Extractive spectrophotometric determination of niobium(V) using 3-hydroxyflavone

A simple, rapid method for the spectrophotometric determination of niobium in trace amounts is presented, employing 3-hydroxyflavone as a ligand for the complexation of the metal ion and extracting the coloured complex into chloroform from 4M HClO₄ solution. Beer's law is obeyed in the range 0.0 to 3.2 g ml^–1 Nb(V), with a lower working limit of 0.1 g ml^–1 Nb(V). Molar absorptivity and Sandell's sensitivity of the complex at 395 nm are 4.088 × 10⁴l mol^–1 cm^–1 and 0.002g Nb(V) cm^–2, respectively. The stoichiometry of the complex is established as 12 by Job's and mole ratio methods. The method is free from the interference of a large number of analytically important elements. The proposed system handles satisfactorily the analysis of several samples of varying complexity. The results are highly reproducible with a relative standard deviation of 0.34% for 20 g of Nb.     

Electroconductivity of Potassium Orthophosphate Modified by Four-Charged Cations

Solid solutions based on K₃PO₄ in systems K_{3 – 4x} E" _x PO₄ (E" = Si, Ti, Ge, Zr, Sn, Hf, Ce) are synthesized. The crystal structure, thermal behavior, and electroconduction of the synthesized solutions is studied. The narrowest single-phase regions take place in the systems where E" = Si, Ge (x 0.025), and the widest, in the system with Zr (x 0.125, at 700°C). Introducing Ti or Sn additives (x 0.05) and minimum quantities of Zr, Hf, or Ce (x = 0.025) into potassium orthophosphate leads to stabilization of highly-conductive -modification of K₃PO₄ at room temperature. Maximum values of potassium-cation conduction in all the systems studied correspond to regions of single-phase solid solutions based on K₃PO₄. The maximum electroconductivity (0.005 S cm^–1 at 300°C, 0.1 S cm^–1 at 700°C) and the smallest activation energies (32–35 kJ mol^–1) take place in the systems with Zr and Hf.     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.     

Application of the extended geminal theory to the BH molecule

Extended geminal theory is applied to the ground state of BH at R=2.329 bohr. It is found that the inclusion of only one-electron transfer configurations leads to a lowering in the energy of 0.01 hartree, compared to the antisymmetrized geminal product wavefunction. This improvement is >90% of that achieved by a full configuration-interaction wavefunction. A contracted doublezeta basis set is also found to be quite good.

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Zusammenfassung Die erweiterte Geminaltheorie wird auf den Grundzustand des BH für R=2,329 Bohr angewendet. Es wird gefunden, da der Einschlu von nur Ein-Elektron-Transfer-Konfigurationen zu einer Energieerniedrigung von 0,01 Hartree, verglichen mit der antisymmetrisierten Geminal-Produkt-Wellenfunktion, führt. Diese Verbesserung beträgt mehr als 90% gegenüber dem Wert, der mit einer vollen CI-Funktion erreicht wird. Ein kontrahierter doppelt-zeta-Basis-Satz liefert ebenfalls gute Ergebnisse.

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Résumé La théorie des géminales généralisée est appliquée à l'état fondamental de BH pour R=2,329 bohr. On trouve que l'introduction des seules configurations à «un transfert d'électron» conduit à un abaissement de l'énergie de 0,01 hartree, par rapport à celle correspondant à un simple produit antisymmétrisé de géminales. Cette amélioration est supérieure à 90% de celle obtenue par I.C. complète. Une base double zèta «contractée» s'avère aussi fort bonne.

     

Energy Transfer Electrogenerated Chemiluminescence for the Determination of Sulfite

A simple and novel electrogenerated chemiluminescence (ECL) method for the determination of sulfite has been developed based on the energy transfer ECL process. It was found that a weak ECL signal of sulfite was electrochemically generated on a platinum electrode in neutral aqueous solution. The signal was strongly enhanced by rhodamine B as an energy receptor and further enhanced by the neutral surfactant Tween 80. In 0.10M phosphate buffer solution (pH=7.5) containing 2.0×10^–6gmL^–1 rhodamine B and 0.4% (v/v) Tween 80, the ECL response to the concentration of sulfite at a potential of 0.82V was linear over a range of 1.0×10^–7gmL^–1 to 8.0×10^–6gmL^–1, and the detection limit was 5×10^–8gmL^–1. The relative standard deviation (n=11, 1.0×10^–6gmL^–1) was 3.8%. The proposed method has been successfully applied to the determination of sulfite in pharmaceutical injections and white sugar samples.     

Synergetic effect of silver and molybdenum (VI) oxide additives in vanadia catalysts for the selective oxidation of benzene

It has been shown that the selectivity of V₂O₅–MoO₃ catalysts for benzene oxidation to maleic anhydride can be enhanced by small amounts of silver introduced by impregnation with AgNO₃ solution. The effect of Ag₂O additive is synergetic and increases with increasing concentration of MoO₃ up to 28.5 mol %. The best effect was obtained when about 7 Ag atoms were introduced for 1000 (V+Mo) atoms at the surface.

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, V₂O₅–MoO₃ - AgNO₃. Ag₂O MoO₃ 28,5 . %. , 7 Ag 1000 (V+Mo).

     

Fluorimetric Determination of Europium Based on the Co-Fluorescence System Eu-Y-Sparfloxacin-SDS

A new room temperature fluorescence enhancement system based on complex formation between europium and sparfloxacin in the presence of yttrium in sodium dodecyl sulfate micelle solution has been discovered. The characteristic fluorescence spectra and the effect factors of the fluorescence intensity of the system have been studied in detail. The study results show that the binary complex formed by europium with sparfloxacin in sodium dodecyl sulfate micelle solution can emit intrinsic fluorescence of the lanthanide ion. In the presence of yttrium, the fluorescence intensity of this system was enhanced about 5-fold compared with that of the system without Y³⁺. Under the optimum conditions selected, the fluorescence intensity is a linear function of the concentration of europium in the range of 5.0×10^–11–5.0×10^–7molL^–1, and the detection limit of europium is 1.0×10^–13molL^–1. The system was used for the determination of trace amounts of europium in rare earth samples with satisfactory results.     

Electrochemical Behavior of Epinephrine at a Penicillamine Self-Assembled Gold Electrode,and its Analytical Application

The fabrication and electrochemical characteristics of a penicillamine (PCA) self-assembled monolayer modified gold electrode were investigated. The self-assembled electrode shows obvious electrocatalytic activity for the oxidation of epinephrine (EP). In phosphate buffer (pH 7.73), a sensitive oxidation peak was observed at 0.190V with the PCA modified Au electrode. The peak current is proportional to the concentration of EP in the range of 2.0×10^–56.0×10^–4molL^–1 and 5.0×10^–6 2.0×10^–4molL^–1 for cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with the detection limits of 1.8×10^–7 and 1.3×10^–7molL^–1, respectively. The possible reaction mechanism is also discussed. The PCA self-assembled monolayer modified gold electrode is highly stable and can be applied to the determination of EP in practical injection samples. Application is simple, rapid and produces accurate results.     

Triterpene glycosides ofHedera taurica XIV. Structures of glycosides St-G0–2, St-J, and St-K from the stems of Crimean ivy

The structures of new triterpene glycosides isolated from the stems of Crimean ivyHedera taurica Carr. (fam. Araliaceae) — St-J, St-K, and St-G_0–2 — have been established as the 3-0--L-glucopyranuronoside 28-O-[O-L-rhamnopyranosyl-(14)-O--D-glucopyranosyl-(16)--D-glucopyranoside]s of oleanolic acid and of hederagenin and the 3–0(6-O-ethyl--D-glucopyranuronoside) 28-O-[O-L-rhamnopyranosyl0(14)-O--D-glucopyranosyl-(16)-glucopyranoside of hederagenin, respectively.Simferopol' State University. Translated from Khimiya Prirodnykh Soedinenii No. 3, pp. 397–403, May–June, 1997.     

Electrochemical Determination of Ascorbic Acid at γ-MnO<Subscript>2</Subscript> Modified Carbon Black Microelectrodes

A carbon black microelectrode modified by -MnO₂ has been prepared. The electrocatalytical oxidation of ascorbic acid (AA) at this microelectrode was investigated. The 2nd-order linear scan voltammograms of AA are recorded from –0.5 to 0.5V (vs. SCE). The relationship between the oxidation peak current of AA and its concentration in the range of 1.0×10^–64.0×10^–3molL^–1 is linear. The detection limit (3) was found to be 6.0×10^–7molL^–1. Also, the determination of AA in samples is evaluated, and the results are satisfactory.     

Saure Hydrolyse von 2-(4-Chlorphenylazo)-2-(N-carbamidino-ureido)-propan

Zusammenfassung Die saure Hydrolyse der Arylazo-Verbindung1 wird beschrieben und interpretiert: Als Zwischenprodukte werden ungeladenes Aryldiazen (Ar–N=N–H) sowie zwitterionisches Aryldiazen (Ar–NH⁺=N:^–)und im weiteren Verlauf des Reaktionsgeschehens 1,4-Diaryltetrazenimionen postuliert.

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Acid hydrolysis of 2-(4-Chlorophenylazo)-2-(N-carbamidinoureido)-propane

Acid hydrolysis of the arylazo compound1 is described and discussed. As reaction intermediates uncharged aryldiazene (Ar–N=N–H) as well as zwitterionic aryldiazene (Ar–NH⁺=N:^–) and subsequently 1.4-diaryltetrazenium ions are postulated.

     

Application of Functionalized Ag Nanoparticles for the Determination of Proteins at Nanogram Levels Using the Resonance Light Scattering Method

A novel method for the determination of proteins in aqueous solutions has been developed based on the enhancement of resonance light scattering (RLS) of Ag nanoparticles in the presence of proteins. Factors including acidity of the media, concentration of Ag hydrosol, reaction time, temperature, and interference of non-protein substances were investigated. Under the optimal conditions, with the enhanced RLS signals at 452nm, the linear ranges of calibration curves were 0–0.8µgmL^–1 for bovine serum albumin (BSA), 0–1.2µgmL^–1 for human serum albumin (HSA), and 0–2.5µgmL^–1 for human -IgG (-IgG), respectively. The detection limits were 1.3ngmL^–1 for BSA, 10ngmL^–1 for HAS, and 5.7ngmL^–1 for -IgG.This method has been applied to the analysis of synthetic samples and real human serum samples, and the results were in good agreement with those reported by the hospital, indicating that the method presented here is not only sensitive and simple, but also reliable and suitable for practical applications.     

Selective Solid Phase Extraction and Pre-Concentration of Heavy Metals from Seawater by Physically and Chemically Immobilized 4-Amino-3-Hydroxy-2-(2-Chlorobenzene)-Azo-1-Naphthalene Sulfonic Acid Silica Gel

4-Amino-3-hydroxy-2-(2-chlorobenzene)-azo-1-naphthalene sulfonic acid (AHCANSA) was used as a chelating modifier to improve the reactivity of the silica gel surface in terms of selective binding and extraction of heavy metal ions. The surface coverage values were found to be 0.488 and 0.473mmolg^–1 for the newly modified physically adsorbed silica gel phase (I) and chemically immobilized-AHCANSA phase (II), respectively. The modified silica gel phases (I, II) were tested for stability in different acidic buffer solutions (pH 1–6) and found to be highly resistant to hydrolysis and leaching by buffer solutions above pH 2. The application of these two phases as solid extractors for a series of mono-, di-, and tri-valent metal ions from aqueous solutions was also performed with different controlling factors such as the pH value of metal ion solutions and equilibrium shaking time. The mmolg^–1 metal capacity values determined by silica gel phases (I, II) were found to confirm high affinity and selectivity characters for binding with heavy metal ions such as Cr³⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ in a range of 0.250–0.483. The tested alkali and alkaline earth metals, Na⁺, K⁺, Mg²⁺ and Ca²⁺, were found to exhibit little interaction and binding ability with the modified silica gel phases. The selectivity characters incorporated into the modified silica gel phases were further utilized and applied in solid phase extraction and pre-concentration of trace concentration levels (1.0µgmL^–1 and 2.00–2.50ngmL^–1) from real seawater samples. The percentage recovery values determined for Cr³⁺, Cu²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were found to be in the range of 95.2–98.1±2.0–5.0%, and the pre-concentration recovery values for the same tested heavy metal ions were found to be in the range of 92.5–97.1±3.0–6.0% for the two newly modified silica gel phases with a pre-concentration factor of 500.Received December 20, 2002; accepted May 14, 2003 published online September 1, 2003     

A Highly Sensitive and Selective Assay for Cysteine Using the Chemiluminescence Reaction of Luminol and Hydrogen Peroxide

A very simple, highly sensitive and selective chemiluminescence (CL) method was established for the determination of cysteine. This method is based on the fact that the CL reaction of luminol and hydrogen peroxide can be greatly enhanced by cysteine. The CL intensities at maximum light emission were linearly correlated with the concentration of cysteine over the range of 2.0×10^–8–6.0×10^–6molL^–1 with a detection limit of 7.5×10^–9molL^–1. The relative standard deviation was 1.7% for the determination of 1.0×10^–7molL^–1 cysteine (n=9). The feasibility of utilizing the proposed method for the determination of total concentration of cysteine in human serum was examined.     

Triterpene glycosides of alfalfa VIII. Medinoside E from the leaves

From the leaves ofMedicago sativa L. (Leguminosae) we have isolated the glycoside soyasapogenol B — medinoside E. Medinoside E has the structure of olean-12-ene-3,22,24-triol 3-O-[O--L-rhamnopyranosyl-(12)-O--D-galactopyranosyl-(12)-O--D-glucopyranosyl-(12)--D-glucopyranuronoside].Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan Tashkent. Institute of Organic Chemistry, Russian Academy of Sciences, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 705–710, September–October, 1993.     

Kinetic Determination of Microquantities of Rutin by Perturbation of the Bray-Liebhafsky Oscillatory Reaction in an Open System

A kinetic method is described for the microquantitative (microconcentration/microvolume) determination of rutin based on potentiometric monitoring of the concentration perturbations of the Bray-Liebhafsky (BL) oscillatory reaction being in a non-equilibrium stationary state close to a bifurcation point. The experiments are carried out in an open reactor. The response of the matrix system to perturbations by different concentrations of rutin ethanolic solutions is followed by a Pt-electrode. In the concentration range between 7.8×10^–8moldm^–3 and 9.1×10^–6mol dm^–3, we found a linear dependence of the maximal potential shift, E_m, on the logarithm of the rutin concentrations. The unknown concentrations can be determined from the calibration curve up to an accuracy of ±5%. The detection limit is 3.6×10^–8mol dm^–3. The amount of required sample can be as small as 10µL.     

Fluorescence Quenching Studies of Curcumin by Hydrogen Peroxide in Acetonitrile Solution

Summary. Steady state quenching studies of curcumin, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, fluorescence by hydrogen peroxide were conducted in acetonitrile solution. A quenching rate constant, k_q, of 1.05×10¹⁰M^–1·s^–1 was obtained with a short fluorescence lifetime of 347ps. The reaction rate constant, which is within the diffusion-limited regime, is activation-controlled. The rate constant of deactivation of the thermally excited curcumin was 1.2 orders of magnitude more nonradiative (2.67×10⁹s^–1) than radiative (2.16×10⁸s^–1). The reaction was exothermic with a G° of –1.97eV and solvent reorganization energy of 1.37eV. These values indicate that the electron transfer reaction is solvent-mediated with electron transfer rate constant, k_ET, of 2.16×10¹⁰s^–1.     

Application of L-Cysteine-Capped ZnS Nanoparticles in the Determination of Nucleic Acids Using the Resonance Light Scattering Method

Nanometer-sized L-cysteine-capped ZnS particles were synthesized by a colloidal aqueous method. The functionalized nanoparticles are water-soluble and suitable for biological applications. In Tris-HCl buffer solution, nucleic acids combine with cysteine-capped nano-ZnS particles by intermolecular forces to form larger nanoparticles. There are two resonance light scattering peaks at 304.5nm and 373.8nm, respectively. The enhanced RLS is related to the concentration of nucleic acids in the range of 0.04 to 1.2µgmL^–1 for calf thymus DNA and 0.2 to 1.0µgmL^–1 for fish sperm DNA. The detection limits (3) are 19ngmL^–1 for calf thymus DNA and 23ngmL^–1 for fish sperm DNA, respectively. Four synthetic samples were analyzed satisfactorily.