Evaluation of thermodynamic and kinetic stability of CuAlO<Subscript>2</Subscript> and CuGaO<Subscript>2</Subscript>

Thermodynamic and kinetic stabilities of CuAlO₂ and CuGaO₂ have been evaluated by using thermogravimetry and thermodynamic calculations. It has been revealed that CuAlO₂ and CuGaO₂ are not thermodynamically stable in air below 800 °C and 1,200 °C, respectively, and that the oxidation reaction, 4CuMO₂ + O₂ → 2CuO + 2CuM₂O₄ (M = Al, Ga), should occur if the reaction kinetics are high enough. However, rate constants and activation energies indicated slow kinetics of the oxidation reaction, showing kinetic stability of CuMO₂ even under some thermodynamically unstable temperatures and atmospheres. It was also concluded that CuAlO₂ showed higher thermodynamic and kinetic stability than CuGaO₂.     

Heat capacities and absolute entropies of UTi<Subscript>2</Subscript>O<Subscript>6</Subscript> and CeTi<Subscript>2</Subscript>O<Subscript>6</Subscript>

Summary As part of a larger study of the physical properties of potential ceramic hosts for nuclear wastes, we report the molar heat capacity of brannerite (UTi₂O₆) and its cerium analog (CeTi₂O₆) from 10 to 400 K using an adiabatic calorimeter. At 298.15 K the standard molar heat capacities are (179.46±0.18) J K^-1 mol^-1 for UTi₂O₆ and (172.78±0.17) J K^-1 mol^-1 for CeTi₂O₆. Entropies were calculated from smooth fits of the experimental data and were found to be (175.56±0.35) J K^-1 mol^-1 and (171.63±0.34) J K^-1 mol^-1 for UTi₂O₆ and CeTi₂O₆, respectively. Using these entropies and enthalpy of formation data reported in the literature, Gibb’s free energies of formation from the elements and constituent oxides were calculated. Standard free energies of formation from the elements are (-2814.7±5.6) kJ mol^-1 for UTi₂O₆ and (-2786.3±5.6) kJ mol^-1 for CeTi₂O₆. The free energy of formation from the oxides at T=298.15 K are (-5.31±0.01) kJ mol^-1 and (15.88±0.03) kJ mol^-1 for UTi₂O₆ and CeTi₂O₆, respectively.     

Interatomic interactions and electronic structure of NbSe<Subscript>2</Subscript> and Nb<Subscript>1.25</Subscript>Se<Subscript>2</Subscript> nanotubes

Atomic models of achiral NbSe₂ nanotubes are suggested. Band structure calculations have been performed to investigate the electronic structure and determine the parameters of interatomic interactions. The distribution of the density of states and pair bond occupancies of NbSe₂ nanotubes are analyzed in relation to the type of the atomic configuration and the tube diameter; the results are compared with the band structure of the 2H-NbSe₂ crystal. Calculations have been carried out on hypothetical superstoichiometric nanotubes with a formal composition Nb_1.25Se₂ as possible quasi-one-dimensional nanoforms of autointercalated niobium diselenide.Original Russian Text Copyright © 2004 by A. N. Enyashin, V. V. Ivanovskaya, I. R. Shein, Yu. N. Makurin, N. I. Medvedeva, A. A. Sofronov, and A. L. IvanovskiiTranslated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 4, pp. 579–588, July–August, 2004.This revised version was published online in April 2005 with a corrected cover date.     

Generation and IR spectra of ionic and molecular complexes of aluminum chloride with <Emphasis Type="Italic">tert</Emphasis>- and <Emphasis Type="Italic">sec</Emphasis>-butyl chlorides

Sec-butyl and tert-butyl cations were first stabilized upon cocondensation of aluminum chloride and haloalkanes (2-chlorobutane and 2-chloro-2-methylpropane, respectively) and their IR spectra and thermal stability investigated. Aluminum chloride anions participating in stabilization of carbenium ions were revealed. Ionic complexes and both 1:1 and 2:1 molecular complexes of reagents were detected and their IR spectra studied. Quantum-chemical calculations at the PBE level of density functional theory with inclusion of electron correlation were employed to optimize the geometric parameters and to determine the vibrational frequencies of aluminum chloride, butyl chlorides, and their complexes of various compositions. The structures of the associates observed were determined on the basis of comparison of the experimental and calculated vibrational spectra.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 147–155, January, 2005.     

Synthesis and characterization of Mn-, La-Mn- and La-Ca-Mn-citrates as precursors for LaMnO<Subscript>3</Subscript> and La<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>MnO<Subscript>3</Subscript>

Mn-, LaMn- and LaCaMn-citrates were synthesized at 60–120°C in ethylene glycol medium using chlorides or nitrates as metal sources. Their composition, IR spectra and thermal decomposition were studied. Equimolar La/Mn ratio has been established in the complex, prepared from chloride solution with the same initial composition of the metals. In the isolated three-metallic complex the molar ratio of the metals deviates from the composition in the initial solution. The final products of the heating of Mn- and mixed-metal LaMn-citrates at 1000°C are phase-homogeneous Mn₃O₄ (hausmannite) and LaMnO₃ respectively. Parasitic phase(s) are observed in La_xCa_1−xMn_yO₃, produced from LaCaMn-citrate.     

Chemical Composition and <em>in Vitro</em> Evaluation of the Antioxidant and Antimicrobial Activities of <em>Eucalyptus gillii </em>Essential Oil and Extracts<em></em>

In this study, essential oil and various extracts (hexane, petroleum ether, acetone, ethanol, methanol and water) of Eucalyptus gilii were screened for their chemical composition, antimicrobial and antioxidant activities. The essential oil chemical composition was analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID), respectively. Thirty four compounds were identified, corresponding to 99.5% of the total essential oil. Tannins [104.9-251.3 g catechin equivalent (CE)/Kg dry mass], flavonoids [3.3-34.3 g quercetin equivalent (QE)/Kg dry mass], phenolics [4.7-216.6 g gallic acid equivalent (GAE)/Kg dry mass] and anthocyannins [1.2-45.3 mg cyanidin-3-glucoside equivalent (C3GE)/Kg dry mass] of various extracts were investigated. Free radical scavenging capacity of all samples was determinedt. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, the IC₅₀ of essential oil was 163.5 ± 10.7 mg/L and in the 2,2'-azinobis-3-ethylbenzothiazoline-6-sulphonate (ABTS) assay, it was 94.7 ± 7.1 mg/L. Among the various extracts, the water extract showed the best result (IC₅₀ = 11.4 ± 0.6 mg/L) in the DPPH assay which was comparable to vitamin C (IC₅₀ = 4.4 ± 0.2 mg/L). The antimicrobial activities were evaluated against different bacterial and fungal strains. Gram positive bacteria were found to be more sensitive to the essential oil and extracts than Gram negative ones. Anthocyanins seem to have a major effect on the growth of Bacillus subtilis (R² = 0.79). A significant antifungal activity was observed against the yeast and fungi. Correlations between chemical composition and antioxidant activities were studied and R² values were about 0.96 for the effect of phenolics on the DPPH assay.     

Methyl­malon­amide and ethyl­malon­amide

In the title compounds, C₄H₈N₂O₂, (I), and C₅H₁₀N₂O₂, (II), respectively, the amide groups are rotated out of the central C—C—C plane by ca 76° in (I) and by 70–73° in (II). Compound (I) has crystallographic mirror symmetry perpendicular to the molecular plane.     

Bleaching of solutions of chlorophylls <Emphasis Type="Italic">a</Emphasis> and <Emphasis Type="Italic">b</Emphasis> with blue and red light

The dependences of the reaction rate constant for bleaching of solutions of chlorophyll under the action of light with a wavelength of 434 and 670 on the type of solvent and additives (O₂, H₂O, HCl, and anthocyanins) have been studied.     

Synthesis and structure of allylated derivatives of fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript>

New chromatographically pure monoand hexamethanofullerenes C₆₀ and C₇₀ containing active allylic groups were synthesized by Bingel—Hirsch reaction. These compounds are promising for the studies of biological activity, as well as for obtaining on their basis new fullerenecontaining materials. The purity and composition of the synthesized compounds were confirmed by MALDI-TOF mass spectrometry and HPLC, their structure was established by ¹H and ¹³C NMR spectroscopy and X-ray diffraction.     

Separation and purification of <Superscript>249</Superscript>Cf and <Superscript>245</Superscript>Cm

There is a need to provide radioactivity standards of the higher actinides in support of both decommissioning and remediation activities as well as routine environmental analysis. In the case ²⁴⁹Cf, this will provide a useful calibration nuclide for both α-and γ-spectrometry as well as improving knowledge of the decay scheme for this nuclide. There is anecdotal evidence to suggest that the chemical yield of americium and curium may differ in radiochemical analysis. Thus, a chemical yield tracer of ²⁴⁵Cm may help to resolve this issue and will be suitable for both, suitable for use as a chemical yield tracer for both α-particle spectrometry and mass spectrometry. An aged source of ²⁴⁹Cf was used as the source material for the separation of these two nuclides by cation-exchange, using 2-hydroxy-2-methyl-propanoic acid at controlled pH as an eluant, ²⁴⁹Cf being eluted before the ²⁴⁵Cm daughter. The purity of both nuclides was measured by γ-ray spectrometry.     

Kinetics of isothermal decomposition of ZnSeO<Subscript>3</Subscript> and CdSeO<Subscript>3</Subscript>

The kinetics of decomposition of ZnSeO₃ and CdSeO₃ was studied under isothermal heating on a derivatograph. The values of activation energy, pre-exponential factor in Arrhenius equation and change of entropy were calculated for the formation of the activated complex by the reagent. The dependencies observed are interpreted according to the generalized perturbation theory of chemical reactivity.     

Viscosity and shrinkage of porous and quartzoid glasses of the Na<Subscript>2</Subscript>O-B<Subscript>2</Subscript>O<Subscript>3</Subscript>-SiO<Subscript>2</Subscript> system

Shrinkage of porous glasses on heating from 20 to 800°C was studied and temperature dependences of the viscosity in the range of 10¹¹–10¹³ P were determined for quartzoid (sintered) glasses based on five glasses with different compositions in the Na₂O-B₂O₃-SiO₂ system. The shrinkage of porous glasses and the viscosity of quartzoid glasses were analyzed in relation to their composition and temperature of preliminary thermal treatment.     

Triclinic polymorphs of tri­phenyl­phosphine and tri­phenyl­phosphine sulfide

New triclinic polymorphs of tri­phenyl­phosphine, (I), and tri­phenyl­phosphine sulfide, (II), were crystallized. For the structure of (I), it is obvious that the highest peaks in the final difference electron‐density map are located at the `lone‐pair regions' of P atoms. We have observed this effect in two further phosphorous‐containing structures.     

Di­methyl­phenyl­sulfonium tri­fluoro­methane­sulfonate and methyl­di­phenyl­sulfonium tri­fluoro­methane­sulfonate

The bonding geometry of sulfur in the cations of the title compounds, C₈H₁₁S⁺·CF₃SO₃^? and C₁₃H₁₃S⁺·CF₃SO₃^?, respectively, is similar and is independent of the ratio of the Me/Ph substituents. As expected, in both cations, the S—Ph bonds are somewhat shorter than the S—Me bonds. In both crystal structures, the interaction between cations and anions is similar.     

“蒸馏酒”还是“发酵酒”——对《科学史导论》中“spirits” 和“distillation”的再思考

科学史奠基者乔治·萨顿在《科学史导论》第二卷的第一部分对我国宋代酿酒著作《北山酒经》予以了简要描述,出现了“spirits”“distillation”等字样;而《北山酒经》被众多学者认为其描述对象是发酵酒(黄酒)。本文从东西方蒸馏技术和相关著作的文本分析对《科学史导论》中提及的蒸馏技术和蒸馏酒存在的可能性提出了质疑。     

Stereochemistry of 1,3‐dipolar‐cycloaddition of 3,4‐dihydroisoquinoline‐ and 3,4‐dihydro‐carboline‐N‐methoxycarbonyl‐ and N‐phenacyl‐methylides with maleic and fumaric nitrile

The 1,3‐dipolar‐cycloadditions of two kind of isoquinolinium and carbolinium ylides with fumaric and maleic nitrile resulted in pyrroloisoquinoline and indolizino[8,7‐b]indole derivatives, respectively, which are analogues of biologically active alkaloids. The cycloadditions were performed in good yield and proved to be stereoselective. The structure elucidation and complete ¹H and ¹³C assignments have been achieved by a combination of various one‐ and two‐dimensional NMR experiments.     

Thermal oxide synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

Fe₃O₄ nanorods and Fe₂O₃ nanowires have been synthesized through a simple thermal oxide reaction of Fe with C₂H₂O₄ solution at 200–600°C for 1 h in the air. The morphology and structure of Fe₃O₄ nanorods and Fe₂O₃ nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals Fe₃O₄ nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air. When the temperature was 600°C, the samples completely became Fe₂O₃ nanowires with hexagonal structure. It was found that C₂H₂O₄ molecules had a significant effect on the formation of Fe₃O₄ nanorods. A possible mechanism was also proposed to account for the growth of these Fe₃O₄ nanorods. Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China (Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010)     

Electrochemical and magnetic characterization of LiFePO<Subscript>4</Subscript> and Li<Subscript>0.95</Subscript>Mg<Subscript>0.05</Subscript>FePO<Subscript>4</Subscript> cathode materials

A series of lithium iron phosphates was synthesized via the sol–gel route. Iron phosphides, which are electronic conductors, were formed when sintered at 850°C. Magnetic susceptibility measurements on the samples show antiferromagnetic behaviour with T _N=50±2 K for LiFePO₄ and Li_0.95Mg_0.05PO₄ sintered at temperatures below 850°C. The LiFePO₄ and Li_0.95Mg_0.05FePO4 cathodes show a stable electrochemical capacity in the range of 150–160 mA h/g on cycling. The cyclability deteriorates with increasing sample sintering temperature due to the increased crystal size and impurities.