Gigahertz repetition rate mode-locked Yb:KYW laser using self-assembled quantum dot saturable absorber

Fundamental mode-locking is achieved in a 1.036 GHz cavity using a semiconductor quantum dot saturable absorber mirror with a fast relaxation time component of down to 550 fs. The dispersive cavity delivers 1.7 ps wide pulses with spectra supporting sub-picosecond pulse durations and an M² of 1.3. An average output power of up to 339 mW at wavelengths around 1,032 nm is achieved and the saturable absorber’s damage threshold is identified as a limitation for further power scaling.     

Intercalation of Toluidines into α-Zirconium Hydrogenphosphate

Intercalates of o-, m-, and p-toluidine into α-Zr(HPO₄)₂ · H₂O were prepared and characterized by powder X-ray diffraction, thermogravimetric analysis and infrared spectroscopy. As follows from IR, toludine molecules are protonated in the interlayer space. Toluidine molecules are arranged in a bimolecular way in the intercalates containing more than 1.5 toluidine molecules per Zr atom. On the other hand, a monolayer of the toluidine molecules is supposed in the intercalates with less than one toluidine molecule per Zr atom.     

Absolute Asymmetric Synthesis: The Origin, Control, and Amplification of Chirality

Biomolecular homochirality, the origin of which is still a puzzle, has challenged scientists to design chemical systems that provide chiral molecules through absolute asymmetric synthesis and to amplify a small stereochemical bias in such systems. The photoresolution of the enantiomers of helical-shaped, sterically overcrowded alkene 1 with circularly polarized light and the transduction of the stereochemical information by triggering the helical arrangement of a large collection of achiral molecules in a twisted nematic liquid crystalline phase (2) are examples of control and amplification of chirality.     

Role of ion-selective membranes in the carbon balance for CO2 electroreduction via gas diffusion electrode reactor designs

In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO₂ reduction in GDE-type flow electrolyzers. By using different ion-selective membranes, we show nearly identical catalytic selectivity for CO₂ reduction, which is primarily due to a similar local reaction environment created at the cathode/electrolyte interface via the introduction of a catholyte layer. In addition, based on a systematic exploration of gases released from electrolytes and the dynamic change of electrolyte speciation, we demonstrate the explicit discrepancy in carbon balance paths for the captured CO₂ at the cathode/catholyte interface via reaction with OH⁻ when using different ion-selective membranes: (i) the captured CO₂ could be transported through an anion exchange membrane in the form of CO₃²⁻, subsequently releasing CO₂ along with O₂ in the anolyte, and (ii) with a cation exchange membrane, the captured CO₂ would be accumulated in the catholyte in the form of CO₃²⁻, while (iii) with the use of a bipolar membrane, the captured CO₂ could be released at the catholyte/membrane interface in the form of gaseous CO₂. The unique carbon balance path for each type of membrane is linked to ion species transported through the membranes.

In this work, the effect of ion-selective membranes on the detailed carbon balance was systematically analyzed for high-rate CO₂ reduction in GDE-type flow electrolyzers.     

Physicochemical Properties of Oosporein,the Major Secreted Metabolite of the Entomopathogenic Fungus Beauveria brongniartii

Oosporein ( 1 ) is the major secondary metabolite excreted by Beauveria brongniartii (Sacc. ) Petch (Ascomycota: Clavicipitaceae), an entomopathogenic fungus infesting the larvae of Melolontha melolontha L. (Coleoptera: Scarabaeidae; common European cockchafer). Physicochemical parameters were established to allow a better understanding of the spatiotemporal distribution of this marker substance in the environment. i) The dependence of the oosporein solubility (C_s) from proton concentration and temperature was assessed. Oosporein is a rather strong organic acid. The basal solubility of oosporein (Cequation/tex2gif-inf-2.gif in aqueous citrate/HCl buffer at pH 1.23) was found to be 24.8±0.3 μM . The pK_a of the first deprotonation step was determined to be 2.42±0.02. A nonlinear van't Hoff equation was established for the temperature dependency of the oosporein solubility (lnC_s=a+bT^?1+clnT, with a=?123.3, b=2678.9, and c=19.5). ii) A second and third deprotonation step was found in Britton–Robinson‐buffered aqueous solution. The associated pK_a values were determined as 6.79±0.08 and 9.19±0.03. iii) The stability of oosporein at different pH values and temperatures was addressed. Oosporein degraded quickly under moderate alkaline conditions and with increased temperatures. The half‐life dropped below 20 h at pH≥8.0 and T≥43°. The analysis of the Arrhenius plot allowed to calculate the activation energies (E_a) as 102±17 (pH 6), 100±5 (pH 8), and 91±6 kJ/mol (pH 10). iiii) The octanol/water partition coefficient (P_O) and its pH dependence were also determined. The distribution coefficient (D_O) for oosporein at pH 1.2 was found to be 53.7±4.1 (logD_O=1.73±0.03). The partition coefficient P_O for undissociated oosporein was calculated as 56.6 (logP_O=1.75). From the physicochemical properties, it can be concluded that oosporein can hardly be adsorbed by organisms.     

A One‐Pot Cascade Reaction Combining an Encapsulated Decarboxylase with a Metathesis Catalyst for the Synthesis of Bio‐Based Antioxidants

The combination of enzymes with traditional chemical catalysts unifies the high selectivity of the former with the versatility of the latter. A major challenge of this approach is the difference in the optimal reaction conditions for each catalyst type. In this work, we combined a cofactor‐free decarboxylase with a ruthenium metathesis catalyst to produce high‐value antioxidants from bio‐based precursors. As suitable ruthenium catalysts did not show satisfactory activity under aqueous conditions, the reaction required the use of an organic solvent, which in turn significantly reduced enzyme activity. Upon encapsulation of the decarboxylase in a cryogel, the decarboxylation could be conducted in an organic solvent, and the recovery of the enzyme after the reaction was facilitated. After an intermediate drying step, the subsequent metathesis in pure organic solvent proved to be straightforward. The synthetic utility of the cascade was demonstrated by the synthesis of the antioxidant 4,4′‐dihydroxystilbene in an overall yield of 90 %.     

Isoeichlerianic acid from Aglaia silvestris and revision of the stereochemistry of foveolin B

A new series of 20,24-epoxy (tetrahydrofuryl) type dammarane triterpenoids were established. So far two series were described, based on the stereochemistries of the tetrahydrofurane ring linked to the D ring of the triterpenoid skeleton. Eichlerianic acid was characterised by the absolute configuration (20S,24S) and shoreic acid by (20S,24R). Foveolins A and B were correlated with these compounds and published also as (20S,24S) and (20S,24R), respectively. ¹³C NMR analysis of a further stereoisomer of the acids isolated from Aglaia silvestris allowed the conclusion that the new isoeichlerianic acid, its methyl ester and the known foveolin B belonged to the new stereochemical series (20R,24S).     

Samarium(II) Iodide Promoted Tandem Reductive Fragmentation and Aldol Reaction

 We report a new reductive fragmentation/aldol tandem reaction in a 1,4-diketone induced by samarium(II) iodide. Due to the particular stereoelectronic situation in the molecule, an alternative pathway was avoided despite the fact that it would have greatly reduced the strain in the tricyclic molecule.     

Ueber Thermometer und Temperaturmessungen

Ohne Zusammenfassung