Angle-resolved electron spectroscopy of laser-assisted Auger decay induced by a few-femtosecond x-ray pulse

Two-color (x-ray+infrared) electron spectroscopy is used for investigating laser-assisted KLL Auger decay following 1s photoionization of atomic Ne with few-femtosecond x-ray pulses from the Linac Coherent Light Source. In an angle-resolved experiment, the overall width of the laser-modified Auger-electron spectrum and its structure change significantly as a function of the emission angle. The spectra are characterized by a strong intensity variation of the sidebands revealing a gross structure. This variation is caused, as predicted by theory, by the interference of electrons emitted at different times within the duration of one optical cycle of the infrared dressing laser, which almost coincides with the lifetime of the Ne 1s vacancy.     

A family of multicyclic indolosesquiterpenes from a bacterial endophyte

Three novel indolosesquiterpenes, xiamycin B (1b), indosespene (2), and sespenine (3), along with the known xiamycin A (1a) were isolated from the culture broth of Streptomyces sp. HKI0595, a bacterial endophyte of the widespread mangrove tree Kandelia candel. Agar diffusion assays revealed moderate to strong antimicrobial activities against several bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis, while no cytotoxicity against human tumor cell lines was observed. Together with the previously reported oridamycin, the endophyte metabolites represent the first indolosesquiterpenes isolated from prokaryotes.     

An approach to the core structure of leiodermatolide

The synthesis of the 16-membered core structure of leiodermatolide 40 has been achieved in 26 linear steps starting from (R)-Roche ester. The key steps in the synthesis of 40 are a Stille cross-coupling between two main fragments 11 and 33 having roughly equal size. For the trisubstituted C4/C5 double bond a carbometalation reaction followed by a Suzuki coupling was used. A Yamaguchi macrolactonization furnished macrolactone 39.     

Synthesis of a pladienolide B analogue with the fully functionalized core structure

Starting from (R)-(-)-linalool (6), terminus differentiation and chain extension via aldol type reactions led to ketophosphonate 16 (C1-C8 building block). In a Horner-Wadsworth-Emmons reaction, 16 reacted with aldehyde 22, which contained the vicinal anti-Me-OH pattern and a vinyl iodide function, to provide the C1-C13 part of pladienolide B. After Shiina macrolactonization, reduction of the enone 26 gave the core structure 27. A Stille cross-coupling of vinyl iodide 27 with tributylphenylstannane eventually furnished analogue 30.     

The Effect of Specific Adsorption of Cations and Their Size on the Charge‐Compensation Mechanism in Carbon Micropores: The Role of Anion Desorption

Combined application of cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) technique reveals a complicated interplay between the adsorption of ammonium and lower molecular weight tetraalkyl ammonium cations and desorption of Cl^? anions inside carbon micropores at low surface charge densities, which results in failure of their permselectivity. Higher negative surface charge densities induce complete exclusion (desorption) of the Cl^? co‐ions, which imparts purely permselective behavior on the carbon micropores. The second fundamental effect discovered herein relates to the dominant role of anion desorption (as compared to cation adsorption), that is, overwhelming failure of permselectivity extends to high negative charge densities of the electrode in the presence of bulky tetraalkyl ammonium cations, which tend to be confined in the micropores of the carbon. The results obtained are important for advancement of high power density carbon‐based supercapacitors, nanofiltration technologies with porous carbon membranes, and studies of ionic transport across biological membranes.     

Confinement effects for ionic carriers in SrTiO3 ultrathin films: first-principles calculations of oxygen vacancies

One-dimensional confinement effects are modelled within the hybrid HF-DFT LCAO approach considering neutral and single-charged oxygen vacancies in SrTiO(3) ultrathin films. The calculations reveal that confinement effects are surprisingly short-range in this partly covalent perovskite; already for film thickness of 2-3 nm (and we believe, similar size nanoparticles) only the surface-plane defect properties differ from those in the bulk. This includes a pronounced decrease of the defect formation energy (by ～1 eV), a much deeper defect band level and a noticeable change in the electronic density redistribution at the near-surface vacancy site with respect to that in the bulk. The results also show that the size effect pertains to the interactions between the oxygen vacancy and two neighboring titanium atoms and orientation (parallel or perpendicular to the surface) of the Ti-V(O)-Ti complex. In particular, we predict considerable oxygen vacancy segregation towards the surface.     

Electronic absorption spectra of protonated pyrene and coronene in neon matrixes

Protonated pyrene and coronene have been isolated in 6 K neon matrixes. The cations were produced in the reaction of the parent aromatics with protonated ethanol in a hot-cathode discharge source, mass selected, and co-deposited with neon. Three electronic transitions of the most stable isomer of protonated pyrene and four of protonated coronene were recorded. The strongest, S(1) ← S(0) transitions, are in the visible region, with onset at 487.5 nm for protonated pyrene and 695.6 nm for protonated coronene. The corresponding neutrals were also observed. The absorptions were assigned on the basis of ab initio coupled-cluster and time-dependent density functional theory calculations. The astrophysical relevance of protonated polycyclic aromatic hydrocarbons is discussed.     

An oxidative coupling route to macrocyclic thiophenes and its application in the synthesis of a donor/acceptor hybrid molecule

A route towards phenylene-bithiophene macrocycles via oxidative thiophene coupling under pseudo-high dilution conditions is reported. This method is applied to the synthesis of a shape-persistent thiophene macrocycle with extraannularly attached perylenebisimide moieties that forms supramolecular aggregates at the solid/liquid interface.     

Additive polynomials for finite groups of Lie type

This paper provides a realization of all classical finite groups of Lie type as well as a number of exceptional ones (with low-dimensional representations) as Galois groups over function fields over F _q and derives explicit additive polynomials for the extensions. Our unified approach is based on results of Matzat which give bounds for Galois groups of Frobenius modules and uses the structure and representation theory of the corresponding connected linear algebraic groups.