Structure and stability of ion pairs A−·K+·H2O with a strong anion

Characteristics of the ion pairs HCOO^–·Na⁺·H₂O, HCOO^–·K⁺·H₂O, and also Na⁺·H₂O and K⁺·H₂O were calculated by the nonempirical Hartree—Fock—Roothan linear-combination-of-atomic-orbitals self-consistent-field (SCF) molecular-orbital method in a two-exponent Dunning basis using an extended set of Huzinaga—Dunning Gaussian functions. The basis was supplemented by polarization functions ofd type for the oxygen atom andp type for the H atom and also by diffusion functions ofp type for the oxygen atom. Characteristics of the ion pairs HCOO^–·Li⁺ and HCOO^–·Na⁺ were calculated taking into account the electronic correlation according to the Möller — Plesset second-order perturbation theory. Significant quantitative difference was observed in the hydration of ionogens and free cations. The stability of the ionogens HCOOMe in aqueous solutions, increasing from Li⁺ to Cs⁺, is not explained by the difference between the energies of complexation and the energies of hydration of the cations. The better solubility of the salt molecule with a cation of smaller radius is due to the higher degree of hydration of that ionogen.N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2700–2707, December, 1992.     

Eine verbesserte fluorimetrische Bestimmung des Glycerid-Glycerins

Zusammenfassung Glycerid-Glycerin gibt bei der Oxydation mit Perjodat Formaldehyd, der sich fluorimetrisch als 3,5-Diacetyl-1,4-dihydrolutidin bestimmen läßt. Überschüssiges Perjodat liefert hohe Blankwerte. Durch Reduktion mit KJ/Na₂S₂O₃ oder Rhamnose wird die Blankfluoreszenz verringert. Rhamnose beeinflußt im Gegensatz zum Thiosulfat die Fluoreszenz des gebildeten 3,5-Diacetyl-1,4-dihydrolutidins nicht. Der Bestimmungsbereich beträgt 3·10^–10 —3·10^–8 Mol Glycerin.

---

An improved fluorimetric determination of glycerid-glycerol

Summary Oxidation of glycerid-glycerol with periodate results in liberation of formaldehyde, which is detected fluorimetrically as 3,5-diacetyl-1,4-dihydrolutidine. Excess of periodate gives high blank values. This fluorescence is reduced through KI/Na₂S₂O₃ or rhamnose. In contrast to sodium thiosulfate rhamnose shows no effect on the 3,5-diacetyl-1,4-dihydrolutidine formed. The method here described permits determination of glycerol within a range of 3·10^–10—3·10^–8mol.

     

Field-evaporation mass spectroscopy applied to crown ether complexes with alkali and alkaline-earth metals

Field evaporation from solution has been used to detect crown-ether 15K5 and 18K6 coordination compounds formed with Na⁺, K⁺, Cs⁺, Ba²⁺ and Ca²⁺ in aqueous solution, both hydrated and unhydrated; the Ca²⁺·18K6·(H₂O)_n (n=0, 1, 2,...) compounds have been observed before. 18K6 present in the solution greatly increases the yields of 18K6 compounds with the dissociation products from Ba(NO₃)₂. The detection limits for 15K5 and 18K6 combined with Na⁺, K⁺, and Cs⁺ are approximately the same at 10^–7 g.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 239–242, March–April 1988.     

121Sb,123Sb AND209Bi NQR spectra of antimony(III) and bismuth(III) ethylenediaminetetraacetate compounds

A¹²¹Sb,¹²³Sb, and²⁰⁹Bi NQR spectral study was carried out on SbHEDTA·nH₂O, BiHEDTA·nH₂O(n=2, 0), MBiEDTA·H₂O, M₂Bi(OH)EDTA·nH₂O (n=3,1, M=K,NH₄), and K₂BiFEDTA·3H₂ O. Piezoelectric properties were found in MHEDTA·2H₂O (M=Sb,Bi) and SbHEDTA. The temperature range of the piezoelectric phase for SbHEDTA was found to be 100–270 K.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1915–1918, August, 1989.     

Synthesis and study of binuclear vanadyl complexes with acyldihydrazones of salicylaldehyde and dicarboxylic acids

The binuclear vanadyl(ii) complexes [(VO)₂·2Py·2EtOH]·mH₂O with acyldihydrazones of salicylaldehyde (H₄L) and dicarboxylic acids were synthesized and studied. In these complexes, two chelate vanadyl(ii) complexes with the tridentate bicyclic ligands are linked to each other by the polymethylene bridges —(CH₂) _n — of different lengths varying from one to four units. The ESR spectra of solutions of these complexes, unlike those of analogous copper(ii) complexes, have an isotropic signal with an eight-line hyperfine structure (g = 1.972, a _V = 93·10^–4 cm^–1) typical of monomeric vanadyl complexes, which indicates that no exchange interactions occur between the paramagnetic centers through the polymethylene chain.     

ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated -diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu₂L·2Py (H₄L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, a _Cu = (39—40)·10^–4 cm^–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the -bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, a _Cu = (55—63)·10^–4 cm^–1) typical of mononuclear copper complexes.     

Sulfurization of polymers. 6. Poly(vinylene polysulfide), poly(thienothiophene), and related structures from polyacetylene and elemental sulfur

Polyacetylene obtained by the dehydrochlorination of polyvinyl chloride in the NaOH—DMSO system undergoes sulfurization with elemental sulfur at 120—300 °C to liberate hydrogen sulfide and to form electroconducting (0.7·10^–12—5.8·10^–15Sm nm^–1) and paramagnetic (1.5·10¹⁷—1.7·10¹⁹sp g^–1, g = 2.0035—2.0045, H= 0.44—0.66 mT) dark powders with a metallic luster. Their IR spectra and comparison with the samples of sulfurized polyethylene show that sulfurized polyacetylene contains poly(vinylene polysulfide), poly(thienothiophene), and related structures. The polymers afford the cathode discharge capacity of lithium batteries up to 950 mA h g^–1(in the first cycle) and stable cycling at a level of 500—300 mA h g^–1(25 cycles).     

The N—H and O—H bond dissociation energies in 4-hydroxydiphenylamine and its phenoxyl and aminyl radicals

The N—H and O—H bond dissociation energies in 4-hydroxydiphenylamine Ph—NH—C₆H₄—OH (D _NH= 353.4, D _OH=339.3 kJ mol^–1) and its semiquinone radicals D _NH(Ph—NH—C₆H₄—O^·) = 273.6, D _OH(Ph—N^·—C₆H₄—OH) = 259.5 kJ mol^–1 were first estimated using the parabolic model and experimental data (rate constants) on two elementary reactions with participation of N-phenyl-1,4-benzoquinonemonoimine (2). One of the reactions, namely, that of 2 with aromatic amines, was studied in this work using a specially developed method.     

Der Einfluß großer Salzkonzentrationen auf die Oxydationsreaktion von Fe(phen) 3 2+ mit Ce(IV) in Schwefelsäure

The influence of NaClO₄, NaCl and Na₂SO₄ on the oxidation of Fe(phen) ₃ ²⁺ by Ce(IV) was investigated by means of the stopped-flow method. At the concentrations range of NaClO₄ and NaCl 0.1–1.0M the rate constant values decrease from 1.03·10⁵ to 0.56·10⁵M^–1s^–1 and from 1.08·10⁵ to 0.81·10⁵M^–1s^–1 respectively.In varying concentrations of Na₂SO₄ solutions (0.05–0.35M) the rate constant values decrease from 1.05·10⁵M^–1s^–1 to 0.45·10⁵M^–1s^–1.Taking into account the negative salt effect the mechanism of the reaction progress is proposed.

     

Sulfurization of polymers. 5. Poly(6-methyl-5-sulfanylthieno[2,3-b]pyridine-4-thione), poly(thieno[2,3-b]azepine-4,5(6H)-dithione), and related structures from poly(2-methyl-5-vinylpyridine) and elemental sulfur

Poly(2-methyl-5-vinylpyridine) is sulfurized with elemental sulfur at 140—320 °C to release hydrogen sulfide and to give black lustrous powders (sulfur content up to 45%) possessing electric conductivity (6.4·10^–11—1.6·10^–7 S cm^–1), paramagnetism (spin concentration 6.2·10¹⁸—5.0·10¹⁹ sp g^–1, g = 2.0043—2.0046, H = 0.49—0.58 mT), and redox and complex-forming properties. Elemental analysis data, IR, ESR, and mass spectra, DSC and TGA data, electric conductivity, electrochemical activity and chemical properties (salt formation and complexation) of the materials synthesized correspond to cross-liked poly(6-methyl-5-sulfanylthieno[2,3-b]pyridine-4-thione), poly(thieno[2,3-b]azepine-4,5(6H)-dithione), and related structures.     

Microwave-assisted water extraction of acid herbicides from soils coupled to continuous filtration, pre-concentration, chromatographic separation and UV detection

A microwave-assisted extraction procedure using water as extractant has been performed for the extraction of acid herbicides (namely, bentazone, 2,4-D, trichlopyr, 2,4,5-T and 2,4,5-Tp) from different types of soil. Two experimental designs were used for the optimization of the leaching step. The selection of water as extractant provided a clean approach by avoiding the use of organic solvents. The use of water also enhanced the extraction efficiency due to the high interaction of the microwave irradiation with polar solvents. The time required for total removal of the target compounds was 35 min. The recoveries yield were from 87.64 to 106.14% with a repeatability (expressed as relative standard deviation) ranging between 1.34 and 9.24%. A within-laboratory reproducibility, also expressed as relative standard deviation, varied from 3.97 to 10.41%. A flow-injection manifold allowed automation of the whole process by hyphenating the steps subsequent to extraction (namely, filtration, preconcentration, chromatographic separation and UV detection) for the determination of the analytes.     

Corrosion of simulated nuclear waste glass

Glasses are suitable host matrices for the immobilization of high-level radioactive wastes. The corrosion behaviour of nuclear waste glass in water is of considerable importance, since a potential route for returning of radionuclides to the biosphere is their leaching from the waste form into groundwater and subsequent transport by the groundwater to the surface. In this study, the preparation and characterization of borosilicate glasses of different chemical composition were investigated. Borosilicate glasses were doped with simulated nuclear waste oxides. The chemical corrosion in water of these glasses was followed by measuring the leach rates (g·cm^–2·day^–1), as a function of time. It was found that a simulated nuclear waste glass with the chemical composition (weight %), 15.61% Na₂O, 10.39% B₂O₃, 45.31% SiO₂, 13.42% ZnO, 6.61% TiO₂ and 8.66% waste oxides, is characterized by low melting temperature and with good corrosion resistance in water. Influence of passive layers on the leaching behaviour of nuclear waste glasses is discussed.     

A study of HPLC separation and spectrophotometric, polarographic and voltammetric detection of 4-substituted derivatives of N-nitroso-N-methylaniline

Optimised conditions have been found for the separation of N-nitroso-N-methylaniline derivatives substituted in the position 4 (4-R-NMA, where R =- H,- CH₃, - OCH₃, - Cl, - CN, - OH and - NO₂), using reversed phase HPLC with a C18 chemically bonded stationary phase. Suitable mobile phases are mixtures of aqueous 0.01 mol l^–1 KH₂PO₄ with methanol (4+6) or acetonitrile (7+3), or a mixture of water, methanol, acetonitrile and 80% H₃PO₄ (200+200+200+3). Four detection techniques have been investigated: Direct UV photometry, polarography on a hanging mercury drop electrode, anodic voltammetry on a glassy carbon fibre array electrode and indirect anodic voltammetric detection after photolytic denitrosation of the analytes. The UV photometry is the most universal and yields limits of detection around 10^–6 mol l^–1. Polarography exhibits the poorest sensitivity (with a limit of detection of ca. 10^–5 mol l^–1) but it can be used for selective detection of 4-NO₂-NMA. Direct voltammetric detection is selective for the oxidizable derivatives and the limits of detection attained are lower than those obtained by UV photometry (for 4-OH-NMA) or comparable with (for 4-OCH₃-NMA). When the analytes are photolytically denitrosated to yield oxidizable derivatives, the voltammetric detection of 4-H-NMA, 4-Cl-NMA, 4-CH₃-NMA and 4-NO₂-NMA has limits of detection one order of magnitude lower than those obtained UV photometrically.     

Factors affecting interaction of radiostrontium with river sediments

Uptake of radiostrontium by sediments from two small streams was studied as a function of pH and composition of aqueous phase, of the concentration of strontium, of contact time, temperature and liquid-to-solid ratio (V/m), using laboratory model experiments. Between pH 5 and 12 the uptake increased with pH and shifted to higher pH values with increasing V/m ratio. Addition of cations suppressed the uptake in the order Na⁺<K⁺<Ca²⁺. Increase in strontium concentration had negligible effect up to 10^–5–10^–4 mol·dm^–3 concentration due to high concentrations of dissolved and exchangeable strontium present in the systems. The V/m ratio had no influence on K_d in the range of V/m=20–446 cm³ · g^–1 but K_d value for V/m=0.79 cm³ · g^–1 was significantly lower. Two-step kinetics of the uptake was observed in most cases with a rapid first step (<100 min) followed by a slow increase. No difference was found between the uptake at 10°C and 22°C. Adsorbed radiostrontium could be easily desorbed with river water. The easiness of desorption decreased with repeated desorption. Drying of sediment did not affect the first desorption, repeated desorptions slightly decreased. Conclusions were drawn on the mechanism of radiostrontium uptake and on the importance of the factors studied for modelling of radiostrontium migration in rivers.     

Determination of organotin compounds in biological samples using accelerated solvent extraction,sodium tetraethylborate ethylation,and multicapillary gas chromatography–flame photometric detection

A method has been developed for species-selective analysis of organotin compounds in solid, biological samples. The procedure is based on accelerated solvent extraction (ASE) of analytes and includes extraction of the tin species with a methanol–water (90% methanol) solution of acetic acid/sodium acetate containing tropolone (0.03% w/v), their ethylation with NaBEt₄, and separation and detection by GC–FPD. The analytical procedure was optimized with an unspiked sample of harbor porpoise (Phocoena phocoena) liver. Effects of ASE operational variables (extraction temperature and pressure, solvent composition, number of static extraction steps) are discussed. Method detection limits (MDL) were in the range 6–10 ng(Sn) g^–1 dry weight and 7–17 ng(Sn) g^–1 dry weight for butyl- and phenyltin compounds, respectively. Recoveries were comparable with or better than those obtained by use of other procedures reported in the literature. The analytical procedure was validated by analysis of NIES No. 11 (fish tissue) certified reference material.     

Modeling of iron adsorption on HTTA-loaded polyurethane foam using Freundlich,Langmuir and D-R isotherm expressions

The sorption of Fe(III) at low pH range from 1 to 4.5 on open cell polyether type HTTA-loaded polyurethane foam has been carried out using batch technique. The optimum shaking time for 2.5· 10^–4M solution of Fe(III) was found to be 30 minutes. The concept of macropore and micropore nature of polyurethane foam sorbent offers unique advantages of adsorption. Freundlich and Langmuir adsorption isotherms are followed at low concentration range from 1·10^–4 to 3·10^–4M solution of Fe(III). The Freundlich constant (1/n=0.46±0.013 andK=9.16±1.39 mg·g^–1) and Langmuir isotherm constants(M=21.78 mg·g^–1 andb=88.41±9.731·g^–1) were established. The sorption mean free energyE=12.22±0.09 kJ·mol^–1 and loading capacityC _m =145.21±6.1 mg·g^–1 were evaluated using Dubinin-Radushkevich isotherm, which suggested that the adsorption mechanism was chemisorption.     

Capillary zone electrophoresis to study the humic fraction in organic soils and its relationship with radiocaesium mobility

Humic acids and associated radionuclides were extracted from several soil samples with a significant organic matter content, such as peaty soils and forest soil layers. Extractions were made using two alkaline solutions (Na₄P₂O₇ 0.1 mol·1^–1 and NaOH 0.1 mol·1^–1 under N₂). The humic acid content in the extract was determined by the capillary zone electrophoresis technique (CZE) and associated radiocaseium was determined by gamma spectrometry. After analizing a large number of samples and studying the relationship between humic acid and organic matter content it was possible to conclude that the CZE technique may be a good alternative to classical techniques in humic acid determinations, with NaOH extractions leading to higher results than Na₄P₂O₇. Furthermore, the quantification of the radiocaseium desorbed by applying different extractant reagents (NaOH, Na₄P₂O₇, NH₄AcO and CaCl₂) showed that there may be some organic matter-radionuclide interations, other than those originated by humic acids. which may govern radionuclide retention in soils with a high content of organic matter.     

Study of the Evaporation of a Brine Involving the System Na+, Mg2+, K+, Cl−, S 4 2− –H2O: Crystallisation of oceanic salts

The evaporation of a Tunisian brine sample involving the system Na⁺, Mg²⁺, K⁺, Cl^–, S ₄ ^2– –H₂O was studied under atmospheric pressure and at ambient temperature. The selective densities of precipitation of halite (NaCl) and of co-precipitation of halite and astrakanite (Na₂Mg(SO₄)₂·4H₂O), halite and kaïnite (MgSO₄·KCl·H₂O) and epsomite MgSO₄·7H₂O were determined.During the evaporation of the studied brine, calculations related to the hypothetical composition of the solution in terms of the simple salts NaCl, MgSO₄, KCl and MgCl₂.This revised version was published online in November 2005 with corrections to the Cover Date.     

Determination of traces of uranium and thorium in (Ba, Sr) TiO3 ferroelectrics by inductively coupled plasma mass spectrometry

 Traces of uranium and thorium in barium(II), strontium(II) titanate ((Ba, Sr)TiO₃) ferroelectric materials were determined by inductively coupled plasma mass spectrometry (ICP-MS). Samples were completely dissolved by a mixture of 1.4% H₂O₂ and 1.0 mol⋅l^-1 HNO₃. For a complete separation of the analytes from the matrix elements, a two step separation technique involving leaching and anion-exchange was applied. By the leaching step with HNO₃ more than 90% of the matrix can be removed whereas the analytes completely remained in the solution. The anion-exchange step was carried out on a BIO⋅RAD AG1-X8 column with a mixture of 1.0 mol⋅l^-1 HF and 0.5 mol⋅l^-1 HNO₃ as eluent. The content of uranium and thorium was subsequently measured by ICP-MS. The detection limits (D.L.) obtained were 0.043 ng g^-1 and 0.035 ng g^-1 for U and Th, respectively. The reproducibility was satisfactory with a relative standard deviation of less than 3% (at the 1 ng g^-1 level, n=5). The matrix concentrations in the final solution were reduced to the sub-μg ml^-1 level which is in the range of the detection limits of USN-ICP-AES (ultrasonic nebulization-ICP-atomic emission spectroscopy). The method was successfully applied to the determination of uranium and thorium in three synthetic (Ba, Sr)TiO₃ samples spiked with the analytes at levels of 1, 5 and 10 ng g^-1 and three (Ba, Sr)TiO₃ ferroelectric samples containing sub-ng g^-1 levels of the analytes. Received: 26 February 1996/Revised: 28 May 1996/Accepted: 5 June 1996     

Separation and determination of l-tyrosine and its metabolites by capillary zone electrophoresis with a wall-jet amperometric detection

A method of capillary electrophoresis with wall-jet amperometric detection (AD) has been developed for separation and determination of l-tyrosine (Tyr) and its metabolites, such as Tyramine (TA), p-hydroxyphenylpyruvic (pHPP), homogentisic acid (HGA) and some dipeptides containing Tyr, such as Tyr-Gly-Gly (YGG), Tyr-Arg (YR) and Tyr-d-Arg (Y-d-R). A carbon disk electrode was used as the working electrode and the optimal detection potential was 1.00 V (versus Ag/AgCl). At 18 kV of applied voltage, the seven compounds were completely separated within 20 min in 110 × 10⁻³ mol/L Na₂HPO₄–NaH₂PO₄ buffer (pH 7.10) containing 3 × 10⁻³ mol/L β-cyclodextrin (β-CD). Good linear relationship was obtained for all analytes and the detection limits of seven analytes were in the range of 0.95–4.25 ng/mL. The proposed method has been applied to examine the metabolic process of l-tyrosine in rabbit's urine.