Ferroelectric oxide materials have offered a tantalizing potential for applications since the discovery of ferroelectric perovskites more than 50 years ago. Their switchable electric polarization is ...ideal for use in devices for memory storage and integrated microelectronics, but progress has long been hampered by difficulties in materials processing. Recent breakthroughs in the synthesis of complex oxides have brought the field to an entirely new level, in which complex artificial oxide structures can be realized with an atomic-level precision comparable to that well known for semiconductor heterostructures. Not only can the necessary high-quality ferroelectric films now be grown for new device capabilities, but ferroelectrics can be combined with other functional oxides, such as high-temperature superconductors and magnetic oxides, to create multifunctional materials and devices. Moreover, the shrinking of the relevant lengths to the nanoscale produces new physical phenomena. Real-space characterization and manipulation of the structure and properties at atomic scales involves new kinds of local probes and a key role for first-principles theory.
Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure ...of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.
We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature (Tc) in ferroelectric ultrathin films and superlattices. We showed that ...one-unit-cell-thick BaTiO₃ layers in BaTiO₃/SrTiO₃ superlattices are not only ferroelectric (with Tc as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO₃ layers adjacent to them. Tc was tuned by ~500 kelvin by varying the thicknesses of the BaTiO₃ and SrTiO₃ layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.
Continuous flow systems for chemical synthesis are becoming a major focus in organic chemistry and there is a growing interest in the integration of biocatalysts due to their high regio‐ and ...stereoselectivity. Methods established for 3D bioprinting enable the fast and simple production of agarose‐based modules for biocatalytic reactors if thermally stable enzymes are available. We report here on the characterization of four different cofactor‐free phenacrylate decarboxylase enzymes suitable for the production of 4‐vinylphenol and test their applicability for the encapsulation and direct 3D printing of disk‐shaped agarose‐based modules that can be used for compartmentalized flow microreactors. Using the most active and stable phenacrylate decarboxylase from Enterobacter spec. in a setup with four parallel reactors and a subsequent palladium(II) acetate‐catalysed Heck reaction, 4‐hydroxystilbene was synthesized from p‐coumaric acid with a total yield of 14.7 % on a milligram scale. We believe that, due to the convenient direct immobilization of any thermostable enzyme and straightforward tuning of the reaction sequence by stacking of modules with different catalytic activities, this simple process will facilitate the establishment and use of cascade reactions and will therefore be of great advantage for many research approaches.
3D printing in flow chemistry: 4‐Hydroxystilbene is obtained from p‐coumaric acid employing a phenacrylate decarboxylase enzyme immobilized in 3D‐printed agarose‐based flow reactor modules and a subsequent palladium(II) acetate‐catalyzed Heck reaction with a total yield of 14.7 % on a milligram scale.
The effect of weather on public transport usage in Berlin is analysed. The number of single and day tickets sold is used as a proxy for the number of occasional public transport users. Analysing more ...than three years of hourly ticket sale data, it is shown that the most important factor influencing ticket sales is temperature. Temperatures below −5°C lead to an increase in ticket sales by up to 30% on working days, while on hot days (> 28°C) passenger numbers drop by up to 5%. Precipitation increases the number of sales on working days by up to 5%. On weekends, the lowest ticket-sale numbers are associated with wet and either very cold or very hot conditions. Another factor influencing ticket sales is sunshine duration, while wind and snowfall do not seem to play a role for ticket sales in Berlin. It is demonstrated that it is possible to predict ticket sales depending on date, time and weather conditions using a statistical model. On designated public transport routes the effect of weather on passenger numbers can be much stronger than the district average. This is shown for the example of a bus route to a public beach. With each degree of temperature increase, passenger numbers on this line go up by approximately 30%.
Enantiopure α‐hydroxy ketones are important building blocks of active pharmaceutical ingredients (APIs), which can be produced by thiamine‐diphosphate‐dependent lyases, such as benzaldehyde lyase. ...Here we report the discovery of a novel thermostable benzaldehyde lyase from Rhodococcus erythropolis R138 (ReBAL). While the overall sequence identity to the only experimentally confirmed benzaldehyde lyase from Pseudomonas fluorescens Biovar I (PfBAL) was only 65 %, comparison of a structural model of ReBAL with the crystal structure of PfBAL revealed only four divergent amino acids in the substrate binding cavity. Based on rational design, we generated two ReBAL variants, which were characterized along with the wild‐type enzyme in terms of their substrate spectrum, thermostability and biocatalytic performance in the presence of different co‐solvents. We found that the new enzyme variants have a significantly higher thermostability (up to 22 °C increase in T50) and a different co‐solvent‐dependent activity. Using the most stable variant immobilized in packed‐bed reactors via the SpyCatcher/SpyTag system, (R)‐benzoin was synthesized from benzaldehyde over a period of seven days with a stable space‐time‐yield of 9.3 mmol ⋅ L‐1 ⋅ d−1. Our work expands the important class of benzaldehyde lyases and therefore contributes to the development of continuous biocatalytic processes for the production of α‐hydroxy ketones and APIs.
A novel benzaldehyde lyase for the production of chiral α‐hydroxy ketones was identified by a machine learning model and two variants with altered substrate scopes were created by rational design. All three variants exhibit significantly higher thermostability compared to the only previously described benzaldehyde lyase. When immobilized in a packed‐bed reactor, the most thermostable variant showed stable substrate turnover over days.
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