Application of the <Emphasis Type="Italic">k</Emphasis><Subscript>0</Subscript>-NAA method at the HANARO research reactor

The k ₀-standardization method (k ₀-NAA) is known as one of the most remarkable progresses of the NAA with its many advantages. For the application of k ₀-NAA method at the NAA #1 irradiation position where the neutrons are well thermalized in the HANARO research reactor, KAERI, Korea, the determination of the reactor neutron spectrum parameters such as α and f have been carried out. The measured values of α and f using the “Cd-ratio” triple monitor method were 0.127±0.022 and 1010±70, respectively. To evaluate the applicability of k ₀-NAA in our analytical system, the analysis of three kinds of SRMs was executed. The analytical results showed that the relative error of most of the elements was less than 10% and the U-scores were within 2. It is turned out that the procedure of the k ₀-NAA in the HANARO research reactor is available for a practical application in the environmental fields.     

Deoxygenation of Nitrosobenzene by the Electrogenerated Pd<Subscript>3</Subscript>(dppm)<Subscript>3</Subscript>(μ<Subscript>3</Subscript>-CO) Cluster

The 2-electron reduction of the unsaturated Pd₃(dppm)₃(CO)²⁺ cluster ([Pd₃]²⁺) affords the highly reactive neutral cluster [Pd₃]⁰, which reacts with nitrosobenzene (PhNO) yielding the organic azoxybenzene product (PhN(O)NPh) via the formation of “triplet” nitrene “PhN”. The formation of [Pd₃(μ₃-O)] as a possible (relatively unstable) intermediate is also postulated based on MALDI-TOF findings, but not formally demonstrated. Concurrently, no reaction between [Pd₃]⁰ and OPPh₃ occurs. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. This paper is dedicated to Professor Dieter Fenske.     

New metal-rich mixed chalcogenides with an intergrowth structure: Ni<Subscript>5.68</Subscript>SiSe<Subscript>2</Subscript>, Ni<Subscript>5.46</Subscript>GeSe<Subscript>2</Subscript>, and Ni<Subscript>5.42</Subscript>GeTe<Subscript>2</Subscript>

New metal-rich mixed nickel-silicon and nickel-germanium chalcogenides, Ni_5.68SiSe₂, Ni_5.46GeSe₂, and Ni_5.42GeTe₂, were synthesized by high-temperature ceramic techniques. The X-ray diffraction study of single crystals grown from a molten flux revealed that the compounds are isostructural and crystallize in the tetragonal system (space group I4/mmm, Z = 2). These compounds are the first members of the family of M_7−δEX₂-type (M = Ni or Pd; E = Sn or Sb; X is chalcogen) intergrowth structures containing “light” p elements E. Resistivity measurements on pressed textured pellets showed that both selenides are anisotropic metallic conductors in the directions parallel and perpendicular to the heterometallic bond systems. The geometric criteria of stability of the intergrowth structure type under consideration are discussed. Dedicated to Academician G. A. Abakumov on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1632–1638, September, 2007.     

Thermal analysis of (NaF/AlF<Subscript>3</Subscript>)-FeF<Subscript>3</Subscript> and (NaF/AlF<Subscript>3</Subscript>)-FeO systems

Thermal analysis of the two systems, (NaF/AlF₃)-FeF₃ and (NaF/AlF₃)-FeO, was carried out with three different cryolite ratios. In these systems, “impurity compounds” decreased the temperature of primary crystallisation with decreasing cryolite ratios. From the slope of the dependencies, it can be assumed that the excess of AlF₃ plays a more significant role in changes in the “Fe(III)” systems than in “Fe(II)” systems.     

Electron interactions in the (η<Superscript>2</Superscript>-C<Subscript>60</Subscript>)Pd[P(Ph<Subscript>2</Subscript>)C<Subscript>5</Subscript>H<Subscript>4</Subscript>]<Subscript>2</Subscript>Fe complex

The electronic structure of the (η²-C₆₀)Pd[P(Ph₂)C₅H₄]₂Fe complex was calculated by the “hybrid” B3LYP method. Comparison of the experimental X-ray emission C-Kα spectrum and theoretical spectrum of the compound demonstrated that the electron interactions between the C₆₀ core, palladium atom, and organometallic fragment are described correctly in the framework of the quantum chemical method used. The electronic structure of the organometallic fullerene complex can be presented as a set of blocks of orbitals corresponding to different types of chemical bond. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2640–2644, December, 2005.     

Density of the systems (NaF/AlF<Subscript>3</Subscript>)—AlPO<Subscript>4</Subscript> and (NaF/AlF<Subscript>3</Subscript>)—NaVO<Subscript>3</Subscript>

The densities of two systems of molten mixtures (NaF/AlF₃)—NaVO₃ and (NaF/AlF3)—AlPO₄ were measured using an Archimedean method. Each molten mixture contained varying amounts of “impurity” constituents. The measurements were performed at various NaF/AlF₃ mole ratios (CR, cryolite ratio), equal to 3, 2.5, 2, and 1.5.     

Non-isothermal decomposition kinetics of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized using egg white solution route

The thermal decomposition kinetics of nickel ferrite (NiFe₂O₄) precursor prepared using egg white solution route in dynamical air atmosphere was studied by means of TG with different heating rates. The activation energy (E _α) values of one reaction process were estimated using the methods of Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS), which were found to be consistent. The dependent activation energies on extent of conversions of the decomposition reaction indicate “multi-step” processes. XRD, SEM and FTIR showed that the synthesized NiFe₂O₄ precursor after calcination at 773 K has a pure spinel phase, having particle sizes of ~54 ± 29 nm.     

Dissymmetrization of crystal structures of grossular-andradite garnets Ca<Subscript>3</Subscript>(Al,Fe)<Subscript>2</Subscript>(SiO<Subscript>4</Subscript>)<Subscript>3</Subscript>

The crystal structures of three birefringent grossular-andradite natural garnets Ca₃(Al,Fe)₂(SiO₄)₃ were investigated using single-crystal X-ray diffraction data (MoK_α, number of reflections measured 8065, 10619, 9213; R = 2.81, 2.74, 3.26%). According to the values of unit cell constants, inconsistent intensities of reflections and appearance of additional (forbidden) reflections explored garnets have different symmetry: cubic, sp. gr. (Fe/(Fe + Al) = 0.078, Δn = 0.0002); orthorhombic, sp. gr. Fddd (Fe/(Fe + Al) = 0.58, Δn = 0.0089); triclinic, sp. gr. or I1 and pseudo-orthorhombic (Fe/(Fe + Al) = 0.23, Δn = 0.0066). Careful refinement of all crystal structures in space groups , Fddd and has confirmed the symmetry reduction detected on the diffraction patterns and shown that dissymmetrization of cubic garnets connects with partial ordering of trivalent cations over Y-sites. Direct linear relationship between Fe-occupancy, an average Y–O bond lengths and octahedral O–O edges has been revealed. Cluster models of dissymmetrization have been regarded. Evidence for the “growth dissymmetrization” phenomena (kinetic phase transformations) as the reasons of the symmetry reduction of cubic garnets has been discussed. The reasonable assumption that the garnets crystal structures described as orthorhombic are triclinic, but the deviations from the orthorhombic symmetry so small, that cannot be manifested by of X-ray diffraction study has been taken.     

Synthesis,structure, and NO-donor activity of the paramagnetic complex [Fe<Subscript>2</Subscript>(SC<Subscript>3</Subscript>H<Subscript>5</Subscript>N<Subscript>2</Subscript>)<Subscript>2</Subscript>(NO)<Subscript>4</Subscript>] as a model of nitrosyl [2FE-2S] proteins

The neutral dinuclear iron nitrosyl complex [Fe₂(SC₃H₅N₂)₂(NO)₄] (1) of the “g = 2.03” family with a ligand analogous to natural mercaptohistidine was synthesized by the metathesis reaction of the thiosulfate ligands in the [Fe₂(S₂O₃)₂(NO)₄]²⁻ anion with imidazolidine-2-thiolate ligands. The electrochemical determination of nitrogen oxide in solution showed that compound 1 has a lower NO-donor ability compared to the iron complexes with 1-methylimidazole-2-thiol and imidazole-2-thiol synthesized earlier. Study of the magnetic properties of polycrystals of 1 demonstrated that the effective magnetic moment at room temperature is ca. 2.45 μ_B and corresponds to a molecule containing a pair of the noninteracting spins S = 1/2. This is evidence that each iron coordination unit in complex 1 contains one unpaired electron, and the iron atom is in the low-spin state. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 28–34, January, 2007.     

Secreted phospholipase A<Subscript>2</Subscript>, lipoprotein hydrolysis,and atherosclerosis: integration with lipidomics

Phospholipase A₂ (PLA₂) is a group of enzymes that hydrolyze the sn-2 position of glycerophospholipids to yield fatty acids and lysophospholipids. Of many PLA₂s or related enzymes identified to date, secreted PLA₂s (sPLA₂s) comprise the largest family that contains 10 catalytically active isozymes. Besides arachidonic acid released from cellular membranes for eicosanoid synthesis, several if not all sPLA₂s have recently been implicated in hydrolysis of phospholipids in lipoprotein particles. The sPLA₂-processed low-density lipoprotein (LDL) particles contain a large amount of lysophospholipids and exhibit the property of “small-dense” or “modified” LDL, which facilitates foam cell formation from macrophages. Transgenic overexpression of these sPLA₂s leads to development of atherosclerosis in mice. More importantly, genetic deletion or pharmacological inhibition of particular sPLA₂s significantly attenuates atherosclerosis and aneurysm. In this article, we will give an overview of current understanding of the role of sPLA₂s in atherosclerosis, with recent lipidomics data showing the action of a subset of sPLA₂s on lipoprotein phospholipids.     

Fabrication and characterization of TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript> composite nanoparticles and polyurethane/(TiO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>) nanocomposite films

TiO₂–SiO₂ composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO₂–SiO₂ composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO₂–SiO₂) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO₂–SiO₂ composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO₂–SiO₂ composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO₂–SiO₂ core surface via surface functionalized reaction. The particle size of TiO₂–SiO₂ composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid films. The average particle size of the TiO₂–SiO₂ composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO₂–SiO₂ composite nanoparticles are well dispersed in the PU matrix.     

Formation of impurity Si<Subscript>2</Subscript>OH<Subscript>6</Subscript> in silane synthesized from silicon tetrafluoride

The possibility of the reduction of hexafluorodisiloxane by calcium hydride in the synthesis of silane from silicon tetrafluoride has been studied. This reaction is shown to be not decisive for oxygen contamination of silane. The most likely reason for the appearance of impurity Si₂OH₆ in “fluoride” silane is the Ca(OH)₂-catalyzed reaction of silane with trace water. The concentration of impurity Si₂OH₆ in silane at the stage of synthesis may be efficiently decreased by the preliminary purging of calcium hydride with a hydrogen (grade A) flow.     

Selective oxidation of primary alkanols into the “symmetrical” esters with the H<Subscript>2</Subscript>O<Subscript>2</Subscript>-MBr-HCl system

Oxidation of linear or branched primary alkanols with H₂O₂-MBr (M = Li, Na, K)-HCl system in water affords the corresponding “symmetrical” esters in almost quantitative yield.     

Interaction of a Co<Subscript>6</Subscript> cluster with oxides of different nature: a quantum chemical study

Density functional theory was applied to investigate the interaction of Co₆ nanoparticle with various oxide supports including γ-Al₂O₃, silicalite, and zeolite HZSM-5. The introduction of cobalt into silicalite leads to insignificant stabilization of the metal cluster and induction of a small positive charge. The interaction of the Co₆ particle with the acid zeolite or alumina is accompanied by transfer of either a proton from the Br?nsted acid site or hydrogen atoms from terminal OH groups to the surface of the metal cluster with the formation of a hydride-like complex cation. Geometric parameters and energy characteristics of adsorption complexes of carbon monoxide molecule with Co₆ particles on different supports were calculated. For isolated particle on silicalite, “linear” adsorption is predicted. According to calculations, one can expect “angular” adsorption in the case of the acid zeolite and “two-point” adsorption (precursor of active surface carbon) in the system Co₆/γ-Al₂O₃.     

Preparation,Thermal Behaviour,and Crystal Structure of MgAl<Subscript>2</Subscript>F<Subscript>8</Subscript>(H<Subscript>2</Subscript>O)<Subscript>2</Subscript>

Summary.  Single crystals of MgAl₂F₈(H₂O)₂ have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF₃ and MgAlF₅(H₂O)₂ in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F ² > 2σ (F ²)) = 0.0282, wR(F ² all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF₆ octahedra with an overall composition of AlF₄ ⁻ which are connected via common fluorine atoms of [MgF_4/2(H₂O)_2/1] octahedra. Group-subgroup relations of MgAl₂F₈(H₂O)₂ to WO₃(H₂O)_0.33 and to other M(II)M(III)₂ F₈(H₂O)₂ structures are briefly discussed. Above 570°C, MgAl₂F₈(H₂O)₂ decomposes under elimination of water into α-AlF₃, β-AlF₃, and MgF₂. Received October 29, 2001. Accepted (revised) December 6, 2001     

The kinetics and main pathways for the liquid-phase oxidation of cyclohexene by air in the presence of cobalt,chromium, iron,and nickel µ<Subscript>3</Subscript>-oxotrimetallohexapivalates

It was found that during the liquid-phase oxidation of cyclohexene (CH) by air (323–343 K) in the presence of a series of homo-and heteronuclear μ ₃-oxotrimetallohexapivalates with a M₂M′O (M, M′ = Co, Cr, Fe, Ni) core insignificant amounts of the corresponding epoxide are formed, and 3-hydroperoxy-2-cyclohexene (HP), 3-hydroxy-2-cyclohexene (CHol), and 2-cyclohexen-3-one (CHone) accumulate in the oxidate. It is suggested that CHone and CHol are “dead-end” products from the oxidation of CH under the investigated conditions while the HP is a unique “intermediate-damper” that gives rise to the realization of alternative paths (catalytic cycles) for the formation of these products. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 85–90, March–April, 2007.     

D<Subscript>2</Subscript>O — H<Subscript>2</Subscript>O Solvent Isotope Effects on the Apparent Molar Volumes of Tetramethyl-<Emphasis Type="Italic">bis</Emphasis>-urea (Mebicarum) Solutions

Densities of solutions of tetramethyl-bis-urea (TMbU) or “Mebicarum” in H₂O and D₂O, with solute mole fraction concentrations (x ₂) ranging up to 3.2 × 10⁻³, have been measured at 288.15, 298.15, 308.15 and 318.15 K using a precision vibrating-tube densimeter. The limiting apparent molar volumes, V _φ,2 ^∞, and expansibilities, E _{p, φ, 2} ^∞, of the solute have been calculated. The isotope effect δ V _φ,2 ^∞(H₂O → D₂O;T) is negative, monotonously decreases in magnitude with temperature and reverses sign at T ≈ 318 K. Water (H₂O, D₂O) and TMbU molecules in infinitely- and highly-dilute aqueous solutions form H(D)-bonded hydration complexes with a high packing density. The hydration of TMbU should be treated as a superposition of two mechanisms, hydrophobic and hydrophilic, with the latter one predominating.     

Structure and lithium mobility of Li<Subscript>4</Subscript>Pt<Subscript>3</Subscript>Si

The lithium-rich silicide Li₄Pt₃Si was synthesised from the elements by high-temperature synthesis in a sealed niobium ampoule. Its structure was refined on the basis of single-crystal X-ray diffraction data: R32, a = 693.7(2), c = 1627.1(4) pm, wR2 = 0.0762, 525 F² values and 21 variables. The striking structural motifs of the Li₄Pt₃Si structure are silicon atoms with a slightly distorted trigonal prismatic platinum coordination with short Si–Pt distances (238–246 pm). Always two trigonal prisms are condensed via a common Pt₃ triangle, and these double units built up a three-dimensional network by condensation via common corners. The channels left by this prismatic network are filled by two crystallographically independent lithium sites in a 3:1 ratio. The single crystal X-ray data were fully confirmed by neutron powder diffraction and ⁷Li magic-angle spinning (MAS)–nuclear magnetic resonance (NMR) results. The two distinct lithium sites are well differentiated by their ⁷Li isotropic chemical shift and nuclear electric quadrupolar interaction parameters. MAS-NMR spectra reveal signal coalescence effects above 300 K, indicating chemical exchange between the lithium sites on the millisecond timescale. The spectra can be simulated with a simple two-site exchange model. From the resulting temperature-dependent correlation times, an activation energy of 50 kJ/mol is extracted.     

Enthalpy of formation of talc Mg<Subscript>3</Subscript>[Si<Subscript>4</Subscript>O<Subscript>10</Subscript>](OH)<Subscript>2</Subscript> according to dissolution calorimetry

A thermochemical study of natural talc was performed by high-temperature melt dissolution calorimetry on a Tian-Calvet calorimeter. Based on the total values of the increment in enthalpy upon heating the sample from room temperature to 973 K, and of the dissolution enthalpy at 973 K measured in this work for talc and gibbsite (along with those determined for tremolite, brucite, and their corresponding oxides), the enthalpy of formation was calculated for talc composed of elements, Mg₃[Si₄O₁₀](OH)₂, at 298.15 K: Δ_f H _el^o(298.15 K) = −5900.6 ± 4.7 kJ/mol.     

Non-isothermal kinetics of the thermal decomposition of sodium oxalate Na<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The thermal transformation of Na₂C₂O₄ was studied in N₂ atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na₂C₂O₄ and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique (XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS) methods. The activation energies (E _α) of Na₂C₂O₄ decomposition were found to be consistent. Decreasing E _α at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated through the Liqing–Donghua method was ‘cylindrical symmetry (R₂ or F_1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy pathway and revealed a very hard mechanism.