TY - JOUR AB - The development of a continuous flow multistep strategy for the synthesis of linear peptoids and their subsequent macrocyclization via Click chemistry is described. The central transformation of this process is an Ugi four-component reaction generating the peptidomimetic core structure. In order to avoid exposure to the often toxic and malodorous isocyanide building blocks, the continuous approach was telescoped by the dehydration of the corresponding formamide. In a concurrent operation, the highly energetic azide moiety required for the subsequent intramolecular copper-catalyzed azide–alkyne cycloaddition (Click reaction) was installed by nucleophilic substitution from a bromide precursor. All steps yielding to the linear core structures can be conveniently coupled without the need for purification steps resulting in a single process generating the desired peptidomimetics in good to excellent yields within a 25 min reaction time. The following macrocyclization was realized in a coil reactor made of copper without any additional additive. A careful process intensification study demonstrated that this transformation occurs quantitatively within 25 min at 140 °C. Depending on the resulting ring strain, either a dimeric or a monomeric form of the cyclic product was obtained. AU - Salvador, Carlos Eduardo M. AU - Pieber, Bartholomäus AU - Neu, Philipp M. AU - Torvisco, Ana AU - Kleber Z. Andrade, Carlos AU - Kappe, C. Oliver ID - 11977 IS - 9 JF - The Journal of Organic Chemistry SN - 0022-3263 TI - A sequential Ugi multicomponent/Cu-catalyzed azide–alkyne cycloaddition approach for the continuous flow generation of cyclic peptoids VL - 80 ER - TY - CHAP AB - In recent years, the high demand for sustainable processes resulted in the development of highly attractive oxidation protocols utilizing molecular oxygen or even air instead of more uneconomic and often toxic reagents. The application of these sustainable, gaseous oxidants in conventional batch reactors is often associated with severe safety risks and process challenges especially on larger scales. Continuous flow technology offers the possibility to minimize these safety hazards and concurrently allows working in high-temperature/high-pressure regimes to access highly efficient oxidation protocols. This review article critically discusses recent literature examples of flow methodologies for selective aerobic oxidations of organic compounds. Several technologies and reactor designs for biphasic gas/liquid as well as supercritical reaction media are presented in detail. © Springer International Publishing Switzerland 2015. AU - Pieber, Bartholomäus AU - Kappe, C. Oliver ED - Noël, Timothy ID - 11989 SN - 1436-6002 T2 - Organometallic Flow Chemistry TI - Aerobic oxidations in continuous flow VL - 57 ER - TY - JOUR AB - Clustering of fine particles is of crucial importance in settings ranging from the early stages of planet formation to the coagulation of industrial powders and airborne pollutants. Models of such clustering typically focus on inelastic deformation and cohesion. However, even in charge-neutral particle systems comprising grains of the same dielectric material, tribocharging can generate large amounts of net positive or negative charge on individual particles, resulting in long-range electrostatic forces. The effects of such forces on cluster formation are not well understood and have so far not been studied in situ. Here we report the first observations of individual collide-and-capture events between charged submillimetre particles, including Kepler-like orbits. Charged particles can become trapped in their mutual electrostatic energy well and aggregate via multiple bounces. This enables the initiation of clustering at relative velocities much larger than the upper limit for sticking after a head-on collision, a long-standing issue known from pre-planetary dust aggregation. Moreover, Coulomb interactions together with dielectric polarization are found to stabilize characteristic molecule-like configurations, providing new insights for the modelling of clustering dynamics in a wide range of microscopic dielectric systems, such as charged polarizable ions, biomolecules and colloids. AU - Lee, Victor AU - Waitukaitis, Scott R AU - Miskin, Marc AU - Jaeger, Heinrich ID - 120 IS - 9 JF - Nature Physics TI - Direct observation of particle interactions and clustering in charged granular streams VL - 11 ER - TY - JOUR AB - We show that the simplest building blocks of origami-based materials - rigid, degree-four vertices - are generically multistable. The existence of two distinct branches of folding motion emerging from the flat state suggests at least bistability, but we show how nonlinearities in the folding motions allow generic vertex geometries to have as many as five stable states. In special geometries with collinear folds and symmetry, more branches emerge leading to as many as six stable states. Tuning the fold energy parameters, we show how monostability is also possible. Finally, we show how to program the stability features of a single vertex into a periodic fold tessellation. The resulting metasheets provide a previously unanticipated functionality - tunable and switchable shape and size via multistability. AU - Waitukaitis, Scott R AU - Menaut, Rémi AU - Chen, Bryan AU - Van Hecke, Martin ID - 121 IS - 5 JF - APS Physics, Physical Review Letters TI - Origami multistability: From single vertices to metasheets VL - 114 ER - TY - JOUR AB - In this paper, we develop an energy method to study finite speed of propagation and waiting time phenomena for the stochastic porous media equation with linear multiplicative noise in up to three spatial dimensions. Based on a novel iteration technique and on stochastic counterparts of weighted integral estimates used in the deterministic setting, we formulate a sufficient criterion on the growth of initial data which locally guarantees a waiting time phenomenon to occur almost surely. Up to a logarithmic factor, this criterion coincides with the optimal criterion known from the deterministic setting. Our technique can be modified to prove finite speed of propagation as well. AU - Julian Fischer AU - Grün, Günther ID - 1311 IS - 1 JF - SIAM Journal on Mathematical Analysis TI - Finite speed of propagation and waiting times for the stochastic porous medium equation: A unifying approach VL - 47 ER -