Kinetik und Mechanismus der Photolyse von Aryldiazoniumsalzen in Methanol. Ermittlung absoluter Geschwindigkeitskonstanten einiger Teilreaktionen

Kinetics and Mechanism of Aryldiazonium Salt Photolysis in Methanol. Determination of Absolute Rate Constants of Some Reaction Steps For benzene diazonium tetrafluoroborate and some p-substituted derivatives, the following values are determined:

• velocity constants for the photochemical electron transfer from pyrene and benzanthracene to aryl diazonium salts in acetonitrile solution (determination by quenching the donor fluorescence).
• velocity constants for electron transfer under the condition of pulse radiolysis in tert.-butanol-water solution;
• quantum yields and product composition (ArOMe, ArF and ArH, respectively) for the photolyses in methanol in the presence of varying concentrations of 2-methyl-2-nitroso-propane as a quencher of the thermal chain reaction.

The electron transfer reaction comes out be a diffusion controlled reaction, k_E = 2 …︁ 3 × 10¹⁰ M⁻¹ s⁻¹. For the total reaction a kinetic model is set up which affords absolute velocity constants from the experimental results for the following steps: Hydrogen transfer within the case radical pair \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {{\rm Ar} - {\rm N} = {\rm N}{\rm . CH}_{\rm 3} {\rm OH}{\rm .}} {\rm }^ \oplus $\end{document} (formation of ArH) k_H ≈ 10¹¹ s⁻¹; Maximal values for the photo-solvolyses (formation of Ar^⊕ → ArOMe and ArF, respectively), k_s ≲ 10⁻¹; Trapping of aryl radicals outside of the solvent cage by t-BuNO, k_q ≈ 2 × 10⁷ M⁻¹ s⁻¹. The results are discussed in the light of the kinetic model and some other facts.     

SARS-CoV-2 Infection Dysregulates Cilia and Basal Cell Homeostasis in the Respiratory Epithelium of Hamsters

Similar to many other respiratory viruses, SARS-CoV-2 targets the ciliated cells of the respiratory epithelium and compromises mucociliary clearance, thereby facilitating spread to the lungs and paving the way for secondary infections. A detailed understanding of mechanism involved in ciliary loss and subsequent regeneration is crucial to assess the possible long-term consequences of COVID-19. The aim of this study was to characterize the sequence of histological and ultrastructural changes observed in the ciliated epithelium during and after SARS-CoV-2 infection in the golden Syrian hamster model. We show that acute infection induces a severe, transient loss of cilia, which is, at least in part, caused by cilia internalization. Internalized cilia colocalize with membrane invaginations, facilitating virus entry into the cell. Infection also results in a progressive decline in cells expressing the regulator of ciliogenesis FOXJ1, which persists beyond virus clearance and the termination of inflammatory changes. Ciliary loss triggers the mobilization of p73⁺ and CK14⁺ basal cells, which ceases after regeneration of the cilia. Although ciliation is restored after two weeks despite the lack of FOXJ1, an increased frequency of cilia with ultrastructural alterations indicative of secondary ciliary dyskinesia is observed. In summary, the work provides new insights into SARS-CoV-2 pathogenesis and expands our understanding of virally induced damage to defense mechanisms in the conducting airways.     

Steric Crowding Makes Challenging C(sp3)-F Reductive Eliminations Feasible

A high-yielding fluorination of (triphos)Pt-R(+) has been achieved using an array of F(+) sources, with XeF(2) yielding R-F in minutes. The C-F coupling proved to be a stereoretentive process that proceeds via a concerted reductive elimination from a putative dicationic Pt(IV) center. The larger the steric congestion of the (triphos)Pt-C(sp3) (+) complexes, the more efficient the fluorination, seemingly a result of sterically accelerated C-F reductive elimination along with simultaneous deceleration of its competing processes (β-H elimination).     

MESFET MMIC Ka-band transmitter performance forhigh-volume system applications

An MMIC transmitter for high-volume smart munition applications in Ka band is developed using 0.25 μm MESFET technology. The transmitter, consisting of a voltage-controlled oscillator (VCO) and power amplifier (PA), delivers more than 100 mW of power with an overall efficiency of 10% and a linear tuning range of more than 700 MHz around 35 GHz     

Valence band offset in HgTe/Hg1−xCdxTe superlattices

The valence band offset (Λ) between HgTe and CdTe has been determined by means of an optical investigation of (112)B oriented HgTe/Hg_1−xCd_xTe superlattices. Based on the fact that the difference in energy between the first heavy hole and the first light hole subband is to a good approximation due primarily to Λ, it has been shown that Λ=580±40 meV at 5K. In addition Λ has a significant temperature dependence with a linear coefficient of −0.34±0.02 meV/K, i.e., Λ is 480±40 meV at room temperature.