The influence of minor components on the structural reorganization in glassforming materials

Correlation of structure parameters of glasses and related crystals formed in homogeneous or heterogeneous nucleation processes by thermal treatment is discussed on the basis of DTA, TG and EGA measurements in relation to the textural patterns of the materials. For cordierite glass, crystallization of metastable disordered cordierite polymorphs is related to an exothermic heat evolution and simultaneous with a small weight loss (appr. 0.025%). By MS-EGA, evolution of water was determined during the transformation of the metastable melt to a metastable intermediate crystalline phase. Interpretation of the crystallization by comparing the available structure parameters of cordierite glasses and crystals alone is insufficient to explain the role of water in the kinetics of crystallization. Optical and electron microscopy of the primary crystallization phenomena show the metastable solid solution with low quartz-type structure. Interpretation of the crystallization behaviour in terms of conventional theory of nucleation and crystal growth is impossible.     

Investigation of the NMR enhancement factor in CuMn spin glasses

The NMR enhancement factor of a frozenCuMn spin glass has been measured at a temperatureT?T _g /5. The measurements were performed as function of static magnetic fields of different directions. A two component model of a spin glass has been outlined. One component being a “system of single spins” and the other one being a “subsystem of clusters”. Both components were attributed to different kinds of interaction being RKKY and dipole interaction respectively. The effective anisotropy field of the single spin system consists of two unidirectional contributionsH _a ^s andH _a ^c , which have been measured for different conditions. A second anisotropy fieldH _d binds the cluster system to the system of single spins. All anisotropy fields depend on the annealing temperature of the alloys.     

Interplay of Electronic Structure and Bulk Properties in 2D and 3D Ternary Carbonitrides from First Principles

The changes in electronic structure and hardness as inferred from the bulk modulus are investigated for model structures of ternary compounds XC₃N₃ (X = B, Al, P, As, Ga) within the framework of density functional theory (DFT). The optimisations of the proposed two‐ (2D) and three‐dimensional (3D) structures and the calculations of the bulk moduli are performed by a pseudo potential method. The electronic structures are calculated with the augmented sphere wave method (ASW). The obtained hardness for 2D BC₃N₃ system (B₀ ～ 220 GPa) points to a magnitude close to that of graphitic C₃N₄. For heavier X atoms it decreases rapidly. This is equally observed for the 3D systems examined in the β‐C₃N₄ structure for which B₀(β‐BC₃N₃) amounts to ～330 GPa. Within the magnitude of the well known hard material cubic BN, the BC₃N₃ phases can be predicted as candidates for ultra hard materials. The electronic effect induced by the chemical nature of the X substitutional was examined according to its position in the periodic table i.e. X_III or X_V. Both, band structures and the electron localisation function (ELF) were used for this analysis. The ELF plots show a decreasing covalency with heavier X‐atoms. Potential applications of the devised systems are proposed such as dopings with atoms (Li, rare gas) and molecules (N₂).     

Use of a carboxylate exchanger in the determination of copper in distilled water by neutron activation analysis

Copper in distilled water is collected on Zeokarb 226(NH ₄ ⁺ ) and irradiated with thermal neutrons. By comparison of the induced activity of 0.51 MeV photopeak of⁶⁴Cu with that of a standard, irradiated under comparable conditions, copper at ppb levels is easily determined.     

Determination de C,N, O,F et de quelques autres elements par activation au moyen des photons gamma

The (γ, n) activation curves for 17 elements were determined as a function of energy between 25 and 42 MeV. From these are deduced the detection sensitivities intrinsically possible for an average beam intensity of 100 μA. Our experimental results are compared with values calculated byG. J. Lutz. The activation curves relative to certain competitive nuclear reactions on N, O and Na, liable to interfere in the measurements of C, N and F, were also determined. It is shown that the relative importance of these competitive nuclear reactions decreases rapidly for energies below 30 MeV and becomes practically negligible at 25 MeV.      

Substituierte Halogenocarbonylmetallate des Chroms,Molybdäns und Wolframs. IV. Die Kristallstruktur von Tetramethylammonium-Chloropentacarbonylwolframat

Substituted Halocarbonyl Metallates of Chromium, Molybdenum, and Tungsten. IV. Crystal Structure of Tetramethylammonium Chloropentacarbonyltungstate The structure of tetramethylammonium chloropentacarbonyltungstate has been determined from single crystal X-ray data. The compound crystallizes with four formula units in the monoclinic unit cell (space group P2₁/c) of the dimensions a = 1111.3(4) pm, b = 1110.3(4) pm c = 1204.1(3) pm, β = 99.63(3)°, V = 1464.8 × 10⁶ pm³ (R = 0.028). The anion possesses approximately C_4v symmetry with the principal interatomic distances d(W–C(cis)) = 203 pm, d(W–C(trans)) = 197 pm d(W–Cl) = 256.6 pm. No unusual contacts between cation and anion have been found.     

Die Konstitution von Roridin D. Verrucarine und Roridine, 12. Mitteilung

The antibiotic roridin D (C₂₉H₃₈O₉), a companion of roridin A, yields on base catalysed hydrolysis verrucarol ( 3 ) and the hitherto unknown 2, 3-epoxy-2-anhydrororidinic acid ( 4 ) (C₁₄H₁₈O₇). Roridin D is a macrocyclic diester to which structure 1 is assigned. In roridin D an epoxy group replaces the hydroxyl group of roridin A.     

Selective determination of trimethylamine in air by liquid chromatography using solid phase extraction cartridges for sampling

The selective determination of trimethylamine (TMA) in air by liquid chromatography is reported. Sampling is effected by flushing air through C18-packed solid-phase extraction (SPE) cartridges at a flow rate of 15 mL/min for 15 min. Next, TMA is desorbed from the cartridges and injected into the chromatographic system. The analyte is then selectively retained on a precolumn (20 mm x 2.1 mm i.d., packed with 30 microm, Hypersil C18 phase), and derivatized on-line by injecting 9-fluorenylmethyl chloroformate (FMOC). Finally, the TMA-FMOC derivative is transferred to the analytical column (125 mm x 4 mm i.d., LiChrospher 100 RP18, 5 microm), and monitored at 262 nm. The method was applied to the measurement of TMA in air in the 0.25-2.5 microg interval (equivalent to concentrations of TMA of 1.1-11 mg/m3), providing good linearity, reproducibility and accuracy. The mean recovery of TMA was (96 +/- 7%) (n = 12), and the limit of detection was 0.05 microg. The proposed procedure allows the selective determination of TMA in the presence of other primary and secondary short-chain aliphatic amines.     

A facile one‐pot synthesis of novel substituted 1,2,3,4‐tetrahydropyrimidine,part 2: Synthesis of 1‐(aralkyl/aryl)‐3‐(alkyl/aralkyl/aryl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines

1‐(Aralkyl/aryl)‐3‐(alkyyaralkyl)‐5‐aroyl‐1,2,3,4‐tetrahydropyrimidines ( 2a‐c ) have been synthesized by dethiomethylation of 5‐aroyl‐6‐methylthio‐1,2,3,4‐tetrahydropyrimidines ( 1a‐c ). An alternative one‐pot synthetic strategy has been developed for the title compounds 2a‐t by the reaction of enaminones 3 with pri mary amine and formaldehyde in refluxing methanol in good yields.     

Stereochemistry of Macrocyclization of cis-4-Cyclohexene-1,2-dicarboxylic Acid with Dihalogen Derivatives

Stereochemistry of [2+2]- and [1+1]-macrocylization of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane, 1,3-dichloro-2-propanol, and 1,5-dichloro-3-oxapentane was studied. The reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,2-dibromoethane according to the [2+2]-cyclization scheme gave a mixture of stereoisomeric macroheterocycles with cis,syn,cis- and cis,anti,cis-junction of the polyether and cyclohexene rings. In the reaction of cis-4-cyclohexene-1,2-dicarboxylic acid with 1,5-dichloro-3-oxapentane, a mixture of crown compounds with cis,anti,cis- and cis-junction of the polyether and cyclohexene rings was obtained. The structure of the products was established on the basis of their chemical transformations and spectral data.