Penumbral structure and outflows in simulated sunspots

Sunspots are concentrations of magnetic field on the visible solar surface that strongly affect the convective energy transport in their interior and surroundings. The filamentary outer regions (penumbrae) of sunspots show systematic radial outward flows along channels of nearly horizontal magnetic field. These flows were discovered 100 years ago and are present in all fully developed sunspots. Using a comprehensive numerical simulation of a sunspot pair, we show that penumbral structures with such outflows form when the average magnetic field inclination to the vertical exceeds about 45 degrees. The systematic outflows are a component of the convective flows that provide the upward energy transport and result from anisotropy introduced by the presence of the inclined magnetic field.Comment: 19 pages, 8 figures, main Science article + supporting online material combined into one fil

On the relevance of polyynyl-substituted PAHs to astrophysics

We report on the absorption spectra of the polycyclic aromatic hydrocarbon (PAH) molecules anthracene, phenanthrene, and pyrene carrying either an ethynyl (-C2H) or a butadiynyl (-C4H) group. Measurements were carried out in the mid infrared at room temperature on grains embedded in CsI pellets and in the near ultraviolet at cryogenic temperature on molecules isolated in Ne matrices. The infrared measurements show that interstellar populations of polyynyl-substituted PAHs would give rise to collective features in the same way non-substituted PAHs give rise to the aromatic infrared bands. The main features characteristic of the substituted molecules correspond to the acetylenic CH stretching mode near 3.05 mum and to the almost isoenergetic acetylenic CCH in- and out-of-plane bending modes near 15.9 mum. Sub-populations defined by the length of the polyynyl side group cause collective features which correspond to the various acetylenic CC stretching modes. The ultraviolet spectra reveal that the addition of an ethynyl group to a non-substituted PAH molecule results in all its electronic transitions being redshifted. Due to fast internal energy conversion, the bands at shorter wavelengths are significantly broadened. Those at longer wavelengths are only barely affected in this respect. As a consequence, their relative peak absorption increases. The substitution with the longer butadiynyl chain causes the same effects with a larger magnitude, resulting in the spectra to show a prominent if not dominating pi-pi* transition at long wavelength. After discussing the relevance of polyynyl-substituted PAHs to astrophysics, we conclude that this class of highly conjugated, unsaturated molecules are valid candidates for the carriers of the diffuse interstellar bands.Comment: 29 pages, 9 figures, accepted for publication in ApJ 2 April 201

Synthesis of Euchrestifoline Using Iron- and Palladium-Catalyzed C–H Bond Activations

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We describe a short and efficient synthetic route to euchrestifoline. Key steps of our approach are the iron(III)-catalyzed Wacker-type oxidation of a chromene derivative with hexadecafluorophthalocyanine-iron (FePcF16) as catalyst, a palladium(0)-catalyzed Buchwald–Hartwig amination, and the final palladium(II)-catalyzed oxidative cyclization of the resulting diarylamine to the natural product

Enantioselective Total Synthesis and Assignment of the Absolute Configuration of the Furo[3,2- a]carbazole Alkaloid Furoclausine-B

© Copyright 2018 American Chemical Society. We describe the first enantioselective total synthesis and the assignment of the absolute configuration of the furo[3,2-a]carbazole alkaloid furoclausine-B. As key steps for our approach we used a palladium(II)-catalyzed double C-H-bond activation for the construction of the carbazole framework, a Shi epoxidation, and an intramolecular opening of the epoxide for annulation of the dihydrofuran moiety

First Total Synthesis of 7-Isovaleryloxy-8-methoxygirinimbine

© Georg Thieme Verlag Stuttgart New York Synthesis. We describe the first total synthesis of the pyrano[3,2- a ]carbazole alkaloid 7-isovaleryloxy-8-methoxygirinimbine, using a palladium(II)-catalyzed double C-H-bond activation for construction of the carbazole framework and a phenylboronic acid catalyzed annulation of the pyran ring as key steps

Synthesis of Tetranuclear Palladium(II) Complexes and Their Catalytic Activity for Cross-Coupling Reactions

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim We have developed a short and simple synthesis of tetranuclear palladium(II) complexes that have been structurally confirmed by X-ray analysis. These complexes were formed in about 30 % overall yield by spontaneous metalation of dimethylaminoarene derivatives and exhibit a high stability. We have studied the utility of the tetranuclear palladium(II) complexes as precatalysts for Mizoroki–Heck and Suzuki–Miyaura cross-coupling reactions. Our novel complexes show excellent catalytic activities with high turnover numbers (TON) and high turnover frequencies (TOF) (e.g., for the Suzuki–Miyaura reaction: TON up to 538000 and TOF up to 23400 h −1 at room temperature)

Chemical constituents of the soft corals Sinularia vanderlandi and Sinularia gravis from the coast of Madagascar

© 2016 The Royal Society of Chemistry.The crude extracts of the Madagascan soft corals Sinularia vanderlandi and Sinularia gravis (Alcyoniidae) showed activity against Plasmodium falciparum which led us to study their chemical constituents. The new cadinane-type sesquiterpenoid vanderlandin (1) has been obtained from S. vanderlandi along with 24-methylenecholesterol (2). Four new compounds, the spatane-type diterpenoid gravilin (3), the monoalkylmonoacylglycerol 4, the dihomoditerpenoid ketone 5, and isodecaryiol (9), along with the three known compounds (+)-(S)-geranyllinalool (6), (-)-(R)-nephthenol (7), and 11,12-epoxysarcophytol A (8) have been isolated from the methanol extract of S. gravis. The structures were elucidated based on extensive spectroscopic methods, in particular various 2D NMR techniques. The structure of isodecaryiol (9) including its absolute configuration could be confirmed by X-ray diffraction

Chemical constituents of the soft corals Sinularia vanderlandi and Sinularia gravis from the coast of Madagascar

© 2016 The Royal Society of Chemistry. The crude extracts of the Madagascan soft corals Sinularia vanderlandi and Sinularia gravis (Alcyoniidae) showed activity against Plasmodium falciparum which led us to study their chemical constituents. The new cadinane-type sesquiterpenoid vanderlandin (1) has been obtained from S. vanderlandi along with 24-methylenecholesterol (2). Four new compounds, the spatane-type diterpenoid gravilin (3), the monoalkylmonoacylglycerol 4, the dihomoditerpenoid ketone 5, and isodecaryiol (9), along with the three known compounds (+)-(S)-geranyllinalool (6), (-)-(R)-nephthenol (7), and 11,12-epoxysarcophytol A (8) have been isolated from the methanol extract of S. gravis. The structures were elucidated based on extensive spectroscopic methods, in particular various 2D NMR techniques. The structure of isodecaryiol (9) including its absolute configuration could be confirmed by X-ray diffraction

Solid-phase synthesis and characterization of n-terminally elongated Aβ-3-x-peptides

In addition to the prototypic amyloid-beta (A beta) peptides A beta(1-40) and A beta(1-42), several A beta variants differing in their amino and carboxy termini have been described. Synthetic availability of an A beta variant is often the key to study its role under physiological or pathological conditions. Herein, we report a protocol for the efficient solid-phase peptide synthesis of the N-terminally elongated Ab-peptides A beta(-3-38), A beta(-3-40), and A beta(-3-42). Biophysical characterization by NMR spectroscopy, CD spectroscopy, an aggregation assay, and electron microscopy revealed that all three peptides were prone to aggregation into amyloid fibrils. Immunoprecipitation, followed by mass spectrometry, indicated that A beta(-3-38) and A beta(-3-40) are generated by transfected cells even in the presence of a tripartite beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitor. The elongated Ab peptides starting at Val(-3) can be separated from N-terminally-truncated A beta forms by high-resolution isoelectric-focusing techniques, despite virtually identical isoelectric points. The synthetic A beta variants and the methods presented here are providing tools to advance our understanding of the potential roles of N-terminally elongated A beta variants in Alzheimer's disease