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2020 Volume 78 Issue 7
2020, 78(7): 597-612
doi: 10.6023/A20050153
Abstract:
Metal-organic frameworks (MOFs), featuring the ultrahigh surface area, high porosity, tunable geometrical and chemical properties, show potential applications in gas adsorption/separation, heterogenous catalysis, etc. As the ubiquity of water vapor in the ambient environment and industrial gas streams, it is necessary to study on interaction mechanism between MOFs and water molecules and develop highly water-stable MOFs with desirable water adsorption/desorption behaviors. It not only has the scientific significance, but also great importance in promoting the practical applications of MOFs. Given the tailorable abilities of pore size, pore volume, cavity hydrophilicity and water stability, MOFs provide unprecedented advantages to explore the well-defined porous sorbents in molecular level, which facilitates the realization of reversible water vapor uptake and release at expected relative pressure and temperature together with high working capacity. For now, a wide range of hydrolytically stable MOFs including high-valence metal (e.g. Cr3+, Al3+, Zr4+, Ti4+) based frameworks have emerged as the advanced and promising porous sorbents for energy efficient applications, by utilizing water as eco-friendly adsorbate media and renewable heat. This review focuses on the following aspects:(1) the degradation mechanism of MOFs in liquid phase of water and the design concepts of hydrolytically stable MOFs by modulating their coordination bond based on the Pearson' hard/soft acid/base principle; (2) the physical or chemical water ad/desorption properties of MOFs; (3) the classification of numerous MOFs sorbents and conventional desiccants based on their hydrophilicity, which is approximately reflected by the relative humidity (RH) value of the inflection points (the RH where the steep uptake starts) in isotherms; (4) a variety of water adsorption-based applications of MOFs such as industrial gas dehydration, drinking water harvesting in the desert area, adsorption-based heat pump and indoor humidity regulation. Finally, the research priorities and development outlook are summarized and the future challenge with respect to water adsorption-based applications for the next-generation MOFs are outlined.
Metal-organic frameworks (MOFs), featuring the ultrahigh surface area, high porosity, tunable geometrical and chemical properties, show potential applications in gas adsorption/separation, heterogenous catalysis, etc. As the ubiquity of water vapor in the ambient environment and industrial gas streams, it is necessary to study on interaction mechanism between MOFs and water molecules and develop highly water-stable MOFs with desirable water adsorption/desorption behaviors. It not only has the scientific significance, but also great importance in promoting the practical applications of MOFs. Given the tailorable abilities of pore size, pore volume, cavity hydrophilicity and water stability, MOFs provide unprecedented advantages to explore the well-defined porous sorbents in molecular level, which facilitates the realization of reversible water vapor uptake and release at expected relative pressure and temperature together with high working capacity. For now, a wide range of hydrolytically stable MOFs including high-valence metal (e.g. Cr3+, Al3+, Zr4+, Ti4+) based frameworks have emerged as the advanced and promising porous sorbents for energy efficient applications, by utilizing water as eco-friendly adsorbate media and renewable heat. This review focuses on the following aspects:(1) the degradation mechanism of MOFs in liquid phase of water and the design concepts of hydrolytically stable MOFs by modulating their coordination bond based on the Pearson' hard/soft acid/base principle; (2) the physical or chemical water ad/desorption properties of MOFs; (3) the classification of numerous MOFs sorbents and conventional desiccants based on their hydrophilicity, which is approximately reflected by the relative humidity (RH) value of the inflection points (the RH where the steep uptake starts) in isotherms; (4) a variety of water adsorption-based applications of MOFs such as industrial gas dehydration, drinking water harvesting in the desert area, adsorption-based heat pump and indoor humidity regulation. Finally, the research priorities and development outlook are summarized and the future challenge with respect to water adsorption-based applications for the next-generation MOFs are outlined.
2020, 78(7): 613-624
doi: 10.6023/A20040126
Abstract:
With the accelerating process of industrialization and urbanization, as well as the increasing proportion of the elderly in the world's population, we are facing more complex health threats related to bacterial infection. While the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, the continued abuse and misuse of antibiotics has accelerated the spread of antibiotic-resistant bacterial strains and has resulted in substantial new challenges with respect to modern-day antibiotic-based treatments. Therefore, intelligent design of new antibacterial modalities to be used for treating human and livestock diseases is an extremely urgent priority for researchers in the fields of chemistry, chemical engineering, materials and biomedical sciences. Toward this end, the most intriguing of the new developments are metal-organic frameworks (MOFs). MOFs are versatile crystalline porous lattices of organic ligands and metal ion/clusters that formed by self-assembly via coordination bonds. Due to their unique characteristics, including relatively straight forward and simple methods for synthesis, large surface areas, novel and diverse structures, and adjustable porosity, MOFs not only play strong roles with respect to novel methods for gas storage and separation, they may also be utilized in unique applications associated with sensors mechanisms and catalysis. These features contribute to our current understanding of MOFs as promising candidates for the development of pharmaceutical and specifically antibacterial applications. In this review, antibacterial mechanisms, and the development of resistance to current antibiotic strategies are summarized and discussed. The main mechanisms by which bacteria show resistance to antibiotics include altered metabolic pathways, regulation of target sites, and inactivation, modification, and/or reduction in the capacity to accumulate antibacterial drugs. We consider recent progress on the development of MOFs, including the use of specific metal centers and ligands, metal nanoparticles, and drug-encapsulation, all of which have important applications with respect to antibacterial activities, and wound healing. Finally, the challenges and prospects of MOF-based antibacterial materials are discussed, including critical findings, which will help toward the development of the next generation antibacterial MOFs for human use.
With the accelerating process of industrialization and urbanization, as well as the increasing proportion of the elderly in the world's population, we are facing more complex health threats related to bacterial infection. While the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, the continued abuse and misuse of antibiotics has accelerated the spread of antibiotic-resistant bacterial strains and has resulted in substantial new challenges with respect to modern-day antibiotic-based treatments. Therefore, intelligent design of new antibacterial modalities to be used for treating human and livestock diseases is an extremely urgent priority for researchers in the fields of chemistry, chemical engineering, materials and biomedical sciences. Toward this end, the most intriguing of the new developments are metal-organic frameworks (MOFs). MOFs are versatile crystalline porous lattices of organic ligands and metal ion/clusters that formed by self-assembly via coordination bonds. Due to their unique characteristics, including relatively straight forward and simple methods for synthesis, large surface areas, novel and diverse structures, and adjustable porosity, MOFs not only play strong roles with respect to novel methods for gas storage and separation, they may also be utilized in unique applications associated with sensors mechanisms and catalysis. These features contribute to our current understanding of MOFs as promising candidates for the development of pharmaceutical and specifically antibacterial applications. In this review, antibacterial mechanisms, and the development of resistance to current antibiotic strategies are summarized and discussed. The main mechanisms by which bacteria show resistance to antibiotics include altered metabolic pathways, regulation of target sites, and inactivation, modification, and/or reduction in the capacity to accumulate antibacterial drugs. We consider recent progress on the development of MOFs, including the use of specific metal centers and ligands, metal nanoparticles, and drug-encapsulation, all of which have important applications with respect to antibacterial activities, and wound healing. Finally, the challenges and prospects of MOF-based antibacterial materials are discussed, including critical findings, which will help toward the development of the next generation antibacterial MOFs for human use.
2020, 78(7): 625-633
doi: 10.6023/A20030053
Abstract:
Rare earth (RE) resources are in big amount in China, which can be effectively purified based on the strategies developed by Prof. Guangxian Xu et al. last century, which sets up solid fundamentals for applied research on rare earth materials nowadays. Rare earth elements, including scandium, yttrium and lanthanides, feature stable overall chemical properties, variable valence states and coordination form as well as special Lewis acidity due to the unique electron configuration in the outermost and secondary outer orbitals of the lanthanide elements ([Xe] 4fn-15d0~16s2 (n=1~15)), especially on their 4f electron shell structure, having been extensively used in catalysis. However, the efficiency and selectivity to the desired products are always the major challenges due to the complexity of catalysis, in particular, the mechanism by which rare earth metals affect catalytic reactions through structural or electronic effects has not been clarified. Therefore, this mini-review summarizes the research progress on the application of rare earth materials in heterogeneous catalysis (specifically on thermal catalysis). Firstly, a brief summary of rare earth materials' structural properties is provided with emphasis on the unique distribution of the 4f electron. Afterward, the application of RE elements in thermal catalysis was discussed in detail. For example:(1) as a support to promote catalytic reaction, such as CeO2, which has variable chemical valence and can be used as an active support to participate in the redox reaction; (2) as moderate Lewis acid (base) center to catalyze the aldol condensation of acetaldehyde/ethanol mixture and effectively control the C-C bond coupling; (3) as electronic and structural promoters to improve catalytic activity and stability. Hence, the structure-function relationship is illustrated in accordance with the studies of the rare earth materials as the supports, Lewis acid (base) active center and catalytic promoters, suggesting great potential of rare earth materials in catalysis.
Rare earth (RE) resources are in big amount in China, which can be effectively purified based on the strategies developed by Prof. Guangxian Xu et al. last century, which sets up solid fundamentals for applied research on rare earth materials nowadays. Rare earth elements, including scandium, yttrium and lanthanides, feature stable overall chemical properties, variable valence states and coordination form as well as special Lewis acidity due to the unique electron configuration in the outermost and secondary outer orbitals of the lanthanide elements ([Xe] 4fn-15d0~16s2 (n=1~15)), especially on their 4f electron shell structure, having been extensively used in catalysis. However, the efficiency and selectivity to the desired products are always the major challenges due to the complexity of catalysis, in particular, the mechanism by which rare earth metals affect catalytic reactions through structural or electronic effects has not been clarified. Therefore, this mini-review summarizes the research progress on the application of rare earth materials in heterogeneous catalysis (specifically on thermal catalysis). Firstly, a brief summary of rare earth materials' structural properties is provided with emphasis on the unique distribution of the 4f electron. Afterward, the application of RE elements in thermal catalysis was discussed in detail. For example:(1) as a support to promote catalytic reaction, such as CeO2, which has variable chemical valence and can be used as an active support to participate in the redox reaction; (2) as moderate Lewis acid (base) center to catalyze the aldol condensation of acetaldehyde/ethanol mixture and effectively control the C-C bond coupling; (3) as electronic and structural promoters to improve catalytic activity and stability. Hence, the structure-function relationship is illustrated in accordance with the studies of the rare earth materials as the supports, Lewis acid (base) active center and catalytic promoters, suggesting great potential of rare earth materials in catalysis.
2020, 78(7): 634-641
doi: 10.6023/A20040131
Abstract:
Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) system is an adaptive immune system used by many bacteria and archaea to defend the invasion of exogenous nucleic acids. CRISPR-Cas system in different species of archaea and bacteria has different components and working mechanisms. Depending on the numbers of effector proteins, CRISPR-Cas systems can be classified into two major types. CRISPR-Cas9, which is composed of Cas9 nuclease and sgRNA, belongs to class Ⅱ CRISPR-Cas system and can be used as a powerful genome editing tool. It can target and cleave the DNA sequence which contains protospacer adjacent motif (PAM, 5'-NGG-3') sequence. The DNA double-strand breaks (DSBs) can be repaired by homology-directed repair (HDR) or nonhomologous end joining (NHEJ) mechanism. Insertions or deletions (indels) can be introduced at targeted loci in the DSBs repair process. Due to its convenience, low cost and high efficiency, CRISPR-Cas9 has played an important role in promoting the development of gene editing in basic research and clinical medicine. However, off-target effect of CRISPR-Cas9 should not be neglected. The CRISPR-Cas9 is able to cleave the target DNA even when the sgRNA imperfectly matches with the target DNA, leading to the unwanted indels at nontargeted DNA loci, which limits the further application of genome editing, especially for the treatment of genetic diseases. Therefore, it is significant to reduce the off-target cleavage effect of CRISPR-Cas9. Many efforts have been devoted to realize the reduced off-target effect of CRISPR-Cas9. Among these methods, regulating the function of CRISPR-Cas9 at spatiotemporal dimension is a potential strategy to reduce the off-target effect of CRISPR-Cas9 system and improve the specificity of gene editing. In this review, we summarized the research advances in regulating the function of CRISPR-Cas9 and discussed the prospects and challenges of CRISPR-Cas9 regulation.
Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein (Cas) system is an adaptive immune system used by many bacteria and archaea to defend the invasion of exogenous nucleic acids. CRISPR-Cas system in different species of archaea and bacteria has different components and working mechanisms. Depending on the numbers of effector proteins, CRISPR-Cas systems can be classified into two major types. CRISPR-Cas9, which is composed of Cas9 nuclease and sgRNA, belongs to class Ⅱ CRISPR-Cas system and can be used as a powerful genome editing tool. It can target and cleave the DNA sequence which contains protospacer adjacent motif (PAM, 5'-NGG-3') sequence. The DNA double-strand breaks (DSBs) can be repaired by homology-directed repair (HDR) or nonhomologous end joining (NHEJ) mechanism. Insertions or deletions (indels) can be introduced at targeted loci in the DSBs repair process. Due to its convenience, low cost and high efficiency, CRISPR-Cas9 has played an important role in promoting the development of gene editing in basic research and clinical medicine. However, off-target effect of CRISPR-Cas9 should not be neglected. The CRISPR-Cas9 is able to cleave the target DNA even when the sgRNA imperfectly matches with the target DNA, leading to the unwanted indels at nontargeted DNA loci, which limits the further application of genome editing, especially for the treatment of genetic diseases. Therefore, it is significant to reduce the off-target cleavage effect of CRISPR-Cas9. Many efforts have been devoted to realize the reduced off-target effect of CRISPR-Cas9. Among these methods, regulating the function of CRISPR-Cas9 at spatiotemporal dimension is a potential strategy to reduce the off-target effect of CRISPR-Cas9 system and improve the specificity of gene editing. In this review, we summarized the research advances in regulating the function of CRISPR-Cas9 and discussed the prospects and challenges of CRISPR-Cas9 regulation.
2020, 78(7): 642-656
doi: 10.6023/A20040116
Abstract:
Reactive oxygen species (ROS) are categorized as a class of instantaneous intermediate products of oxygen, which are usually produced by a single electron continuous reduction of O2. Examples include hydrogen peroxide (H2O2), superoxide anion (O2-), hydroxyl radical (HO·), hypochlorite radical (OCl-) and singlet oxygen (1O2). The endogenous ROS arise from three major resources:mitochondrial electron transport chain (Mito-ETC), endoplasmic reticulum (ER) and NADPH oxidase (NOX). The produced ROS play vital roles in physiological functions including modulation of functions of proteins, regulation of cell signaling, mediation of inflammation, and elimination of pathogens. However, the cumulative ROS level in vivo could elicit oxidative stress, which is implicated in a multitude of diseases including cancer, autoimmune diseases, inflammation, cardiovascular diseases, neurodegenerative diseases. This abnormal biochemical alteration in tumors has inspired researchers to exploit the relatively high levels of ROS for development of ROS-responsive prodrug systems. In recent years, ROS-responsive prodrug systems based on a spectrum of ROS-sensitive linkers have been designed and developed with aim of precision tumor therapy. Herein, in this review, we would like to illustrate ROS-sensitive linkers developed to date including arylboronic acid or ester, alkyl thioether or selenide, thioketal, peroxalate ester, aminoacrylate, thiazolidinone and α-ketoamide, and elucidate the underlying molecular oxidation mechanism. Furthermore, the design of ROS-responsive prodrugs based on these sensitive linkers and their applications in anti-cancer therapy were reviewed. Additionally, the existing problems and the future research perspectives of prodrug systems were also discussed.
Reactive oxygen species (ROS) are categorized as a class of instantaneous intermediate products of oxygen, which are usually produced by a single electron continuous reduction of O2. Examples include hydrogen peroxide (H2O2), superoxide anion (O2-), hydroxyl radical (HO·), hypochlorite radical (OCl-) and singlet oxygen (1O2). The endogenous ROS arise from three major resources:mitochondrial electron transport chain (Mito-ETC), endoplasmic reticulum (ER) and NADPH oxidase (NOX). The produced ROS play vital roles in physiological functions including modulation of functions of proteins, regulation of cell signaling, mediation of inflammation, and elimination of pathogens. However, the cumulative ROS level in vivo could elicit oxidative stress, which is implicated in a multitude of diseases including cancer, autoimmune diseases, inflammation, cardiovascular diseases, neurodegenerative diseases. This abnormal biochemical alteration in tumors has inspired researchers to exploit the relatively high levels of ROS for development of ROS-responsive prodrug systems. In recent years, ROS-responsive prodrug systems based on a spectrum of ROS-sensitive linkers have been designed and developed with aim of precision tumor therapy. Herein, in this review, we would like to illustrate ROS-sensitive linkers developed to date including arylboronic acid or ester, alkyl thioether or selenide, thioketal, peroxalate ester, aminoacrylate, thiazolidinone and α-ketoamide, and elucidate the underlying molecular oxidation mechanism. Furthermore, the design of ROS-responsive prodrugs based on these sensitive linkers and their applications in anti-cancer therapy were reviewed. Additionally, the existing problems and the future research perspectives of prodrug systems were also discussed.
2020, 78(7): 657-669
doi: 10.6023/A20040132
Abstract:
Photodynamic therapy (PDT) is a new type of non-invasive tumor therapy, which has the advantages of less trauma and toxicity, good selectivity, no drug resistance and repeatable treatment. Thus, PDT has achieved remarkable results in the treatment of cancer. In order to increase its depth of tissue penetration, researchers proposed to build novel PDT nano-theranostic systems based on upconversion nanoparticles (referred as upconversion photodynamic nanotheranostic system). Based on the luminescence resonance energy transfer process, upconversion photodynamic nanotheranostic systems use the emitted fluorescence of upconversion nanoparticles which is excited by the near-infrared laser to further excite the loaded photosensitizer, thus it is advantageous to the treatment of deep tumors. Via the multi-functional structure design, the newly developed upconversion photodynamic nanotheranostic agent could achieve the targeted transportation, imaging diagnosis and stimulation response for the achievement of on-demand treatment, which is the trend for the development of nanomedicine in the future. At present, researchers pay more and more attention to the construction of tumor microenvironment responsive nanotheranostic system, in order to improve the targeting to the tumor section, improve the PDT efficacy, and reduce the toxicity to the surrounding normal tissues. This work mainly discusses the construction and development of upconversion nanotheranostic systems based on the stimulation of pH, enzyme and hydrogen peroxide. In addition, we prospect its development in the future.
Photodynamic therapy (PDT) is a new type of non-invasive tumor therapy, which has the advantages of less trauma and toxicity, good selectivity, no drug resistance and repeatable treatment. Thus, PDT has achieved remarkable results in the treatment of cancer. In order to increase its depth of tissue penetration, researchers proposed to build novel PDT nano-theranostic systems based on upconversion nanoparticles (referred as upconversion photodynamic nanotheranostic system). Based on the luminescence resonance energy transfer process, upconversion photodynamic nanotheranostic systems use the emitted fluorescence of upconversion nanoparticles which is excited by the near-infrared laser to further excite the loaded photosensitizer, thus it is advantageous to the treatment of deep tumors. Via the multi-functional structure design, the newly developed upconversion photodynamic nanotheranostic agent could achieve the targeted transportation, imaging diagnosis and stimulation response for the achievement of on-demand treatment, which is the trend for the development of nanomedicine in the future. At present, researchers pay more and more attention to the construction of tumor microenvironment responsive nanotheranostic system, in order to improve the targeting to the tumor section, improve the PDT efficacy, and reduce the toxicity to the surrounding normal tissues. This work mainly discusses the construction and development of upconversion nanotheranostic systems based on the stimulation of pH, enzyme and hydrogen peroxide. In addition, we prospect its development in the future.
2020, 78(7): 670-674
doi: 10.6023/A20050150
Abstract:
The plasmonic nanostructures have attracted particular attention due to their superior ability to capture and modulate light in ultraviolet-visible and near-infrared range, by changing the size, morphology, and the composition of nanostructures. Especially in plasmon-driven chemical reactions, plasmon-induced hot electrons (HEs) can be transferred from the surface of metal nanostructures to the lowest unoccupied molecular orbital (LUMO) of the adsorbate molecule or the conduction band of the semiconductor to achieve catalytic reaction. Therefore, how to improve the excitation efficiency of HEs has become a key problem to be solved urgently. In this paper, 120 nm Ag nanoparticles (NPs) were synthesized by seed growth method using 45 nm Au as seed. Subsequently, (3-aminopropyl)trimethoxysilane as coupling agent and sodium silicate as the silicon source were used to prepare the shell-isolated Ag NPs with 2~3 nm SiO2 shell (Ag SHINs). Finally, Ag SHINs were modified with poly(allylamine hydrochloride), then small Au (ca. 15 nm) as satellites were electrostatic self-assembled onto the surface of Ag SHINs to form a 3D Ag SHINs-Au superstructure. Using p-aminothiophenol (pATP) as probe molecule, in-situ surface-enhanced Raman spectroscopy (SERS) was employed to real-timely monitor the catalytic reaction processes from pATP to DMAB, using 532, 638, and 785 nm lasers for excitation, respectively. The results showed that the highest conversion efficiency was achieved when 638 nm laser was applied. In addition, the reaction rate under 785 nm excitation was faster than that under exposure to 532 nm laser. Then, we used three dimensional (3D) finite-difference time-domain (FDTD) to simulate the electric field distribution of 3D Ag SHINs-Au superstructure. The electric field simulation results are consistent with the experimental results. In consequence, the stronger the electric field intensity, the higher the HEs excitation efficiency. On the other hand, the intra-band transitions produce HEs more efficiently than inter-band transitions. Therefore, this study is helpful for understanding how the electric field intensity affect the excitation efficiency of the HEs.
The plasmonic nanostructures have attracted particular attention due to their superior ability to capture and modulate light in ultraviolet-visible and near-infrared range, by changing the size, morphology, and the composition of nanostructures. Especially in plasmon-driven chemical reactions, plasmon-induced hot electrons (HEs) can be transferred from the surface of metal nanostructures to the lowest unoccupied molecular orbital (LUMO) of the adsorbate molecule or the conduction band of the semiconductor to achieve catalytic reaction. Therefore, how to improve the excitation efficiency of HEs has become a key problem to be solved urgently. In this paper, 120 nm Ag nanoparticles (NPs) were synthesized by seed growth method using 45 nm Au as seed. Subsequently, (3-aminopropyl)trimethoxysilane as coupling agent and sodium silicate as the silicon source were used to prepare the shell-isolated Ag NPs with 2~3 nm SiO2 shell (Ag SHINs). Finally, Ag SHINs were modified with poly(allylamine hydrochloride), then small Au (ca. 15 nm) as satellites were electrostatic self-assembled onto the surface of Ag SHINs to form a 3D Ag SHINs-Au superstructure. Using p-aminothiophenol (pATP) as probe molecule, in-situ surface-enhanced Raman spectroscopy (SERS) was employed to real-timely monitor the catalytic reaction processes from pATP to DMAB, using 532, 638, and 785 nm lasers for excitation, respectively. The results showed that the highest conversion efficiency was achieved when 638 nm laser was applied. In addition, the reaction rate under 785 nm excitation was faster than that under exposure to 532 nm laser. Then, we used three dimensional (3D) finite-difference time-domain (FDTD) to simulate the electric field distribution of 3D Ag SHINs-Au superstructure. The electric field simulation results are consistent with the experimental results. In consequence, the stronger the electric field intensity, the higher the HEs excitation efficiency. On the other hand, the intra-band transitions produce HEs more efficiently than inter-band transitions. Therefore, this study is helpful for understanding how the electric field intensity affect the excitation efficiency of the HEs.
2020, 78(7): 675-679
doi: 10.6023/A20050145
Abstract:
Metal nanostructures with localized surface plasmon resonance (LSPR) have attracted great attention in catalysis, sensing, nanooptics, and nanomedicine. Charge transfer plasmon (CTP) is a LSPR mode that strongly depends on a conductive junction between metallic nanounits. Benefitting from the charge transfer junction, CTP provides a facile way to generate widely tunable LSPR with highly localized/enhanced light magnetic field and photothermal effect. The limited availability of highly tunable CTP structures and their fabrication techniques hinders a further pursuit of their functions and applications. In response to this situation, the present work aims at developing a simple while highly efficient synthetic route to width-adjustable Au/Cu heterojunctions capable of evoking tunable CTP behaviors. The strategy relies on a non-specific surface adsorption of low-cost, naturally occurred fish sperm DNA on a gold nanoseed to control heterogeneous copper nucleation. Such a process offers a chance to tailor the contact area between the gold and copper nano-domains in the bimetallic structure. Highly tunable CTP resonance from visible to near-infrared region is then realizable on the basis of this method. Experimental and calculated extinction spectra consistently reveal three key variables for the CTP structure, including the width of conductive junction and the sizes of gold and copper particles. These parameters are associated with DNA coverage, copper precursor concentration, and the synthetic conditions for gold nanoparticles, which allow for a CTP tuning from visible to near infrared wavelengths. By fully exploiting these highly controllable parameters, the maximally achievable CTP wavelength readily enters a near infrared Ⅱ domain. The resulting CTP signals have a red-shift of up to 750 nm relative to the 530~570 nm LSPR peaks of individual gold and copper nanoparticles, corresponding to a very narrow Au/Cu conductive contact of 11~13 nm in width. The role of nonspecific DNA adsorption in the above process proves unique (currently irreplaceable) compared to other molecular adsorbates. The easily tunable Au/Cu heterointerface paves a way to integrated CTP and catalytic/sensing functions in future research.
Metal nanostructures with localized surface plasmon resonance (LSPR) have attracted great attention in catalysis, sensing, nanooptics, and nanomedicine. Charge transfer plasmon (CTP) is a LSPR mode that strongly depends on a conductive junction between metallic nanounits. Benefitting from the charge transfer junction, CTP provides a facile way to generate widely tunable LSPR with highly localized/enhanced light magnetic field and photothermal effect. The limited availability of highly tunable CTP structures and their fabrication techniques hinders a further pursuit of their functions and applications. In response to this situation, the present work aims at developing a simple while highly efficient synthetic route to width-adjustable Au/Cu heterojunctions capable of evoking tunable CTP behaviors. The strategy relies on a non-specific surface adsorption of low-cost, naturally occurred fish sperm DNA on a gold nanoseed to control heterogeneous copper nucleation. Such a process offers a chance to tailor the contact area between the gold and copper nano-domains in the bimetallic structure. Highly tunable CTP resonance from visible to near-infrared region is then realizable on the basis of this method. Experimental and calculated extinction spectra consistently reveal three key variables for the CTP structure, including the width of conductive junction and the sizes of gold and copper particles. These parameters are associated with DNA coverage, copper precursor concentration, and the synthetic conditions for gold nanoparticles, which allow for a CTP tuning from visible to near infrared wavelengths. By fully exploiting these highly controllable parameters, the maximally achievable CTP wavelength readily enters a near infrared Ⅱ domain. The resulting CTP signals have a red-shift of up to 750 nm relative to the 530~570 nm LSPR peaks of individual gold and copper nanoparticles, corresponding to a very narrow Au/Cu conductive contact of 11~13 nm in width. The role of nonspecific DNA adsorption in the above process proves unique (currently irreplaceable) compared to other molecular adsorbates. The easily tunable Au/Cu heterointerface paves a way to integrated CTP and catalytic/sensing functions in future research.
2020, 78(7): 680-687
doi: 10.6023/A20030097
Abstract:
Thermally activated delayed fluorescence (TADF) molecules have great potential in developing organic light-emitting diodes (OLEDs) because of their efficient emission and low price. Compared to pure-molecules, exciplex systems are drawing much attention since they can realize small singlet-triplet energy splitting (ΔEST) more easily for TADF. However, the species and molecular design systems of electron-acceptors for exciplex-TADF are still limited even though some acceptors have been reported. In addition, the relationship between TADF properties and the structures of acceptors requires further investigations. Herein, we report the design and synthesis of two novel spiro[fluorine-9, 9'-xanthene]-based acceptors (CNSFDBX and DCNSFDBX) for achieving exciplex-emissions by using tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as a donor. The photoluminescence measurements suggest that both of the doping-systems (TCTA:CNSFDBX and TCTA:DCNSFDBX) possess exciplex emissions. Whereas, it is observed that the TCTA:DCNSFDBX system displays higher photoluminescence quantum yield and electroluminescence efficiency than TCTA:CNSFDBX. For better explaining this phenomenon, we perform low-temperature fluorescence and phosphorescence spectra investigations. The experimental results show that the TCTA:DCNSFDBX system exhibits smaller ΔEST values (0.12 eV) than TCTA:CNSFDBX (0.46 eV). This results indicate that the reverse intersystem crossing from non-radiative triplet states (T1) to radiative singlet states (S1) and TADF processes can be realized more easily in the TCTA:DCNSFDBX system. Moreover, the electrochemical measurements and theoretical calculations suggest that the lowest unoccupied molecular orbital (LUMO) level of DCNSFDBX (-2.86 eV) is lower than that of CNSFDBX (-2.47 eV). This situation implies that DCNSFDBX possesses stronger electron-accepting ability than CNSFDBX with the help of dicyano-substitution. Furthermore, the TCTA:DCNSFDBX system displays larger driving force (0.39 eV) than TCTA:CNSFDBX (0.22 eV) in their exciplex-formation processes, suggesting the exciplex-emission (TCTA:DCNSFDBX) can be achieved more easily. Therefore, the higher exciplex-emission efficiencies of the TCTA:DCNSFDBX system are attributed to the stronger electron-acceptability of DCNSFDBX through dicyano- substitution and larger driving force in its exciplex emission process. This work provides a route to further development of new electron-acceptors for exciplex-TADF.
Thermally activated delayed fluorescence (TADF) molecules have great potential in developing organic light-emitting diodes (OLEDs) because of their efficient emission and low price. Compared to pure-molecules, exciplex systems are drawing much attention since they can realize small singlet-triplet energy splitting (ΔEST) more easily for TADF. However, the species and molecular design systems of electron-acceptors for exciplex-TADF are still limited even though some acceptors have been reported. In addition, the relationship between TADF properties and the structures of acceptors requires further investigations. Herein, we report the design and synthesis of two novel spiro[fluorine-9, 9'-xanthene]-based acceptors (CNSFDBX and DCNSFDBX) for achieving exciplex-emissions by using tris(4-carbazoyl-9-ylphenyl)amine (TCTA) as a donor. The photoluminescence measurements suggest that both of the doping-systems (TCTA:CNSFDBX and TCTA:DCNSFDBX) possess exciplex emissions. Whereas, it is observed that the TCTA:DCNSFDBX system displays higher photoluminescence quantum yield and electroluminescence efficiency than TCTA:CNSFDBX. For better explaining this phenomenon, we perform low-temperature fluorescence and phosphorescence spectra investigations. The experimental results show that the TCTA:DCNSFDBX system exhibits smaller ΔEST values (0.12 eV) than TCTA:CNSFDBX (0.46 eV). This results indicate that the reverse intersystem crossing from non-radiative triplet states (T1) to radiative singlet states (S1) and TADF processes can be realized more easily in the TCTA:DCNSFDBX system. Moreover, the electrochemical measurements and theoretical calculations suggest that the lowest unoccupied molecular orbital (LUMO) level of DCNSFDBX (-2.86 eV) is lower than that of CNSFDBX (-2.47 eV). This situation implies that DCNSFDBX possesses stronger electron-accepting ability than CNSFDBX with the help of dicyano-substitution. Furthermore, the TCTA:DCNSFDBX system displays larger driving force (0.39 eV) than TCTA:CNSFDBX (0.22 eV) in their exciplex-formation processes, suggesting the exciplex-emission (TCTA:DCNSFDBX) can be achieved more easily. Therefore, the higher exciplex-emission efficiencies of the TCTA:DCNSFDBX system are attributed to the stronger electron-acceptability of DCNSFDBX through dicyano- substitution and larger driving force in its exciplex emission process. This work provides a route to further development of new electron-acceptors for exciplex-TADF.
2020, 78(7): 688-694
doi: 10.6023/A20050141
Abstract:
Metal-organic frameworks (MOFs), a class of promising heterogeneous catalysts, though readily recyclable, usually suffer from poor dispersity and ease of sedimentation in liquid-phase reaction systems, which may lead to limited exposure of active sites and unsatisfied activity. Conventional hydrothermal synthesis often results in large MOF particles in bulk form and poor dispersity. The homogenization of MOF catalysts is an exciting but challenging task to integrate the advantages of both homogeneous and heterogeneous catalysts. Herein, by means of microwave-assisted synthetic approach, a soluble porphyrinic MOF, denoted as S-Al-PMOF, has been successfully fabricated. In contrast to the Bulk-Al-PMOF synthesized by the conventional hydrothermal route, which requires 180℃ and 16 h, the S-Al-PMOF obtained by the microwave-assisted method is very efficient and takes 30 min only at 140℃. While the as-synthesized S-Al-PMOF can be completely soluble in acetonitrile by ultrasonic dispersion to give a clear and transparent colloidal solution, the Bulk-Al-PMOF can form a turbid suspension liquid by continuous stirring, which easily aggregate with sedimentation in a short time after standing. Furthermore, the S-Al-PMOF can be easily separated from the solution by suction filtration and then re-dissolved in acetonitrile. This separation and re-dissolution process can be repeated several times to prove its good recovery and recycling. Given the outstanding light harvesting ability of Al-PMOF, photocatalytic H2 production by water splitting has been adopted to examine the activity of both S-Al-PMOF and Bulk-Al-PMOF. As a result, the activity of S-Al-PMOF is around 14 times higher than that of Bulk-Al-PMOF, owing to excellent solubility of the former. Moreover, S-Al-PMOF also exhibits good recyclability in the consecutive three cycles of reaction. We believe that the successful synthesis of soluble Al-PMOF opens a new avenue to the homogenization of heterogeneous catalysts.
Metal-organic frameworks (MOFs), a class of promising heterogeneous catalysts, though readily recyclable, usually suffer from poor dispersity and ease of sedimentation in liquid-phase reaction systems, which may lead to limited exposure of active sites and unsatisfied activity. Conventional hydrothermal synthesis often results in large MOF particles in bulk form and poor dispersity. The homogenization of MOF catalysts is an exciting but challenging task to integrate the advantages of both homogeneous and heterogeneous catalysts. Herein, by means of microwave-assisted synthetic approach, a soluble porphyrinic MOF, denoted as S-Al-PMOF, has been successfully fabricated. In contrast to the Bulk-Al-PMOF synthesized by the conventional hydrothermal route, which requires 180℃ and 16 h, the S-Al-PMOF obtained by the microwave-assisted method is very efficient and takes 30 min only at 140℃. While the as-synthesized S-Al-PMOF can be completely soluble in acetonitrile by ultrasonic dispersion to give a clear and transparent colloidal solution, the Bulk-Al-PMOF can form a turbid suspension liquid by continuous stirring, which easily aggregate with sedimentation in a short time after standing. Furthermore, the S-Al-PMOF can be easily separated from the solution by suction filtration and then re-dissolved in acetonitrile. This separation and re-dissolution process can be repeated several times to prove its good recovery and recycling. Given the outstanding light harvesting ability of Al-PMOF, photocatalytic H2 production by water splitting has been adopted to examine the activity of both S-Al-PMOF and Bulk-Al-PMOF. As a result, the activity of S-Al-PMOF is around 14 times higher than that of Bulk-Al-PMOF, owing to excellent solubility of the former. Moreover, S-Al-PMOF also exhibits good recyclability in the consecutive three cycles of reaction. We believe that the successful synthesis of soluble Al-PMOF opens a new avenue to the homogenization of heterogeneous catalysts.
2020, 78(7): 695-702
doi: 10.6023/A20040125
Abstract:
The adsorption and self-assembly of meso-tetra(p-methoxyphenyl)porphyrinatocobalt(Ⅱ)[Co(TAP)] on Au(111), Ag(111) and Cu(111) have been systematically studied by ultrahigh vacuum low-temperature scanning tunneling microscopy (STM). The atomically flat metal substrate surfaces are prepared by cycled ion sputtering and subsequent annealing at 750 K. Co(TAP) molecules are deposited onto the substrate surfaces via thermal evaporation from a home-made tantalum boat. The as-prepared samples are then annealed to achieve energetically stable self-assembly structures and transferred to the STM chamber for further analyses. All STM measurements are carried out at about 4.4 K. On these metal surfaces, Co(TAP) molecules mainly form two types of two-dimensional molecular assembly structures A and B. Structure A only exists on Au(111) and Ag(111), while Structure B merely appears on Ag(111) and Cu(111). The intermolecular interactions in Structures A and B are due to π-π stacking and hydrogen bonding, respectively. The difference in strength of the molecule-substrate interaction, which induces conformational changes of peripheral p-methoxyphenyl substituent in Co(TAP) on difference substrate, is attributed to govern the formation of different self-assembly structures on the aforementioned surfaces. The substrate surface also has an effect on the formation of the self-assembly structures. At similar coverage, the percentage of dispersed Co(TAP) molecules follow the sequence:Cu(111) > Au(111) > Ag(111). With the coverage increase, the percentage of dispersed Co(TAP) molecules decreases on all metal surfaces employed in this study. Specifically, on Au(111) and Ag(111), the dispersed Co(TAP) molecules disappear at coverages of about 1 ML and 0.1 ML, respectively, while on Cu(111) they survive even at the coverage of about 0.85 ML. In addition, Structure A gradually dominates on Au(111). On Cu(111), Structure B only occupies half of the surface structures even at nearly saturated coverage. The ratio of Structures A to B almost retains over the whole coverage range on Ag(111). Thermal annealing of the molecule-covered Ag(111) substrate helps the transformation from Structure B to A, and the elimination of the structural domain boundaries as well.
The adsorption and self-assembly of meso-tetra(p-methoxyphenyl)porphyrinatocobalt(Ⅱ)[Co(TAP)] on Au(111), Ag(111) and Cu(111) have been systematically studied by ultrahigh vacuum low-temperature scanning tunneling microscopy (STM). The atomically flat metal substrate surfaces are prepared by cycled ion sputtering and subsequent annealing at 750 K. Co(TAP) molecules are deposited onto the substrate surfaces via thermal evaporation from a home-made tantalum boat. The as-prepared samples are then annealed to achieve energetically stable self-assembly structures and transferred to the STM chamber for further analyses. All STM measurements are carried out at about 4.4 K. On these metal surfaces, Co(TAP) molecules mainly form two types of two-dimensional molecular assembly structures A and B. Structure A only exists on Au(111) and Ag(111), while Structure B merely appears on Ag(111) and Cu(111). The intermolecular interactions in Structures A and B are due to π-π stacking and hydrogen bonding, respectively. The difference in strength of the molecule-substrate interaction, which induces conformational changes of peripheral p-methoxyphenyl substituent in Co(TAP) on difference substrate, is attributed to govern the formation of different self-assembly structures on the aforementioned surfaces. The substrate surface also has an effect on the formation of the self-assembly structures. At similar coverage, the percentage of dispersed Co(TAP) molecules follow the sequence:Cu(111) > Au(111) > Ag(111). With the coverage increase, the percentage of dispersed Co(TAP) molecules decreases on all metal surfaces employed in this study. Specifically, on Au(111) and Ag(111), the dispersed Co(TAP) molecules disappear at coverages of about 1 ML and 0.1 ML, respectively, while on Cu(111) they survive even at the coverage of about 0.85 ML. In addition, Structure A gradually dominates on Au(111). On Cu(111), Structure B only occupies half of the surface structures even at nearly saturated coverage. The ratio of Structures A to B almost retains over the whole coverage range on Ag(111). Thermal annealing of the molecule-covered Ag(111) substrate helps the transformation from Structure B to A, and the elimination of the structural domain boundaries as well.
