Pd-Ga intermetallic compounds as highly selective semihydrogenation catalysts

The intermetallic compounds Pd(3)Ga(7), PdGa, and Pd(2)Ga are found to be highly selective semihydrogenation catalysts for acetylene outperforming established systems. The stability of the crystal and electronic structure under reaction conditions allows the direct relation of structural and catalytic properties and a knowledge-based development of new intermetallic catalyst systems. In the crystal structure of PdGa palladium is exclusively surrounded by gallium atoms. The alteration of the Pd coordination in PdGa leads to a strong modification of the electronic structure around the Fermi level in comparison to elemental Pd. Electronic modification and isolation of active sites causes the excellent catalytic semihydrogenation properties.     

Bulk and surface structure and high-temperature thermoelectric properties of inverse clathrate-III in the Si-P-Te system

The creation of thermoelectric materials for waste heat recovery and direct solar energy conversion is a challenge that forces the development of compounds that combine appreciable thermoelectric figure‐of‐merit with high thermal and chemical stability. Here we propose a new candidate for high‐temperature thermoelectric materials, the type‐III Si_172?xP_xTe_y cationic clathrate, in which the framework is composed of partially ordered silicon and phosphorus atoms, whereas tellurium atoms occupy guest positions. We show that the utmost stability of this clathrate (up to 1500 K) in air is ensured by the formation of a nanosized layer of phosphorus‐doped silica on the surface, which prevents further oxidation and degradation. As‐cast (non‐optimized) Si‐P‐Te clathrates display rather high values of the thermoelectric figure‐of‐merit (ZT=0.24–0.36) in the temperature range of 700–1100 K. These ZT values are comparable to the best values achieved for the properly doped transition‐metal‐oxide materials. The methods of the thermoelectric efficiency optimization are discussed.     

Red‐Emitting Rhodamine Dyes for Fluorescence Microscopy and Nanoscopy

Fluorescent markers emitting in the red are extremely valuable in biological microscopy since they minimize cellular autofluorescence and increase flexibility in multicolor experiments. Novel rhodamine dyes excitable with 630 nm laser light and emitting at around 660 nm have been developed. The new rhodamines are very photostable and have high fluorescence quantum yields of up to 80 %, long excited state lifetimes of 3.4 ns, and comparatively low intersystem‐crossing rates. They perform very well both in conventional and in subdiffraction‐resolution microscopy such as STED (stimulated emission depletion) and GSDIM (ground‐state depletion with individual molecular return), as well as in single‐molecule‐based experiments such as fluorescence correlation spectroscopy (FCS). Syntheses of lipophilic and hydrophilic derivatives starting from the same chromophore‐containing scaffold are described. Introduction of two sulfo groups provides high solubility in water and a considerable rise in fluorescence quantum yield. The attachment of amino or thiol reactive groups allows the dyes to be used as fluorescent markers in biology. Dyes deuterated at certain positions have narrow and symmetrical molecular mass distribution patterns, and are proposed as new tags in MS or LC‐MS for identification and quantification of various substance classes (e.g., amines and thiols) in complex mixtures. High‐resolution GSDIM images and live‐cell STED‐FCS experiments on labeled microtubules and lipids prove the versatility of the novel probes for modern fluorescence microscopy and nanoscopy.     

Mitotic slippage in non-cancer cells induced by a microtubule disruptor,disorazole C<Subscript>1</Subscript>

Background

Disorazoles are polyene macrodiolides isolated from a myxobacterium fermentation broth. Disorazole C₁ was newly synthesized and found to depolymerize microtubules and cause mitotic arrest. Here we examined the cellular responses to disorazole C₁ in both non-cancer and cancer cells and compared our results to vinblastine and taxol.

Results

In non-cancer cells, disorazole C₁ induced a prolonged mitotic arrest, followed by mitotic slippage, as confirmed by live cell imaging and cell cycle analysis. This mitotic slippage was associated with cyclin B degradation, but did not require p53. Four assays for apoptosis, including western blotting for poly(ADP-ribose) polymerase cleavage, microscopic analyses for cytochrome C release and annexin V staining, and gel electrophoresis examination for DNA laddering, were conducted and demonstrated little induction of apoptosis in non-cancer cells treated with disorazole C₁. On the contrary, we observed an activated apoptotic pathway in cancer cells, suggesting that normal and malignant cells respond differently to disorazole C₁.

Conclusion

Our studies demonstrate that non-cancer cells undergo mitotic slippage in a cyclin B-dependent and p53-independent manner after prolonged mitotic arrest caused by disorazole C₁. In contrast, cancer cells induce the apoptotic pathway after disorazole C₁ treatment, indicating a possibly significant therapeutic window for this compound.

     

A chiral 6-membered N-heterocyclic carbene copper(I) complex that induces high stereoselectivity

A chiral 6-membered annulated N-heterocyclic (6-NHC) copper complex that catalyzes β-borylations with high yield and enantioselectivity was developed. The chiral 6-NHC copper complex is easy to prepare on the gram scale and is very active, showing 10,000 turnovers at 0.01 mol % of catalyst without significant decrease of enantioselectivity and with useful reaction rates.     

A new class of solutions to the WDVV equation

The known prepotential solutions F to the Witten-Dijkgraaf-Verlinde-Verlinde (WDVV) equation are parametrized by a set {α} of covectors. This set may be taken to be indecomposable, since . We couple mutually orthogonal covector sets by adding so-called radial terms to the standard form of F. The resulting reducible covector set yields a new type of irreducible solution to the WDVV equation.     

Crystal packing in the structures of diethanolamine derivatives

Four distinct hydrogen‐bonding topologies were observed in the structures of six diethanolamine ligands. These compounds are (1R*,2R*)‐2‐[(2‐hydroxyethyl)(methyl)amino]‐1,2‐diphenylethanol, C₁₇H₂₁NO₂, (I), 1‐[(2S)‐2‐(hydroxydiphenylmethyl)pyrrolidin‐1‐yl]‐2‐methylpropan‐2‐ol, C₂₁H₂₇NO₂, (II), 2‐[(2‐hydroxyethyl)(methyl)amino]‐1,1‐diphenylethanol, C₁₇H₂₁NO₂, (III), 1‐{(2‐hydroxy‐2‐methylpropyl)[(1S)‐1‐phenylethyl]amino}‐2‐methylpropan‐2‐ol, C₁₆H₂₇NO₂, (IV), 1‐{[(2R)‐2‐hydroxy‐2‐phenylethyl][(1S)‐1‐phenylethyl]amino}‐2‐methylpropan‐2‐ol, C₂₀H₂₇NO₂, (V), and (1R*,2S*)‐2‐[(2‐hydroxyethyl)(methyl)amino]‐1,2‐diphenylethanol, C₁₇H₂₁NO₂, (VI). In each compound, all `active' hydroxy H atoms are engaged in hydrogen bonding, but the N atoms are not involved in intermolecular hydrogen bonding. In the structures of (I), (II) and (IV)–(VI), molecules are linked into chains by intermolecular O—H...O interactions. These chains are organized in such a way as to hide the hydrophilic groups inside, and so the outer surfaces of the chains are hydrophobic. The structure of (VI) contains two distinct non‐equivalent systems of intermolecular O—H...O hydrogen bonds formed by disordered hydroxy H atoms.     

Synthesis of substituted pyrano[3,2-c]pyridines via Diels-Alder reaction of 3-methylenepyridin-4-one

On heating, the di-Boc-pyridin-4-one derivative 7 gave an unstable 3-methylenepyridin-4-one intermediate 3, which underwent a rearomatising Diels-Alder cycloaddition with activated alkenes to give substituted pyrano[3,2-c]pyridines in moderate yields.     

Long-range carbon-carbon connectivity via unsymmetrical indirect covariance processing of HSQC and HMBC NMR data

It was recently demonstrated that an IDR- (Inverted Direct Response) HSQC-TOCSY data set could be decomposed into a negatively phased direct response spectrum and a positively phased relayed response spectrum that could then be subjected to unsymmetrical indirect covariance processing for the removal of artifacts due to response overlap in the proton NMR spectrum of the molecule. Using experimentally discrete HSQC and HMBC data sets, it is shown that unsymmetrical indirect covariance processing of the pair of NMR spectra affords a presentation containing long-range carbon-carbon connectivity information. The method is demonstrated using strychnine as a model compound. The resulting data are largely free of artifacts although artifacts can arise due to proton response overlap, as previously reported.     

Unsymmetrical covariance processing of COSY or TOCSY and HSQC NMR data to obtain the equivalent of HSQC‐COSY or HSQC‐TOCSY spectra

Artifacts observed in the indirect covariance NMR spectrum of HSQC‐TOCSY data have recently been analyzed and a method for their elimination proposed. More recently, unsymmetrical covariance processing has been applied HSQC and HMBC spectral data to afford long‐range carbon‐carbon correlation information equivalent to that obtained from n, 1‐, 1, n‐ and m,n‐ADEQUATE spectra. We now wish to describe the results obtained through the application of unsymmetrical covariance processing of HSQC and COSY or TOCSY data, which affords the equivalent of HSQC‐COSY and HSQC‐TOCSY data in a fraction of the time required to record these spectra directly and with considerably higher sensitivity.