Alkene Transfer Hydrogenation with Alkaline‐Earth Metal Catalysts

The alkene transfer hydrogenation (TH) of a variety of alkenes has been achieved with simple AeN′′₂ catalysts [Ae=Ca, Sr, Ba; N′′=N(SiMe₃)₂] using 1,4‐cyclohexadiene (1,4‐CHD) as a H source. Reaction of 1,4‐CHD with AeN′′₂ gave benzene, N′′H, and the metal hydride species N′′AeH (or aggregates thereof), which is a catalyst for alkene hydrogenation. BaN′′₂ is by far the most active catalyst. Hydrogenation of activated C=C bonds (e.g. styrene) proceeded at room temperature without polymer formation. Unactivated (isolated) C=C bonds (e.g. 1‐hexene) needed a higher temperature (120 °C) but proceeded without double‐bond isomerization. The ligands fully control the course of the catalytic reaction, which can be: 1) alkene TH, 2) 1,4‐CHD dehydrogenation, or 3) alkene polymerization. DFT calculations support formation of a metal hydride species by deprotonation of 1,4‐CHD followed by H transfer. Convenient access to larger quantities of BaN′′₂, its high activity and selectivity, and the many advantages of TH make this a simple but attractive procedure for alkene hydrogenation.     

N‐Heterocyclic carbenes derived from imidazo‐[1,5‐a]pyridines related to natural products: synthesis,structure and potential biological activity of some corresponding gold(I) and silver(I) complexes

A series of Au(I) complexes ( 12 , 13 , 14 , 15 , 16 ) and Ag(I) complexes ( 17 , 18 , 19 , 20 ) derived from imidazo[1,5‐a]pyridin‐3‐ylidenes were synthesized from AuCl(SMe₂) or by reacting silver(I) acetate with 2,5‐dimethylimidazo[1,5‐a]pyridin‐2‐ium iodide or imidazo[1,5‐a]pyridin‐2‐ium salts, and were characterized using NMR spectroscopy, mass spectrometry and elemental analyses. In addition, the Au(I) complex 13 and the Ag(I) complex 19 were characterized using single‐crystal X‐ray diffraction. Using paclitaxel as a standard, all Au(I) and Ag(I) N‐heterocyclic carbene complexes were evaluated for their in vitro anti‐tumour activity against 12 cell lines using a monolayer cell survival and proliferation assay. The highest anticancer activity was found for complexes 15 , 13 and 14 with mean IC₅₀ values of 10.09, 10.42 and 12.28 μM, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Fast Oxidative Cyclooligomerization towards Low‐ and High‐Symmetry Thiophene Macrocycles

Macrocycles with quaterthiophene subunits were obtained by cyclooligomerization by direct oxidative coupling of unsubstituted dithiophene moieties. The rings were closed with high selectivity by an α,β′‐connection of the thiophenes as proven by NMR spectroscopy. The reaction of the precursor with terthiophene moieties yielded the symmetric α,α′‐linked macrocycle in low yield together with various differently connected isomers. Blocking of the β‐position of the half‐rings yielded selectively the α,α′‐linked macrocycle. Selected cyclothiophenes were investigated by scanning tunneling microscopy, which displayed the formation of highly ordered 2D crystalline monolayers.     

Application of SIMS in Re-Technology Studies: Characterization of Trace-Element Distributions and Quantitative of Carbon-Determination

 The content and the three dimensional distribution of impurities play an important role in the production process of high purity rhenium powder (99.99% purity grade) and for its further use as alloying and coating agent in high temperature applications. In this paper the characterization of raw Re granulate, Re powder, cleaned by heat treatment, Re coatings, produced by most common preparation methods (PVD and VPS) and PM Re by means of SIMS is presented. The analysis of the three dimensional distribution of trace elements is performed by 3D SIMS. The quantification of carbon, which was not possible with other analytical techniques as a result of the high volatility of Re₂O₇ until now, has been carried out by SIMS depth profile analysis. It is discussed if internal standards, produced by introduction of defined amounts of carbon soot to the Re powder lead to useful results.     

Systematic Study on the Cytotoxic Potency of Commonly Used Dimeric Metal Precursors in Human Cancer Cell Lines

The cytotoxicities of seven dimeric metal species of the general formula [M(arene)Cl₂]₂, commonly used as precursors for complex synthesis and deemed biologically inactive, are investigated in seven commonly employed human cancer cell lines. Four of these complexes featured a ruthenium(II) core, where p-cymene, toluene, benzene and indane were used as arenes. Furthermore, the osmium(II) p-cymene dimer, as well as the Cp* dimers of rhodium(III) and its heavier analogue iridium(III) were included in this work (Cp*=1,2,3,4,5-pentamethylcyclopentadienide). While the cytotoxic potencies of the ruthenium(II) and osmium(II) dimers are very low (or not even detectable at applicable concentrations), surprising activity, especially in cells from ovarian malignancies (with one or two-digit micromolar IC₅₀ values), have been found for the rhodium(III) and iridium(III) representatives. This publication is aimed at all researchers using synthetic procedures based on functionalization of these dimeric starting materials to rationalize changes in biological properties, especially cytotoxicity in cancer cells.     

Electrochemical Detection of Asymmetric PCR Products by Labeling with Osmium Tetroxide

Single stranded DNA‐targets from asymmetric polymerase chain reaction (PCR) of a sequence of the gram positive, spore forming bacterium Clostridium acetobutylicum were detected by square‐wave voltammetry after labeling with osmium tetroxide bipyridine and hybridization with DNA capture probes immobilized on gold electrodes. The asymmetric PCR, performed with a 10‐fold excess of the forward‐primer, was used without any further purification for hybridization with protective strands and covalent labeling with osmium tetroxide bipyridine. Square‐wave voltammetric signals of 20 nmol/L targets were significantly higher at 50 °C compared with 23 °C hybridization temperature. A fully noncomplementary protective strand yielded thoroughly modified targets unable for further hybridization. Coupling this with thermal discrimination opens new opportunities for sequence specific DNA detection.     

Efficient photoinduced DNA damage by coralyne

The photoinduced DNA damage by the berberine derivative coralyne is presented. The irradiation of coralyne in the presence of plasmid DNA namely, pBR322, leads to remarkably fast DNA damage by single-strand cleavage, as determined by agarose-gel electrophoresis. Even upon exposure to sunlight, almost all of the supercoiled plasmid is converted to the open circular form in less than a minute [c(pBR322) = 3.5 x 10(-9) M; c(coralyne) = 4.3 x 10(-5) M]. The efficiency of the DNA strand cleavage is not decreased in the presence of radical-trapping reagents such as tert-butanol or DMSO. Moreover, the extent of the DNA damage is the same under aerobic conditions and at reduced oxygen concentration. Thus, the formation of reactive intermediates such as hydroxyl radicals or singlet oxygen is excluded. These results show that the exposure of coralyne and derivatives thereof to light, even with moderate light intensity, needs to be avoided during experiments in which their biological activity is assessed by plasmid unwinding assays.