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2017 Volume 33 Issue 7
2017, 75(7): 655-670
doi: 10.6023/A17040181
Abstract:
Transition-metal-catalyzed asymmetric transformations are among the most powerful and straightforward strategies to access various enantioenriched compounds.Hence, considerable efforts have been focused on the development of novel chiral ligands capable of highly efficient and enantioselective catalysis.The importance of olefin as ligand in transition-metal-catalyzed reactions wasn't realized until the report of the Zeise'salt in 1827.Nevertheless, application of chiral olefins as ligands for asymmetric catalysis has been overlooked for quite a long time owing to their relatively weak binding affinity toward the central metal.Since the groundbreaking work of Hayashi and Carreira in 2003~2004, chiral dienes as steering ligands in asymmetric catalysis have emerged as a fascinating new field.Given the weak coordination ability of olefins to transition-metals, functional groups with high coordination ability were considered to incorporate into the olefin framework to create a new type of hybrid olefin ligands for asymmetric catalysis.Over the past few years, a diverse range of hybrid olefin ligands were developed for various enantioselective transformations.Among these, phosphorus-based olefins represent a particularly interesting class of ligands since the first concept demonstration by Grützmacher in 2004, combining the strong coordinating phosphorus atom and the weak coordinating olefin into one ligand molecule.Typically, three structurally different types of phosphorus-based olefins are known in the literature, including phosphine-olefins, phosphoramidite/phosphinamidite-olefins, and phosphite/phosphinite-olefins.They have been successfully utilized in a series of transition-metal-catalyzed asymmetric reactions, such as iridium-catalyzed asymmetric hydrogenation of imines, allylic substitution; rhodium-catalyzed conjugate addition of organoboron reagents to α, β-unsaturated compounds, 1, 2-addition of organoboron reagents to imines/carbonyl compounds, intramolecular hydroacylation; and palladium-catalyzed asymmetric allylic alkylation/amination/etherification of allylic esters, as well as Suzuki-coupling reactions.In many cases, the reactions occur with high enantioselectivities, allows for access to a broad range of valuable chiral products.This paper reviews the literatures in this field and summarizes the remarkable progress and advances in the use of various P-olefins as powerful ligands for diverse transition metal-catalyzed asymmetric transformations since 2004.The aim is to offer an overview of the recent achievements in the rational design and development of new hybrid chiral olefin ligands for effective enantioselective catalysis.We hope that the current success of chiral phosphorus-olefin catalysis would provide an exciting opportunity for future exploration of chiral olefin ligands in a wide variety of asymmetric reactions.
Transition-metal-catalyzed asymmetric transformations are among the most powerful and straightforward strategies to access various enantioenriched compounds.Hence, considerable efforts have been focused on the development of novel chiral ligands capable of highly efficient and enantioselective catalysis.The importance of olefin as ligand in transition-metal-catalyzed reactions wasn't realized until the report of the Zeise'salt in 1827.Nevertheless, application of chiral olefins as ligands for asymmetric catalysis has been overlooked for quite a long time owing to their relatively weak binding affinity toward the central metal.Since the groundbreaking work of Hayashi and Carreira in 2003~2004, chiral dienes as steering ligands in asymmetric catalysis have emerged as a fascinating new field.Given the weak coordination ability of olefins to transition-metals, functional groups with high coordination ability were considered to incorporate into the olefin framework to create a new type of hybrid olefin ligands for asymmetric catalysis.Over the past few years, a diverse range of hybrid olefin ligands were developed for various enantioselective transformations.Among these, phosphorus-based olefins represent a particularly interesting class of ligands since the first concept demonstration by Grützmacher in 2004, combining the strong coordinating phosphorus atom and the weak coordinating olefin into one ligand molecule.Typically, three structurally different types of phosphorus-based olefins are known in the literature, including phosphine-olefins, phosphoramidite/phosphinamidite-olefins, and phosphite/phosphinite-olefins.They have been successfully utilized in a series of transition-metal-catalyzed asymmetric reactions, such as iridium-catalyzed asymmetric hydrogenation of imines, allylic substitution; rhodium-catalyzed conjugate addition of organoboron reagents to α, β-unsaturated compounds, 1, 2-addition of organoboron reagents to imines/carbonyl compounds, intramolecular hydroacylation; and palladium-catalyzed asymmetric allylic alkylation/amination/etherification of allylic esters, as well as Suzuki-coupling reactions.In many cases, the reactions occur with high enantioselectivities, allows for access to a broad range of valuable chiral products.This paper reviews the literatures in this field and summarizes the remarkable progress and advances in the use of various P-olefins as powerful ligands for diverse transition metal-catalyzed asymmetric transformations since 2004.The aim is to offer an overview of the recent achievements in the rational design and development of new hybrid chiral olefin ligands for effective enantioselective catalysis.We hope that the current success of chiral phosphorus-olefin catalysis would provide an exciting opportunity for future exploration of chiral olefin ligands in a wide variety of asymmetric reactions.
2017, 75(7): 671-674
doi: 10.6023/A17030129
Abstract:
Single entity electrochemistry (SEC) has been attracting increasing interests over the past few years because of its extremely high sensitivity.This method offers the penetrating insights into the properties of individual entities that are masked in traditional ensemble measurements.Electrocatalytic amplification, blocking and direct electrochemical reaction of individual entities by detecting the current transients were employed as single entity collides at an electrode.However, it remains a challenge to enhance the current resolution in the SEC field, especially for the complex electrochemical behaviors.In this work, a strategy using a small-sized ultramicroelectrode and nanoelectrode was performed to reduce both background current and collision frequency, which allowed to reach the typical electrochemical signals.A low-noise electrochemical measurement system was used to acquire the data of single silver nanoparticles (AgNPs) collision at 480 nm Pt nanoelectrode and 10 μm ultramicroelectrode.The electrochemical measurement was carried out in 20 mmol·L-1 phosphate buffer (pH=7.4) at an applied potential of+0.6 V vs.Ag/AgCl wire in the presence of 58 nm AgNPs.The sampling rate was of 100 kHz by using an A/D convertor and the low-pass fitter was set at 5 kHz.Signal-noise ratio was improved by 50% when the diameter of working electrode decreased from 10 μm to 480 nm, resulting in more detailed information available at nanoelectrode during the collision processes of individual AgNPs.Both the employed nanoelectrode as working electrode and low-noise electrochemical measurement platform can significantly enhance the current resolution of SEC.High current resolution signals with picoampere and sub-millisecond sensitivity were observed for electrochemical oxidation of single AgNPs on nanoelectrode.In addition, the experimentally observed collision frequencies at varying size of ultramicroelectrode and nanoelectrode were in reasonable agreement with the theoretically calculated ones by Fick's Diffusion Laws within a typical variation associated with stochastic measurements.The electrochemical result indicate that individual AgNPs collisions are governed mainly by diffusion process.The high accuracy of the proposed current signal makes it possible to understand the electrochemical behavior of individual AgNPs as a function of the dwell time.Our results have demonstrated that the nanoelectrode would be a powerful platform for better delivering a complete picture of electrochemical behavior of individual entities, visualization of the electrons transfer process at single entity level.
Single entity electrochemistry (SEC) has been attracting increasing interests over the past few years because of its extremely high sensitivity.This method offers the penetrating insights into the properties of individual entities that are masked in traditional ensemble measurements.Electrocatalytic amplification, blocking and direct electrochemical reaction of individual entities by detecting the current transients were employed as single entity collides at an electrode.However, it remains a challenge to enhance the current resolution in the SEC field, especially for the complex electrochemical behaviors.In this work, a strategy using a small-sized ultramicroelectrode and nanoelectrode was performed to reduce both background current and collision frequency, which allowed to reach the typical electrochemical signals.A low-noise electrochemical measurement system was used to acquire the data of single silver nanoparticles (AgNPs) collision at 480 nm Pt nanoelectrode and 10 μm ultramicroelectrode.The electrochemical measurement was carried out in 20 mmol·L-1 phosphate buffer (pH=7.4) at an applied potential of+0.6 V vs.Ag/AgCl wire in the presence of 58 nm AgNPs.The sampling rate was of 100 kHz by using an A/D convertor and the low-pass fitter was set at 5 kHz.Signal-noise ratio was improved by 50% when the diameter of working electrode decreased from 10 μm to 480 nm, resulting in more detailed information available at nanoelectrode during the collision processes of individual AgNPs.Both the employed nanoelectrode as working electrode and low-noise electrochemical measurement platform can significantly enhance the current resolution of SEC.High current resolution signals with picoampere and sub-millisecond sensitivity were observed for electrochemical oxidation of single AgNPs on nanoelectrode.In addition, the experimentally observed collision frequencies at varying size of ultramicroelectrode and nanoelectrode were in reasonable agreement with the theoretically calculated ones by Fick's Diffusion Laws within a typical variation associated with stochastic measurements.The electrochemical result indicate that individual AgNPs collisions are governed mainly by diffusion process.The high accuracy of the proposed current signal makes it possible to understand the electrochemical behavior of individual AgNPs as a function of the dwell time.Our results have demonstrated that the nanoelectrode would be a powerful platform for better delivering a complete picture of electrochemical behavior of individual entities, visualization of the electrons transfer process at single entity level.
2017, 75(7): 675-678
doi: 10.6023/A17040191
Abstract:
Solid-state nanopore has emerging as a promising tool for detection and analysis of single molecules due to its advantages of high stability, easy control of diameter and channel length, and the potential for integration into devices and arrays.Therefore, there are intensive studies regarding nanopore-based detection of DNAs, proteins, polymers and other small molecules.The electrochemical confined space of nanopore could efficiently convert the information in single biological molecules with anisotropy characters into measurable electrochemical signatures with high temporal resolution.The anisotropy characters of each analyte, due to its featured physical and chemical properties in different directions, strongly affects the translocation behavior of each single entity (single molecule, single nanoparticle, etc.).To analyze the single-entity anisotropy effects on nanopore translocation, here, we employed gold nanorods (GNRs) as a model for single entities with anisotropy to investigate its translocation behavior through a solid-state nanopore.We performed the GNRs translocation experiments in 10 mmol·L-1 KCl (pH 8) electrolyte solution with a 100 nm SiNx solid-state nanopore.The current trace of GNRs translocation through nanopores had been recorded with an ultra-sensitive current amplifier at a sampling rate of 100 kHz filtered at 5 kHz via a low-pass Bessel filter.At applied voltage of-600 mV, two types of characteristic current blockades were observed when single GNRs translocate through the pore.We found this two types of blockades are mainly related to two translocation orientation of GNRs due to its anisotropy.The smaller current blockades are due to the GNR passing through the pore vertically while the larger current blockades are due to the GNR passing through the pore horizontally.To verify our observation of this two types of GNRs translocation events, we employed a simple model which is based on the relationship between the blockade magnitude and the exclude ion volume.The calculated current blockades of two types of GNRs translocation events agree well with the experimental values.These results illustrate that the anisotropy of single entity is an important factor that should be taken into consideration in nanopore translocation.This work will lead to a better understanding of the translocation behavior of single entity with anisotropy in the electrochemical confined space of nanopore.Such understanding is vital to the development of the solid-state nanopore system as a useful single molecule analytical device.
Solid-state nanopore has emerging as a promising tool for detection and analysis of single molecules due to its advantages of high stability, easy control of diameter and channel length, and the potential for integration into devices and arrays.Therefore, there are intensive studies regarding nanopore-based detection of DNAs, proteins, polymers and other small molecules.The electrochemical confined space of nanopore could efficiently convert the information in single biological molecules with anisotropy characters into measurable electrochemical signatures with high temporal resolution.The anisotropy characters of each analyte, due to its featured physical and chemical properties in different directions, strongly affects the translocation behavior of each single entity (single molecule, single nanoparticle, etc.).To analyze the single-entity anisotropy effects on nanopore translocation, here, we employed gold nanorods (GNRs) as a model for single entities with anisotropy to investigate its translocation behavior through a solid-state nanopore.We performed the GNRs translocation experiments in 10 mmol·L-1 KCl (pH 8) electrolyte solution with a 100 nm SiNx solid-state nanopore.The current trace of GNRs translocation through nanopores had been recorded with an ultra-sensitive current amplifier at a sampling rate of 100 kHz filtered at 5 kHz via a low-pass Bessel filter.At applied voltage of-600 mV, two types of characteristic current blockades were observed when single GNRs translocate through the pore.We found this two types of blockades are mainly related to two translocation orientation of GNRs due to its anisotropy.The smaller current blockades are due to the GNR passing through the pore vertically while the larger current blockades are due to the GNR passing through the pore horizontally.To verify our observation of this two types of GNRs translocation events, we employed a simple model which is based on the relationship between the blockade magnitude and the exclude ion volume.The calculated current blockades of two types of GNRs translocation events agree well with the experimental values.These results illustrate that the anisotropy of single entity is an important factor that should be taken into consideration in nanopore translocation.This work will lead to a better understanding of the translocation behavior of single entity with anisotropy in the electrochemical confined space of nanopore.Such understanding is vital to the development of the solid-state nanopore system as a useful single molecule analytical device.
2017, 75(7): 679-685
doi: 10.6023/A17040169
Abstract:
The phase transition behavior of zeolite Y (HY and NaY) to zeolite MER in the KOH solution under hydrothermal conditions was systematically investigated.Zeolite MER has four types of 8-membered ring channels (3.1 Å×3.5 Å, 2.7 Å×3.6 Å, 3.4 Å×5.1 Å, 3.3 Å×3.3 Å) and important potential applications in small molecule catalysis and separation.Seven to ten days are needed to synthesize highly crystalline zeolite MER with traditional hydrothermal synthesis.With phase transition of zeolite Y in the KOH solution under hydrothermal treatment, highly crystalline zeolite MER can be obtained within two days.The synthetic system contains zeolite Y (HY and NaY), KOH, and water, where KOH/SiO2 and H2O/SiO2 are changeable.Hydrothermally treating the equivalent amorphous aluminosilicate gel resulted in the mixture of zeolite MER and zeolite LTL (for HY) or zeolite CHA (for NaY) with low degree of crystallinity.Phase transition of HY can be conducted at either 100 or 150℃, whereas that of NaY can only be conducted at 150℃.As a common process for the hydrothermal phase transition of zeolite Y to zeolite MER in the absence of organic templates, potassium hydroxide was first dissolved into deionized H2O.After stirring at room temperature for 5 min, zeolite Y (HY or NaY) as aluminum and silicon sources was introduced into the potassium hydroxide solution.After further stirring for 1 h, the mixture was transferred into an autoclave for crystallization at elevated temperature (i.e.100 or 150℃).After filtrating, washing with deionized water and drying, zeolite products were obtained.The zeolite products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and inductively coupled plasma emission spectrometer (ICP).KOH/SiO2 and H2O/SiO2 have significant influence on the phase transition behavior of zeolite Y.Highly crystalline zeolite MER can only be obtained with the optimized KOH/SiO2 and H2O/SiO2.With this method, the synthesis period of zeolite MER is greatly reduced, which might be applied to the synthesis of other industrially important zeolites in a shortened time.
The phase transition behavior of zeolite Y (HY and NaY) to zeolite MER in the KOH solution under hydrothermal conditions was systematically investigated.Zeolite MER has four types of 8-membered ring channels (3.1 Å×3.5 Å, 2.7 Å×3.6 Å, 3.4 Å×5.1 Å, 3.3 Å×3.3 Å) and important potential applications in small molecule catalysis and separation.Seven to ten days are needed to synthesize highly crystalline zeolite MER with traditional hydrothermal synthesis.With phase transition of zeolite Y in the KOH solution under hydrothermal treatment, highly crystalline zeolite MER can be obtained within two days.The synthetic system contains zeolite Y (HY and NaY), KOH, and water, where KOH/SiO2 and H2O/SiO2 are changeable.Hydrothermally treating the equivalent amorphous aluminosilicate gel resulted in the mixture of zeolite MER and zeolite LTL (for HY) or zeolite CHA (for NaY) with low degree of crystallinity.Phase transition of HY can be conducted at either 100 or 150℃, whereas that of NaY can only be conducted at 150℃.As a common process for the hydrothermal phase transition of zeolite Y to zeolite MER in the absence of organic templates, potassium hydroxide was first dissolved into deionized H2O.After stirring at room temperature for 5 min, zeolite Y (HY or NaY) as aluminum and silicon sources was introduced into the potassium hydroxide solution.After further stirring for 1 h, the mixture was transferred into an autoclave for crystallization at elevated temperature (i.e.100 or 150℃).After filtrating, washing with deionized water and drying, zeolite products were obtained.The zeolite products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and inductively coupled plasma emission spectrometer (ICP).KOH/SiO2 and H2O/SiO2 have significant influence on the phase transition behavior of zeolite Y.Highly crystalline zeolite MER can only be obtained with the optimized KOH/SiO2 and H2O/SiO2.With this method, the synthesis period of zeolite MER is greatly reduced, which might be applied to the synthesis of other industrially important zeolites in a shortened time.
2017, 75(7): 686-691
doi: 10.6023/A17030134
Abstract:
The selective hydrogenation of carbonyl groups of the conjugated carbonyl compounds is an important reaction in the pharmaceutical and chemical industries, and several selective hydrogenation approaches have been developed.Using stoichiometric hydrides (LiAlH4, NaBH4, etc.) as hydrogenation reagents has some shortcomings, including the unsatisfied selectivity of target product owing to the simultaneous hydrogenation of conjugated double bonds and carbonyl groups, as well as the flammability and explosibility of hydrides.Hydrogen is an alternative hydrogenation reagent, which can selectively hydrogenate carbonyl groups by homogeneous and heterogeneous catalytic processes.The noble metal (Ru, Pd, etc.) complexes were usually used in the homogeneous catalytic process, which caused some serious issues such as the metal residues in products and the difficulties of recovering precious catalysts.These problems can be effectively solved by the heterogeneous catalytic process using the supported catalysts.Carbon-based materials, metal oxides and β-Zeolite are commonly used supports.Among them, carbon-based materials are preferable due to their features of abundant morphologies and structures, good stability, adjustable specific surface areas and pore structures, easy doping, etc.Interestingly, the introduction of heteroatoms into carbon matrix can provide a plenty of anchoring sites to disperse catalytically active species and regulate the interaction between active species and support, and hence promotes their catalytic properties.In addition, the high specific surface areas of the supports are beneficial to the dispersion of the catalytically active species.In recent years, our group has developed hierarchical carbon-based nanocages by in situ MgO template method.The mesostructured nanocages feature the high specific surface area, coexisting micro-meso-macropore structure, rich defects, easy doping, etc., which demonstrated excellent electrochemical performance in energy conversion and storage.Herein, taking advantage of the anchoring functions of nitrogen heteroatoms and high specific surface area of nitrogen-doped carbon nanocage (hNCNC), 10 wt% Ru/hNCNC catalyst was conveniently prepared by microwave-assisted ethylene glycol reduction.The Ru nanoparticles of ca.2.4 nm are highly dispersed on the outer surface of hNCNC.As the catalyst for the selective hydrogenation of acetophenone to 1-phenylethanol, Ru/hNCNC exhibits excellent catalytic activity, selectivity and recyclability in mild conditions of 50.0℃ and 2.0 MPa H2.Specifically, after 2.0 h of reaction, the conversion of acetophenone is up to 96.2%, obviously higher than that of Ru/carbon nanocages (Ru/hCNC, 80%) and Ru/AC (0.7%), and the selectivity of 1-phenylethanol is 95.8%.More importantly, after recycle use for 6 times, the conversion of acetophenone only slightly drops from 96.2% to 94.0% for Ru/hNCNC, while obviously decreases from 80.0% to 63.0% for Ru/hCNC.Such excellent catalytic performance of Ru/hNCNC could be ascribed to the synergism of (ⅰ) the high dispersion of Ru nanoparticles owing to the high specific surface area and nitrogen doping of hNCNC, (ⅱ) the regulated electron structure of Ru catalyst owing to nitrogen incorporation, ⅲ) the facilitated mass transportation by unique hierarchical pore structures of hNCNC support.
The selective hydrogenation of carbonyl groups of the conjugated carbonyl compounds is an important reaction in the pharmaceutical and chemical industries, and several selective hydrogenation approaches have been developed.Using stoichiometric hydrides (LiAlH4, NaBH4, etc.) as hydrogenation reagents has some shortcomings, including the unsatisfied selectivity of target product owing to the simultaneous hydrogenation of conjugated double bonds and carbonyl groups, as well as the flammability and explosibility of hydrides.Hydrogen is an alternative hydrogenation reagent, which can selectively hydrogenate carbonyl groups by homogeneous and heterogeneous catalytic processes.The noble metal (Ru, Pd, etc.) complexes were usually used in the homogeneous catalytic process, which caused some serious issues such as the metal residues in products and the difficulties of recovering precious catalysts.These problems can be effectively solved by the heterogeneous catalytic process using the supported catalysts.Carbon-based materials, metal oxides and β-Zeolite are commonly used supports.Among them, carbon-based materials are preferable due to their features of abundant morphologies and structures, good stability, adjustable specific surface areas and pore structures, easy doping, etc.Interestingly, the introduction of heteroatoms into carbon matrix can provide a plenty of anchoring sites to disperse catalytically active species and regulate the interaction between active species and support, and hence promotes their catalytic properties.In addition, the high specific surface areas of the supports are beneficial to the dispersion of the catalytically active species.In recent years, our group has developed hierarchical carbon-based nanocages by in situ MgO template method.The mesostructured nanocages feature the high specific surface area, coexisting micro-meso-macropore structure, rich defects, easy doping, etc., which demonstrated excellent electrochemical performance in energy conversion and storage.Herein, taking advantage of the anchoring functions of nitrogen heteroatoms and high specific surface area of nitrogen-doped carbon nanocage (hNCNC), 10 wt% Ru/hNCNC catalyst was conveniently prepared by microwave-assisted ethylene glycol reduction.The Ru nanoparticles of ca.2.4 nm are highly dispersed on the outer surface of hNCNC.As the catalyst for the selective hydrogenation of acetophenone to 1-phenylethanol, Ru/hNCNC exhibits excellent catalytic activity, selectivity and recyclability in mild conditions of 50.0℃ and 2.0 MPa H2.Specifically, after 2.0 h of reaction, the conversion of acetophenone is up to 96.2%, obviously higher than that of Ru/carbon nanocages (Ru/hCNC, 80%) and Ru/AC (0.7%), and the selectivity of 1-phenylethanol is 95.8%.More importantly, after recycle use for 6 times, the conversion of acetophenone only slightly drops from 96.2% to 94.0% for Ru/hNCNC, while obviously decreases from 80.0% to 63.0% for Ru/hCNC.Such excellent catalytic performance of Ru/hNCNC could be ascribed to the synergism of (ⅰ) the high dispersion of Ru nanoparticles owing to the high specific surface area and nitrogen doping of hNCNC, (ⅱ) the regulated electron structure of Ru catalyst owing to nitrogen incorporation, ⅲ) the facilitated mass transportation by unique hierarchical pore structures of hNCNC support.
2017, 75(7): 692-698
doi: 10.6023/A17040162
Abstract:
G-quadruplexes play vital roles in telomere maintenance and other biological systems.An effective G-quadruplexes stabilizer can be a promising medicine for cancer therapy.Here, a Zinc (Ⅱ) with salen derivatives as ligands (ZSC) has been prepared through two simple steps syntheses.2, 4-Dihydroxybenzaldehyde (1 equiv.), 1-(2-chloroethyl) pyrrolidine hydrochloride (1 equiv.) and potassium carbonate (2 equiv.) were dissolved in 150 mL acetone.After reflux for 20 h in Ar atmosphere and purification, the product 2-hydroxy-4-(2-(pyrrolidin-1-yl) ethoxy) benzaldehyde was obtained to yield 3.24 g (68.8%) as a pale solid.For the other step, 2-hydroxy-4-(2-(pyrrolidin-1-yl) ethoxy) benzaldehyde (2 equiv.) and diaminomaleonitrile (1 equiv.) were dissolved into 10 mL methanol.After 20 min stirring at 60℃ in dark atmosphere, the Zinc acetate dehydrate (1 equiv.) was added in the solution for further 2 h reaction time.The final product Zinc (Ⅱ)-salen Complex (ZSC) was purified to yield 245 mg (67.7%) as a red powder.The fluorescence, CD spectra are reported, giving insight into the intrinsic properties of the compound.The Zinc (Ⅱ)-salen Complex could simply discriminate G-quadruplex from other DNA conformations such as hairpin, double-stranded DNA and single-stranded DNA by using fluorescence spectra.To the best of our knowledge, ZSC is the first Zinc (Ⅱ)-salen Complex bearing features of inducing, stabilizing, fluorescence-based switch-on detecting G-quadruplex.In addition, ZSC can also change the Z G-quadruplex to parallel G-quadruplex.Such a sensitive and topology-specific probe is able to light up G-quadruplexes and gain an excellently quantitative detection of DNA bearing G-quadruplexes sequences.The detailed study of the interactions of ZSC with different topology DNAs has allowed us to build the most vital features that Zinc (Ⅱ)-salen Complex can be a potential anticancer drug and in application to other bioanalytes.In the future, we will use the Zinc (Ⅱ)-salen Complex to downstream the gene expression in the gene promoter area to help analyze more biological processes or use it to selectively inhibit viruses which containing G-quadruplexes.
G-quadruplexes play vital roles in telomere maintenance and other biological systems.An effective G-quadruplexes stabilizer can be a promising medicine for cancer therapy.Here, a Zinc (Ⅱ) with salen derivatives as ligands (ZSC) has been prepared through two simple steps syntheses.2, 4-Dihydroxybenzaldehyde (1 equiv.), 1-(2-chloroethyl) pyrrolidine hydrochloride (1 equiv.) and potassium carbonate (2 equiv.) were dissolved in 150 mL acetone.After reflux for 20 h in Ar atmosphere and purification, the product 2-hydroxy-4-(2-(pyrrolidin-1-yl) ethoxy) benzaldehyde was obtained to yield 3.24 g (68.8%) as a pale solid.For the other step, 2-hydroxy-4-(2-(pyrrolidin-1-yl) ethoxy) benzaldehyde (2 equiv.) and diaminomaleonitrile (1 equiv.) were dissolved into 10 mL methanol.After 20 min stirring at 60℃ in dark atmosphere, the Zinc acetate dehydrate (1 equiv.) was added in the solution for further 2 h reaction time.The final product Zinc (Ⅱ)-salen Complex (ZSC) was purified to yield 245 mg (67.7%) as a red powder.The fluorescence, CD spectra are reported, giving insight into the intrinsic properties of the compound.The Zinc (Ⅱ)-salen Complex could simply discriminate G-quadruplex from other DNA conformations such as hairpin, double-stranded DNA and single-stranded DNA by using fluorescence spectra.To the best of our knowledge, ZSC is the first Zinc (Ⅱ)-salen Complex bearing features of inducing, stabilizing, fluorescence-based switch-on detecting G-quadruplex.In addition, ZSC can also change the Z G-quadruplex to parallel G-quadruplex.Such a sensitive and topology-specific probe is able to light up G-quadruplexes and gain an excellently quantitative detection of DNA bearing G-quadruplexes sequences.The detailed study of the interactions of ZSC with different topology DNAs has allowed us to build the most vital features that Zinc (Ⅱ)-salen Complex can be a potential anticancer drug and in application to other bioanalytes.In the future, we will use the Zinc (Ⅱ)-salen Complex to downstream the gene expression in the gene promoter area to help analyze more biological processes or use it to selectively inhibit viruses which containing G-quadruplexes.
2017, 75(7): 699-707
doi: 10.6023/A17030083
Abstract:
To study the mechanism of the photo-thermochemical cycle (PTC), titanium dioxide (ST) and Ni-doped TiO2(NT) films were produced using a sol-gel method and applied in the PTC for CO2 reduction.And commercial P25(PT) has been used as a compared sample.A comparison of CO production shows that Ni-doped TiO2 performed better than undoped TiO2 and P25.Average CO production of NT PTCs was 5.30 μmol/g-cat and it was nearly 3.13 times of ST PTCs'CO production and 2.28 times of PT PTCs'.Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) were used to assess the crystal structure and morphology of the films.Ni element could be found in NT by EDXS and inductively coupled plasma-atomic emission spectrometry (ICP-AES), and the mass fraction of Ni was 0.54% and 0.436% which were agreed with experiments.This result of XRD indicated that Ni2+ may have high dispersion without significant change in TiO2 and Ni2+ ions were doped into the TiO2 lattice so that Ni-O-Ti bonds were formed.Photoluminescence (PL), time-resolved PL, UV-visible diffuse reflectance spectra (UV-visible DRS) and X-ray photoelectron spectroscopy (XPS) analyses were also conducted to investigate the charge transfer and reaction mechanisms on the sample surface.The incorporation of Ni into TiO2 resulted in a weaker PL intensity than that of bare TiO2, which suggests that the introduction of Ni into TiO2 effectively suppressed the undesirable recombination of electrons and holes.According to UV-visible DRS results, the Eg of PT is approximately 3.07 eV, which is smaller than that of ST (Eg=3.23 eV) and PT (Eg=3.20 eV).The narrower band gap of NT indicates that NT absorbed light with a wider wavelength range than that absorbed by ST and PT.By XPS patterns, the increase of Ni+/0 and Ti3+ indicated that the VO may have been produced on the bond of Ni-O-Ti after UV illumination, and oxygen vacancies (VO) have been consumed after thermal step in PTC.Density functional theory (DFT) calculations related to the anatase (101) surface of TiO2 and Ni doped TiO2 was performed to verify and provide guidance for enhancing the PTC mechanism.Single and second VO formation energy have been calculated.The Ni-doped surface exhibits better performance than the undoped surface in the first step in PTC, because of its lower VO formation energy which produce more VO sites.Density of states (DOS) and partial density of states (PDOS) results indicated that narrow energy gap and impurity energy level of Ni-doped TiO2 may lead to a wider wavelength range of NT.As a result, several key factors of the mechanism have been clarified.
To study the mechanism of the photo-thermochemical cycle (PTC), titanium dioxide (ST) and Ni-doped TiO2(NT) films were produced using a sol-gel method and applied in the PTC for CO2 reduction.And commercial P25(PT) has been used as a compared sample.A comparison of CO production shows that Ni-doped TiO2 performed better than undoped TiO2 and P25.Average CO production of NT PTCs was 5.30 μmol/g-cat and it was nearly 3.13 times of ST PTCs'CO production and 2.28 times of PT PTCs'.Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) were used to assess the crystal structure and morphology of the films.Ni element could be found in NT by EDXS and inductively coupled plasma-atomic emission spectrometry (ICP-AES), and the mass fraction of Ni was 0.54% and 0.436% which were agreed with experiments.This result of XRD indicated that Ni2+ may have high dispersion without significant change in TiO2 and Ni2+ ions were doped into the TiO2 lattice so that Ni-O-Ti bonds were formed.Photoluminescence (PL), time-resolved PL, UV-visible diffuse reflectance spectra (UV-visible DRS) and X-ray photoelectron spectroscopy (XPS) analyses were also conducted to investigate the charge transfer and reaction mechanisms on the sample surface.The incorporation of Ni into TiO2 resulted in a weaker PL intensity than that of bare TiO2, which suggests that the introduction of Ni into TiO2 effectively suppressed the undesirable recombination of electrons and holes.According to UV-visible DRS results, the Eg of PT is approximately 3.07 eV, which is smaller than that of ST (Eg=3.23 eV) and PT (Eg=3.20 eV).The narrower band gap of NT indicates that NT absorbed light with a wider wavelength range than that absorbed by ST and PT.By XPS patterns, the increase of Ni+/0 and Ti3+ indicated that the VO may have been produced on the bond of Ni-O-Ti after UV illumination, and oxygen vacancies (VO) have been consumed after thermal step in PTC.Density functional theory (DFT) calculations related to the anatase (101) surface of TiO2 and Ni doped TiO2 was performed to verify and provide guidance for enhancing the PTC mechanism.Single and second VO formation energy have been calculated.The Ni-doped surface exhibits better performance than the undoped surface in the first step in PTC, because of its lower VO formation energy which produce more VO sites.Density of states (DOS) and partial density of states (PDOS) results indicated that narrow energy gap and impurity energy level of Ni-doped TiO2 may lead to a wider wavelength range of NT.As a result, several key factors of the mechanism have been clarified.
2017, 75(7): 708-714
doi: 10.6023/A17030107
Abstract:
The first principles density theory calculations have been performed to investigate different Mg3N2 surface and the corresponding properties of H2 adsorption.The calculation of surface energy present that Mg3N2(011) is the most stable surface.The result show that the H2 parallel to the surface is a favorable adsorption and the most stable structure is H2 adsorbed onto the Model Ⅱ surface, which have the lowest energy.There are three main modes of chemical adsorption:The first adsorption mode is that H2 is dissociated into two H, and each H connect with N atom respectively to form double NH.This is the best adsorption model, which mainly results from the interaction between the H 1s orbit and N 1s, 2p orbits.By the analysis of the charge distribution variation H atom and N atom lose electrons, Mg obtain electrons.The second mode, H2 dissociated partly and the two H are adsorbed onto the same N forming one NH2, forms covalent bond.From the analysis of the bond population, we conclude that the covalent bonds strengthen the structure of NH.In other words, the hydrogen desorption of NH2 is easier than NH.H2 is fully dissociated in the third mode.One H atom is adsorbed onto N forming a NH group, which is connected by covalent bond, while the other H atom is adsorbed onto Mg forming MgH, which is forming ionic bond.The reaction energy barrier show that there is no competition among the three adsorption modes.The model of forming two NH is the easiest pathway, which have the lowest reaction energy barrier of 0.848 eV.The second is that the adsorption of H2 molecules on the surface forming NH2 have the reaction energy barrier of 1.596 eV.The most unlikely adsorption model is that H2 is dissociated and forming the structure of NH+MgH, which have the reaction energy barrier of 5.495 eV.In addition, H2 also can be physically adsorbed onto Mg3N2(011) surface.
The first principles density theory calculations have been performed to investigate different Mg3N2 surface and the corresponding properties of H2 adsorption.The calculation of surface energy present that Mg3N2(011) is the most stable surface.The result show that the H2 parallel to the surface is a favorable adsorption and the most stable structure is H2 adsorbed onto the Model Ⅱ surface, which have the lowest energy.There are three main modes of chemical adsorption:The first adsorption mode is that H2 is dissociated into two H, and each H connect with N atom respectively to form double NH.This is the best adsorption model, which mainly results from the interaction between the H 1s orbit and N 1s, 2p orbits.By the analysis of the charge distribution variation H atom and N atom lose electrons, Mg obtain electrons.The second mode, H2 dissociated partly and the two H are adsorbed onto the same N forming one NH2, forms covalent bond.From the analysis of the bond population, we conclude that the covalent bonds strengthen the structure of NH.In other words, the hydrogen desorption of NH2 is easier than NH.H2 is fully dissociated in the third mode.One H atom is adsorbed onto N forming a NH group, which is connected by covalent bond, while the other H atom is adsorbed onto Mg forming MgH, which is forming ionic bond.The reaction energy barrier show that there is no competition among the three adsorption modes.The model of forming two NH is the easiest pathway, which have the lowest reaction energy barrier of 0.848 eV.The second is that the adsorption of H2 molecules on the surface forming NH2 have the reaction energy barrier of 1.596 eV.The most unlikely adsorption model is that H2 is dissociated and forming the structure of NH+MgH, which have the reaction energy barrier of 5.495 eV.In addition, H2 also can be physically adsorbed onto Mg3N2(011) surface.
2017, 75(7): 715-722
doi: 10.6023/A17010002
Abstract:
Chiral epoxides are versatile intermediates that can be readily converted into a wide variety of enantiomerically pure compounds by means of region-and stereo-selective ring opening reactions.The asymmetric epoxidation of unfunctionalized olefins is an important approach for synthesizing optically active epoxides, and thus is widely used in the synthesis of fine chemicals, such as pharmaceuticals, agrochemicals and perfumes.Chiral salen Mn (Ⅲ) complexes have demonstrated activities and selectivities for the enantioselective epoxidation of unfunctionalized olefins under homogeneous conditions.Compared with the homogeneous asymmetric catalysts, the heterogeneous ones have the advantages of easy catalyst/product separation and simple catalyst recycling.And more and more interests have been focused on the studies of heterogenization of chiral complexes.New types of supported catalysts are obtained by anchoring chiral salen Mn (Ⅲ) complex on a series of phenoxy-modified aluminium poly (styrene-phenylvinylphosphonate)-phosphate (AlPS-PVPA) in the text.All the prepared catalysts are characterized by FT-IR, UV-vis, XPS, SEM, TG and elemental analysis.The catalytic capabilities are investigated with m-CPBA as an oxidant and with indene and α-methylstyrene as substrates for asymmetric epoxidation of unfunctionalized olefins.The supported catalysts indicate superior catalytic activities in the asymmetric epoxidation of α-methylstyrene and indene with m-CPBA as oxidative system, compared with the corresponding homogeneous catalyst (ee, > 97% vs.54% and > 99% vs.65%).The steric properties of the linkages really play vital impacts on the configuration of the transition state for the asymmetric reactions.Contrary to most of the literatures reported, the results show that the heterogeneous catalysts 3a~3d exhibit excellent catalytic activities, and their conversions and ee values increase remarkably in the absence of N-methylmorpholine N-oxide (NMO) under the same catalytic conditions.The structures of the immobilized cat-alysts similar to the N-oxide ligand act as axial ligands leading to the unusual phenomenon.Simultaneously, additives are generally regarded as axial ligands on the transition metal catalyst, which make for activating the catalyst either toward oxidation or toward reactivity with the olefin.Thus, there is a steric hindrance when the N-oxide ligand is added and the optimal geometric configuration of the reactive intermediate salen Mn (V)=O was altered.It is steric hindrance that makes olefins approaching salen Mn (V)=O difficult and lower ee values are obtained.Furthermore, these catalysts are easily separated and are relatively stable and reused nine times without significant loss of activities.
Chiral epoxides are versatile intermediates that can be readily converted into a wide variety of enantiomerically pure compounds by means of region-and stereo-selective ring opening reactions.The asymmetric epoxidation of unfunctionalized olefins is an important approach for synthesizing optically active epoxides, and thus is widely used in the synthesis of fine chemicals, such as pharmaceuticals, agrochemicals and perfumes.Chiral salen Mn (Ⅲ) complexes have demonstrated activities and selectivities for the enantioselective epoxidation of unfunctionalized olefins under homogeneous conditions.Compared with the homogeneous asymmetric catalysts, the heterogeneous ones have the advantages of easy catalyst/product separation and simple catalyst recycling.And more and more interests have been focused on the studies of heterogenization of chiral complexes.New types of supported catalysts are obtained by anchoring chiral salen Mn (Ⅲ) complex on a series of phenoxy-modified aluminium poly (styrene-phenylvinylphosphonate)-phosphate (AlPS-PVPA) in the text.All the prepared catalysts are characterized by FT-IR, UV-vis, XPS, SEM, TG and elemental analysis.The catalytic capabilities are investigated with m-CPBA as an oxidant and with indene and α-methylstyrene as substrates for asymmetric epoxidation of unfunctionalized olefins.The supported catalysts indicate superior catalytic activities in the asymmetric epoxidation of α-methylstyrene and indene with m-CPBA as oxidative system, compared with the corresponding homogeneous catalyst (ee, > 97% vs.54% and > 99% vs.65%).The steric properties of the linkages really play vital impacts on the configuration of the transition state for the asymmetric reactions.Contrary to most of the literatures reported, the results show that the heterogeneous catalysts 3a~3d exhibit excellent catalytic activities, and their conversions and ee values increase remarkably in the absence of N-methylmorpholine N-oxide (NMO) under the same catalytic conditions.The structures of the immobilized cat-alysts similar to the N-oxide ligand act as axial ligands leading to the unusual phenomenon.Simultaneously, additives are generally regarded as axial ligands on the transition metal catalyst, which make for activating the catalyst either toward oxidation or toward reactivity with the olefin.Thus, there is a steric hindrance when the N-oxide ligand is added and the optimal geometric configuration of the reactive intermediate salen Mn (V)=O was altered.It is steric hindrance that makes olefins approaching salen Mn (V)=O difficult and lower ee values are obtained.Furthermore, these catalysts are easily separated and are relatively stable and reused nine times without significant loss of activities.
