From propargylic amides to functionalized oxazoles: domino gold catalysis/oxidation by dioxygen

A new, highly efficient, and atom-economic access to a series of functionalized 2,5-disubstituted oxazoles from propargylic amides is reported. A series of propargylic amides were transformed to the corresponding alkylideneoxazolines by a gold(I) catalyst. The next step was an autoxidation to hydroperoxides bearing the heteroaromatic oxazoles. Experiments addressing the reaction mechanism reveal a radical pathway for this autoxidation process. The hydroperoxides could conveniently be converted to the corresponding alcohols by reduction with sodium borohydride.     

The Gröbner ring conjecture in one variable

We prove that a valuation domain V has Krull dimension ≤ 1 if and only if for every finitely generated ideal I of V[X] the ideal generated by the leading terms of elements of I is also finitely generated. This proves the Gröbner ring conjecture in one variable. The proof we give is both simple and constructive. The same result is valid for semihereditary rings.     

The reaction of water with guanosine radical cation in DNA

Structural analyses of DNA oligonucleotides indicate the presence of strongly bound water molecules in the major and minor grooves. These water molecules may react with guanosine radical cation to form 8-oxo-7,8-dihydroguanine and other oxidation products, which can result in strand scission or other DNA damage. We probed the reaction of guanosine radical cation with water by incorporating alkyl-substituted cytidines and thymidines into anthraquinone-linked DNA duplexes and irradiating them with UV light at 350 nm. The incorporation of these hydrophobic substituents disrupts the DNA spine of hydration and we have observed that these modifications do not affect the trapping or long-distance hopping of radical cations in DNA.     

Triplet topology of self-assembled zinc porphyrin-pyridylfullerene complex

This work extends a recent EPR study on light-driven electron and energy transfer in a self-assembled zinc porphyrin-pyridylfullerene (ZnP-PyrF) complex. We report on a triplet line shape analysis of the photoexcited PyrF monomer and the ZnP-PyrF complex dissolved in isotropic and anisotropic matrixes of different polarity, namely, toluene, tetrahydrofuran (THF), and the nematic liquid crystals (LCs), E-7 and ZLI-4389. The line shape of the unbound *(3)PyrF obtained in both isotropic matrixes exhibits triplet parameters similar to those obtained for other monoadducts of C(60) under similar experimental conditions. On the other hand, 8(3)PyrF oriented in the LCs shows a complicated line shape, which is attributed to two conformers: (a) an axial dominant (85%) configuration characterized by triplet parameters, similar to those obtained in the isotropic matrixes and (b) a bent configuration associated with spin density localized about the poles accompanied by sign reversal of the ZFS parameter D of the *(3)C(60) moiety. Further, since in both LCs the ZnP-PyrF complex mainly exhibits a conformation with axial symmetry, the differences between the electron and the energy transfer routes in each LC are attributed to their different polarity. This study reflects the strength of LC matrixes to serve as a topological tool, enabling us to determine the conformers' distribution and to differentiate between electron and energy transfer routes.     

Synthesis of the first rNHC (remote N-heterocyclic carbene) complexes with no heteroatom in the carbene carbon-containing ring

Two cationic carbene complexes with no heteroatom in the ring containing the carbene carbon, trans-bromo(2-methyl-2,6-dihydroisoquinolin-6-ylidene)bis(triphenylphosphine)palladium(II) triflate (3) and trans-chloro(1,2-dimethyl-1,7-dihydroquinolin-7-ylidene)bis(triphenylphosphine)palladium(II) triflate (4), were synthesized by oxidative substitution of Pd(PPh3)4 with N-methylated 6-bromoisoquinolinium and 7-chloro-2-methylquinolinium cations, respectively. Compound 3 was also prepared by methylation of neutral trans-bromo(2-methylisoquinolin-6-yl)bis(triphenylphosphine)palladium(II) (5). All complexes were unambiguously characterized by NMR and X-ray crystallographic studies.     

Changes in the intra- and inter-fibrillar structure of lyocell (TENCEL®) fibers caused by NaOH treatment

Some effects of NaOH treatment at concentrations of up to 8 M on (1) the porous structure, (2) the degree of swelling, (3) carboxyl content using methylene blue sorption and 9H-fluoren-2-yl-diazomethane (FDAM) methods, (4) dyeing, (5) the molecular weight distribution measured by gel permeation chromatography (GPC), (6) crystallinity determined by wide angle X-ray diffraction (WAXD) and (7) the tensile properties of lyocell fibers were investigated. The porous structure of fibers was visualised using fluorescence microscopy and transmission electron microscopy (TEM) on fiber cross-sections and was also studied by inversion size exclusion chromatography (ISEC). Mean pore diameter and pore area of fibers were not changed by NaOH treatments. The pore volume increased above 2.5 M NaOH. NaOH-treated samples showed higher dye uptake, higher swelling, but lower carboxyl and moisture content and increased crystallinity. As the NaOH concentration increased, the depth of colour following dyeing with C.I. Direct Red 81 also increased due to deep penetration of alkali into the fiber. In general, fiber properties were distinctly different in the ranges 0 to approximately 3 and 3–8 M NaOH. A part of this paper was presented at the 5th Central European Conference 2007, Fiber Grade Polymers, Chemical Fibers and Special Textiles, Krakow-Bielsko-Biala, Poland, 5–8 September 2007. Hale Bahar ?ztürk, Antje Potthast, Thomas Rosenau, Bill MacNaughtan, John R. Mitchell, Thomas Bechtold—Members of European Polysaccharide Network of Excellence (EPNOE), .     

Spatial optical filter sensor based on hollow-core silica tube

A spatial optical filter based on a hollow-core silica tube is proposed. Because of the hollow-core dimensions, it is possible to obtain a periodical spatial filter ranging from 1200 to 1700 nm with a channel spacing of 2.64 THz. The bandwidth is approximately 5.32 nm, and the isolation loss is ~30 dB. The optical losses are approximately ~0.67 dB/mm for a wavelength of 1500 nm. The 40 mm long spatial optical filter is tested as a sensing element and subjected to different physical parameters. The spatial optical filter is wavelength sensitive to strain and temperature, while for refractive-index variations there is an optical power dependency. This fiber structure can be used as a sensing element for extreme conditions, such as in very high temperature environments, where it presents a sensitivity of 27.5 pm °C(-1).     

Entropic Contributions to Sodium Solvation and Solvent Stabilization upon Electrochemical Sodium Deposition from Diglyme and Propylene Carbonate Electrolytes

The formation of an appropriate solid electrolyte interphase (SEI) at the anode of a sodium battery is crucially dependent on the electrochemical stability of solvent and electrolyte at the redox potential of Na/Na⁺ in the respective system. In order to determine entropic contributions to the relative stability of the electrolyte solution, we measure the reaction entropy of Na metal deposition for diglyme (DG) and propylene carbonate (PC) based electrolyte solutions by electrochemical microcalorimetry at single electrodes. We found a large positive reaction entropy for Na⁺ deposition in DG of Δ_R 234 J mol⁻¹ K⁻¹ (c.f.: Δ_R 83 J mol⁻¹ K⁻¹), which signals substantial entropic destabilization of Na⁺ in DG by about 0.73 eV, thus increasing the stability of solvent and electrolyte relative to Na⁺ reduction. We attribute this strong entropic destabilization to a highly negative solvation entropy of Na⁺, due to the low dielectric constant and high freezing entropy of DG.