Abstract Transition metal-catalyzed asymmetric hydrogenation is one of the most efficient methods for the preparation of chiral α-substituted propionic acids. However, research on this method, employing cleaner earth-abundant metal catalysts, is still insufficient in both academic and industrial contexts. Herein, we report an efficient nickel-catalyzed asymmetric hydrogenation of α-substituted acrylic acids affording the corresponding chiral α-substituted propionic acids with up to 99.4% ee (enantiomeric excess) and 10,000 S/C (substrate/catalyst). In particular, this method can be used to obtain ( R )-dihydroartemisinic acid with 99.8:0.2 dr (diastereomeric ratio) and 5000 S/C, which is an essential intermediate for the preparation of the antimalarial drug Artemisinin. The reaction mechanism has been investigated via experiments and DFT (Density Functional Theory) calculations, which indicate that the protonolysis of the C-Ni bond of the key intermediate via an intramolecular proton transfer from the carboxylic acid group of the substrate, is the rate-determining step.
<p indent="0mm">Triboelectrification (CE) is a universal phenomenon between any two materials interface. Among them, the triboelectric between semiconductors has unique properties. When a p-type semiconductor slides on an n-type semiconductor surface, the chemical bond between the two material interfaces breaks and new chemical bonds are formed under the action of mechanical sliding, releasing energy “bindington” and exciting the electron-hole pairs at the semiconductor interface. The mechanical sliding excited electron-hole pairs separate under the action of the built-in electric field at the p-n junction and generate a direct current. This process is similar to the photovoltaic effect, so the phenomenon is called tribovoltaic effect. The only difference between the tribovoltaic effect and the photovoltaic effect is that the electron-hole pairs in the tribovoltaic effect are excited by mechanical sliding, while the photovoltaic effect is excited by photons. In this paper, the research progress of the tribovoltaic effect in recent years is reviewed, and the technology of tribovoltaic nanogenerator based on the tribovoltaic effect and its potential applications are elaborated. The tribovoltaic effect is an important part of contact electrification at the semiconductor interface, and its research not only contributes to a better understanding of the mechanism of contact electrification but also has the potential to advance the development and application of triboelectrification nanogenerators and semiconductors.
Recent density functional theory (DFT) calculations have demonstrated the potential of mechanically bent graphene as a piezoelectric energy harvesting material. We develop a two-dimensional (2D) model of hexagonal materials and demonstrate quantitatively the potential of a single layer of graphene to function as an effective piezoelectric nanogenerator. The piezoelectricity of graphene stems from a dynamically generated surface charge density proportional to the local curvature of the graphene layer, and the proportionality constant is found from DFT calculations on a single layer of bent graphene. By virtue of different tailored mechanical and electrical loadings, explored in this work, it is demonstrated that graphene can be as effective an energy harvester as a single flat layer of 2D MoS2, which is strongly piezoelectric due to its inversion-asymmetric unit cell. Demonstrations are carried out for graphene and MoS2 using a 2D finite element model to determine the generated voltage, current, and power density.
