Utilization of thiazolylacetonitriles in the synthesis of thiophene,thiazole, pyrazolo[1,5‐a]pyrimidine and pyrazolo [5,1‐c]triazine derivatives

Thiazolylcyanothioacetanilides react with α‐haloketones and haloesters to give the corresponding thiophene or thiazole derivatives according to the reaction conditions. Pyrazolo[1,5‐a]pyrimidines and pyrazolo[5,1‐c]triazines were synthesized by reaction of 3‐amino‐4‐(4′‐arylthiazol‐2′‐yl)‐5‐phenylaminopyrazole with different reagents. Structures of the new compounds were confirmed by elemental analyses, spectral data, and alternative methods of synthesis whenever possible. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 508–516, 1999     

Ti2Nb6Cl14O4: A Unique 2D–1D Network Combination in Niobium Cluster Chemistry

Layers of niobium clusters that are linked to each other through zigzag chains of edge-sharing [TiCl₄O₂] ocatahedra are the central structural features of the title compound. Bridging of the chains by [(Nb₆Cl₈ⁱO₄ⁱ)Cl₆^a]⁶⁻ clusters results in the formation of empty tunnels (a section of the structure is shown on the right).     

An efficient method for the synthesis of spiro and fused N-heterocyclic phosphor esters. Reactions of triketoindan-2-oxime with α-phosphonyl carbanions

Treatment of triketoindan-2-oxime with α-phosphonyl carbanions in sodium ethanolate solution at reflux temperature led to a number of the corresponding substituted spiroisooxazole-, fused 1,3-oxazole, and 1,4-oxazine phosphor esters in moderate to high yields. Mechanisms for the formation of five- and six-membered rings are provided. A comparison of Wittig-Horner and Wittig reagent counterparts in reactions with the oxime is discussed. The various biological properties of selected examples of the synthesized products were studied. Correspondence: Wafaa M. Abdou, Chemical Industries Division, National Research Center, Elbohouth St., D-12622 Dokki, Cairo, Egypt.     

A shallow-water sedimentation model with friction and Coriolis: An existence theorem

We present an existence theorem of a two-dimensional sedimentation model coupling a shallow water system with a sediment transport equation. The shallow water system includes Coriolis and friction terms. A Galerkin method is used to obtain a finite-dimensional problem which is solved using a Brouwer fixed point theorem. We prove that the limits of the resulting solution sequences satisfy the model equations.     

Thermodynamics ofp-nitroanilinium ion and the acidity function in ethylene carbonate-water mixtures at 25°C

Hydrochloric acid solutions (0.05–1.18m) containing p-nitroaniline (8×10^–5M) as indicator base have H _o values which increase with increase of ethylene carbonate (EC) content in the solvent mixture for a fixed molality of the acid. This behavior confirms similar results obtained in AN-H₂O, MCS-H₂O, DMSO-H₂O and NMF-H₂O systems. This trend indicates that the solvent basicity increases by successive addition of the organic solvent. The partition of the proton between water and EC has been calculated using Sadek's theory. It is clear that [H₃O⁺] decreases gradually with increase of EC content. The change in the dissociation constant of p-nitroanilinium ion, decreases sharply with increasing dielectric constant. The free energy change of transfer, G _t ^o , has been attributed to an electrostatic, G _t(el) ^o , and a nonelectrostatic, electrostatic, G _t(non) ^o component. It has been found that G _t(non) ^o is negative.     

Tetranuclear Gold(I) Clusters with Nitrogen Donor Ligands: Luminescence and X-Ray Structure of Gold(I) Naphthyl Amidinate Complex

The syntheses and characterization of gold(I) naphthyl, pentafluorophenyl, and trifluoromethylphenyl amidinate complexes are reported. The tetranuclear clusters are obtained from the reaction of Au(tetrahydrothiophene)Cl with the potassium salt of the corresponding amidinate in a THF solvent. The crystal structures of the gold(I) naphthyl, 2, and pentafluorophenyl, 3, amidinates show a short Au···Au distance of ~3. 0 Å typical of compounds having an aurophilic interaction. The gold atoms are arranged in a square (Au···Au···Au = 87°–92°) in the pentafluorophenyl derivative and in a parallelogram (Au···Au···Au = 68°–110°) in the naphthyl amidinate complexes. The naphthyl and trifluoromethylphenyl complexes are visibly luminescent in the solid state at liquid nitrogen temperature displaying asymmetric emission bands at 538 and 473 nm, respectively. The luminescent lifetimes of these species are in the millisecond range indicating phosphorescent processes.     

Synthesis and crystal structure of indium arsenate and phosphate dihydrates with variscite and metavariscite structure types

The hydrothermal synthesis, crystal structure analysis, and spectroscopic studies of InPO₄·2H₂O (1) and InAsO₄·2H₂O (2) are reported. Compound 1 is isomorphic with metavariscite: monoclinic P2₁/n (No. 14), a = 5.4551(3) Å, b = 10.2293(4) Å, c = 8.8861(3) Å, = 91.489(4)°, Z = 4, and compound 2 is isomorphic with variscite: orthorhombic Pbca (No. 61), a = 10.478(1) Å, b = 9.0998(8) Å, c = 10.345(1) Å, Z = 8. Their three-dimensional frameworks are built of corner sharing InO₄(H₂O)₂ octahedra and MO₄ (M = P⁵⁺ or As⁵⁺) tetrahedra. The water molecules in both compounds have different environments and are involved in different types of hydrogen bonding. Infrared spectroscopy indicates that water molecules are true H₂O species.     

Advances in math search

As digital libraries of mathematical and scientific contents become available, it is essential to have math-aware search systems. The search systems must understand math symbols and structures, and allow users to enter queries that involve not only text keywords but also mathematical expressions and fragments of expressions. In addition, the search results must be presented in a way that enables the user to find the desired information rapidly. This short paper gives a quick overview of the state of the art of math search, and focuses on the math search system that the author has developed for the Digital Library of Mathematical Functions (DLMF) project of the National Institute of Standards and Technology. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of Cu,Zn, and Se in microvolumes of liquid biological samples

Cu, Zn, and Se were successfully determined in a few microliters (<100 μl) of biological samples using discrete injection atomic absorption spectrometry. Different factors were investigated in order to obtain a biological sample volume which is valid for analysis. Among them are the effect of microsampling volume variations (starting from 40 to 200 μl), nebulization efficiency, detection limits, precision, and finally the calibration and sensitivity of the proposed method. It was found that 60 μl of the biological sample was adequate for the quantitative analysis with reasonable precision. The advantages of the proposed method are not only rapidity, simplicity, sensitivity, and good precision, but also, contrary to conventional flame atomic absorption spectrometry, the capability of analyzing microvolumes of samples.     

Stability and index of the meet game on a lattice

We study the stability and the stability index of the meet game form defined on a meet semilattice. Given any active coalition structure, we show that the stability index relative to the equilibrium, to the beta core and to the exact core is a function of the Nakamura number, the depth of the semilattice and its gap function.