Catalytic Asymmetric Syntheses of Alkylidenecyclopropanes from Allenoates with Donor-Acceptor and Diacceptor Diazo Reagents

The first diastereo- and enantioselective cyclopropanation reactions of electron-deficient allenes with donor-acceptor and diacceptor diazo reagents are described. The desired enantioenriched alkylidenecyclopropanes (ACPs) were obtained in high yields with high diastereo- and enantioselectivities in the presence of Rh₂((S)-TCPTAD)₄ or Rh₂((R)-BTPCP)₄ catalysts (up to 95 % yield, >95 : 5 d.r. and 99 : 1 e.r.). This methodology gave a direct access to ACPs bearing multiple electron-deficient substituents and allows to further expand the availability of ACPs chemistry. Interestingly, during the examination of the scope of this reaction, the asymmetric intramolecular C−H insertion reaction into tert-butyl group was observed as a side reaction with up to 94 : 6 e.r.     

Luminescent Surface-Tethered Polymer Brush Materials

Surface-tethered polymers are unique molecular architectures that have been recently used in advanced sensors, electronics and biomedical applications. However, techniques for characterizing these materials in their surface-tethered form remain limited. The incorporation of luminescent functionality into these materials has enabled new characterization methods, while also unlocking new applications in optoelectronics, stenography and sensing. Micron-scale photolithography techniques have recently enabled the preparation of high-resolution patterns, as well as architectures with unique photophysical properties. Herein, we provide an overview of the techniques used to prepare luminescent polymer brush materials and their applications in stimuli-responsive sensors, cell adhesion materials, and optoelectronics. We also provide our perspective on the promising future uses of surface-tethered polymers, as well as the short-term challenges and opportunities in the field.     

Copper-Photocatalyzed Borylation of Organic Halides under Batch and Continuous-Flow Conditions

The copper-photocatalyzed borylation of aryl, heteroaryl, vinyl and alkyl halides (I and Br) was reported. The reaction proceeded using a new heteroleptic Cu complex under irradiation with blue LEDs, giving the corresponding boronic-acid esters in good to excellent yields. The reaction was extended to continuous-flow conditions to allow an easy scale-up. The mechanism of the reaction was studied and a mechanism based on a reductive quenching (Cu^I/Cu^I*/Cu⁰) was suggested.     

Highly Reproducible Flexible Ion-selective Electrodes for the Detection of Sodium and Potassium in Artificial Sweat

It is well known that potentiometric sensors provide a versatile, cost-effective, and efficient platform for wearable applications. Unfortunately, mass production and commercialization of such devices is often constrained by the requirement of a calibration step, which is due to the poor sensor-to-sensor reproducibility and the need of conditioning the electrodes in the analyte before use. Herein, we fabricated calibration-free flexible sensors including ion-selective electrode and reference electrode by integrating single-walled carbon nanotubes (SWCNTs) with poly(3-octylthiophene) (POT) and applying on polyethylene terephthalate (PET) substrate. The developed sodium and potassium ion-selective electrodes (ISEs) display excellent repeatability, selectivity, stability as well as high sensor-to-sensor reproducibility, with a standard deviation of as low as 1.0 mV in artificial sweat microliter samples volume.     

Copper‐Mediated Formation of Aryl,Heteroaryl, Vinyl and Alkynyl Difluoromethylphosphonates: A General Approach to Fluorinated Phosphate Mimics

A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF₂PO(OEt)₂, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates.     

Temperaturverteilung in einem spiralförmig beheizten Rohr

Zusammenfassung Diese theoretische Arbeit befaßt sich mit der stationären Temperaturverteilung in einer Rohrwand, die von außen von einem oder mehreren parallelen elektrischen Heizleitern beheizt wird. Die Heizleiter sind spiralförmig auf das Rohr aufgewickelt. Innen wird das Rohr konvektiv gekühlt. Zur Lösung des Problems läßt sich die Wärmeleitgleichung in einem spiralförmigen Koordinatensystem aufstellen und dann mit der Annahme vereinfachen, daß alle Isothermen spiralförmig verlaufen. Die so erhaltene Differentialgleichung wird mit der Methode der Trennung der Variablen gelöst. Von besonderem Interesse sind die Temperaturunterschiede auf der Rohrinnenwand, die sich auf Grund der ungleichförmigen Beheizung ergeben. Die Rechnung zeigt, das man die Innenwandtemperatur als konstant annehmen darf, solange der axiale Abstand zweier Heizleiter, bei einer einfachen Wicklung also die Ganghöhe, kleiner ist als die Wandstärke des Rohres. Ist dieser Abstand jedoch doppelt so groß wie die Wandstärke, so können die Temperaturschwankungen auf der Rohrinnenwand in derselben Größenordnung sein wie die mittlere Differenz zwischen der Innenwandtemperatur und der Temperatur des strömenden Mediums.

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Temperature distribution in a helically heated tube

The paper is concerned with the steady state temperature distribution in a tube wall which is heated by one or several parallel line sources. The line sources are wound helically on the outer wall of the tube, which is internally cooled by convection. The heat conduction equation is formulated in helical coordinates and solved by the method of separation of variables. Special attention is paid to the temperature inhomogenities on the inner tube wall. It is shown that the inner tube wall can be assumed isothermal, if the axial distance between two line sources is smaller than the wall thickness. If this distance is twice as large as the wall thickness the temperature inhomogenities on the inner surface can be of the same order of magnitude as the difference between the average temperature of the inner surface and the temperature of the cooling medium.

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Formelzeichen Biot-Zahl - H Ganghöhe einer Spirale - I, K Assoziierte Bessel-Funktionen - N_jm siehe Gl. (34) - Q_L Heizleistung eines Heizleiters pro Längeneinheit - R_a, R_i Außen- und Innenradius des Rohres - T Temperatur - T=T₁–T₂ Temperaturdifferenz zwischen dem wärmsten und kältesten Punkt auf der Rohrinnenwand - T_m Temperatur des Kühlmediums im Rohr - a_j, b_j, c_j, d_j Koeffizienten in Gl. (11) - e_j Fourier-Koeffizienten in Gl. (23) - k_j Eigenwerte der Differentialgleichung - l_j=j · m Ordnung der assoziierten Bessel-Funktionen - m Zahl der Heizleiter - q Mittlere Wärmestromdichte auf der Rohrinnenwand - q_a Wärmestromdichteverteilung auf der Außenwand - r,, z Zylinderkoordinaten - s=R_a–R_i Wandstärke des Rohres - u, v, w Schraubenkoordinaten - a Wärmeübergangszahl auf der Rohrinnenwand - Wärmeleitfähigkeit der Rohrwand - _a, _r axiale und radiale Wärmeleitfähigkeit Herrn Professor Dr. P. Grassmann zum 65. Geburtstag gewidmet.     

Excited State Dynamics of Isolated 6- and 8-Hydroxyquinoline Molecules

The photoinduced dynamics of isolated n-hydroxyquinoline (nHQ) molecules (n=6,8) was investigated in femtosecond pump-probe experiments. A qualitative difference was found between 8HQ and 6HQ. After an initial rapid decay corresponding to the departure of the initial wavepacket out of the Franck-Condon region of the excitation, the 8HQ probe signal decays to zero in 0.37 ps whereas a much longer time constant of 10.4 ps is observed in 6HQ. This interrogates on the role played by the intramolecular H-bond N HO which is at play the 8HQ molecule. Ab-initio were performed at the MCSCF/aug-cc-pVDZ level on the 8HQ molecule to help the discussion. A complex energy landscape was found, which includes a conical intersection.     

Copper-Photocatalyzed Hydrosilylation of Alkynes and Alkenes under Continuous Flow

Herein, the photocatalytic hydrosilylation of alkynes and alkenes under continuous flow conditions is described. By using 0.2 mol % of the developed [Cu(dmp)(XantphosTEPD)]PF₆ under blue LEDs irradiation, a large panel of alkenes and alkynes was hydrosilylated in good to excellent yields with a large functional group tolerance. The mechanism of the reaction was studied, and a plausible scenario was suggested.