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2020 Volume 78 Issue 9
2020, 78(9): 827-832
doi: 10.6023/A20060227
Abstract:
Nature has served as a dominant source of inspiration in the area of chemistry, serving as prototypes for the design of materials with proficient performance. In this account, we present our effort to explore porous organic polymers (POPs) as a platform for the construction of biomimetic catalysts to enable new technologies to achieve efficient conversions. For each aspect, we firstly describe the chemical basis of nature, followed by presenting the principles and design strategies involved for functionalizing POPs along with a summary of critical requirements for materials, culminating in a demonstration of unique features of POPs. Our endeavors of using POPs to address the fundamental scientific problems related to biomimetic catalysis are then presented to show their enormous potential and capabilities for a wide range of catalytic transformations. To conclude, a personal perspective on the challenges and opportunities in this emerging field are presented.
Nature has served as a dominant source of inspiration in the area of chemistry, serving as prototypes for the design of materials with proficient performance. In this account, we present our effort to explore porous organic polymers (POPs) as a platform for the construction of biomimetic catalysts to enable new technologies to achieve efficient conversions. For each aspect, we firstly describe the chemical basis of nature, followed by presenting the principles and design strategies involved for functionalizing POPs along with a summary of critical requirements for materials, culminating in a demonstration of unique features of POPs. Our endeavors of using POPs to address the fundamental scientific problems related to biomimetic catalysis are then presented to show their enormous potential and capabilities for a wide range of catalytic transformations. To conclude, a personal perspective on the challenges and opportunities in this emerging field are presented.
2020, 78(9): 833-847
doi: 10.6023/A20050167
Abstract:
Carbon-enriched materials, including carbon allotropes, polycyclic aromatic hydrocarbons, polymers, frameworks, etc., are rising as stars in functional materials field. Large amount of reported work focused on development of new structures with typical features for novel applications, and has long ignored the intrinsic relationship between similar structures. The superficial relationships of those carbon-enriched materials in textbook, e.g., isomers, allotropes and topological defects, are no longer enough for fundamental understanding the structure-property relationship study due to more and more carbon-enriched materials have been developed. Such disadvantage has long hindered development of new materials based on well-established material systems. In this work, meso-entropy concept is proposed for understanding and development of different kinds of carbon-enriched materials by comparing their relative entropy values. Based on theoretical models and case-to-case discussion, meso-entropy concept has been found compatible with the concept of isomers, allotropes and topological defects in carbon-enriched materials. From now on, hopefully, the meso-entropy defined relationship for carbon-enriched materials will be no longer staying at the geometric level, and provide new thinking development of new carbon-enriched materials and other meso-entropy materials.
Carbon-enriched materials, including carbon allotropes, polycyclic aromatic hydrocarbons, polymers, frameworks, etc., are rising as stars in functional materials field. Large amount of reported work focused on development of new structures with typical features for novel applications, and has long ignored the intrinsic relationship between similar structures. The superficial relationships of those carbon-enriched materials in textbook, e.g., isomers, allotropes and topological defects, are no longer enough for fundamental understanding the structure-property relationship study due to more and more carbon-enriched materials have been developed. Such disadvantage has long hindered development of new materials based on well-established material systems. In this work, meso-entropy concept is proposed for understanding and development of different kinds of carbon-enriched materials by comparing their relative entropy values. Based on theoretical models and case-to-case discussion, meso-entropy concept has been found compatible with the concept of isomers, allotropes and topological defects in carbon-enriched materials. From now on, hopefully, the meso-entropy defined relationship for carbon-enriched materials will be no longer staying at the geometric level, and provide new thinking development of new carbon-enriched materials and other meso-entropy materials.
2020, 78(9): 848-864
doi: 10.6023/A20050197
Abstract:
Stretchable organic electronic devices are characterized with high mechanical stability, superior electronic stability, low cost, satisfactory biocompatibility, etc., thus having been regarded as an inevitable trend in the development of future electronics. Furthermore, the functional stretchable organic electronic devices provide pathways toward the emerging high-tech fields such as wearable and implantable devices, intelligent medical diagnosis system, software robots, etc. This review focuses on the research advances in functional stretchable organic electronic devices, including stretchable organic transistors (field-effect transistors, phototransistors, memory transistors and sensors), stretchable organic optoelectronic devices (light-emitting diodes, alternating current electroluminescent devices and light-emitting electrochemical cells), stretchable organic energy storage and conversion devices (solar cells, supercapacitors and nanogenerators), stretchable organic sensors (pressure sensors, strain sensors, tactile sensors, temperature sensors, gas sensors and other sensors), stretchable organic memory (resistive memory, magnetic memory and bionic synaptic memory) and other functional stretchable organic electronic devices. Finally, through the analyses of the existing scientific problems and future development of the functional stretchable organic electronic devices, we put forward some suggestions.
Stretchable organic electronic devices are characterized with high mechanical stability, superior electronic stability, low cost, satisfactory biocompatibility, etc., thus having been regarded as an inevitable trend in the development of future electronics. Furthermore, the functional stretchable organic electronic devices provide pathways toward the emerging high-tech fields such as wearable and implantable devices, intelligent medical diagnosis system, software robots, etc. This review focuses on the research advances in functional stretchable organic electronic devices, including stretchable organic transistors (field-effect transistors, phototransistors, memory transistors and sensors), stretchable organic optoelectronic devices (light-emitting diodes, alternating current electroluminescent devices and light-emitting electrochemical cells), stretchable organic energy storage and conversion devices (solar cells, supercapacitors and nanogenerators), stretchable organic sensors (pressure sensors, strain sensors, tactile sensors, temperature sensors, gas sensors and other sensors), stretchable organic memory (resistive memory, magnetic memory and bionic synaptic memory) and other functional stretchable organic electronic devices. Finally, through the analyses of the existing scientific problems and future development of the functional stretchable organic electronic devices, we put forward some suggestions.
2020, 78(9): 865-876
doi: 10.6023/A20060219
Abstract:
Shape memory polymers are the most widely studied smart deformable materials at present. Due to their low density, large deformation, high stress resistance, various driving methods, good biocompatibility, easier modification and processing, shape memory polymers have become a cutting-edge research in the field of smart materials. Under certain external stimulus (such as temperature, light, electric field, magnetic field, pH, specific ions, enzymes, etc.), shape memory polymers can change their shapes according to pre-designed way and quickly change from temporary shape to permanent shape. Shape memory polymers have shown great application potential in aerospace, biomedicine, bionic engineering, electronic devices, intelligent robots and other fields, which effectively overcome the bottleneck problems in the corresponding fields. In order to make the shape memory polymers more suitable for various fields, not only a simple deformation process from a temporary shape to a permanent shape is needed, the deformation mode should also be improved to adapt the actual situation in practical applications. In this paper, the deformation modes of shape memory polymers are divided into four categories, including the simple dual shape memory deformation mode, the multiple shape memory deformation mode with multiple temporary shapes, the self-folding deformation mode, and the reversible two-way shape memory deformation mode. Multiple shape memory polymers generally have multiple reversible switches or a wide range of temperature switches, which have greater freedom in practical applications. The self-folding structure can spontaneously fold/unfold to the desired shape under stimulation conditions without artificially giving shape, so it has great application prospects in the fields of space systems and self-assembly systems. The reversible shape memory polymer can reversibly convert between permanent and temporary shapes under stimulation conditions, which show great application prospects in the fields of sensors and drivers. The deformation modes are more diversified which can fulfill different requirements in various applications. The deformation mode is an important functional index of shape memory materials. Therefore, from the perspective of different deformation modes of shape memory polymers, this paper reviews the different deformation modes of shape memory polymers and the progress of their related applications, as well as the challenges faced by different deformation modes and their potential research directions.
Shape memory polymers are the most widely studied smart deformable materials at present. Due to their low density, large deformation, high stress resistance, various driving methods, good biocompatibility, easier modification and processing, shape memory polymers have become a cutting-edge research in the field of smart materials. Under certain external stimulus (such as temperature, light, electric field, magnetic field, pH, specific ions, enzymes, etc.), shape memory polymers can change their shapes according to pre-designed way and quickly change from temporary shape to permanent shape. Shape memory polymers have shown great application potential in aerospace, biomedicine, bionic engineering, electronic devices, intelligent robots and other fields, which effectively overcome the bottleneck problems in the corresponding fields. In order to make the shape memory polymers more suitable for various fields, not only a simple deformation process from a temporary shape to a permanent shape is needed, the deformation mode should also be improved to adapt the actual situation in practical applications. In this paper, the deformation modes of shape memory polymers are divided into four categories, including the simple dual shape memory deformation mode, the multiple shape memory deformation mode with multiple temporary shapes, the self-folding deformation mode, and the reversible two-way shape memory deformation mode. Multiple shape memory polymers generally have multiple reversible switches or a wide range of temperature switches, which have greater freedom in practical applications. The self-folding structure can spontaneously fold/unfold to the desired shape under stimulation conditions without artificially giving shape, so it has great application prospects in the fields of space systems and self-assembly systems. The reversible shape memory polymer can reversibly convert between permanent and temporary shapes under stimulation conditions, which show great application prospects in the fields of sensors and drivers. The deformation modes are more diversified which can fulfill different requirements in various applications. The deformation mode is an important functional index of shape memory materials. Therefore, from the perspective of different deformation modes of shape memory polymers, this paper reviews the different deformation modes of shape memory polymers and the progress of their related applications, as well as the challenges faced by different deformation modes and their potential research directions.
2020, 78(9): 877-887
doi: 10.6023/A20060216
Abstract:
Due to the unique physicochemical properties, graphene oxide has been widely applied in material chemistry, biomedical science and life science. However, here is still a great challenge to maximize the advantages of graphene oxide and overcome the deleterious effects caused by its inherent properties. For a better understanding of current status in this research field, recent progress in surface chemical modifications of graphene oxide and interaction mechanisms at the nano-bio interface has been comprehensively reviewed. First, the physicochemical properties of graphene oxide and the representative strategies of surface chemical modifications will be briefly introduced, including oxidation and reduction, carboxylation, amination, small organic molecule modification, polymer modification, peptide/protein modification, nucleic acid modification and nanoparticle modification, as well as their potential roles in mediating the graphene oxide-resulted biological effects. Following, we will present the primary interaction mechanisms of pristine and surface-modified graphene oxide at the nano-bio interface, including the formation of protein corona, cell membrane damage, membrane receptor interaction and oxidative stress. Finally, the knowledge gaps and future challenges in this research field will be detailedly discussed.
Due to the unique physicochemical properties, graphene oxide has been widely applied in material chemistry, biomedical science and life science. However, here is still a great challenge to maximize the advantages of graphene oxide and overcome the deleterious effects caused by its inherent properties. For a better understanding of current status in this research field, recent progress in surface chemical modifications of graphene oxide and interaction mechanisms at the nano-bio interface has been comprehensively reviewed. First, the physicochemical properties of graphene oxide and the representative strategies of surface chemical modifications will be briefly introduced, including oxidation and reduction, carboxylation, amination, small organic molecule modification, polymer modification, peptide/protein modification, nucleic acid modification and nanoparticle modification, as well as their potential roles in mediating the graphene oxide-resulted biological effects. Following, we will present the primary interaction mechanisms of pristine and surface-modified graphene oxide at the nano-bio interface, including the formation of protein corona, cell membrane damage, membrane receptor interaction and oxidative stress. Finally, the knowledge gaps and future challenges in this research field will be detailedly discussed.
2020, 78(9): 888-900
doi: 10.6023/A20060221
Abstract:
Proton exchange membranes (PEMs) are important components for novel fuel cells. A significant effort has been made by researchers towards proton conductive materials and membranes, some of which have been successfully commercialized. However, commercial perfluorosulfonic acid membranes like Nafion suffer key issues which limit their large-scale applications in a wide temperature range, including high cost and low operation temperature. Therefore, it is highly desirable to prepare new-type PEMs possessing high proton conductivity, thermal and chemical stability, water uptake and excellent durability. Metal organic frameworks (MOFs) are attractive candidates for proton exchange membranes due to their high porosity, ordering pore structures and excellent designability. This review focuses on the recent progress on proton-conductive MOF structures and their proton exchange membranes. In the first section, the authors briefly introduce the proton conducting mechanism of MOFs and their testing methods. The Grotthuss mechanism refers to the proton transferring process in a continuous and long-range hydrogen network, whereas the Vehicular mechanism involves in the diffusion of proton carrier molecules. Then in the next section, the authors summarize the progress on bulk MOFs proton conductors. According to the work condition, proton-conducting MOFs can be divided into two types, namely working under humid and anhydrous environment. These works show the potential of proton-conductive MOFs to be applied in a wide temperature range, and some of them even have reached a relatively high conductivity larger than 10-2 S·cm-1, comparable with Nafion. In the third section, a review on the MOFs-based proton exchange membranes is shown. Researchers have proven that MOFs thin films have huge potential on proton conduction. Nevertheless, most of the MOFs-based PEMs are still mixed matrix membrane (MMM) structure. In order to boost the performance of MMMs-type MOFs-based PEMs, several strategies can be applied such as modifying MOF with functional groups, using 1D/2D MOFs structure and introducing the third phase into membranes. Last, the authors discuss the current issues and perspectives on MOFs proton conductors and their PEMs.
Proton exchange membranes (PEMs) are important components for novel fuel cells. A significant effort has been made by researchers towards proton conductive materials and membranes, some of which have been successfully commercialized. However, commercial perfluorosulfonic acid membranes like Nafion suffer key issues which limit their large-scale applications in a wide temperature range, including high cost and low operation temperature. Therefore, it is highly desirable to prepare new-type PEMs possessing high proton conductivity, thermal and chemical stability, water uptake and excellent durability. Metal organic frameworks (MOFs) are attractive candidates for proton exchange membranes due to their high porosity, ordering pore structures and excellent designability. This review focuses on the recent progress on proton-conductive MOF structures and their proton exchange membranes. In the first section, the authors briefly introduce the proton conducting mechanism of MOFs and their testing methods. The Grotthuss mechanism refers to the proton transferring process in a continuous and long-range hydrogen network, whereas the Vehicular mechanism involves in the diffusion of proton carrier molecules. Then in the next section, the authors summarize the progress on bulk MOFs proton conductors. According to the work condition, proton-conducting MOFs can be divided into two types, namely working under humid and anhydrous environment. These works show the potential of proton-conductive MOFs to be applied in a wide temperature range, and some of them even have reached a relatively high conductivity larger than 10-2 S·cm-1, comparable with Nafion. In the third section, a review on the MOFs-based proton exchange membranes is shown. Researchers have proven that MOFs thin films have huge potential on proton conduction. Nevertheless, most of the MOFs-based PEMs are still mixed matrix membrane (MMM) structure. In order to boost the performance of MMMs-type MOFs-based PEMs, several strategies can be applied such as modifying MOF with functional groups, using 1D/2D MOFs structure and introducing the third phase into membranes. Last, the authors discuss the current issues and perspectives on MOFs proton conductors and their PEMs.
2020, 78(9): 901-915
doi: 10.6023/A20050190
Abstract:
Fluorescence imaging plays an important role in the diagnosis and treatment of major diseases by virtue of its high sensitivity, strong specificity and excellent spatio-temporal resolution. However, traditional near-infrared-I (NIR-I, 700~900 nm) fluorescence imaging often encounters multiple concerns such as poor tissue penetration, which limits its clinical application. In recent years, near-infrared-II (NIR-II, 1000~1700 nm) fluorescence imaging has been proven to provide better imaging qualities, higher signal-to-noise ratio and deeper tissue penetration than those observed in the NIR-I window due to the diminished photon scattering and tissue auto-fluorescence. Among NIR-II fluorescent probes, organic small molecules are becoming research hotspots in this field due to their advantages of low toxicity, simple structure and fast metabolism. This review describes the recent progress in the design of organic small molecule NIR-II probes and the strategies for improving the fluorescence quantum yield. The application of small molecule NIR-II probes in activatable imaging, multimode imaging and theranostics are evaluated systematically. Current challenges and future perspectives in this emerging field are also prospected.
Fluorescence imaging plays an important role in the diagnosis and treatment of major diseases by virtue of its high sensitivity, strong specificity and excellent spatio-temporal resolution. However, traditional near-infrared-I (NIR-I, 700~900 nm) fluorescence imaging often encounters multiple concerns such as poor tissue penetration, which limits its clinical application. In recent years, near-infrared-II (NIR-II, 1000~1700 nm) fluorescence imaging has been proven to provide better imaging qualities, higher signal-to-noise ratio and deeper tissue penetration than those observed in the NIR-I window due to the diminished photon scattering and tissue auto-fluorescence. Among NIR-II fluorescent probes, organic small molecules are becoming research hotspots in this field due to their advantages of low toxicity, simple structure and fast metabolism. This review describes the recent progress in the design of organic small molecule NIR-II probes and the strategies for improving the fluorescence quantum yield. The application of small molecule NIR-II probes in activatable imaging, multimode imaging and theranostics are evaluated systematically. Current challenges and future perspectives in this emerging field are also prospected.
2020, 78(9): 916-927
doi: 10.6023/A20060207
Abstract:
Ammonia is not only the main raw material of nitrogen fertilizer, but also a promising energy carrier for the storage and utilization of renewable energy. The fossil fuel-based Haber-Bosch ammonia synthesis industry is an energy-consuming and high CO2-emission process. For the sustainable growth of human society, it is critically important to develop "green" ammonia synthesis processes driven by renewable energies. This scenario motivates growing interests on ammonia synthesis via heterogeneous catalysis, electro-chemical and photo-chemical routes as well as chemical looping process. Chemical looping ammonia synthesis (CLAS) process involves a series of individual reactions which produce ammonia in a distinctly different manner to the catalytic process. The CLAS could be operated under ambient pressure, and the switching on/off operation is flexible. Therefore, CLAS may be more amenable to variable and intermittent operation compared to the conventional catalytic process. More importantly, the competitive adsorption of N2 and H2 or H2O in the catalytic process can be circumvented to a great extent, which opens new opportunities for the design and development of nitrogen carriers especially for low-temperature ammonia production. Because of these unique features, the application of chemical looping technology for ammonia synthesis has been received increasing attention in recent years. The development of high-efficiency nitrogen carriers is the key component for the implementation of CLAS. A wide range of materials including metal nitrides, metal imides, nitride-hydrides and oxynitrides have been evaluated as nitrogen carriers for CLAS. The knowledge accumulated during the past decade will no doubt beneficial for the further optimization and development of nitrogen carriers. This article reviews the research progress in the field of chemical looping ammonia synthesis in recent years, with the focuses on the materials development of nitrogen carriers in CLAS. Furthermore, the challenges and future directions of CLAS are also discussed. With the development of nitrogen carriers and process design, CLAS would potentially play an important role in the green ammonia synthesis as well as the future energy system.
Ammonia is not only the main raw material of nitrogen fertilizer, but also a promising energy carrier for the storage and utilization of renewable energy. The fossil fuel-based Haber-Bosch ammonia synthesis industry is an energy-consuming and high CO2-emission process. For the sustainable growth of human society, it is critically important to develop "green" ammonia synthesis processes driven by renewable energies. This scenario motivates growing interests on ammonia synthesis via heterogeneous catalysis, electro-chemical and photo-chemical routes as well as chemical looping process. Chemical looping ammonia synthesis (CLAS) process involves a series of individual reactions which produce ammonia in a distinctly different manner to the catalytic process. The CLAS could be operated under ambient pressure, and the switching on/off operation is flexible. Therefore, CLAS may be more amenable to variable and intermittent operation compared to the conventional catalytic process. More importantly, the competitive adsorption of N2 and H2 or H2O in the catalytic process can be circumvented to a great extent, which opens new opportunities for the design and development of nitrogen carriers especially for low-temperature ammonia production. Because of these unique features, the application of chemical looping technology for ammonia synthesis has been received increasing attention in recent years. The development of high-efficiency nitrogen carriers is the key component for the implementation of CLAS. A wide range of materials including metal nitrides, metal imides, nitride-hydrides and oxynitrides have been evaluated as nitrogen carriers for CLAS. The knowledge accumulated during the past decade will no doubt beneficial for the further optimization and development of nitrogen carriers. This article reviews the research progress in the field of chemical looping ammonia synthesis in recent years, with the focuses on the materials development of nitrogen carriers in CLAS. Furthermore, the challenges and future directions of CLAS are also discussed. With the development of nitrogen carriers and process design, CLAS would potentially play an important role in the green ammonia synthesis as well as the future energy system.
2020, 78(9): 928-932
doi: 10.6023/A20060198
Abstract:
Attempts to synthesize the 4,5-spirocycle skeleton of Phainanoids by rhodium-catalyzed arylative cyclization of alkynone 5 and the addition of Grignard reagent 9 to α-alkoxyl cyclobutone 8, followed by intramolecular SNAr reaction are reported. Phainanoids, highly modified triterpenoids, were isolated from Phyllanthus hainanensis by Yue and co-workers. They have been found to show intriguing immunosuppressive activities. The most potent of them, Phainanoid F, inhibit the proliferation of T cells with an IC50 value of (2.04±0.01) nmol/L and B cells with an IC50 value <(1.60±0.01) nmol/L. The noteworthy activities and the lack of Phainanoids in nature resources make the synthesis of them for further biological evaluation a challenge for chemists. Our synthesis started from known compound 1, after Birch reduction and alkylation to give alkynone 5. The rhodium-catalyzed arylative cyclization of alkynone 5 to deliver tetrasubstituted cyclobutene 6 was performed by the following procedure. Under an atmosphere of Ar, to an oven-dried Schlenk tube with[Rh(OH)(cod)]2 (35.5 mg, 0.078 mmol, 0.012n5), phenylboronic acid (2.0 g, 16.3 mmol, 2.5n5), were added a solution of ketone 5 (1.9 g, 6.5 mmol, 1.0n5) in 1,4-dioxane (32.0 mL) and H2O (0.3 mL) at room temperature. The mixture was stirred at 35℃ for 12 h. Another [Rh(OH)(cod)]2 (35.5 mg, 0.078 mmol, 0.012n5) and phenylboronic acid (2.0 g, 16.3 mmol, 2.5n5) was added to the mixture. The mixture was stirred at 35℃ for 12 h. Subsequently, hydroxyl group was protected with ethoxymethyl (EOM) group to furnish 7, followed by ozonolysis to generate ketone 8. Ketone 8 was reacted with fresh prepared Grignard reagent 9 in Felkin-Anh modelinstead ofthe Cram's chelation-control model to deliver alcohol 10. The explanation of the diastereoselectivity of this reaction could be illustrated from two aspects:(1) the rigid structure of α-alkoxyl cyclobutone 8 increased the energy barrier for the transition state of chelation between magnesium ions and alkoxyl substituent; (2) the magnesium ions were not chelated with the alkoxyl substituent as well as the carbonyl oxygen was due to the intramolecular chelation with fluorine atom. Alcohol 10 underwent intramolecular SNAr reaction and deprotection to deliver 4,5-spirocycle compound 18.
Attempts to synthesize the 4,5-spirocycle skeleton of Phainanoids by rhodium-catalyzed arylative cyclization of alkynone 5 and the addition of Grignard reagent 9 to α-alkoxyl cyclobutone 8, followed by intramolecular SNAr reaction are reported. Phainanoids, highly modified triterpenoids, were isolated from Phyllanthus hainanensis by Yue and co-workers. They have been found to show intriguing immunosuppressive activities. The most potent of them, Phainanoid F, inhibit the proliferation of T cells with an IC50 value of (2.04±0.01) nmol/L and B cells with an IC50 value <(1.60±0.01) nmol/L. The noteworthy activities and the lack of Phainanoids in nature resources make the synthesis of them for further biological evaluation a challenge for chemists. Our synthesis started from known compound 1, after Birch reduction and alkylation to give alkynone 5. The rhodium-catalyzed arylative cyclization of alkynone 5 to deliver tetrasubstituted cyclobutene 6 was performed by the following procedure. Under an atmosphere of Ar, to an oven-dried Schlenk tube with[Rh(OH)(cod)]2 (35.5 mg, 0.078 mmol, 0.012n5), phenylboronic acid (2.0 g, 16.3 mmol, 2.5n5), were added a solution of ketone 5 (1.9 g, 6.5 mmol, 1.0n5) in 1,4-dioxane (32.0 mL) and H2O (0.3 mL) at room temperature. The mixture was stirred at 35℃ for 12 h. Another [Rh(OH)(cod)]2 (35.5 mg, 0.078 mmol, 0.012n5) and phenylboronic acid (2.0 g, 16.3 mmol, 2.5n5) was added to the mixture. The mixture was stirred at 35℃ for 12 h. Subsequently, hydroxyl group was protected with ethoxymethyl (EOM) group to furnish 7, followed by ozonolysis to generate ketone 8. Ketone 8 was reacted with fresh prepared Grignard reagent 9 in Felkin-Anh modelinstead ofthe Cram's chelation-control model to deliver alcohol 10. The explanation of the diastereoselectivity of this reaction could be illustrated from two aspects:(1) the rigid structure of α-alkoxyl cyclobutone 8 increased the energy barrier for the transition state of chelation between magnesium ions and alkoxyl substituent; (2) the magnesium ions were not chelated with the alkoxyl substituent as well as the carbonyl oxygen was due to the intramolecular chelation with fluorine atom. Alcohol 10 underwent intramolecular SNAr reaction and deprotection to deliver 4,5-spirocycle compound 18.
2020, 78(9): 933-937
doi: 10.6023/A20060248
Abstract:
A shelf-stable reagent for the preparation of fluoroalkylthiolated compounds, [(diethylphosphonate)difluoro-methylthio]phthalimide 1, was successfully developed, which reacted with a variety of nucleophiles such as electron-rich heteroarenes, β-ketoesters, oxindoles, benzofuranones in high yield, thus providing a new and efficient approach for the introduction of fluoroalkylthiolated phosphonate moiety. General procedure for the preparation of[(diethylphosphonate)difluoromethylthio]phthalimide 1:to a suspension of silver fluoride (7.6 g, 60 mmol) in anhydrous acetonitrile (100 mL) was added diethyl (difluoro(trimethylsilyl)methyl)phosphonate (13.0 g, 50.0 mmol) at -40℃. The mixture was allowed to stir at 0℃ until a dark brown solution was formed (approximately 15 min). N-(Chlorosulfenyl)phalimide (16.0 g, 75.0 mmol) was then added at -40℃, and the resulting mixture was stirred at -40℃ for 2 h. The mixture was filtered, and the solvent was evaporated in vacuo. The residue was recrystallized using the mixed solvent (petroleum ether/dichlor-omethane) three times to give[(diethylphosphonate)difluoromethylthio]phthalimide 1 as a white solid (5.5 g, 30%). General procedure for reaction of indoles with 1:to a 25 mL Schlenk tube charged with indole (35.1 mg, 0.3 mmol) and reagent 1 (132 mg, 0.36 mmol) and magnesium bromide (82 mg, 0.45 mmol) was added 1,2-dichloroethane (2.0 mL). The mixture was stirred at room temperature for 15 min. The mixture was filtered and the solvent was evaporated in vacuo. The residue was purified by flash chromatography on silica gel to give diethyl (((1H-indol-3-yl)thio)difluoromethyl)phosphonate 3a (93 mg, 93%) as a brown oil. General procedure for reaction of soft carbon nucleophile with reagent 1:to a 25 mL Schlenk tube charged with carbon nucleophiles (153 mg, 0.750 mmol), K2CO3 (103 mg, 0.75 mmol) and reagent 1 (182 mg, 0.50 mmol) was added dichloromethane (3.0 mL). The mixture was stirred at room temperature for 12 h. The reaction mixture was filtered and the solvent was evaporated in vacuo. The residue was purified by flash chromatography on silica gel to give ethyl-2-(((diethoxyphosphoryl)difluoromethyl)thio)-1-oxo-2,3-dihydro-1H-indene-2-carboxylate 5b (160 mg, 76%) as a yellow oil.
A shelf-stable reagent for the preparation of fluoroalkylthiolated compounds, [(diethylphosphonate)difluoro-methylthio]phthalimide 1, was successfully developed, which reacted with a variety of nucleophiles such as electron-rich heteroarenes, β-ketoesters, oxindoles, benzofuranones in high yield, thus providing a new and efficient approach for the introduction of fluoroalkylthiolated phosphonate moiety. General procedure for the preparation of[(diethylphosphonate)difluoromethylthio]phthalimide 1:to a suspension of silver fluoride (7.6 g, 60 mmol) in anhydrous acetonitrile (100 mL) was added diethyl (difluoro(trimethylsilyl)methyl)phosphonate (13.0 g, 50.0 mmol) at -40℃. The mixture was allowed to stir at 0℃ until a dark brown solution was formed (approximately 15 min). N-(Chlorosulfenyl)phalimide (16.0 g, 75.0 mmol) was then added at -40℃, and the resulting mixture was stirred at -40℃ for 2 h. The mixture was filtered, and the solvent was evaporated in vacuo. The residue was recrystallized using the mixed solvent (petroleum ether/dichlor-omethane) three times to give[(diethylphosphonate)difluoromethylthio]phthalimide 1 as a white solid (5.5 g, 30%). General procedure for reaction of indoles with 1:to a 25 mL Schlenk tube charged with indole (35.1 mg, 0.3 mmol) and reagent 1 (132 mg, 0.36 mmol) and magnesium bromide (82 mg, 0.45 mmol) was added 1,2-dichloroethane (2.0 mL). The mixture was stirred at room temperature for 15 min. The mixture was filtered and the solvent was evaporated in vacuo. The residue was purified by flash chromatography on silica gel to give diethyl (((1H-indol-3-yl)thio)difluoromethyl)phosphonate 3a (93 mg, 93%) as a brown oil. General procedure for reaction of soft carbon nucleophile with reagent 1:to a 25 mL Schlenk tube charged with carbon nucleophiles (153 mg, 0.750 mmol), K2CO3 (103 mg, 0.75 mmol) and reagent 1 (182 mg, 0.50 mmol) was added dichloromethane (3.0 mL). The mixture was stirred at room temperature for 12 h. The reaction mixture was filtered and the solvent was evaporated in vacuo. The residue was purified by flash chromatography on silica gel to give ethyl-2-(((diethoxyphosphoryl)difluoromethyl)thio)-1-oxo-2,3-dihydro-1H-indene-2-carboxylate 5b (160 mg, 76%) as a yellow oil.
2020, 78(9): 938-944
doi: 10.6023/A20060268
Abstract:
Fixation and transformation of CO2 are of the great importance, especially the conversion of CO2 into valuable organic compounds catalyzed by the cheap and biocompatible metal catalysts. Zinc is an abundant, biocompatible and environmentally friendly element. ZnEt2 is commercial available, and has been widely used as reducing or transmetalation agent in hydrocarboxylation of unsaturated hydrocarbons with CO2. In these reactions, ZnEt2 is generally used in stoichiometric amount or excess amout. This manuscript reports the hydrosilylation of CO2 into methoxysilane promoted by a catalytic amount of ZnEt2 (1.0 mol%), the ZnEt2 promoted formylation or urealation of amines with CO2 as a one-carbon (C1) building block is also described. The hydrosilylation of CO2 into methoxysilane (CH3OSi(OEt)3) with (EtO)3SiH as a hydrosilylation reagent is affected by CO2 pressure, ZnEt2 amount, reaction temperature and reaction time. Under the reaction conditions of 1.0 MPa CO2 (the initial CO2 pressure) and 1.0 mol% ZnEt2, the yield of methoxysilane is up to ca. 90% after 7 h at 90℃, and no solvent is used for this reaction. In the presence of organic amine, the reaction gives formamide or urea instead of methoxysilane. Under 1.5 MPa CO2, 1.0 mol% ZnEt2, 2.4 equiv. (EtO)3SiH and 100℃, a series of secondary amines, both the aromatic ones and the aliphatic ones, can be formylated into formamides. In the formylation of N-methylanilines with different substituents at para-position, the isolated yields of the formylation products are in the order of OMe≈Me>H>F>Cl≈Br>CF3>NO2, indicating the electron-donating group at the para-position of the N-methylanilines is benefit for the formylation reaction. When primary amines are used as the substrates, the reactions prefer to produce urea derivatives under the same reaction conditions. In the urealation reaction, the electronic effect is not as significant as that in the formylation reaction.
Fixation and transformation of CO2 are of the great importance, especially the conversion of CO2 into valuable organic compounds catalyzed by the cheap and biocompatible metal catalysts. Zinc is an abundant, biocompatible and environmentally friendly element. ZnEt2 is commercial available, and has been widely used as reducing or transmetalation agent in hydrocarboxylation of unsaturated hydrocarbons with CO2. In these reactions, ZnEt2 is generally used in stoichiometric amount or excess amout. This manuscript reports the hydrosilylation of CO2 into methoxysilane promoted by a catalytic amount of ZnEt2 (1.0 mol%), the ZnEt2 promoted formylation or urealation of amines with CO2 as a one-carbon (C1) building block is also described. The hydrosilylation of CO2 into methoxysilane (CH3OSi(OEt)3) with (EtO)3SiH as a hydrosilylation reagent is affected by CO2 pressure, ZnEt2 amount, reaction temperature and reaction time. Under the reaction conditions of 1.0 MPa CO2 (the initial CO2 pressure) and 1.0 mol% ZnEt2, the yield of methoxysilane is up to ca. 90% after 7 h at 90℃, and no solvent is used for this reaction. In the presence of organic amine, the reaction gives formamide or urea instead of methoxysilane. Under 1.5 MPa CO2, 1.0 mol% ZnEt2, 2.4 equiv. (EtO)3SiH and 100℃, a series of secondary amines, both the aromatic ones and the aliphatic ones, can be formylated into formamides. In the formylation of N-methylanilines with different substituents at para-position, the isolated yields of the formylation products are in the order of OMe≈Me>H>F>Cl≈Br>CF3>NO2, indicating the electron-donating group at the para-position of the N-methylanilines is benefit for the formylation reaction. When primary amines are used as the substrates, the reactions prefer to produce urea derivatives under the same reaction conditions. In the urealation reaction, the electronic effect is not as significant as that in the formylation reaction.
2020, 78(9): 945-954
doi: 10.6023/A20060208
Abstract:
Fe3O4@SiO2 particles were synthesized by a solvothermal method and a classical stber method. Superparamagnetic Fe3O4 was the core, and a sol-gel coating of SiO2 was the shell. After the SiO2 surface was modified with amino groups, benzaldehyde was conjugated to the particles by a Schiff base reaction. The Fe3O4@SiO2 particles were emulsified in paraffin/water as a solid emulsifier to obtain an oil-in-water Pickering emulsion. After cooling the paraffin, the particles were fixed on the surface of the emulsion droplets. The particles were etched in ammonium fluoride aqueous solution, and Janus particles with different structures could be obtained by adjusting the etching time. Via the in situ growth of metal Pt or Ag nanoparticles, superparamagnetic Fe3O4@SiO2-Pt or Fe3O4@SiO2-Ag Janus particles were obtained. The movement of Fe3O4@SiO2-Pt Janus particles was observed due to the catalytic decomposition of hydrogen peroxide aqueous solution. It was found that in the short term, there was a linear motion, while in the long term, the motion direction and trajectory were random. Fe3O4@SiO2-Ag Janus particles were used as magnetic solid surfactants to stabilize the emulsions and catalyze the nitro reduction. About 60% of the surficial area of the Janus particles was modified by phenyl groups, while the remaining 40% was covered with Ag nanoparticles. Under the premise of maintaining the Janus balance, the whole particle became more hydrophobic, which was conducive to the formation of the water-in-oil emulsion. In addition, the Ag side of the Janus particles was towards the aqueous phase, and the opposite hydrophobic side was towards the oil phase. The Janus particles possessed a fixed orientation assembly at the oil-water interface. The assemble membrane possessed Janus characteristics, and it facilitated the stable dispersion of the emulsion and the catalysis. The method has the advantages of a simple principle, capability for mass production, universality and versatility. It is expected that Janus particles will be used to more precisely regulate the zoning with different functional substances.
Fe3O4@SiO2 particles were synthesized by a solvothermal method and a classical stber method. Superparamagnetic Fe3O4 was the core, and a sol-gel coating of SiO2 was the shell. After the SiO2 surface was modified with amino groups, benzaldehyde was conjugated to the particles by a Schiff base reaction. The Fe3O4@SiO2 particles were emulsified in paraffin/water as a solid emulsifier to obtain an oil-in-water Pickering emulsion. After cooling the paraffin, the particles were fixed on the surface of the emulsion droplets. The particles were etched in ammonium fluoride aqueous solution, and Janus particles with different structures could be obtained by adjusting the etching time. Via the in situ growth of metal Pt or Ag nanoparticles, superparamagnetic Fe3O4@SiO2-Pt or Fe3O4@SiO2-Ag Janus particles were obtained. The movement of Fe3O4@SiO2-Pt Janus particles was observed due to the catalytic decomposition of hydrogen peroxide aqueous solution. It was found that in the short term, there was a linear motion, while in the long term, the motion direction and trajectory were random. Fe3O4@SiO2-Ag Janus particles were used as magnetic solid surfactants to stabilize the emulsions and catalyze the nitro reduction. About 60% of the surficial area of the Janus particles was modified by phenyl groups, while the remaining 40% was covered with Ag nanoparticles. Under the premise of maintaining the Janus balance, the whole particle became more hydrophobic, which was conducive to the formation of the water-in-oil emulsion. In addition, the Ag side of the Janus particles was towards the aqueous phase, and the opposite hydrophobic side was towards the oil phase. The Janus particles possessed a fixed orientation assembly at the oil-water interface. The assemble membrane possessed Janus characteristics, and it facilitated the stable dispersion of the emulsion and the catalysis. The method has the advantages of a simple principle, capability for mass production, universality and versatility. It is expected that Janus particles will be used to more precisely regulate the zoning with different functional substances.
2020, 78(9): 945-953
doi: 10.6023/A20050170
Abstract:
Conjugated polymer materials with good photoelectric performance, solution processing ability and flexibility are widely used as active layers in optoelectronic devices. Here, using Stille and Suzuki coupling reactions, we designed and synthesized two new conjugated polymers, poly(1,2-bis(2,5-bis(iso-octyloxy)phenylenevinylene-2,1,3-benzothiadiazole)) (PVBT) and poly(1,2-bis(2,5-bis(n-octyloxy)phenylenevinylene-2,1,3-benzothiadiazole)) (nPVBT), which contain structural element styrene fragments and an conjugated unit benzothiadiazole. Styrene fragments are conducive to luminescent properties of materials, such as phenylenevinylene (PPV) derivatives, while benzothiadiazole unit is electron withdrawing, and matches with many structural units of a donor. The conjugated polymers were characterized by gel permeation chromatography (GPC), elemental analysis and differential scanning calorimetry (DSC). The results indicate that each of these two polymers has good thermal stability. Their melting points were around 240~250℃ and decomposition temperatures around 380℃. Due to the presence of the structural alkoxy chains, these two polymers exhibit good solubility, which is conducive to solution-processed film formation. PVBT and nPVBT have strong fluorescence characters with maximum emission in the range of 590~605 nm. The photoluminescence quantum yield of these two polymers in dichloromethane solution (1×10-5 mol·L-1) is 23%~35%, and 12%~20% in solid films, which are annealed at 180℃ for 10 min. Due to benzothiadiazole's regulation of molecular energy levels, the highest occupied molecular orbital (HOMO) energy level of PVBT and nPVBT were modulated to be -5.73 and -5.61 eV, and the lowest unoccupied molecular orbital (LUMO) energy level were -3.37 and -3.32 eV, respectively. Typical p-type transporting property was determined by using PVBT and nPVBT films as active layers in organic field effect transistors. Because of the improved conjugation of the skeleton structures and the close packing between benzothiadiazole of main chains, these two conjugated polymers both exhibit efficient charge transport characteristics with saturation hole carrier mobility is up to 1.1×10-4 cm2·V-1·s-1 and high switching on/off ratio of 103~104. This work provides new insight into the development of high-performance optoelectronic conjugated polymer materials and sheds light on the research of organic optoelectronic integrated devices.
Conjugated polymer materials with good photoelectric performance, solution processing ability and flexibility are widely used as active layers in optoelectronic devices. Here, using Stille and Suzuki coupling reactions, we designed and synthesized two new conjugated polymers, poly(1,2-bis(2,5-bis(iso-octyloxy)phenylenevinylene-2,1,3-benzothiadiazole)) (PVBT) and poly(1,2-bis(2,5-bis(n-octyloxy)phenylenevinylene-2,1,3-benzothiadiazole)) (nPVBT), which contain structural element styrene fragments and an conjugated unit benzothiadiazole. Styrene fragments are conducive to luminescent properties of materials, such as phenylenevinylene (PPV) derivatives, while benzothiadiazole unit is electron withdrawing, and matches with many structural units of a donor. The conjugated polymers were characterized by gel permeation chromatography (GPC), elemental analysis and differential scanning calorimetry (DSC). The results indicate that each of these two polymers has good thermal stability. Their melting points were around 240~250℃ and decomposition temperatures around 380℃. Due to the presence of the structural alkoxy chains, these two polymers exhibit good solubility, which is conducive to solution-processed film formation. PVBT and nPVBT have strong fluorescence characters with maximum emission in the range of 590~605 nm. The photoluminescence quantum yield of these two polymers in dichloromethane solution (1×10-5 mol·L-1) is 23%~35%, and 12%~20% in solid films, which are annealed at 180℃ for 10 min. Due to benzothiadiazole's regulation of molecular energy levels, the highest occupied molecular orbital (HOMO) energy level of PVBT and nPVBT were modulated to be -5.73 and -5.61 eV, and the lowest unoccupied molecular orbital (LUMO) energy level were -3.37 and -3.32 eV, respectively. Typical p-type transporting property was determined by using PVBT and nPVBT films as active layers in organic field effect transistors. Because of the improved conjugation of the skeleton structures and the close packing between benzothiadiazole of main chains, these two conjugated polymers both exhibit efficient charge transport characteristics with saturation hole carrier mobility is up to 1.1×10-4 cm2·V-1·s-1 and high switching on/off ratio of 103~104. This work provides new insight into the development of high-performance optoelectronic conjugated polymer materials and sheds light on the research of organic optoelectronic integrated devices.
2020, 78(9): 961-967
doi: 10.6023/A20060244
Abstract:
CuS@MoS2 core-shell nanotubes were prepared by microwave-induced assembly techniques in the present work. Firstly, the Cu nanowires were vulcanized into hollow CuS nanotubes. Secondly, the sheet-shaped MoS2 were uniformly intercalated and assembled onto the surface of CuS nanotubes. The as-prepared CuS@MoS2 core-shell nanotubes were used in photocatalytic Fenton-like reaction system to remove high-concentration rhodamine B (RhB) in aqueous solution, which exhibited 100% degradation rate within 30 min under visible light (λ>420 nm) irradiation. The morphology and structure of the as-obtained catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS) and X-ray diffractometry (XRD). UV-Vis absorption spectroscopy (UV-vis DRS) was used to characterize its basic optical properties. And to further learn the catalytic mechanism and make sure the active species of the photocatalytic Fenton-like reaction system, the heterojunction structure of the catalyst was analyzed and electron spin resonance (ESR) spectrum was carried to prove the existence of superoxide (·O2-) species. The high activity could be attributed to the unique multi-layer structure of CuS@MoS2, corresponding to the enhanced absorption and exciting ability of visible lights. Meanwhile, the heterojunction structure formed between MoS2 and CuS also promoted the transfer of photogenerated electrons, which could inhibit their recombination with photogenerated holes. More importantly, the cooperation mechanism formed between photocatalysis and Fenton-like reactions may exhibit strong promoting effect. The Cu2+ ions in CuS reacted with H2O2 to form a Fenton-like cycle, allowing the generation of reactive hydroxyl (·OH) species. While, the photogenerated electrons reacted with both the H2O2 and the molecular oxygen activated by MoS2 to produce ·OH and ·O2- species. Both ·OH and ·O2- species worked together to oxidize pollutants rapidly. This work developed a recycled photocatalytic Fenton-like reaction system, which may offer new pathway for the treatment of environmental pollution.
CuS@MoS2 core-shell nanotubes were prepared by microwave-induced assembly techniques in the present work. Firstly, the Cu nanowires were vulcanized into hollow CuS nanotubes. Secondly, the sheet-shaped MoS2 were uniformly intercalated and assembled onto the surface of CuS nanotubes. The as-prepared CuS@MoS2 core-shell nanotubes were used in photocatalytic Fenton-like reaction system to remove high-concentration rhodamine B (RhB) in aqueous solution, which exhibited 100% degradation rate within 30 min under visible light (λ>420 nm) irradiation. The morphology and structure of the as-obtained catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS) and X-ray diffractometry (XRD). UV-Vis absorption spectroscopy (UV-vis DRS) was used to characterize its basic optical properties. And to further learn the catalytic mechanism and make sure the active species of the photocatalytic Fenton-like reaction system, the heterojunction structure of the catalyst was analyzed and electron spin resonance (ESR) spectrum was carried to prove the existence of superoxide (·O2-) species. The high activity could be attributed to the unique multi-layer structure of CuS@MoS2, corresponding to the enhanced absorption and exciting ability of visible lights. Meanwhile, the heterojunction structure formed between MoS2 and CuS also promoted the transfer of photogenerated electrons, which could inhibit their recombination with photogenerated holes. More importantly, the cooperation mechanism formed between photocatalysis and Fenton-like reactions may exhibit strong promoting effect. The Cu2+ ions in CuS reacted with H2O2 to form a Fenton-like cycle, allowing the generation of reactive hydroxyl (·OH) species. While, the photogenerated electrons reacted with both the H2O2 and the molecular oxygen activated by MoS2 to produce ·OH and ·O2- species. Both ·OH and ·O2- species worked together to oxidize pollutants rapidly. This work developed a recycled photocatalytic Fenton-like reaction system, which may offer new pathway for the treatment of environmental pollution.
2020, 78(9): 968-979
doi: 10.6023/A20050154
Abstract:
Lanthanide ions doped tetragonal LiYF4 has became an investigative focus of upconversion luminescence (UCL) materials for its well properties of multi-photon UCL and as a comparable matrix material with hexagonal NaYF4. While the cause for its well performance on short bands emission is still unrevealed. After the exploration of crystal structure characteristic of tetragonal LiYF4, a hexagonal circle sublattice structure of Y3+ with 0.3710 nm interval between adjacent Y3+ ions and larger than 0.5 nm interval between meta-position and para-position Y3+ ions were revealed. The energy transfer of rare earth ions are easy take place around the hexagonal circles or among the cluster of five adjacent trivalent ions. Base on the sublattice structure characteristic of tetragonal LiYF4, we have an idea to study UCL mechanism systematically of tetragonal LiYF4:RE by the construction of sublattice energy cluster 1M-xYb (M=Er, Ho, Tm) and the manipulation of crystal field symmetry by introducing different amount Yb3+ ions and Sc3+ or Hf4+ ions, respectively. Hydrothermal method was employed to prepare LiY0.98-xYbxEr0.02F4, LiY0.98-xYbxHo0.02F4, LiY0.995-xYbxTm0.005F4, LiY0.68-xYb0.3Er0.02ScxF4 and LiY0.68-xYb0.3Er0.02HfxF4 series samples. A typical preparation process demonstrate as follows, at first, (1-x) mmol Y(NO3)3 (0.2 mol/L), x mmol (x=0.2, 0.5, 0.7 and 0.9) Yb(NO3)3 (0.20 mol/L) and Er(NO3)3 (0.02 mmol) solution was dropwise added into 20 mL deionized (DI) water with 1 mmol EDTA to form a solution under vigorous stirring for 30 min. Secondly, 3.0 mL LiOH (1.0 mol/L) and 4.0 mL NH4HF2(1.0 mol/L) aqueous solution were dropwise added to the solution under thorough stirring for 30 min until the solution completely became a white emulsion, the pH value of the emulsion is 3~4. Finally, the white emulsion was slowly transferred into a 50 mL Teflon-lined autoclave, sealed and heated at 190℃ for 18 h. The final products were collected by centrifugation, and then washed with DI water several times. The collected samples were dried at 60℃ over night. X-ray powder diffraction (XRD) and Rietveld refinement method were employed to reveal the variation of crystal structure, field emission scanning electron microscopy (FESEM) and field emission transmission electron microscopy (FETEM) were employed to the analysis of crystal morphology and crystal structure. UCL performance was analyzed by Edinburgh fluorescence spectrophotometer FSP920. After investigation, we found excited energy levels distribution of different RE ions is diverse, and the level matching with Yb3+ are different too, it result in different luminescence quenching of energy cross relaxation, so the different sublattice energy clusters 1Er-2Yb, 1Ho-2Yb and 1Tm-4Yb of different active rare earth ions can be constructed for the best UCL performance. The cystal field symmetry of tetragonal LiYF4:Yb/Er were manipulated successfully by 6 mol% Sc3+ or 4 mol% Hf4+ doping, and UCL intensity were enhanced about 50% with 6 mol% Sc3+, while the UCL intensity were weaken after Hf4+ doping. After Sc3+ or Hf4+ doping, there are only three Yb3+ ions in the five trivalence ions cluster that can't realize two-photon cooperation upconversion synchronous electron population of 4F5/2 excited state level of Er3+ ions and 2G7/2 or 4Fo5/2 excited state level of Sc3+ or Hf4+ respevticely, and then Sc3+ and Hf4+ ions become a quenching center in the asymmetric crystal field that is conversed with them doped hexagonal NaYF4:Yb/Er that Sc3+ and Hf4+ ions were taken as energy storage ions and dramatically enhanced UCL performance. In this work, the UCL mechanism of sublattice energy cluster construction and crystal field manipulation were revealed that may be an inspiration for high efficient UC luminescence materials design and preparation.
Lanthanide ions doped tetragonal LiYF4 has became an investigative focus of upconversion luminescence (UCL) materials for its well properties of multi-photon UCL and as a comparable matrix material with hexagonal NaYF4. While the cause for its well performance on short bands emission is still unrevealed. After the exploration of crystal structure characteristic of tetragonal LiYF4, a hexagonal circle sublattice structure of Y3+ with 0.3710 nm interval between adjacent Y3+ ions and larger than 0.5 nm interval between meta-position and para-position Y3+ ions were revealed. The energy transfer of rare earth ions are easy take place around the hexagonal circles or among the cluster of five adjacent trivalent ions. Base on the sublattice structure characteristic of tetragonal LiYF4, we have an idea to study UCL mechanism systematically of tetragonal LiYF4:RE by the construction of sublattice energy cluster 1M-xYb (M=Er, Ho, Tm) and the manipulation of crystal field symmetry by introducing different amount Yb3+ ions and Sc3+ or Hf4+ ions, respectively. Hydrothermal method was employed to prepare LiY0.98-xYbxEr0.02F4, LiY0.98-xYbxHo0.02F4, LiY0.995-xYbxTm0.005F4, LiY0.68-xYb0.3Er0.02ScxF4 and LiY0.68-xYb0.3Er0.02HfxF4 series samples. A typical preparation process demonstrate as follows, at first, (1-x) mmol Y(NO3)3 (0.2 mol/L), x mmol (x=0.2, 0.5, 0.7 and 0.9) Yb(NO3)3 (0.20 mol/L) and Er(NO3)3 (0.02 mmol) solution was dropwise added into 20 mL deionized (DI) water with 1 mmol EDTA to form a solution under vigorous stirring for 30 min. Secondly, 3.0 mL LiOH (1.0 mol/L) and 4.0 mL NH4HF2(1.0 mol/L) aqueous solution were dropwise added to the solution under thorough stirring for 30 min until the solution completely became a white emulsion, the pH value of the emulsion is 3~4. Finally, the white emulsion was slowly transferred into a 50 mL Teflon-lined autoclave, sealed and heated at 190℃ for 18 h. The final products were collected by centrifugation, and then washed with DI water several times. The collected samples were dried at 60℃ over night. X-ray powder diffraction (XRD) and Rietveld refinement method were employed to reveal the variation of crystal structure, field emission scanning electron microscopy (FESEM) and field emission transmission electron microscopy (FETEM) were employed to the analysis of crystal morphology and crystal structure. UCL performance was analyzed by Edinburgh fluorescence spectrophotometer FSP920. After investigation, we found excited energy levels distribution of different RE ions is diverse, and the level matching with Yb3+ are different too, it result in different luminescence quenching of energy cross relaxation, so the different sublattice energy clusters 1Er-2Yb, 1Ho-2Yb and 1Tm-4Yb of different active rare earth ions can be constructed for the best UCL performance. The cystal field symmetry of tetragonal LiYF4:Yb/Er were manipulated successfully by 6 mol% Sc3+ or 4 mol% Hf4+ doping, and UCL intensity were enhanced about 50% with 6 mol% Sc3+, while the UCL intensity were weaken after Hf4+ doping. After Sc3+ or Hf4+ doping, there are only three Yb3+ ions in the five trivalence ions cluster that can't realize two-photon cooperation upconversion synchronous electron population of 4F5/2 excited state level of Er3+ ions and 2G7/2 or 4Fo5/2 excited state level of Sc3+ or Hf4+ respevticely, and then Sc3+ and Hf4+ ions become a quenching center in the asymmetric crystal field that is conversed with them doped hexagonal NaYF4:Yb/Er that Sc3+ and Hf4+ ions were taken as energy storage ions and dramatically enhanced UCL performance. In this work, the UCL mechanism of sublattice energy cluster construction and crystal field manipulation were revealed that may be an inspiration for high efficient UC luminescence materials design and preparation.
2020, 78(9): 980-988
doi: 10.6023/A20050165
Abstract:
Two-dimensional nanomaterials have received extensive attention because of their unique physicochemical properties. However, bottom-up synthesis of two-dimensional (2D) stable nanomaterials still remains great challenge. In this work, a novel 2D metal-organic (Cu-BDT) nanosheet is constructed at room temperature by coordinative self-assembly, namely, using monovalent copper ion as the metal precursor and 1,4-benzenedithiol as organic ligand. As-synthesized Cu-BDT nanosheets are fully characterized by various techniques including powder-diffraction of X-rays (P-XRD), Fourier transform infrared spectrometer (FT-IR), Raman spectra (Raman), scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometer (ICP-OES) and contact angle test. The catalytic result verifies that the Cu-BDT nanosheet surfaces possess abundant active sites and good hydrophobicity, which facilitate oxidation of sulfides into sulfoxide compounds.
Two-dimensional nanomaterials have received extensive attention because of their unique physicochemical properties. However, bottom-up synthesis of two-dimensional (2D) stable nanomaterials still remains great challenge. In this work, a novel 2D metal-organic (Cu-BDT) nanosheet is constructed at room temperature by coordinative self-assembly, namely, using monovalent copper ion as the metal precursor and 1,4-benzenedithiol as organic ligand. As-synthesized Cu-BDT nanosheets are fully characterized by various techniques including powder-diffraction of X-rays (P-XRD), Fourier transform infrared spectrometer (FT-IR), Raman spectra (Raman), scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectrometer (ICP-OES) and contact angle test. The catalytic result verifies that the Cu-BDT nanosheet surfaces possess abundant active sites and good hydrophobicity, which facilitate oxidation of sulfides into sulfoxide compounds.
2020, 78(9): 989-993
doi: 10.6023/A20060269
Abstract:
As the most common bioluminescence (BL), firefly BL, is of great significance in the fields of biotechnology, biomedicine and so on. The entire BL process involves a series of complicate in vivo chemical reactions. The BL is initiated by the enzymatic oxidation of luciferin. This is a spin-forbidden reaction of low efficiency, because that luciferin is in singlet state and O2 is in triplet state. However, firefly is till-now the most efficient system of converting chemical energy to light energy. Why this spin-forbidden reaction occurs efficiently? A single electron transfer (SET) mechanism has been confirmed on this reaction by experiments. However, there is lack of a complete and detailed description of the mechanism and reaction process. Via a calculation of density functional theory (DFT), this article described the complete process of this reaction. The oxygenation of luciferin is initiated by a SET from singlet L3- to triplet O2 to form RC 3[L·2-…O2·-]. Then the reaction is carried out on the potential energy surface (PES) of triplet state (T1), on which O2·- performs a nucleophilic attack on C4 of L·2-. There is an intersystem crossing between the ground (S0) and T1 PESs nearby the first transition state (TS1). After the ISC (intersystem crossing), the reaction continuously undergoes on the S0 PES to produce dioxetanone FDO- via two TSs and two intermediates (Ints). The analysis on electron densities and natural orbitals indicates that there is a quick reaction of biradical annihilation around the ISC. About 11.9 kcal·mol-1 energy is needed to reach the ISC before the whole reaction occurs on the S0 PES. The highest barrier of the reactions on the S0 PES is only 4.2 kcal·mol-1. The biradical annihilation around the ISC and the very low energy barriers explain the reason of the spin-forbidden reaction with high efficiency. This study is helpful for understanding the initiation of firefly BL and the other oxygen-dependent BL.
As the most common bioluminescence (BL), firefly BL, is of great significance in the fields of biotechnology, biomedicine and so on. The entire BL process involves a series of complicate in vivo chemical reactions. The BL is initiated by the enzymatic oxidation of luciferin. This is a spin-forbidden reaction of low efficiency, because that luciferin is in singlet state and O2 is in triplet state. However, firefly is till-now the most efficient system of converting chemical energy to light energy. Why this spin-forbidden reaction occurs efficiently? A single electron transfer (SET) mechanism has been confirmed on this reaction by experiments. However, there is lack of a complete and detailed description of the mechanism and reaction process. Via a calculation of density functional theory (DFT), this article described the complete process of this reaction. The oxygenation of luciferin is initiated by a SET from singlet L3- to triplet O2 to form RC 3[L·2-…O2·-]. Then the reaction is carried out on the potential energy surface (PES) of triplet state (T1), on which O2·- performs a nucleophilic attack on C4 of L·2-. There is an intersystem crossing between the ground (S0) and T1 PESs nearby the first transition state (TS1). After the ISC (intersystem crossing), the reaction continuously undergoes on the S0 PES to produce dioxetanone FDO- via two TSs and two intermediates (Ints). The analysis on electron densities and natural orbitals indicates that there is a quick reaction of biradical annihilation around the ISC. About 11.9 kcal·mol-1 energy is needed to reach the ISC before the whole reaction occurs on the S0 PES. The highest barrier of the reactions on the S0 PES is only 4.2 kcal·mol-1. The biradical annihilation around the ISC and the very low energy barriers explain the reason of the spin-forbidden reaction with high efficiency. This study is helpful for understanding the initiation of firefly BL and the other oxygen-dependent BL.
2020, 78(9): 994-1000
doi: 10.6023/A20060249
Abstract:
Intrinsically disordered proteins (IDPs) are a unique class of proteins without stable native structures. Like globular proteins, the structure and the dynamics of IDPs are also encoded in their amino acid sequences. IDPs usually contain a larger proportion of hydrophilic or charged amino acids than globular proteins. Interestingly, even with the same hydrophobicity and number of charged residues, the differences in sequence arrangement can lead to different structures of the peptides. In this work, to model such an effect, we conduct molecular simulations based on a series of peptides with randomly composed of charged residues (including glutamic acids and lysines) and isoleucine. In the simulation, we use the ABSINTH (self-Assembly of Biomolecules Studied by an Implicit, Novel, and Tunable Hamiltonian) implicit solvation model and employ the all-atom Markov Chain Monte Carlo method with replica-exchange sampling. Our simulations clearly show a transition between the extended conformations to compact structures for each peptide. The corresponding transition temperature is found to be dependent on the portion of the hydrophobic and charged residues. When the mean hydrophobicity is larger than a certain threshold, the transition temperature is higher than the room temperature, and vice versa. Such a result has outlined the borderline between intrinsically disordered proteins and the folded proteins. It is also consistent with previous analysis based on bioinformatics techniques. Furthermore, the contributions of different kinds of interactions to the structural variation of peptides are analyzed based on the contact statistics and the charge-pattern dependence of the gyration radii of the peptides. Our simulation results imply that the hydrophobicity of the sequence dominates the order-disorder transitions of IDPs, while the charge distribution can also affect such transitions. Based on these results, we achieve a comprehensive understanding of the sequence-structure relation of the natural proteins and the underlying physics. Our results may broaden our perspective of the sequence-structure relation of protein systems and shed light on the design of both ordered and disordered proteins.
Intrinsically disordered proteins (IDPs) are a unique class of proteins without stable native structures. Like globular proteins, the structure and the dynamics of IDPs are also encoded in their amino acid sequences. IDPs usually contain a larger proportion of hydrophilic or charged amino acids than globular proteins. Interestingly, even with the same hydrophobicity and number of charged residues, the differences in sequence arrangement can lead to different structures of the peptides. In this work, to model such an effect, we conduct molecular simulations based on a series of peptides with randomly composed of charged residues (including glutamic acids and lysines) and isoleucine. In the simulation, we use the ABSINTH (self-Assembly of Biomolecules Studied by an Implicit, Novel, and Tunable Hamiltonian) implicit solvation model and employ the all-atom Markov Chain Monte Carlo method with replica-exchange sampling. Our simulations clearly show a transition between the extended conformations to compact structures for each peptide. The corresponding transition temperature is found to be dependent on the portion of the hydrophobic and charged residues. When the mean hydrophobicity is larger than a certain threshold, the transition temperature is higher than the room temperature, and vice versa. Such a result has outlined the borderline between intrinsically disordered proteins and the folded proteins. It is also consistent with previous analysis based on bioinformatics techniques. Furthermore, the contributions of different kinds of interactions to the structural variation of peptides are analyzed based on the contact statistics and the charge-pattern dependence of the gyration radii of the peptides. Our simulation results imply that the hydrophobicity of the sequence dominates the order-disorder transitions of IDPs, while the charge distribution can also affect such transitions. Based on these results, we achieve a comprehensive understanding of the sequence-structure relation of the natural proteins and the underlying physics. Our results may broaden our perspective of the sequence-structure relation of protein systems and shed light on the design of both ordered and disordered proteins.
Investigation on Oxygen Reduction Reaction Mechanism on S Doped Fe-NC lsolated Single Atoms Catalyst
2020, 78(9): 1001-1006
doi: 10.6023/A20060223
Abstract:
Heteratom-doped Fe-NC catalyst is promising for highly efficiently oxygen reduction reaction (ORR). In this work, density functional theory with the Vienna Ab initio Simulation Package (VASP) has been employed to systematically study the electronic structure regulation mechanism and oxygen reduction promoting mechanism on sulfur atom doped Fe-NC catalyst. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional within a generalized gradient approximation (GGA) was used in this work. The computataional hydrogen electron model was used to calculate the changes in Gibbs free energy. To consider the influence of S doping proportion, we build FeNSx models with 1~4 S atoms. The thermodynamic stability of catalysts was firstly considered based on formation energy, following by electronic structure analysis through Bader charge analysis and densities of states. Then, the oxygen adsorption ability was considered based on oxygen adsorption configurations and energies analyses. At last, reaction overpotentials were calculated based on computational hydrogen electrode model to study activity of catalytic sites. The results show that the catalyst doped with few sulfur atoms around the active sites of FeN4 could remain stable. Three possible ORR promoting mechanisms of S atoms doping were investigated. Firstly, the doping of sulfur atoms would reduce the band gap of the catalyst, thus improving the conductivity of the catalyst, which is beneficial to electrocatalytic oxygen reduction reactions. Secondly, the doping of a small amount of S atoms can improve the affinity between oxygen and the catalysts, which is also important for oxygen reduction reaction. At last, the introduction of four S atoms in the system would reduce the overpotential of ORR, thus improving the activity of the active sites to catalyze the oxygen reduction reaction. Our results predict that few S atoms doping would improve ORR performance of the Fe-NC catalyst through reducing band gap, improving ability to adsorb oxygen, and improving catalytic activity of FeN4 site. This work may give a new insight into regulation rules of heteratom doping on single atom catalysts based on carbon materials.
Heteratom-doped Fe-NC catalyst is promising for highly efficiently oxygen reduction reaction (ORR). In this work, density functional theory with the Vienna Ab initio Simulation Package (VASP) has been employed to systematically study the electronic structure regulation mechanism and oxygen reduction promoting mechanism on sulfur atom doped Fe-NC catalyst. The Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional within a generalized gradient approximation (GGA) was used in this work. The computataional hydrogen electron model was used to calculate the changes in Gibbs free energy. To consider the influence of S doping proportion, we build FeNSx models with 1~4 S atoms. The thermodynamic stability of catalysts was firstly considered based on formation energy, following by electronic structure analysis through Bader charge analysis and densities of states. Then, the oxygen adsorption ability was considered based on oxygen adsorption configurations and energies analyses. At last, reaction overpotentials were calculated based on computational hydrogen electrode model to study activity of catalytic sites. The results show that the catalyst doped with few sulfur atoms around the active sites of FeN4 could remain stable. Three possible ORR promoting mechanisms of S atoms doping were investigated. Firstly, the doping of sulfur atoms would reduce the band gap of the catalyst, thus improving the conductivity of the catalyst, which is beneficial to electrocatalytic oxygen reduction reactions. Secondly, the doping of a small amount of S atoms can improve the affinity between oxygen and the catalysts, which is also important for oxygen reduction reaction. At last, the introduction of four S atoms in the system would reduce the overpotential of ORR, thus improving the activity of the active sites to catalyze the oxygen reduction reaction. Our results predict that few S atoms doping would improve ORR performance of the Fe-NC catalyst through reducing band gap, improving ability to adsorb oxygen, and improving catalytic activity of FeN4 site. This work may give a new insight into regulation rules of heteratom doping on single atom catalysts based on carbon materials.
