A Retro-Diels Alder route to Tetramethyldisilene Me2Si=SiMe2 revisited: Flow Pyrolysis of 1,1,2,2-Tetramethyl-1,2-disilacyclohex-4-ene

Reinvestigation of the flow pyrolysis of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene did not identify conditions under which the retro-Diels Alder reaction was the exclusive process. Extrusion of Me₂Si=SiMe₂was confirmed, but dimerization of directly extruded Me₂Si: contributes significantly to its formation. Rearrangement of 1,1,2,2-tetramethyl-1,2-disilacyclohex-4-ene to 1,1,3,3-tetramethyl-1,3-disilacyclohex-4-ene is a major process under a variety of conditions. Computational studies reduced the number of viable pathways. Both experimental and computational results point to stepwise extrusion of Me₂Si=SiMe₂ via a diradical intermediate and to linkage by one or more common intermediates of the extrusion pathway and the pathway leading to rearranged disilacyclohexene. Such a mechanism receives support from the formation of 1,2- and 1,3-disilacyclohex-4-enes, that is both the Diels-Alder product and the rearrangement product, in the addition of Me₂Si=SiMe₂ to butadiene. Dedicated to Professor Mitsuo Kira on the occasion of his being honored for his inspiring work as the recipient of the 2005 Wacker Silicon Award.     

Transition metal complexes with a polydentate Schiff base derived from 3-formylsalicylic acid and 1,2-bis(o-aminophenylthio)ethane

The reaction of 3-formylsalicylic acid with 1,2-bis(o-aminophenylthio)ethane yielded a Schiff base with eight donor centres N₂S₂O₄ of which the inner compartment is of an N₂S₂O₂ type and the outer is of the O₂O₂ type. The base forms several mononuclear homo- and hetero-dinuclear complexes: e.g. mononuclear Cu^II, Ni^II and dinuclear Cu^II, Ni^II, UO₂ ^VI complexes. Hetero-dinuclear complexes {[M]M}, where M = the inner metal ion Cu^II, Ni^II and M = the outer metal ion Pd^II, UO₂ ^VI are also reported. The complexes were characterised by elemental analyses, spectral, thermal and magnetic measurements. Dicopper and dinickel complexes exhibit subnormal magnetic moments showing spin pairing between two metal centres, via the phenolato oxygen, whereas other mono-copper and mono-nickel complexes (both mononuclear and hetero-dinuclear) show the expected magnetic behaviour for 1e and 2e, respectively. The e.s.r. spectra of copper complexes also support the above behaviour.     

O,O′-dialkyl and alkylene dithiophosphate derivatives of silver(I). X-ray crystal structure of [Ag{S2POCH2CMe2CH2O} PPh3]2 · 2H2O

Silver(I) dialkyl/alkylene dithiophosphates of the types [Ag{S₂P(OR)₂}] and [Ag{S₂P(OGO)}] (where R = –Pr ⁿ ; G = –CMe₂CH₂CHMe–, –CH₂CMe₂CH₂–, –CMe₂CMe₂– or –CH₂CH₂CHMe–) have been prepared by treating an aqueous solution of AgNO₃ with ammonia salts of the respective dithiophosphoric acid. The derivatives form 1:1 adducts readily with 2,2-bipyridine or Ph₃P in CH₂Cl₂ solution. These novel complexes have been characterized by elemental analyses, molecular weight measurements and spectral (i.r., ¹H- and ³¹P-n.m.r.) studies. The crystal structure of [Ag{S₂POCH₂CMe₂CH₂O · PPh₃]₂ · 2H₂O exhibits an unsymmetrical attachment of the silver(I) to the ligand moiety.     

Selective Reduction of Conjugated Ethylenic Linkage in the Presence of Ion-Exchange Resin Bound Borohydride

The use of crosslinked polystyrene anion-exchange resin as a support for borohydride ions made it possible to reduce conjugated olefinic bonds selectively under very mild conditions. The isolation of the reduced products by a simple filtration and evaporation process is another interesting feature of this reaction.     

Leucine pools in Escherichia coli biofilm discovered by Raman imaging

In structured communities of bacteria known as biofilms, a variety of biomolecules have been shown to play a unique role as signals and/or regulators in biofilm formation. Here, we report that high levels of the amino acid leucine (leucine pool) were detected, for the first time, within microcolonies in a 30‐h‐old Escherichia coli biofilm by Raman imaging. Localization of leucine revealed by multifrequency Raman images indicates leucine accumulation during the early stage of the E. coli biofilm formation, which may have resulted from physiological environment‐specific metabolic adaptation. We demonstrate that our label‐free Raman imaging method provides a useful platform for directly identifying still unknown natural products produced in biofilms as well as for visualizing heterogeneous distributions of biofilm constituents in situ. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and conformational analysis of bicyclic sulfonium salts. Structures related to the glycosidase inhibitor australine

The syntheses of eight sulfonium compounds with structures related to the naturally occurring pyrrolizidine alkaloid, australine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, are described. The synthetic strategy relies on the intramolecular attack of a cyclic thioether across a terminal double bond in the presence of a suitable electrophile. We postulate that these compounds, having a permanent positive charge on the sulfur atom, will mimic the highly unstable oxacarbenium ion transition state in a glycosidase-catalyzed hydrolysis reaction. The conformational preferences of these compounds, based on analysis of 1H-1H vicinal coupling constants and 1D-NOESY data, are attributed to both steric and electrostatic interactions. These compounds will be used in the study of structure-activity relationships with glycosidase enzymes.     

Synthesis of a sulfonium ion analogue of the glycosidase inhibitor swainsonine

The synthesis of a bicyclic sulfonium ion analogue of a naturally occurring indolizidine alkaloid, swainsonine, in which the bridgehead nitrogen atom is replaced by a sulfonium ion, has been achieved by a multistep synthesis starting from (2S,3S,4R)-2,3-dibenzyloxy-4-formaldehyde-thiolane. The synthetic strategy relies on the intramolecular displacement of a leaving group on a pendant acyclic chain by a cyclic thioether. This bicyclic sulfonium salt provides a candidate with which to further probe the hypothesis that a sulfonium salt carrying a permanent positive charge would be an effective glycosidase inhibitor.     

Aromatic core modified decaphyrins with the largest two-photon absorption cross-sections: syntheses and characterization

[structure: see text] Core-modified aromatic decaphyrins with 42pi conjugated electrons exhibit the highest two-photon absorption cross-section value (sigma(2) = 108,000 GM) known for any organic molecule, suggesting possible device applications in the field of nonlinear optics.     

Studies of the electrocatalytic activity of binary palladium ruthenium anode catalyst on Ni support for ethanol alkaline fuel cells

In extension to our earlier study on the electro-catalytic activity of binary palladium ruthenium anode catalyst on Ni support for ethanol alkaline fuel cells, we hereby report the optimum loading of Pd Ru electro-deposit and concentration of ethanol for better performance of the system. It is observed that the electro-catalytic activity increases with increase of loading of electro-catalyst on planar Ni foil electrode but decreases with its excess. The order with respect to ethanol and hence its adsorption in the process of its oxidation has been found to be both potential and concentration dependent. The results have been obtained from the studies on cyclic voltammetry, steady state polarization, scanning electron microscopy, energy dispersive X-ray spectroscopy and further analysis of our chronopotentiometric study executed previously. Electrodes constructed by deposition at the rate of current density, 5 mA cm⁻² for 10 min and 0.2 M ethanol concentration have been recommended for the better performance of this system.