High-power all-normal-dispersion femtosecond pulse generation from a Yb-doped large-mode-area microstructure fiber laser

We report on an all-normal-dispersion mode-locked fiber laser based on a large-mode-area Yb-doped microstructure fiber and using a high nonlinear modulation depth semiconductor saturable absorber mirror. The laser delivers 3.3 W of average output power with positively chirped 5.5 ps pulses at a center wavelength of 1033 nm. The pulse repetition rate is 46.4 MHz, which results in an energy per pulse of 71 nJ. These pulses are extracavity dechirped down to 516 fs by using bulk gratings. The average power of the dechirped pulses is 2.3 W, which corresponds to a peak power of more than 96 kW.     

Morphologic changes in the urethral epithelium in an ethanol-drinking rat strain (UChA and UChB)

The extreme use of ethanol causes metabolic and pathologic changes in testes and urogenital system in different animal species. The enzyme alcohol dehydrogenase (ADH) catalyses the conversion of ethanol into carcinogenic metabolite acetaldehyde which is partly excreted into the urine. However, papers relating the chronic ethanol consumption to the urethral morphology are unknown. This work evaluates the toxic effect of the chronic ethanol ingestion on the urethral epithelium of UChA and UChB rats. Conventional techniques of histology, histochemistry, immunohistochemistry and ultrastructural analysis were used. The analysis showed the presence of lipid drops and intercellular spaces in the epithelial cells in the urethra of UChA and UChB rats compared to control rats. Urethral neuroendocrine cell were observed and characterized for presenting vesicles containing electron-dense granules associated with nervous fibers. We conclude that the chronic consumption of ethanol induces the presence lipid drops in the epithelial cells of the urethra of UChA and UChB rats. The NE cells of the urethra of UChA and UChB rats did not show alterations under chronic effect of the ethanol.     

Ordered Mesoporous ZSM‐5 Employing an Imidazolium‐Based Ionic Liquid

Hierarchically porous ZSM‐5 was achieved by using a simple bottom‐up strategy combining zeolite seeds with imidazolium‐based ionic liquids. The bimodal ZSM‐5 with hexagonal arranged mesopores (3 nm) shows important activity in the acid catalysis of bulky compounds relative to conventional ZSM‐5.     

On the Synthesis,Characterization and Reactivity of N‐Heteroaryl–Boryl Radicals,a New Radical Class Based on Five‐Membered Ring Ligands

The synthesis and physical characterization of a new class of N‐heterocycle–boryl radicals is presented, based on five membered ring ligands with a N(sp²) complexation site. These pyrazole–boranes and pyrazaboles exhibit a low bond dissociation energy (BDE; B?H) and accordingly excellent hydrogen transfer properties. Most importantly, a high modulation of the BDE(B?H) by the fine tuning of the N‐heterocyclic ligand was obtained in this series and could be correlated with the spin density on the boron atom of the corresponding radical. The reactivity of the latter for small molecule chemistry has been studied through the determination of several reaction rate constants corresponding to addition to alkenes and alkynes, addition to O₂, oxidation by iodonium salts and halogen abstraction from alkyl halides. Two selected applications of N‐heterocycle–boryl radicals are also proposed herein, for radical polymerization and for radical dehalogenation reactions.     

Polymeric biocomposites of poly (butylene adipate-co-terephthalate) reinforced with natural Munguba fibers

In this work, polymeric biocomposites of poly (butylene adipate-co-terephthalate), PBAT, were reinforced with Munguba fibers (Pseudobombax munguba). This tree is found in great abundance in the marshy areas of the Amazon forest. The motivation for using this fiber in polymer composites comes from the fact that although research for this fiber has not been reported in the scientific literature, it is commonly used by the local population because its bark is strong and flexible. Most important is that the extraction of Munguba fibers does not damage the supplier tree because as it is extracted from the bark, its regeneration starts as it is removed. The fibers were chemically treated by mercerization/acetylation and evaluated by Fourier transform infrared spectroscopy, thermogravimetric analysis and tensile tests. The Munguba fiber presented mechanical properties similar to those of other natural fibers traditionally used in composites, and the chemical treatment provided improvements of its thermal stability and stiffness. The biocomposites showed a better elastic modulus in relation to the pure PBAT. The addition of fibers caused changes in the T _g, T _m and T _c of PBAT as observed by differential scanning calorimetry analysis. The Russel, Halpin-Tsai and Maxwell models were employed to provide the theoretical elastic modulus of the biocomposites.     

Investigation of Growth Conditions for the Expansion of Porcine Mesenchymal Stem Cells on Microcarriers in Stirred Cultures

The extensive use of mesenchymal stem cells (MCS) in tissue engineering and cell therapy increases the necessity to improve their expansion. Among these, porcine MCS are valuable models for tissue engineering and are classically expanded in static T-flasks. In this work, different processes of stirred cultures were evaluated and compared. First, the effect of glucose, glutamine, antioxidant, and growth factors concentrations on porcine MSC expansion were analyzed in a suitable medium by performing kinetic studies. Results showed that a lower glucose concentration (5.5 mM) enabled to increase maximal cell concentration by 40 % compared with a higher one (25 mM), while addition of 2 to 6 mM of glutamine increased maximal cell concentration by more than 25 % compared with no glutamine supplementation. Moreover, supplementation with 1 μM thioctic acid increased maximal cell concentration by 40 % compared with no supplementation. Using this adapted medium, microcarriers cultures were performed and compared with T-flasks expansion. Porcine MSC were shown to be able to proliferate on the five types of microcarriers tested. Moreover, cultures on Cytodex 1, Cytopore 2, and Cultispher G exhibited a MSC growth rate more than 40 % higher compared with expansion in T-flasks, while MSC metabolism was similar.     

Terminal Alkyne Coupling Reactions Through a Ring: Effect of Ring Size on Rate and Regioselectivity

Terminal alkyne coupling reactions promoted by rhodium(I) complexes of macrocyclic NHC-based pincer ligands—which feature dodecamethylene, tetradecamethylene or hexadecamethylene wingtip linkers viz. [Rh(CNC-n)(C₂H₄)][BAr^F₄] (n=12, 14, 16; Ar^F=3,5-(CF₃)₂C₆H₃)—have been investigated, using the bulky alkynes HC≡CtBu and HC≡CAr’ (Ar’=3,5-tBu₂C₆H₃) as substrates. These stoichiometric reactions proceed with formation of rhodium(III) alkynyl alkenyl derivatives and produce rhodium(I) complexes of conjugated 1,3-enynes by C−C bond reductive elimination through the annulus of the ancillary ligand. The intermediates are formed with orthogonal regioselectivity, with E-alkenyl complexes derived from HC≡CtBu and gem-alkenyl complexes derived from HC≡CAr’, and the reductive elimination step is appreciably affected by the ring size of the macrocycle. For the homocoupling of HC≡CtBu, E-tBuC≡CCH=CHtBu is produced via direct reductive elimination from the corresponding rhodium(III) alkynyl E-alkenyl derivatives with increasing efficacy as the ring is expanded. In contrast, direct reductive elimination of Ar'C≡CC(=CH₂)Ar’ is encumbered relative to head-to-head coupling of HC≡CAr’ and it is only with the largest macrocyclic ligand studied that the two processes are competitive. These results showcase how macrocyclic ligands can be used to interrogate the mechanism and tune the outcome of terminal alkyne coupling reactions, and are discussed with reference to catalytic reactions mediated by the acyclic homologue [Rh(CNC-Me)(C₂H₄)][BAr^F₄] and solvent effects.     

A Convergent Total Synthesis of the Death Cap Toxin α‐Amanitin

The toxic bicyclic octapeptide α‐amanitin is mostly found in different species of the mushroom genus Amanita, with the death cap (Amanita phalloides) as one of the most prominent members. Due to its high selective inhibition of RNA polymerase II, which is directly linked to its high toxicity, particularly to hepatocytes, α‐amanitin received an increased attention as a toxin‐component of antibody‐drug conjugates (ADC) in cancer research. Furthermore, the isolation of α‐amanitin from mushrooms as the sole source severely restricts compound supply as well as further investigations, as structure–activity relationship (SAR) studies. Based on a straightforward access to the non‐proteinogenic amino acid dihydroxyisoleucine, we herein present a robust total synthesis of α‐amanitin providing options for production at larger scale as well as future structural diversifications.