Room temperature phosphorescence lifetime and quantum yield of erythrosine B and rose bengal in aerobic alkaline aqueous solution

The room-temperature phosphorescence behavior of erythrosine B (ER) and rose bengal (RB) in aerobic aqueous solution at pH 10 (10^?4 M NaOH) is investigated. The samples were excited with sliced second harmonic pulses of a Q-switched Nd:glass laser. A gated photomultiplier tube was used for instantaneous fluorescence signal discrimination and a digital oscilloscope was used for signal recording. For phosphorescence lifetime measurement the oscilloscope response time was adjusted to appropriate time resolution and sensitivity by the ohmic input resistance. In the case of phosphorescence quantum yield determination the gated photomultiplier – oscilloscope arrangement was operated in integration mode using 10 MΩ input resistance. Phosphorescence quantum yield calibration was achieved with erythrosine B and rose bengal doped starch films of known quantum yields. The determined phosphorescence lifetimes (quantum yields) of ER and RB in 0.1 mM NaOH are τ_P=1.92±0.1 μs (?_P=(1.5±0.3)×10^?5) and 2.40±0.1 μs ((5.7±0.9)×10^?5), respectively. The results are discussed in terms of triplet state deactivation by dissolved molecular oxygen.     

Analysis of Tb3+- and melittin-binding with the C-terminal domain of centrin in Euplotes octocarinatus

Centrin is a low molecular mass (20 KDa) protein that belongs to the EF-hand superfamily. In this work, the interaction between the Tb³⁺-saturated C-terminal domain of Euplotes octocarinatus centrin (Tb₂-C-EoCen) and 2-p-toluidinylnaphthalene-6-sulfonate (TNS) was investigated using difference UV–vis spectra and the fluorescence spectra methods. In 100 mM N-2-hydroxy-ethylpiperazine-N-2-ethanesulfonic acid (Hepes) at pH 7.4, with the addition of Tb₂-C-EoCen, four new peaks were observed at 265 nm, 278 nm, 317 nm and 360 nm by absorptivity compared with blank solution of TNS. At the same time, the reaction could be measured by fluorescence spectra. The fluorescence emission of TNS was shifted from 480 nm to 445 nm in the presence of Tb₂-C-EoCen. Meanwhile, its fluorescence intensity was increased markedly. The 1:1 stoichiometric ratio of C-EoCen to TNS was confirmed by fluorescence titration curves. The conditional binding constants of TNS with C-EoCen and Tb₂-C-EoCen were calculated to be log K_{(C-EoCen-TNS)}=5.32±0.04  M^?1 and log K_{(Tb2-C-EoCen-TNS)}=5.58±0.12 M^?1, respectively. In addition, the protein of Tb₂-C-EoCen binding with melittin was also studied. Based on the fluorescence titration curves, the 1:1 stoichiometric ratio of Tb₂-C-EoCen to melittin was confirmed. And the conditional binding constant of C-EoCen with melittin was calculated to be log Ka′=6.79±0.17 M^?1.     

Sonochemical reactions with mesoporous alumina

Herein, we report the sonochemical reactions with MSU-X mesoporous alumina (m-Al₂O₃) in aqueous solutions. Sonication (f = 20 kHz, I = 30 W cm^?2, W_aq = 0.67 W mL^?1, T = 36–38 °C, Ar) causes significant acceleration of m-Al₂O₃ dissolution in the pH range of 4–11. Moreover, power ultrasound has a dramatic effect on the textural properties and phase composition of m-Al₂O₃. Short-time sonication at pH = 4 leads to the formation of nanorods and nanofibers of boehmite, AlO(OH). Prolonged ultrasonic treatment causes high aspect morphology transformation to aggregated nanosheets in weakly acid solutions or plated nanocrystals in alkaline solutions. Sonochemical products in alkaline medium are composed principally from boehmite and small amounts of bayerite, Al(OH)₃. Silent hydrolysis of m-Al₂O₃ yields boehmite at pH = 4 and bayerite at pH = 11. The effect of ultrasound on the textural properties of mesoporous alumina as well as on the transformation of nanosized bayerite to boehmite can be consistently attributed to the transient strong heating of the liquid shell surrounding the cavitation bubble which caused the chemical processes similar to those occurred during hydrothermal treatment.     

Investigation on the interactions of silymarin to bovine serum albumin and lysozyme by fluorescence and absorbance

The interactions of silymarin with bovine serum albumin (BSA) and lysozyme (LYS) were investigated in physiological buffer (pH = 7.4) by fluorescence spectroscopy and UV–vis absorption spectroscopy. The mechanism study indicated that silymarin could strongly quench the intrinsic fluorescence of BSA and LYS through static quenching procedures. At 291 K, the values of the binding constant K_A were 4.20×10⁴ and 4.71×10⁴ L mol^?1 for silymarin–BSA and silymarin–LYS, respectively. Using thermodynamic equations, the conclusion that hydrophobic and electrostatic forces played an important role in stabilizing complex of silymarin–BSA or silymarin–LYS was obtained. The effects of Cu²⁺, Mg²⁺, Ca²⁺, Fe²⁺, and Fe³⁺ on the binding were also studied at 291 K. According to Förster’s nonradiative energy transfer theory, the distances r₀ between donor and acceptor were calculated to be 3.36 and 2.71 nm for silymarin–BSA and silymarin–LYS, respectively. Synchronous fluorescence spectra showed that the conformation of BSA and LYS were changed by silymarin.     

Study on the conjugation mechanism of colistin sulfate with bovine serum albumin and effect of the metal ions on the reaction

Colistin sulfate (CS) can quench the fluorescence of bovine serum albumin (BSA) in an aqueous solution at pH 7.40. The static fluorescence-quenching process between BSA and CS was confirmed and the binding constant, the number of binding sites and thermodynamic data for the interaction between BSA and CS were also obtained. Results showed that the order of magnitude of binding constant (K_a) was 10⁴, and the number of binding site (n) in the binary system was approximately equal to 1; electrostatic force played an important role on the conjugation reaction between BSA and CS. On the basis of the Förster theory of the resonance energy transfer, the binding distance (r) between CS and BSA was less than 7 nm. Comparing the quenching of protein fluorescence excited at 280 nm and 295 nm and from the site marker replacement experiments, it was shown that the primary CS binding site was located in the sub-domain IIA (site I) of BSA. Synchronous fluorescence spectra clearly revealed that the binding of CS with BSA can induce conformation changes in BSA. In addition, the effects of common metal ions on the binding constants of CS–BSA complex were also discussed. It was shown that, except Cu²⁺, the high metal ion concentrations improved the CS efficacy.     

Interaction of dioxouranium(VI) ion with EDTA at different ionic strengths

The formation of complex species of dioxouranium(VI) ion with EDTA was studied in the pH range of 1–3.5 and at 25 °C using a combination of potentiometric and spectrophotometric techniques. Results showed evidence for formation of the following species: [UO₂H₄EDTA]²⁺, [UO₂H₃EDTA]⁺, and [UO₂H₂EDTA]. Investigations were performed in sodium perchlorate as background electrolyte at 0.1, 0.3, 0.5, 0.7, and 1.0 mol dm^? 3. The parameters based on the formation constants were calculated, and the dependences of protonation and the stability constants on ionic strength are described. The dependence on ionic strength of the formation constants was analyzed using the specific ion interaction theory (SIT) model. The stability constant values at infinite dilution, obtained using SIT model, are log β°₁₄₁ = 6.77, log β°₁₃₁ = 5.99 and log β°₁₂₁ = 9.29, where indexes for the overall stability constant, β_pqr, refer to the equilibrium pUO₂²⁺ + qH⁺ + rL^4? ? M_pH_qL_r^{(2p + q ? 4r)}. The specific interaction coefficients are also reported.     

Hydrothermal synthesis of functionalized CdS nanoparticles and their application as fluorescence probes in the determination of uracil and thymine

A novel, sensitive, and convenient method for the determination of uracil and thymine by functionalized CdS nanoparticles (NPs) was proposed. CdS NPs were prepared by hydrothermal process and modified with thioglycollic acid (TGA) in aqueous solution. The fluorescence intensity of functionalized CdS NPs was quenched in the presence of uracil or thymine. Under optimal conditions, the relative fluorescence intensity (F₀/F) was proportional to the concentration in the range of 9.0×10^?6–1.0×10^?4 mol/L for uracil (r=0.9985) and 8.8×10^?7–1.5×10^?4 mol/L for thymine (r=0.9960). The corresponding detection limits were 9.6×10^?7 mol/L and 3.2×10^?7 mol/L, respectively. In addition, the possible quenching mechanism was also discussed.     

Investigation of three flavonoids binding to bovine serum albumin using molecular fluorescence technique

The three flavonoids including naringenin, hesperetin and apigenin binding to bovine serum albumin (BSA) at pH 7.4 was studied by fluorescence quenching, synchronous fluorescence and UV–vis absorption spectroscopic techniques. The results obtained revealed that naringenin, hesperetin and apigenin strongly quenched the intrinsic fluorescence of BSA. The Stern–Volmer curves suggested that these quenching processes were all static quenching processes. At 291 K, the value and the order of the binding constant were K_{A (naringenin)}=4.08×10⁴<K_{A (hesperetin)}=5.40×10⁴≈K_{A (apigenin)}=5.32×10⁴ L mol^?1. The main binding force between the flavonoid and BSA was hydrophobic and electrostatic force. According to the Förster theory of non-radiation energy transfer, the binding distances (r₀) were obtained as 3.36, 3.47 and 3.30 nm for naringenin–BSA, hesperetin–BSA and apigenin–BSA, respectively. The effect of some common ions such as Fe³⁺, Cu²⁺, Mg²⁺, Mn²⁺, Zn²⁺ and Ca²⁺ on the binding was also studied in detail. The competition binding was also performed. The apparent binding constant (K′_A) obtained suggested that one flavonoid had an obvious effect on the binding of another flavonoid to protein when they coexisted in BSA solution.     

Evaluation of correlation between chemical dosimetry and subharmonic spectrum analysis to examine the acoustic cavitation

Currently several therapeutic applications of ultrasound in cancer treatment are under progress which uses cavitation phenomena to deliver their effects. There are several methods to evaluate cavitation activity such as chemical dosimetry and measurement of subharmonic signals. In this study, the cavitation activity induced by the ultrasound irradiation on exposure parameters has been measured by terephthalic acid chemical dosimetry and subharmonic analysis. Experiments were performed in the near 1 MHz fields in the progressive wave mode and effect of duty cycles changes with 2 W/cm² intensity (I_SATA) and acoustic intensity changes in continuous mode on both fluorescence intensity and subharmonic intensity were measured. The dependence between fluorescence intensity of terephthalic acid chemical dosimetry and subharmonic intensity analysis were analyzed by Pearson correlation (p-value < 0.05). It has been shown that the subharmonic intensity and the fluorescence intensity for continuous mode is higher than for pulsing mode (p-value < 0.05). Also results show that there is a significant difference between the subharmonic intensity and the fluorescence intensity with sonication intensity (p-value < 0.05). A significant correlation between the fluorescence intensity and subharmonic intensity at different duty cycles (R = 0.997, p-value < 0.05) and different intensities (R = 0.985, p-value < 0.05) were shown. The subharmonic intensity (μW/cm²) significantly correlated with the fluorescence intensity (count) (R = 0.901; p < 0.05) and the fluorescence intensity due to chemical dosimetry could be estimated with subharmonic intensity due to subharmonic spectrum analysis. It is concluded that there is dependence between terephthalic acid chemical dosimetry and subharmonic spectrum analysis to examine the acoustic cavitation activity.     

Field-assisted sustainable O− ion emission from fluorine-substituted 12CaO·7Al2O3 with improved thermal stability

We examined the electric field-assisted thermionic emission of atomic oxygen radical anion (O^?) in a vacuum from fluorine-substituted derivatives of 12CaO·7Al₂O₃ (C12A7) with a composition of (12 ? x)CaO·7Al₂O₃·xCaF₂ (0 ≤ x ≤ 0.8). Unsubstituted C12A7 easily decomposed into 5CaO?3Al₂O₃ (C5A3) and 3CaO?Al₂O₃ (C3A) above 830 °C during the emission experiment in a vacuum. The decomposition temperature range became narrower as the amount of F^? ion substitution increased, e.g. the sample with x = 0.4 kept a single phase after the emission experiment at 900 °C. The emitted anionic species from the x = 0.4 sample were dominated by O^? ions (～ 92%) together with a small amount of O₂^? ions (～ 4%) and F^? ions (～ 4%). The absence of an O₂ gas supply to the opposite side of the emission surface led to a nearly steady co-emission of O^? ions and electrons with a ratio of < 1/1. The O₂ gas supply markedly enhanced the O^? ion emission, and suppressed the electron emission. A sustainable and high-purity O^? ion emission with a current density of 11 nA cm^? 2 was achieved at 830 °C with the supply of 40 Pa O₂ gas. The similarity in these emission features to the unsubstituted C12A7, together with the improved thermal stability demonstrates that the F^? ion-substituted C12A7 is a promising material for higher intensity O^? ion emission at higher temperatures.     

Photoluminescence properties of a new Eu2+-activated CaLaGa3S7 yellowish-green phosphor for white LED applications

A thiogallate chalcogenide phosphor CaLaGa₃S₇:Eu²⁺ was synthesized by a solid-state reaction at 950 °C in a H₂S atmosphere. The photoluminescence excitation,emission spectra, concentration quenching, fluorescence lifetime, and thermal quenching process of the phosphor were investigated in detail. It was found that the synthesized phosphor emitted intense and broadband yellowish-green light with a peak at 554 nm. Thus, the proposed phosphor is suitable for the development of blue or near UV LED. The critical dopant concentration of Eu²⁺ (R_c=15 Å) per unit formula was found to be 0.15 mol. At room temperature, the fluorescence lifetime of Eu²⁺ in CaLaGa₃S₇ was found to be 0.216 μs. The activation energy for thermal quenching was 0.29 eV. The chromaticity coordinates of our phosphor is very close in color to Y₃Al₅O₁₂:Ce³⁺. Therefore, CaLaGa₃S₇:Eu²⁺ can be a good alternative as a yellowish-green phosphor and can be used for white light generation in phosphor-converted LEDs.     

Sequestration of some biogenic amines and poly(allyl)amine by high molecular weight polycarboxylic ligands in aqueous solution

The interactions of two high molecular weight polycarboxylic ligands [polyacrylic-co-maleic, MW = 70 kDa, and poly(methyl vinyl ether-co-maleic acid), MW = 15 kDa] with some polyamines [1,4-diaminobutane (or putrescine), histamine and poly(allyl)amine, MW = 15 kDa] were studied, at t = 25 °C and at low ionic strength (I = 0.015 mol L^? 1) by potentiometric measurements. For all investigated systems, the formation of (am)(L)H_i species was found (am = amine, L = polycarboxylic ligand, i = 1…4); the stability of polyammonium–polycarboxylate complexes is fairly high and the formation percentage of most species reaches ～ 90% in the experimental conditions (mmolar concentration of reactants). The dependence on temperature and ionic strength of the stability of polyamine–polycarboxylate species was studied using some semiempirical equations and enthalpy data for the protonation of both components. The sequestering ability of polyelectrolytes towards amines was modeled by a sigmoid Boltzman type equation and was defined by calculating the parameter pL₅₀ (the total ligand concentration, as ? log C_L, able to bind 50% of cation); this parameter gives an objective representation of this ability. The dependence of pL₅₀ on pH, ionic strength and temperature was studied too.     

Interactions between 4-(2-dimethylaminoethyloxy)-N-octadecyl-1,8-naphthalimide and serum albumins: Investigation by spectroscopic approach

A novel 4-(2-dimethylaminoethyloxy)-N-octadecyl-1,8-naphthalimide (DON) has been synthesized as a spectrofluorimetric probe for the determination of proteins. Photophysics of DON in different solvents has been delineated in this paper. Progressive redshift with polarity of solvents in emission and absorption spectra hints at intramolecular charge transfer. The interactions of DON with serum albumins (i.e., human serum albumin (HSA) and bovine serum albumin (BSA)) were studied by fluorescence and absorption spectroscopy. Fluorescence data revealed that the quenching of HSA/BSA by DON were static quenching and the DON–HSA/BSA complexes were formed. The binding constant (K_b) for HSA and was found to be 8.44×10^?4 and 60.26×10^?4 M^?1 and the number of binding sites (n) were 1.00 and 1.40, respectively. The thermodynamic parameters, ΔH and ΔS, for the DON–HSA system was calculated to be ?14.83 kJ mol^?1 and 23.61 J mol^?1 K^?1, indicating the hydrogen bonds and hydrophobic interactions were the dominant intermolecular force. ΔH and ΔS for the binding of DON with BSA was ?60.08 kJ mol^?1 and ?90.7441 mol^?1 K^?1, suggesting the hydrogen bonds and van der Waals force played the main role in the interaction. The results of displacement experiments showed that DON bound HSA/BSA occurred at the Trp-214 proximity, located in subdomain IIA of the serum albumin structure (the warfarin binding pocket). The effect of DON on the conformation of HSA was also analyzed by synchronous and three-dimensional fluorescence spectra. The fluorescence of DON could be quenched by HSA, based on which, a fluorometric method for the determination of microamount protein using DON in the medium of HCl?Tris buffer solution (pH=7.4) was developed. The linear range of the calibration curves was 0.1–10.0 μM for HSA, 0.1–11.2 μM for BSA and 0.2–9.7 μM for egg albumin (EA). The detection limit (3σ) for HSA was 1.12×10^?10 M, for BSA it was 0.92×10^?10 M and for EA it was 4.33×10^?10 M. The effect of metal cations on the fluorescence spectra of DON in ethanol was also investigated. The method has been applied to detect the total proteins in human serum samples and the results were in good agreement with those reported by the hospital.     

Spectral characteristics and fluorescence quenching of N,N′-bis(4-pyridyl)-3,4:9,10-perylenebis(dicarboximide) (BPPD)

The photophysical properties such as electronic absorption, molar absorptivity, emission spectra, fluorescence quantum yield and fluorescence lifetime of N,N′-bis(4-pyridyl)-3,4:9,10-perylene bis(dicarboximide) (BPPD) have been measured in different solvents. Both electronic absorption and fluorescence spectra are not sensitive to medium polarity, while the fluorescence quantum yield (?_f) is solvent dependent. The ground state geometry has been computed by using density functional theory (DFT), the transition from HOMO to LUMO from perylene core with maximum absorption at 512 nm and HOMO–LUMO energy difference equal 2.53 eV. BPPD dye undergoes molecular aggregation to dimmer or higher aggregates in dimethyl sulfoxide (DMSO). Crystalline solids of BPPD gives excimer-like emission at 676 nm. The fluorescence quenching of BPPD is also studied using hydrated ferric oxide nanoparticle (FeOOH), and the Stern–Volmer rate constants (K_sv) were calculated as 8×10⁶ and 9.2×10⁶ M^?1 in ethanol and ethylene glycol, respectively.     

Formation of nickel and nickel,zinc-bearing ferrite in aqueous suspension by air oxidation

Stoichiometric Ni-bearing ferrite was formed by air oxidation of an iron(II) hydroxide suspension at an initial Ni : Fe_tot mol ratio (r_Ni) of 0.20 : 2.80 at pH 10.0 and 65°C. Most of products formed at r_Ni=0.40 : 2.60 and 0.60 : 2.40 were Ni-bearing ferrites, of which vacancies of Fe³⁺ ion on the lattice points may be considered. Only Ni, Zn-bearing ferrites were formed in the suspensions at initial (Ni + Zn)  : Fe_tot mol ratios (r_{Ni + Zn}) of 0.20 : 2.80–0.60 : 2.40 at pH 10.0 and 65°C. At higher r_Ni or r_{Ni + Zn} by-products containing Ni, Fe and O₄²⁻ were formed. The formation of the by-products was depressed in the suspensions containing chloride ions in the place of sulfate ions.     

Ultrasonic assisted-Fenton-like degradation of nitrobenzene at neutral pH using nanosized oxides of Fe and Cu

Ultrasonic-assisted heterogeneous Fenton reaction was used for degradation of nitrobenzene (NB) at neutral pH conditions. Nano-sized oxides of α-Fe₂O₃ and CuO were prepared, characterized and tested in degradation of NB (10 mg L⁻¹) under sonication of 20 kHz at 25 °C. Complete degradation of NB was effected at pH 7 in presence of 10 mM H₂O₂ after 10 min of sonication in presence of α-Fe₂O₃ (1.0 g L⁻¹), (k = 0.58 min⁻¹) and after 25 min in case of CuO (k = 0.126 min⁻¹). α-Fe₂O₃ showed also effective degradation under the conditions of 0.1 g L⁻¹ oxide and 5.0 mM of H₂O₂, even though with a lower rate constant (0.346 min⁻¹). Sonication plays a major role in enhancing the production of hydroxyl radicals in presence of solid oxides. Hydroxyl radicals-degradation pathway is suggested and adopted to explain the differences noted in rate constants recorded on using different oxides.     

Ultrasonic-assisted synthesis of 1,4-disubstituted 1,2,3-triazoles via various terminal acetylenes and azide and their quorum sensing inhibition

An efficient synthesis of 1,4-disubstituted 1,2,3-triazole derivatives was studied. 1,4-Disubstituted 1,2,3-triazoles containing isoxazole and thymidine structures were synthesized in 84–96% yields starting from various terminal isoxazole ether alkynes and β-thymidine azide derivatives via a 1,3-dispolar cycloaddition using copper acetate, sodium ascorbate as the catalyst under ultrasonic assisted condition. All the target compounds were characterized by HRMS, FT-IR, ¹H NMR and ¹³C NMR spectroscopy. Furthermore, the quorum sensing inhibitory activities of synthesized compounds were evaluated with Chromobacterium violaceum (C. Violaceum CV026) based on their inhibition of violacein production, with compound C₁₀-HSL as a positive control. The compounds 8a, 8c and 8f exhibited considerable levels of inhibitory activity against violacein production, and IC₅₀ values were 217 ± 19, 223 ± 20 and 42.8 ± 4.5 μM, respectively, which highlighted the potential of these compounds as lead structures for further research towards the development of novel QS inhibitors.     

Optimization of a heterogeneous catalytic hydrodynamic cavitation reactor performance in decolorization of Rhodamine B: Application of scrap iron sheets

A low pressure pilot scale hydrodynamic cavitation (HC) reactor with 30 L volume, using fixed scrap iron sheets, as the heterogeneous catalyst, with no external source of H₂O₂ was devised to investigate the effects of operating parameters of the HC reactor performance. In situ generation of Fenton reagents suggested an induced advanced Fenton process (IAFP) to explain the enhancing effect of the used catalyst in the HC process. The reactor optimization was done based upon the extent of decolorization (ED) of aqueous solution of Rhodamine B (RhB). To have a perfect study on the pertinent parameters of the heterogeneous catalyzed HC reactor, the following cases as, the effects of scrap iron sheets, inlet pressure (2.4–5.8 bar), the distance between orifice plates and catalyst sheets (submerged and inline located orifice plates), back-pressure (2–6 bar), orifice plates type (4 various orifice plates), pH (2–10) and initial RhB concentration (2–14 mg L^?1) have been investigated. The results showed that the highest cavitational yield can be obtained at pH 3 and initial dye concentration of 10 mg L^?1. Also, an increase in the inlet pressure would lead to an increase in the ED. In addition, it was found that using the deeper holes (thicker orifice plates) would lead to lower ED, and holes with larger diameter would lead to the higher ED in the same cross-sectional area, but in the same holes’ diameters, higher cross-sectional area leads to the lower ED. The submerged operation mode showed a greater cavitational effects rather than the inline mode. Also, for the inline mode, the optimum value of 3 bar was obtained for the back-pressure condition in the system. Moreover, according to the analysis of changes in the UV–Vis spectra of RhB, both degradation of RhB chromophore structure and N-deethylation were occurred during the catalyzed HC process.     

Color tunable emission from (GdxY1−x)2O3: Er3+, Yb3+ phosphor prepared by combustion method

The (Gd_xY_1?x)₂O₃: Er³⁺, Yb³⁺ [x=0.0, 0.1, 0.5, 0.9, 1.0] phosphor samples with 0.5 mol% concentration of Er³⁺ and 3.0 mol% of Yb³⁺, have been prepared using combustion route. The effect of variation of composition on the morphology, crystallinity and photoluminescence characteristics of the material has been investigated. The samples were post-heated at a temperature 1200 °C, for 5 h. We find systematic color tunability from red to green with an increase of Gd₂O₃ content in Y₂O₃ lattice. Further, the post-heated samples show an enhancement of fluorescence intensity for more than fifteen times. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence measurement and Fourier transform infrared (FTIR) techniques in order to find out the structural changes in host lattice. An increase in crystallite size has been marked with increasing Gd content while FTIR analysis explains the reason of variation in the fluorescence of rare earth ions in different host matrices.     

Mono(pyridine-N-oxide) analog of DOTA as a suitable organic reagent for a sensitive and selective fluorimetric determination of Ln(III) ions

The mono(pyridine-N-oxide) analog of the H₄dota macrocylic ligand, H₃do3a-py^NO, is capable of forming thermodynamically stable and kinetically inert Ln(III) complexes. Its Eu(III) and Tb(III) complexes display a strong long-lived fluorescence as a result of the antenna effect of the pyridine-N-oxide fluorophore in the reagent. It is shown that H₃do3a-py^NO can be used as a fluorogenic reagent for the determination of Eu(III) and Tb(III) at pH 6.5 and c_L=1 mM. At an excitation wavelength of 286 nm, the emission maxima are 615 nm (Eu(III)-complex), and 547 nm (Tb(III)complex). Detection limits are at concentrations around 1.0 μM and linearity of the method spans over 2 orders of magnitude. The method was applied to artificial and real samples (spiked mineral waters, extracts from cathode ray tube luminophore dust) and gave satisfactory results. The method is simple, rapid, and hardly interfered by other metal ions.