Self-Sorting Supramolecular Polymerization: Helical and Lamellar Aggregates of Tetra-Bay-Acyloxy Perylene Bisimide

A new perylene bisimide (PBI), with a fluorescence quantum yield up to unity, self-assembles into two polymorphic supramolecular polymers. This PBI bears four solubilizing acyloxy substituents at the bay positions and is unsubstituted at the imide position, thereby allowing hydrogen-bond-directed self-assembly in nonpolar solvents. The formation of the polymorphs is controlled by the cooling rate of hot monomer solutions. They show distinctive absorption profiles and morphologies and can be isolated in different polymorphic liquid-crystalline states. The interchromophoric arrangement causing the spectral features was elucidated, revealing the formation of columnar and lamellar phases, which are formed by either homo- or heterochiral self-assembly, respectively, of the atropoenantiomeric PBIs. Kinetic studies reveal a narcissistic self-sorting process upon fast cooling, and that the transformation into the heterochiral (racemic) sheetlike self-assemblies proceeds by dissociation via the monomeric state.     

The solubility of Co in TiO2 anatase and rutile and its effect on the magnetic properties

Co-doped anatase and rutile bulk-samples prepared by the sol-gel technique are found to be paramagnetic at room-temperature. Only further annealing in Ar/H₂ gas results in a ferromagnetic behavior. X-ray diffraction and electron-microscope studies reveal for low doping levels <4% the formation of Co-doped rutile samples and the formation of CoTiO₃ as a new phase. Co₃O₄ can be detected in anatase samples with Co doping levels ?4%. The observed Co oxides are reduced by Ar/H₂ to Co metal. The room-temperature ferromagnetism can therefore be traced back to a segregation of metallic Co.     

Microstructural identification of Cu in solar cells sensitive to light‐induced degradation

Light‐induced degradation (mc‐LID or LeTID) can lead to a severe efficiency loss in multi‐crystalline solar cells. The underlying mechanism clearly distinguishes from known mechanisms as B‐O‐LID and Fe‐B‐LID. Various defect models have been suggested for mc‐LID mainly based on metal impurities, including Cu which is known to cause light‐induced degradation. We investigate mc‐LID sensitive PERC cells that show an efficiency degradation of 15%_rel. The weaker degradation of the grain boundaries (GBs) typical for mc‐LID is identified and further investigated from front and rear side with respect to recombination activities. The combination of local electrical measurements (LBIC), target preparation (REM, FIB) and element analysis (EDX, TEM) unveil Cu‐containing precipitates at the rear side of the solar cells. They accumulate at grain boundaries and at the rear surface of the Si‐bulk material where the passivation stack is damaged. We conclude that Cu originates from the cell material and discuss its relation to mc‐LID.

LBIC mapping (EQE at fixed wavelength) of a degraded mc‐Si PERC cell from front and rear side results in qualitatively different appearance of GBs.     

Parasitic behavior in competing chemically fueled reaction cycles

Non-equilibrium, fuel-driven reaction cycles serve as model systems of the intricate reaction networks of life. Rich and dynamic behavior is observed when reaction cycles regulate assembly processes, such as phase separation. However, it remains unclear how the interplay between multiple reaction cycles affects the success of emergent assemblies. To tackle this question, we created a library of molecules that compete for a common fuel that transiently activates products. Often, the competition for fuel implies that a competitor decreases the lifetime of these products. However, in cases where the transient competitor product can phase-separate, such a competitor can increase the survival time of one product. Moreover, in the presence of oscillatory fueling, the same mechanism reduces variations in the product concentration while the concentration variations of the competitor product are enhanced. Like a parasite, the product benefits from the protection of the host against deactivation and increases its robustness against fuel variations at the expense of the robustness of the host. Such a parasitic behavior in multiple fuel-driven reaction cycles represents a lifelike trait, paving the way for the bottom-up design of synthetic life.

Non-equilibrium, fuel-driven reaction cycles serve as model systems of the intricate reaction networks of life.     

Fabrication of Stiffness Gradients of GelMA Hydrogels Using a 3D Printed Micromixer

Many properties in both healthy and pathological tissues are highly influenced by the mechanical properties of the extracellular matrix. Stiffness gradient hydrogels are frequently used for exploring these complex relationships in mechanobiology. In this study, the fabrication of a simple, cost‐efficient, and versatile system is reported for creation of stiffness gradients from photoactive hydrogels like gelatin‐methacryloyl (GelMA). The setup includes syringe pumps for gradient generation and a 3D printed microfluidic device for homogenous mixing of GelMA precursors with different crosslinker concentration. The stiffness gradient is investigated by using rheology. A co‐culture consisting of human adipose tissue‐derived mesenchymal stem cells (hAD‐MSCs) and human umbilical cord vein endothelial cells (HUVECs) is encapsulated in the gradient construct. It is possible to locate the stiffness ranges at which the studied cells displayed specific spreading morphology and migration rates. With the help of the described system, variable mechanical gradient constructs can be created and optimal 3D cell culture conditions can be experientially identified.     

Electrochemical Synthesis of Aryl Iodides by Anodic Iododesilylation

An electrochemical access to iodinated aromatic compounds starting from trimethylsilyl‐substituted arenes is presented. By design of experiments, highly efficient and mild conditions were identified for a wide range of substrates. A functional group stability test and the synthesis of an important 3‐iodobenzylguanidine radiotracer illustrate the scope of this process.     

In situ recording of particle network formation in liquids by ion conductivity measurements

The formation of fractal silica networks from a colloidal initial state was followed in situ by ion conductivity measurements. The underlying effect is a high interfacial lithium ion conductivity arising when silica particles are brought into contact with Li salt-containing liquid electrolytes. The experimental results were modeled using Monte Carlo simulations and tested using confocal fluorescence laser microscopy and ζ-potential measurements.     

Chemical Genetics Reveals a Role of dCTP Pyrophosphatase 1 in Wnt Signaling

Cell‐based screening is a powerful approach to identify novel chemical modulators and biological components of relevant biological processes. The canonical Wnt pathway is essential for normal embryonic development and tissue homeostasis, and its deregulation plays a crucial role in carcinogenesis. Therefore, the identification of new pathway members and regulators is of significant interest. By means of a cell‐based assay monitoring Wnt signaling we identified the pyrrolocoumarin Pyrcoumin as inhibitor of canonical Wnt signaling. Target identification and validation revealed that Pyrcoumin is a competitive inhibitor of dCTP pyrophosphatase 1 (dCTPP1). We demonstrate a yet unknown interaction of dCTPP1 with ubiquitin carboxyl‐terminal hydrolase (USP7) that is counteracted by dCTPP1 inhibitors. These findings indicate that dCTPP1 plays a role in regulation of Wnt/β‐catenin signaling most likely through a direct interaction with USP7.     

Anionic Boraza-Crown Ethers

Making one out of two : Dimeric boraza-crown ethers bridge the gap between metallacrowns and aza-crown ethers with a strikingly simple synthesis. Dioxazaborocanes react with alkoxides to form the corresponding anionic boronates, which combine to form dimers upon ring-opening reactions. The presence of the dimers was proven in the solid state and in solution by X-ray crystallography and NMR spectroscopy, respectively. The influence of the sodium and potassium ions on the stability of boraza-crown ethers was examined using DFT calculations. The dissociation of the dimers to the monomeric species was found to be endothermic, independently of the counterion. Finally, their ability to engage in cross-coupling reactions was validated for two different compounds.