Intermolecular interactions in cyanodimethylarsine and cyanodimethyl­stibine

Cyano­di­methyl­arsine, [As(CH₃)₂(CN)], and cyano­di­methyl­stibine, [Sb(CH₃)₂(CN)], have closely related, but not isomorphous, crystal structures containing XCN?XCN? chains. The N?As distance of 3.185 (3) Å is slightly shorter than the expected van der Waals distance of 3.5 Å, while the N?Sb distance of 2.862 (9) Å, compared with the expected value of 3.7 Å, is much shorter. This is consistent with Sb being a stronger Lewis acid than As.     

Preparation and Some Reactions of 1H-1,4-Benzothiazine Ylides (= 1H-1,4-Benzothioniaazin-4-ide)

A series of fifteen 1H-1,4-benzothiazine ylides were obtained by alkylation of the corresponding 4H-1,4-benzothiazines 1 . Ylides of type 2g–r showed slight [1,2] rearrangements upon thermolysis besides main dealkylation to 1 and olefin production. The ylides of this type underwent redox reactions when treated with hydrazine hydrate alone, giving 3,4-dihydro-2H-1,4-benzothiazines mainly, while ylides of type 2a–f failed to react.     

Foldamer dynamics expressed via Markov state models. I. Explicit solvent molecular-dynamics simulations in acetonitrile, chloroform, methanol, and water

In this article, we analyze the folding dynamics of an all-atom model of a polyphenylacetylene (pPA) 12-mer in explicit solvent for four common organic and aqueous solvents: acetonitrile, chloroform, methanol, and water. The solvent quality has a dramatic effect on the time scales in which pPA 12-mers fold. Acetonitrile was found to manifest ideal folding conditions as suggested by optimal folding times on the order of approximately 100-200 ns, depending on temperature. In contrast, chloroform and water were observed to hinder the folding of the pPA 12-mer due to extreme solvation conditions relative to acetonitrile; chloroform denatures the oligomer, whereas water promotes aggregation and traps. The pPA 12-mer in a pure methanol solution folded in approximately 400 ns at 300 K, compared relative to the experimental 12-mer folding time of approximately 160 ns measured in a 1:1 v/v THF/methanol solution. Requisite in drawing the aforementioned conclusions, analysis techniques based on Markov state models are applied to multiple short independent trajectories to extrapolate the long-time scale dynamics of the 12-mer in each respective solvent. We review the theory of Markov chains and derive a method to impose detailed balance on a transition-probability matrix computed from simulation data.     

The spectrofluorqmetric determination of anthracene, fluorene and phenanthrene in mixtures

A procedure is presented for the spectrofluorometric determination of mixtures of anthracene, fluorene and phenanthrene. The determination depends on differences in fluorescence emission spectra and on selective excitation of anthracene fluorescence. Some of the fluorescence and absorption spectra involved overlap, but these difficulties can be overcome by empirical corrections. The average relative error in this method is less than 5 % over the concentration range 0 to 5 ppm.     

Recent progress in the restoration of archeological metallic artifacts by means of low-pressure plasma treatment

A new method for the restoration and conservation of archeological artifacts made of metals, such as iron, silver, bronze, and others, has been developed and succesfully tested on more than 14,000 objects. Compared with the conventional restoration techniques, the method, which is based on a partial reduction of the incrustation and corrosion layer by a hydrogen-containing glow discharge plasma, offers significant advantages as regards the quality of the surface of the objects, their stability against postcorrosion, and time and labor savings. The present status of the development will be described, which allows the conservator a routine application of the new method.     

Synthesis of 1-azapyrene

The environmental contaminants 1-azapyrene 15 , 2-azapyrene 13 and several other azapyrene derivatives were synthesized from a common intermediate, 2,2a,3,4-tetrahydrocyclopenta[cd]phenalen-1-one oxime 6 . The synthesis of 1-azapyrene 15 completes the series of azapyrenes.     

The fluorometric determination of o-phthalic acid

A fluorometric procedure for the determination of o-phthalic acid by conversion to fluoresceln is described. The optimum amount of o-phthalic acid for application of the method is 50–5000 μg. The determination can be carried out with a relative error of less than 5% even when significant quantities of common o-phthalic acid contaminants are present.     

A stochastic frontier approach to running performance

^** Email: e.sterken{at}eco.rug.nl Long-distance running performance depends on age of the runnerand race distance. In this paper we apply a stochastic frontierapproach to estimate optimal running performance across distancesfrom 5000 m up to and including the marathon. We present agecorrection factors for 5000, 10000 and 15000 m, half-marathonand marathon distances for women and men. Two conclusions emerge:(1) official age grading tables are too optimistic for olderrunners and (2) running performance–age curves differacross distances.     

On the mechanisms of silicon atom abstraction reactions

A set of experiment were designed to verify that recoil ³¹Si atoms abstracts H and F atoms via a stepwise mechanism instead of a simulatenous mechanism to give silylenes suh as ³¹SiH₂, ³¹SiHF and ³¹SiF₂. In addition, a novel compound 1-flourosilacyclopent-3-ene, was synthesized     

Strongly driven dissipative systems —An approach by Robertson's theory

Robertson's theory is used for quantumstatistical treatment of dissipative systems driven at high power. Assuming a weak internal interaction and a Markoff-like approximation, tractable nonlinear equations of motion result for expectation values. The systematic part of the driving fields is exactly treated. Two examples of thermal open systems demonstrate the significance of the presented theory.