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2019 Volume 77 Issue 10
2019, 77(10): 951-963
doi: 10.6023/A19040127
Abstract:
Molecular electronics is an interdisciplinary science that mainly studies the charge transport through molecules and its main goal is to fabricate molecular devices with electrical functionalities. In the state-of-art of molecular electronics, the research paradigm is to fabricate electrodes pair with nanometer-sized separation and construct the molecular junction through the assembly of target molecules with the electrodes pair. With this framework, the target molecule can be integrated to the macroscopic measurement circuit. DNA is one of the most significant biomolecules in natural sciences. It had drawn great attentions in biomedicine because of the carried genetic instructions. In molecular electronics, DNA also had attracted much interest due to the distinct structure and its capability of long-range charge transport. Nevertheless, in the early stage of molecular electronics, the probe molecules were limited to those with simple structures and short lengths. In recent years, molecular electronics had witnessed a rapid progress due to the developments in micro/nano-fabrication and the detection for weak current signal. Specifically, it includes the improvements in the success rate, efficiency, and stability of the fabricated molecular device. Benefiting from that, the probe molecules had been extended to a number of complex compounds like DNA. We give a brief introduction to the recent progress in the fabrication of DNA molecular junctions and the studies on the corresponding charge transport, most of which were made by using the research paradigm of fabricating electrodes pair with nanometer-sized separation. According to the fabrication methods that employed, these advances were introduced in two classes. One is that made by the as-called break junction methods, which include STM-break junction, conductive AFM and mechanically controllable break junction. The other is that made by the as-called cutting methods, which include cutting of carbon nanotube, graphene and silicon nanowire. We summarize the historical development of these methods and give a comparison between them. We also introduce some representative research on the charge transport through DNA molecular junction, and discuss the distinct features of DNA in electrical properties compared to the conventional small molecules. To conclude, we give a prospect on the future development of the studies on charge transport through DNA molecular junction.
Molecular electronics is an interdisciplinary science that mainly studies the charge transport through molecules and its main goal is to fabricate molecular devices with electrical functionalities. In the state-of-art of molecular electronics, the research paradigm is to fabricate electrodes pair with nanometer-sized separation and construct the molecular junction through the assembly of target molecules with the electrodes pair. With this framework, the target molecule can be integrated to the macroscopic measurement circuit. DNA is one of the most significant biomolecules in natural sciences. It had drawn great attentions in biomedicine because of the carried genetic instructions. In molecular electronics, DNA also had attracted much interest due to the distinct structure and its capability of long-range charge transport. Nevertheless, in the early stage of molecular electronics, the probe molecules were limited to those with simple structures and short lengths. In recent years, molecular electronics had witnessed a rapid progress due to the developments in micro/nano-fabrication and the detection for weak current signal. Specifically, it includes the improvements in the success rate, efficiency, and stability of the fabricated molecular device. Benefiting from that, the probe molecules had been extended to a number of complex compounds like DNA. We give a brief introduction to the recent progress in the fabrication of DNA molecular junctions and the studies on the corresponding charge transport, most of which were made by using the research paradigm of fabricating electrodes pair with nanometer-sized separation. According to the fabrication methods that employed, these advances were introduced in two classes. One is that made by the as-called break junction methods, which include STM-break junction, conductive AFM and mechanically controllable break junction. The other is that made by the as-called cutting methods, which include cutting of carbon nanotube, graphene and silicon nanowire. We summarize the historical development of these methods and give a comparison between them. We also introduce some representative research on the charge transport through DNA molecular junction, and discuss the distinct features of DNA in electrical properties compared to the conventional small molecules. To conclude, we give a prospect on the future development of the studies on charge transport through DNA molecular junction.
2019, 77(10): 964-976
doi: 10.6023/A19040143
Abstract:
Since the introduction of perovskite solar cells in 2009, perovskite solar cells have developed rapidly due to their low-cost and high theoretical photoelectric conversion efficiency. Among them, the inverted structure of perovskite solar cells has received more and more attention due to its good stability and low hysteresis effect. Since its inception in 2013, its photoelectric conversion efficiency has rapidly increased from the initial 3.9% to 21.5%. However, compared with the traditional upright structure perovskite solar cells, there is still a gap in the photoelectric conversion efficiency of inverted perovskite solar cells. Due to the nature of the organic materials used, perovskites are more severely affected by moisture in the air environment. They are heavily dependent on nitrogen protection during device manufacturing. In the future, if perovskite solar cells are put into production, the fully enclosed waterless environment will obviously increase the production costs. At the same time, the development of large-area preparation technology is still a difficult problem to be solved. The development of inverted perovskite solar cells, the selection of carrier transport materials, interface optimization, and the development of flexible devices are systematically reviewed in this paper. For example, PEDOT:PSS was doped by GeO2 and DMSO, and PEDOT:PSS was modified by MoO3 and GO to improve its work function, acidity and hygroscopicity. A NiOx dense layer is usually doped with Mg2+, Li+ and Cs4+ to increase its conductivity, which can be prepared by different methods such as magnetron sputtering and sol-gel method. The PCBM interface is modified by C60, BCP, LiF etc., to enhance its ohmic contact with the metal counter electrode. And the PCBM is doped by graphene, CoSe, SnO2 etc., to reduce the charge recombination caused by the interfacial resistance and the defects of the perovskite film. This paper would provide a way to obtain a high efficiency inverted perovskite solar cells by structure and material optimization. And it also give insights into the general rules for preparing large area and flexible devices.
Since the introduction of perovskite solar cells in 2009, perovskite solar cells have developed rapidly due to their low-cost and high theoretical photoelectric conversion efficiency. Among them, the inverted structure of perovskite solar cells has received more and more attention due to its good stability and low hysteresis effect. Since its inception in 2013, its photoelectric conversion efficiency has rapidly increased from the initial 3.9% to 21.5%. However, compared with the traditional upright structure perovskite solar cells, there is still a gap in the photoelectric conversion efficiency of inverted perovskite solar cells. Due to the nature of the organic materials used, perovskites are more severely affected by moisture in the air environment. They are heavily dependent on nitrogen protection during device manufacturing. In the future, if perovskite solar cells are put into production, the fully enclosed waterless environment will obviously increase the production costs. At the same time, the development of large-area preparation technology is still a difficult problem to be solved. The development of inverted perovskite solar cells, the selection of carrier transport materials, interface optimization, and the development of flexible devices are systematically reviewed in this paper. For example, PEDOT:PSS was doped by GeO2 and DMSO, and PEDOT:PSS was modified by MoO3 and GO to improve its work function, acidity and hygroscopicity. A NiOx dense layer is usually doped with Mg2+, Li+ and Cs4+ to increase its conductivity, which can be prepared by different methods such as magnetron sputtering and sol-gel method. The PCBM interface is modified by C60, BCP, LiF etc., to enhance its ohmic contact with the metal counter electrode. And the PCBM is doped by graphene, CoSe, SnO2 etc., to reduce the charge recombination caused by the interfacial resistance and the defects of the perovskite film. This paper would provide a way to obtain a high efficiency inverted perovskite solar cells by structure and material optimization. And it also give insights into the general rules for preparing large area and flexible devices.
2019, 77(10): 977-983
doi: 10.6023/A19040139
Abstract:
Persistent Organic Pollutants (POPs), represented by dioxins and dioxin-like polychlorinated biphenyls have the property of teratogenic, carcinogenic and mutagenic, which have been classified as Group A human carcinogen by the international agency for research on cancer (IARC) and put into the initial list of Stockholm Convention managed by the United Nations Environment Program. POPs have posed a threat and impact on food security through the food chain from environment. The conventional detection methods, such as liquid chromatography-tandem mass spectrometry, high resolution gas chromatography-mass spectrometry and two-dimensional gas chromatography with time-of-flight mass spectrometry are sufficiently accurate, but fail to meet the requirements of on-site detection. Meanwhile, the rapid testing technologies for PCBs mainly included fluorescence detection, electrochemical sensors, and so on. As a new type of rapid detection technology, Surface-enhanced Raman Spectroscopy (SERS) has attracted significant attention as a promising analytical technique. With its ultra-sensitivity, high speed detection, ease of operation, SERS is particularly well-suited for the rapid detection of POPs. However, the multiple molecules in matrices may generate interfering Raman signals via competitive adsorption with the target compound on the substrate surface in the SERS detection of real samples. In addition, reproducibility represents a major bottleneck for the widespread application of SERS. Metal nanoparticle colloids are widely used as SERS substrates due to the hot spots formed between the nanoparticles. However, metal nanoparticle aggregation in colloidal solutions is difficult to control, leading to the random formation of hot spots. When the target POPs exist near the hot spots, the intensities of the enhanced Raman signals were unstable. Other factors influenced by the chemical adsorption such as vibration, charge transfer, and the deformation or distortion of molecules also affect the Raman signals. In the review, we provide an overview of the recent advances in SERS for POPs determination, especially the different types of enhanced substrates. And several key technical points of SERS detection including sensitivity, selectivity, and reproducibility have been summarized. Finally, the development of SERS for POPs detection in the future are proposed.
Persistent Organic Pollutants (POPs), represented by dioxins and dioxin-like polychlorinated biphenyls have the property of teratogenic, carcinogenic and mutagenic, which have been classified as Group A human carcinogen by the international agency for research on cancer (IARC) and put into the initial list of Stockholm Convention managed by the United Nations Environment Program. POPs have posed a threat and impact on food security through the food chain from environment. The conventional detection methods, such as liquid chromatography-tandem mass spectrometry, high resolution gas chromatography-mass spectrometry and two-dimensional gas chromatography with time-of-flight mass spectrometry are sufficiently accurate, but fail to meet the requirements of on-site detection. Meanwhile, the rapid testing technologies for PCBs mainly included fluorescence detection, electrochemical sensors, and so on. As a new type of rapid detection technology, Surface-enhanced Raman Spectroscopy (SERS) has attracted significant attention as a promising analytical technique. With its ultra-sensitivity, high speed detection, ease of operation, SERS is particularly well-suited for the rapid detection of POPs. However, the multiple molecules in matrices may generate interfering Raman signals via competitive adsorption with the target compound on the substrate surface in the SERS detection of real samples. In addition, reproducibility represents a major bottleneck for the widespread application of SERS. Metal nanoparticle colloids are widely used as SERS substrates due to the hot spots formed between the nanoparticles. However, metal nanoparticle aggregation in colloidal solutions is difficult to control, leading to the random formation of hot spots. When the target POPs exist near the hot spots, the intensities of the enhanced Raman signals were unstable. Other factors influenced by the chemical adsorption such as vibration, charge transfer, and the deformation or distortion of molecules also affect the Raman signals. In the review, we provide an overview of the recent advances in SERS for POPs determination, especially the different types of enhanced substrates. And several key technical points of SERS detection including sensitivity, selectivity, and reproducibility have been summarized. Finally, the development of SERS for POPs detection in the future are proposed.
2019, 77(10): 984-988
doi: 10.6023/A19060202
Abstract:
Nanopore technology are being developed for large areas in life science, not only in DNA sequencing and protein sequencing, but also in biomolecule detection, bio-interaction measurement and drug screening. Aerolysin is regarded as new powerful tool for oligonucleotide sensing and peptide sensing due to its high charged pore lumen. Applied a transmembrane potential with a pair of Ag/AgCl electrodes, the negatively charged oligonucleotides are driven into the aerolysin nanopore, inducing a series of ionic current blockages, which could distinguish the oligonucleotides with different length or single base variation. However, due to the lack of high-resolution structure of aerolysin nanopore, the mechanism of its high sensing capability is not clear, limiting the further applications of aerolysin. Recently, we presented two sensing regions inside aerolysin, R1 (near R220) and R2 (near K238), having huge influences on oligonucleotide sensing. Especially, the R1 is responsible for distinguished all 4 bases and 2 modified based in the mixture. However, the detailed mechanism of synergistic effect for these two regions in detection of single nucleotides is still unclear. Here, we use dA14-4-X, dA14-11-X, dA14-4-X-11-X (X=C, T, G) as probes to investigate the effects of base types on the sensing ability of R1 and R2. The results show that the A, C or T in R2 region did not change the sensing ability of R1 region, while G in R2 would hinder the base discrimination in R1 region. This may be caused by the large volume of G that would nearly fully occupy the R2 region and the stronger non-covalent interaction between G and R2 region, resulting in determining the residual current of the whole nanopore. Moreover, we evaluated the interaction between different bases with the sensing region. The results show that the interaction is independent with the volume of the bases, which is ordered by A > G > C > T, suggesting the interaction inside the aerolysin lumen is a considerable factor for its sensing capability. These results would guide us to directly design the mutant Aerolysin nanopore that aims for DNA sequencing and peptide sequencing.
Nanopore technology are being developed for large areas in life science, not only in DNA sequencing and protein sequencing, but also in biomolecule detection, bio-interaction measurement and drug screening. Aerolysin is regarded as new powerful tool for oligonucleotide sensing and peptide sensing due to its high charged pore lumen. Applied a transmembrane potential with a pair of Ag/AgCl electrodes, the negatively charged oligonucleotides are driven into the aerolysin nanopore, inducing a series of ionic current blockages, which could distinguish the oligonucleotides with different length or single base variation. However, due to the lack of high-resolution structure of aerolysin nanopore, the mechanism of its high sensing capability is not clear, limiting the further applications of aerolysin. Recently, we presented two sensing regions inside aerolysin, R1 (near R220) and R2 (near K238), having huge influences on oligonucleotide sensing. Especially, the R1 is responsible for distinguished all 4 bases and 2 modified based in the mixture. However, the detailed mechanism of synergistic effect for these two regions in detection of single nucleotides is still unclear. Here, we use dA14-4-X, dA14-11-X, dA14-4-X-11-X (X=C, T, G) as probes to investigate the effects of base types on the sensing ability of R1 and R2. The results show that the A, C or T in R2 region did not change the sensing ability of R1 region, while G in R2 would hinder the base discrimination in R1 region. This may be caused by the large volume of G that would nearly fully occupy the R2 region and the stronger non-covalent interaction between G and R2 region, resulting in determining the residual current of the whole nanopore. Moreover, we evaluated the interaction between different bases with the sensing region. The results show that the interaction is independent with the volume of the bases, which is ordered by A > G > C > T, suggesting the interaction inside the aerolysin lumen is a considerable factor for its sensing capability. These results would guide us to directly design the mutant Aerolysin nanopore that aims for DNA sequencing and peptide sequencing.
2019, 77(10): 989-992
doi: 10.6023/A19060230
Abstract:
Cyclic di-AMP (c-di-AMP) is a ubiquitous second messenger in prokaryotic cells. c-di-AMP can not only effectively regulate various physiological processes such as cell growth, ion transport and cell wall metabolism balance, but also trigger type I interferon response to inspire the body's immune response. Nanopore-based single molecule detection technology is an emerging single molecule detection method which is currently applied to various fields since it has many advantages such as high speed, label-free, high sensitivity and low cost. Aerolysin is a robust biological nanopore with high temporal resolution and high current resolution, which has achieved single oligonucleotide detection, polysaccharide analysis and the studies of enzymolysis kinetics. Aerolysin nanopore is negatively-charged protein nanopore which has numerous negatively charged amino acid residues around its cis entrances. The electrostatic repulsion between the negatively charged c-di-AMP and negatively charged amino acid residues around the cis entrances prevents c-di-AMP entering the nanopore. In this study, 1.0 mol/L LiCl was used as electrolyte solution to facilitate aerolysin analysis of single c-di-AMP molecule. Each event can be characterized by two parameters, the current blockade, I/I0, and the blockade time, τoff. The blockades are classified into two populations as PI and PII. The PI events are assigned to c-di-AMP that bump into the pore and then diffuse away. PII events are assigned to traversing of c-di-AMP through the nanopore. Compared with potassium ions, lithium ion can be more effectively to associate with the negative charges on the aerolysin nanopore surface and reduce the electrostatic repulsion between the c-di-AMP molecule and the Aerolysin. The results showed that number of PI events in per minute was significantly increased in 1.0 mol/L LiCl. The number of PI events in per minute in LiCl is 30 times than that in KCl at 90 mV. Hence, Aerolysin nanopore can be used as an ultrasensitive single molecule sensor for cyclic dinucleotides.
Cyclic di-AMP (c-di-AMP) is a ubiquitous second messenger in prokaryotic cells. c-di-AMP can not only effectively regulate various physiological processes such as cell growth, ion transport and cell wall metabolism balance, but also trigger type I interferon response to inspire the body's immune response. Nanopore-based single molecule detection technology is an emerging single molecule detection method which is currently applied to various fields since it has many advantages such as high speed, label-free, high sensitivity and low cost. Aerolysin is a robust biological nanopore with high temporal resolution and high current resolution, which has achieved single oligonucleotide detection, polysaccharide analysis and the studies of enzymolysis kinetics. Aerolysin nanopore is negatively-charged protein nanopore which has numerous negatively charged amino acid residues around its cis entrances. The electrostatic repulsion between the negatively charged c-di-AMP and negatively charged amino acid residues around the cis entrances prevents c-di-AMP entering the nanopore. In this study, 1.0 mol/L LiCl was used as electrolyte solution to facilitate aerolysin analysis of single c-di-AMP molecule. Each event can be characterized by two parameters, the current blockade, I/I0, and the blockade time, τoff. The blockades are classified into two populations as PI and PII. The PI events are assigned to c-di-AMP that bump into the pore and then diffuse away. PII events are assigned to traversing of c-di-AMP through the nanopore. Compared with potassium ions, lithium ion can be more effectively to associate with the negative charges on the aerolysin nanopore surface and reduce the electrostatic repulsion between the c-di-AMP molecule and the Aerolysin. The results showed that number of PI events in per minute was significantly increased in 1.0 mol/L LiCl. The number of PI events in per minute in LiCl is 30 times than that in KCl at 90 mV. Hence, Aerolysin nanopore can be used as an ultrasensitive single molecule sensor for cyclic dinucleotides.
2019, 77(10): 993-998
doi: 10.6023/A19060210
Abstract:
Functionalized N-carbonylmethylene-2-pyridones are some of the most important structural motifs and exist in many natural products and bioactive compounds. Thus, the efficient construction of such skeletons has attracted much attention. Generally, the synthesis of N-carbonylmethylene-2-pyridones is realized via an intermolecular nucleophilic substitution of 2-hydroxypyridines and appropriate electrophiles. However, the above reactions often suffer from low yields caused by poor O/N chemoselectivities due to the dual nucleophilicity of the 2-hydroxypyridines. As far as the structure is concerned, N-carbonylmethylene-2-pyridones can be divided into three sections:a pyridone, a carbonylmethyl group and a side chain. When the side chain is a H atom, the N-substituted pyridones can be constructed conveniently via a reaction of 2-hydroxypyridines and primary α-bromocarbonyl compounds in high yields with excellent chemoselectivities. However, when the side chain is not a H atom, for example an alkyl group, only limited examples have been reported and only moderate yields of the desired N-substituted pyridine products are obtained by a combination of 2-hydroxypyridines and bulky secondary α-bromocarbonyl compounds, mainly due to the poor O/N chemoselectivities. To achieve a general synthetic pathway for the latter, the following practical strategy was designed. 2-Hydroxypyridines were first treated with primary α-bromocarbonyl compounds to generate the unique N-substituted intermediates in situ, which then reacted with the side chain electrophiles to give only the N-alkylated final products. Thus, a Pd-catalyzed three-component chemospecific allylic substitution cascade has been developed for the synthesis of N-carbonylmethylene-2-pyridone derivatives, with the desired products being obtained in up to 98% yield. No O-alkylated by-product was observed. The results suggested that the N-carbonylmethylene-2-pyridones are constructed via a cascade reaction consisting of a nucleophilic substitution followed by an allylic alkylation. The reaction was performed on a gram scale and the corresponding alkylated product was conveniently converted to a pyridone-containing unnatural amino acid. This methodology allows for the highly chemoselective synthesis of biologically important N-carbonylmethylene-2-pyridone derivatives.
Functionalized N-carbonylmethylene-2-pyridones are some of the most important structural motifs and exist in many natural products and bioactive compounds. Thus, the efficient construction of such skeletons has attracted much attention. Generally, the synthesis of N-carbonylmethylene-2-pyridones is realized via an intermolecular nucleophilic substitution of 2-hydroxypyridines and appropriate electrophiles. However, the above reactions often suffer from low yields caused by poor O/N chemoselectivities due to the dual nucleophilicity of the 2-hydroxypyridines. As far as the structure is concerned, N-carbonylmethylene-2-pyridones can be divided into three sections:a pyridone, a carbonylmethyl group and a side chain. When the side chain is a H atom, the N-substituted pyridones can be constructed conveniently via a reaction of 2-hydroxypyridines and primary α-bromocarbonyl compounds in high yields with excellent chemoselectivities. However, when the side chain is not a H atom, for example an alkyl group, only limited examples have been reported and only moderate yields of the desired N-substituted pyridine products are obtained by a combination of 2-hydroxypyridines and bulky secondary α-bromocarbonyl compounds, mainly due to the poor O/N chemoselectivities. To achieve a general synthetic pathway for the latter, the following practical strategy was designed. 2-Hydroxypyridines were first treated with primary α-bromocarbonyl compounds to generate the unique N-substituted intermediates in situ, which then reacted with the side chain electrophiles to give only the N-alkylated final products. Thus, a Pd-catalyzed three-component chemospecific allylic substitution cascade has been developed for the synthesis of N-carbonylmethylene-2-pyridone derivatives, with the desired products being obtained in up to 98% yield. No O-alkylated by-product was observed. The results suggested that the N-carbonylmethylene-2-pyridones are constructed via a cascade reaction consisting of a nucleophilic substitution followed by an allylic alkylation. The reaction was performed on a gram scale and the corresponding alkylated product was conveniently converted to a pyridone-containing unnatural amino acid. This methodology allows for the highly chemoselective synthesis of biologically important N-carbonylmethylene-2-pyridone derivatives.
2019, 77(10): 999-1007
doi: 10.6023/A19060233
Abstract:
Apigenin-7-O-β-D-glucuronide (1) and scutellarin (scutellarein-7-O-β-D-glucuronide, 2) are two major flavone glucuronide components occurring in breviscapines, which are prepared from the traditional Chinese herb Erigeron breviscapus. These two flavone glycosides show potent anti-oxidative, anti-inflammatory and neuroprotective activities in various evaluations. Synthesis of these natural glycosides in an efficiently manner would facilitate studies on their structure activity relationships. As a persistent effort on the chemical syntheses of the diverse glycoconjugates from traditional Chinese herbs in our group, we report herein the synthesis of these two representative flavone O-glucuronides. It is known that the solubility of flavone compounds is rather low and this property would greatly hinder their glycosylation reactions. In order to increase the solubility of the flavone derivatives in the glycosylation solvents, hexanoyl and benzyl groups were selected as the permanent protecting groups for the hydroxyl groups of apigenin (7) and scutellarein (8). The construction of the phenolic O-glucuronide is known to be a difficult task, especially the glycosylation of the poorly nucleophilic 7-hydroxyl group which locates at the para-position of the flavone carbonyl group. We achieved the glycosylation of the flavone 7-OH with 2, 3, 4-tri-O-benzoyl-6-O-TBDPS-glucopyranosyl ortho-alkynylbenzoate (9) under the catalysis of Ph3PAuNTf2 (0.2 equiv., 4 Å MS, CH2Cl2, r.t., 5 h) in excellent yields. After that, the 6-O-TBDPS groups were removed, and the requisite glucuronides were then elaborated by oxidation of the resulting 6-OH under the conditions of DAIB/TEMPO (CH2Cl2/H2O, V:V=2:1, r.t.) in good yields. After global deprotection, the desired products apigenin-7-O-β-D-glucuronide (1) and scutellarin (2) were obtained in overall yields of 36% (5 steps) and 7% (9 steps), respectively, from the starting flavone aglycones. Following the same strategy, four naturally occurring flavone-7-O-glycosides, namely apigetrin (3), plantaginin (4), apigenin 7-O-β-D-xylopyranoside (5) and apigenin 7-O-α-L-rhamnopyranoside (6), were smoothly synthesized in 4~7 steps with the overall yields of 61%, 13%, 58% and 61%, respectively.
Apigenin-7-O-β-D-glucuronide (1) and scutellarin (scutellarein-7-O-β-D-glucuronide, 2) are two major flavone glucuronide components occurring in breviscapines, which are prepared from the traditional Chinese herb Erigeron breviscapus. These two flavone glycosides show potent anti-oxidative, anti-inflammatory and neuroprotective activities in various evaluations. Synthesis of these natural glycosides in an efficiently manner would facilitate studies on their structure activity relationships. As a persistent effort on the chemical syntheses of the diverse glycoconjugates from traditional Chinese herbs in our group, we report herein the synthesis of these two representative flavone O-glucuronides. It is known that the solubility of flavone compounds is rather low and this property would greatly hinder their glycosylation reactions. In order to increase the solubility of the flavone derivatives in the glycosylation solvents, hexanoyl and benzyl groups were selected as the permanent protecting groups for the hydroxyl groups of apigenin (7) and scutellarein (8). The construction of the phenolic O-glucuronide is known to be a difficult task, especially the glycosylation of the poorly nucleophilic 7-hydroxyl group which locates at the para-position of the flavone carbonyl group. We achieved the glycosylation of the flavone 7-OH with 2, 3, 4-tri-O-benzoyl-6-O-TBDPS-glucopyranosyl ortho-alkynylbenzoate (9) under the catalysis of Ph3PAuNTf2 (0.2 equiv., 4 Å MS, CH2Cl2, r.t., 5 h) in excellent yields. After that, the 6-O-TBDPS groups were removed, and the requisite glucuronides were then elaborated by oxidation of the resulting 6-OH under the conditions of DAIB/TEMPO (CH2Cl2/H2O, V:V=2:1, r.t.) in good yields. After global deprotection, the desired products apigenin-7-O-β-D-glucuronide (1) and scutellarin (2) were obtained in overall yields of 36% (5 steps) and 7% (9 steps), respectively, from the starting flavone aglycones. Following the same strategy, four naturally occurring flavone-7-O-glycosides, namely apigetrin (3), plantaginin (4), apigenin 7-O-β-D-xylopyranoside (5) and apigenin 7-O-α-L-rhamnopyranoside (6), were smoothly synthesized in 4~7 steps with the overall yields of 61%, 13%, 58% and 61%, respectively.
2019, 77(10): 1008-1016
doi: 10.6023/A19060197
Abstract:
Pesticides and their metabolites often coexist in the real environment. The combined toxicity (synergism or antagonism) between pesticide and metabolites directly affects the environment risk assessment of pesticide. Dichlorvos (A) has three main metabolites, 2, 2-dichloroethanol (B), 2, 2-dichloroacetic acid (C) and dimethyl phosphate (D), in water and soil environment. Under different environmental conditions, metabolites with various concentration compositions form a variety of mixtures with dichlorvos. In this paper, five mixture rays with different mixture ratios were selected by optimal experimental design method. A typical aquatic (Vibrio qinghaiensis sp. -Q67) and a soil organisms (Caenorhabditis elegans) were selected as the tested organisms. The photoluminescence inhibitory toxicity (IT) of parent A and its metabolites B, C and D as well as their mixtures to Q67 and the lethal toxicity (LT) to C. elegans at different exposure time and concentration levels were determined by microplate toxicity analysis. The combination index with 95% observation-based confidence intervals was used to evaluate the change of combined toxicity of each mixture ray under different exposure times and the concentration levels. The results showed that the ITs of parent A and two metabolites C and D to Q67 do not change with the exposure time, but the IT of metabolite B at 12 h is significantly larger than that at 0.25 h. However, at two exposure times, the IT of parent A is greater than that of any of metabolites. The LTs of A and B, C and D to C. elegans do not change with the exposure time. The LTs of A, C and D to C. elegans are basically the same and significantly greater than that of B. The ITs of five mixture rays to Q67 at 12 h are significantly greater than those at 0.25 h at various concentration levels. The combined toxicities of the mixture rays to Q67 are concentration additive at low concentration levels and antagonistic at high concentration levels whether at 0.25 h or 12 h. For C. elegans, the LTs of five mixture rays at various concentration levels do not basically change with the exposure time. At two exposure times (12 h and 24 h), the combined toxicities of mixture rays are concentration additive except for the slight antagonism in the rays of R2 and R5.
Pesticides and their metabolites often coexist in the real environment. The combined toxicity (synergism or antagonism) between pesticide and metabolites directly affects the environment risk assessment of pesticide. Dichlorvos (A) has three main metabolites, 2, 2-dichloroethanol (B), 2, 2-dichloroacetic acid (C) and dimethyl phosphate (D), in water and soil environment. Under different environmental conditions, metabolites with various concentration compositions form a variety of mixtures with dichlorvos. In this paper, five mixture rays with different mixture ratios were selected by optimal experimental design method. A typical aquatic (Vibrio qinghaiensis sp. -Q67) and a soil organisms (Caenorhabditis elegans) were selected as the tested organisms. The photoluminescence inhibitory toxicity (IT) of parent A and its metabolites B, C and D as well as their mixtures to Q67 and the lethal toxicity (LT) to C. elegans at different exposure time and concentration levels were determined by microplate toxicity analysis. The combination index with 95% observation-based confidence intervals was used to evaluate the change of combined toxicity of each mixture ray under different exposure times and the concentration levels. The results showed that the ITs of parent A and two metabolites C and D to Q67 do not change with the exposure time, but the IT of metabolite B at 12 h is significantly larger than that at 0.25 h. However, at two exposure times, the IT of parent A is greater than that of any of metabolites. The LTs of A and B, C and D to C. elegans do not change with the exposure time. The LTs of A, C and D to C. elegans are basically the same and significantly greater than that of B. The ITs of five mixture rays to Q67 at 12 h are significantly greater than those at 0.25 h at various concentration levels. The combined toxicities of the mixture rays to Q67 are concentration additive at low concentration levels and antagonistic at high concentration levels whether at 0.25 h or 12 h. For C. elegans, the LTs of five mixture rays at various concentration levels do not basically change with the exposure time. At two exposure times (12 h and 24 h), the combined toxicities of mixture rays are concentration additive except for the slight antagonism in the rays of R2 and R5.
2019, 77(10): 1017-1023
doi: 10.6023/A19060203
Abstract:
The chemical transformation of ZVI micro-surface and the degradation mechanism in the process of synergistic removal of copper ions and methylene blue pollutants by ZVI-Fenton system were studied systematically. The samples of ZVI, before and after reaction in the ZVI/H2O2 and ZVI/H2O2-Cu systems, were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and Fourier Transform infrared spectroscopy (FTIR) to research the changes of ZVI surface structure, Fe and Cu species' chemical conversion. The results showed that the residual corrosion products on the surface of ZVI were more and the corrosion products were mainly Fe3O4 and Fe2O3 after reaction in the ZVI/H2O2 system. However, in the ZVI/H2O2-Cu system, the corrosion effect of ZVI was more significant, but the residual corrosion products of ZVI surface were less, and the proportion of Fe3O4 increased. In addition, the main reduction product of Cu2+ was Cu0, which was accompanied by the generation of CuO. Furthermore, the effects of pH on the removal of pollutants from the five systems (ZVI, ZVI-Cu, H2O2-Cu, ZVI/H2O2 and ZVI/H2O2-Cu) were compared and the changes in TCu and TFe concentrations under different pH conditions were monitored. The results indicated that the ZVI/H2O2-Cu system not only simultaneous effectively remove MB and TCu compared with other three systems, but also enlarged the effective pH range (pH=2.5~5.5) of ZVI-Fenton system. In addition, free radical capture experiments showed that hydroxyl radicals played an important role in the oxidative degradation of methylene blue, and 10 mmol/L tert-butanol could completely capture hydroxyl radicals in the system. Finally, the mechanism of synergistic removal of TCu and MB degradation by ZVI-Fenton system was revealed. The substitution reaction between ZVI and Cu2+, the action of Cu0 and ZVI galvanic cells, the acid corrosion effect, and the redox cycle of iron and copper together accelerate the degradation of MB by the system and promote the conversion of ZVI surface substances. This study provides a theoretical basis for collaborative treatment of industrial complex pollutants.
The chemical transformation of ZVI micro-surface and the degradation mechanism in the process of synergistic removal of copper ions and methylene blue pollutants by ZVI-Fenton system were studied systematically. The samples of ZVI, before and after reaction in the ZVI/H2O2 and ZVI/H2O2-Cu systems, were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and Fourier Transform infrared spectroscopy (FTIR) to research the changes of ZVI surface structure, Fe and Cu species' chemical conversion. The results showed that the residual corrosion products on the surface of ZVI were more and the corrosion products were mainly Fe3O4 and Fe2O3 after reaction in the ZVI/H2O2 system. However, in the ZVI/H2O2-Cu system, the corrosion effect of ZVI was more significant, but the residual corrosion products of ZVI surface were less, and the proportion of Fe3O4 increased. In addition, the main reduction product of Cu2+ was Cu0, which was accompanied by the generation of CuO. Furthermore, the effects of pH on the removal of pollutants from the five systems (ZVI, ZVI-Cu, H2O2-Cu, ZVI/H2O2 and ZVI/H2O2-Cu) were compared and the changes in TCu and TFe concentrations under different pH conditions were monitored. The results indicated that the ZVI/H2O2-Cu system not only simultaneous effectively remove MB and TCu compared with other three systems, but also enlarged the effective pH range (pH=2.5~5.5) of ZVI-Fenton system. In addition, free radical capture experiments showed that hydroxyl radicals played an important role in the oxidative degradation of methylene blue, and 10 mmol/L tert-butanol could completely capture hydroxyl radicals in the system. Finally, the mechanism of synergistic removal of TCu and MB degradation by ZVI-Fenton system was revealed. The substitution reaction between ZVI and Cu2+, the action of Cu0 and ZVI galvanic cells, the acid corrosion effect, and the redox cycle of iron and copper together accelerate the degradation of MB by the system and promote the conversion of ZVI surface substances. This study provides a theoretical basis for collaborative treatment of industrial complex pollutants.
2019, 77(10): 1024-1030
doi: 10.6023/A19050191
Abstract:
In recent years, food safety problems caused by illegal additions in infant foods have received widespread attention. Surface-enhanced Raman scattering (SERS) technique is used to rapidly and non-destructively detect the banned RhB that is usually added in food. In this study, we have prepared g-C3N4/Ag composites via a simple method successfully, their morphology and structure were characterized by transmission electron microscope (TEM), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), fluorescence spectrophotometer and confocal micro-Raman spectrometer (Raman). The g-C3N4 nanosheet possesses good adsorption performance due to its highly delocalized π-conjugated system, which acts as a carrier for Ag nanoparticles. Therefore, Ag nanoparticles are more uniformly and stably distributed on the surface of g-C3N4 nanosheets to form g-C3N4/Ag nanocomposite, which can be used for rapid adsorption and trace detection of RhB. In the experiment, the pH of the test and the absorbed time between the substrate and RhB were optimized. The influence of pH on the SPR of the substrate and the SERS intensity of the probe molecule were investigated in detail. As g-C3N4/Ag nanocomposite shows a significant higher absorption in the visible region around 500 nm than Ag nanoparticles, g-C3N4/Ag nanocomposite is more favorable for SPR absorption. A wide SPR absorption range is achieved due to the synergy between g-C3N4 and Ag nanoparticles, providing an improved SERS enhancement performance. Under the optimal experimental conditions by using RhB as probe molecule, an enhancement factor of 7.6×105 is achieved. Due to the electrostatic interaction and π-π interaction between the substrate and the probe molecules, the substrate can enrich in a large amount of cationic dyes, offering a detection of RhB. The g-C3N4/Ag SERS substrate can be used to detect RhB with a linear relationship from 1.0×10-9 to 1.0×10-6 mol/L and a detection limit as low as 0.39 nmol/L. In addition, the g-C3N4/Ag nanocomposite SERS substrate can also detect trace amounts of RhB molecules in the commercially available rainbow lollipops with a high sensitivity, and the recovery were 93.6%~95.04%. In summary, the g-C3N4/Ag nanocomposite is not only a SERS substrate with high sensitivity, uniformity and stability, but also can be used as a rapid trace detection method of Rhodamine B in real food and environment.
In recent years, food safety problems caused by illegal additions in infant foods have received widespread attention. Surface-enhanced Raman scattering (SERS) technique is used to rapidly and non-destructively detect the banned RhB that is usually added in food. In this study, we have prepared g-C3N4/Ag composites via a simple method successfully, their morphology and structure were characterized by transmission electron microscope (TEM), ultraviolet-visible (UV-Vis), X-ray diffraction (XRD), fluorescence spectrophotometer and confocal micro-Raman spectrometer (Raman). The g-C3N4 nanosheet possesses good adsorption performance due to its highly delocalized π-conjugated system, which acts as a carrier for Ag nanoparticles. Therefore, Ag nanoparticles are more uniformly and stably distributed on the surface of g-C3N4 nanosheets to form g-C3N4/Ag nanocomposite, which can be used for rapid adsorption and trace detection of RhB. In the experiment, the pH of the test and the absorbed time between the substrate and RhB were optimized. The influence of pH on the SPR of the substrate and the SERS intensity of the probe molecule were investigated in detail. As g-C3N4/Ag nanocomposite shows a significant higher absorption in the visible region around 500 nm than Ag nanoparticles, g-C3N4/Ag nanocomposite is more favorable for SPR absorption. A wide SPR absorption range is achieved due to the synergy between g-C3N4 and Ag nanoparticles, providing an improved SERS enhancement performance. Under the optimal experimental conditions by using RhB as probe molecule, an enhancement factor of 7.6×105 is achieved. Due to the electrostatic interaction and π-π interaction between the substrate and the probe molecules, the substrate can enrich in a large amount of cationic dyes, offering a detection of RhB. The g-C3N4/Ag SERS substrate can be used to detect RhB with a linear relationship from 1.0×10-9 to 1.0×10-6 mol/L and a detection limit as low as 0.39 nmol/L. In addition, the g-C3N4/Ag nanocomposite SERS substrate can also detect trace amounts of RhB molecules in the commercially available rainbow lollipops with a high sensitivity, and the recovery were 93.6%~95.04%. In summary, the g-C3N4/Ag nanocomposite is not only a SERS substrate with high sensitivity, uniformity and stability, but also can be used as a rapid trace detection method of Rhodamine B in real food and environment.
2019, 77(10): 1031-1035
doi: 10.6023/A19050192
Abstract:
We demonstrate in this work that the performance of self-assembled monolayer (SAM) molecular devices can be modulated by the composition and supramolecular structure of the molecular layer using mixed self-assembled monolayer strategy. We prepared the mixed monolayer on gold surface (with ca. 1 nm roughness) by co-adsorption of 11-(ferrocenyl)-undecanethiol (FUT, rectifier) and 1-undecanethiol (C11-SH, diluent). Micrometer scale molecular junctions were formed by using indium gallium eutectic alloy (EGaIn) as the top electrode. Electrical characterization of the junction found that the ratio of FUT and C11-SH molecules can tune the rectifying performance of the monolayer device:the higher the proportion of ferrocene is, the better the rectifying performance is. To our surprise, mixed monolayer prepared by 20% C11-SH and 80% FUT mixed solution exhibited higher rectification ratio than pure FUT monolayer, due to reduced leaking current. Surface reflective IR spectroscopy and the monolayer thickness characterization by the ellipsometer revealed loosely packed molecules on the surface in the pure FUT monolayer due to the bulky head group of the FUT and the rough gold substrate. FUT that partially lied down on the surface, or buried in the layer therefore created defects, which in turn become the origin of the leakage current. Upon insertion of C11-SH molecules in between the ferrocene molecules, the molecules in the monolayer become more ordered with the support of the C11-SH, as evidenced by decreased wave number of the C-H stretching mode of methylene group by reflective IR spectroscopy. Meanwhile, an increase in thickness for 80% FUT monolayer relative to pure FUT monolayer implied a better orientation of the FUT molecule in mixed monolayer. The ordered structure and better orientation largely improved the stability and reproducibility of the molecular device, reduced the leaking current and afforded higher rectification ratio. Our approach therefore provides a facile and effective strategy for regulating the performance of monolayer devices by molecule aggregation state.
We demonstrate in this work that the performance of self-assembled monolayer (SAM) molecular devices can be modulated by the composition and supramolecular structure of the molecular layer using mixed self-assembled monolayer strategy. We prepared the mixed monolayer on gold surface (with ca. 1 nm roughness) by co-adsorption of 11-(ferrocenyl)-undecanethiol (FUT, rectifier) and 1-undecanethiol (C11-SH, diluent). Micrometer scale molecular junctions were formed by using indium gallium eutectic alloy (EGaIn) as the top electrode. Electrical characterization of the junction found that the ratio of FUT and C11-SH molecules can tune the rectifying performance of the monolayer device:the higher the proportion of ferrocene is, the better the rectifying performance is. To our surprise, mixed monolayer prepared by 20% C11-SH and 80% FUT mixed solution exhibited higher rectification ratio than pure FUT monolayer, due to reduced leaking current. Surface reflective IR spectroscopy and the monolayer thickness characterization by the ellipsometer revealed loosely packed molecules on the surface in the pure FUT monolayer due to the bulky head group of the FUT and the rough gold substrate. FUT that partially lied down on the surface, or buried in the layer therefore created defects, which in turn become the origin of the leakage current. Upon insertion of C11-SH molecules in between the ferrocene molecules, the molecules in the monolayer become more ordered with the support of the C11-SH, as evidenced by decreased wave number of the C-H stretching mode of methylene group by reflective IR spectroscopy. Meanwhile, an increase in thickness for 80% FUT monolayer relative to pure FUT monolayer implied a better orientation of the FUT molecule in mixed monolayer. The ordered structure and better orientation largely improved the stability and reproducibility of the molecular device, reduced the leaking current and afforded higher rectification ratio. Our approach therefore provides a facile and effective strategy for regulating the performance of monolayer devices by molecule aggregation state.
2019, 77(10): 1036-1044
doi: 10.6023/A19060226
Abstract:
In recent years, fluorescent bioimaging technology has great advantages in the fields of life science research and medical diagnosis because of its advantages of fast and effective, high sensitivity, easy realization of multi-channel imaging and economic efficiency. Organic fluorescent dyes have been widely used as biological imaging reagents due to their excellent photoelectric properties, functional modification, adjustable optical properties, and good biocompatibility. However, conventional organic fluorescent molecules cause aggregation-caused quenching (ACQ) due to π-π stacking in the aggregated state, limiting their bioimaging applications in aggregated or high concentrations. Since the discovery of the unique luminescence phenomenon of aggregation-induced emission (AIE), the ACQ phenomenon of traditional fluorescent materials has been eliminated. Stimulating responsive polymer nanoparticles have been widely used in the life sciences due to their combination of nanoparticle and polymer advantages and their ability to respond intelligently with environmental changes. Therefore, nanomaterials with excellent aggregation-induced emission (AIE) property, environmental stimuli responsiveness and biocompatibility based on AIE molecules and smart responsive polymers have shown attractive application prospects in the life sciences. A kind of multi-responsive AIE-active polymer nanospheres, which were composed of tetraphenylethylene (TPE) and stimuli-responsive poly[N]-2-(diethylamino)-ethyl]acrylamide (PDEAEAM), were constructed in this study. Firstly, a multi-stimulation responsive monomer N-[2-(diethylamino)ethyl]acrylamide (DEAEAM) and TPE derivative tetraphenylethene-4-(12-hydroxydodecyl-2-methylpropionyl) (TPE-BIB) with propionyl bromide were synthesized, respectively, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly[N-[2-(diethylamino)ethyl]acrylamide] (TPE-g-PDEAEAM) was then successfully synthesized by atom transfer radical polymerization (ATRP) using TPE-BIB as initiator. Lastly, polymer nanospheres TPE-g-PDEAEAM of approximately 200 nm were formed by a self-assembling process. The results of the performed experiments showed that the LCST of TPE-g-PDEAEAM in aqueous solution is about 60℃. Meanwhile, the luminescence change of TPE-g-PDEAEAM at different temperatures from 20 to 66℃ was observed. The fluorescence intensity of TPE-g-PDEAEAM firstly decreased with increasing temperature from 20 to 58℃, and the fluorescence intensity increased with increasing temperature from 58 to 66℃. The phase transfer of PDEAEAM in TPE-g-PDEAEAM may be the reason of luminescence change which may lead to the fluorescent temperature response. Moreover, the fluorescence intensity of TPE-g-PDEAEAM nanospheres in aqueous solution increased with increasing temperature pH. Besides, the fluorescence intensity of TPE-g-PDEAEAM decreased dramatically when the volume of CO2 increased from 0.0 to 1.2 mL. Therefore, TPE-g-PDEAEAM was a new temperature and pH/CO2 responsive materials and might be used as multi-functional smart fluorescent sensors. More importantly, the fluorescent signals were significantly strong in HeLa cells after cells were incubated with TPE-g-PDEAEAM for 24 h based on the characteristic of AIE fluorescence and low cytotoxicity. The resultant nanospheres were able to be internalized by the cancer cells and effectively track the HeLa cells for as long as 11 passages. So, the polymer nanomaterial is an ideal living cell fluorescent tracer probe, which is expected to be applied as biosensors, long-term cell traces and medical biomaterials.
In recent years, fluorescent bioimaging technology has great advantages in the fields of life science research and medical diagnosis because of its advantages of fast and effective, high sensitivity, easy realization of multi-channel imaging and economic efficiency. Organic fluorescent dyes have been widely used as biological imaging reagents due to their excellent photoelectric properties, functional modification, adjustable optical properties, and good biocompatibility. However, conventional organic fluorescent molecules cause aggregation-caused quenching (ACQ) due to π-π stacking in the aggregated state, limiting their bioimaging applications in aggregated or high concentrations. Since the discovery of the unique luminescence phenomenon of aggregation-induced emission (AIE), the ACQ phenomenon of traditional fluorescent materials has been eliminated. Stimulating responsive polymer nanoparticles have been widely used in the life sciences due to their combination of nanoparticle and polymer advantages and their ability to respond intelligently with environmental changes. Therefore, nanomaterials with excellent aggregation-induced emission (AIE) property, environmental stimuli responsiveness and biocompatibility based on AIE molecules and smart responsive polymers have shown attractive application prospects in the life sciences. A kind of multi-responsive AIE-active polymer nanospheres, which were composed of tetraphenylethylene (TPE) and stimuli-responsive poly[N]-2-(diethylamino)-ethyl]acrylamide (PDEAEAM), were constructed in this study. Firstly, a multi-stimulation responsive monomer N-[2-(diethylamino)ethyl]acrylamide (DEAEAM) and TPE derivative tetraphenylethene-4-(12-hydroxydodecyl-2-methylpropionyl) (TPE-BIB) with propionyl bromide were synthesized, respectively, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly[N-[2-(diethylamino)ethyl]acrylamide] (TPE-g-PDEAEAM) was then successfully synthesized by atom transfer radical polymerization (ATRP) using TPE-BIB as initiator. Lastly, polymer nanospheres TPE-g-PDEAEAM of approximately 200 nm were formed by a self-assembling process. The results of the performed experiments showed that the LCST of TPE-g-PDEAEAM in aqueous solution is about 60℃. Meanwhile, the luminescence change of TPE-g-PDEAEAM at different temperatures from 20 to 66℃ was observed. The fluorescence intensity of TPE-g-PDEAEAM firstly decreased with increasing temperature from 20 to 58℃, and the fluorescence intensity increased with increasing temperature from 58 to 66℃. The phase transfer of PDEAEAM in TPE-g-PDEAEAM may be the reason of luminescence change which may lead to the fluorescent temperature response. Moreover, the fluorescence intensity of TPE-g-PDEAEAM nanospheres in aqueous solution increased with increasing temperature pH. Besides, the fluorescence intensity of TPE-g-PDEAEAM decreased dramatically when the volume of CO2 increased from 0.0 to 1.2 mL. Therefore, TPE-g-PDEAEAM was a new temperature and pH/CO2 responsive materials and might be used as multi-functional smart fluorescent sensors. More importantly, the fluorescent signals were significantly strong in HeLa cells after cells were incubated with TPE-g-PDEAEAM for 24 h based on the characteristic of AIE fluorescence and low cytotoxicity. The resultant nanospheres were able to be internalized by the cancer cells and effectively track the HeLa cells for as long as 11 passages. So, the polymer nanomaterial is an ideal living cell fluorescent tracer probe, which is expected to be applied as biosensors, long-term cell traces and medical biomaterials.
2019, 77(10): 1045-1053
doi: 10.6023/A19060205
Abstract:
The surface potential of the liquid-vapor interface of water plays a critical role in electrochemistry, interfacial reactivity, and solvation thermodynamics. However, direct experimental measurement of the surface potential of pure water is exceedingly challenging. Here we present a methodology to explore the effect of external electric field on the water surface potential. The methodology contains constant electrostatic potential molecular dynamics simulation[J. Chem. Phys., 126, 084704(2007)], in which, the electrode charges are allowed to fluctuate to keep the potential fixed, as well as a recently developed probe and average method[J. Phys.:Cond. Matter, 28, 464006(2016)] to accurately map out the electrostatic potential across the water surfaces. The methodology is applied to the coexistence of the vapor phase and the liquid phase of the room temperature pure water (described by a simple SPC/E water model) under different magnitudes of E-fields generated from the nearby electrodes, yielding a first-time calculation of the external E-field dependent water surface potential profiles, and the relationship between the water surface potential and the external E-field strength which has been rarely reported. We found an asymmetric effect of external E-field on the surface potential, i.e., the surface potential decreases with increasing the external E-field strength for the water surface close to the cathode, while the surface potential increases with increasing field strength for the surface close to the anode. The water surfaces are also characterized by calculating the number density and dipole polarization density profiles, which depict the presence of the external E-fields induced bulk polarization under high strength field. By comparing the dipole polarization density profiles and the potential profiles, we conclude that the asymmetric effect of external E-field on the surface potential is due to the asymmetric behavior in surface polarization under external E-field for the water surfaces near cathode or anode, and is also due to the polarization within bulk part of the liquid water. The methodology presented in the current study can be easily applied to more advanced water models such as polarizable water models which are beyond the SPC/E used in current work. The achievement of the fundamental data and the physics relationship between the surface potential of water and the applied external E-field could potentially facilitate the advancements in electrodynamics and thermodynamics of the liquid-vapor interfaces.
The surface potential of the liquid-vapor interface of water plays a critical role in electrochemistry, interfacial reactivity, and solvation thermodynamics. However, direct experimental measurement of the surface potential of pure water is exceedingly challenging. Here we present a methodology to explore the effect of external electric field on the water surface potential. The methodology contains constant electrostatic potential molecular dynamics simulation[J. Chem. Phys., 126, 084704(2007)], in which, the electrode charges are allowed to fluctuate to keep the potential fixed, as well as a recently developed probe and average method[J. Phys.:Cond. Matter, 28, 464006(2016)] to accurately map out the electrostatic potential across the water surfaces. The methodology is applied to the coexistence of the vapor phase and the liquid phase of the room temperature pure water (described by a simple SPC/E water model) under different magnitudes of E-fields generated from the nearby electrodes, yielding a first-time calculation of the external E-field dependent water surface potential profiles, and the relationship between the water surface potential and the external E-field strength which has been rarely reported. We found an asymmetric effect of external E-field on the surface potential, i.e., the surface potential decreases with increasing the external E-field strength for the water surface close to the cathode, while the surface potential increases with increasing field strength for the surface close to the anode. The water surfaces are also characterized by calculating the number density and dipole polarization density profiles, which depict the presence of the external E-fields induced bulk polarization under high strength field. By comparing the dipole polarization density profiles and the potential profiles, we conclude that the asymmetric effect of external E-field on the surface potential is due to the asymmetric behavior in surface polarization under external E-field for the water surfaces near cathode or anode, and is also due to the polarization within bulk part of the liquid water. The methodology presented in the current study can be easily applied to more advanced water models such as polarizable water models which are beyond the SPC/E used in current work. The achievement of the fundamental data and the physics relationship between the surface potential of water and the applied external E-field could potentially facilitate the advancements in electrodynamics and thermodynamics of the liquid-vapor interfaces.
2019, 77(10): 1054-1062
doi: 10.6023/A19060219
Abstract:
The mesoporous SBA-15 molecular sieves doped in situ by W with channels parallel to the short axis (W-s-SBA-15) were synthesized by using decane as cosolvent and trimethylbenzene (TMB) as pore-expanding agent, which were used as the supports for the preparation of the Pt/W-s-SBA-15 catalysts. The effect of the loadings of Pt and W on the catalytic performance in glycerol hydrogenolysis to 1, 3-propanediol (1, 3-PDO) was investigated. The morphology, chemical states of Pt and W, and acidity of the catalysts were systematically characterized by using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), CO pulsed adsorption, X-ray photoelectron spectroscopy (XPS), Raman, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), Fourier transform infrared spectroscopy (FT-IR) and FT-IR of adsorbed pyridine analysis (Py-IR). The BET and TEM results revealed that there are two kinds of pores in the structure:the mesoporous channels parallel to the short axis and honeycomb-like macropores. The Pt dispersion and active surface area calculated from CO chemical adsorption, firstly increased and then decreased with the increase in the Pt and W loadings. The highly dispersed tungsten species were assigned to the single-site WO4 on the basis of the characterization results of Raman, UV-Vis DRS, and FT-IR. The XPS results indicated that the amount of the Pt-O-Si/W linkages and the Ptδ+/(Pt0+Ptδ+) ratio are the highest on the 4Pt/W-s-SBA-15(1/480) catalyst which promote the dispersion of the Pt particles on the catalyst surface. With the increase in the loadings of Pt and W, the conversion of glycerol and the conversion of glycerol to liquid products (CTL) increased monotonically, while the selectivity to 1, 3-PDO experienced a volcanic-type evolution. At the reaction temperature of 433 K, H2 pressure of 4.0 MPa, and reaction time of 24 h, the highest yield of 1, 3-PDO of 49.0% was resulted on the 4Pt/W-s-SBA-15(1/480) catalyst. It is identified that the conversion of glycerol on the Pt/W-s-SBA-15 catalysts is proportional to the active surface area of Pt on the catalyst, while the small Pt particle size and the strong synergy between Pt and the highly dispersed WO4 species are advantageous to the formation of 1, 3-PDO.
The mesoporous SBA-15 molecular sieves doped in situ by W with channels parallel to the short axis (W-s-SBA-15) were synthesized by using decane as cosolvent and trimethylbenzene (TMB) as pore-expanding agent, which were used as the supports for the preparation of the Pt/W-s-SBA-15 catalysts. The effect of the loadings of Pt and W on the catalytic performance in glycerol hydrogenolysis to 1, 3-propanediol (1, 3-PDO) was investigated. The morphology, chemical states of Pt and W, and acidity of the catalysts were systematically characterized by using Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), CO pulsed adsorption, X-ray photoelectron spectroscopy (XPS), Raman, ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS), Fourier transform infrared spectroscopy (FT-IR) and FT-IR of adsorbed pyridine analysis (Py-IR). The BET and TEM results revealed that there are two kinds of pores in the structure:the mesoporous channels parallel to the short axis and honeycomb-like macropores. The Pt dispersion and active surface area calculated from CO chemical adsorption, firstly increased and then decreased with the increase in the Pt and W loadings. The highly dispersed tungsten species were assigned to the single-site WO4 on the basis of the characterization results of Raman, UV-Vis DRS, and FT-IR. The XPS results indicated that the amount of the Pt-O-Si/W linkages and the Ptδ+/(Pt0+Ptδ+) ratio are the highest on the 4Pt/W-s-SBA-15(1/480) catalyst which promote the dispersion of the Pt particles on the catalyst surface. With the increase in the loadings of Pt and W, the conversion of glycerol and the conversion of glycerol to liquid products (CTL) increased monotonically, while the selectivity to 1, 3-PDO experienced a volcanic-type evolution. At the reaction temperature of 433 K, H2 pressure of 4.0 MPa, and reaction time of 24 h, the highest yield of 1, 3-PDO of 49.0% was resulted on the 4Pt/W-s-SBA-15(1/480) catalyst. It is identified that the conversion of glycerol on the Pt/W-s-SBA-15 catalysts is proportional to the active surface area of Pt on the catalyst, while the small Pt particle size and the strong synergy between Pt and the highly dispersed WO4 species are advantageous to the formation of 1, 3-PDO.
