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2016 Volume 74 Issue 6
2016, 74(6): 467-471
doi: 10.6023/A16040200
Abstract:
Two-dimensional (2D) organic assemblies possess many intriguing properties such as planar structure, extended surface, flexibility and tailorability. The fabrication of 2D organic structures in a controlled manner is crucial to realize their potential functions and applications. In recent years, we have developed three methods to fabricate 2D organic assemblies through the rational design of building blocks. Firstly, hydrotropic anions will induce cationic bolaamphiphiles to form 2D assemblies, because such anions can insert their hydrophobic parts into the assemblies and weaken the electrostatic repulsion between adjacent headgroups. Secondly, the topology of supra-amphiphiles can be easily tuned because of the dynamic nature of non-covalent bonds, thus providing a facile approach for the fabrication of 2D assemblies. Thirdly, through molecular modification or introduction of new non-covalent bonds, we can lower the dimensionality of three-dimensional (3D) networks to form 2D assemblies. It is highly anticipated that these methods can be further applied for the preparation of functional 2D nano/micro materials for optoelectronics.
Two-dimensional (2D) organic assemblies possess many intriguing properties such as planar structure, extended surface, flexibility and tailorability. The fabrication of 2D organic structures in a controlled manner is crucial to realize their potential functions and applications. In recent years, we have developed three methods to fabricate 2D organic assemblies through the rational design of building blocks. Firstly, hydrotropic anions will induce cationic bolaamphiphiles to form 2D assemblies, because such anions can insert their hydrophobic parts into the assemblies and weaken the electrostatic repulsion between adjacent headgroups. Secondly, the topology of supra-amphiphiles can be easily tuned because of the dynamic nature of non-covalent bonds, thus providing a facile approach for the fabrication of 2D assemblies. Thirdly, through molecular modification or introduction of new non-covalent bonds, we can lower the dimensionality of three-dimensional (3D) networks to form 2D assemblies. It is highly anticipated that these methods can be further applied for the preparation of functional 2D nano/micro materials for optoelectronics.
2016, 74(6): 472-487
doi: 10.6023/A16030153
Abstract:
Diazo compounds represent a type of very important synthetic intermediates, which demonstrate wide applications in organic synthesis, continuous-in-flow technology, polymer synthesis, medicinal chemistry, chemical biology, material science and many other fields. On the other hand, diazo intermediates can be easily prepared from commercial available substrates through facile transformations, such as base-promoted decomposition of N-tosylhydrazones, diazo-transfer reaction, diazotization of alkyl amines, oxidation of hydrazones, decomposition of N-nitroso compounds. Traditional transformations of diazo compounds include nucleophilic addition/substitution by using diazo compounds as the nucleophiles, ylide type reactions, dimerization or olefination, Wolff rearrangement, transition-metal-carbene or carbenoid mediated X—H insertion reactions, catalytic cyclopropanations or cyclopropenations, and the recently developed transition-metal-catalyzed carbenoid cross-coupling reactions. In addition to these classic reactions, the diazo compounds also undergo nitrogen group retaining reactions, in which the diazo moiety is incorporated into the nitrogen-containing moiety in the target molecules. This strategy has provided an efficient and selective synthetic approach towards nitrogen atom containing functional molecules, especially for the synthesis of various N-heterocyclic compounds. Among them, the enantioselective C—N bond forming reaction as well as the asymmetric N-heterocyclic scaffold construction has important synthetic value and remains great challenge to the organic chemists. Thus, nitrogen component retaining reactions of diazo compounds has opened up a superior avenue in organic synthesis. Considering about the significant importance and the great growth in the past decade of this area, this review article will focus on the nitrogen group retaining reaction of diazo compounds. According to the reaction mechanism of these transformations, this review will be divided into the following parts: diazo compounds as nucleophiles, diazo compounds as 1, 3-dipoles in cycloaddition reaction, diazo compounds as electrophiles, intramolecular reactions of vinyldiazo compounds, reduction reaction, and miscellaneous transformation. We hope that this review will corroborate the practical use of this research area as a convenient and valuable synthetic strategy.
Diazo compounds represent a type of very important synthetic intermediates, which demonstrate wide applications in organic synthesis, continuous-in-flow technology, polymer synthesis, medicinal chemistry, chemical biology, material science and many other fields. On the other hand, diazo intermediates can be easily prepared from commercial available substrates through facile transformations, such as base-promoted decomposition of N-tosylhydrazones, diazo-transfer reaction, diazotization of alkyl amines, oxidation of hydrazones, decomposition of N-nitroso compounds. Traditional transformations of diazo compounds include nucleophilic addition/substitution by using diazo compounds as the nucleophiles, ylide type reactions, dimerization or olefination, Wolff rearrangement, transition-metal-carbene or carbenoid mediated X—H insertion reactions, catalytic cyclopropanations or cyclopropenations, and the recently developed transition-metal-catalyzed carbenoid cross-coupling reactions. In addition to these classic reactions, the diazo compounds also undergo nitrogen group retaining reactions, in which the diazo moiety is incorporated into the nitrogen-containing moiety in the target molecules. This strategy has provided an efficient and selective synthetic approach towards nitrogen atom containing functional molecules, especially for the synthesis of various N-heterocyclic compounds. Among them, the enantioselective C—N bond forming reaction as well as the asymmetric N-heterocyclic scaffold construction has important synthetic value and remains great challenge to the organic chemists. Thus, nitrogen component retaining reactions of diazo compounds has opened up a superior avenue in organic synthesis. Considering about the significant importance and the great growth in the past decade of this area, this review article will focus on the nitrogen group retaining reaction of diazo compounds. According to the reaction mechanism of these transformations, this review will be divided into the following parts: diazo compounds as nucleophiles, diazo compounds as 1, 3-dipoles in cycloaddition reaction, diazo compounds as electrophiles, intramolecular reactions of vinyldiazo compounds, reduction reaction, and miscellaneous transformation. We hope that this review will corroborate the practical use of this research area as a convenient and valuable synthetic strategy.
2016, 74(6): 488-497
doi: 10.6023/A16010035
Abstract:
Two-dimensional (2D) materials have attracted broad interest because of their low-dimensional effect, and black phosphorus has become a member of them due to the successful preparation. Phosphorus has several allotropes, white phosphorus, red phosphorus and black phosphorus. Black phosphorus is most thermodynamic stable in them. Black phosphorus was obtained by a phase transition from white or red phosphorus at high pressure and high temperature. It is a natural p-type semiconductor in which each layer is vertically stacked by the van der Waals force. The thickness of black phosphorus can be scaled down to the atomic layer scale known as phosphorene by mechanical exfoliation or liquid exfoliation. In nowadays, pulsed laser deposition (PLD) has also been used in synthesis of phosphorene film. Compared with black phosphorus, phosphorene's physical properties have significant changes. The band gap in bulk black phosphorus is 0.3 eV and can be expanded to 1.0 to 1.5 eV depending on the layer numbers. The range of phosphorene band gap corresponds to an absorption spectrum between visible light to infrared. Moreover, the band gap of phosphorene is also highly sensitive to the strain either in-plane or out-of-plane. The phosphorene based field effect transistor (FET) exhibits a high mobility and appreciably high on/off ratios, and the mobility is thickness dependent. Unlike other two-dimensional (2D) materials, phosphorene has in-plane anisotropy which is suitable for the detecting of polarized light. Hence, the unique properties in black phosphorus, along with its high carrier mobility, make it as a promising material in electronic applications. Nevertheless, the poor chemical and structural stability of black phosphorus and phosphorene raises important concerns. In the past century, the synthesis, physical properties, and device applications have been extensively investigated in various studies. In this review article, a lot of references of black phosphorus are cited to introduce systematically the research progresses of structure and preparation, the study of material properties and device performance, the chemistry of the degradation process and the anti-degradation treatments. At last, the development trend of phosphorene is mentioned.
Two-dimensional (2D) materials have attracted broad interest because of their low-dimensional effect, and black phosphorus has become a member of them due to the successful preparation. Phosphorus has several allotropes, white phosphorus, red phosphorus and black phosphorus. Black phosphorus is most thermodynamic stable in them. Black phosphorus was obtained by a phase transition from white or red phosphorus at high pressure and high temperature. It is a natural p-type semiconductor in which each layer is vertically stacked by the van der Waals force. The thickness of black phosphorus can be scaled down to the atomic layer scale known as phosphorene by mechanical exfoliation or liquid exfoliation. In nowadays, pulsed laser deposition (PLD) has also been used in synthesis of phosphorene film. Compared with black phosphorus, phosphorene's physical properties have significant changes. The band gap in bulk black phosphorus is 0.3 eV and can be expanded to 1.0 to 1.5 eV depending on the layer numbers. The range of phosphorene band gap corresponds to an absorption spectrum between visible light to infrared. Moreover, the band gap of phosphorene is also highly sensitive to the strain either in-plane or out-of-plane. The phosphorene based field effect transistor (FET) exhibits a high mobility and appreciably high on/off ratios, and the mobility is thickness dependent. Unlike other two-dimensional (2D) materials, phosphorene has in-plane anisotropy which is suitable for the detecting of polarized light. Hence, the unique properties in black phosphorus, along with its high carrier mobility, make it as a promising material in electronic applications. Nevertheless, the poor chemical and structural stability of black phosphorus and phosphorene raises important concerns. In the past century, the synthesis, physical properties, and device applications have been extensively investigated in various studies. In this review article, a lot of references of black phosphorus are cited to introduce systematically the research progresses of structure and preparation, the study of material properties and device performance, the chemistry of the degradation process and the anti-degradation treatments. At last, the development trend of phosphorene is mentioned.
2016, 74(6): 498-502
doi: 10.6023/A16040164
Abstract:
Development of straightforward and selective approaches to functionalize vinyl groups is an important and continuing goal. A novel convenient route to vinylhalides or enol esters by a Markovnikov regioselective addition of hydrogen chloride or carboxylic acid to the C≡C bond of alkynes in the presence of an ammonium hydrochloride/B(C6F5)3 catalytic system is reported. Thus, when treated with catalytic amounts of ammonium hydroborate ([TMPH]+[Cl-B(C6F5)3]-), equimolar mixtures of hydrogen chloride and alkynes are converted into a variety of chloroalkenes as monoadducts. The yields of the monoadducts are usually higher than 90% for terminal aromatic alkynes, while for the terminal aliphatic alkynes they are considerably lower, with the worst observed for sterically hindered tert-butylacetylene (only 67%). NMR monitoring of the reaction mixtures reveals that under ambient conditions the main by-products are the corresponding diadducts (gem-dihalides). At higher temperatures (50 ℃) for equimolar alkyne/HCl mixtures or at ambient temperature for alkyne-enriched mixtures, the diadduct formation can be nearly completely suppressed. Noteworthy, that both ammonium and borane (-ate) components of the catalytic system are essential for the conversion success. In the case of trifuoroacetic acid addition to alkynes, presence of the ammonium component is not required, with the reaction yields usually exceeding 95% for terminal aromatic alkynes and being modest to good for the aliphatic ones. The reported catalytic system presents the first example of the "metal-free" catalysts for the selective addition of acids to alkynes.
Development of straightforward and selective approaches to functionalize vinyl groups is an important and continuing goal. A novel convenient route to vinylhalides or enol esters by a Markovnikov regioselective addition of hydrogen chloride or carboxylic acid to the C≡C bond of alkynes in the presence of an ammonium hydrochloride/B(C6F5)3 catalytic system is reported. Thus, when treated with catalytic amounts of ammonium hydroborate ([TMPH]+[Cl-B(C6F5)3]-), equimolar mixtures of hydrogen chloride and alkynes are converted into a variety of chloroalkenes as monoadducts. The yields of the monoadducts are usually higher than 90% for terminal aromatic alkynes, while for the terminal aliphatic alkynes they are considerably lower, with the worst observed for sterically hindered tert-butylacetylene (only 67%). NMR monitoring of the reaction mixtures reveals that under ambient conditions the main by-products are the corresponding diadducts (gem-dihalides). At higher temperatures (50 ℃) for equimolar alkyne/HCl mixtures or at ambient temperature for alkyne-enriched mixtures, the diadduct formation can be nearly completely suppressed. Noteworthy, that both ammonium and borane (-ate) components of the catalytic system are essential for the conversion success. In the case of trifuoroacetic acid addition to alkynes, presence of the ammonium component is not required, with the reaction yields usually exceeding 95% for terminal aromatic alkynes and being modest to good for the aliphatic ones. The reported catalytic system presents the first example of the "metal-free" catalysts for the selective addition of acids to alkynes.
2016, 74(6): 503-512
doi: 10.6023/A16020074
Abstract:
Metal-organic frameworks (MOFs) have attracted enormous research interests not only because of their merits such as high specific surface area, high porosity, and regular pore channels, but also due to their peculiarities of extremely abundant chemical and structural diversity and tunability. In this work, we synthesized MIL-53(Al) and MIL-53(Cr) containing one coordination metal and the novel MIL-53(AlxCr1)(x=1, 2, 3, and 4) MOFs containing two coordination metals as the supports for the Ru-B/MIL-53 catalysts, which were prepared by the facile impregnation-chemical reduction method. In the challenging partial hydrogenation of benzene to cyclohexene, it is revealed that the Al/Cr ratio had pronounced influences on both the initial hydrogenation rate (r0) and the initial selectivity to cyclohexene (S0). In general, MIL-53 containing a higher fraction of Al affords a higher r0, while MIL-53 containing both Al and Cr is conducive to a higher S0 than either MIL-53(Al) or MIL-53(Cr) containing only one coordination metal. On the Ru-B/MIL-53(Al3Cr1) catalyst exhibiting the highest selectivity to cyclohexene, the r0 and S0 were 9.2 mmol/(min·g) and 71%, respectively. The best Ru-B/MIL-53(Al3Cr1) catalyst and the Ru-B/MIL-53(Cr) catalyst displaying the lowest selectivity to cyclohexene were comparatively characterized to have an insight into the difference in their catalytic performance. It is found that while both catalysts had similar Ru/B molar ratio, electronic property, and microstructure, the Ru-B/MIL-53(Al3Cr1) catalyst had higher active surface area (Sact), smaller and more highly dispersed Ru-B nanoparticles (NPs), and stronger metal-support interaction than the Ru-B/MIL-53(Cr) catalyst. The smaller Ru-B NPs could not only provide more active sites for the hydrogenation of benzene, but also be beneficial to the formation of cyclohexene. By further optimization of the reaction conditions, at 180 ℃, H2 pressure of 5.0 MPa, and using 100 mL of ethanolamine as the modifier, a cyclohexene yield of 29% was obtained over the Ru-B/MIL-53(Al3Cr1) catalyst.
Metal-organic frameworks (MOFs) have attracted enormous research interests not only because of their merits such as high specific surface area, high porosity, and regular pore channels, but also due to their peculiarities of extremely abundant chemical and structural diversity and tunability. In this work, we synthesized MIL-53(Al) and MIL-53(Cr) containing one coordination metal and the novel MIL-53(AlxCr1)(x=1, 2, 3, and 4) MOFs containing two coordination metals as the supports for the Ru-B/MIL-53 catalysts, which were prepared by the facile impregnation-chemical reduction method. In the challenging partial hydrogenation of benzene to cyclohexene, it is revealed that the Al/Cr ratio had pronounced influences on both the initial hydrogenation rate (r0) and the initial selectivity to cyclohexene (S0). In general, MIL-53 containing a higher fraction of Al affords a higher r0, while MIL-53 containing both Al and Cr is conducive to a higher S0 than either MIL-53(Al) or MIL-53(Cr) containing only one coordination metal. On the Ru-B/MIL-53(Al3Cr1) catalyst exhibiting the highest selectivity to cyclohexene, the r0 and S0 were 9.2 mmol/(min·g) and 71%, respectively. The best Ru-B/MIL-53(Al3Cr1) catalyst and the Ru-B/MIL-53(Cr) catalyst displaying the lowest selectivity to cyclohexene were comparatively characterized to have an insight into the difference in their catalytic performance. It is found that while both catalysts had similar Ru/B molar ratio, electronic property, and microstructure, the Ru-B/MIL-53(Al3Cr1) catalyst had higher active surface area (Sact), smaller and more highly dispersed Ru-B nanoparticles (NPs), and stronger metal-support interaction than the Ru-B/MIL-53(Cr) catalyst. The smaller Ru-B NPs could not only provide more active sites for the hydrogenation of benzene, but also be beneficial to the formation of cyclohexene. By further optimization of the reaction conditions, at 180 ℃, H2 pressure of 5.0 MPa, and using 100 mL of ethanolamine as the modifier, a cyclohexene yield of 29% was obtained over the Ru-B/MIL-53(Al3Cr1) catalyst.
2016, 74(6): 513-517
doi: 10.6023/A16030136
Abstract:
Telomerase is a ribonucleoprotein complex that is usually activated in the cancer cells and is closely related to telomere maintenance and immortalization of cancer cells. Telomerase activity detection is important for early diagnosis of human cancers as well as the screening of telomerase-target anti-cancer drugs. A new simple and fast method to detect the telomerase activity has been developed based on hybridization chain reaction (HCR) and magnetic separation. In the assay of experiment, the biotin-labeled telomerase substrate is elongated by telomerase generating a special DNA with repeated sequences-(ggttag)n at their terminals. These telomerase elongated products are fixedly connected with streptavidin-coated magnetic beads through the specific combination of streptavidin with biotin. At the same time, other cell extracts are removed by magnetic separation. A specific DNA probe I is designed as the initiator of HCR. 3'-Terminus of DNA probe I is complementary with three repeated sequences of telomerase elongated product. So, DNA probe I could be fixed on magnetic bead through hybridization. 5'-Terminus of DNA probe I is in charge of triggering HCR with DNA probe II and probe III. DNA probe II and probe III are modified with fluorophores. So, the HCR amplification results can be easily detected by fluorescence. All of excessive DNA probes can be removed by magnetic separation. Under the optimal conditions, telomerase activity in 1.0×105 Hela cells has been obviously detected. Because no enzyme involves in the signal amplification process of HCR, our proposed method can effectively avoid the interference of nonspecific amplification which usually exists in the polymerase amplification processes and increase the accuracy of the test results. Furthermore, enzyme-free signal amplification can effectively avoid the potential interference of telomerase inhibitor to the enzyme activity and improve the reliability of screening of telomerase inhibitors.
Telomerase is a ribonucleoprotein complex that is usually activated in the cancer cells and is closely related to telomere maintenance and immortalization of cancer cells. Telomerase activity detection is important for early diagnosis of human cancers as well as the screening of telomerase-target anti-cancer drugs. A new simple and fast method to detect the telomerase activity has been developed based on hybridization chain reaction (HCR) and magnetic separation. In the assay of experiment, the biotin-labeled telomerase substrate is elongated by telomerase generating a special DNA with repeated sequences-(ggttag)n at their terminals. These telomerase elongated products are fixedly connected with streptavidin-coated magnetic beads through the specific combination of streptavidin with biotin. At the same time, other cell extracts are removed by magnetic separation. A specific DNA probe I is designed as the initiator of HCR. 3'-Terminus of DNA probe I is complementary with three repeated sequences of telomerase elongated product. So, DNA probe I could be fixed on magnetic bead through hybridization. 5'-Terminus of DNA probe I is in charge of triggering HCR with DNA probe II and probe III. DNA probe II and probe III are modified with fluorophores. So, the HCR amplification results can be easily detected by fluorescence. All of excessive DNA probes can be removed by magnetic separation. Under the optimal conditions, telomerase activity in 1.0×105 Hela cells has been obviously detected. Because no enzyme involves in the signal amplification process of HCR, our proposed method can effectively avoid the interference of nonspecific amplification which usually exists in the polymerase amplification processes and increase the accuracy of the test results. Furthermore, enzyme-free signal amplification can effectively avoid the potential interference of telomerase inhibitor to the enzyme activity and improve the reliability of screening of telomerase inhibitors.
2016, 74(6): 518-522
doi: 10.6023/A16030158
Abstract:
A series of immobilized laccase-mediator microreactor (LMMR) was prepared in a one-pot process by simultaneously immobilizing Trametes versicolor laccase and acetylacetone (AA) into size-tunable chitosan copper-polyacrylamide hydrogel beads. The polymerization was induced by a laccase-AA-persulfate ternary initiating system and was finished within the chitosan beads at room temperature. The preparation conditions for the LMMR were optimized by an orthogonal array design. The method developed in this work, for the first time, realized the co-immobilization of laccase and mediator in microreactors of tunable size and mechanic strength. Experimental results from scanning electron microscopy and nitrogen adsorption-desorption analysis indicate that the resulting LMMR had a core-shell structure. Chitosan copper served as the mechanical shell, whereas polyacrylamide hydrogel was the core of three-dimensional network. Throughout the hydrogel beads, there were abundant mesopores of size in the range of 2~8 nm. The microreactor beads could endure a 20 N pressure in the axial direction, ensuring the structural integrity in the practical application in wastewater. The loading efficiency of laccase in the microreactor reached up to 93.5%. As compared with the free laccase, the LMMR showed better storage stability and higher tolerance to changes in solution pH and temperature. In the enzymatic conversion of malachite green (MG), benefited from the mediation effect of the immobilized AA, the LMMR still worked after 17 cycling runs (12 h for each cycle), which was 3-fold longer than that of a free laccase-mediator system. The successful recovery of both laccase and mediator is promising to reduce the cost for the application of laccase in wastewater treatment and might be helpful to cut down the secondary pollution from free laccase mediators. These results demonstrate that this novel one-pot synthesis was a useful strategy in the immobilization of laccase. The LMMR has a great potential in large-scale application for dyeing effluent treatment.
A series of immobilized laccase-mediator microreactor (LMMR) was prepared in a one-pot process by simultaneously immobilizing Trametes versicolor laccase and acetylacetone (AA) into size-tunable chitosan copper-polyacrylamide hydrogel beads. The polymerization was induced by a laccase-AA-persulfate ternary initiating system and was finished within the chitosan beads at room temperature. The preparation conditions for the LMMR were optimized by an orthogonal array design. The method developed in this work, for the first time, realized the co-immobilization of laccase and mediator in microreactors of tunable size and mechanic strength. Experimental results from scanning electron microscopy and nitrogen adsorption-desorption analysis indicate that the resulting LMMR had a core-shell structure. Chitosan copper served as the mechanical shell, whereas polyacrylamide hydrogel was the core of three-dimensional network. Throughout the hydrogel beads, there were abundant mesopores of size in the range of 2~8 nm. The microreactor beads could endure a 20 N pressure in the axial direction, ensuring the structural integrity in the practical application in wastewater. The loading efficiency of laccase in the microreactor reached up to 93.5%. As compared with the free laccase, the LMMR showed better storage stability and higher tolerance to changes in solution pH and temperature. In the enzymatic conversion of malachite green (MG), benefited from the mediation effect of the immobilized AA, the LMMR still worked after 17 cycling runs (12 h for each cycle), which was 3-fold longer than that of a free laccase-mediator system. The successful recovery of both laccase and mediator is promising to reduce the cost for the application of laccase in wastewater treatment and might be helpful to cut down the secondary pollution from free laccase mediators. These results demonstrate that this novel one-pot synthesis was a useful strategy in the immobilization of laccase. The LMMR has a great potential in large-scale application for dyeing effluent treatment.
2016, 74(6): 523-528
doi: 10.6023/A16010067
Abstract:
The Re (I) complexes originally reported by Lehn et al. is one of the most important catalysts used for photocatalytical reduction of CO2 in homogeneous system. The mechanism for the photocatalytic reduction of CO2 to CO with Re (I) complexes has been thoroughly investigated recently. In this study, a series of rhenium tricarbonyl catalysts (Re-Me, Re-Ac, Re-Qa and Re-Im) with different substituents on 2, 2-bipyridine ligand were synthesized and characterized. These catalysts were successfully applied to a light induced CO2 reduction system with triethanolamine (TEOA) as sacrificial reagent, exhibiting different turnover numbers for different catalysts. The highest turnover number was achieved for the catalyst of Re-Qa, and Re-Me and Re-Ac exhibit similar activity, while Re-Im exhibits almost no activity in the photocatalytic conversion of CO2 to CO. UV-vis spectra show that the rate of deactivation is linked to the decomposition of the catalysts in the photocatalytic system. No decomposition was observed in the absence of TEOA, suggesting that the deactivation occurs via the intermediate of one-electron-reduced (OER) species. The transient absorption spectra conformed the formation of OER in the catalytic system. The reasons for the highest turnover number of Re-Qa may be attributed to the quaternary ammonium salt group, which can serve as a mediator to facilitate the reduction process. While in the case of Re-Im, the imidazolium group might accelerate the deactivation of OER species by an intramolecular interaction. Further experiments on this effect are the subject of ongoing investigations.
The Re (I) complexes originally reported by Lehn et al. is one of the most important catalysts used for photocatalytical reduction of CO2 in homogeneous system. The mechanism for the photocatalytic reduction of CO2 to CO with Re (I) complexes has been thoroughly investigated recently. In this study, a series of rhenium tricarbonyl catalysts (Re-Me, Re-Ac, Re-Qa and Re-Im) with different substituents on 2, 2-bipyridine ligand were synthesized and characterized. These catalysts were successfully applied to a light induced CO2 reduction system with triethanolamine (TEOA) as sacrificial reagent, exhibiting different turnover numbers for different catalysts. The highest turnover number was achieved for the catalyst of Re-Qa, and Re-Me and Re-Ac exhibit similar activity, while Re-Im exhibits almost no activity in the photocatalytic conversion of CO2 to CO. UV-vis spectra show that the rate of deactivation is linked to the decomposition of the catalysts in the photocatalytic system. No decomposition was observed in the absence of TEOA, suggesting that the deactivation occurs via the intermediate of one-electron-reduced (OER) species. The transient absorption spectra conformed the formation of OER in the catalytic system. The reasons for the highest turnover number of Re-Qa may be attributed to the quaternary ammonium salt group, which can serve as a mediator to facilitate the reduction process. While in the case of Re-Im, the imidazolium group might accelerate the deactivation of OER species by an intramolecular interaction. Further experiments on this effect are the subject of ongoing investigations.
2016, 74(6): 529-537
doi: 10.6023/A16020077
Abstract:
The effect of reaction conditions and acidic property of Beta zeolite on the transalkylation reaction between toluene and trimethylbenzene (TMB) was studied systematically. The results indicate that the activity and stability of catalysts are strongly dependent on the reaction conditions including reactant composition, reaction temperature and pressure, and crystal size as well as the acidic property of the zeolite. For TMB disproportionation reaction, the addition of toluene should be helpful to the increase of selectivity of xylene. In the meantime, for the disproportionation reaction of toluene, the mixing of TMB into feedstocks can also increase the xylene yield. Therefore, the higher yield of xylene is obtained at the equal molar ratio of toluene and TMB as feedstocks. The temperature of reaction plays an important role on the transalkylation of toluene with TMB. The catalytic activity of transalkylation increases gradually with the increasing of reaction temperature until 450 ℃, and then the dealkylation reaction and the formation of coke will be intensified with the further increasing of temperature, which leads to the decrease of catalytic stability. Therefore, the optimum temperature for transalkylation reaction is 450 ℃. The increasing of reaction pressure also has a positive effect on the catalytic activity of transalkylation. Thus, the transalkylation reaction is conducted at the pressure of 3 MPa taking into account the bearing capacity of reactor. The transalkylation catalytic activity is decreased with the increase of Si/Al ratio of Beta zeolite because of the reduction of the amount of acid sites that act as the active sites for transformation of alkylaromatics. The catalytic stability of zeolite could be significantly improved with the decrease of crystal size. In order to investigate the reaction mechanism of transalkylation, gas chromatography-mass spectrometry (GC-MS) technique is used to study the generation and decomposition of intermediate species over Beta zeolite during the transalkylation reaction at the lower experiment temperature of 150 ℃ because the intermediate species is instable at higher reaction temperature. The results indicate that the transalkylation of toluene with 1, 2, 4-TMB occurs via the bimolecular intermediate mechanism. As the bulky species, the formation and decomposition of these intermediate species require a large zeolite channel. Therefore, the Beta zeolite with 12 member-ring large pore shows higher catalytic activity for transalkylation reaction.
The effect of reaction conditions and acidic property of Beta zeolite on the transalkylation reaction between toluene and trimethylbenzene (TMB) was studied systematically. The results indicate that the activity and stability of catalysts are strongly dependent on the reaction conditions including reactant composition, reaction temperature and pressure, and crystal size as well as the acidic property of the zeolite. For TMB disproportionation reaction, the addition of toluene should be helpful to the increase of selectivity of xylene. In the meantime, for the disproportionation reaction of toluene, the mixing of TMB into feedstocks can also increase the xylene yield. Therefore, the higher yield of xylene is obtained at the equal molar ratio of toluene and TMB as feedstocks. The temperature of reaction plays an important role on the transalkylation of toluene with TMB. The catalytic activity of transalkylation increases gradually with the increasing of reaction temperature until 450 ℃, and then the dealkylation reaction and the formation of coke will be intensified with the further increasing of temperature, which leads to the decrease of catalytic stability. Therefore, the optimum temperature for transalkylation reaction is 450 ℃. The increasing of reaction pressure also has a positive effect on the catalytic activity of transalkylation. Thus, the transalkylation reaction is conducted at the pressure of 3 MPa taking into account the bearing capacity of reactor. The transalkylation catalytic activity is decreased with the increase of Si/Al ratio of Beta zeolite because of the reduction of the amount of acid sites that act as the active sites for transformation of alkylaromatics. The catalytic stability of zeolite could be significantly improved with the decrease of crystal size. In order to investigate the reaction mechanism of transalkylation, gas chromatography-mass spectrometry (GC-MS) technique is used to study the generation and decomposition of intermediate species over Beta zeolite during the transalkylation reaction at the lower experiment temperature of 150 ℃ because the intermediate species is instable at higher reaction temperature. The results indicate that the transalkylation of toluene with 1, 2, 4-TMB occurs via the bimolecular intermediate mechanism. As the bulky species, the formation and decomposition of these intermediate species require a large zeolite channel. Therefore, the Beta zeolite with 12 member-ring large pore shows higher catalytic activity for transalkylation reaction.
2016, 74(6): 538-544
doi: 10.6023/A16010053
Abstract:
In living body, Ca2+-responsive ion channels play crucial roles in many biological activities. Inspired by nature, the design and fabrication of artificial smart nanochannels system become a very significant research subject, mimicking the biological Ca2+-responsive signals in ion channels. In this article, by using track-etched artificial polyethylene terephthalate (PET) multiporous membrane materials and modifying intelligent molecules O-Phospho-L-tyrosine (OPLT) through chemical modification method, we demonstrate a new biomimetic artificial smart responsive ion channel system, which presents the cooperative response to pH and calcium. The nanosystem shows ion selective transport, ion gating and ion rectification property, which is similar to the property of biological Ca2+-responsive ion channels. And the cooperative responsive property of pH and calcium in OPLT modified nanochannels was also investigated by measuring the current-voltage (I-V) curves. At a low pH value, the surface charge of the nanochannels walls is positive as a result of the amino group (NH3+) of OPLT, the nanosystem attracts the anions and inhibits the cations due to electrostatic interactions between the anions passing through the nanochannels and the nanochannels cations walls, resulting in ion current rectification property. Meanwhile, after adding calcium to the nanosystem, no significant changes of ion current are found. The system presents no calcium responsive property. At a high pH value, the surface charge of the nanochannels walls is negative due to the phosphate group (HPO42-) of OPLT, the nanosystem shows cations-selective. After adding calcium to the solution, the bonding of phosphate group (HPO42-) with calcium (Ca2+) results in the neutralization of the surface charge in the nanochannels. This nanochannels switch the polarity of ion transport from cation-selective to non-selective, and turn from the highly conductive state to the low conductive state. The significant decline of the ion current can be observed. Thus, the OPLT modified nanofluidic gating device displays the cooperative effect of pH and calcium. This system provides a new idea for the multiple signal induced ion gating in conical nanochannel devices.
In living body, Ca2+-responsive ion channels play crucial roles in many biological activities. Inspired by nature, the design and fabrication of artificial smart nanochannels system become a very significant research subject, mimicking the biological Ca2+-responsive signals in ion channels. In this article, by using track-etched artificial polyethylene terephthalate (PET) multiporous membrane materials and modifying intelligent molecules O-Phospho-L-tyrosine (OPLT) through chemical modification method, we demonstrate a new biomimetic artificial smart responsive ion channel system, which presents the cooperative response to pH and calcium. The nanosystem shows ion selective transport, ion gating and ion rectification property, which is similar to the property of biological Ca2+-responsive ion channels. And the cooperative responsive property of pH and calcium in OPLT modified nanochannels was also investigated by measuring the current-voltage (I-V) curves. At a low pH value, the surface charge of the nanochannels walls is positive as a result of the amino group (NH3+) of OPLT, the nanosystem attracts the anions and inhibits the cations due to electrostatic interactions between the anions passing through the nanochannels and the nanochannels cations walls, resulting in ion current rectification property. Meanwhile, after adding calcium to the nanosystem, no significant changes of ion current are found. The system presents no calcium responsive property. At a high pH value, the surface charge of the nanochannels walls is negative due to the phosphate group (HPO42-) of OPLT, the nanosystem shows cations-selective. After adding calcium to the solution, the bonding of phosphate group (HPO42-) with calcium (Ca2+) results in the neutralization of the surface charge in the nanochannels. This nanochannels switch the polarity of ion transport from cation-selective to non-selective, and turn from the highly conductive state to the low conductive state. The significant decline of the ion current can be observed. Thus, the OPLT modified nanofluidic gating device displays the cooperative effect of pH and calcium. This system provides a new idea for the multiple signal induced ion gating in conical nanochannel devices.
