In article number 1908299, Marcy Zenobi-Wong and co-workers introduce a novel two-photon patterning strategy based on enzymatic couplings, nonfouling hydrophilic photocages, and improved protein functionalization reagents. Using time- and spatially controlled laser exposure, precise anchoring of growth factors within a hydrogel can guide the axons along biochemical paths. Illustration: Axon guided through a maze by Riccardo Rizzo.

Three-dimensional (3D) control over the placement of bioactive cues is fundamental to understand cell guidance and develop engineered tissues. Two-photon patterning (2PP) provides such placement at micro- to millimeter scale, but nonspecific interactions between proteins and functionalized extracellular matrices (ECMs) restrict its use. Here, a 2PP system based on nonfouling hydrophilic photocages and Sortase A (SA)-based enzymatic coupling is presented, which offers unprecedented orthogonality and signal-to-noise ratio in both inert hydrogels and complex mammalian matrices. Improved photocaged peptide synthesis and protein functionalization protocols with broad applicability are introduced. Importantly, the method enables 2PP in a single step in the presence of fragile biomolecules and cells, and is compatible with time-controlled growth factor presentation. As a corollary, the guidance of axons through 3D-patterned nerve growth factor (NGF) within brain-mimetic ECMs is demonstrated. The approach allows for the interrogation of the role of complex signaling molecules in 3D matrices, thus helping to better understand biological guidance in tissue development and regeneration.

New bifunctional potassium acyltrifluoroborate (KAT) substrates have been synthesized in gram scale using optimized reaction conditions. Chemoselective transformation of functional groups in the presence of an acyltrifluoroborate has been demonstrated, and orthogonal reactions of bifunctional KAT reagents are reported. This allows for the incorporation of KAT moieties into peptides and dyes.

The covalent immobilization of peptides, proteins, and other biomolecules to hydrogels provides a biologically mimicking environment for cell and tissue growth. Bioorthogonal chemical reactions can serve as a tool for this, but the paucity of such reactions and mutual incompatibilities limits the number of distinct molecules that can be introduced. We now report that the potassium acyltrifluoroborate (KAT) amide‐forming ligation is orthogonal to both thiol‐Michael and strain promoted azide alkyne cycloadditions (SPAAC) and the requisite functional groups – KATs and hydroxylamines – are stable and compatible to hydrogel formation, protein modification, and post‐assembly immobilization of biomolecules onto hydrogels. In combination these ligations enables stepwise covalent protein immobilization of multiple BSA‐derivatives onto the hydrogel scaffold regardless of the order of addition.

The synthesis of novel PEG-based hydrogel via chemoselective potassium acyl trifluoroborate (KAT) and O-carbamoyl hydroxylamines amide ligation is reported. The gelation kinetics, determined by dynamic rheometry, is pH dependent and allows fine-tuning of the gelation time. For a 4 wt % PEG hydrogel, at low acidic pHs (3 to 6) gelation proceeds rapidly within few minutes, comparable or existing the faster known gelation times. At neutral and physiological pHs (7 and 7.4) the reaction is slower, forming a hydrogel in ca. 80 min. The gels are suitable for the encapsulation of bovine chondrocytes with the high viability (96% after 2 days), demonstrating the biocompatibility of the KAT ligation for the first time.

Boronic acid-substituted shapeshifting bullvalenes bearing a (13)C label are employed as sensor arrays for polyhydroxylated compounds, such as carbohydrates, flavanols, and sialic acids. The dynamic nature of the bullvalene core allows for covalent binding to a wide variety of analytes, allowing for specific analyte detection by a single NMR measurement. The resulting (13)C NMR patterns permit an inference to the identity of a particular analyte bound. Conversion of the (13)C NMR to an easy-to-read barcode provides a convenient method to catalog polyol analytes. The synthesis and study of a structurally related static sensor, which is not suitable for analyte recognition, underscores the advantages of the shapeshifting nature of the sensor.

A potentially biomimetic approach toward the complex polyketide A-74528 is described. It is based on highly substituted biaryl compounds, synthesized using advanced cross-coupling and condensation methodologies.

The rapidly growing applications of nanomagnets require acid/base stable, oxidation-resistant shells with chemically controlled surface structure. An ideal core should be metallic and highly magnetic. We demonstrate the production of iron-based nanoparticles, ranging from iron oxide to iron and iron carbide, by systematically modifying the degree of reduction during flame spray synthesis under a controlled atmosphere. At a laboratory scale, continuous production yields iron-based particles of 20-50 nm at a production rate of > 10 g h(-1). Carbon-encapsulated iron carbide (C/Fe3C) combines exceptionally high saturation magnetization (140 emu g(-1)), air stability (up to 200 degrees C), and resistance against acidic dissolution (1 week in 24% HCl). The top graphene-like carbon layer could be covalently functionalized with various linkers, thus allowing us to chemically design the particle surface. Activity was demonstrated by reacting 2-phenyl ethyl amine functionalized nanomagnets with carboxylic acid chlorides as a model reaction. The present nanomagnets consist of biologically well-accepted constituents. They combine the required chemical reliability, improved magnetization if compared to magnetite with the potential for technical scale manufacturing, and therefore open stable nanomagnets to a broad range of fascinating separation problems (extraction/water treatment) and biomedical research.