A study of sample mineralization methods for arsenic analysis of blood and urine by hydride generation and graphite furnace atomic absorption spectrometry

Mineralization procedures for blood and urine suitable for the determination of arsenic by Hydride Generation Atomic Absorption Spectrometry (HGAAS) are studied on model samples, and the results are utilized in biological monitoring investigations. The objective of this work is to obtain good total As recoveries for both matrices regardless of added As species (As(III), As(V), DMA, MMA, AsB, or AsC). Prior to the HGAAS analyses, preparation procedures were controlled under optimised conditions by graphite furnace atomic absorption spectrometry (GFAAS). Two preparation procedures for urine give As recoveries close to 100% by HGAAS: a) dry ashing at 420°C with Mg(NO₃)₂ on a hot plate, and b) microwave oven decomposition with (NH₄)₂S₂O₈. For blood samples, As recoveries by HGAAS range between 95 and 108% for all species when using dry ashing after a pretreatment of samples with HNO₃ and H₂O₂ in a microwave oven. Wet digestion with (NH₄)₂S₂O₈ in a microwave oven gives recoveries very near 100% for As _inorg. and MMA. For other As species in spiked blood samples, recoveries of less than 20% As are found. Precision and detection limits obtained by both techniques are evaluated as well. For arsenic concentrations of 20 μg dm⁻³ or more in blood and urine, a chemical modifier is recommended for GFAAS analysis; it may or may not be proceeded by a mineralization step. For low As levels encountered in the unexposed population, the HGAAS technique provides reliable results only if a very complete mineralization procedure is used.     

Reactions of peroxyacetyl radicals with reduced sulfur compounds

Summary The reaction of peroxyacetyl radicals with reduced sulfur compounds was studied at 55°C in N₂ at 1 000 mbar total pressure. The radicals were generated in equilibrium with peroxyacetyl nitrate and NO₂ in large excess. The pseudo first order decay ofPAN was measured in the absence and presence of several 100 ppm CH₃SH, C₂H₅SH,n-C₄H₉SH, (CH₃)₂S, and (CH₃S)₂. Computer simulations yielded the following rate constants of peroxyacetyl radicals with the above mentioned sulfur compounds: 3.7, 2.8, 13.0, 0.9, and 1.8·10^–16 cm³/s, respectively. An electron capturing compound of the thiols with NO₂ was observed.

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Reaktionen von Peroxyacetylradikalen mit reduzierten Schwefelverbindungen

Zusammenfassung Die Reaktionen von Peroxyacetylradikalen mit reduzierten Schwefelverbindungen wurden bei 55°C in NO₂ bei einem Totaldruck von 1 000 mbar untersucht. Die Radikale wurden im Gleichgewicht mit Peroxyacetylnitrat und NO₂ in großem Überschuß generiert. Der nach erster Ordnung verlaufende Zerfall vonPAN wurde in Abwesenheit und Anwesenheit und von einigen ppm CH₃SH, C₂H₅SH,n-C₄H₉SH, (CH₃)₂S und (CH₃S)₂ gemessen. Computersimulierung der Geschwindigkeitskonstanten für die Peroxyacetylradikale ergab mit den genannten Schwefelverbindungen 3.7, 2.8, 13.0, 0.9 und 1.8·10^–16 ch³/s. Eine elektronenfangende Verbindung der Thiole mit NO₂ wurde beobachtet.

     

Crystal Structures and Magnetic Properties of Rare-Earth Ultraphosphates, RP5O14 (R=La, Nd, Sm, Eu, Gd)

The single-crystal X-ray structures of lanthanum, europium, and gadolinium ultraphosphate, RP₅O₁₄ (R=rare-earth) are reported herein [monoclinic, P2₁/c, a=8.8206(1), 8.7491(1), 8.7493(1) Å, b=9.1196(2), 8.9327(1), 8.9189(1) Å, c= 13.1714(2), 12.9768(2), 12.9717(1) Å, β=90.661(1), 90.534(1), 90.6682(3)°, respectively; Z=4; R1=0.0250, 0.0346, 0.0270, respectively]. The structures are all type (I) compounds as classified by Bagieu-Beucher and Tranqui [Bull. Soc. Fr. Miner. Cryst. 93, 505 (1970)]. The minimum R…R separations are compared with all other structural reports of lanthanide ultraphosphates. Type (I) compounds have the lowest minimum R…R separation, which decreases with atomic number and appears not to perturb the optical properties of any rare-earth ultraphosphate. In each case, R is surrounded exclusively by eight oxygen atoms that form a distorted square antiprism. A P–O network holds together the three-dimensional structure. The magnetic susceptibilities of neodymium, samarium, and gadolinium ultraphosphate as a function of temperature are also reported along with corresponding magnetization measurements. All compounds exhibit a paramagnetic response, following Curie's law except in the regions where crystal field splittings are significant.     

On the electrodeposition of coherent gadolinium dendrites from molten fluoride electrolytes

The morphology of gadolinium dendrites deposited in molten fluorides may be linked with the stability of electroactive associates. Quantum chemical calculations of moieties, based on the solid state structure of GdF₃, reveal an increased overall stabilizing attraction in the following order: $$Gd_{1 - x} Ba_x F_{3 - x}< GdF_3< Gd_{1 - x} F_{3 - 2x} O_x< Gd_{1 - x} Ca_x F_{3 - x} $$ The stabilization of the 75 LiF-25 mol% GdF₃ electrolyte by oxyfluorocomplexes led to the deposition of essentially pure gadolinium dendrites. The fluorine contamination caused by salt inclusions was consequently reduced from the 1,500–2,000 ppm, as obtained in the pure LiF-GdF₃ electrolyte, to less than 3 ppm.     

Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO₄ was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT] _o , fractional-order in [substrate] _o , and inverse fractional-order in [H⁺]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D₂O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH₃C₆H₄SO₂NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics.     

Evaluation of <Superscript>13</Superscript>C NMR spectra of cyclopropenyl and cyclopropyl acetylenes by theoretical calculations

A convenient methodology was developed for a very accurate calculation of ¹³C NMR chemical shifts of the title compounds. GIAO calculations with density functional methods (B3LYP, B3PW91, PBE1PBE) and 6-311+G(2d,p) basis set predict experimental chemical shifts of 3-ethynylcyclopropene (1), 1-ethynylcyclopropane (2) and 1,1-diethynylcyclopropane (3) with high accuracy of 1–2 ppm. The present article describes in detail the effect of geometry choice, density functional method, basis set and effect of solvent on the accuracy of GIAO calculations of ¹³C NMR chemical shifts. In addition, the particular dependencies of ¹³C chemical shifts on the geometry of cyclopropane ring were investigated.     

Purification and characterization of two xylanases from alkalophilic and thermophilic Bacillus licheniformis 77-2

The alkalophilic bacteria Bacillus licheniformis 77-2 produces significant quantities of thermostable cellulase-free xylanases. The crude xylanase was purified to apparent homogeneity by gel filtration (G-75) and ionic exchange chromatography (carboxymethyl sephadex, Q sepharose, and Mono Q), resulting in the isolation of two xylanases. The molecular masses of the enzymes were estimated to be 17 kDa (X-I) and 40 kDa (X-II), as determined by SDS-PAGE. The K _m and V _max values were 1.8 mg/mL and 7.05 U/mg protein (X-I), and 1.05 mg/mL and 9.1 U/mg protein (X-II). The xylanases demonstrated optimum activity at pH 7.0 and 8.0–10.0 for xylanase X-I and X-II, respectively, and, retained more than 75% of hydrolytic activity up to pH 11.0. The purified enzymes were most active at 70 and 75°C for X-I and X-II, respectively, and, retained more than 90% of hydrolytic activity after 1 h of heating at 50°C and 60°C for X-I and X-II, respectively. The predominant products of xylan hydrolysates indicated that these enzymes were endoxylanases.     

Röntgenstrukturanalyse des Methyl-5-acetylamino-7,8-anhydro-4,9-bis-O-(t-butyldimethylsilyl)-3,5-didesoxy-L-glycero-β-D-galakto-2-nonulopyranosidon-säuremethylesters

An X-ray crystal structure analysis of the title compound was carried out at –168°C in order to assign the stereochemistry around the oxirane: C₂₅H₄₉NO₈Si₂, trigonal, R3,a=25.18(1),c=13.55(1) Å (hexagonal axes),Z=9,d _x =1.105.The structure was solved with direct methods and refined to anR-factor of 0.086.

     

Gas Electron Diffraction and Quantum-Mechanical Study of Dimethyloxalate

The geometrical structure and conformation of dimethyloxalate, CH₃OC(O)–C(O)OCH₃, have been studied by gas electron diffraction (GED) and quantum-chemical calculations (MP2 and B3LYP methods with 6-31G* and cc-pVTZ basis sets). The GED analysis with a dynamic model (T = 323 K) results in a mixture of two planar conformers, anti (C_2h symmetry) and syn (C_2v symmetry) orientation of the two C=O bonds. The energy difference between these conformers is 0.02(0.18) kcal/mol and barrier to internal rotation around the C–C bond is 0.44(0.41) kcal/mol. The CH₃ groups occupy synperiplanar positions with respect to the C=O bonds. The following main geometrical parameters for the anti conformer (Å and degrees) have been derived: r_g(C–C) = 1.532(3), r_g(C=O) = 1.203(2), r_g(C_sp3–O) = 1.436(3), r_g(C_sp2–O) = 1.333(3), (C_sp2–C_sp2–O) = 111.9(1.9), (C_sp2–O–C_sp3) = 116.3(1.6), (O–C= O) = 127.0(1.8).This paper is devoted to the 75th anniversary of gas electron diffraction method.     

Equilibrium studies of Mn(II), Mg(II), Ca(II), Sr(II) and Ba(II) withp-fluoro-,p-chloro-,p-bromo-,p-methyl-benzoylacetones and 1-(4-fluorophenyl)-1,3-pentanedione

The rawpH-data, obtained from the potentiometric titrations of the titled ligands with NaOH in 75% (v/v) dioxane-water mixture performed at 20, 30 and 40°C at constant ionic strength (=0.1M-NaClO₄), have been adequately corrected for dilution, and solvent effects in order to evaluate thermodynamic dissociation constants. Variance of the latter as a function of temperature has also been accounted for. The differing magnitudes of thermodynamic dissociation constants of the titled ligands have been explained on the basis of the non coplanar orientation of the phenyl ring in the ligands and a comparison has been made with those of unsubstituted benzoylacetone, dibenzoylmethane and acetylacetone.Following similar technique, thermodynamic stepwise and overall formation constants of the titled metal-ligand systems have been obtained and the results correlated with ligand basicity inverse metal crystal radii and second potentials of metals. Decrease in the free enthalpy (–G) of complexation reaction has also been evaluated.

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Untersuchung der Gleichgewichte von Mn(II), Mg(II), Ca(II), Sr(II) und Ba(II) mit p-Fluor-, p.-Chlor-, p-Brom-, p-Methyl-benzoylaceton und 1-(4-Fluorphenyl)-1,3-pentanedion

Zusammenfassung Aus der potenitometrischen Titration der Titelverbindungen mit NaOH in 75 (v/v) Dioxan—Wasser bei, 20, 30 und 40°C bei konstanter Ionenstärke (=0,1M-NaClO₄) wurden die thermodynamischen Dissoziationskonstanten ermittelt. Verdünnungs-, Lösungsmittel-und Temperatureffekte wurden berücksichtigt. Die unterschiedlichen Dissoziationskonstanten werden mit der Nichtplanarität des Phenylrings in den Liganden erklärt. Außerdem wurden die Komplexbildungskonstanten bestimmt; sie sind in die Diskussion miteinbezogen.

     

New thallium(III) chloride complexes with pyridine carboxylic acids: from molecular compounds to supramolecular associations

Reactions of TlCl₃ with picolinic acid (Hpic), nicotinic acid (Hnic), isonicotinic acid (Hinic) and 3-hydroxy-picolinic acid (H3hpic) afford the isolation of new chlorothallium(III) complexes. The compounds are characterized by IR, Raman and multinuclear NMR (¹H,¹³C,²⁰⁵Tl). The molecular structures of [TlCl₂(pic)(Hpic)]·0.5H₂O (1), [TlCl₂(nic)(Hnic)] (2), [TlCl(inic)₂]·0.6C₂H₅OH (3) and [TlCl(3hpic)₂(h3hpic)] (4) are determined by single-crystal X-ray diffraction. A distorted octahedral TlCl₂N₂O₂ core containing the O,N-chelating ligands is achieved in the monomeric complex 1. The coordination polyhedron in compounds 2–4 is pentagonal bipyramidal, i.e. TlCl₂NO₄ in 2, and TlClN₂O₄ in 3 and 4, respectively. O,O′,N-Bridging ligands result in a polymer chain for 2 and a three-dimensional polymeric association in 3, while compound 4 is monomeric (O, N-and O,O-chelating ligands).     

Organic-inorganic hybrid materials based on N=C=O functionalised silan modified with titanium and zirconium

This work investigates the influence of the precursor trimethylsilil isocyanate on the sol-gel synthesis of hybrid materials. The obtained Si−O−C−N network is additionally modified by titanium and zirconium alcoxypropoxides in the range of 10 to 30 wt. %. The structure of the obtained hybrid materials before and after pyrolysis up to 1100°C was investigated by methods of XRD, FTIR and ²⁹Si MAS NMR. We established that the hybrid structure was stable up to 600°C based on IR study. The structural transformation of the hybrid materials into oxycarbonitrogen system started at 800°C. The network of the hybrids modified by titanium remained stable and amorphous up to the final temperature of the pyrolysis (1100°C) compared to the gels modified by more than 10 wt.% Zr. It was confirmed by XRD analysis that the last mentioned are nanocomposite materials, built from carbooxynitrogen vitreous matrix and ZrO₂-nanocrystals (tetragonal). The NMR method verified the presence of heterometallic bonds (Si−O−Ti and Si−O−Zr) and Q₄, ZrQ₃ or TiQ₃, NSiO₃ and D structural units in the gels.     

Hochdruckuntersuchungen zur Löslichkeit von Stickstoff in Wolfram

The paper reports investigations about the solubility of nitrogen in tungsten at nitrogen pressures up to 30 MPa (300 bar). The solubility of nitrogen obeysSieverts' law in the whole pressure range and can be represented by the equation logC _N=1/2 logp _{N 2}+4.0–9520/T (C _N in wt·ppm.p _{N 2} in bar,T in K).

     

Crystal structure and spectral characterization of dimethylthallium (III) complexes with 2-mercaptonicotinic acid and esters

Synthesis, spectral properties and crystal structure of dimethylthallium(III) complexes with 2-mercaptonicotinic acid (2mna), 2-mercapto-methyl-nicotinate (2mmn), 2-mercapto-ethyl-nicotinate (2men) and 2-mercapto-isopropyl-nicotinate (2min) are reported. The compounds were characterized using IR, multinuclear NMR (¹H,¹³C,²⁰⁵Tl) and mass spectrometry (electrospray, ES-API). The molecular structures of [TlMe₂(2mna)]·H₂O, (1), [TlMe₂(2mmn)], (2), [TlMe₂(2men)], (3) and [TlMe₂(2min)], (4) were determined by the single-crystal X-ray diffraction. In 1, the monodeprotonate O,S-bidentate ligand chelates one dimethylthallium (III) unit and simultaneously bridges (O and S) between two of these organometallic units. The Tl-O1′ and Tl-S″ interactions are leading to polymeric chain linked in a three-dimensional network by the hydrogen bonds formed between the water molecule and the oxygen O (2) atom of the acid. The thallium atom is in a distorted octahedral environment with a [TlC₂O₂S₂] kernel. Compounds 2, 3 and 4 are similar, in all the cases already mentioned the ligand is NH deprotonated and is strongly coordinated to two dimethylthallium (III) units through the N and S atoms. Two additional weak interactions with the O and S atoms lead to a [TlC₂NOS₂] kernel for the metal atom, in which the coordination polyhedron is a very distorted octahedron with the methyl groups occupying the apical positions.     

The influence of film thickness and process temperature on <Emphasis Type="Italic">c</Emphasis>-axis orientation of Bi<Subscript>3</Subscript>TiTaO<Subscript>9</Subscript> thin films

Bi-layered ferroelectric Bi₃TiTaO₉ (BTT) thin films with different thickness (ranging from 100 to 400 nm) were successfully fabricated on Pt(111)/TiO₂/SiO₂/(100)Si substrates using chemical solution deposition (CSD) technique at different annealing temperatures. The c-axis orientation of the films was affected by film thickness and process temperature. The thinner the film and the higher the process temperature, the higher the c-axis orientation. With the increase of film thickness, the stress decreased but the film roughness increased, which led to the decrease of c-axis orientation of films. BTT films annealed at 800°C were found to have much improved remament polarization (P _r ) than that of films annealed at 650 and 750°C. The P _r and coercive field (E _c ) values were measured to be 2 μC/cm² and 100 kV/cm, respectively. BTT films showed well-defined ferroelectric properties with grain size larger than 100 nm.     

H NMR Dynamic study of thermal Z/E isomerization of 5-substituted 2-alkylidene-4-oxothiazolidine derivatives: Barriers to rotation about CC bond

The rotational barriers between the configurational isomers of two structurally related push–pull 4-oxothiazolidines, differing in the number of exocyclic CC bonds, have been determined by dynamic ¹H NMR spectroscopy. The equilibrium mixture of (5-ethoxycarbonylmethyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone (1a) in CDCl₃ at room temperature to 333 K consists of the E- and Z-isomers which are separated by an energy barrier ΔG^# 98.5 kJ/mol (at 298 K). The variable-temperature ¹H NMR data for the isomerization of ethyl (5-ethoxycarbonylmethylidene-4-oxothiazolidin-2-ylidene)ethanoate (2b) in DMSO-d₆, possessing the two exocyclic CC bonds at the C(2)- and C(5)-positions, indicate that the rotational barrier ΔG^# separating the (2E,5Z)-2b and (2Z,5Z)-2b isomers is 100.2 kJ/mol (at 298 K). In a polar solvent-dependent equilibrium the major (2Z,5Z)-form (>90%) is stabilized by the intermolecular resonance-assisted hydrogen bonding and strong 1,5-type S · · · O interactions within the SCCCO entity. The ¹³C NMR Δδ_C(2)C(2′) values, ranging from 58 to 69 ppm in 1a–d and 49-58 ppm in 2a–d, correlate with the degree of the push-pull character of the exocyclic C(2)C(2′) bond, which increases with the electron withdrawing ability of the substituents at the vinylic C(2′) position in the following order: COPh COEt > CONHPh > CONHCH₂CH₂Ph. The decrease of the Δδ_C(2)C(2′) values in 2a–d has been discussed for the first time in terms of an estimation of the electron donor capacity of the S fragment on the polarization of the CC bonds.     

Magnetische Messungen im Nahordnungsbereich vonHeusler-Phasen (Co,T)2 XY

Magnetic measurements onHeusler alloys (Co,T)₂ XY (field and temperature dependence) are performed around theCurie points (temperature range:T _C–50 toT _C+50). A method otherwise used to get rid of ferromagnetic impurities only ( _g versus 1/H plot) is applied to pure ferromagnets and yields completely new _g (extrap.) versusT curves with a maximumT _max> T _C. The method was applied to pure gadolinium first which has aCurie point within the accessible region of the susceptibility measuring device.

     

Determination of rare earth elements in Gd2O3 by ICP-OES

Summary Rare earth impurities in high-purity Gd₂O₃ have been determined by ICP-OES. HREE except Ho were analysed by directly nebulising 1 mg/ml of the matrix solution and the LREE were analysed after separation on an anionexchange Dowex 1×8 resin. The recovery studies show nearly 100% separation. The determination of 30 ppm of HREE in gadolinium oxide is possible.     

Preparation and C NMR study on 1-aryl-3,3-difluoro-2-(phenylethynyl)cyclopropenes: long distance Hammett substituent effect

Coupling of 1-aryl-3,3-difluoro-2-chlorocyclopropenes and phenylacetylene using Sonogashira reaction with Pd(OAc)₂ and CuI as the catalyst with K₂CO₃ as a base yields phenylethynylcyclopropenes in high selectivity and good yields. The ¹³C chemical shifts of C? of ∼105 ppm on acetylene group significantly different from phenylacetylene (84 ppm) suggest that the acetylene group possesses less sp hybrid character due to an unusual long distance Hammett substituent effect. It is also confirmed by the substituent parameter analysis, while the Cβ and C? display the strong resonance effect (their values are 6.89 and 3.37, respectively).     

Nanosized SrCO3-based chemiluminescence sensor for ethanol

The development of a nanosized SrCO₃-based sensor based on the generated chemiluminescence (CL) from catalytic oxidation of organic vapors was demonstrated. The luminescence characteristics and effect of different parameters, such as temperature and flow rate, were discussed with a prepared CL detection system. This sensor was evaluated for the measurement of gaseous ethanol as a model analyte. Under the optimized conditions, the linear range of CL intensity versus concentration of ethanol vapor is 6-3750 ppm (r=0.998, n=8), with the limit of detection of 2.1 ppm. This SrCO₃ sensor shows high selectivity to ethanol. There is no response while the foreign substances, such as gasoline, ammonia and hydrogen, are passing through the sensor. The hydrocarbons can slightly interfere with the ethanol measurement. The sensor also exhibits good stability and durability during 100 h reaction with 2000 ppm ethanol. The interactions between ethanol molecules and SrCO₃ involving CL emission were investigated by utilizing gas chromatography in this paper and the possible mechanism of CL from ethanol oxidation on SrCO₃ was discussed.