Determination of the dispersion of the specific heat of glycerol by light scattering

We have performed light scattering experiments to study the Rayleigh-Mountain coupling in liquid and supercooled glycerol. The ratio of the Mountain widths on both sides of the coupling has been deduced and found to be about 1. This value is in good agreement with theoretical predictions for a structural relaxation, but not with experimental determinations by calorimetric methods.     

Tetrathiafulvalene in a perylene-3,4:9,10-bis(dicarboximide)-based dyad: a new reversible fluorescence-redox dependent molecular system

A donor-acceptor dyad system involving tetrathiafulvalene (TTF) as donor attached by a flexible spacer to perylene-3,4:9,10-bis(dicarboximide) (PDI) as acceptor was synthesized and characterized. The strategy used the preliminary synthesis of an unsymmetrical PDI unit bearing an alcohol functionality as anchor group. Single-crystal analysis revealed a highly organized arrangement in which all PDI molecules are packed in a noncentrosymmetrical pattern. It was shown that the fluorescence emission intensity of the TTF-PDI dyad can be reversibly tuned depending on the oxidation states of the TTF unit. This behavior is attributed to peculiar properties of TTF linked to a PDI acceptor, which fluoresces intrinsically. Consequently, this dyad can be considered as a new reversible fluorescence-redox dependent molecular system.     

Highly enantioselective copper(I)-phosphoramidite-catalysed additions of organoaluminium reagents to enones

Simple phosphoramidite ligands afford good to excellent levels of enantioselectivity in 1,4-additions of AlR3 species to enones; sequential carboalumination-ACA cascades are possible.     

Synthesen von 2-Pyronen aus α, β-ungesättigten Säurechloriden und tertiären Aminen

A new synthesis of 2-pyrones has been developed. Two molecules of α, β-unsaturated acid chlorides ( 8 , 12 and 18 ) condense, with loss of two molecules hydrogen chloride, to pairs of substituted 2-pyrones ( 9 and 10 , 13 and 14 , 19 and 20 ) when treated with triethyl amine in chloroform or methylene chloride at room temperature. In the case of 18 , two additional products were obtained, namely the resorcinol derivative 21 and traces of the 1, 3-cyclobutanedione derivative 22 . Under the same conditions the α, β-unsaturated acid chlorides 8 , 15 , 18 and 41 were condensed with trichloroacetyl chloride to give 6-trichloromethyl-2-pyrones ( 42 , 43 , 44 and 46 ). These 2-pyrones are valuable intermediates for the synthesis of 6-carboxy-2-pyrones and 6-methyl-2-pyrones. A methyl group in β-position of the α, β-unsaturated acid chloride appears to be essential for the described condensations, for the acid chlorides 16 and 17 did not yield defined products and the acid chloride 40 reacted with trichloroacetyl chloride in a very low yield. It is considered that the described reactions proceed via the 1, 4-addition of an acid chloride to a vinyl ketene or through the acylation of an intermediate anion by an acyl derivative as outlined in reaction scheme 1. The structures of the 2-pyrones were confirmed by their spectroscopic properties, summarized in table 3, and by some of their chemical transformations.     

Specular reflectivity of 13.5-nm light from Sn islands deposited on grazing incidence mirror surfaces

We have investigated the effect of exposure to thermal Sn atoms on the 13.5-nm specular reflectivity of single-layer Pd mirror surfaces. The mirror surfaces were characterized using low-energy ion scattering spectroscopy (LEISS) and the relative 13.5-nm specular reflectivity measured in situ during exposure to doses up to several 10¹⁶ cm^-2 Sn particles. The relative reflectivity loss at 13.5 nm is found to deviate from the theoretical Fresnel reflectivity. Losses are < 20% for fluence levels > 10¹⁶ cm^-2. The difference is due to deposited Sn nucleating at early stages of exposure and coalescing to nanoscale islands. Sn atomic surface fraction from LEISS reaches 50 a/o (atomic percent) at a fluence of 0.25×10¹⁶ cm^-2 and ultimately levels off at 93–95% for fluences greater than 2.0×10¹⁶ cm^-2. The specular reflectivity approaches the Fresnel theoretical value of 38.7% for thermal Sn deposition at large doses and equilibrates to 36.4%. The difference is mainly due to surface roughness of the deposited Sn film. PACS 61.18.Bn; 79.20.Rf; 78.70.Ck; 78.67.Bf     

One‐Pot Synthesis of Well‐Defined Amphiphilic and Adaptative Block Copolymers via Versatile Combination of “Click” Chemistry and ATRP

Well‐defined amphiphilic PCL‐b‐PDMAEMA block copolymers were successfully synthesized by a combination of ATRP and “click” chemistry following either a commutative two‐step procedure or a straightforward one‐pot process using CuBr · 3Bpy as the sole catalyst. Compared to the traditional coupling method, combining ATRP and click chemistry even in a “one‐pot” process allows the preparation of PCL‐b‐PDMAEMA diblock copolymers characterized by a narrow molecular weight distribution and quantitative conversion of azides and alkynes into triazole functions. Moreover, the amphiphilic character of these copolymers was demonstrated by surface tension measurements and critical micellization concentration was calculated.

     

Stereoselective synthesis and conformational analysis of aromatic C‐thionucleosides

Tetrahydrothiophene derivatives 2a–2d , which are useful intermediates in the synthesis of C‐thionucleosides, were obtained by a tandem strategy that involves the base‐catalyzed conjugate addition of ethyl 2‐mercaptoacetate to trans‐cinnamaldehyde followed by cyclization. The solvent and the nature of the amine used as Lewis base influence the stereo‐ selectivity of the reaction. The reduction of each isolated derivative 2a–2d was performed with LiAlH₄ to afford C‐thionucleosides 3a–3d . The configuration and conformation of each diastereomer 2a–2d and 3a–3d was assigned by means of the analysis of vicinal proton–proton coupling constants. The X‐ray structure of 2d, 3a , and 3b confirmed the configuration assigned to each isomeric tetrahydrothiophenes. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:289–298, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20205