The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing both axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted ...3,3′‐bisindoles with 3‐indolylmethanols (up to 98 % yield, all >95:5 d.r., >99 % ee). This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles. This reaction not only provides a good example for simultaneously controlling axial and central chirality in one operation, but also serves as a new strategy for catalytic enantioselective construction of axially chiral 3,3′‐bisindole backbones from prochiral substrates.
Bulk up: The first catalytic asymmetric construction of 3,3′‐bisindole skeletons bearing axial and central chirality has been established by organocatalytic asymmetric addition reactions of 2‐substituted 3,3′‐bisindoles with electrophiles. This reaction also represents the first highly enantioselective construction of axially chiral 3,3′‐bisindole skeletons, and utilizes the strategy of introducing a bulky group to the ortho‐position of prochiral 3,3′‐bisindoles.
Lactic acid bacteria (LAB) are the most frequently used probiotics in fermented foods and beverages and as food supplements for humans or animals, owing to their multiple beneficial features, which ...appear to be partially associated with their antioxidant properties. LAB can help improve food quality and flavor and prevent numerous disorders caused by oxidation in the host. In this review, we discuss the oxidative stress tolerance, the antioxidant capacity related herewith, and the underlying mechanisms and signaling pathways in probiotic LAB. In addition, we discuss appropriate methods used to evaluate the antioxidant capacity of probiotic LAB. The aim of the present review is to provide an overview of the current state of the research associated with the oxidative stress tolerance and antioxidant capacity of LAB.
In the last few decades, worldwide scientists have been motivated by the promising production of chemicals from the widely existing methane (CH
) under mild conditions for both chemical synthesis ...with low energy consumption and climate remediation. To achieve this goal, a whole library of catalytic chemistries of transforming CH
to various products under mild conditions is required to be developed. Worldwide scientists have made significant efforts to reach this goal. These significant efforts have demonstrated the feasibility of oxidation of CH
to value-added intermediate compounds including but not limited to CH
OH, HCHO, HCOOH, and CH
COOH under mild conditions. The fundamental understanding of these chemical and catalytic transformations of CH
under mild conditions have been achieved to some extent, although currently neither a catalyst nor a catalytic process can be used for chemical production under mild conditions at a large scale. In the academic community, over ten different reactions have been developed for converting CH
to different types of oxygenates under mild conditions in terms of a relatively low activation or catalysis temperature. However, there is still a lack of a molecular-level understanding of the activation and catalysis processes performed in extremely complex reaction environments under mild conditions. This article reviewed the fundamental understanding of these activation and catalysis achieved so far. Different oxidative activations of CH
or catalytic transformations toward chemical production under mild conditions were reviewed in parallel, by which the trend of developing catalysts for a specific reaction was identified and insights into the design of these catalysts were gained. As a whole, this review focused on discussing profound insights gained through endeavors of scientists in this field. It aimed to present a relatively complete picture for the activation and catalytic transformations of CH
to chemicals under mild conditions. Finally, suggestions of potential explorations for the production of chemicals from CH
under mild conditions were made. The facing challenges to achieve high yield of ideal products were highlighted and possible solutions to tackle them were briefly proposed.
Comprehensive Summary
A new strategy for the enantioselective synthesis of axially chiral 3,3'‐bisindoles was devised by the direct coupling of two indole rings. This strategy makes use of the ...C3‐umpolung reactivity of 2‐indolylmethanols, which enables the catalytic asymmetric addition reaction of 2‐indolylmethanols with rationally designed 2‐substituted indoles, thus constructing axially chiral 3,3'‐bisindole scaffolds in overall excellent yields (up to 98%) with high enantioselectivities (up to 96 : 4 er). This approach not only has overcome the challenges in constructing axially chiral five‐five‐membered heterobiaryls, but also represents a new application of the C3‐umpolung reactivity of 2‐indolylmethanols in asymmetric catalysis. More importantly, this class of axially chiral 3,3'‐bisindoles can undergo a variety of post‐functionalizations to give axially chiral 3,3'‐bisindole‐based organocatalysts, which have found their preliminary applications in asymmetric catalysis.
A new strategy for the enantioselective synthesis of axially chiral 3,3'‐bisindoles was devised by the direct coupling of two indole rings. This strategy makes use of the C3‐umpolung reactivity of 2‐indolylmethanols to enable the reaction with rationally designed 2‐substituted indoles. This class of axially chiral 3,3'‐bisindoles can undergo post‐functionalizations to give 3,3'‐bisindole‐based chiral organocatalysts with potential applications in asymmetric catalysis.
An imidazolium‐type room‐temperature ionic liquid containing silsesquioxane frameworks is successfully prepared. The polar ionic liquid products are grafted onto the surface of prepared aromatic ...polyamide (PA) membranes to improve water flux of PA membranes. Membranes grafted with an ionic liquid exhibit a water flux of 1.89 L m−2 h−1 bar−1), 48% higher than that of pure PA membranes while the salt rejection still remains at 96%. This improvement can be attributed to the enhanced hydrophilicity of the membrane surface, as evidenced by the reduced water contact angle.
Imidazolium‐type ionic liquids containing silsesquioxane frameworks are prepared and grafted onto the surface of polyamide membranes to enhance the water flux of polyamide membranes. The results show that the water flux of membranes grafted with ionic liquid is increased by 48% compared with pure polyamide membranes while salt rejection is still high at 96%.
Human-computer interaction (HCI) is an important supporting technology in the computer vision area, especially in physical education. HCI can promote the efficiency of physical education class, which ...is of great help to improve the learning efficiency. It is developing towards naturalization, intelligence, high efficiency, and materialization. Gesture recognition is very important in HCI, and plays a very important role in artistic understanding and image perception. Traditional gesture recognition methods are prone to misrecognition and result in low accuracy. In this paper, we propose a new gesture recognition method based on mask RCNN and single shot multibox detector (SSD) in HCI. Firstly, feature extraction and region segmentation are performed on the red, green, and blue (RGB) three-channel images, and the hand instance segmentation and mask are obtained. Then we modify the SSD model to obtain a new convolution layer, which can realize the fusion of shallow visual convolution layer and deep semantic convolution layer in the network structure. To solve the problem of poor classification performance caused by the imbalance of positive and negative samples, an improved loss function is proposed to improve the model ability of classifying target gestures. The experimental results show that compared with state-of-the-art methods, the proposed method has better robustness and faster detection speed while maintaining higher gesture detection accuracy.
Organic emitters with persistent phosphorescence have shown potential application in optoelectronic devices. However, rational design and phosphorescence tuning are still challenging. Here, a series ...of metal-free luminophores without heavy atoms and carbonyl groups from commercial/lab-synthesized carbazole and benzene were synthesized to realize tunable molecular emission from fluorescence to phosphorescence by simply substituent variation. All the molecules emit blue fluorescence in both solution and solid state. Upon removal of excitation source, the fluorinated luminophores show obvious phosphorescence. The lab-synthesized carbazole based molecules exhibit a huge lifetime difference to the commercially purchased ones due to the existence of isomer in the latter samples. The small energy gap between singlet and triplet state and low reorganization energy help enhance intersystem crossing to contribute to a more competitive radiative process from triplet to ground state. Blue and white organic light-emitting devices are fabricated by using fluorinated luminophore as emitting layer.
Artificial intelligence (AI) art is the product of AI technology applied to art. In terms of technical application, AI art has two methods: symbolism and connectivism. In terms of the human-machine ...system, there are three levels: human using machine, human guiding machine and human-machine separation. AI art is a special form, existing between natural beauty and human art: AI art, first of all, is not a natural aesthetic object, given that it is the product of artefacts. Its appreciation is mixed with interests, and its artistic generation is a kind of "purposeful non-purposefulness." Secondly, AI art is not equal to traditional human art, because AI has no intentionality or consciousness. Thirdly, AI participates in the construction of artistic logic and breaks the boundary of traditional art. AI can be regarded as an "agent" in art generation, and together with people constitute the "actor network" of art. The processes of generation, identification and appreciation of AI art include the judgment of true and false. AI art reflects the forced integration of intelligent technology into art, an attempt to rid of contingency, dialectics, and negativity of art. But what we need is the real harmonisation of art and technology. People should use aesthetic reason to guide AI technology.
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•Chiral AIE compounds are recently developed very rapidly.•Chiral AIEgens display excellent chiral recognition, ee analysis and CPL properties.•Review paper about preparation of ...chiral AIEgens and their applications is scarce.
Due to immense potential in using as chemo/biosensors and solid emitters, aggregation-induced emission (AIE) phenomenon is attracting huge interest in scientific community. After endowed with chirality, the resultant chiral AIE luminogens (AIEgen), just like a tiger with added wings, can display more and stronger promising functionalities. Moreover, many classic luminophores can be transformed into AIEgens from notorious aggregation-caused quenching (ACQ) compounds as soon as they are attached with chiral groups. Compared with other chiral fluorescent receptors and chiral emitter, chiral AIEgens have displayed unique and outstanding advantages. Firstly, chiral AIEgen can differentiate two enantiomers of chiral analyte by 1.68 × 104 fold difference and get a chiral magnification up to 2.5 × 103 times due to aggregation. In addition, two enantiomers of up to 18 chiral carboxylic acids can be recognized just by using only one chiral AIEgen receptor and enantiomeric excess (ee) of chiral analytes at uM level can be measured. Furthermore, accurate ee analysis was carried out for the first time from fluorescence wavelength change rather than intensity change of the chiral AIEgen receptor. Therefore, the chiral AIEgens show unprecedentedly high selectivity, high sensitivity, high applicability, and high accuracy. Secondly, in the area of organic circularly polarized luminescence (CPL) materials, the CPL dissymmetry factor (glum) of chiral AIEgen can get to 1.42 that is near to the theoretical value of 2, making a breakthrough progress while the |glum| of previous organic luminophores is generally between 10−5 and 10−2. Furthermore, the highly efficient circularly polarized organic light-emitting diodes (CPOLEDs) are constructed for the first time by chiral AIEgens. Thirdly, chiral AIEgens enable novel display technology under different lighting conditions to be possible. More importantly, due to AIE effect, AIEgens are very beneficial for disclosing the mechanism of chiral transfer and magnification between molecules, which is thought to be the key for evolution of homochirality in natural world and preparation of chiral materials with hierarchical structures. For the above reason, chiral AIEgens have been brought to extensive attention and a large number of research works about them are reported. To take an overall view on chiral AIEgens and facilitate the development of chiral AIEgens, it is necessary to make a full review on the chiral AIEgens. This review covers the following contents: (1) construction of chiral AIEgens including propeller-like chiral AIEgens, chiral AIEgens with optically pure groups, polymer chiral AIEgens and supramolecular chiral AIEgen system; (2) chiral recognition and ee determination of chiral carboxylic acids, chiral amines, α-amino acids, and chiral neutral molecules by chiral AIEgens; (3) performance of chiral AIEgens in circular dichroism (CD), CPL and CPOLEDs; (4) other versatile application researches related to chiral AIEgens.
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