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2019 Volume 77 Issue 12
2019, 77(12): 1221-1229
doi: 10.6023/A19080299
Abstract:
Glycans are important components of mammalian cells, which exists extensively in eukaryocytes. Glycans are mainly consisted of monosaccharides, oligosaccharides and polysaccharides. They are connected to proteins or lipids through glycosylation, which constitute glycoconjugates. Glycosylation is one of the most important post-modifications of proteins, which mediate a wide variety of biological processes, including cell growth and differentiation, cell-cell communication, immune response, pathogen interaction, and intracellular signaling events. Because of the complex marshalling sequences, diversiform connection types and multiple branch structures, glycans are endowed with various structures. The diversity of glycan structure brings glycoconjugates with abundant information of cellular function. Among all the factors, human diseases act as an important ingredient which can induce unnatural glycosylation process. Glycoconjugates have been chosen as an efficient biomarker in the area of disease surveillance and targeted drug therapy. Thus, analysis of secreted glycans is of great importance for monitoring the states of cells or diseases in clinical diagnosis and treatment. Based on recent research of extracellular glycans, this review introduces the types of glycans in cellular secretion and their biological functions or significances, summarizes the identification or detection techniques of the secreted glycans, including lectin identifications, chemical covalent identifications and glycan metabolic marker techniques. Detection technologies of cell secretory glycan have been emphatically introduced in this review, which mainly contain spectrophotometry techniques, chromatography techniques, mass-spectrography techniques, fluorescence methods, electrochemical processes, enzyme linked immunosorbent assay techniques and western blot methods. After summarizing the progresses in this field during the past few decades, we outlook the future development of the analysis of cell secretory glycans. As far as we concern, in situ identification and quantitative detection will be the most challenging but meaningful topic of this field. We hope this review can be provided as a useful guidance for the investigating of glycosylation or glycan-related biological processes.
Glycans are important components of mammalian cells, which exists extensively in eukaryocytes. Glycans are mainly consisted of monosaccharides, oligosaccharides and polysaccharides. They are connected to proteins or lipids through glycosylation, which constitute glycoconjugates. Glycosylation is one of the most important post-modifications of proteins, which mediate a wide variety of biological processes, including cell growth and differentiation, cell-cell communication, immune response, pathogen interaction, and intracellular signaling events. Because of the complex marshalling sequences, diversiform connection types and multiple branch structures, glycans are endowed with various structures. The diversity of glycan structure brings glycoconjugates with abundant information of cellular function. Among all the factors, human diseases act as an important ingredient which can induce unnatural glycosylation process. Glycoconjugates have been chosen as an efficient biomarker in the area of disease surveillance and targeted drug therapy. Thus, analysis of secreted glycans is of great importance for monitoring the states of cells or diseases in clinical diagnosis and treatment. Based on recent research of extracellular glycans, this review introduces the types of glycans in cellular secretion and their biological functions or significances, summarizes the identification or detection techniques of the secreted glycans, including lectin identifications, chemical covalent identifications and glycan metabolic marker techniques. Detection technologies of cell secretory glycan have been emphatically introduced in this review, which mainly contain spectrophotometry techniques, chromatography techniques, mass-spectrography techniques, fluorescence methods, electrochemical processes, enzyme linked immunosorbent assay techniques and western blot methods. After summarizing the progresses in this field during the past few decades, we outlook the future development of the analysis of cell secretory glycans. As far as we concern, in situ identification and quantitative detection will be the most challenging but meaningful topic of this field. We hope this review can be provided as a useful guidance for the investigating of glycosylation or glycan-related biological processes.
2019, 77(12): 1230-1238
doi: 10.6023/A19070262
Abstract:
Combining the specific recognition ability of DNA molecules with the superior physical and chemical properties of two-dimensional (2D) layered materials, a DNA-2D layered nanomaterial sensing platform was constructed. More and more researchers are devoted to develop this sensing platform, which has become one of the important research directions in the field of chemical/biological sensors. In view of the rapid development of the 2D layered materials, this paper firstly introduces the construction principle of the DNA-2D layered material sensing platform. Then we mainly review the application of the sensing platform in the analysis of chemical and biological molecules, including metal ions, mycotoxins, ATP, amino acid, antibiotics, nucleic acids, proteins and cancer cells. Finally, the future of this sensing platform is prospected.
Combining the specific recognition ability of DNA molecules with the superior physical and chemical properties of two-dimensional (2D) layered materials, a DNA-2D layered nanomaterial sensing platform was constructed. More and more researchers are devoted to develop this sensing platform, which has become one of the important research directions in the field of chemical/biological sensors. In view of the rapid development of the 2D layered materials, this paper firstly introduces the construction principle of the DNA-2D layered material sensing platform. Then we mainly review the application of the sensing platform in the analysis of chemical and biological molecules, including metal ions, mycotoxins, ATP, amino acid, antibiotics, nucleic acids, proteins and cancer cells. Finally, the future of this sensing platform is prospected.
Research Progress on Rare Earth Nanocrystals for In Vivo Imaging and Sensing in Near Infrared Region
2019, 77(12): 1239-1249
doi: 10.6023/A19080305
Abstract:
In vivo imaging and sensing play a critical role in modern biological and medical research. Compared with other techniques such as computed tomography (CT), positron emission tomography (PET) and nuclear magnetic resonance (NMR), fluorescence imaging and analysis are featured by fast feedback, high sensitivity, and high spatiotemporal resolution. Especially, the application of near infrared (NIR) light as both excitation and emission signals provides increased tissue penetration and improved imaging quality and sensitivity due to reduced light scattering and auto-fluorescence. Among various materials investigated for in vivo imaging and bio-sensing, lanthanide-based nanocrystals display rich excitation/emission wavelengths in the NIR range, good photo and chemical stability, large Stokes shifts. In recent years, the research on lanthanide-based nanocrystals for in vivo imaging and sensing has seen rapid progress. Through nanoscale material design and synthesis, it is possible to fine tune the optical properties of lanthanide-based nanocrystals. By properly choosing different lanthanide ions as activators and sensitizers, multiple excitation/emission wavelengths can be obtained. The careful design of core-shell structure of nanocrystals enables improved fluorescence efficiency and tailorable fluorescence life time through controlled energy transfer. On the other side, the surface of lanthanide-based nanocrystals can be modified through coating, absorption or ligand exchange to enhance the biocompatibility, targeting capability, and bio-responsiveness. Taking advantage of this high flexibility and versatility, there are great opportunities for these lanthanide-based nanocrystals in various in vivo imaging and sensing applications. This review first outlines the general technique requirements for in vivo imaging and sensing. Then, the composition, synthesis and basic properties of lanthanide-based nanocrystals are briefly introduced. Subsequently, the routes for tailoring the optical and biochemical properties of lanthanide-based nanocrystals are discussed in detail, with an emphasis on the material designs and surface modifications for in vivo imaging and analysis. It is expected that this work will inspire new ideas for accelerating the clinic translation of rare earth nanocrystals-based imaging and sensing techniques.
In vivo imaging and sensing play a critical role in modern biological and medical research. Compared with other techniques such as computed tomography (CT), positron emission tomography (PET) and nuclear magnetic resonance (NMR), fluorescence imaging and analysis are featured by fast feedback, high sensitivity, and high spatiotemporal resolution. Especially, the application of near infrared (NIR) light as both excitation and emission signals provides increased tissue penetration and improved imaging quality and sensitivity due to reduced light scattering and auto-fluorescence. Among various materials investigated for in vivo imaging and bio-sensing, lanthanide-based nanocrystals display rich excitation/emission wavelengths in the NIR range, good photo and chemical stability, large Stokes shifts. In recent years, the research on lanthanide-based nanocrystals for in vivo imaging and sensing has seen rapid progress. Through nanoscale material design and synthesis, it is possible to fine tune the optical properties of lanthanide-based nanocrystals. By properly choosing different lanthanide ions as activators and sensitizers, multiple excitation/emission wavelengths can be obtained. The careful design of core-shell structure of nanocrystals enables improved fluorescence efficiency and tailorable fluorescence life time through controlled energy transfer. On the other side, the surface of lanthanide-based nanocrystals can be modified through coating, absorption or ligand exchange to enhance the biocompatibility, targeting capability, and bio-responsiveness. Taking advantage of this high flexibility and versatility, there are great opportunities for these lanthanide-based nanocrystals in various in vivo imaging and sensing applications. This review first outlines the general technique requirements for in vivo imaging and sensing. Then, the composition, synthesis and basic properties of lanthanide-based nanocrystals are briefly introduced. Subsequently, the routes for tailoring the optical and biochemical properties of lanthanide-based nanocrystals are discussed in detail, with an emphasis on the material designs and surface modifications for in vivo imaging and analysis. It is expected that this work will inspire new ideas for accelerating the clinic translation of rare earth nanocrystals-based imaging and sensing techniques.
2019, 77(12): 1250-1262
doi: 10.6023/A19060227
Abstract:
Flexible electronic skins (E-skins) with human-like multiple sensing capabilities of perceiving various stimuli, have attracted more and more attentions for their wide applications in wearable electronics, health monitoring, humanoid robotics and smart prosthesis. However, to meet the rigorous requirements for these complicated applications, challenges still exist in multifunctional integration, high performance, simple structure, low-cost fabrication and easy signal processing. This review focuses on the significant sensing capabilities that are necessarily required in E-skins, including perceiving stimuli of pressure, temperature, humidity, flow and materials. Various mechanisms are utilized in multiple kinds of sensors in current study, such as piezoresistivity, thermoelectricity, electrical impedance, convective heat transfer, etc. Multisensory integration is the basic characteristics of E-skins that various stimuli are perceived simultaneously. There are mainly three mechanisms applied in multisensory integration, that is, direct-integration method, functional-materials based method and uniform sensing method. The advantages and disadvantages of each method are analyzed. Finally, the challenges and future development on multisensory integration of E-skins are summarized.
Flexible electronic skins (E-skins) with human-like multiple sensing capabilities of perceiving various stimuli, have attracted more and more attentions for their wide applications in wearable electronics, health monitoring, humanoid robotics and smart prosthesis. However, to meet the rigorous requirements for these complicated applications, challenges still exist in multifunctional integration, high performance, simple structure, low-cost fabrication and easy signal processing. This review focuses on the significant sensing capabilities that are necessarily required in E-skins, including perceiving stimuli of pressure, temperature, humidity, flow and materials. Various mechanisms are utilized in multiple kinds of sensors in current study, such as piezoresistivity, thermoelectricity, electrical impedance, convective heat transfer, etc. Multisensory integration is the basic characteristics of E-skins that various stimuli are perceived simultaneously. There are mainly three mechanisms applied in multisensory integration, that is, direct-integration method, functional-materials based method and uniform sensing method. The advantages and disadvantages of each method are analyzed. Finally, the challenges and future development on multisensory integration of E-skins are summarized.
2019, 77(12): 1263-1267
doi: 10.6023/A19090325
Abstract:
Fluorine-containing compounds have been widely used in the fields of pharmaceuticals, agrochemicals and functional materials, mainly due to the well-known "fluorine effect" of the fluoroalkyl groups on the physical, chemical and biological properties of molecules. Tri- and difluoromethyl ethers play an important role in many medicinally compounds. Among various fluorinated moieties, ORf-containing groups have attracted much more attention very recently owing to the impressive conformational changes and maximal shifts in electron distribution brought by fluorine. The α-fluorine substitution of ethers shortens and strengthens the C-O bond and thus improves the in vivo oxidative stability of the ether moiety of a drug. Over the past few decades, there are some reliable ways on accessing trifluoromethyl ethers and difluomethyl ethers. Considering the importance of synthesis of monofluoromethoxy arenes and the substrate limitation (phenols or alcohols) of current state, a method was developed to access monofluoromethoxy arenes from aryl halides, arylboronic acids and arenes via a one-pot synthesis. Phenols can be prepared by the hydroxylation of aryl halides catalyzed by transition-metal complexes. In this work, a new strategy was envisioned a two-step sequence for the conversion of aryl halides to monofluoromethoxy arenes based on the palladium-catalyzed conversion of aryl phenols and in situ conversion of the resulting phenoxides with monofluoromethylating reagents. The investigation began with optimization of the conversion of 1-chloro-4-methoxy-benzene. The approach was achieved by using Pd2(dba)3 (2 mol%) as the catalyst under an inert atmosphere, di-tert-bu-tyl(2', 4', 6'-triisopropyl-[1, 1'-biphenyl]-2-yl)phosphane (8 mol%) as the ligand, KOH (1 equiv.) as the nucleophile, and 1, 4-dioxane/H2O (V:V=5:3) as the solvent. Further monofluoromethylation used fluoromethyl iodide (2 equiv.) as the monofluoromethylating reagent and CH3CN as the co-solvent. Finally, the desired product was obtained in 82% yield. Therefore, this method was also applied to drugs, for example, Loratadine could be converted to the corresponding product (2o) in 53% yield and Fenofibrate, reacting to form the monofluoromethoxy arenes (2p) in modest yield. One-pot method to access aryl monofluoromethyl ethers from arylboronic acids and arenes were also under consideration and the yields were objective.
Fluorine-containing compounds have been widely used in the fields of pharmaceuticals, agrochemicals and functional materials, mainly due to the well-known "fluorine effect" of the fluoroalkyl groups on the physical, chemical and biological properties of molecules. Tri- and difluoromethyl ethers play an important role in many medicinally compounds. Among various fluorinated moieties, ORf-containing groups have attracted much more attention very recently owing to the impressive conformational changes and maximal shifts in electron distribution brought by fluorine. The α-fluorine substitution of ethers shortens and strengthens the C-O bond and thus improves the in vivo oxidative stability of the ether moiety of a drug. Over the past few decades, there are some reliable ways on accessing trifluoromethyl ethers and difluomethyl ethers. Considering the importance of synthesis of monofluoromethoxy arenes and the substrate limitation (phenols or alcohols) of current state, a method was developed to access monofluoromethoxy arenes from aryl halides, arylboronic acids and arenes via a one-pot synthesis. Phenols can be prepared by the hydroxylation of aryl halides catalyzed by transition-metal complexes. In this work, a new strategy was envisioned a two-step sequence for the conversion of aryl halides to monofluoromethoxy arenes based on the palladium-catalyzed conversion of aryl phenols and in situ conversion of the resulting phenoxides with monofluoromethylating reagents. The investigation began with optimization of the conversion of 1-chloro-4-methoxy-benzene. The approach was achieved by using Pd2(dba)3 (2 mol%) as the catalyst under an inert atmosphere, di-tert-bu-tyl(2', 4', 6'-triisopropyl-[1, 1'-biphenyl]-2-yl)phosphane (8 mol%) as the ligand, KOH (1 equiv.) as the nucleophile, and 1, 4-dioxane/H2O (V:V=5:3) as the solvent. Further monofluoromethylation used fluoromethyl iodide (2 equiv.) as the monofluoromethylating reagent and CH3CN as the co-solvent. Finally, the desired product was obtained in 82% yield. Therefore, this method was also applied to drugs, for example, Loratadine could be converted to the corresponding product (2o) in 53% yield and Fenofibrate, reacting to form the monofluoromethoxy arenes (2p) in modest yield. One-pot method to access aryl monofluoromethyl ethers from arylboronic acids and arenes were also under consideration and the yields were objective.
2019, 77(12): 1268-1278
doi: 10.6023/A19090349
Abstract:
In recent years, polymer dots (Pdots) have been developed as an excellent organic fluorescent nanoparticles due to its excellent optical properties, diverse structures, easy surface modification and good biocompatibility. So, they have important application potential in biological imaging, sensing and detection, drug delivery and therapeutic diagnosis. However, the fluorescence quenching of semiconducting Pdots with large conjugated structure due to aggregation-caused quenching (ACQ) effect limits its applications for bioimaging in aggregated states. The ACQ phenomenon of Pdots could been eliminated by introducing aggregation-induced emission (AIE)-active molecules in Pdots. In this paper, a kind of responsive AIE-active Pdots, which were composed of tetraphenylethylene (TPE) with blue fluorescent light emission and poly(N-vinyl-2-pyrrolidone)-Eu(Ⅲ) complex (PVP-Eu(Ⅲ)) with red fluorescent light emission, were constructed. Firstly, a TPE derivative initiator (TPE-tetraAZO) containing four arms was synthesized by using 4, 4'-azobis-(4-cyanovaleric acid) to modify TPE, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly(N-vinyl-2-pyrrolidone) (TPE-tetraPVP) was then successfully synthesized by using TPE-tetraAZO as initiator. Finally, the complex TPE-tetraPVP-Eu(Ⅲ) with AIE characteristic and dual fluorescence was obtained through the coordination between TPE-tetraPVP and rare earth element Eu(Ⅲ). The amphiphilic 4-arm star polymer TPE-tetraPVP-Eu(Ⅲ) formed Pdots consisted of hydrophobic AIEgens TPE core and hydrophilic PVP shell by a self-assembling process. The morphology and particle size of Pdots were investigated by transmission electron microscope (TEM). Results showed that Pdots was a relatively uniform diameter around 20 nm and exhibited regular sphere morphology. The results of fluorescence experiments showed that TPE-tetraPVP-Eu(Ⅲ) Pdots had two emission bands centered at about 435 (blue) and 615 nm (red) with a wavelength difference of 180 nm, which were obtained under optimum excitation at 360 and 395 nm, respectively. Among them, the blue emission showed typical AIE property. Moreover, the lower critical solution temperature (LCST) of TPE-tetraPVP-Eu(Ⅲ) in aqueous solution was about 37℃, which was close to normal body temperature. Meanwhile, at different temperatures from 10 to 60℃, photoluminescence (PL) intensities of TPE-tetraPVP-Eu(Ⅲ) Pdots firstly decreased with increasing temperature from 10 to 36℃, and then increased with increasing temperature from 37 to 60℃. It was interesting that the fluorescent response of Pdots could be caused by the phase transfer of PVP. Besides, the PL intensity of Pdots in aqueous solution changed at different pH. Therefore, TPE-tetraPVP-Eu(Ⅲ) Pdots might be used as multi-functional and smart fluorescent sensors. Furthermore, the results of cellular imaging indicated the efficient cellular uptake and low cytotoxicity of Pdots in HeLa, HepG2 and A549 cells. And, the photoswitchable dual-emission could be easily realized in three cells by simply tuning the excitation wavelength. Thus, the non-conjugated Pdots is an ideal dual-color live cell imaging probe.
In recent years, polymer dots (Pdots) have been developed as an excellent organic fluorescent nanoparticles due to its excellent optical properties, diverse structures, easy surface modification and good biocompatibility. So, they have important application potential in biological imaging, sensing and detection, drug delivery and therapeutic diagnosis. However, the fluorescence quenching of semiconducting Pdots with large conjugated structure due to aggregation-caused quenching (ACQ) effect limits its applications for bioimaging in aggregated states. The ACQ phenomenon of Pdots could been eliminated by introducing aggregation-induced emission (AIE)-active molecules in Pdots. In this paper, a kind of responsive AIE-active Pdots, which were composed of tetraphenylethylene (TPE) with blue fluorescent light emission and poly(N-vinyl-2-pyrrolidone)-Eu(Ⅲ) complex (PVP-Eu(Ⅲ)) with red fluorescent light emission, were constructed. Firstly, a TPE derivative initiator (TPE-tetraAZO) containing four arms was synthesized by using 4, 4'-azobis-(4-cyanovaleric acid) to modify TPE, and a multi-stimuli-responsive amphiphilic polymer of tetraphenylethene-graft-poly(N-vinyl-2-pyrrolidone) (TPE-tetraPVP) was then successfully synthesized by using TPE-tetraAZO as initiator. Finally, the complex TPE-tetraPVP-Eu(Ⅲ) with AIE characteristic and dual fluorescence was obtained through the coordination between TPE-tetraPVP and rare earth element Eu(Ⅲ). The amphiphilic 4-arm star polymer TPE-tetraPVP-Eu(Ⅲ) formed Pdots consisted of hydrophobic AIEgens TPE core and hydrophilic PVP shell by a self-assembling process. The morphology and particle size of Pdots were investigated by transmission electron microscope (TEM). Results showed that Pdots was a relatively uniform diameter around 20 nm and exhibited regular sphere morphology. The results of fluorescence experiments showed that TPE-tetraPVP-Eu(Ⅲ) Pdots had two emission bands centered at about 435 (blue) and 615 nm (red) with a wavelength difference of 180 nm, which were obtained under optimum excitation at 360 and 395 nm, respectively. Among them, the blue emission showed typical AIE property. Moreover, the lower critical solution temperature (LCST) of TPE-tetraPVP-Eu(Ⅲ) in aqueous solution was about 37℃, which was close to normal body temperature. Meanwhile, at different temperatures from 10 to 60℃, photoluminescence (PL) intensities of TPE-tetraPVP-Eu(Ⅲ) Pdots firstly decreased with increasing temperature from 10 to 36℃, and then increased with increasing temperature from 37 to 60℃. It was interesting that the fluorescent response of Pdots could be caused by the phase transfer of PVP. Besides, the PL intensity of Pdots in aqueous solution changed at different pH. Therefore, TPE-tetraPVP-Eu(Ⅲ) Pdots might be used as multi-functional and smart fluorescent sensors. Furthermore, the results of cellular imaging indicated the efficient cellular uptake and low cytotoxicity of Pdots in HeLa, HepG2 and A549 cells. And, the photoswitchable dual-emission could be easily realized in three cells by simply tuning the excitation wavelength. Thus, the non-conjugated Pdots is an ideal dual-color live cell imaging probe.
2019, 77(12): 1279-1286
doi: 10.6023/A19090331
Abstract:
Cyclic dipeptide (CDP) is a kind of the smallest cyclic peptide with two amino acids cyclization through amide bonds. The two amide bonds with four hydrogen bonding sites give CDPs a high self-assembly propensity, mainly driven by the hydrogen bonding interactions. In this paper, we have designed four CDPs, c-SF, c-SY, c-SH and c-DF, and studied their self-assembly performance in aqueous solution with circular dichroism spectroscopy (CD) and atomic force microscopy (AFM), including the effects of pH and zinc ion coordination on self-assembly. The fluorescence properties of CDP self-assemblies have also been studied. CD results showed that c-SF, c-SY and c-DF adopted a β-sheet conformation, while c-SH was random coil secondary structure at the concentration of 2.0 mmol/L and pH 5.0. AFM results showed that c-SF, c-SY and c-DF could form nanofibers with different diameters ranged from 1.0 to 3.0 nm. In addition, c-SY self-assembled hierarchically over time. Not only the nanofiber diameter gradually increased, but also the nanofibers entangled into 3D networks. Although c-SH did not self-assemble at the concentration of 3.0 mmol/L and pH 7.0, it could form monolayers with the induction of zinc ion at pH 9.0. The self-assemblies of each CDP had different multiple fluorescent emission peaks with excitation of different wavelengths. Especially, c-SF emitted green fluorescent light under UV light of 365 nm. The fluorescent emission intensity of CDPs was much stronger than their corresponding linear dipeptides. It was assumed that the diketopiperazine structure contributed to the fluorescence enhancement. Moreover, the fluorescent emission intensity of CDP self-assemblies was much higher than that of their free molecules, which meant that the ordered aggregation made a significant contribution to the fluorescent properties. Both the coordination of zinc ions with the imidazole groups on histidine and the oxidation of phenolic hydroxyl groups in tyrosine could enhance the fluorescent emission intensity of CDPs. It was assumed that CDP molecules stacked one by one to form nanofibers during self-assembly. The diketopiperazine ring of CDPs and its self-assembly endowed CDPs with special fluorescent properties.
Cyclic dipeptide (CDP) is a kind of the smallest cyclic peptide with two amino acids cyclization through amide bonds. The two amide bonds with four hydrogen bonding sites give CDPs a high self-assembly propensity, mainly driven by the hydrogen bonding interactions. In this paper, we have designed four CDPs, c-SF, c-SY, c-SH and c-DF, and studied their self-assembly performance in aqueous solution with circular dichroism spectroscopy (CD) and atomic force microscopy (AFM), including the effects of pH and zinc ion coordination on self-assembly. The fluorescence properties of CDP self-assemblies have also been studied. CD results showed that c-SF, c-SY and c-DF adopted a β-sheet conformation, while c-SH was random coil secondary structure at the concentration of 2.0 mmol/L and pH 5.0. AFM results showed that c-SF, c-SY and c-DF could form nanofibers with different diameters ranged from 1.0 to 3.0 nm. In addition, c-SY self-assembled hierarchically over time. Not only the nanofiber diameter gradually increased, but also the nanofibers entangled into 3D networks. Although c-SH did not self-assemble at the concentration of 3.0 mmol/L and pH 7.0, it could form monolayers with the induction of zinc ion at pH 9.0. The self-assemblies of each CDP had different multiple fluorescent emission peaks with excitation of different wavelengths. Especially, c-SF emitted green fluorescent light under UV light of 365 nm. The fluorescent emission intensity of CDPs was much stronger than their corresponding linear dipeptides. It was assumed that the diketopiperazine structure contributed to the fluorescence enhancement. Moreover, the fluorescent emission intensity of CDP self-assemblies was much higher than that of their free molecules, which meant that the ordered aggregation made a significant contribution to the fluorescent properties. Both the coordination of zinc ions with the imidazole groups on histidine and the oxidation of phenolic hydroxyl groups in tyrosine could enhance the fluorescent emission intensity of CDPs. It was assumed that CDP molecules stacked one by one to form nanofibers during self-assembly. The diketopiperazine ring of CDPs and its self-assembly endowed CDPs with special fluorescent properties.
2019, 77(12): 1287-1293
doi: 10.6023/A19070279
Abstract:
A novel liquid-liquid phase-change organic amine mixed absorbent for the removal of sulfur dioxide (SO2) was developed. This absorbent could surmount the shortcomings that the atmosphere is contaminated by volatile organic solvents and a lot of energy is consumed in the process of recovering solvent in the traditional flue gas desulfurization process. The homogeneous absorption solution consists of stronger alkaline N, N-dimethyl-n-octylamine (DMOA) as absorbent and high-boiling hexadecane as a solvent, because hexadecane is the best one among various kinds of solvents tested. The solution would be automatically separated into two immiscible phases after introducing SO2 and setting. Hexadecane was in the upper phase and the absorption product of SO2 and DMOA was in the lower phase after absorption. The former could be directly recycled, and the latter could be recovered by removing SO2 from the lower phase. The absorption product was proved to be a charge-transfer complex by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). Subsequently, the effects of temperature, concentration and SO2 partial pressure on absorption capacity and cycle absorption performance were studied. The absorption capacity was determined by passing SO2 through the solution in gas bottle and weighing the system including the bottle and the solution. The desorption capacity was determined by passing N2 through the solution absorbed SO2, and then the content of each component in different phases was determined by gas chromatography using internal standard method. It was found that the mole absorption capacity was 2.1 mol SO2/mol DMOA under the condition of 1.013×105 Pa and 20℃, which was 38 times as much as the absorption capacity of carbon dioxide (CO2). The absorbent revealed the good cycle absorption performance in the experiment, and the DMOA could be completely regenerated under 1.013×105 Pa and 120℃. All the results showed that the mixed absorbent has good prospects for SO2 capture.
A novel liquid-liquid phase-change organic amine mixed absorbent for the removal of sulfur dioxide (SO2) was developed. This absorbent could surmount the shortcomings that the atmosphere is contaminated by volatile organic solvents and a lot of energy is consumed in the process of recovering solvent in the traditional flue gas desulfurization process. The homogeneous absorption solution consists of stronger alkaline N, N-dimethyl-n-octylamine (DMOA) as absorbent and high-boiling hexadecane as a solvent, because hexadecane is the best one among various kinds of solvents tested. The solution would be automatically separated into two immiscible phases after introducing SO2 and setting. Hexadecane was in the upper phase and the absorption product of SO2 and DMOA was in the lower phase after absorption. The former could be directly recycled, and the latter could be recovered by removing SO2 from the lower phase. The absorption product was proved to be a charge-transfer complex by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). Subsequently, the effects of temperature, concentration and SO2 partial pressure on absorption capacity and cycle absorption performance were studied. The absorption capacity was determined by passing SO2 through the solution in gas bottle and weighing the system including the bottle and the solution. The desorption capacity was determined by passing N2 through the solution absorbed SO2, and then the content of each component in different phases was determined by gas chromatography using internal standard method. It was found that the mole absorption capacity was 2.1 mol SO2/mol DMOA under the condition of 1.013×105 Pa and 20℃, which was 38 times as much as the absorption capacity of carbon dioxide (CO2). The absorbent revealed the good cycle absorption performance in the experiment, and the DMOA could be completely regenerated under 1.013×105 Pa and 120℃. All the results showed that the mixed absorbent has good prospects for SO2 capture.
