9-CIS, 11-CIS-RETINAL* FROM DIRECT IRRADIATION OF ALL-TRANS-RETINAL. NEW GEOMETRIC ISOMERS OF VITAMIN A AND CAROTENOIDS 9

Abstract The irradiation mixture of all-trans-retinal in acetonitrile was shown to contain four cis,cis isomers as well as the four cis isomers reported earlier. The relatively new 9-cis, 11-cis-retinal was isolated and characterized.     

Time resolved Fano resonances

Recent advances in the generation of sub-fs extreme ultraviolet pulses and attosecond metrology have opened up the possibility to trace the time evolution of electronic wave packets inside atoms in pump-probe experiments. We investigate the feasibility of observing the buildup of a Fano resonance in the time domain by attosecond streaking techniques. A time-resolved resonance is initialized by a sub-fs extreme ultraviolet-pump pulse in the presence of a synchronized phase-controlled probe laser pulse. The time evolution of the coherent superposition of resonant state and continuum is mapped onto a modulation of the electron spectrum as a function of the time delay between pump and probe pulse. (super-)Coster-Kronig transitions with lifetimes of approximately 400 asec( are identified as prime candidates.     

Synthesis and absolute configuration of (S)-(+)-chichimol ketone: the defensive secretion of walking stick Agathemera elegans

The first enantioselective synthesis of chichimol ketone (4-methyl-1-hepten-3-one) is described and the absolute configuration of the main semiochemical compound is determined as having an (S)-configuration. The synthesis features the use of a ruthenium catalytic asymmetric hydrogenation reaction to introduce chirality into acid 2. The synthetic chichimol ketone (S)-1 displayed a specific rotation that was in accordance with that of the natural product, thereby supporting the (S) configuration for natural chichimol ketone. To assure the correct stereochemical assignment, (S)-1 was converted in the known ketone (S)-5: the main alarm pheromone of the ant Atta texana that is 400 times more active than its (R)-enantiomers.     

Immunolocalization of an osteopontin-like protein in dense granules of Toxoplasma gondii tachyzoites and its association with the parasitophorous vacuole

Toxoplasma gondii is an apicomplexan parasite infecting a broad host range, including humans. The parasite invades host cell by active penetration with the participation of its secretory organelles proteins during this process. Until now, only a limited number of secretory proteins have been discovered, and the effectors molecules involved in parasite invasion and survival are not well understood. Osteopontin (OPN) is a multifunctional glycophosphoprotein, secreted by different cell types, which is involved in various physiological and pathological events including cell signaling and survival. For the first time we demonstrated in this work by immunofluorescence and immunoelectron microscopy approaches the localization of an OPN-like protein in dense granules of extracellular T. gondii tachyzoites. Western blotting and RT-PCR confirmed this protein expression by the parasites. Our results also showed, after macrophage invasion, an intense positive labeling for OPN-like protein at the sub-apical portion of tachyzoites, the site of dense granules secretion, and the localization of this protein at the parasitophorous vacuole membrane. These data suggest that dense granules secrete an OPN-like protein, and we speculate that this protein participates during the parasite interaction process with host cells and parasitophorous vacuole formation.     

Direct Synthesis of Hexagonal NaGdF4 Nanocrystals from a Single‐Source Precursor: Upconverting NaGdF4:Yb3+,Tm3+ and Its Composites with TiO2 for Near‐IR‐Driven Photocatalysis

A novel single‐source precursor NaGd(TFA)₄(diglyme) (TFA=trifluoroacetate) was synthesized, characterized thoroughly, and used to obtain the hexagonal phase of NaGdF₄ nanoparticles as an efficient matrix for lanthanide‐doped upconverting nanocrystals (NCs) that convert near‐infrared radiation into shorter‐wavelength UV/visible light. These NCs were then used to prepare well‐characterized TiO₂@NaGdF₄:Yb³⁺,Tm³⁺ nanocomposites to extend the absorption range of the TiO₂ photocatalyst from the UV to the IR region. While the visible/near IR part of the photoluminescent spectra remains almost unaffected by the presence of TiO₂, the UV part is strongly quenched due to the absorption of TiO₂ above its gap at approximately 380 nm by energy transfer or FRET. Preliminary results on the photocatalytic activity of the above obtained nanocomposites are presented.     

Maximum Spin Polarization in Chromium Dimer Cations as Demonstrated by X‐ray Magnetic Circular Dichroism Spectroscopy

X‐ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr₂⁺. Our results indicate that the removal of a single electron from the 4sσ_g bonding orbital of Cr₂ drastically changes the preferred coupling of the 3d electronic spins. While the neutral molecule has a zero‐spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of S=11/2, and almost twice the bond length of the neutral molecule. This spin configuration can be interpreted as a result of indirect exchange coupling between the 3d electrons of the two atoms that is mediated by the single 4s electron through a strong intraatomic 3d‐4s exchange interaction. Our finding allows an estimate of the relative energies of two states that are often discussed as ground‐state candidates, the ferromagnetically coupled ¹²Σ and the low‐spin ²Σ state.     

<Emphasis Type="Italic">Yarrowia lipolytica</Emphasis> Growth Under Increased Air Pressure: Influence on Enzyme Production

Improvement of microbial cell cultures oxygenation can be achieved by the increase of total air pressure, which increases oxygen solubility in the medium. In this work, a pressurized bioreactor was used for Yarrowia lipolytica batch cultivation under increased air pressure from 1 to 6 bar. Cell growth was strongly enhanced by the pressure rise. Fivefold and 3.4-fold increases in the biomass production and in specific growth rate, respectively, were observed under 6 bar. The increase of oxygen availability caused the induction of the antioxidant enzyme superoxide dismutase, which indicates that the defensive mechanisms of the cells against oxidative stress were effective and cells could cope with increased pressure. The pregrowth of Y. lipolytica under increased pressure conditions did not affect the lipase production ability of the cells. Moreover, the extracellular lipase activity increased 96% using a 5-bar air pressure instead of air at 1-bar pressure during the enzyme production phase. Thus, air pressure increase in bioreactors is an effective mean of cell mass and enzyme productivity enhancement in bioprocess based in Y. lipolytica cultures.     

Palladium asymmetric reduction of β-carboline imines mediated by chiral auxiliaries assisted by microwave irradiation

An alternative synthetic approach for the introduction of chirality in β-carboline moiety through in situ reduction of N-acyliminium ion intermediates generated from imine 2 and chloroformate of 8-phenylmenthyl as chiral auxiliary was achieved. The method applied microwave-assisted irradiation and used PdCl₂/Et₃SiH protocol as a mild reducing agent, which decreased reaction times to minutes when compared to the conventional thermal reactions. The diastereoselectivity (4-12:1) of the reduction produced R-amines, which were assigned after chiral auxiliary removal and spectroscopic data compared to products obtained from Noyori asymmetric hydrogenation catalyst.     

Cyclochiral resorcin[4]arenes as effective enantioselectors in the gas phase

The effect of cyclochirality of rccc-2,8,14,20-tetra-n-decyl-4,10,16,22-tetra-O-methylresorcin[4]arene (C) on the enantiodiscrimination of a number of chiral bidentate and tridentate aromatic and aliphatic biomolecules (G) has been investigated by nano-electrospray ionization (nano-ESI)-Fourier transform ion cyclotron resonance mass spectrometry. The experimental approach is based on the formation of diastereomeric proton-bound [C·H·G](+) complexes by nano-ESI of solutions containing an equimolar amount of quasi-enantiomers (C) together with the chiral guest (G) and the subsequent measurement of the rate of the G substitution by the attack of several achiral and chiral amines. In general, the heterochiral complexes react faster than the homochiral ones, except when G is an aminoalcoholic neurotransmitter whose complexes, beyond that, exhibit the highest enantioselectivity. The kinetic results were further supported by both collision-induced dissociation experiments on some of the relevant [C(2) ·H·G](+) three-body species and Density functional theory (DFT) calculations performed on the most selective systems.