Fabrication of Crescent Shaped Microparticles for Particle Templated Droplet Formation.

Crescent-shaped hydrogel microparticles are shown to template uniform volume aqueous droplets upon simple mixing with aqueous and oil media for various bioassays. This emerging "lab on a particle" technique requires hydrogel particles with tunable material properties and dimensions. The crescent shape of the particles is attained by aqueous two-phase separation of polymers followed by photopolymerization of the curable precursor. In this work, the phase separation of poly(ethylene glycol) diacrylate (PEGDA, Mw 700) and dextran (Mw 40 000) for tunable manufacturing of crescent-shaped particles is investigated. The particles' morphology is precisely tuned by following a phase diagram, varying the UV intensity, and adjusting the flow rates of various streams. The fabricated particles with variable dimensions encapsulate uniform aqueous droplets upon mixing with an oil phase. The particles are fluorescently labeled with red and blue emitting dyes at variable concentrations to produce six color-coded particles. The blue fluorescent dye shows a moderate response to the pH change. The fluorescently labeled particles are able to tolerate an extremely acidic solution (pH 1) but disintegrate within an extremely basic solution (pH 14). The particle-templated droplets are able to effectively retain the disintegrating particle and the fluorescent signal at pH 14.

Ambient Catalytic Spinning of Polyethylene Nanofibers.

A novel single-atom Ni(II) catalyst (Ni-OH) is covalently immobilized onto the nano-channels of mesoporous Santa Barbara Amorphous (SBA)-15 particles and isotropic Anodized Aluminum Oxide (AAO) membrane for confined-space ethylene extrusion polymerization. The presence of surface-tethered Ni complexes (Ni@SBA-15 and Ni@AAO) is confirmed by the inductively coupled plasma-optical emission spectrometry (ICP-OES) and X-ray photoelectron spectroscopy (XPS). In the catalytic spinning process, the produced PE materials exhibit very homogeneous fibrous morphology at nanoscale (diameter: ~50 nm). The synthesized PE nanofibers extrude in a highly oriented manner from the nano-reactors at ambient temperature. Remarkably high Mw (1.62×106  g mol-1 ), melting point (124 °C), and crystallinity (41.8 %) are observed among PE samples thanks to the confined-space polymerization. The chain-walking behavior of surface tethered Ni catalysts is greatly limited by the confinement inside the nano-channels, leading to the formation of very low-branched PE materials (13.6/1000 C). Due to fixed supported catalytic topology and room temperature, the filaments are expected to be free of entanglement. This work signifies an important step towards the realization of a continuous mild catalytic-spinning (CATSPIN) process, where the polymer is directly synthesized into fiber shape at negligible chain branching and elegantly avoiding common limitations like thermal degradation or molecular entanglement.

Highly Isoselective Ring-Opening Polymerization of rac-ß-Butyrolactone: Access to Synthetic Poly(3-hydroxybutyrate) with Polyolefin-like Material Properties.

We report the highly isoselective ring-opening polymerization (ROP) of racemic ß-butyrolactone (ß-BL) using in situ-generated catalysts based on Y[N(SiHMe2)2]3(THF)2 and salan-type pro-ligands. The catalyst system produces isotactic poly(3-hydroxybutyrate) (PHB) with record productivity (TOF up to 32 000 h-1) and the highest isoselectivity (Pm up to 0.89) in ROP of ß-BL achieved to date. In contrast to bacterial PHB, the chemically synthesized PHB has beneficial material properties, such as increased melt processing window attributed to a lowered melting temperature (Tm ≈ 140 °C) and drastically reduced brittleness. The produced PHB showed an elongation at break of 392%, thus demonstrating promising polyolefin-like thermomechanical material properties.

A Carbodiimide-Fueled Reaction Cycle That Forms Transient 5(4H)-Oxazolones.

In life, molecular architectures, like the cytoskeletal proteins or the nucleolus, catalyze the conversion of chemical fuels to perform their functions. For example, tubulin catalyzes the hydrolysis of GTP to form a dynamic cytoskeletal network. In contrast, myosin uses the energy obtained by catalyzing the hydrolysis of ATP to exert forces. Artificial examples of such beautiful architectures are scarce partly because synthetic chemically fueled reaction cycles are relatively rare. Here, we introduce a new chemical reaction cycle driven by the hydration of a carbodiimide. Unlike other carbodiimide-fueled reaction cycles, the proposed cycle forms a transient 5(4H)-oxazolone. The reaction cycle is efficient in forming the transient product and is robust to operate under a wide range of fuel inputs, pH, and temperatures. The versatility of the precursors is vast, and we demonstrate several molecular designs that yield chemically fueled droplets, fibers, and crystals. We anticipate that the reaction cycle can offer a range of other assemblies and, due to its versatility, can also be incorporated into molecular motors and machines.

A Nanometric Probe of the Local Proton Concentration in Microtubule-Based Biophysical Systems.

We show a double-functional fluorescence sensing paradigm that can retrieve nanometric pH information on biological structures. We use this method to measure the extent of protonic condensation around microtubules, which are protein polymers that play many roles crucial to cell function. While microtubules are believed to have a profound impact on the local cytoplasmic pH, this has been hard to show experimentally due to the limitations of conventional sensing techniques. We show that subtle changes in the local electrochemical surroundings cause a double-functional sensor to transform its spectrum, thus allowing a direct measurement of the protonic concentration at the microtubule surface. Microtubules concentrate protons by as much as one unit on the pH scale, indicating a charge storage role within the cell via the localized ionic condensation. These results confirm the bioelectrical significance of microtubules and reveal a sensing concept that can deliver localized biochemical information on intracellular structures.

The Role of Chemically Innocent Polyanions in Active, Chemically Fueled Complex Coacervate Droplets.

Complex coacervation describes the liquid-liquid phase separation of oppositely charged polymers. Active coacervates are droplets in which one of the electrolyte's affinity is regulated by chemical reactions. These droplets are particularly interesting because they are tightly regulated by reaction kinetics. For example, they serve as a model for membraneless organelles that are also often regulated by biochemical transformations such as post-translational modifications. They are also a great protocell model or could be used to synthesize life-they spontaneously emerge in response to reagents, compete, and decay when all nutrients have been consumed. However, the role of the unreactive building blocks, e.g., the polymeric compounds, is poorly understood. Here, we show the important role of the chemically innocent, unreactive polyanion of our chemically fueled coacervation droplets. We show that the polyanion drastically influences the resulting droplets' life cycle without influencing the chemical reaction cycle-either they are very dynamic or have a delayed dissolution. Additionally, we derive a mechanistic understanding of our observations and show how additives and rational polymer design help to create the desired coacervate emulsion life cycles.

Synthesis of a Triphenylphosphinimide-Substituted Silirane as a "Masked" Acyclic Silylene.

Phosphinimides are long known as useful ligands in transition metal chemistry, but examples of these in low-valent silicon chemistry are rather rare. Hence, in this work, we report on the implementation of a triphenylphosphinimide moiety as a ligand of a novel silylene that is trapped as a silirane with cyclohexene. By performing activation reactions with B(p-Tol)3, HSiEt3, N2O, and NH3, we demonstrate that the silirane exhibits a silylene-like behavior, making it a "masked" silylene. Furthermore, we treated the silirane with ethylene, propylene, and trans-butene, which led to an olefin exchange. In the case of ethylene and propylene, an additional insertion of the olefin into the silicon-silicon bonds of the respective siliranes could be achieved. As the insertion of trans-butene was not feasible, we surmise that the scope of this reactivity is restricted by the steric demand of the olefin.

Solvent-Free Synthesis and Processing of Conductive Elastomer Composites for Green Dielectric Elastomer Transducers.

Stretchable electrodes are more suitable for dielectric elastomer transducers (DET) the closer the mechanical characteristics of the electrodes and elastomer are. Here, a solvent-free synthesis and processing of conductive composites with excellent electrical and mechanical properties for transducers are presented. The composites are prepared by in situ polymerization of cyclosiloxane monomers in the presence of graphene nanoplatelets. The low viscosity of the monomer allows for easy dispersion of the filler, eliminating the need for a solvent. After the polymerization, a cross-linking agent is added at room temperature, the composite is solvent-free screen-printed, and the cross-linking reaction is initiated by heating. The best material shows conductivity σ = 8.2 S cm-1 , Young's modulus Y10%  = 167 kPa, and strain at break s = 305%. The electrode withstands large strains without delamination, shows no conductivity losses during repeated operation for 500 000 cycles, and has an excellent recovery of electrical properties upon being stretched at strains of up to 180%. Reliable prototype capacitive sensors and stack actuators are manufactured by screen-printing the conductive composite on the dielectric film. Stack actuators manufactured from dielectric and conductive materials that are synthesized solvent-free are demonstrated. The stack actuators even self-repair after a breakdown event.

In situ activation of green sorbents for CO2 capture upon end group backbiting.

Thermolysis of a urethane end group was observed as a first time phenomenon during activation. This unzipping mechanism revealed a new amine tethering point producing a diamine-terminated oligourea ([10]-OU), acting as a green sorbent for CO2 capturing. The oligomer backbites its end group to form propylene carbonate (PC), as proved by in situ TGA-MS, which can reflect the polymer performance by maximizing its capturing capacity. Cross polarization magic angle spinning (CP-MAS) NMR spectroscopy verified the formation of the proven ionic carbamate (1:2 mechanism) with a chemical shift at 161.7 ppm due to activation desorption at higher temperatures, viz., 100 °C (in vacuo) accompanied with bicarbonate ions (1:1 mechanism) with a peak centered at 164.9 ppm. Fortunately, the amines formed from in situ thermolysis explain the abnormal behavior (carbamates versus bicarbonates) of the prepared sample. Finally, ex situ ATR-FTIR proved the decomposition of urethanes, which can be confirmed by the disappearance of the pre-assigned peak centered at 1691 cm-1. DFT calculations supported the thermolysis of the urethane end group at elevated temperatures, and provided structural insights into the formed products.

Perfectly Isotactic Polypropylene upon In Situ Activation of Ultrarigid meso Hafnocenes.

For more than 40 years, the synthesis of C2 -symmetric indenyl-based racemic metallocenes for the isoselective polymerization of propylene relied on a tedious separation of the produced rac and meso isomers. Status quo, latter are considered wasteful as they produce atactic polypropylene (aPP) rather than isotactic polypropylene (iPP) if activated with methylaluminoxane (MAO). Unexpectedly, the in situ activation of meso hafnocene I yielded perfectly isotactic polypropylene. We verified an isomerization of the meso compound to the corresponding racemic one upon triisobutylaluminum (TIBA) addition via nuclear magnetic resonance (NMR) spectroscopy and established an easy and convenient polymerization protocol, enabling productivities comparable to pure rac-I if applied to pure meso-I or a mixture of both isomers. With this established isomerization protocol, the potential yield of iPP was enhanced by more than 400 %. This protocol was also shown to be applicable to other meso hafnocenes and some initial mechanistic insights were received.

Molecular Design of Chemically Fueled Peptide-Polyelectrolyte Coacervate-Based Assemblies.

Complex coacervated-based assemblies form when two oppositely charged polyelectrolytes combine to phase separate into a supramolecular architecture. These architectures range from complex coacervate droplets, spherical and worm-like micelles, to vesicles. These assemblies are widely applied, for example, in the food industry, and as underwater or medical adhesives, but they can also serve as a great model for biological assemblies. Indeed, biology relies on complex coacervation to form so-called membraneless organelles, dynamic and transient droplets formed by the coacervation of nucleic acids and proteins. To regulate their function, membraneless organelles are dynamically maintained by chemical reaction cycles, including phosphorylation and dephosphorylation, but exact mechanisms remain elusive. Recently, some model systems also regulated by chemical reaction cycles have been introduced, but how to design such systems and how molecular design affects their properties is unclear. In this work, we test a series of cationic peptides for their chemically fueled coacervation, and we test how their design can affect the dynamics of assembly and disassembly of the emerging structures. We combine them with both homo- and block copolymers and study the morphologies of the assemblies, including morphological transitions that are driven by the chemical reaction cycle. We deduce heuristic design rules that can be applied to other chemically regulated systems. These rules will help develop membraneless organelle model systems and lead to exciting new applications of complex coacervate-based examples like temporary adhesives.

Modular Assembly of Vibrationally and Electronically Coupled Rhenium Bipyridine Carbonyl Complexes on Silicon.

Hybrid inorganic/organic heterointerfaces are promising systems for next-generation photocatalytic, photovoltaic, and chemical-sensing applications. Their performance relies strongly on the development of robust and reliable surface passivation and functionalization protocols with (sub)molecular control. The structure, stability, and chemistry of the semiconductor surface determine the functionality of the hybrid assembly. Generally, these modification schemes have to be laboriously developed to satisfy the specific chemical demands of the semiconductor surface. The implementation of a chemically independent, yet highly selective, standardized surface functionalization scheme, compatible with nanoelectronic device fabrication, is of utmost technological relevance. Here, we introduce a modular surface assembly (MSA) approach that allows the covalent anchoring of molecular transition-metal complexes with sub-nanometer precision on any solid material by combining atomic layer deposition (ALD) and selectively self-assembled monolayers of phosphonic acids. ALD, as an essential tool in semiconductor device fabrication, is used to grow conformal aluminum oxide activation coatings, down to sub-nanometer thicknesses, on silicon surfaces to enable a selective step-by-step layer assembly of rhenium(I) bipyridine tricarbonyl molecular complexes. The modular surface assembly of molecular complexes generates precisely structured spatial ensembles with strong intermolecular vibrational and electronic coupling, as demonstrated by infrared spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy analysis. The structure of the MSA can be chosen to avoid electronic interactions with the semiconductor substrate to exclusively investigate the electronic interactions between the surface-immobilized molecular complexes.

Understanding entrapped molecular photosystem and metal-organic framework synergy for improved solar fuel production.

Artificial photosystems assembled from molecular complexes, such as the photocatalyst fac-ReBr(CO)3(4,4'-dcbpy) (dcbpy = dicarboxy-2,2'-bipyridine) and the photosensitiser Ru(bpy)2(5,5'-dcbpy)Cl2 (bpy = 2,2'-bipyridine), are a wide-spread approach for solar fuel production. Recently metal-organic framework (MOF) entrapping of such complexes was demonstrated as a promising concept for catalyst stabilisation and reaction environment optimisation in colloidal-based CO2 reduction. Building on this strategy, here we examined the influence of MIL-101-NH2(Al) MOF particle size, the electron donor source, and the presence of an organic base on the photocatalytic CO2-to-CO reduction performance, and the differences to homogeneous systems. A linear relation between smaller scaffold particle size and higher photocatalytic activity, longer system lifetimes for benign electron donors, and increased turnover numbers (TONs) with certain additive organic bases, were determined. This enabled understanding of key molecular catalysis phenomena and synergies in the nanoreactor-like host-guest assembly, and yielded TONs of ∼4300 over 96 h of photocatalysis under optimised conditions, surpassing homogeneous TON values and lifetimes.

Introduction of Photolatent Bases for Locally Controlling Dynamic Exchange Reactions in Thermo-Activated Vitrimers.

Vitrimers exhibit a covalently crosslinked network structure, as is characteristic of classic thermosetting polymers. However, they are capable of rearranging their network topology by thermo-activated associative exchange reactions when the topology freezing transition temperature (Tv ) is exceeded. Despite the vast number of developed vitrimers, there is a serious lack of methods that enable a (spatially) controlled onset of these rearrangement reactions above Tv . Herein, we highlight the localized release of the efficient transesterification catalyst 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) by the UV-induced cleavage of a photolatent base within a covalently crosslinked thiol-epoxy network. Demonstrated with stress relaxation measurements conducted well above the network's Tv , only the controlled release of TBD facilitates the immediate onset of transesterification in terms of a viscoelastic flow. Moreover, the spatially resolved UV-mediated photoactivation of vitrimeric properties is confirmed by permanent shape changes induced locally in the material.

Host-Guest Interactions in a Metal-Organic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction.

A strategy to improve homogeneous molecular catalyst stability, efficiency, and selectivity is the immobilization on supporting surfaces or within host matrices. Herein, we examine the co-immobilization of a CO2 reduction catalyst [ReBr(CO)3 (4,4'-dcbpy)] and a photosensitizer [Ru(bpy)2 (5,5'-dcbpy)]Cl2 using the isoreticular series of metal-organic frameworks (MOFs) UiO-66, -67, and -68. Specific host pore size choice enables distinct catalyst and photosensitizer spatial location-either at the outer MOF particle surface or inside the MOF cavities-affecting catalyst stability, electronic communication between reaction center and photosensitizer, and consequently the apparent catalytic rates. These results allow for a rational understanding of an optimized supramolecular layout of catalyst, photosensitizer, and host matrix.

Maximizing PHB content in Synechocystis sp. PCC 6803: a new metabolic engineering strategy based on the regulator PirC.

BACKGROUND: PHB (poly-hydroxy-butyrate) represents a promising bioplastic alternative with good biodegradation properties. Furthermore, PHB can be produced in a completely carbon-neutral fashion in the natural producer cyanobacterium Synechocystis sp. PCC 6803. This strain has been used as model system in past attempts to boost the intracellular production of PHB above ~ 15% per cell-dry-weight (CDW). RESULTS: We have created a new strain that lacks the regulatory protein PirC (product of sll0944), which exhibits a higher activity of the phosphoglycerate mutase resulting in increased PHB pools under nutrient limiting conditions. To further improve the intracellular PHB content, two genes involved in PHB metabolism, phaA and phaB, from the known producer strain Cupriavidus necator, were introduced under the control of the strong promotor PpsbA2. The resulting strain, termed PPT1 (ΔpirC-REphaAB), produced high amounts of PHB under continuous light as well under a day-night regime. When grown in nitrogen and phosphorus depleted medium, the cells produced up to 63% per CDW. Upon the addition of acetate, the content was further increased to 81% per CDW. The produced polymer consists of pure PHB, which is highly isotactic. CONCLUSION: The amounts of PHB achieved with PPT1 are the highest ever reported in any known cyanobacterium and demonstrate the potential of cyanobacteria for a sustainable, industrial production of PHB.

CO2 activation through C-N, C-O and C-C bond formation.

A comparative model for the chemisorption of CO2 was explored via three representative reaction pathways: carboxylation of cyclohexanone, carbonation of cyclohexanol, and carbamation of cyclohexylamine. The model substrates were activated using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, an amidine superbase). For each of these reactions, the formation of the corresponding CO2 adducts was confirmed by 13C nuclear magnetic resonance and Fourier-transform infrared spectroscopy measurements. It was demonstrated that CO2 fixation occurred through either an enol-CO2 adduct (i.e. carboxylation), proton shuttling process (i.e. carbonation), or self-activation mechanism (i.e. carbamation). Volumetric adsorption measurements indicated that cyclohexanol was superior in its uptake capacity (11.7 mmol CO2 g-1 sorbent) in comparison to cyclohexylamine (9.3 mmol CO2 g-1 sorbent) or cyclohexanone (8.5 mmol CO2 g-1 sorbent). As supported by density functional theory calculations, this trend was expected given the fact that the carbonation reaction proceeded through a more thermodynamically favorable reaction process.

Pathway Dependence in the Fuel-Driven Dissipative Self-Assembly of Nanoparticles.

We describe the self-assembly of gold and iron oxide nanoparticles regulated by a chemical reaction cycle that hydrolyzes a carbodiimide-based fuel. In a reaction with the chemical fuel, the nanoparticles are chemically activated to a state that favors assembling into clusters. The activated state is metastable and decays to the original precursor reversing the assembly. The dynamic interplay of activation and deactivation results in a material of which the behavior is regulated by the amount of fuel added to the system; they either did not assemble, assembled transiently, or assembled permanently in kinetically trapped clusters. Because of the irreversibility of the kinetically trapped clusters, we found that the behavior of the self-assembly was prone to hysteresis effects. The final state of the system in the energy landscape depended on the pathway of preparation. For example, when a large amount of fuel was added at once, the material would end up kinetically trapped in a local minimum. When the same amount of fuel was added in small batches with sufficient time for the system to re-equilibrate, the final state would be the global minimum. A better understanding of pathway complexity in the energy landscape is crucial for the development of fuel-driven supramolecular materials.

Unprecedented High Oxygen Evolution Activity of Electrocatalysts Derived from Surface-Mounted Metal-Organic Frameworks.

The oxygen evolution reaction (OER) is a key process for renewable energy storage. However, developing non-noble metal OER electrocatalysts with high activity, long durability and scalability remains a major challenge. Herein, high OER activity and stability in alkaline solution were discovered for mixed nickel/cobalt hydroxide electrocatalysts, which were derived in one-step procedure from oriented surface-mounted metal-organic framework (SURMOF) thin films that had been directly grown layer-by-layer on macro- and microelectrode substrates. The obtained mass activity of ∼2.5 mA·µg-1 at the defined overpotential of 300 mV is 1 order of magnitude higher than that of the benchmarked IrO2 electrocatalyst and at least 3.5 times higher than the mass activity of any state-of-the-art NiFe-, FeCoW-, or NiCo-based electrocatalysts reported in the literature. The excellent morphology of the SURMOF-derived ultrathin electrocatalyst coating led to a high exposure of the most active Ni- and Co-based sites.

Silicon nanosheets as co-initiators for diaryliodonium induced radical and cationic polymerization.

A system of silicon nanosheets and a diaryliodonium salt was found to initiate cationic and radical polymerizations. The polymerization relies on a syngergistic interaction between the silicon nanomaterial and the diaryliodonium salt, whereby the silicon nanomaterial acts as a co-initiator, inducing the decomposition of the diaryliodonium salt. The decomposition products, in turn, are able to initiate both cationic and radical polymerizations thereby enabling a mild and straightforward reaction procedure to obtain a variety of polymer/nanomaterial composites with cationically and radically polymerizable monomers. Most importantly, this work highlights the potential of using silicon nanomaterials' unique properties not just for physical applications, but also in chemical applications.