Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions

The spectral features of the squarylium near-infrared (NIR) dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is λ=663 nm in methanol. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission wavelength of the dye in methanol is λ_em=670 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The Stern–Volmer quenching constant, K_SV, was calculated from the Stern–Volmer plot to be K_SV=2.70×10⁷ M⁻¹ for Co(II) ion. The K_SV value for Fe(III) ion could not be established due to the non-linearity of the Stern–Volmer plot and the modified Stern–Volmer plot for this ion. The detection limit is 6.24×10⁻⁸ M for Fe(III) ion and 1.55×10⁻⁵ M for Co(III) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant, K_S, of the metal–dye complex was calculated to be 3.14×10⁶ M⁻¹ for the Fe–dye complex and 2.64×10⁵ M⁻¹ for the Co–dye complex.     

新型荧光试剂1,5-二(4,6-二氯三嗪)-氨基萘与酪氨酸相互作用

合成了一种新型三嗪荧光探针1,5-二(4,6-二氯三嗪)-氨基萘并利用元素分析、IR和核磁共振谱进行了表征。在pH=12.0的柠檬酸钠-NaOH缓冲溶液中,与酪氨酸在35℃下反应30 min后,λex/λem=400 nm/465 nm处,1,5-二(4,6-二氯三嗪)-氨基萘与酪氨酸反应使体系的荧光强度增强,且增强的荧光强度与酪氨酸的浓度成正比,依此建立了一种测定酪氨酸的新方法。测定的线性范围是1.1×10-7~1.1×10-5mol/L,检出限为6.8×10-8mol/L。该方法成功用于测定人尿和血清样品中的酪氨酸。     

Spectrofluorimetric quantification of bromazepam using a highly selective optical probe based on Eu–bromazepam complex in pharmaceutical and serum samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of bromazepam is developed. In phosphate buffer of pH 7.4. The bromazepam enhance the luminescence intensity of the Eu³⁺ ion in Eu³⁺–bromazepam complex at λ_ex = 390 nm. The produced luminescence intensity of Eu³⁺–bromazepam complex is in proportion to the concentration of bromazepam. The working range for the determination of bromazepam is 2.3 × 10⁻⁸ to 6.2 × 10⁻⁷ M with detection limit (LoD) and quantitative detection limit (LoQ) of 3 × 10⁻⁹ and 1.2 × 10⁻⁸ M, respectively. While, the working range, detection limit (LoD) and quantitative detection limit (LoQ) in case of the quantum yield calculations are 3.7 × 10⁻⁸ to 3.4 × 10⁻⁷ M with of 3.4 × 10⁻⁹ and 9.2 × 10⁻⁸ M, respectively. The enhancement mechanism of the luminescence intensity in the Eu³⁺–bromazepam system has been also explained.     

Spectrofluorometric study of 1,4-diaminoanthraquinone-calcium complex in aqueous sulfuric acid mediums: Spectrofluorometric determination of calcium

The spectrofluorometric study was made of the complex 1,4-diaminoanthraquinone-Ca in aqueous sulfuric mediums [λ_max,ex = 410 nm; λ_max,em = 580 nm; 50% H₂O; stable for at least 4 hr; range temperature OPTIMUM = 20–35 °C; [R]_optimum = 2 × 10⁻⁴M; stoichiometry 2:1 (fluorescent complex) and 1:1 (no fluorescent complex)]. A new method for the spectrofluorometric determination of Ca traces is proposed for concentrations between 150 and 400 ppb. The relative error and the interferences of the method have been investigated.     

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0 × 10⁻⁶ M and the progress of reaction was followed spectrophotometrically at 525 nm (λ_max of purple-red complex [Ru(CN)₅NRS]³⁻,  = 3.1 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 8.75 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 3.50 × 10⁻⁴ M [nitroso-R-salt], pH 7.00 ± 0.02, ionic strength, I = 0.1 M (KCl), temp 45.0 ± 0.1 °C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t = 15, 20 and 25 min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0 × 10⁻⁷ M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

Spectrophotometric study of pseudopurpurin-Pd(II) dimer complex. Spectrophotometric determination of traces of Pd(II)

We have studied spectrophotometrically the Pseudopurpurin-Pd(II) complex in an ethanolic-water medium ¦Ethanolamine ¦_optimum = 4 × 10⁻¹M; λ = 670 nm; 20% H₂O; stable for at least 4 hr; ¦Reagent¦_optimum = 5 × 10⁻⁵M; stoichiometry 2:2; log K = 17.7. A new method for the spectrophotometric determination of Pd traces is proposed for concentrations between 0.30 and 2.40 ppm. The relative error and the interferences of the method have been investigated.     

Interactions of thioflavin T with serum albumins: Spectroscopic analyses

The interaction of thioflavin T (ThT) with serum albumins from four different mammalian species i.e. human, bovine, porcine and rabbit, has been investigated by circular dichroism (CD), fluorescence spectroscopy and ITC. The binding constant (K) for HSA was found to be 9.9 × 10⁴ M⁻¹, 4.3 × 10⁴ M⁻¹ for RSA, 1.07 × 10⁴ M⁻¹ for PSA and 0.3 × 10⁴ M⁻¹ for BSA and the number of binding sites (n) were 1.14, 1.06, 0.94 and 0.8, respectively, which is very significant. By using unfolding pathway of HSA in the presence of urea, domain II of HSA has been assigned to possess binding site of ThT. Its binding constant is comparable to many drugs that bind at domain II of HSA, like salicylate, warfarin, digitoxin, etc. Acting force between HSA and ThT is showing that both hydrophobic and electrostatic forces have contributed for the interaction. ΔG_binding, ΔH and ΔS were calculated to be −28.46 kJ mol⁻¹, −3.50 kJ mol⁻¹ and 81.04 J K⁻¹ mol⁻¹, respectively. The data described here will help to increase our understanding about the interaction of ThT with native proteins. The results also indicate that care must be taken while using ThT as a probe for detecting amyloid fibrils.     

A novel fluorescent distinguished probe for Cr (VI) in aqueous solution

Salicylaldehyde rhodamine B hydrazone (SRBH) was developed as a new spectrofluorimetric probe for the selective and sensitive detection of CrO₄²⁻ in acidic conditions. The proposed method was based on the special oxidation reaction between non-fluorescent SRBH by potassium dichromate to produce a highly fluorescent rhodamine B, as a product. Under the optimum conditions described, the fluorescence enhancement at 591 nm was good linearly related to the concentration of CrO₄²⁻ from 1.0 × 10⁻⁸ to 3.0 × 10⁻⁷ M (0.42–12.6 ng mL⁻¹) with a correlation coefficient of R² = 0.9989 (n = 10) and a detection limit of 1.5 × 10⁻⁹ M (0.063 ng mL⁻¹). The relative standard deviation (R.S.D.) was 2.0% (n = 6). The proposed method was also successfully applied to the determination of chromium (VI) in drinking water, river water and synthetic samples.     

L-Cysteine-coated CdSe/CdS core-shell quantum dots as selective fluorescence probe for copper(II) determination

Quantum dots (QDs) or semiconductor nanocrystals have been receiving great interest in the last few years. In this paper, L-cysteine-coated CdSe/CdS core-shell QDs (λ_em = 585 nm) have been prepared, which have excellent water-solubility. The full width at half maximum (FWHM) of the photoluminescence of these nanocrystals is very narrow (about 30 nm), and the quantum yield (QY) is 15% relative to Rhodamine 6G in ethanol (QY = 95%). With excess free L-cysteine in the solution, the fluorescence intensity of L-cysteine-coated CdSe/CdS QDs showed improved stability. It was found that the fluorescence of L-cysteine-capped CdSe/CdS QDs could be quenched only by copper (II) ions and was insensitive to other physiologically important cations, such as Ca²⁺, Mg²⁺, Zn²⁺, Al³⁺, Fe³⁺, Mn²⁺ and Ni²⁺ etc. Based on this finding, the quantitative analysis of Cu²⁺ with L-cysteine-capped CdSe/CdS QDs has been established. The linear range was from 1.0 × 10^− 8 to 2.0 × 10^− 7 mol L^− 1 and the limit of detection (LOD) was 3.0 × 10^− 9 mol L^− 1 (S/N = 3). The proposed method has first been applied to the determination of Cu²⁺ in vegetable samples with recoveries of 99.6–105.8%.     

Palladized aluminum electrode covered by Prussian blue film as an effective transducer for electrocatalytic oxidation and hydrodynamic amperometry of N-acetyl-cysteine and glutathione

The mediated oxidation of N-acetyl cysteine (NAC) and glutathione (GL) at the palladized aluminum electrode modified by Prussian blue film (PB/Pd–Al) is described. The catalytic activity of PB/Pd–Al was explored in terms of Fe^III[Fe^III(CN)₆]/Fe^III[Fe^II(CN)₆]¹⁻ system by taking advantage of the metallic palladium layer inserted between PB film and Al, as an electron-transfer bridge. The best mediated oxidation of NAC and GL on the PB/Pd–Al electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 2. The mechanism and kinetics of the catalytic oxidation reactions of the both compounds were monitored by cyclic voltammetry and chronoamperometry. The charge transfer-rate limiting step as well as overall oxidation reaction of NAC or GL is found to be a one-electron abstraction. The values of transfer coefficients α, catalytic rate constant k and diffusion coefficient D are 0.5, 3.2 × 10² M⁻¹ s⁻¹ and 2.45 × 10⁻⁵ cm² s⁻¹ for NAC and 0.5, 2.1 × 10² M⁻¹ s⁻¹ and 3.7 × 10⁻⁵ cm² s⁻¹ for GL, respectively. The modifying layers on the Pd–Al substrate have reproducible behavior and a high level of stability in the electrolyte solutions. The modified electrode is exploited for hydrodynamic amperometry of NAC and GL. The amperometric calibration graph is linear in concentration ranges 2 × 10⁻⁶–40 × 10⁻⁶ for NAC and 5 × 10⁻⁷–18 × 10⁻⁶ M for GL and the detection limits are 5.4 × 10⁻⁷ and 4.6 × 10⁻⁷ M, respectively.     

Evaluation of a chloramine-T-selective electrode for catalytic titration of silver and mercury(II) based on iodide-catalyzed chloramine-T reactions

Semiautomatic methods are described for the catalytic titrimetric determination of microamounts of silver and mercury(II) using a chloramine-T-selective electrode as monitor. The methods are based on the inhibitory effect of Ag(I) and Hg(II) on the iodide-catalyzed chloramine-T-arsenite and chloramine-T-H₂O₂ reactions. Microamounts of silver in the range 0.2–200 μg (1 × 10⁻⁷−1 × 10⁻⁴ M) and of mercury(II) in the range 0.1–200 μg (2.5 × 10⁻⁸−5 × 10⁻⁵ M) were determined using the chloramine-T-As(III) indicator reaction. Mercury(II) in the range 4–2000 μg (1 × 10⁻⁶−5 × 10⁻⁴ M) was also determined using the chloramine-T-H₂O₂ indicator reaction. The accuracy and precision were in the range 0.1–1%.     

UV–visible spectrum of the phenyl radical and kinetics of its reaction with NO in the gas phase

Pulse radiolysis transient UV–visible absorption spectroscopy was used to study the UV–visible absorption spectrum (225–575 nm) of the phenyl radical, C₆H₅(), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225–340 nm. In the presence of NO phenyl radicals are converted into nitrosobenzene. The phenyl radical spectrum was measured relative to that of nitrosobenzene. Based upon σ(C₆H₅NO)_{270 nm}=3.82×10⁻¹⁷ cm² molecule⁻¹ we derive an absorption cross-section for phenyl radicals at 250 nm, σ(C₆H₅())_{250 nm}=(2.75±0.58)×10⁻¹⁷ cm² molecule⁻¹. At 295 K in 200–1000 mbar of Ar diluent k(C₆H₅()+NO)=(2.09±0.15)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.     

Study on dynamic interfacial tension of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide at liquid/liquid interface

Dynamic interfacial tension between aqueous solutions of 3-dodecyloxy-2-hydroxypropyl trimethyl ammonium bromide (R₁₂HTAB) and n-hexane were measured using the spinning drop method. The effects of the R₁₂HTAB concentration (the concentration below the CMC) and temperature on the dynamic interfacial tension have been investigated; the reason of the change of dynamic interfacial tension with time has been discussed. The effective diffusion coefficient, D_a, and the adsorption barrier, _a, have been obtained from the experimental data using the extended Word–Tordai equation. The results show that the dynamic interfacial tension becomes smaller while _a becomes higher with increasing R₁₂HTAB concentration in the bulk aqueous phase. D_a decreases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 0.87 × 10⁻¹² m⁻² s⁻¹ while _a increases from 5.41 kJ mol⁻¹ to 7.74 kJ mol⁻¹ with the increase of concentration in the bulk solution of R₁₂HTAB from 0.5 × 10⁻³ mol dm⁻³ to 4 × 10⁻³ mol dm⁻³. Change of temperature affects the adsorption rate through altering D_a and _a. The value of D_a increases from 5.56 × 10⁻¹² m⁻² s⁻¹ to 13.98 × 10⁻¹² m⁻² s⁻¹ while that of _a decreases from 5.41 kJ mol⁻¹ to 5.07 kJ mol⁻¹ with temperature ascending from 303 K to 323 K. The adsorption of surfactant from the bulk phase into the interface follows a mixed diffusion–activation mechanism, which has been discussed in the light of interaction between surfactant molecules, diffusion and thermo-motion of molecules.     

Sequential Injection Photometric Determination of Molybdenum Using Organic Wetting Film Extraction

Wetting film extraction was combined with colorimetry to determine nanogram amounts of molybdenum(VI). The simple extraction procedure enhanced sensitivity and selectivity while maintaining a high sample throughput. Extraction and back extraction steps were exploited to exclude interference from the 31 metal species and 11 anions tested. In the first step, molybdenum(VI) was extracted into a toluene film as an ion paired complex. Molybdenum(VI) reacted with thiocyanate to form anionic molybdenum(V) and/or molybdenum(VI) thiocyanate complexes. The complexes were extracted into a toluene film containing tetraheptylammonium bromide as ion pairing reagent. The thiocyanate ligands were displaced by 1,5-diphenylcarbazone (DPC) to form a more intensely colored complex (λ_max= 540 nm). DPC was introduced in the back extraction solvent, methanol. The relative standard deviation was 2.5% for 50 ng ml⁻¹of molybdenum(VI) (n= 10) at a rate of 25 samples h⁻¹. The detection limit (3 × baseline noise) was 2.5 × 10⁻⁸M.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

Fluorescein labeling of estrogen for application of fluorescence polarization binding assays for antibody and receptor

The fluorescence polarization binding assay (FPBA) using fluorescein-labeled estrogen tracer is a homogeneous assay applicable to both estrogen antibody and estrogen receptor-binding assays. Two estrogen-ethylendiamine fluoresceinthiobamyl (E-EDF) tracers were synthesized; estrogen-6-EDF (E-6-F) derived from 6-ketoestradiol 6-(o-carboxymethyl) oxime and estrogen-17-EDF (E-17-F) was from 17β-estradiol 17-hemisuccinate. In both FPBAs using antibody and receptor, E-6-F tracer (Rf_365nm=0.58) showed a better binding response than E-17-F (Rf_365nm=0.70) indicating that the 17-position of estrogen seems to play an essential role as a binding site for antibody or receptor. In the optimized conditions of FPBA for E₂ using E-6-F tracer, antibody binding (K_d=9.4×10⁻⁹ M) is 50 times sensitive than receptor binding (K_d=4.6×10⁻⁸ M). Binding responses of estrogen and its related chemicals by FPBA indicate that antibody binding assay is able to screen the structural similarity of estrogen showing some response with methyltestosterone (K_i=2.1×10⁻⁵ M). On the other hand, the receptor assay is able to screen for estrogenic chemicals such as tamoxifen (K_i=4.5×10⁻⁹ M) and diethylstilbesterol (K_i=8.1×10⁻⁷ M). Therefore, E-6-F tracer is useful as a tracer for FPBA that is able to screen for chemicals structurally similar to estrogen using antibody, and that is able to screen for chemicals functionally similar to estrogen using receptor binding assay.     

Synthesis and structure analysis of tetragonal Li7La3Zr2O12 with the garnet-related type structure

We have successfully synthesized a high-purity polycrystalline sample of tetragonal Li₇La₃Zr₂O₁₂. Single crystals have been also grown by a flux method. The single-crystal X-ray diffraction analysis verifies that tetragonal Li₇La₃Zr₂O₁₂ has the garnet-related type structure with a space group of I4₁/acd (no. 142). The lattice constants are a=13.134(4) Å and c=12.663(8) Å. The garnet-type framework structure is composed of two types of dodecahedral LaO₈ and octahedral ZrO₆. Li atoms occupy three crystallographic sites in the interstices of this framework structure, where Li(1), Li(2), and Li(3) atoms are located at the tetrahedral 8a site and the distorted octahedral 16f and 32g sites, respectively. The structure is also investigated by the Rietveld method with X-ray and neutron powder diffraction data. These diffraction patterns are identified as the tetragonal Li₇La₃Zr₂O₁₂ structure determined from the single-crystal data. The present tetragonal Li₇La₃Zr₂O₁₂ sample exhibits a bulk Li-ion conductivity of σ_b=1.63×10⁻⁶ S cm⁻¹ and grain-boundary Li-ion conductivity of σ_gb=5.59×10⁻⁷ S cm⁻¹ at 300 K. The activation energy is estimated to be E_a=0.54 eV in the temperature range of 300–560 K.     

Positronium inhibition and quenching by organic electronic acceptors and charge transfer complexes

Positron lifetime measurements were performed on a series of organic electron acceptors and charge-transfer complexes in solution. The acceptors cause both positronium (Ps) inhibition (with maybe one exception) and quenching, but when an acceptor takes part in a charge-transfer complex the inhibition intensifies and the quenching almost vanishes. The reaction constants between ortho-Ps and the acceptors were determinded to be: 1.5 × 10¹⁰ M⁻¹ s⁻¹ for SO₂ in dioxane 3.7 × 10¹⁰ M⁻¹ s⁻¹ for SO₂ in n-heptane, 3.4 × 10¹⁰ M⁻¹ s⁻¹ for tetracyanoquinodimethane in tetrahydrofurane and 1.6 × 10¹⁰ M⁻¹ s⁻¹ for tetracyanoethylene in dioxane. From the ortho-Ps lifetimes in solutions containing charge-transfer complexes complexity constants were determined that were in reasonable agreement with constants obtained from optical data. The influence of acceptors and charge-transfers complexes on the Ps yield was interpreted in terms of the spur reaction model of Ps formation. Correlation was also made to gas phase reaction between electron acceptors and free electron, as well as to pulse radiolysis data.     

A new Tb-selective fluorescent sensor based on 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide

A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quenching upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M and the detection limit is 1.4 × 10⁻⁷ M. The association constant of the 1:1 complex formation for L–Tb⁺³ was calculated to be 6.01 × 10⁶ M⁻¹, and the fluorescent probe exhibits high selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for Tb(III) ions over a large number of interfering cations.