5,12-Dimethyl-3,10-diphenyl-1,3,4,8,10,11-hexaazatetracyclo[6.6.1.02,6.09,13]pentadeca-2(6),4,9(13),11-tetraene,a new Tröger's base analogue

The synthesis of the title Tröger's base analogue, C₂₃H₂₂N₆, was undertaken in order to study the influence of a methyl substituent on the structure. Minor differences were found in the bond lengths of the title structure in comparison with the values for free pyrazole and for the first pyrazolic Tröger's base reported in the literature. There are two mol­ecules of opposite chirality in the asymmetric unit and the packing in the lattice is characterized by a non-crystallographic n-glide plane relating these mol­ecules.     

Synthesis of LeX and LeY Oligosaccharides with Azido-Type Spacer-Arms. Comparison of 3- and 4-Methoxybenzyl Groups as Key Temporary Protective Groups

Abstract

5-Azido-3-oxa-l-pentanol was prepared from 2-(2-chloroethoxy)ethanol and used as a spacer in the chemical synthesis of the trisaccharide β-D-Gal-(1→4)-[α-L-Fuc-(1→3)]-GlcNAc and the tetrasaccharide α-L-Fuc-α-(1→2)-β-D-Gal-(1→4)-[α-L-Fuc-(1→3)]-GlcNAc that represent the epitopes defining the human blood groups Le^x and Le^y. The classical 4-methoxybenzyl group and the remarably acid-stable 3-methoxybenzyl group were compared as temporary protective groups for position 3 at the glucosamine unit to circumvent the problems associated with the simultaneous presence of allyl and azido groups. The resulting oligosaccharides were coupled to proteins with high efficiency.

     

Comparative study of ZnO and CuSCN semiconducting nanowire electrodeposition on different substrates

In this study, we are reporting on the electrochemical deposition of two kinds of semiconducting nanowires (ZnO and CuSCN) on different substrates. ZnO and CuSCN are n- and p-type transparent semiconductors whose electrochemical preparation has some similarity, and it is a combination of two steps: an electrochemical reduction with consecutive chemical precipitation. Here, we show that despite the different physicochemical nature of the studied materials, when they are deposited electrochemically, their dimensions depend mainly on the surface state of the used substrate. Thus, depending on the substrate morphology, nanowires with diameters between 50 and 380 nm from both semiconductors could be grown. It is also shown that ZnO and CuSCN nanowires could be successfully grown on glass and plastic substrates as well as on a metallic one. The possibility of growing these transparent semiconductors on flexible substrates opens new perspectives for their use in “invisible” electronic devices.     

Reactions of aryl acetates with secondary alicyclic amines in ethanol/water mixtures: Effect of the solvent composition on the kinetics and mechanism

We report a kinetic study on the reactions of secondary alicyclic amines toward 4‐nitrophenyl, 2,4‐dinitrophenyl, and 2,4,6‐trinitrophenyl acetates ( 1, 2 , and 3 ) in ethanol/water mixtures of different compositions. It is found that (i) the intermediate in the reaction of 1 is stabilized in a mixture of 90 vol% ethanol; (ii) for the reaction of 2 , the mechanism is stepwise in water but concerted in the mixtures; (iii) For the reaction of 3 , the mechanism is concerted along the whole range of composition; (iv) the effect of ? NO₂ outweighs the solvent effect; (v) preferential solvation in the core of reaction can be ruled out. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 687–693, 2011     

Specifically (π → π*)-Induced Cyclohexenone Reactions 6-Benzylbicyclo [4.4.0]dec-1-en-3-ones

6-Benzylbicyclo [4.4.0]dec-1-en-3-one ( 9 ) and the 2-methyl homologue ( 10 ) underwent a (γ → α )-1, 3-benzyl shift to the β,γ-unsaturated ketones 21 and 22 , respectively, when excited in the π π* absorption band. The quantum yield was ca. 0.1 at 254 nm for the formation of both products in alkane solvents. These reactions occur specifically from the S₂(π, π*) state in competition with its decay to the S₁(n, π*) and T states. The triplet reaction of 9 , initiated by n → π* irradiation and by sensitization, was a double-bond shift to 20 , whereas no identifiable product was observed from 10 under these conditions. Direct and acetone-sensitized irradiations of 21 and 22 resulted in oxadi-π-methane rearrangements to mixtures of syn- and anti- 30 and syn- and anti- 31 , respectively.     

The influence of the transition metal and the heteroatomic-bridge on the action of metallocene/methyl aluminoxane catalysts in ethylene polymerization and on the properties of the polymer

This work reports a comparative study of the catalytic behaviour for a series of metallocenes derived from Ti, Zr, Hf and Nb, which after activation with methylaluminoxane can polymerize ethylene. Results show that the Zr metallocene with a  (CH₃)₂Si Bridge presents the highest activity, and the metallocenes based on Hf and Nb do not show any significant activity under the tested conditions.     

New low viscous polyisocyanates for VOC compliant systems

Since 1961, aliphatic polyisocyanates based on HDI-biurets are used as light stable hardeners for 2-K polyurethane coatings. The market introduction of the HDI-isocyanurates or simply 'trimers' in the early 1980's was driven by their lower viscosity and their better monomer stability. The most recent development in HDI-polyisocyanate research are the iminooxadiazinediones (asymmetric trimers). In this paper, a new product based on that technology with a very low viscosity (700 mPas@23°C) and a NCO-functionality of more than 3 is presented. Because of its low viscosity, this hardener can be easily incorporated into aqueous systems and is the solution for high and full solids coatings as well.