Synthesis,Characterization, and Structure of Some New Substituted 5,6-Fused Ring Pyridazines

Pyridazines are an important class of heterocyclic compounds as a result of their materials and commercial applications. The synthesis of 5,6-fused ring pyridazines 2a–h from 1,2-diacylcyclopentadienes (fulvenes) 1a–h is described herein. This route was quite general, and features an efficient and convenient two-step synthesis of a series of 5,6-fused ring 1,2-disubstituted pyridazines using enolized 1,2-disubstituted fulvenes in a methanolic solution of hydrazine. Full characterization of newly formed fulvene 1e and pyridazines 2a–h are reported. Single-crystal X-ray analysis confirms the molecular structure of pyridazine 2f, which displayed the expected pyridazine fused to the cyclopentadienyl moiety. Adding to their real world capabilities in electronic devices, compounds 2a–h display reasonably high stability in solution and in air at room temperature.

Synthesis and properties of N3 and CN delivery compounds and related precursors for nitride and ceramic fabrication

The simple azido and cyano compounds Cl₂AsN₃, Br₂AsN₃, (C₆H₅)SiH₂N₃, (C₆H₅)SiH₂CN and p‐(tolyl)SiH₂CN have been prepared for the first time by metathesis reactions involving the corresponding halides and NaN₃, LiN₃ and LiCN. These compounds represent a highly reactive and efficient family of delivery reagents for the preparation of N₃ and CN molecular precursors to bulk ceramics and nitride thin films. They are isolated as low volatility liquids and characterized by spectroscopic methods and chemical analysis. Ab initio simulations were used to elucidate the structural and vibrational properties of the simpler, fully inorganic Cl₂AsN₃ and Br₂AsN₃ species. This theoretical treatment was extended to include the hypothetical H₂AsN₃ and HClAsN₃ derivatives which are particularly desirable as single‐source low‐temperature As? N sources for the formation of highly sought after, metastable GaAs_1?xN_x materials for solar cell applications. The practical utility of the title molecules is also demonstrated by synthesizing several representative compounds of B, Be, Ga and Al, which are of interest for the development of open frameworks, optoelectronic nitrides and refractory B? C? N hybrids. The cyanide derivatives (C₆H₅)SiH₂CN and p‐(tolyl)SiH₂CN react readily with Be and B halides to yield crystalline Be(CN)₂ and amorphous B? C? N. The latter is crystallized upon heating to form graphite‐like polymorphs with homogeneous nanoscale morphologies. The azide derivatives Cl₂AsN₃, Br₂AsN₃ and (C₆H₅)SiH₂N₃ react readily with GaBr₃, GaCl₃ and BBr₃ to produce high yields of the previously reported Br₂GaN₃, Cl₂GaN₃ and Br₂BN₃, respectively. The latter is shown to possess a trimeric molecular structure in which the α‐nitrogen of the azide group bridges the boron atoms to form cyclohexane‐like B₃N₃ rings. Copyright © 2008 John Wiley & Sons, Ltd.     

DuPont qualicon BAX system real-time PCR assay for Escherichia coli O157:H7

Evaluations were conducted to test the performance of the BAX System Real-Time PCR assay, which was certified as Performance Tested Method 031002 for screening E. coli O157:H7 in ground beef, beef trim, spinach, and lettuce. Method comparison studies performed on samples with low-level inoculates showed that the BAX System demonstrates a sensitivity equivalent or superior to the FDA-BAM and the USDA-FSIS culture methods, but with a significantly shorter time to result. Tests to evaluate inclusivity and exclusivity returned no false-negative and no false-positive results on a diverse panel of isolates, and tests for lot-to-lot variability and tablet stability demonstrated consistent performance. Ruggedness studies determined that none of the factors examined affect the performance of the assay. An accelerated shelf life study determined an initial 36 month shelf life for the test kit.     

Surface-enhanced Raman scattering from silver-coated opals

We describe surface-enhanced Raman scattering measurements from a benzenethiol monolayer adsorbed on a silver-coated film that is, in turn, deposited on an artificial opal, where the latter is a close-packed three-dimensional dielectric lattice formed from polystyrene spheres. Data for a range of sphere sizes, silver film thicknesses, and laser excitation wavelengths are obtained. Enhancement factors can be in the range of 10(7). To partially explain these large enhancements, we have performed model finite-difference time domain simulations of the position-dependent electric fields generated at the opal surfaces for several experimentally studied laser wavelengths and sphere diameters.     

Dynamics and Stability of Surface Waves with Bulk-Soluble Surfactants

In this paper we study the dynamics of a layer of incompressible viscous fluid bounded below by a rigid boundary and above by a free boundary, in the presence of a uniform gravitational field. We assume that a mass of surfactant is present both at the free surface and in the bulk of the fluid, and that conversion from one species to the other is possible. The surfactants couple to the fluid dynamics through the coefficient of surface tension, which depends on the surface density of surfactants. Gradients in this concentration give rise to Marangoni stress on the free surface. In turn, the fluid advects the surfactants and distorts their concentration through geometric distortions of the free surface. We model the surfactants in a way that allows absorption and desorption of surfactant between the surface and bulk. We prove that small perturbations of the equilibrium solutions give rise to global-in-time solutions that decay to equilibrium at an exponential rate. This establishes the asymptotic stability of the equilibrium solutions.

     

The stability of W2 and WRe adatom clusters on (110) tungsten surfaces

Kinetics of formation and dissociation of W₂ and WRe adatom clusters and dissociation reaction equilibria on (110) W were studied by field ion microscopy. Deposits of two adatoms only on the (110) face of a tungsten FIM tip were used and these reached an equilibrium state at 400 K. For the W₂ dissociation reaction $\text{ΔA}{}^{\mathrm{?}}\text{(430}\text{K}\text{) = 30 ± 5}\text{kJ mol}{}^{\mathrm{?1}}$; for WRe dissociation $\text{ΔA}{}^{\mathrm{?}}\text{(400}\text{K}\text{) = 14 ± 2}\text{kJ mol}{}^{\mathrm{?1}}$. The dissociation energies indicated by kinetics were consistent with these values.     

Synthesis and structure of some group VII 1,2-diacyl cyclopentadiene complexes and their pyridazine derivatives

A series of 1,2-diacyl cyclopentadienyl tricarbonyl manganese and rhenium complexes, [M(CO)₃{η⁵-1,2-C₅H₃(CO-(R)₂}] (3a–c and 4a–b), were isolated utilizing a straightforward, 3-step route. The synthetic pathway began with a 1,2-diacyl cyclopentadiene (fulvene), followed by the formation of its corresponding thallium salt and transmetallation with the appropriate pentacarbonyl metal bromide. X-ray crystallographic analysis and high-accuracy mass spectrometry confirmed the structures of the both the 4-methoxyphenyl and 4-chlorophenyl diacyl rhenium complexes, [Re(CO)₃{η⁵-1,2-C₅H₃(CO-(4-OCH₃)C₆H₄)₂}] (4a) and [Re(CO)₃{η⁵-1,2-C₅H₃(CO-(4-Cl)C₆H₄)₂}] (4b). Diacyl complexes 3a–c and 4a–b were then ring-closed with hydrazine hydrate to form their corresponding pyridazine complexes, [M(CO)₃{η⁵-1,2-C₅H₃(1,4-(R)₂N₂C₂}] (5a–c and 6a–b), in good yields (60–83%). The pyridazyl ligands were found to be relatively labile, and recrystallization of the target complexes 5a–c and 6a–b afforded only the free pyridazine ligands.     

The Compressible Viscous Surface-Internal Wave Problem: Stability and Vanishing Surface Tension Limit

This paper concerns the dynamics of two layers of compressible, barotropic, viscous fluid lying atop one another. The lower fluid is bounded below by a rigid bottom, and the upper fluid is bounded above by a trivial fluid of constant pressure. This is a free boundary problem: the interfaces between the fluids and above the upper fluid are free to move. The fluids are acted on by gravity in the bulk, and at the free interfaces we consider both the case of surface tension and the case of no surface forces. We establish a sharp nonlinear global-in-time stability criterion and give the explicit decay rates to the equilibrium. When the upper fluid is heavier than the lower fluid along the equilibrium interface, we characterize the set of surface tension values in which the equilibrium is nonlinearly stable. Remarkably, this set is non-empty, i.e., sufficiently large surface tension can prevent the onset of the Rayleigh-Taylor instability. When the lower fluid is heavier than the upper fluid, we show that the equilibrium is stable for all non-negative surface tensions and we establish the zero surface tension limit.     

C,O-dialkylation of Meldrum's acid: synthesis and reactivity of 1,3,7,7-tetramethyl-4H,10H-6,8,9-trioxa-2-thiabenz[f]azulen-5-one

Reaction of Meldrum's acid with 3,4-bis(chloromethyl)-2,5-dimethylthiophene (1) or 3,4-bis(bromomethyl)-2,5-dimethylthiophene (2) produces the kinetically favored C,O-dialkylation product, 1,3,7,7-tetramethyl-4H,10H-6,8,9-trioxa-2-thiabenz[f]azulen-5-one (4). Recrystallization of 4 from refluxing methanol results in the methanolysis product 5-(4-methoxymethyl-2,5-dimethylthiophen-3-ylmethyl)-2,2-dimethyl[1,3]dioxane-4,6-dione (5). Attempts to isomerize 4 to the thermodynamically favored C,C-dialkylation product, 1,3-dimethyl-5,6-dihydro-4H-cyclopenta[c]thiophene(2-spiro-5)2,2-dimethyl-4,6-dione (8), result in the formation of 1,3-dimethyl-7,8-dihydro-4H-thieno[3,4-c]oxepin-6-one (6). The transformation occurs via a retro-Diels-Alder elimination of acetone followed by hydrolysis and decarboxylation of the resulting ketene. The ketene is trapped by tert-butyl alcohol, furnishing 1,3-dimethyl-6-oxo-7,8-dihydro-4H,6H-thieno[3,4-c]oxepine-7-carboxylic acid tert-butyl ester (7). All compounds are characterized spectroscopically as well as by X-ray crystallography of products 4-7.