Facile preparation of an α-Keggin-type [H3W12O40] complex: Does it exist in aqueous solution?

The formation processes of α-Keggin-type [H₂W₁₂O₄₀]⁶⁻ and [H₃W₁₂O₄₀]⁵⁻ complexes were investigated in aqueous W^VI (0.05–0.50 M) solutions. The formation of [H₂W₁₂O₄₀]⁶⁻ was ascertained by the appearance of a ¹⁸³W NMR line at −117 ppm, but no evidence was found for the existence of [H₃W₁₂O₄₀]⁵⁻ in the solution at the accessible pH range. The addition of (CH₃)₄N⁺ (Me₄N⁺) to the W^VI solution directly precipitated the (Me₄N)₆[H₂W₁₂O₄₀] salt. On the other hand, the addition of the larger Bu₄N⁺ cation precipitates the (Bu₄N)_4.5H_0.5[H₃W₁₂O₄₀] salt, because a naked proton formed during the crystallization process or in the solid state may enter into the Keggin shell to produce [H₃W₁₂O₄₀]⁵⁻. This explanation is based on the fact that [H₂W₁₂O₄₀]⁶⁻ is not spontaneously converted into [H₃W₁₂O₄₀]⁵⁻ in acidified aqueous solution. On the basis of their voltammetric properties, a simple diagnostic criterion was developed to distinguish between [H₂W₁₂O₄₀]⁶⁻ and [H₃W₁₂O₄₀]⁵⁻.     

Technetium tetrachloride as a precursor for small technetium(IV) complexes

Polymeric technetium tetrachloride reacts with monodentate donor ligands such as THF, acetonitrile, DMSO, thioxane (1-oxa-4-thiacyclohexane), PMe2Ph, PPh3, OPPh3, or OH2 via cleavage of the polymeric network and the formation of [TcCl4(L)2] complexes. The configuration of the products is dependent on the donor atoms such that trans coordination is established with "soft" donor atoms such as sulfur or phosphorus, while cis-[TcCl4(L)2] complexes are formed with the "harder" donors oxygen or nitrogen. The ambivalent thioxane binds to technetium via the sulfur atom. The trans products are air stable and resistant to hydrolysis. The cis complexes, however, undergo stepwise hydrolysis, during which complexes of the composition [Cl3(L)2TcOTc(L)2Cl3] (L = CH3CN, DMSO, or OH2) are formed. They are the first representatives of a new class of technetium(IV) complexes with a bridging oxo ligand. The Tc-O bond lengths in these bridges are between 1.803(1) and 1.823(2) A.     

N-propargylamides via the asymmetric michael addition of B-alkynyl-10-TMS-9- borabicyclo[3.3.2]decanes to N-acylimines

[Structure: see text] The asymmetric synthesis of N-propargylamides through Michael addition of the alkynylborane 1 to N-acylimines is reported. The N-acetylimines provide the best substrates for the process exhibiting high selectivity (56-95% ee) with predictable stereochemistry. In several cases, 5 crystallizes in essentially pure form (97-99% ee) and a single-crystal X-ray structure was also obtained for 5g (R1=R2=Me, R3=o-Cl-C6C4). The process regenerates 4 for its direct conversion back to 1 and facilitates the efficient recovery of the pseudoephedrine.     

Finite sheeted covering maps over 2-dimensional connected, compact Abelian groups

Let G be a 2-dimensional connected, compact Abelian group and s be a positive integer. We prove that a classification of s-sheeted covering maps over G is reduced to a classification of s-index torsionfree supergroups of the Pontrjagin dual . Using group theoretic results from earlier paper we demonstrate its consequences. We also prove that for a connected compact group Y:

(1)

Every finite-sheeted covering map from a connected space over Y is equivalent to a covering homomorphism from a compact, connected group.

(2)

If two finite-sheeted covering homomorphisms over Y are equivalent, then they are equivalent as topological homomorphisms.

     

Miniature Non-thermal Plasma Induced Cell Cycle Arrest and Apoptosis in Lung Carcinoma Cells

Plasma Chemistry and Plasma Processing - Non-thermal plasma has been a promising new cancer treatment modality in plasma oncology field. It generates extracellular and intracellular reactive...     

Mechanism of Reaction of Polyvinyl Chloride) with Triethylaluminum

Polyvinyl chloride) was treated with triethylaluminum in 1,2-dichloroethane solution. Negligibly small amounts of hydrogen chloride are evolved from the modified polyvinyl chloride) in decomposition at 180°C for 150 min in nitrogen. Quantitative analysis of the rate of dehydrochlorination of the modified polymer gave a calculated activation energy for the alkylation of 8.3 kcal/mole in 1,2-dichloroethane solution; the concentration of the labile chlorines in the original polyvinyl chloride) was less than 0.25 mole % Furthermore, the fact that the average polyene length of the modified polymer for the thermal decomposition was much shorter than that of the starting material suggests that the labile chlorines inherent in the polymer exist not only in the chain end but also in the polymer chain.     

A general model for batch building processes under the timeout and capacity rules

In manufacturing systems, batch building processes are very common, as goods are often transported or processed in batches and must therefore be collected before these transport or processing steps can occur. In this paper, we present a method for the performance analysis of general batch building processes in material flow systems under the timeout and capacity rules. The proposed model allows for stochastic collecting times and incorporates no restrictions with respect to the number of arriving units and their interarrival times. The accuracy of the discrete-time approach is demonstrated by comparing this approach with a discrete-event simulation model in continuous-time. Subsequently, the model is applied to two cases: a transportation case from the health care industry and the process of building a batch for a batch processor.     

Asymmetric allyl- and crotylboration with the robust, versatile, and recyclable 10-TMS-9-borabicyclo[3.3.2]decanes

The remarkable versatility and selectivity of the 10-(trimethylsilyl)-9-borabicyclo[3.3.2]decanes (10-TMS-9-BBDs) in the allyl- and crotylboration of representative aldehydes are reported. The new reagents are prepared through air-stable crystalline pseudoephedrine borinic ester complexes of the 10-TMS-9-BBDs (4), which are available in 63% overall yield from B-MeO-9-BBN through a simple two-step procedure. These complexes 4 are directly converted to the corresponding B-allyl-10-TMS-9-BBDs (1) with allylmagnesium bromide, which either can be isolated (98%) or used in situ for the allylations. The remarkable enantioselectivity (96 to > or =99% ee) of these reagents in the rapid (<3 h), asymmetric allylboration process at -78 degrees C is only slightly diminished when it is conducted at 25 degrees C, a phenomenon attributable to its rigid bicyclic structure. In addition to providing the homoallylic alcohols 6 efficiently (68-80%), the procedure also permits the efficient recovery of 4 (68-84%) for the direct regeneration of 1. Alternatively, an oxidative workup procedure can be used for the preparation of 6. The reagent gives predictable stereochemistry and exhibits an extremely high level of reagent control in the allylboration of d-glyceraldehyde acetonide. A simple and efficient procedure has been developed for the preparation of all four geometric and enantiomeric isomers of the B-crotyl-10-TMS-9-BBDs (10) from optically pure enantiomers of B-MeO-10-TMS-9-BBD (3). These reagents 10 also add rapidly (<3 h) and efficiently to representative aldehydes at -78 degrees C, providing ready access to all four of the possible stereoisomers of the beta-methyl homoallylic alcohols 12-15 (69-92%) in high dr (> or =98:2) and ee (94-99%).     

XPS and NEXAFS studies of aliphatic and aromatic amine species on functionalized surfaces

The chemical constitution of functionalized supports is an important parameter that determines their performance in a broad range of applications, e.g. for immobilization of biomolecules. Supports with amino functionalized surfaces are also often used for DNA microarray experiments. However, spectral data which have been reported for surfaces with amino functionalities suffer from some inconsistencies. In this article a detailed XPS (X-ray photoelectron spectroscopy) and NEXAFS (Near edge X-ray absorption fine structure) database for amino functionalized surfaces is presented. Amino-terminated surfaces prepared from aliphatic and aromatic aminosilanes or aminothiols and a field sample are considered. Effects of aging in air and damage by radiation are addressed as well.