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2019 Volume 77 Issue 11
2019, 77(11): 1075-1088
doi: 10.6023/A19080292
Abstract:
photocatalytic pollutant degradation and the synthesis of chemical fuels or other high value-added products via photocatalysis have drawn plenty of attentions in green chemistry and renewable energy research. In recent years, metal-halide perovskites with superior photoelectric properties are successfully utilized into high-efficiency photocatalytic reactions in addition to conventional metal oxide semiconductor materials. In this paper, we reviewed the recent advances of metal-halide perovskite based photocatalyst, especially lead-halide perovskites in photocatalytic hydrogen production, photocatalytic degradation and CO2 reduction. The reaction mechanisms and key challenges for metal halide perovskites photocatalyst are discussed and we prospect the further development of highly efficient and stable metal halide perovskite photocatalysis in the future.
photocatalytic pollutant degradation and the synthesis of chemical fuels or other high value-added products via photocatalysis have drawn plenty of attentions in green chemistry and renewable energy research. In recent years, metal-halide perovskites with superior photoelectric properties are successfully utilized into high-efficiency photocatalytic reactions in addition to conventional metal oxide semiconductor materials. In this paper, we reviewed the recent advances of metal-halide perovskite based photocatalyst, especially lead-halide perovskites in photocatalytic hydrogen production, photocatalytic degradation and CO2 reduction. The reaction mechanisms and key challenges for metal halide perovskites photocatalyst are discussed and we prospect the further development of highly efficient and stable metal halide perovskite photocatalysis in the future.
2019, 77(11): 1089-1098
doi: 10.6023/A19080296
Abstract:
Apolipoprotein B mRNA catalytically edited protein APOBEC3 (A3) is a family of proteins in the intracellular retrotransposon defense system, including seven members APOBEC3A (A3A), APOBEC3B (A3B), APOBEC3C (A3C), APOBEC3DE (A3DE), APOBEC3F (A3F), APOBEC3G (A3G) and APOBEC3H (A3H) encoded in a tandem array on human chromosome 22. They deaminate cytosine in single-stranded DNA and RNA substrates, which play a variety of roles in human health and disease. Among them, A3DE, A3F, A3G and A3H restrict replication of human immunodeficiency virus-1 (HIV-1) in strains lacking the virus infectivity factor protein (Vif) by deaminating cytidine in virus cDNA. Subsequent replication of the virus cDNA generates the hallmark G-to-A hyper-mutations, causing proviral inactivation. HIV-1 develops countermeasures to antagonize this intrinsic host defense response. Its Vif protein facilitates polyubiquitination of A3 members by recruiting an E3 ubiquitin ligase complex, which results in the proteasomal degradation of A3 proteins. To better understand the deamination mechanism of A3 proteins, we here reviewed the research progress on the structures of free A3 family members and their complexes with single-stranded DNA or double-stranded RNA. It includes the structures of the apo-forms of N- and/or C-termini domains of A3A, A3B, A3C, A3F, A3G and A3H, or the chimeric forms of their functional domains, and their complexes with nucleic acids, which demonstrate the basis of how A3 proteins to identify target base cytosine in hot motifs 5'-TC or 5'-CC in DNA, and then to conduct catalytic deamination. We simply described how the key residues of A3 members are involved in DNA or RNA interactions, the common properties of their structures, and their interactions with DNA or RNA. We partially discussed the interactions between A3 proteins and Vif, therefore, this review might be helpful to rationally design anti-virus drugs to disrupt these interactions. We finally suggested the new research directions about how to make full-length A3 proteins containing N-terminal CD1 and C-terminal CD2 domains, and how to study the interactions between these full-length A3 proteins and nucleic acids through cryo-EM and other techniques.
Apolipoprotein B mRNA catalytically edited protein APOBEC3 (A3) is a family of proteins in the intracellular retrotransposon defense system, including seven members APOBEC3A (A3A), APOBEC3B (A3B), APOBEC3C (A3C), APOBEC3DE (A3DE), APOBEC3F (A3F), APOBEC3G (A3G) and APOBEC3H (A3H) encoded in a tandem array on human chromosome 22. They deaminate cytosine in single-stranded DNA and RNA substrates, which play a variety of roles in human health and disease. Among them, A3DE, A3F, A3G and A3H restrict replication of human immunodeficiency virus-1 (HIV-1) in strains lacking the virus infectivity factor protein (Vif) by deaminating cytidine in virus cDNA. Subsequent replication of the virus cDNA generates the hallmark G-to-A hyper-mutations, causing proviral inactivation. HIV-1 develops countermeasures to antagonize this intrinsic host defense response. Its Vif protein facilitates polyubiquitination of A3 members by recruiting an E3 ubiquitin ligase complex, which results in the proteasomal degradation of A3 proteins. To better understand the deamination mechanism of A3 proteins, we here reviewed the research progress on the structures of free A3 family members and their complexes with single-stranded DNA or double-stranded RNA. It includes the structures of the apo-forms of N- and/or C-termini domains of A3A, A3B, A3C, A3F, A3G and A3H, or the chimeric forms of their functional domains, and their complexes with nucleic acids, which demonstrate the basis of how A3 proteins to identify target base cytosine in hot motifs 5'-TC or 5'-CC in DNA, and then to conduct catalytic deamination. We simply described how the key residues of A3 members are involved in DNA or RNA interactions, the common properties of their structures, and their interactions with DNA or RNA. We partially discussed the interactions between A3 proteins and Vif, therefore, this review might be helpful to rationally design anti-virus drugs to disrupt these interactions. We finally suggested the new research directions about how to make full-length A3 proteins containing N-terminal CD1 and C-terminal CD2 domains, and how to study the interactions between these full-length A3 proteins and nucleic acids through cryo-EM and other techniques.
2019, 77(11): 1099-1114
doi: 10.6023/A19060240
Abstract:
With the rapid development of modern industry, coal, petroleum, natural gas and other fossil fuels have been excessively consumed, along with an increasing large quantities of greenhouse gases (e.g. carbon dioxide, CO2) are produced. It is urgent to develop sustainable green energy and abate the detriment of carbon dioxide on global environment. CO2 is a cheap carbon source that can be converted into high value-added chemicals by chemical, photochemical, electrochemical or enzymatic methods to realize the recycling of CO2. It is a win-win strategy to solve the energy and environmental crisis caused by global carbon emissions. Inspired by natural CO2 metabolic process, enzymatic transformation provides an alternative strategy for efficient recycling of CO2. Compared with traditional chemical, photochemical or electrochemical methods, the enzymatic route holds advantages of green, high efficiency, mild and excellent selectivity, which is expected to bring new revolutionary opportunities for efficient utilization of CO2. Thus, in this present review, we firstly introduce the brief background about enzymatic conversion for CO2 capture, sequestration and utilization. Next, we depict six major routes of the CO2 metabolic process in cells, which are taken as the inspiration source for the construction of enzymatic systems in vitro. Subsequently, recent advances in enzymatic conversion of CO2 that catalyzed by various single enzymes and multi-enzyme cascade systems are systematically reviewed. Some emerging approaches for construction of immobilized single-or multi-enzyme systems, directed evolution and artificial modification of enzymes, and cofactor regulation during the enzymatic processes are also discussed. Finally, the defects and shortcomings of enzymatic approaches are summarized, and the future perspectives are finally put forward. Based on this present review, we aim to provide theoretical reference and practical basis for more efficient enzymatic utilization of CO2 to produce high value-added chemicals.
With the rapid development of modern industry, coal, petroleum, natural gas and other fossil fuels have been excessively consumed, along with an increasing large quantities of greenhouse gases (e.g. carbon dioxide, CO2) are produced. It is urgent to develop sustainable green energy and abate the detriment of carbon dioxide on global environment. CO2 is a cheap carbon source that can be converted into high value-added chemicals by chemical, photochemical, electrochemical or enzymatic methods to realize the recycling of CO2. It is a win-win strategy to solve the energy and environmental crisis caused by global carbon emissions. Inspired by natural CO2 metabolic process, enzymatic transformation provides an alternative strategy for efficient recycling of CO2. Compared with traditional chemical, photochemical or electrochemical methods, the enzymatic route holds advantages of green, high efficiency, mild and excellent selectivity, which is expected to bring new revolutionary opportunities for efficient utilization of CO2. Thus, in this present review, we firstly introduce the brief background about enzymatic conversion for CO2 capture, sequestration and utilization. Next, we depict six major routes of the CO2 metabolic process in cells, which are taken as the inspiration source for the construction of enzymatic systems in vitro. Subsequently, recent advances in enzymatic conversion of CO2 that catalyzed by various single enzymes and multi-enzyme cascade systems are systematically reviewed. Some emerging approaches for construction of immobilized single-or multi-enzyme systems, directed evolution and artificial modification of enzymes, and cofactor regulation during the enzymatic processes are also discussed. Finally, the defects and shortcomings of enzymatic approaches are summarized, and the future perspectives are finally put forward. Based on this present review, we aim to provide theoretical reference and practical basis for more efficient enzymatic utilization of CO2 to produce high value-added chemicals.
2019, 77(11): 1115-1128
doi: 10.6023/A19070265
Abstract:
With the rapid development of electric cars and energy storage power stations, there is an increasing demand for lithium ion batteries with high energy density. Li- and Mn-rich (LMR) cathode materials with large specific capacity (>250 mAh·g-1) are supposed to accomplish lithium ion batteries with high energy density (>350 Wh·kg-1). The high capacity performance of LMR cathode materials are resulted from the lattice oxygen redox reaction induced by the electrochemical activation of the Li2MnO3 phase. However, the activation of the Li2MnO3 phase and oxygen redox reaction lead to lattice oxygen release and structure transformation, which cause some serious problems such as low initial columbic efficiency, poor rate capability, voltage and capacity degradation after subsequent cycles. The oxygen release and structure transformation always start from the surface, indicating that the surface stability is significant to LMR cathode materials. In this paper, surface modifications such as surface coating, surface doping and surface chemical treatment are reviewed and the mechanism of three surface modification methods for LMR cathode materials are discussed in further. Surface coating is one of the most widely surface modification methods, which can suppress the electrode/electrolyte side reaction and reduce the transition metal dissolution. The effect of surface coating on improving electrochemical performance of LMR cathode materials is always determined by the characteristic of coating layer materials including non-active coating layer, electrochemical active coating layer, Li+ conductive coating layer and electronic conductive coating layer. Surface doping has shown to be an effective method in suppressing oxygen release and structural transformation. Surface chemical treatment has resulted in reducing irreversible capacity loss by activating Li2MnO3 phase. On this basis, surface integrated strategies combined several surface modified methods are introduced and discussed in recent years. The surface intergrated strategies not only enhance the structural stability and suppress electrode/electrolyte surface-interface reaction, but also have an effective role on mitigating structure transformation and lattice oxygen release. Finally, we wish that our review would provide research directions for surface modified strategies of LMR cathode materials in future.
With the rapid development of electric cars and energy storage power stations, there is an increasing demand for lithium ion batteries with high energy density. Li- and Mn-rich (LMR) cathode materials with large specific capacity (>250 mAh·g-1) are supposed to accomplish lithium ion batteries with high energy density (>350 Wh·kg-1). The high capacity performance of LMR cathode materials are resulted from the lattice oxygen redox reaction induced by the electrochemical activation of the Li2MnO3 phase. However, the activation of the Li2MnO3 phase and oxygen redox reaction lead to lattice oxygen release and structure transformation, which cause some serious problems such as low initial columbic efficiency, poor rate capability, voltage and capacity degradation after subsequent cycles. The oxygen release and structure transformation always start from the surface, indicating that the surface stability is significant to LMR cathode materials. In this paper, surface modifications such as surface coating, surface doping and surface chemical treatment are reviewed and the mechanism of three surface modification methods for LMR cathode materials are discussed in further. Surface coating is one of the most widely surface modification methods, which can suppress the electrode/electrolyte side reaction and reduce the transition metal dissolution. The effect of surface coating on improving electrochemical performance of LMR cathode materials is always determined by the characteristic of coating layer materials including non-active coating layer, electrochemical active coating layer, Li+ conductive coating layer and electronic conductive coating layer. Surface doping has shown to be an effective method in suppressing oxygen release and structural transformation. Surface chemical treatment has resulted in reducing irreversible capacity loss by activating Li2MnO3 phase. On this basis, surface integrated strategies combined several surface modified methods are introduced and discussed in recent years. The surface intergrated strategies not only enhance the structural stability and suppress electrode/electrolyte surface-interface reaction, but also have an effective role on mitigating structure transformation and lattice oxygen release. Finally, we wish that our review would provide research directions for surface modified strategies of LMR cathode materials in future.
2019, 77(11): 1129-1139
doi: 10.6023/A19070260
Abstract:
Supported catalysts have been widely used in a large variety of industrial processes, including ammonia synthesis, energy conversion and fine chemical synthesis. Layered double hydroxides (LDHs) are a class of two-dimensional functional anionic materials. By virtue of the unique structural characteristics (e.g., tunability of host layers, high dispersion of metal cations and structure topological transformation), LDHs have shown potential applications in heterogeneous catalysis as precursors or supports. In this review, high-performance monometallic or bimetallic supported catalysts by using LDHs as supports/precursors, or by utilizing mixed metal oxides (MMO) as supports via topotactic transformation from LDHs is highlighted. Their recent progresses in electrocatalysis, oxidative dehydrogenation, selective hydrogenation and syngas conversion reaction are reviewed. In the final section, future opportunities and challenges in the preparation of LDHs-based catalysts are discussed, and some strategies to resolve these critical problems are further proposed.
Supported catalysts have been widely used in a large variety of industrial processes, including ammonia synthesis, energy conversion and fine chemical synthesis. Layered double hydroxides (LDHs) are a class of two-dimensional functional anionic materials. By virtue of the unique structural characteristics (e.g., tunability of host layers, high dispersion of metal cations and structure topological transformation), LDHs have shown potential applications in heterogeneous catalysis as precursors or supports. In this review, high-performance monometallic or bimetallic supported catalysts by using LDHs as supports/precursors, or by utilizing mixed metal oxides (MMO) as supports via topotactic transformation from LDHs is highlighted. Their recent progresses in electrocatalysis, oxidative dehydrogenation, selective hydrogenation and syngas conversion reaction are reviewed. In the final section, future opportunities and challenges in the preparation of LDHs-based catalysts are discussed, and some strategies to resolve these critical problems are further proposed.
2019, 77(11): 1140-1155
doi: 10.6023/A19050174
Abstract:
This paper summarized and collated domestic and foreign literatures on graphene anti-corrosion films and organic anti-corrosion coatings, and formed hierarchical and organized knowledge structures. The preparation, optimization and improvement of graphene anti-corrosion film were reviewed. The corrosion acceleration problems and solutions in the application were discussed. According to the role of graphene in organic anti-corrosion coatings, the improvement of shielding, bonding and self-repairing effect of graphene-based composite materials on organic anti-corrosion coatings are reviewed from the perspective of applied and theoretical research. And the improvement of graphene-based materials on electrochemical protection performance of cathodic-protective organic anti-corrosion coatings are discussed.
This paper summarized and collated domestic and foreign literatures on graphene anti-corrosion films and organic anti-corrosion coatings, and formed hierarchical and organized knowledge structures. The preparation, optimization and improvement of graphene anti-corrosion film were reviewed. The corrosion acceleration problems and solutions in the application were discussed. According to the role of graphene in organic anti-corrosion coatings, the improvement of shielding, bonding and self-repairing effect of graphene-based composite materials on organic anti-corrosion coatings are reviewed from the perspective of applied and theoretical research. And the improvement of graphene-based materials on electrochemical protection performance of cathodic-protective organic anti-corrosion coatings are discussed.
2019, 77(11): 1156-1163
doi: 10.6023/A19070259
Abstract:
Malignant tumor is considered to be one of the most threatening diseases to human health because it is easy to metastasis and relapse, hard to cure with high mortality. Construction of anti-tumor drug delivery systems would effectively improve the therapeutic efficiency of traditional tumor therapy agents. However, the complicated tumor micro-environment as well as the individual diversity of tumor would lead to low efficiency or treatment failure. The conventional tumor treatments, such as chemotherapy, radiotherapy and surgery, have been unable to satisfy the demand for tumor therapy owing to the severe side effect and low therapeutic efficiency. In recent years, researchers have designed a lot of multifunctional nano-drug carriers for efficient tumor therapy with reduced side effects. Metal-organic frameworks (MOFs), a class of ordered porous crystal materials, have received significant research attention for their applications in gas adsorption and separation, catalysis, drug delivery, immobilized bio-macromolecules and tumor therapy. Due to tunable inorganic building blocks and organic linkers, MOFs can not only integrate drugs or photosensitizers into periodic arrays, but also possess large pore sizes and high surface areas for drug encapsulation. Currently, the biomedical research of MOFs mainly includes the preparation of multifunctional biocompatible nanomaterials through controllable synthesis and reasonable surface modification. MOFs based nanomaterials with desired physiological functions have been widely used for targeting tumor imaging and therapy by utilizing their unique physical and chemical properties. The recent progress on the bio-functionalization of MOFs, including new design strategies and application in tumor therapy is summarized. Particularly, the construction of MOF-based nanoplatforms for tumor therapy on the basis of biomedical polymer modified MOFs is also described in detail. The development trends of MOFs for biomedical application are also prospected. We believe that this work will offer a preliminary understanding to design MOF-based drug delivery systems and acquire the therapeutic strategies of MOF-based nano-medicine for future clinical biomedical applications.
Malignant tumor is considered to be one of the most threatening diseases to human health because it is easy to metastasis and relapse, hard to cure with high mortality. Construction of anti-tumor drug delivery systems would effectively improve the therapeutic efficiency of traditional tumor therapy agents. However, the complicated tumor micro-environment as well as the individual diversity of tumor would lead to low efficiency or treatment failure. The conventional tumor treatments, such as chemotherapy, radiotherapy and surgery, have been unable to satisfy the demand for tumor therapy owing to the severe side effect and low therapeutic efficiency. In recent years, researchers have designed a lot of multifunctional nano-drug carriers for efficient tumor therapy with reduced side effects. Metal-organic frameworks (MOFs), a class of ordered porous crystal materials, have received significant research attention for their applications in gas adsorption and separation, catalysis, drug delivery, immobilized bio-macromolecules and tumor therapy. Due to tunable inorganic building blocks and organic linkers, MOFs can not only integrate drugs or photosensitizers into periodic arrays, but also possess large pore sizes and high surface areas for drug encapsulation. Currently, the biomedical research of MOFs mainly includes the preparation of multifunctional biocompatible nanomaterials through controllable synthesis and reasonable surface modification. MOFs based nanomaterials with desired physiological functions have been widely used for targeting tumor imaging and therapy by utilizing their unique physical and chemical properties. The recent progress on the bio-functionalization of MOFs, including new design strategies and application in tumor therapy is summarized. Particularly, the construction of MOF-based nanoplatforms for tumor therapy on the basis of biomedical polymer modified MOFs is also described in detail. The development trends of MOFs for biomedical application are also prospected. We believe that this work will offer a preliminary understanding to design MOF-based drug delivery systems and acquire the therapeutic strategies of MOF-based nano-medicine for future clinical biomedical applications.
2019, 77(11): 1164-1167
doi: 10.6023/A19070281
Abstract:
The essence of electrochemical reaction was the electron transfer process on the electrode while the premise for electrochemical reaction happening was the migration and diffusion of electro-active species. Interpreting the monitoring process of electrode towards the electro-active species during the electrochemical reaction would really do favor to the further understanding of the electrochemical evolution process at the electrode-electrolyte interface. In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was adopted for the in-situ monitoring of the electrode-electrolyte interface during the electrochemical reaction with the cooperation of a microfluidic electrochemical cell which was constructed for the liquid sample analysis under the high vacuum environment. With the application of the primary ion beam on the silicon nitride membrane of the microfluidic cell, a micro-hole with the diameter of 2 μm would be fabricated for the direct monitoring of the electrode-electrolyte interface. The migration process of KCl aqueous solution in the confined micropore under the monitoring of gold electrode was investigated by ToF-SIMS here. The direct observation of K+(H2O)n and H+(H2O)n in the electrolyte provided information of the electrode-electrolyte interface at molecular level. Besides, the chemical distributions of K+ and H+(H2O)n under different potential were also studied to verify the feasibility of pore-confined ToF-SIMS in visualizing electrochemical evolution process on the electrode-electrolyte interface. The chemical distributions of K+ and H+(H2O)n obtained by ToF-SIMS showed that K+ would enrich to the surface of gold electrode when the negative potential was applied but diffuse to the bulk solution when positive potential was applied. For H+(H2O)n, they would be repulsed away from the electrode when the positive potential was applied and enrich to the surface of electrode when the negative potential was applied. The potential-dependent behaviors of K+ and H+(H2O)n indicated that visualization of the migration process of electrolyte on the electrode-electrolyte interface was realized, which may help the further study of the evolution at electrode-electrolyte interface during the electrochemical reaction, providing new insight into the revealment of the mechanism of electrochemical reaction.
The essence of electrochemical reaction was the electron transfer process on the electrode while the premise for electrochemical reaction happening was the migration and diffusion of electro-active species. Interpreting the monitoring process of electrode towards the electro-active species during the electrochemical reaction would really do favor to the further understanding of the electrochemical evolution process at the electrode-electrolyte interface. In this work, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was adopted for the in-situ monitoring of the electrode-electrolyte interface during the electrochemical reaction with the cooperation of a microfluidic electrochemical cell which was constructed for the liquid sample analysis under the high vacuum environment. With the application of the primary ion beam on the silicon nitride membrane of the microfluidic cell, a micro-hole with the diameter of 2 μm would be fabricated for the direct monitoring of the electrode-electrolyte interface. The migration process of KCl aqueous solution in the confined micropore under the monitoring of gold electrode was investigated by ToF-SIMS here. The direct observation of K+(H2O)n and H+(H2O)n in the electrolyte provided information of the electrode-electrolyte interface at molecular level. Besides, the chemical distributions of K+ and H+(H2O)n under different potential were also studied to verify the feasibility of pore-confined ToF-SIMS in visualizing electrochemical evolution process on the electrode-electrolyte interface. The chemical distributions of K+ and H+(H2O)n obtained by ToF-SIMS showed that K+ would enrich to the surface of gold electrode when the negative potential was applied but diffuse to the bulk solution when positive potential was applied. For H+(H2O)n, they would be repulsed away from the electrode when the positive potential was applied and enrich to the surface of electrode when the negative potential was applied. The potential-dependent behaviors of K+ and H+(H2O)n indicated that visualization of the migration process of electrolyte on the electrode-electrolyte interface was realized, which may help the further study of the evolution at electrode-electrolyte interface during the electrochemical reaction, providing new insight into the revealment of the mechanism of electrochemical reaction.
2019, 77(11): 1168-1172
doi: 10.6023/A19080303
Abstract:
Oxazole derivatives are widely found in natural products and pharmaceuticals with impressive biological properties, tremendous efforts have been devoted to the development of new methodologies and strategies to construct the oxazole rings. However, most of these reactions require harsh reaction conditions, limiting the wide application of these classical oxazole synthetic methods in organic synthesis. N-Acyliminium ions represent important electron deficient carbocations intermediates in organic synthesis because they provide various biologically important natural and unnatural products via C-C and C-heteroatom bondforming methodologies using an inter-or intramolecular path. The removal of a good leaving group at the α-position of amides or lactams usually generates N-acyliminium ions, which act as more electron-deficient carbocations toward nucleophiles. In this paper, a novel tandem metal relay catalytic system of Zn/Ni has been successfully developed. By using this unprecedented Zn(OTf)2/Ni(ClO4)2·6H2O bimetallic relay catalytic system, a variety of oxazole derivatives were obtained from easily available N-(propargyl)-arylamides and various γ-hydroxy lactams through intramolecular cycloisomerization/intermolecular amidoalkylation under mild conditions. The first step of the one-pot procedure is that Zn(OTf)2 acts as a π acid to activate the triple bond of N-(propargyl)-arylamides, and a subsequent intramolecular 5-exo-dig cyclization forms the oxazoline intermediate. Separately, Ni(ClO4)2·6H2O acts as Lewis acid to activate and facilitate the departure of 3-hydroxyl group to form the electrophilic acyliminium ions, which then in an intermolecular reaction is transformed to the oxazole derivatives in good to excellent yield. Control experiments in the optimization section disclose the fact that Zn(OTf)2 and Ni(ClO4)2·6H2O are both indispensable for this intramolecular cycloisomerization/intermolecular amidoalkylation reaction. Generally, the synthetic reactions run under air atmosphere by heating all the substrates and reagents in one-pot at 100℃. The N-(propargyl)-arylamide containing different types of electron-donating substituents, different electron-rich aromatic rings and different electron-withdrawing substituents can react with 3-hydroxy-2-benzyl-isoindolin-1-one to give the corresponding oxazole derivatives. In contrast, the propargyl amide containing an electron withdrawing group has a lower yield than the one using other propargyl amide, because the activity of the oxazoline intermediate obtained by the propargyl amide containing an electron withdrawing group is lower. 3-Hydroxy-2-phenylisoindoline-1-one, 3-hydroxy-2-phenylmethylisoindoline-1-one and 3-hydroxy-2-phenylethylisoindoline-1-one have also been found applicable to this reaction. The present method benefits from the distinctive features of simple reaction conditions, high atom economy and broad substrate tolerance. It is of great significance for the synthesis of oxazole derivatives and the formation of acyliminium ions.
Oxazole derivatives are widely found in natural products and pharmaceuticals with impressive biological properties, tremendous efforts have been devoted to the development of new methodologies and strategies to construct the oxazole rings. However, most of these reactions require harsh reaction conditions, limiting the wide application of these classical oxazole synthetic methods in organic synthesis. N-Acyliminium ions represent important electron deficient carbocations intermediates in organic synthesis because they provide various biologically important natural and unnatural products via C-C and C-heteroatom bondforming methodologies using an inter-or intramolecular path. The removal of a good leaving group at the α-position of amides or lactams usually generates N-acyliminium ions, which act as more electron-deficient carbocations toward nucleophiles. In this paper, a novel tandem metal relay catalytic system of Zn/Ni has been successfully developed. By using this unprecedented Zn(OTf)2/Ni(ClO4)2·6H2O bimetallic relay catalytic system, a variety of oxazole derivatives were obtained from easily available N-(propargyl)-arylamides and various γ-hydroxy lactams through intramolecular cycloisomerization/intermolecular amidoalkylation under mild conditions. The first step of the one-pot procedure is that Zn(OTf)2 acts as a π acid to activate the triple bond of N-(propargyl)-arylamides, and a subsequent intramolecular 5-exo-dig cyclization forms the oxazoline intermediate. Separately, Ni(ClO4)2·6H2O acts as Lewis acid to activate and facilitate the departure of 3-hydroxyl group to form the electrophilic acyliminium ions, which then in an intermolecular reaction is transformed to the oxazole derivatives in good to excellent yield. Control experiments in the optimization section disclose the fact that Zn(OTf)2 and Ni(ClO4)2·6H2O are both indispensable for this intramolecular cycloisomerization/intermolecular amidoalkylation reaction. Generally, the synthetic reactions run under air atmosphere by heating all the substrates and reagents in one-pot at 100℃. The N-(propargyl)-arylamide containing different types of electron-donating substituents, different electron-rich aromatic rings and different electron-withdrawing substituents can react with 3-hydroxy-2-benzyl-isoindolin-1-one to give the corresponding oxazole derivatives. In contrast, the propargyl amide containing an electron withdrawing group has a lower yield than the one using other propargyl amide, because the activity of the oxazoline intermediate obtained by the propargyl amide containing an electron withdrawing group is lower. 3-Hydroxy-2-phenylisoindoline-1-one, 3-hydroxy-2-phenylmethylisoindoline-1-one and 3-hydroxy-2-phenylethylisoindoline-1-one have also been found applicable to this reaction. The present method benefits from the distinctive features of simple reaction conditions, high atom economy and broad substrate tolerance. It is of great significance for the synthesis of oxazole derivatives and the formation of acyliminium ions.
2019, 77(11): 1173-1176
doi: 10.6023/A19060241
Abstract:
Chirality is ubiquitous in nature and it plays an important role in both biological and material sciences. Inspired by nature, scientists have prepared various chiral structures or hybrid materials by self-assembly of polypeptides, amino acids, carbohydrates and their derivatives. These studies provide a good model for understanding of supramolecular chirality and mimicking the self-assembly of organisms. In the past decade, diphenylalanine (FF) and its derivatives have attracted great attentions and have been substantially studied. FF is derived from the core recognition motif of the Alzheimer's disease β-amyloid polypeptide, and it could readily self-assemble into nanotubes, nanowires, nanovesicles, nanofibers and microtubes. Moreover, the polymorphisms of FF-based assemblies can be easily manipulated by controlling the experimental conditions such as concentrations, solvents, pH and temperatures. However, there is few report on the chiral structures obtained from the self-assembly of FF and its derivatives. In this paper, we selected cationic diphenylalanine peptide (CDP) as the assembly units and have obtained CDP nanofibers and helical fibers in ethanol solution by controlling the aging time. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to characterize the morphologies of CDP assemblies. The mechanism for the formation of CDP nanofibers and helical fibers in ethanol solution was studied by infrared spectroscopy and circular dichroism spectroscopy. It was found that CDP was first assembled into nanofibers. With the increase of aging time, CDP nanofibers twisted and finally assembled into helical fibers similar to the ropes. Spectral data analysis showed that the transformation of nanofibers into helical fibers was mainly due to the strong electrostatic repulsion between positive charges in adjacent peptide molecules and the β-sheet secondary structure controlled by hydrogen bonding between peptide segments. This work realizes the regulation of supramolecular assembly structure by simply controlling the ripening time, and provides a simple and feasible method for the controlled preparation of supramolecular chiral assembly.
Chirality is ubiquitous in nature and it plays an important role in both biological and material sciences. Inspired by nature, scientists have prepared various chiral structures or hybrid materials by self-assembly of polypeptides, amino acids, carbohydrates and their derivatives. These studies provide a good model for understanding of supramolecular chirality and mimicking the self-assembly of organisms. In the past decade, diphenylalanine (FF) and its derivatives have attracted great attentions and have been substantially studied. FF is derived from the core recognition motif of the Alzheimer's disease β-amyloid polypeptide, and it could readily self-assemble into nanotubes, nanowires, nanovesicles, nanofibers and microtubes. Moreover, the polymorphisms of FF-based assemblies can be easily manipulated by controlling the experimental conditions such as concentrations, solvents, pH and temperatures. However, there is few report on the chiral structures obtained from the self-assembly of FF and its derivatives. In this paper, we selected cationic diphenylalanine peptide (CDP) as the assembly units and have obtained CDP nanofibers and helical fibers in ethanol solution by controlling the aging time. Scanning electron microscope (SEM) and atomic force microscope (AFM) were used to characterize the morphologies of CDP assemblies. The mechanism for the formation of CDP nanofibers and helical fibers in ethanol solution was studied by infrared spectroscopy and circular dichroism spectroscopy. It was found that CDP was first assembled into nanofibers. With the increase of aging time, CDP nanofibers twisted and finally assembled into helical fibers similar to the ropes. Spectral data analysis showed that the transformation of nanofibers into helical fibers was mainly due to the strong electrostatic repulsion between positive charges in adjacent peptide molecules and the β-sheet secondary structure controlled by hydrogen bonding between peptide segments. This work realizes the regulation of supramolecular assembly structure by simply controlling the ripening time, and provides a simple and feasible method for the controlled preparation of supramolecular chiral assembly.
2019, 77(11): 1177-1183
doi: 10.6023/A19070276
Abstract:
Graphene oxide (GO) is widely used in energy chemical, environmental restoration, nanomaterials, liquid phase catalysis, etc. due to its excellent physical and chemical properties. At the same time, GO is inevitably discharged into nature during the application process, and the toxicity released into the environment may lead to instability of the biological system. Therefore, this paper systematically studied several common cations (Na+, K+, Ca2+, Mg2+), anions (PO43-, SO42-, CO32-, HCO3-, Cl-) and clay minerals (montmorillonite, kaolin, bentonite, nano-alumina) on GO coagulation at different concentrations. And FTIR is used to characterize the clay minerals before and after the precipitation of GO. The experimental results show that the cations have strong GO coagulation ability, and the coagulation ability of different valence cations has a large difference. After analysis, the electrical properties of GO in aqueous solution are negative, the cation acts as a counter ion, and the coagulation behavior conforms to the Schulze-Hardy rule. The main reason for the difference in coagulation ability between isovalent cations is electronegativity and ionic hydration. The anion acts to increase the stability of GO, and the coagulation ability of the cation is more effective than the stabilization ability of the anion. The ability of sodium salts with the same valence anion to coagulate GO also differs, mainly because the hydrolysis of HCO3- and CO32- causes a decrease in the negative charges, resulting in a decrease in the ability to stabilize GO. The clay minerals contain hydroxyl and metal-oxygen bonds that interact with GO. According to the maximum removal rate, the clay minerals have the coagulation ability:nano-alumina > kaolin > bentonite > montmorillonite. The main influencing factors are the electrical properties of clay minerals in aqueous solution. This paper is helpful to understand the coagulation behavior of GO in different water environments, and it is of great significance for the future application of graphene engineering in pollution control.
Graphene oxide (GO) is widely used in energy chemical, environmental restoration, nanomaterials, liquid phase catalysis, etc. due to its excellent physical and chemical properties. At the same time, GO is inevitably discharged into nature during the application process, and the toxicity released into the environment may lead to instability of the biological system. Therefore, this paper systematically studied several common cations (Na+, K+, Ca2+, Mg2+), anions (PO43-, SO42-, CO32-, HCO3-, Cl-) and clay minerals (montmorillonite, kaolin, bentonite, nano-alumina) on GO coagulation at different concentrations. And FTIR is used to characterize the clay minerals before and after the precipitation of GO. The experimental results show that the cations have strong GO coagulation ability, and the coagulation ability of different valence cations has a large difference. After analysis, the electrical properties of GO in aqueous solution are negative, the cation acts as a counter ion, and the coagulation behavior conforms to the Schulze-Hardy rule. The main reason for the difference in coagulation ability between isovalent cations is electronegativity and ionic hydration. The anion acts to increase the stability of GO, and the coagulation ability of the cation is more effective than the stabilization ability of the anion. The ability of sodium salts with the same valence anion to coagulate GO also differs, mainly because the hydrolysis of HCO3- and CO32- causes a decrease in the negative charges, resulting in a decrease in the ability to stabilize GO. The clay minerals contain hydroxyl and metal-oxygen bonds that interact with GO. According to the maximum removal rate, the clay minerals have the coagulation ability:nano-alumina > kaolin > bentonite > montmorillonite. The main influencing factors are the electrical properties of clay minerals in aqueous solution. This paper is helpful to understand the coagulation behavior of GO in different water environments, and it is of great significance for the future application of graphene engineering in pollution control.
2019, 77(11): 1184-1193
doi: 10.6023/A19070268
Abstract:
The novel 3 dimension (3D) nanocomposite photocatalyst Eu-ZnO/MIL-53(Fe) was successfully prepared with in situ synthesis. Firstly the rare earth element Eu was doped into semiconductor ZnO and then Eu-ZnO was combined with MIL-53(Fe). The structure, morphology, optical and electrical properties of the nanocomposites were thoroughly characterized by X-ray diffraction (XRD), fourier infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherms (SBET), photoluminescence spectra (PL) and electrochemical impedance (EIS) spectra and the like. The FT-IR and XRD results showed that the photocatalysts were successfully prepared and SEM results showed that morphology of the MIL-53(Fe) were all well remained after the preparing process. The photocatalytic experiment data, UV-Vis DRS spectra and PL spectra and the like results showed that the introduction of rare earth elements Eu could greatly improve the photocatalytic efficiency of MIL-53 (Fe), and promote the effective separation of photogenerated electron-hole, which further improved the catalytic activity. The results of electrochemical impedance spectra further supported the conclusion. By exploring the photocatalytic activity of Eu-ZnO/MIL-53(Fe) under visible light conditions, the photocatalyst showed excellent photocatalytic activity. Some derivatives of benzalcohol were more affected by electronic effects, the conversion of the derivative having an electron-withdrawing group was relatively high, and the conversion of the derivative having an electron-donating group was low. The possible mechanism of the photocatalytic reaction was explored via the active species capture experiment and Mott-schottky (M-S) curve test. The results showed that the photocatalytic selective oxidation of alcohols achieved with photogenerated holes (h+) and hydroxyl radicals (·OH). The photo stability and thermal stability of the photocatalyst was investigated by cyclic experiments and the structure characterization of the photocatalyst before and after the photoreaction. The results showed that the photocatalyst had outstanding light stability and thermal stability.
The novel 3 dimension (3D) nanocomposite photocatalyst Eu-ZnO/MIL-53(Fe) was successfully prepared with in situ synthesis. Firstly the rare earth element Eu was doped into semiconductor ZnO and then Eu-ZnO was combined with MIL-53(Fe). The structure, morphology, optical and electrical properties of the nanocomposites were thoroughly characterized by X-ray diffraction (XRD), fourier infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption isotherms (SBET), photoluminescence spectra (PL) and electrochemical impedance (EIS) spectra and the like. The FT-IR and XRD results showed that the photocatalysts were successfully prepared and SEM results showed that morphology of the MIL-53(Fe) were all well remained after the preparing process. The photocatalytic experiment data, UV-Vis DRS spectra and PL spectra and the like results showed that the introduction of rare earth elements Eu could greatly improve the photocatalytic efficiency of MIL-53 (Fe), and promote the effective separation of photogenerated electron-hole, which further improved the catalytic activity. The results of electrochemical impedance spectra further supported the conclusion. By exploring the photocatalytic activity of Eu-ZnO/MIL-53(Fe) under visible light conditions, the photocatalyst showed excellent photocatalytic activity. Some derivatives of benzalcohol were more affected by electronic effects, the conversion of the derivative having an electron-withdrawing group was relatively high, and the conversion of the derivative having an electron-donating group was low. The possible mechanism of the photocatalytic reaction was explored via the active species capture experiment and Mott-schottky (M-S) curve test. The results showed that the photocatalytic selective oxidation of alcohols achieved with photogenerated holes (h+) and hydroxyl radicals (·OH). The photo stability and thermal stability of the photocatalyst was investigated by cyclic experiments and the structure characterization of the photocatalyst before and after the photoreaction. The results showed that the photocatalyst had outstanding light stability and thermal stability.
2019, 77(11): 1194-1202
doi: 10.6023/A19080306
Abstract:
Mechanofluorochromism (MFC) and mechanoluminescence (ML) are two types of significant solid-state optical phenomena which are closely dependent on conformations, packing modes and intermolecular interactions. Herein, through a three-step route involving aromatic nucleophilic substitution, reduction and oxidative cyclization in DMSO under air, a benzo[d]imidazole with triphenylamine and 4-cyanophenyl respectively located at C(2)- and N(1)-position is obtained in good yields. Two polymorphs TBIMB and TBIMG of 4-(2-(4-(diphenylamino)phenyl)-1H-benzo[d]imidazol-1-yl)benzonitrile (TBIM) corespondingly exhibit intense deep-blue (435 nm) and green fluorescence (505 nm). Under force stimuli, both polymorphs turn into amorphous phase with cyan fluorescence (457 nm). By fuming in solvent vapor or annealing treatment, only the ground TBIMB sample can be completely restored into the original crystalline structure, the ground TBIMG sample is just transformed into TBIMBcrystal. It is assumed that the enhanced energy barrier induced by the denser packing in TBIMG crystal makes the conversion from in amorphous phase to crystalline one kinetically infeasible. The crystallography reveals that triphenylamine moiety in TBIMG crystal is less restrained by intermolecular interactions than that in TBIMB crystal, which results in the long-wavelength TICT emission in the former crystal and the short-wavelength LE emission in the latter one. In exposure to force stimuli, TBIMB and TBIMG crystals respectively give out the blue (432 nm) and green (500 nm) flash. It is revealed by crystallography that both polymorphs hold centrosymmetric space groups. DFT calculations based on the molecular couples with strong intermolecular interactions demonstrate that the close-to-zero net dipole moments occurs on these couples. Hence, neither piezoelectric effect nor excitation of molecules on cracked surfaces by discharges between molecular couples should account for the ML behaviors of these two polymorphs. Due to the readily force-induced cleavage of the two crystals by particular chain-shaped packing, the endogenous friction discharge caused by relative movements between cleavage planes would excite molecules on these planes, and this mechanism is assumed to be mainly responsible for the ML activity of the two crystals.
Mechanofluorochromism (MFC) and mechanoluminescence (ML) are two types of significant solid-state optical phenomena which are closely dependent on conformations, packing modes and intermolecular interactions. Herein, through a three-step route involving aromatic nucleophilic substitution, reduction and oxidative cyclization in DMSO under air, a benzo[d]imidazole with triphenylamine and 4-cyanophenyl respectively located at C(2)- and N(1)-position is obtained in good yields. Two polymorphs TBIMB and TBIMG of 4-(2-(4-(diphenylamino)phenyl)-1H-benzo[d]imidazol-1-yl)benzonitrile (TBIM) corespondingly exhibit intense deep-blue (435 nm) and green fluorescence (505 nm). Under force stimuli, both polymorphs turn into amorphous phase with cyan fluorescence (457 nm). By fuming in solvent vapor or annealing treatment, only the ground TBIMB sample can be completely restored into the original crystalline structure, the ground TBIMG sample is just transformed into TBIMBcrystal. It is assumed that the enhanced energy barrier induced by the denser packing in TBIMG crystal makes the conversion from in amorphous phase to crystalline one kinetically infeasible. The crystallography reveals that triphenylamine moiety in TBIMG crystal is less restrained by intermolecular interactions than that in TBIMB crystal, which results in the long-wavelength TICT emission in the former crystal and the short-wavelength LE emission in the latter one. In exposure to force stimuli, TBIMB and TBIMG crystals respectively give out the blue (432 nm) and green (500 nm) flash. It is revealed by crystallography that both polymorphs hold centrosymmetric space groups. DFT calculations based on the molecular couples with strong intermolecular interactions demonstrate that the close-to-zero net dipole moments occurs on these couples. Hence, neither piezoelectric effect nor excitation of molecules on cracked surfaces by discharges between molecular couples should account for the ML behaviors of these two polymorphs. Due to the readily force-induced cleavage of the two crystals by particular chain-shaped packing, the endogenous friction discharge caused by relative movements between cleavage planes would excite molecules on these planes, and this mechanism is assumed to be mainly responsible for the ML activity of the two crystals.
2019, 77(11): 1203-1210
doi: 10.6023/A19080316
Abstract:
This work aims to explore a new method for the efficient enrichment of baicalin in Scutellaria baicalensis Georgi by using metal organic frameworks (MOFs) materials, and to open up new applications for MOFs in the adsorption direction. The zeolitic imidazolate framework-8 (ZIF-8) was synthesized by solvothermal method and characterized by structure to ensure its accurate synthesis. Baicalin was extracted from Scutellaria baicalinsis Georgi by ethanol extraction and acid precipitation method. The ZIF-8 was used to carry out the static adsorption experiment on the crude extract of Radix Scutellariae. After the adsorption equilibrium was reached, the mixture was centrifuged, and the residual concentration of baicalin was detected by high performance liquid chromatography method (HPLC). The recovered saturated adsorbed ZIF-8 material was washed with water and dried, and the phosphate buffered saline (PBS) solution of pH 6.8 was used as a desorption solution, and the desorption was performed by shaking. The content of baicalin in the desorbed solution was determined by HPLC to calculate the desorption rate and achieve the purpose of adsorbent recovery. In the adsorbing process, the effects of adsorbent dosage, pH and adsorbate concentration of the crude extract of Radix Scutellariae were also optimized, and the response surface test (RSM) was performed using Design Expert software to obtain optimal adsorption conditions. Under these conditions, the adsorption rate of ZIF-8 to baicalin in Radix Scutellariae was as high as 98.22%, and the adsorption effect was not significant on other components in Radix Scutellariae. The desorption rate of ZIF-8 adsorbed baicalin in pH 6.8 solution was 62.46%, and the purity of baicalin increased from 21.55% before adsorption to 64.27% after desorption, and ZIF-8 had good stability before and after adsorption, and the recovery rate reached 83.50%. Therefore, ZIF-8 has potential application value in the adsorption and purification of baicalin. The adsorption law and mechanism of ZIF-8 on baicalin were studied:The adsorption of baicalin on ZIF-8 accorded with the quasi-second-order kinetic equation, and the equilibrium adsorption data accorded with the Langmuir adsorption isotherm model.
This work aims to explore a new method for the efficient enrichment of baicalin in Scutellaria baicalensis Georgi by using metal organic frameworks (MOFs) materials, and to open up new applications for MOFs in the adsorption direction. The zeolitic imidazolate framework-8 (ZIF-8) was synthesized by solvothermal method and characterized by structure to ensure its accurate synthesis. Baicalin was extracted from Scutellaria baicalinsis Georgi by ethanol extraction and acid precipitation method. The ZIF-8 was used to carry out the static adsorption experiment on the crude extract of Radix Scutellariae. After the adsorption equilibrium was reached, the mixture was centrifuged, and the residual concentration of baicalin was detected by high performance liquid chromatography method (HPLC). The recovered saturated adsorbed ZIF-8 material was washed with water and dried, and the phosphate buffered saline (PBS) solution of pH 6.8 was used as a desorption solution, and the desorption was performed by shaking. The content of baicalin in the desorbed solution was determined by HPLC to calculate the desorption rate and achieve the purpose of adsorbent recovery. In the adsorbing process, the effects of adsorbent dosage, pH and adsorbate concentration of the crude extract of Radix Scutellariae were also optimized, and the response surface test (RSM) was performed using Design Expert software to obtain optimal adsorption conditions. Under these conditions, the adsorption rate of ZIF-8 to baicalin in Radix Scutellariae was as high as 98.22%, and the adsorption effect was not significant on other components in Radix Scutellariae. The desorption rate of ZIF-8 adsorbed baicalin in pH 6.8 solution was 62.46%, and the purity of baicalin increased from 21.55% before adsorption to 64.27% after desorption, and ZIF-8 had good stability before and after adsorption, and the recovery rate reached 83.50%. Therefore, ZIF-8 has potential application value in the adsorption and purification of baicalin. The adsorption law and mechanism of ZIF-8 on baicalin were studied:The adsorption of baicalin on ZIF-8 accorded with the quasi-second-order kinetic equation, and the equilibrium adsorption data accorded with the Langmuir adsorption isotherm model.
