped at about 350 nm in PNIPAM₃₂-b-PAzoMM₈, the fluorescent emission intensity at 612 nm of Eu(DBM)₃Phen could be modulated by irradiation with UV and visible light. However, when the absorption of the azobenzene-moiety red-shifted to 477 nm in PNIPAM₃₂-b-PAzoNO₁₀, the luminescence intensity of Eu(DBM)₃Phen was not affected any longer. The difference between these two systems was possibly caused by the energy allocation in the luminescence process, which was discussed in detail.     

Direct electrochemistry of hemoglobin at vertically-aligned self-doping TiO2 nanotubes: A mediator-free and biomolecule-substantive electrochemical interface

The present work is dedicated to making the best of vertically-aligned TiO₂ nanotubes (TNTs) array to serve as a prospectively ideal “vessel” for protein immobilization and biosensor applications. The TNTs fabricated by electrochemical anodizing possess the advantageous of perpendicular alignment and tailored tubular architecture, as well as the good biocompatibility and hydrophilicity. But the electron-transfer resistance of the as-grown (AG-) TNTs is too large for the direct electron transfer and electrochemical biosensing. A simple strategy on controllable electrochemical reduction treatment of TNTs is adopted on it, leading TNTs in situ self-doped with Ti(III), which makes the Ti(III)–TNTs much better conductivity while the tubular and crystal structure of TNTs array still well maintained. Results show that the TNTs can be used as a super vessel for rapid and substantive immobilization of hemoglobin (Hb), with a large surface electroactive Hb coverage (Γ*) of 1.5 × 10^?9 mol cm^?2. The enhanced direct electron transfer of Hb is commendably observed on the Ti(III)–TNTs/Hb biosensor with a couple of well-defined redox peaks compared with the AG-TNTs/Hb. The biosensor further exhibits fast response, high sensitivity and stability for the amperometric biosensing of H₂O₂ with the detection limit of 1.5 × 10^?6 M, and the apparent Michaelis–Menten constant of 1.02 mM.     

Synthesis and characterization of titanium tetraisocyanide complexes, [CpTi(CNXyl)4E], E = I,SnPh3, and SnMe3

Oxidation of [CpTi(CO)₄]^? by I₂, Ph₃SnCl, and Me₃SnCl in the presence of four equivalents of CNXyl, Xyl = 2,6-dimethylphenyl, affords unprecedented titanium tetraisocyanide complexes, [CpTi(CNXyl)₄E], E = I, SnPh₃, SnMe₃. These have been isolated and characterized by spectroscopic methods as well as single-crystal X-ray crystallography. A by-product of the iodine reaction was the Ti(III) complex, [CpTi(CNXyl)₂I₂], which was also characterized by X-ray crystallography.     

Ti in dilute slurries of TiO2 nanoparticles by in-torch vaporization sector field inductively coupled plasma-mass spectrometry☆

A Re coil-filament in-torch vaporization (ITV) sample introduction system was interfaced to a sector field inductively coupled plasma-mass spectrometry (SFICP-MS) system. In this first report on an un-optimized ITV-SF-ICP-MS system, detection limits were established using 5 μL volumes of 100 pg mL^− 1 standard solutions, translating to 0.5 pg absolute. Such absolute amounts of a dried solution are near or below the detection limit of many ICP-based techniques. The absolute detection limits for Cd, Eu, Pb, Ti, U and Zn were in the 0.2–2 fg range (or, in the 10's of millions to millions of atoms for Pb, Cd, Zn and Ti, about one million atoms for U and about 800 thousand for Eu). These absolute detection limits along with the ability of ITV to handle minute amounts of discrete samples (thus eliminating memory effects from nanoparticles adhering to the walls of pneumatic nebulization sample introduction systems and from clogging of the mass spectrometer orifice), use of sonicated water-based slurries (that eliminated contamination from acid digestion reagents or from slurry stabilization reagents), and elimination of oxygen containing molecular ion interferences due to use of dry samples enabled concentration determinations of Ti (and consequently of TiO₂) in pg mL^− 1 concentrations of slurries of manufactured, 20 nm diameter TiO₂ nanoparticles.     

Demonstration of cavity enhanced FTIR spectroscopy using a femtosecond laser absorption source

A proof of principle experiment was performed by recording the cavity enhanced absorption spectrum of the weak b–X transition of molecular oxygen in the atmosphere using a Ti:Sa femtosecond laser as an absorption source and a high resolution continuous scan Fourier transform interferometer. The cavity was mode matched and either continuously scanned or stabilized at the so-called magic point. An optimal rms noise equivalent absorption of 3 × 10^?7 cm^?1 Hz^?1/2 was reached in the latter case, corresponding to α_min = 3 × 10^?7 cm^?1.     

Sparkle model for AM1 calculation of neodymium(III) coordination compounds

The Sparkle/AM1 model, the only available semiempirical quantum chemical model for the calculation of complexes of lanthanide ions, recently defined for Eu(III), Gd(III) and Tb(III), is now extended to Nd(III). Accordingly, all 57 Nd(III) complexes of high crystallographic quality (R-factor < 0.05 Å), possessing oxygen or nitrogen as directly coordinating atoms, present in the Cambridge Structural Database 2003, were considered. A subset of 15 structures was chosen by cluster analysis to constitute the parameterization training set. All 57 complexes were considered back in the validation part, and the Sparkle/AM1 unsigned mean error, for all interatomic distances between the Nd(III) ion and the ligand atoms of the first sphere of coordination, was found to be 0.07 Å, a level of accuracy useful for luminescent complex design and comparable to present day rare earth complex ab initio/ECP calculations, while being hundreds of times faster.     

Mononuclear ruthenium(III) complexes containing chelating thiosemicarbazones: Synthesis,characterization and catalytic property

Mononuclear ruthenium(III) complexes of the type [RuX(EPh₃)₂(L)] (E = P or As; X = Cl or Br; L = dibasic terdentate dehydroacetic acid thiosemicarbazones) have been synthesized from the reaction of thiosemicarbazone ligands with ruthenium(III) precursors, [RuX₃(EPh₃)₃] (where E = P, X = Cl; E = As, X = Cl or Br) and [RuBr₃(PPh₃)₂(CH₃OH)] in benzene. The compositions of the complexes have been established by elemental analysis, magnetic susceptibility measurement, FT-IR, UV–vis and EPR spectral data. These complexes are paramagnetic and show intense d–d and charge transfer transitions in dichloromethane. The complexes show rhombic EPR spectra at LNT which are typical of low-spin distorted octahedral ruthenium(III) species. All the complexes are redox active and display an irreversible metal centered redox processes. Complex [RuCl(PPh₃)₂(DHA–PTSC)] (5) was used as catalyst for transfer hydrogenation of ketones in the presence of isopropanol/KOH and was found to be the active species.     

Photoredox reactions of Cr(III) mixed-ligand complexes

Irradiation of chromium(III) complexes with oxalate and pyridinedicarboxylate ligands (pda = 2,3-, 2,4-, or 2,5-dicarboxylate) leads to diverse behaviors, dictated by light energy, presence of oxygen and the ligand nature. Irradiation within the MC bands is unaffected by O₂ and results in ligand substitution. The LMCT excitation is effective only when oxalate is coordinated to Cr(III); then electron transfer from oxalate to central ion generates an intermediate, consisted of a Cr(II)species and the C₂O₄^? radicals. The species undergo fast redox reactions dependent on the presence of O₂ and the pda ligand.(1) In anoxic medium the fast outersphere electron transfer from Cr(II) to solvent, generates hydrated electrons and re-oxidizes the chromium centre to Cr^III. Then geminate recombination regenerates substrate, whereas competitive release of the C₂O₄^? radical leads to substitution of one oxalate ligand by two water molecules (aquation induced by the LMCT excitation). In the presence of the pda ligand the outersphere electron transfer is accompanied by the innersphere CT, generating Cr(III) coordinated to two radical ligands: C₂O₄^? and pda^3?; the intermediate releases also e_aq^?, but this reaction is slower than that of the homoleptic oxalate complex. Hydrated electrons are scavenged also by the released radicals. All these processes are completed within microseconds and in consequence, the Cr(III) complexes irradiated in deoxygenated solutions are insensitive to subsequent oxygenation.(2) When UV-irradiation is carried out in oxygenated medium reaction of Cr(II) species with molecular oxygen competes with the outer- or inner electron transfer observed in anoxic medium. Both these pathways result in generation of chromate(VI). Quantum yield of the Cr(VI) production is sensitive to the presence and structure of pda ligand, decreasing within the series 2,3-pda > 2,4-pda > 2,5-pda.     

Improved luminescent behavior of YVO4:Eu3+ ceramic phosphors by Li contents

Crystalline phase and surface morphology of phosphors are important factors to determine luminescent characteristics. Li-doped YVO₄:Eu³⁺ ceramic samples were prepared by a solid state reaction method. The Li⁺ concentration was varied from 1 to 3 wt% to improve crystallinity and surface morphology of ceramics. Influence of Li doping on luminescent properties of YVO₄:Eu³⁺ ceramics has been investigated. Photoluminescence spectra have been measured at room temperature using a luminescence spectrometer and excitation by a broadband incoherent ultraviolet light source with an excitation wavelength of 325 nm. The emitted radiation was dominated by a red emission peak at 620 nm radiated from the ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. As Li⁺ ion content increases from 0 to 2 wt%, the photoluminescence (PL) brightness improved. The brightness of 2 wt% Li-doped YVO₄:Eu³⁺ ceramic was increased by a factor of 1.43 in comparison with that of YVO₄:Eu³⁺ ceramic. The enhanced luminescence resulted not only from the improved crystallinity but also from the enhanced surface roughness. The luminescent intensity and surface roughness exhibited similar behavior as a function of Li⁺ ion concentration.