Comment on "direct observation of laser filamentation in high-order harmonic generation"

We argue for a different physical interpretation of the results given in the recent Letter by Painter et al. [Opt. Lett.31, 3471 (2006)] in which an elongated Ti:saphire beam with two distinct waists is considered as direct evidence of laser filamentation. As the pulse power is well below the critical power for self-focusing, the authors pleaded for new examination of the n(2) value for He. A three-dimensional numerical modeling, using the published n(2) value for He, reproduces very well the measured data and invalidates the filamentation hypothesis.     

Benzofurobenzthiazole: VI—1H- und 13C-NMR-Spektren von 2-Aminobenzofuro[2,3-f] benzthiazol und 2-Aminobenzofuro[2,3-e]benzthiazol im Vergleich mit Dibenzofuran und 2-Aminobenzthiazol

Cyclization of 3-dibenzofurylthiourea under the conditions of the Hugershoff reaction gives the linear structure 1. ¹H n.m.r. and ¹³C n.m.r. spectra of the two isomeric aminobenzofurobenzothiazoles (1 and 3), recorded at 220 MHz, 60 MHz and 22,62 MHz respectively, were used as aids for the structure determination. The magnetic parameters were obtained partly by first-order analysis and partly by simulation of spectra using LAOCOON 3. The assignments were made by comparing the chemical shifts and coupling constants with those of the parent compounds dibenzofuran (4a) and 2-aminobenzothiazole (5c). In so far as the assignments of ¹H n.m.r. and ¹³C n.m.r. frequencies of the parent compounds themselves were unknown or supported by analogy only, they have been determined using experimental criteria such as deuterium substitution and investigation of changes in chemical shifts caused by derivation.     

Synthèse et réactivité d'un nouvel hydrure organostannique à “queue polaire”: le dibutyl-4,7,10-trioxaundécylstannane

A new tin hydride was prepared by reduction of the tin chloride obtained in the addition of hydrogenochlorodibutylstannane to the allyl methyl ether of diethyleneglycol. The efficiency of this compound in reductions and reductive additions to alkenes of alkyl halides was demonstrated as well as the easy separation of the organic products of reaction from the organotin compounds by liquid-solid chromatography over silica.     

Baker’s yeast reduction of 2-ethoxycarbonyl-cyclanones precursors of free radical chirons of the 2(S)-hydroxycycloalkyl moiety

The reduction of 2-ethoxycarbonyl-cyclopentanone and-cyclohexanone by baker’s yeast yielded in good yields (IS, 2R) 2-ethoxycarbonyl-cyclopentanol and cyclohexanol. The above two hydroxyesters were used as starting materials to prepare, via free radical reactions, various 2-substituted (Cl, Br, CH₂CH₂CO₂Et, S-Py) 1-ethoxymethoxy-cyclopentanes (d.e. 92–398%) and-cyclohexanes (d.e. 11–60%).     

The changing anisotropy character of weathered low-density polyethylene films recognized by quasi-static and ultrasonic mechanical testing

Unstabilised polyethylene films used for greenhouse covering have been exposed outdoors under the severe weathering conditions in the Sahara.The chemical and the morphological changes followed by infrared spectroscopy and by differential scanning calorimetry (DSC) show that the damages caused by oxidation to the tie molecules increase crystallinity and lead to a severe deterioration of the mechanical properties.The mechanical aspect of aging was studied by using standard quasi-static (QS) tensile testing measurements and by a non-destructive method based on ultrasound (US). This latter technique consists of measuring velocities and attenuations of ultrasonic waves propagating in several directions in the film plane.Both methods show the changing anisotropic character of the films with aging. The transverse direction has been found to be the principal axis of anisotropy consequently to a little more significant chain orientation in this direction acquired during processing.The connection between the chemical aspect of aging and the mechanical one (i.e. the viscoelastic properties and the anisotropic character) is discussed.     

Enzymatic Reactions in Organic Synthesis 4- Hydrolyses of Diesters

Enzpatic hydrolyses allowed discriminations of esters functions present in the same moiecule.     

Convergent synthesis and discovery of a natural product-inspired paralog-selective Hsp90 inhibitor

A convergent synthesis of benzoquinone ansamycin analogs is described that proceeds by a sequence of metallacycle-mediated alkyne-alkyne coupling, followed by site- and stereoselective dihydroxylation and global carbamate formation. These studies have led to (1) validation of alkyne-alkyne coupling to produce geldanamycin analogs that lack the problematic quinone, (2) the discovery that C6-C7 bis-carbamate functionality is compatible with Hsp90 inhibition, and (3) the identification of 1 as a nonquinone geldanamycin-inspired paralog-selective Hsp90 inhibitor.