X-ray Fluorescence Analysis of Flux-Cored Wire Burden

Interelement effects were estimated for the burden components of the PP-AN4 flux-cored wire, and the predominance of absorption effects was demonstrated. Reasons for the variation of the effective wavelengths in the primary excitation spectrum were revealed for some analytes. An iteration -correction method was proposed for calculating the weight portions of elements. This method is based on the regression analysis of the absorption parameters of test samples; it takes into account the variation of the effective wavelength of the primary radiation. The convergence of the iteration procedure was shown in the calculations of the weight portions of burden elements under real conditions. A method was proposed for the preparation of burden samples for analysis taking into account the peculiar features of the technological process. Metrological certification was performed in accordance with the industry-specific regulations. The results of X-ray fluorescence analysis of the burden were used for the quality control of the produced flux-cored wire.     

Error of sample preparation in pressing emitters for X-ray fluorescence analysis

When determining element concentrations in geological samples by X-ray fluorescence spectrometry using emitters obtained by pressing tablets from powder samples, we revealed the effect of a significant difference in line intensities of characteristic long-wavelength emission (ΔI _i) from opposite sides of the emitter. The effects of compacting pressure, mass of emitter, and its surface area on ΔI _i were investigated. It was shown that the account of this effect can reduce the error of sample preparation in using compacting pressures lower than 20 t.     

Effect of the conditions of sample preparation for x-ray fluorescence analysis on the effect of microabsorption heterogeneity

The dual effect of the microabsorption heterogeneity (MAH) of emitters on the fluorescence intensity (I _fl) is shown on the basis of the literature data. The duality is due to the covering of large fluorescent grains by small filler particles (II type effect) and its absence (I type effect). For some materials, the effect of MAH can change not only in magnitude but also in sign. It is shown experimentally that the prediction of the covering effect is difficult. It was found that, upon crushing multicomponent materials, different granulometric fractions differ in their chemical composition. This makes the theoretical account of the effect of the MAH of the emitter on the results x-ray fluorescence analysis hardly probable. It is shown that the experimental account by means of radiation scattered (I _σ) or absorbed (I _ab) by the sample possible only in a particular case, because the dependences I _fl,I _σ, and I _ab on the particle size differ in nature.     

Rigidochromism by imide functionalisation of an aminomaleimide fluorophore

Fluorescent dyes that exhibit high solid state quantum yields and sensitivity to the mechanical properties of their local environment are useful for a wide variety of applications, but are limited in chemical diversity. We report a trityl-functionalised maleimide that displays rigidochromic behaviour, becoming highly fluorescent when immobilised in a solid matrix, while displaying negligible fluorescence in solution. Furthermore, the dye''s quantum yield is shown to be sensitive to the nature of the surrounding matrix. Computational studies reveal that this behaviour arises from the precise tuning of inter- and intramolecular noncovalent interactions. This work expands the diversity of molecules exhibiting solid state environment sensitivity, and provides important fundamental insights into their design.

In this study, by systematic tuning of imide substituent a maleimides dye with sensitivity to its solid-state environment was investigated.     

SPE–TLC Profiling of Impurities in 1-(3,4-Methylenedioxyphenyl)-2-nitropropene, an Intermediate in 3,4-Methylenedioxy- methamphetamine (MDMA) Synthesis

Impurity profiling of 1–(3,4-methylenedioxyphenyl)-2-nitropropene, an intermediate in the synthesis of 3,4-methylenedioxymethamphetamine (MDMA), has been studied by SPE combined with TLC. Extraction of impurities was performed on C₁₈ columns. TLC separation was performed on 0.2 mm silica gel 60 plates, with fluorescent indicator F₂₅₄, in a horizontal developing chamber. To improve the quality of the profile (increase the TLC sensitivity) SPE extracts were concentrated by evaporation in a stream of nitrogen. The usefulness of methanol, ethanol, ethyl acetate, chloroform, acetonitrile, and their mixtures as mobile phases was tested by use of Gibbss triangle. Spots of the separated impurities were observed under UV light (_exc=254 and 366 nm). The proposed characteristics of profile quality (optimization criteria) are based on matrix presentation of the TLC pattern. They take into account, simultaneously, the number of spots revealed, differences between R_F values, and the intensity of fluorescence.     

Biodegradable nanoprobe based on MnO<Subscript>2</Subscript> nanoflowers and graphene quantum dots for near infrared fluorescence imaging of glutathione in living cells

Near infrared (NIR) emitting semiconductor quantum dots can be excellent fluorescent nanoprobes, but the poor biodegradability and potential toxicity limits their application. The authors describe a fluorescent system composed of graphene quantum dots (GQDs) as NIR emitters, and novel MnO₂ nanoflowers as the fluorescence quenchers. The system is shown to be an activatable and biodegradable fluorescent nanoprobe for the “turn-on” detection of intracellular glutathione (GSH). The MnO₂-GQDs nanoprobe is obtained by adsorbing GQDs onto the surface of MnO₂ nanoflowers through electrostatic interaction. This results in the quenching of the NIR fluorescence of the GQDs. In the presence of GSH, the MnO₂-GQDs nanoprobe is degraded and releases Mn²⁺ and free GQDs, respectively. This gives rise to increased fluorescence. The nanoprobe displays high sensitivity to GSH and with a 2.8 μM detection limit. It integrates the advantages of NIR fluorescence and biodegradability, selectivity, biocompatibility and membrane permeability. All this makes it a promising fluorescent nanoprobe for GSH and for cellular imaging of GSH as shown here for the case of MCF-7 cancer cells.

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Graphical abstract A biodegradable NIR fluorescence nanoprobe (MnO₂-GQDs) for the “turn-on” detection of GSH in living cell was established, with the NIR GQD as the fluorescence reporter and the MnO₂ nanoflower as the fluorescence quencher.

     

Use of liposomes to evaluate the role of membrane interactions on antioxidant activity

In this study the possibility of using liposomes as membrane mimetic systems was evaluated to estimate the antioxidant properties of oxicams and establish a relationship between the interactions of the drugs with the membrane and their consequent antioxidant activity. Different experiments were performed covering the study of the protective effect of oxicams in lipid peroxidation induced by the peroxyl radical (ROO) derived from 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) and using two fluorescence probes with distinct lipophilic properties. Lipid peroxidation using the hydrophilic probe fluorescein was evaluated in lipid and aqueous media. Lipid systems labelled with the fluorescent probe diphenylhexatriene propionic acid (DPH-PA) were used to assess the effects of the drugs on membrane peroxidation simultaneously by fluorescence intensity decay and changes in membrane fluidity by steady-state anisotropy measurements. The use of different probes and liposomes as membrane mimetic systems allowed to conclude that membrane lipoperoxidation is related not only to the scavenging characteristics of the antioxidants but also to their ability to interact with the lipid bilayers.     

Methodological Peculiarities of the Electron Probe X-Ray Microanalysis of Environmental Samples

A set of procedures was developed for the electron probe X-ray microanalysis (EPMA) of fish and animal bone tissues, solid snow sediments, and coal ashes. Various sample-preparation procedures and two variants of the optimum conditions for analytical measurements were considered. In calculating analyte concentrations, matrix effects were taken into account using ZAF methods and the function of generated X-ray distribution with depth, namely, by the PAP method and by adding a joint correction for absorption and atomic number within a biexponential (z) model. For EPMA of small fractions 1–5 m in size, an approach was proposed that takes into account the test sample size using an analytical expression. In calculations of concentrations for micron-sized particles, this approach can lower the relative deviation from the stoichiometric composition from 36.8% to 22.2%. In developing the procedures, the potentialities of the proposed technique were assessed and its metrological characteristics were determined.     

Fluorescence properties of the Zimmermann chromogen: Paper chromatography of ketosteroids

Summary This investigation was prompted by the observation that formation of the Zimmermann chromogen of 17-ketosteroids on paper chromatograms using the Epstein and Zak method, gave products which were not only colored but also fluorescent. The Zimmermann chromogen of dehydroepiandrosterone (DHA) was prepared. It showed no observable fluorescence in solution, weak fluorescence in the solid state and on thin layers of silica gel, but strong fluorescence in the dry state on filter paper. Other 17-ketosteroids behaved similarly on chromotograms, as did 3,20-diketopregnanes. Saturated and unsaturated 3-ketosteroids gave no fluorescence. These experiments lend support to the theory that fluorescence is sometimes induced by occlusion of potential fluorophors in the dry matrix of cellulose.

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Zusammenfassung Diese Untersuchung wurde durch die Beobachtung angeregt, daß bei der Bildung des Zimmermann-Chromogens aus 17-Ketosteroiden auf Papierchromatogrammen nach der Methode vonEpstein undZak Produkte entstehen, die nicht nur gefärbt sind, sondern außerdem auch fluoreszieren. Das Zimmermann-Chromogen des Dehydroepiandrosterons (DHA) wurde präpariert. Dieses fluoreszierte in Lösung nicht merkbar, in festem Zustand und in Dünnschichten auf Kieselgel nur schwach, jedoch stark in trockenem Zustand auf Filterpapier. Andere 17-Ketosteroide verhalten sich auf Chromatogrammen ähnlich wie 3,20-Diketopregnane. Gesättigte und ungesättigte 3-Ketosteroide zeigen keine Fluoreszenz. Diese Befunde stützen die Theorie, daß Fluoreszenz manchmal durch Einschluß potentieller Fluorophore in die trockene Zellulosematrix induziert wird.

     

Basicity and mechanism of transmission of electronic effects of substituents in the series of 2-amino-5-aryl-1,3,4-thiadiazoles

The basicity of 2-amino-5-aryl-1,3,4-thiadiazoles was studied. A correlation was obtained between the pK_BH+ values of the compounds and the constants of the substituents. It was shown that the electronic effects of the substituents in the phenyl ring are transmitted both on account of conjugation and by an induction mechanism.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 267–270, February, 1987.     

Detection of cyanide via extended π-conjugation-induced fluorescence enhancement of a metal organic framework composed of terbium(III), bipyridyl and adenosine diphosphate

A metal-organic framework (MOF) was designed and prepared from luminescent Tb(III), adenosine diphosphate (ADP) and bipyridyl (Bipy). Its green fluorescence at 545 nm is shown to enable the fluorometric detection of cyanide ion based on the principle of π-conjugation-induced fluorescence enhancement. The fluorescence of the probe is strongly increased by cyanide due to extended π-conjugation between probe MOF and cyanide which sensitizes the fluorescence of Tb(III). This effect can be used to quantify cyanide at levels as low as 30 nM in aqueous solution. The method was applied to the determination of cyanide in saliva samples. The lack of interference by acetate and fluoride is a specific feature of this method. The method based on the principle of π-conjugation-induced fluorescence enhancement provides a new sensing way for widely used fluorescence assays.

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Graphical abstract A cyanide-selective Tb-ADP-Bipy MOF was designed and synthesized for the detection of cyanide based on the principle of π-conjugation-induced fluorescence enhancement.

     

Bimetallic nanoclusters with strong red fluorescence for sensitive detection of hypochlorite in tap water

Gold-silver nanoclusters (Au-AgNCs) were synthesized by simultaneous chemical reduction of Au(III) and Ag(I) ions in one pot, using bovine serum albumin as both a template and a reductant. The Au-AgNCs have an average size of 2.4 nm and display strong red fluorescence (with an emission peak at 610 nm on excitation at 360 nm). The fluorescence quantum yield can reach 18.6%. Fluorescence is strongly quenched by hypochlorite, while other common anions have minor (or no) effects on fluorescence. Based on these findings, a fluorometric method was developed for the determination of hypochlorite. The method has a linear response in the 0.7 to 15 μM concentration range, with a limit of detection as low as 80 nM. It was successfully applied to the determination of hypochlorite in (spiked) tap water.

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Graphical abstract Gold-silver nanoclusters with strong red fluorescence were synthesized by simultaneous chemical reduction of Au(III) and Ag(I) ions in one pot, and a sensitive and selective method for the detection of hypochlorite was developed based on the quenching of the fluorescence of the nanoclusters.

     

Excitation energy dependence of the quantum yields of fluorescence and electron formation from aqueous phenol by means of the heavy atom effect

The formation of hydrated electrons and H atoms from phenol in neutral aqueous solutions has been studied by excitation in its first and second excited singlet state. The quantum yields of both H and

show a strong increase at higher excitation energies. However, this increase cannot fully account for the corresponding decrease of the fluorescence quantum yield. Using Cs⁺ as a heavy atom quencher, it could be shown that there are at least two pathways for electron formation, one in competition to internal conversion to the fluorescing state and another occurring after population of the fluorescing state, but most likely not from the triplet state.     

Fabrication of Patterned Images in Photochromic Organic Microfibers

Photochromic spiropyran molecules were embedded in electrospun polymer microfibers. Electrospinning of a clear viscous chloroform solution containing a spiropyran and a matrix polymer, such as polystyrene and polyethylene oxide, affords polymer microfibers that are photoswitchable. Photomasked, 365 nm UV irradiation of the microfibers results in the generation of patterned color images owing to the selective transformation of the spiropyran molecules from their ring‐closed SP to ring‐opened MC form. The UV‐irradiated areas display brilliant red fluorescence, which changes to green fluorescence upon prolonged irradiation.

     

Investigation of NH-tautomerism of alkyl derivatives of porphine by means of low-temperature selective excitation spectroscopy

In isotropic media at 4.2°K with selective laser excitation, fine-structure fluorescence spectra have been obtained for NH-tautomers of 2,3,12,13-tetramethylporphine (TMP) and their derivatives in which the central protons have been replaced by deuterons. For each of the phototautomers, polarization measurements have been made for individual background-free lines, and the symmetry of the normal vibrations has been determined. From an analysis of the experimental data and the results obtained in calculating the normal vibrations of the 2,3,12,13-TPM molecule with various possible positions of the imine protons, it has been shown that the phototautomer with fluorescence in the shorter-wave region corresponds to location of the central protons on the pyrrole rings with methyl substituents, and the tautomer with fluorescence in the longer-wave region corresponds to location of the protons on the porphine pyrrole rings. For porphine 2,3,12,13-TMP, and also for 2,3,7,8-TMP and 2,3,7,8-TEP, no phototautomers with adjacent positions of the NH-protons were detected.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 554–560, September–October, 1985.     

Fabrication and Characterization of Sol-Gel GeO2-SiO2Erbium-Doped Planar Waveguides

GeO2-SiO2 sol-gel planar waveguides doped with Er were deposited by spinning on silica substrates. P2 O5 or Al2O3 were used as co-dopants to improve erbium dissolution in the GeO2-SiO2 matrix. Multilayer amorphous films were obtained at 600 or 700°C.Er ions in the planar waveguide pumped at 980 nm showed fluorescence features around 1530 nm. Narrow fluorescence spectra (20 nm) and long lifetimes (6 ms) were found in P2O5 co-doped samples, whereas Al2O3 co-doping gave wider spectra (50 nm) with slightly lower lifetimes (5 ms). The quenching concentration in the Al2O3 co-doped samples was 0.9 mol% Er.Heat treatments in CCl4 improve the active properties and the addition of Yb enhances the pump absorption efficiency.     

Fluorimetric determination of bromate by ion-exchange separation and post-column derivatization

For the determination of bromate in drinking water a stopped-flow post-column reaction was developed following the separation of bromate from the matrix by an anion-exchange column. In the post-column reaction the analyte was used to oxidize the azo dye sulfonaphtholazoresorcinol, SNAR, and the residual amount was converted into a fluorescent binuclear complex by an excess of gallium ions. The fluorescence was monitored at 585 nm, with a maximum excitation wavelength at 521 nm. The determination of bromate is based on the decrease of the fluorescence intensity with increasing bromate concentration. The given hydrodynamic parameters and the condition of equal flow rates of the two branch streams at each T-piece have to be considered as an important criterion for the experimental set-up. The volume flows and the concentrations required for the reagent solutions in the influent of each T-piece were determined as a result of batch experiments and theoretical considerations. The limit of detection was 0.28 g L^–1bromate for the flow method, which shows linearity up to 15 gL^–1 bromate.     

Preparation of brightly fluorescent silica nanoparticles modified with lucigenin and chitosan,and their application to an aptamer-based sandwich assay for thrombin

We report on the preparation of fluorescent silica nanoparticles (SiNPs) modified with chitosan and lucigenin by using a reverse microemulsion method. The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. In this protocol, thrombin was sandwiched between streptavidin-coated magnetic beads and the fluorescent SiNPs modified with a thrombin-binding aptamer. The method was successfully applied to the determination of thrombin in human serum and showed a detection limit as low as 0.02 nM. In our perception, the protocol presented here is promising in that such SiNPs may be applied to the sensitive fluorescent detection of other analytes by changing the corresponding aptamer.

The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. The effect of chitosan concentration on fluorescence intensity of lucigenin/SiO₂ nanoparticles (the volume of chitosan solution is 100 μL)

     

On a possible excited state proton transfer in N-formylkynurenine derivatives

It is shown that intramolecular hydrogen bonding between the

and the ortho carbonyl on the side chain of N'formylkynurenine and some parent compounds plays an important role on their spectroscopic properties. The fluorescence emissionλ_max is shifted by about 4000 cm^?1 in going from polar to non-polar solvents. This abnormally red-shifted fluorescence is attributed to an excited state proton transfer from the formamido to the ortho carbonyl of the side chain.