The oxidative Glaser–Hay coupling of two terminal alkynes to furnish a butadiyne is a key reaction for acetylenic scaffolding. Although the reaction is performed under rather simple conditions [CuCl/TMEDA/O2 (air)], the mechanism is still under debate. Herein we present detailed studies on the scope of this reaction by using both 13C NMR and UV/Vis spectroscopic methods. The former method was used to study the kinetics of the coupling of aryl‐substituted alkynes as the aryl carbon resonances of the reactants and products have similar NOEs and relaxation times. The reaction was found to be zero‐order with respect to the terminal alkyne reactant under standard preparative conditions. Moreover, as the reaction proceeded, a clear change to slower reaction kinetics was observed, but it was still apparently zero‐order. The onset of this change was found to depend on the catalyst loading. This unfavorable change in reaction profile could be avoided by adding molecular sieves to the reaction mixture, thereby removing the water that is accumulated from the air and produced in the reaction in which dioxygen acts as the oxidizing agent. Not unexpectedly, the stirring rate, and hence uptake of air (O2), was found to have a significant effect on the rate of the reaction: The percentage of alkyne remaining after a certain time decreased linearly with the rate of stirring. On the basis of systematic studies, the optimized conditions for the coupling reaction using CuCl/TMEDA as the catalyst system are presented. Finally, we investigated the effect of different ligands and found that piperidine can also be conveniently employed as a ligand, albeit monodentate, in accord with related studies.
The histone demethylase KDM5B is considered to be a promising target for anticancer therapy. Single-chain antibodies from llama (nanobodies) have been raised to aid in crystallization and structure determination of this enzyme. The antigen-binding properties of 15 of these nanobodies have been characterized. The crystal structure of one of these (NB17) has been determined to a resolution of 1.85 Å. NB17 crystallizes in space group P4322 with six molecules in the asymmetric unit. The six molecules in the asymmetric unit pack as an entity with approximate D3 symmetry with interactions mediated by the CDR loops, which could act as a crystallization nucleus. NB17 does not bind to monomeric KDM5B residues 1-820, but is found to bind to aggregates formed after incubation at 310 K.
Functionalized oligo(phenyleneethynylene)s (OPEs) show potential as molecular wires for molecular electronics. A selection of OPEs with vertically disposed extended tetrathiafulvalene (TTF) units has been synthesized by a combination of metal-catalyzed cross-coupling and Wittig reactions. Two general synthetic routes were developed. In one route, the OPE scaffold was first constructed and finally the extended TTF units were incorporated by Wittig reactions. In the second route, the extended TTF module was first prepared and subsequently incorporated into an OPE backbone by palladium-catalyzed cross-coupling reactions. The latter route was employed for functionalization with protected thiol endgroups. Owing to the shape of these redox-active molecules, they are termed 'OPE-TTF cruciforms'. The electronic properties were investigated by UV-Vis spectroscopy and by cyclic voltammetry.
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