Conspectus Axially chiral compounds have received much attention from chemists because of their widespread appearance in natural products, biologically active compounds, and useful chiral ligands in ...asymmetric catalysis. Because of the importance of this structural motif, the catalytic enantioselective construction of axially chiral scaffolds has been intensively investigated, and great progress has been accomplished. However, the majority of methodologies in this field focus on the use of metal catalysis, whereas approaches involving organocatalysis have started to emerge only recently. This Account describes certain advances in the organocatalytic asymmetric synthesis of axially chiral compounds involving the following strategies: kinetic resolution, desymmetrization, cyclization/addition, direct arylation, and so on. We began our investigation by developing a highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid-catalyzed imine formation and transfer hydrogenation cascade process, thereby providing a convenient route to generate chiral BINAM derivatives in high yields with excellent enantioselectivities. The desymmetrization of 1-aryltriazodiones (ATADs) through an organocatalyzed tyrosine clicklike reaction wherein a nucleophile was added to the ATAD afforded an interesting type of axially chiral N-arylurazole in an excellent remote enantiocontrolled manner. We then focused on a direct construction strategy involving cyclization and the addition strategy given the inherent limitations of the kinetic resolution in terms of the chemical yield and the desymmetrization in terms of the substrate scope. By utilizing the catalytic enantioselective Paal–Knorr reaction, we disclosed a general and efficient cyclization method to access enantiomerically pure arylpyrroles. The direct heterocycle formation and the stepwise method, which was executed in a one-pot fashion containing enantioselective cyclization and subsequent aromatization, were successfully applied for the construction of diverse axially chiral arylquinazolinones catalyzed by chiral Brønsted acids. We discovered the asymmetric organocatalytic approach to construct axially chiral styrenes through the 1,4-addition of arylalkynals in good chemical yields and enantioselectivities. Such structural motifs are important precursors for further transformations into biologically active compounds and useful synthetic intermediates and may have potential applications in asymmetric syntheses as olefin ligands or organocatalysts. To further tackle this challenge, we accomplished the phosphoric acid-catalyzed enantioselective direct arylative reactions of 2-naphthol and 2-naphthamine with quinone derivatives to deliver efficient access to a class of axially chiral BINOL and NOBIN derivatives in good yields with excellent enantioselectivities under mild reaction conditions. Most importantly, we discovered that the azo group can effectively perform as a directing and activating group for organocatalytic formal aryl C–H functionalization via formal nucleophilic aromatic substitution of azobenzene derivatives. Thus, a wide range of axially chiral arylindoles were synthesized in good yields with excellent enantioselectivities. We anticipate that this strategy will foster the development of many other transformations and motivate a new enthusiasm for organocatalytic enantioselective aryl functionalization. Moreover, SPINOLs are fundamental synthetic precursors in the construction of other chiral organocatalysts and ligands. We have successfully developed a phosphoric acid-catalyzed enantioselective approach for SPINOLs. This approach is highly convergent and functional-group-tolerant for the efficient generation of SPINOLs with good results, thus delivering practical access to this privileged structure.
Knowledge graph (KG) embedding is to embed components of a KG including entities and relations into continuous vector spaces, so as to simplify the manipulation while preserving the inherent ...structure of the KG. It can benefit a variety of downstream tasks such as KG completion and relation extraction, and hence has quickly gained massive attention. In this article, we provide a systematic review of existing techniques, including not only the state-of-the-arts but also those with latest trends. Particularly, we make the review based on the type of information used in the embedding task. Techniques that conduct embedding using only facts observed in the KG are first introduced. We describe the overall framework, specific model design, typical training procedures, as well as pros and cons of such techniques. After that, we discuss techniques that further incorporate additional information besides facts. We focus specifically on the use of entity types, relation paths, textual descriptions, and logical rules. Finally, we briefly introduce how KG embedding can be applied to and benefit a wide variety of downstream tasks such as KG completion, relation extraction, question answering, and so forth.
Characteristics of extracellular polymeric substances (EPS) in activated sludge strongly depend on wastewater substrates. Proteinaceous substrates (ProS) present in heterogeneous polymeric form are ...intrinsic and important parts of wastewater substrates for microorganisms in activated sludge systems. However, correlations between ProS and characteristics of EPS are scarce. This study systematically explored the impacts of monomeric (Mono-), low polymeric (LoP-) and high polymeric (HiP-) ProS on compositions and functional groups of EPS in activated sludge. The results showed that the change of polymerization degree of ProS significantly altered the composition of EPS. Compared to EPSMono-ProS, the proportion of proteins in EPSLoP-ProS and EPSHiP-ProS increased by 12.8% and 27.7%, respectively, while that of polysaccharides decreased by 22.9% and 63.6%, respectively. Moreover, the proportion of humic compounds in EPSLoP-ProS and EPSHiP-ProS were ∼6 and ∼16–fold higher than that in EPSMono-ProS, respectively. The accumulation of humic compounds in EPS increased the unsaturation degree of EPS molecules, and thereby reduced the energy requirement for electrons transition of amide bonds and aromatic groups. Size exclusion chromatography (SEC) analyses detected more molecular clusters in EPSHiP-ProS, indicating more complex composition of EPS in HiP-ProS fed activated sludge. Spectroscopic characterization revealed the dominance of hydrocarbon, protein, polysaccharide and aromatic associated bonds in all three EPS. Nevertheless, with the increase of polymerization degree of ProS, the protein associated bonds (such as CONH, CO, NC, NH) increased, while the polysaccharide associated bonds (such as COC, COH, OCOH) decreased. This paper paves a path to understand the role of ProS in affecting the production and characteristics of EPS in biological wastewater treatment systems.
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•Higher polymeric ProS create higher protein/polysaccharide ratio of EPS.•More humic compounds are introduced into EPS with higher polymeric ProS.•EPS have more complex MW distribution with higher polymeric ProS.•Humic compounds have large impact on unsaturation degree of EPS molecules.•Polymerization degree of ProS have great impacts on functionalities of EPS.
N‐arylcarbazole structures are important because of their prevalence in natural products and functional OLED materials. C−H amination of arenes has been widely recognized as the most efficient ...approach to access these structures. Conventional strategies involving transition‐metal catalysts suffer from confined substrate generality and the requirement of exogenous oxidants. Organocatalytic enantioselective C–N chiral axis construction remains elusive. Presented here is the first organocatalytic strategy for the synthesis of novel axially chiral N‐arylcarbazole frameworks by the assembly of azonaphthalenes and carbazoles. This reaction accommodates broad substrate scope and gives atropisomeric N‐arylcarbazoles in good yields with excellent enantiocontrol. This approach not only offers an alternative to metal‐catalyzed C–N cross‐coupling, but also brings about opportunities for the exploitation of structurally diverse N‐aryl atropisomers and OLED materials.
In the frame: Presented here is the first organocatalytic strategy for the synthesis of novel axially chiral N‐arylcarbazole frameworks by the assembly of azonaphthalenes and carbazoles. This reaction accommodates broad substrate scope and gives atropisomeric N‐arylcarbazoles in good yields with excellent enantiocontrol. This approach offers opportunities for the exploitation of structurally diverse N‐aryl atropisomers and OLED materials. CPA=chiral phosphoric acid.
The synergistically enhanced polyurethane (PU) composites, in which the cellulose nanocrystal (CNC) was incorporated, were in situ polymerized and then the increasingly closer grid network structures ...for PU/CNC composites were achieved by adjusting chain extenders and adding different low contents of CNC, due to the introduction of different hard segments or the evolution of spherulites. As a result, the onset of the light transmission of PU elastomers and CNC‐filled composites showed an obvious red shift from UV light to visible light region, which meant that all UV light regions could be shielded entirely. Therefore, compared with Rhodamine B in water solution unprotected, the excellent UV‐light shielding was further verified by the inefficient photodegradation of Rhodamine B in water solution protected by PU‐PDA, PU‐BDI or PU‐PDA/CNC films under UV‐light irradiation. Meanwhile, enhanced light shielding behavior for PU‐PDA composites was observed with adding the CNC fillers. Moreover, the significantly enhanced mechanical properties were achieved, more than two or three times at elastic modulus, tensile strength and elongation at break. Finally, synergistically Enhanced mechanical properties in PU composites were found. Therefore, the study was of great significance in the potential light application.
The microstructure of PU with different extenders and CNC contents resulted in different light properties.
Cesium lead iodide (CsPbI3) perovskite has shown great potential as a light absorbing material for solar cell applications. Despite intense research leading to increasing power conversion efficiency, ...a major problem concerning CsPbI3 lies in the long term stability and interconversion between different CsPbI3 polymorphs, a subject barely studied from the thermodynamic perspective. We report the formation enthalpies of two CsPbI3 polymorphs, α and δ CsPbI3, using a combination of room temperature solution calorimetry in dimethyl sulfoxide (DMSO) and differential scanning calorimetry. We show that both polymorphs are stable with respect to their binary halides and confirm that the α-phase is a high temperature polymorph, metastable under ambient conditions. This work sheds light on patterns in polymorphism, possible decomposition reactions, materials stability, and compatibility within halide perovskites and related systems. Thermodynamic instability near ambient temperature of functional perovskites may be a general phenomenon related to their vibrational density of states.
Rechargeable flexible solid Zn‐air battery, with a high theoretical energy density of 1086 Wh kg−1, is among the most attractive energy technologies for future flexible and wearable electronics; ...nevertheless, the practical application is greatly hindered by the sluggish oxygen reduction reaction/oxygen evolution reaction (ORR/OER) kinetics on the air electrode. Precious metal‐free functionalized carbon materials are widely demonstrated as the most promising candidates, while it still lacks effective synthetic methodology to controllably synthesize carbocatalysts with targeted active sites. This work demonstrates the direct utilization of the intrinsic structural defects in nanocarbon to generate atomically dispersed Co–Nx–C active sites via defect engineering. As‐fabricated Co/N/O tri‐doped graphene catalysts with highly active sites and hierarchical porous scaffolds exhibit superior ORR/OER bifunctional activities and impressive applications in rechargeable Zn‐air batteries. Specifically, when integrated into a rechargeable and flexible solid Zn‐air battery, a high open‐circuit voltage of 1.44 V, a stable discharge voltage of 1.19 V, and a high energy efficiency of 63% at 1.0 mA cm−2 are achieved even under bending. The defect engineering strategy provides a new concept and effective methodology for the full utilization of nanocarbon materials with various structural features and further development of advanced energy materials.
A defect‐engineering strategy in nanocarbon is developed to generate atomically dispersed Co–Nx–C active sites for effective electrocatalysts. As‐obtained Co/N/O tri‐doped graphene exhibits excellent oxygen reduction reaction/oxygen evolution reaction bifunctional activities and impressive performances in rechargeable and flexible Zn‐air batteries. This work provides a novel concept to fully utilize the structural defects in nanocarbon for advanced energy storage and conversion.
The slow oxygen reduction reaction (ORR) kinetics on Pt catalysts is among the most limiting factors in the energy conversion efficiency of the state-of-the-art PEMFC. Also, Pt is scarcely available ...at a high price. Alternative materials are therefore highly sought for fuel cell applications. This review will concentrate on the electrochemical ORR on non-Pt catalysts, especially the experimental development during the past five years. Emphasis is placed on the understanding of the fundamental materials chemistry. This understanding seems pivotal for new designs of PEM cathode materials. Future outlooks are provided for researchers in engineering to select promising candidates for ORR.
