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  • Author or Editor: Holger Löwe x
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Abstract

MUC1-type glycopeptides have already shown their potential as possible cancer vaccine candidates. In addition, first examples of fluorinated antigen structures, especially containing the Thomsen–Friedenreich antigen, with similar antibody recognition have been reported. Using microreactor techniques for improvement of the crucial step, the complex glycosylation reactions, is an efficient way to find optimized reaction parameter as well as to circumvent well-known scale-up drawbacks. Besides, this is the first report of continuous flow glycosylations of glycosyl amino acids, in particular with fluorinated glycosyl building blocks.

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To synthesize nickel(0) nanoparticles by wet chemical reduction using hydrazine with an average size distribution below 100 nm, two different reactor concepts were developed. With a cone channel nozzle, the reactant solutions were sprayed into a batch for further processing and reduction at elevated temperatures. Another concept uses a micro-coaxial injection mixer connected to a heated tube to establish a fully continuously operating reactor. To shorten the time for reduction of the nickel, salt temperatures up to 180 °C are applied. To avoid uncontrolled residence time, the whole system was pressurized up to 80 bar. Approximately 80 L reactant solution, i.e., 1 kg nickel(0) nanoparticles, could be processed within 30 h.

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A new way to perform reactions in core—shell double emulsions is reported herein. The phase boundaries of the threephase droplet flow were used to pressurize the reactants in the shell liquid, enhancing the reaction rate of a cycloaddition greatly in comparison to known methods. As key parameters, solvophobic effects and precise control over the droplet sizes were used to exploit a reaction with a negative volume of activation. The internal pressure of the reaction solution was regulated purely by the thickness of the shell liquid without adding additional reagents. Additionally, the reaction performed better when the core droplet was used to stir the shell droplet, considerably improving the mass transfer inside the otherwise diffusion-limited process.

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Journal of Flow Chemistry
Authors: Viktor Misuk, Andreas Mai, Konstantinos Giannopoulos, Dominik Karl, Julian Heinrich, Daniel Rauber and Holger Löwe

The method of combining the concept of fluorous biphasic catalysis (FCB) with micro multiple emulsions benefits from the advantages of homogeneous as well as from heterogeneous catalysis in continuous micro flow. In this particular case, three immiscible fluid phases in continuous micro segmented flow were used to perform palladium-catalyzed Heck cross-coupling reactions of styrene with aryl halides. A capillary tube-in-tube coaxial flow setup in combination with a glass micro reactor was used to produce monodisperse aqueous phase/organic phase/perfluorinated phase double emulsions. The resulting emulsions had a core–shell droplet structure composed of a perfluorcarbon fluid in which a palladium catalyst with fluorinated phosphine ligands was dissolved, an organic phase consisting of a solvent and two reagents, and an alkaline aqueous solution. The fluorous and organic phases of the double emulsion form a thermomorphous system which can be converted into one phase by an increase of temperature above 150 °C, and the catalytic reaction is performed temporarily. By decreasing the temperature, a phase separation takes place; after that, the organic phase contains the product and the catalyst is located in the fluorous phase. The separated catalyst solution was reused several times without a noticeable loss of activity. The main advantage of this method is to use temporarily very high catalyst concentrations in each droplet, while employing only small amounts of the catalyst for the overall reaction volume.

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Journal of Flow Chemistry
Authors: Viktor Misuk, Andreas Mai, Yuning Zhao, Julian Heinrich, Daniel Rauber, Konstantinos Giannopoulos and Holger Löwe

Fast mixing is essential for many microfluidic applications, especially for flow at low Reynolds numbers. A capillary tube-in-tube coaxial flow setup in combination with a glass microreactor was used to produce immiscible multiphase segments. These double emulsion segments are composed of an organic solvent as the shell (outer) phase and a completely fluorinated liquid (Fluorinert® FC-40) as the core (inner) phase. Due to the higher density of the core droplets, they are responsive to changing their position to the force of gravity (g-force). By gently shaking or jiggling the reactor, the core drop flows very fast in the direction of the g-field without leaving the shell organic phase segment. Furthermore, by shaking or jiggling the reactor, the inner droplet moves along the phase boundary of the shell segment and continuous phase. Computational fluid dynamics (CFD) calculations show an enhancement of the internal circulations, i.e., causing an exceptional mixing inside of the shell segment. For reactions which are limited by mass transfer, where the conversion significantly increases with improved mixing, these recirculation zones are decisive because they also accelerate the mixing process. With a common phase-transfer catalytic (PTC) etherification of phenol with dimethyl sulphate, a remarkable increase of yield (85% gas chromatography [GC]) could be achieved by applying active mixing within a segment in continuous flow.

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