Investigation of the Photocatalytic Hydrogen Production of Semiconductor Nanocrystal-Based Hydrogels

Destabilization of a ligand-stabilized semiconductor nanocrystal solution with an oxidizing agent can lead to a macroscopic highly porous self-supporting nanocrystal network entitled hydrogel, with good accessibility to the surface. The previously reported charge carrier delocalization beyond a single nanocrystal building block in such gels can extend the charge carrier mobility and make a photocatalytic reaction more probable. The synthesis of ligand-stabilized nanocrystals with specific physicochemical properties is possible, thanks to the advances in colloid chemistry made in the last decades. Combining the properties of these nanocrystals with the advantages of nanocrystal-based hydrogels will lead to novel materials with optimized photocatalytic properties. This work demonstrates that CdSe quantum dots, CdS nanorods, and CdSe/CdS dot-in-rod-shaped nanorods as nanocrystal-based hydrogels can exhibit a much higher hydrogen production rate compared to their ligand-stabilized nanocrystal solutions. The gel synthesis through controlled destabilization by ligand oxidation preserves the high surface-to-volume ratio, ensures the accessible surface area even in hole-trapping solutions and facilitates photocatalytic hydrogen production without a co-catalyst. Especially with such self-supporting networks of nanocrystals, the problem of colloidal (in)stability in photocatalysis is circumvented. X-ray photoelectron spectroscopy and photoelectrochemical measurements reveal the advantageous properties of the 3D networks for application in photocatalytic hydrogen production.     

Isotope-Guided Metabolomics Reveals Divergent Incorporation of Valine into Different Flavor Precursor Classes in Chives

Plants of the genus Allium such as chives, onions or garlic produce S-alk(en)yl cysteine sulfoxides as flavor precursors. Two major representatives are S-propenyl cysteine sulfoxide (isoalliin) and S-propyl cysteine sulfoxide (propiin), which only differ by a double bond in the C₃ side chain. The propenyl group of isoalliin is derived from the amino acid valine, but the source of the propyl group of propiin remains unclear. Here, we present an untargeted metabolomics approach in seedlings of chives (Allium schoenoprasum) to track mass features containing sulfur and/or ¹³C from labeling experiments with valine-¹³C₅ guided by their isotope signatures. Our data show that propiin and related propyl-bearing metabolites incorporate carbon derived from valine-¹³C₅, but to a much lesser extent than isoalliin and related propenyl compounds. Our findings provide new insights into the biosynthetic pathways of flavor precursors in Allium species and open new avenues for future untargeted labeling experiments.     

Micro-Cup Architecture for Printing and Coating Asymmetric 2d-Material-Based Solid-State Supercapacitors

High energy density micro-supercapacitors (MSCs) are in high demand for miniaturized electronics and microsystems. Research efforts today focus on materials development, applied in the planar interdigitated, symmetric electrode architecture. A novel “cup & core” device architecture that allows for printing of asymmetric devices without the need of accurately positioning the second finger electrode here have been introduced. The bottom electrode is either produced by laser ablation of a blade-coated graphene layer or directly screen-printed with graphene inks to create grids with high aspect ratio walls forming an array of “micro-cups”. A quasi-solid-state ionic liquid electrolyte is spray-deposited on the walls; the top electrode material -MXene inks- is then spray-coated to fill the cup structure. The architecture combines the advantages of interdigitated electrodes for facilitated ion-diffusion, which is critical for 2D-material-based energy storage systems by providing vertical interfaces with the layer-by-layer processing of the sandwich geometry. Compared to flat reference devices, volumetric capacitance of printed “micro-cups” MSC increased considerably, while the time constant decreased (by 58%). Importantly, the high energy density (3.99 µWh cm⁻²) of the “micro-cups” MSC is also superior to other reported MXene and graphene-based MSCs.     

Enabling Technologies in Carbohydrate Chemistry: Automated Glycan Assembly,Flow Chemistry and Data Science

The synthesis of defined oligosaccharides is a complex task. Several enabling technologies have been introduced in the last two decades to facilitate synthetic access to these valuable biomolecules. In this concept, we describe the technological solutions that have advanced glycochemistry using automated glycan assembly, flow chemistry and data science as examples. We highlight how the synergies between these different technologies can further advance the field, with progress toward the realization of a self-driving lab for glycan synthesis.     

Lipid modification of amino acids,carbohydrates and polyols

Agricultural crops provide a considerable reservoir of useful and low cost raw materials like fats and oils, plant proteins and carbohydrates. By selective combination of their molecular constituents (e. g. fatty acids, glycerol, amino acids, saccharides), a wide variety of surface active materials can be prepared. Due to their molecular constitution, all of them are potentially biodegradable. In this article we describe two generally applicable methods for the synthesis of such combination products using fatty acids from plant oils – one of the most important renewable materials as feedstock for the chemical industry – in combination with amino acids and monosaccharides including sugar alcohols. Using the high selectivities displayed by lipases, which catalyze a wide variety of transformations under very mild conditions (pH, temperature) with high atom efficiency in various non‐toxic solvents and without the production of by‐products or waste, numerous useful products can be obtained ranging all the way from surface active compounds (detergents and emulsifiers for food and personal care products) such as mono‐ and diglycerides, sugar esters, synthetic building blocks, products for food and dietary applications, all the way to novel methods for the production of biofuels (biodiesel). In our continuing effort to devise novel and generally applicable methods for the syntheses of such combination products we recently discovered a novel class of building blocks, fatty acid modified anhydrides of hydroxy carboxylic acids such as citric acid, tartaric acid and malic acid which led to alternative synthetic approaches towards new classes of the title compounds.     

Parallel integration of aligned carbon strings in polymer composite: Dielectrophoretic preparation,finite element simulation,and electrical characterization

We report on dielectrophoretic alignment of carbon black particles into radially arranged string‐like assemblies in oligourethane mixtures followed by photopolymerization. Using finite element modelling and optical microscopy we find significant difference in field distributions depending on the substrate beneath aligned films. On glass, the field is concentrated between the electrode tips leading to string‐like assemblies between the tips. On oxide covered silicon, the field is distributed along the electrode circumference leading to more distributed fractal assemblies. Using comprehensive dc resistance measurements and ac‐impedance spectroscopy we show that the resistance of the strings varies from 120 kΩ to 5 MΩ with a mean of 1.03 MΩ. Strings on oxide covered silicon show significantly higher resistances than the strings on glass. We also demonstrate the effect of aging and an increase in resistance through elongating aligned strings. POLYM. COMPOS., 36:1866–1874, 2015. © 2014 Society of Plastics Engineers     

Electronic Structure of Colloidal 2H-MoS2 Mono and Bilayers Determined by Spectroelectrochemistry

The electronic structure of mono and bilayers of colloidal 2H-MoS₂ nanosheets synthesized by wet-chemistry using potential-modulated absorption spectroscopy (EMAS), differential pulse voltammetry, and electrochemical gating measurements is investigated. The energetic positions of the conduction and valence band edges of the direct and indirect bandgap are reported and observe strong bandgap renormalization effects, charge screening of the exciton, as well as intrinsic n-doping of the as-synthesized material. Two distinct transitions in the spectral regime associated with the C exciton are found, which overlap into a broad signal upon filling the conduction band. In contrast to oxidation, the reduction of the nanosheets is largely reversible, enabling potential applications for reductive electrocatalysis. This work demonstrates that EMAS is a highly sensitive tool for determining the electronic structure of thin films with a few nanometer thicknesses and that colloidal chemistry affords high-quality transition metal dichalcogenide nanosheets with an electronic structure comparable to that of exfoliated samples.     

Brominative Deoxygenation of some aldehydes and ethers

Three aldehydes ( 4a–c ) are transformed into 1,1-dibromides ( 6a–c ) by 2,2,2-tribromo-2,2-dihydro-1,3,2-benzodioxaphosphole ( 2 ). This reagent ( 2 ) is also very active in the cleavage of ethers; its reactions may show some features of carbonium as well as of S_N2 character.     

Functionalized Fullerene for Inhibition of SARS-CoV-2 Variants

As virus outbreaks continue to pose a challenge, a nonspecific viral inhibitor can provide significant benefits, especially against respiratory viruses. Polyglycerol sulfates recently emerge as promising agents that mediate interactions between cells and viruses through electrostatics, leading to virus inhibition. Similarly, hydrophobic C₆₀ fullerene can prevent virus infection via interactions with hydrophobic cavities of surface proteins. Here, two strategies are combined to inhibit infection of SARS-CoV-2 variants in vitro. Effective inhibitory concentrations in the millimolar range highlight the significance of bare fullerene's hydrophobic moiety and electrostatic interactions of polysulfates with surface proteins of SARS-CoV-2. Furthermore, microscale thermophoresis measurements support that fullerene linear polyglycerol sulfates interact with the SARS-CoV-2 virus via its spike protein, and highlight importance of electrostatic interactions within it. All-atom molecular dynamics simulations reveal that the fullerene binding site is situated close to the receptor binding domain, within 4 nm of polyglycerol sulfate binding sites, feasibly allowing both portions of the material to interact simultaneously.