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2017 Volume 33 Issue 3
2017, 33(3):
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2017, 33(3): 441-442
doi: 10.3866/PKU.WHXB201702241
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2017, 33(3): 443-444
doi: 10.3866/PKU.WHXB201701093
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2017, 33(3): 445-446
doi: 10.3866/PKU.WHXB201702173
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2017, 33(3): 449-450
doi: 10.3866/PKU.WHXB201702131
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2017, 33(3): 451-452
doi: 10.3866/PKU.WHXB201702151
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2017, 33(3): 453-453
doi: 10.3866/PKU.WHXB201702171
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2017, 33(3): 454-454
doi: 10.3866/PKU.WHXB201702172
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2017, 33(3): 457-457
doi: 10.3866/PKU.WHXB201701061
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2017, 33(3): 458-463
doi: 10.3866/PKU.WHXB201701041
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We report an in situ liquid cell scanning transmission electron microscopy (STEM) study of the heterogeneous deposition of palladium (Pd) on spherical gold (Au) nanoparticles in solution. The dynamic processes observed here revealed different behaviors of Pd deposition on Au nanoparticles. Under irradiation by an energetic electron beam, Pd was reduced and selectively deposited on Au nanoparticles through the island deposition mode. The deposition processes were accompanied with structural relaxation and surface migration of the Pd islands, and the size of the Au-Pd composite particles showed oscillatory growth behavior. In contrast, the Pd coverage on Au increased monotonically. In addition, we also captured the formation of Pd clusters through homogeneous nucleation and growth, and the subsequent coalescence of Pd clusters with islands on the Au-Pd heterostructures. The associated heterogeneous deposition mechanisms were proposed and quantitatively analyzed. The shapes and structures of the Au-Pd composite particles were characterized by highresolution transmission electron microscopy (HRTEM), which revealed the deposited Pd on the Au spherical nanoparticles was polycrystalline and contained several Pd crystallites with random orientations. The results presented here will serve as an important reference to understand heterogeneous growth in liquid solutions.
We report an in situ liquid cell scanning transmission electron microscopy (STEM) study of the heterogeneous deposition of palladium (Pd) on spherical gold (Au) nanoparticles in solution. The dynamic processes observed here revealed different behaviors of Pd deposition on Au nanoparticles. Under irradiation by an energetic electron beam, Pd was reduced and selectively deposited on Au nanoparticles through the island deposition mode. The deposition processes were accompanied with structural relaxation and surface migration of the Pd islands, and the size of the Au-Pd composite particles showed oscillatory growth behavior. In contrast, the Pd coverage on Au increased monotonically. In addition, we also captured the formation of Pd clusters through homogeneous nucleation and growth, and the subsequent coalescence of Pd clusters with islands on the Au-Pd heterostructures. The associated heterogeneous deposition mechanisms were proposed and quantitatively analyzed. The shapes and structures of the Au-Pd composite particles were characterized by highresolution transmission electron microscopy (HRTEM), which revealed the deposited Pd on the Au spherical nanoparticles was polycrystalline and contained several Pd crystallites with random orientations. The results presented here will serve as an important reference to understand heterogeneous growth in liquid solutions.
2017, 33(3): 464-475
doi: 10.3866/PKU.WHXB201611152
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Graphene and graphene-like two-dimensional (2D) materials exhibit broad prospects for application in emerging electronics owing to their unique structure and excellent properties. However, there are still many challenges facing the achievement of controllable growth, which is the main bottleneck that limits the practical application of these materials. Chemical vapor deposition (CVD) is the most effective method for the controllable growth of high-quality graphene, in which the design of the catalytic substrate catches the most attention because it directly determines the two most significant basal processes——catalyzation and mass transfer. Recently, compared with the selection of the chemical composition of the catalyst, the change of the physical state of the catalyst from a solid phase to liquid phase is expected to lead to a qualitative change and improvement in the CVD of graphene and graphene-like two-dimensional materials. Unlike solid substrates, liquid substrates exhibit a loose atomic arrangement and intense atom movement, which contribute to a smooth and isotropic liquid surface and a fluidic liquid phase that can embed heteroatoms. Therefore, liquid metal shows many unique behaviors during the catalyzation of the growth of graphene, graphene-like two dimensional materials, and their heterostructures, such as strict self-limitation, ultra-fast growth, and smooth stitching of grains. More importantly, the rheological properties of a liquid substrate can even facilitate the self-assembly and transfer of 2D materials grown on it, in which the liquid metal substrate can be regarded as the 'philosopher's stone'. This feature article summarizes the growth, assembly, and transfer behavior of 2D materials on liquid metal catalysts. These primary technology developments will establish a solid foundation for the practical application of 2D materials.
Graphene and graphene-like two-dimensional (2D) materials exhibit broad prospects for application in emerging electronics owing to their unique structure and excellent properties. However, there are still many challenges facing the achievement of controllable growth, which is the main bottleneck that limits the practical application of these materials. Chemical vapor deposition (CVD) is the most effective method for the controllable growth of high-quality graphene, in which the design of the catalytic substrate catches the most attention because it directly determines the two most significant basal processes——catalyzation and mass transfer. Recently, compared with the selection of the chemical composition of the catalyst, the change of the physical state of the catalyst from a solid phase to liquid phase is expected to lead to a qualitative change and improvement in the CVD of graphene and graphene-like two-dimensional materials. Unlike solid substrates, liquid substrates exhibit a loose atomic arrangement and intense atom movement, which contribute to a smooth and isotropic liquid surface and a fluidic liquid phase that can embed heteroatoms. Therefore, liquid metal shows many unique behaviors during the catalyzation of the growth of graphene, graphene-like two dimensional materials, and their heterostructures, such as strict self-limitation, ultra-fast growth, and smooth stitching of grains. More importantly, the rheological properties of a liquid substrate can even facilitate the self-assembly and transfer of 2D materials grown on it, in which the liquid metal substrate can be regarded as the 'philosopher's stone'. This feature article summarizes the growth, assembly, and transfer behavior of 2D materials on liquid metal catalysts. These primary technology developments will establish a solid foundation for the practical application of 2D materials.
2017, 33(3): 476-485
doi: 10.3866/PKU.WHXB201611141
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Photoelectrochemical (PEC) bioanalysis is a newly emerged and rapidly developing analysis technique that provides an elegant route for sensitive bioanalysis. The sensing mechanism of PEC bioanalysis is based on the fact that variations in photocurrent signal can be produced by biological interactions between various recognition elements and their corresponding targets. Owing to its excellent sensitivity, selectivity, and great potential for future bioanalysis, PEC bioanalysis has drawn increasing research attention and substantial progress has been made in its analytical applications. Currently, it has become a hot research topic and its recent momentum has grown rapidly, as demonstrated by the increased number of published research articles. Given the pace of advances in this area, this review first introduces the fundamentals and general instrumentation of this methodology. Then, with recent illustrative examples, we summarize the new developments in PEC bioanalysis according to its main bioanalytical applications, i.e., direct PEC detection of biomolecules, PEC enzymatic bioanalysis, PEC DNA detection, and PEC immunoassay. The future challenges and developments in this field are also discussed.
Photoelectrochemical (PEC) bioanalysis is a newly emerged and rapidly developing analysis technique that provides an elegant route for sensitive bioanalysis. The sensing mechanism of PEC bioanalysis is based on the fact that variations in photocurrent signal can be produced by biological interactions between various recognition elements and their corresponding targets. Owing to its excellent sensitivity, selectivity, and great potential for future bioanalysis, PEC bioanalysis has drawn increasing research attention and substantial progress has been made in its analytical applications. Currently, it has become a hot research topic and its recent momentum has grown rapidly, as demonstrated by the increased number of published research articles. Given the pace of advances in this area, this review first introduces the fundamentals and general instrumentation of this methodology. Then, with recent illustrative examples, we summarize the new developments in PEC bioanalysis according to its main bioanalytical applications, i.e., direct PEC detection of biomolecules, PEC enzymatic bioanalysis, PEC DNA detection, and PEC immunoassay. The future challenges and developments in this field are also discussed.
2017, 33(3): 486-499
doi: 10.3866/PKU.WHXB201611181
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The aprotic Li-O2 battery has attracted considerable interest in recent years because of its high theoretical specific energy that is far greater than that achievable with state-of-the-art Li-ion technologies. To date, most Li-O2 studies, based on a cell configuration with a Li metal anode, aprotic Li+ electrolyte and porous O2 cathode, have focused on O2 reactions at the cathode. However, these reactions might be complicated by the use of Li metal anode. This is because both the electrolyte and O2 (from cathode) can react with the Li metal and some parasitic products could cross over to the cathode and interfere with the O2 reactions occurring therein. In addition, the possibility of dendrite formation on the Li anode, during its multiple plating/stripping cycles, raises serious safety concerns that impede the realization of practical Li-O2 cells. Therefore, solutions to these issues are urgently needed to achieve a reversible and safety Li anode. This review summarizes recent advances in this field and strategies for achieving high performance Li anode for use in aprotic Li-O2 batteries. Topics include alternative counter/reference electrodes, electrolytes and additives, composite protection layers and separators, and advanced experimental techniques for studying the Li anode|electrolyte interface. Future developments in relation to Li anode for aprotic Li-O2 batteries are also discussed.
The aprotic Li-O2 battery has attracted considerable interest in recent years because of its high theoretical specific energy that is far greater than that achievable with state-of-the-art Li-ion technologies. To date, most Li-O2 studies, based on a cell configuration with a Li metal anode, aprotic Li+ electrolyte and porous O2 cathode, have focused on O2 reactions at the cathode. However, these reactions might be complicated by the use of Li metal anode. This is because both the electrolyte and O2 (from cathode) can react with the Li metal and some parasitic products could cross over to the cathode and interfere with the O2 reactions occurring therein. In addition, the possibility of dendrite formation on the Li anode, during its multiple plating/stripping cycles, raises serious safety concerns that impede the realization of practical Li-O2 cells. Therefore, solutions to these issues are urgently needed to achieve a reversible and safety Li anode. This review summarizes recent advances in this field and strategies for achieving high performance Li anode for use in aprotic Li-O2 batteries. Topics include alternative counter/reference electrodes, electrolytes and additives, composite protection layers and separators, and advanced experimental techniques for studying the Li anode|electrolyte interface. Future developments in relation to Li anode for aprotic Li-O2 batteries are also discussed.
2017, 33(3): 500-505
doi: 10.3866/PKU.WHXB201611111
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The dissociation and photoionization dynamics of C3H5Cl were studied at 200, 400, and 800 nm with femtosecond laser pulses. The time-of-flight mass spectra, laser power index and photoelectron images were recorded. At short wavelength (200 nm), ionization of the parent molecule was found to be the dominant channel, while other ions were generated by the dissociation of C3H5Cl+. With the shift to long wavelength (e.g., 800 nm), fragment ions became dominant, and were generated through the multiphoton ionization of neutral fragments after the photodissociation of C3H5Cl. These results imply that photodissociation plays a significant role at long wavelength, because neutral fragments are supposed to be generated from the intermediate states reached by 800 nm photons. At 400 nm, the dissociation on the intermediate states is also critical, but is not as high as that at 800 nm. Taken together, our results demonstrate that the dissociation/ionization behaviors of allyl chloride are wavelength-dependent, and reveal the complex dynamics of allyl chloride at 200, 400 and 800 nm.
The dissociation and photoionization dynamics of C3H5Cl were studied at 200, 400, and 800 nm with femtosecond laser pulses. The time-of-flight mass spectra, laser power index and photoelectron images were recorded. At short wavelength (200 nm), ionization of the parent molecule was found to be the dominant channel, while other ions were generated by the dissociation of C3H5Cl+. With the shift to long wavelength (e.g., 800 nm), fragment ions became dominant, and were generated through the multiphoton ionization of neutral fragments after the photodissociation of C3H5Cl. These results imply that photodissociation plays a significant role at long wavelength, because neutral fragments are supposed to be generated from the intermediate states reached by 800 nm photons. At 400 nm, the dissociation on the intermediate states is also critical, but is not as high as that at 800 nm. Taken together, our results demonstrate that the dissociation/ionization behaviors of allyl chloride are wavelength-dependent, and reveal the complex dynamics of allyl chloride at 200, 400 and 800 nm.
2017, 33(3): 506-512
doi: 10.3866/PKU.WHXB201612061
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Excited-state dynamics of 2-methyl furan has been studied by femtosecond time-resolved photoelectron imaging. The molecule 2-methyl furan was simultaneously excited to the n=3 Rydberg series of S1[1A"(π3s)], 1A'(π3px), 1A"(π3py) and 1A"(π3pz) and the valence state of 1A'(ππ*) by two 400 nm photons and subsequently probed by two 800 nm photons. The average lifetime of the Rydberg series and the valence state was measured to be on the time scale of 50 fs by the time-dependent ion yield of the parent ion. Ultrafast internal conversions among these excited states were observed and extracted from the time-dependences of the photoelectron kinetic energy components of these excited states in the photoelectron kinetic energy spectra. Furthermore, it is identified that the 1A'(ππ*) state might play an important role in internal conversions among these excited states. The Rydberg-valence mixings, which result in numerous conical intersections, act as the driving force to accomplish such ultrafast internal conversions.
Excited-state dynamics of 2-methyl furan has been studied by femtosecond time-resolved photoelectron imaging. The molecule 2-methyl furan was simultaneously excited to the n=3 Rydberg series of S1[1A"(π3s)], 1A'(π3px), 1A"(π3py) and 1A"(π3pz) and the valence state of 1A'(ππ*) by two 400 nm photons and subsequently probed by two 800 nm photons. The average lifetime of the Rydberg series and the valence state was measured to be on the time scale of 50 fs by the time-dependent ion yield of the parent ion. Ultrafast internal conversions among these excited states were observed and extracted from the time-dependences of the photoelectron kinetic energy components of these excited states in the photoelectron kinetic energy spectra. Furthermore, it is identified that the 1A'(ππ*) state might play an important role in internal conversions among these excited states. The Rydberg-valence mixings, which result in numerous conical intersections, act as the driving force to accomplish such ultrafast internal conversions.
2017, 33(3): 513-519
doi: 10.3866/PKU.WHXB201610251
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The density and viscosity of aqueous solutions of an ionic liquid (IL) based on alanine,[C2mim] [Ala], with various molalities were measured in the temperature range of T=288.15-328.15 K with intervals of 5 K. From the Jones-Dole equation, a viscosity B-coefficient with a large positive value and dB/dT<0 were obtained. According to Feakins, the contribution of the solute to the activation free energy for viscous flow of the solution, Δμ2≠0, was obtained. The relationship between Δμ2≠0 and temperature was linear, allowing the standard molar activation entropy, ΔS2≠0, and enthalpy, ΔH2≠0, to be obtained. On the basis of Eyring's theory, a new semi-empirical method to estimate the viscosity of aqueous[C2mim] [Ala] was proposed. The values estimated using this method agreed well with the corresponding experimental ones.
The density and viscosity of aqueous solutions of an ionic liquid (IL) based on alanine,[C2mim] [Ala], with various molalities were measured in the temperature range of T=288.15-328.15 K with intervals of 5 K. From the Jones-Dole equation, a viscosity B-coefficient with a large positive value and dB/dT<0 were obtained. According to Feakins, the contribution of the solute to the activation free energy for viscous flow of the solution, Δμ2≠0, was obtained. The relationship between Δμ2≠0 and temperature was linear, allowing the standard molar activation entropy, ΔS2≠0, and enthalpy, ΔH2≠0, to be obtained. On the basis of Eyring's theory, a new semi-empirical method to estimate the viscosity of aqueous[C2mim] [Ala] was proposed. The values estimated using this method agreed well with the corresponding experimental ones.
2017, 33(3): 520-529
doi: 10.3866/PKU.WHXB201611151
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Based on density functional theory (DFT) with the dispersion correction method, the formation energies, charge transfer, cell potential, and migration process for Na storage in bilayer graphene (BLG) with double vacancy (DV) defects were studied. The formation energy results indicate that one Na atom adsorption or intercalation on or into the center of the vacancy is more favorable. The charge density distribution and Bader charge results indicate that the interactions between Na atoms and BLG are ionic. During Na intercalation in DV defective BLG, the transformation from AB to AA stacking may be delayed as the defect density is increased, and the stable capacity increases to 262.75 mAh·g-1 (Na:C mole ratio=2:17) for Na adsorption on the surface and intercalation into the interlayer of BLG with DV defects. With increasing Na concentration, Na atoms on the surface tend to aggregate into clusters and eventually macroscopic dendrites. The diffusion energy barrier is increased for adsorbed Na on the surface migrating toward the center of DV defects, while that for the reverse direction is decreased by the intercalated Na atoms, which enhances the storage of Na on the surface of BLG with DV defects.
Based on density functional theory (DFT) with the dispersion correction method, the formation energies, charge transfer, cell potential, and migration process for Na storage in bilayer graphene (BLG) with double vacancy (DV) defects were studied. The formation energy results indicate that one Na atom adsorption or intercalation on or into the center of the vacancy is more favorable. The charge density distribution and Bader charge results indicate that the interactions between Na atoms and BLG are ionic. During Na intercalation in DV defective BLG, the transformation from AB to AA stacking may be delayed as the defect density is increased, and the stable capacity increases to 262.75 mAh·g-1 (Na:C mole ratio=2:17) for Na adsorption on the surface and intercalation into the interlayer of BLG with DV defects. With increasing Na concentration, Na atoms on the surface tend to aggregate into clusters and eventually macroscopic dendrites. The diffusion energy barrier is increased for adsorbed Na on the surface migrating toward the center of DV defects, while that for the reverse direction is decreased by the intercalated Na atoms, which enhances the storage of Na on the surface of BLG with DV defects.
2017, 33(3): 530-538
doi: 10.3866/PKU.WHXB201611211
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Surface-enhanced Raman spectroscopy (SERS) is one of the most powerful techniques for obtaining fingerprint information on molecules adsorbed on coinage metal surfaces. Its detection sensitivity has reached the single-molecule level. On the basis of density functional theoretical (DFT) calculations and Raman scattering theory, we investigated the normal Raman spectra of two isomers and surface-enhanced Raman scattering (SERS) spectra of 4-mercaptopyridine (4MPY) adsorbed on silver. The results aided us in uncovering the relationships between normal Raman spectra and SERS spectra and adsorption configuration, tautomerization, protonation, and hydrogen bonding interactions as well as low-lying excited states. First, we compared the relative stability and normal Raman spectra of two isomers of 4MPY in the gas phase and aqueous solution with a solvent model similar to the solvation model of density (SMD). We then studied the Raman spectra of 4MPY interacting with silver clusters. Our results indicate that the Raman spectra were not dependent on the size of the silver clusters, owing to the formation of strong Ag-S bonds. We also considered two cases of Nend interaction in the 4MPY-Ag5 complex. (1) For the hydrogen bond interaction between the nitrogen in 4MPY and water clusters or hydrated proton clusters, the theoretical results indicated that the vibrational frequencies of the pyridine ring increase. (2) For the interaction of the 4MPY-Ag5 complex with a silver cluster Ag4 through the lone-paired orbital in nitrogen of the pyridine ring, the theoretical results further revealed that the vibrational frequency shift is in good agreement with SERS peaks reported in the literature. Finally, our calculated results focused on the relationship between the Raman spectra and the charge transfer mechanism when the excitation photonic energy matches the transition energy of low-lying excited states in single-end and double-end adsorption configuration. Particularly for the case of the double-end adsorption configuration, the charge transfer states from the excitation from the silver cluster binding to the pyridine ring not only enhance the Raman signals of v12, v1, and v8a modes, but also selectively enhance the Raman signal of the v9a mode associated with the symmetric C-H in-plane bending vibration.
Surface-enhanced Raman spectroscopy (SERS) is one of the most powerful techniques for obtaining fingerprint information on molecules adsorbed on coinage metal surfaces. Its detection sensitivity has reached the single-molecule level. On the basis of density functional theoretical (DFT) calculations and Raman scattering theory, we investigated the normal Raman spectra of two isomers and surface-enhanced Raman scattering (SERS) spectra of 4-mercaptopyridine (4MPY) adsorbed on silver. The results aided us in uncovering the relationships between normal Raman spectra and SERS spectra and adsorption configuration, tautomerization, protonation, and hydrogen bonding interactions as well as low-lying excited states. First, we compared the relative stability and normal Raman spectra of two isomers of 4MPY in the gas phase and aqueous solution with a solvent model similar to the solvation model of density (SMD). We then studied the Raman spectra of 4MPY interacting with silver clusters. Our results indicate that the Raman spectra were not dependent on the size of the silver clusters, owing to the formation of strong Ag-S bonds. We also considered two cases of Nend interaction in the 4MPY-Ag5 complex. (1) For the hydrogen bond interaction between the nitrogen in 4MPY and water clusters or hydrated proton clusters, the theoretical results indicated that the vibrational frequencies of the pyridine ring increase. (2) For the interaction of the 4MPY-Ag5 complex with a silver cluster Ag4 through the lone-paired orbital in nitrogen of the pyridine ring, the theoretical results further revealed that the vibrational frequency shift is in good agreement with SERS peaks reported in the literature. Finally, our calculated results focused on the relationship between the Raman spectra and the charge transfer mechanism when the excitation photonic energy matches the transition energy of low-lying excited states in single-end and double-end adsorption configuration. Particularly for the case of the double-end adsorption configuration, the charge transfer states from the excitation from the silver cluster binding to the pyridine ring not only enhance the Raman signals of v12, v1, and v8a modes, but also selectively enhance the Raman signal of the v9a mode associated with the symmetric C-H in-plane bending vibration.
2017, 33(3): 539-547
doi: 10.3866/PKU.WHXB201611252
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In this study, a coarse-grained lattice Monte Carlo model was used to investigate the formation of Sierpiński triangle (ST) fractals through self-assembly on a triangular lattice surface. In the simulations, both symmetric and asymmetric molecular building blocks can spontaneously form ST fractal patterns, although the mixture of enantiomers of asymmetric molecule is more difficult to self-organize into ST of a high order owing to the presence of a large variety of competing three-membered nodes. The formation of ST fractals is favored at low surface coverage and is sensitive to temperature. Furthermore, to test whether the assembly pathway and outcome could be controlled by molecular design, we guided the self-assembly process forming ST fractal into the otherwise disfavored self-assembled structures using templates different from the assembling molecules. The templates are designed to act as"catassemblers"that initiate the self-assembling but are excluded from the final assembled structure.
In this study, a coarse-grained lattice Monte Carlo model was used to investigate the formation of Sierpiński triangle (ST) fractals through self-assembly on a triangular lattice surface. In the simulations, both symmetric and asymmetric molecular building blocks can spontaneously form ST fractal patterns, although the mixture of enantiomers of asymmetric molecule is more difficult to self-organize into ST of a high order owing to the presence of a large variety of competing three-membered nodes. The formation of ST fractals is favored at low surface coverage and is sensitive to temperature. Furthermore, to test whether the assembly pathway and outcome could be controlled by molecular design, we guided the self-assembly process forming ST fractal into the otherwise disfavored self-assembled structures using templates different from the assembling molecules. The templates are designed to act as"catassemblers"that initiate the self-assembling but are excluded from the final assembled structure.
2017, 33(3): 548-553
doi: 10.3866/PKU.WHXB201612081
Abstract:
A series of AlAs nanotubes (NTs) can be formed by rolling up two dimensional periodic (111) single layer sheets, namely (n,0) and (n,m) nanotubes. Optimized parameters of the atomic arrangement, energy levels and electronic structure of corresponding nanotubes of different types were calculated and compared by the density functional theory (DFT) method. The calculated results showed that strain energies (Es) are negative over most of the diameter range for the (n,0) and (n,m) series, indicating that these NTs are more stable than a planar AlAs(111) single layer. The strain energy gradually decreases with increasing diameter. The calculated electronic band structures and density of states profiles reveal that the indirect band gaps (Eg) of armchair AlAs nanotubes gradually decreases with increasing diameter, which is distinct behavior from the zigzag nanotubes. The zigzag AlAs nanotubes feature a direct Eg with a peak value (2.11 eV) for a tube of radius 1.87 nm. The origin of the differences in band gaps could be attributed to the p-p coupling interaction between Al 3p orbitals in the conduction band of the AlAs zigzag nanotube.
A series of AlAs nanotubes (NTs) can be formed by rolling up two dimensional periodic (111) single layer sheets, namely (n,0) and (n,m) nanotubes. Optimized parameters of the atomic arrangement, energy levels and electronic structure of corresponding nanotubes of different types were calculated and compared by the density functional theory (DFT) method. The calculated results showed that strain energies (Es) are negative over most of the diameter range for the (n,0) and (n,m) series, indicating that these NTs are more stable than a planar AlAs(111) single layer. The strain energy gradually decreases with increasing diameter. The calculated electronic band structures and density of states profiles reveal that the indirect band gaps (Eg) of armchair AlAs nanotubes gradually decreases with increasing diameter, which is distinct behavior from the zigzag nanotubes. The zigzag AlAs nanotubes feature a direct Eg with a peak value (2.11 eV) for a tube of radius 1.87 nm. The origin of the differences in band gaps could be attributed to the p-p coupling interaction between Al 3p orbitals in the conduction band of the AlAs zigzag nanotube.
2017, 33(3): 554-562
doi: 10.3866/PKU.WHXB201611171
Abstract:
In the present work, graphene oxide (GO)-ZnO bilayer composites were fabricated by depositing GO on ZnO by an anodic electrophoretic method. The composite films were then subjected to a cathodic electrochemical treatment with different GO reduction times. The as-prepared films were characterized by Xray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM) to study changes in the GO structure. The evolution of the material's energy levels over time was also determined by ultraviolet-visible (UV-Vis) spectroscopy and electrochemical measurements. A series of structural transformations of GO occurred even after it had reached the maximum degree of reduction. Prolonged treatment saw the GO flakes fracture into smaller GO particles with a sharp increase in the proportion of carboxyl groups. The energy gap of GO varied and extended into the visible range with longer reduction time. The energy levels and charge carrier type also varied. Photoelectrochemical tests on the samples revealed that the 60 to 600-s reduced GO-ZnO composite films showed photoelectric conversion behavior as photoanodes. However, the sample reduced for 1800 s was not effective at light-harvesting owing to lowering of the GO conduction band below that of ZnO. The differences in performance indicated that the transformation of the laminated GO geometry to a more disordered distribution enhanced conversion efficiency.
In the present work, graphene oxide (GO)-ZnO bilayer composites were fabricated by depositing GO on ZnO by an anodic electrophoretic method. The composite films were then subjected to a cathodic electrochemical treatment with different GO reduction times. The as-prepared films were characterized by Xray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM) to study changes in the GO structure. The evolution of the material's energy levels over time was also determined by ultraviolet-visible (UV-Vis) spectroscopy and electrochemical measurements. A series of structural transformations of GO occurred even after it had reached the maximum degree of reduction. Prolonged treatment saw the GO flakes fracture into smaller GO particles with a sharp increase in the proportion of carboxyl groups. The energy gap of GO varied and extended into the visible range with longer reduction time. The energy levels and charge carrier type also varied. Photoelectrochemical tests on the samples revealed that the 60 to 600-s reduced GO-ZnO composite films showed photoelectric conversion behavior as photoanodes. However, the sample reduced for 1800 s was not effective at light-harvesting owing to lowering of the GO conduction band below that of ZnO. The differences in performance indicated that the transformation of the laminated GO geometry to a more disordered distribution enhanced conversion efficiency.
2017, 33(3): 563-572
doi: 10.3866/PKU.WHXB201612072
Abstract:
A series of Pt/C, Pt-Ni1/3/C, Pt-SnO2/C and Pt-Nix-SnO2/C (x=1/4, 1/3, 2/3, 1) anode electro-catalysts have been synthesized by an improved Bönnemann method. The crystal structure, surface morphology and surface electronic structure were characterizated by X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The electro-catalytic activities were characterizated by linear sweep voltammetry (LSV) and amperometric current density-time (j-t) curve techniques for ethanol oxidation reaction (EOR). In situ spectroelectrochemical studies have been used to identity adsorbed reaction intermediates and products (in situ Fourier transform infrared spectroscopy, FT-IR). XRD and HR-TEM analysis revealed two phases in the ternary Pt-Ni-SnO2/C catalyst:Pt-Ni alloys and SnO2. XPS results show that the electronic structure of the Pt in Pt-Ni1/3-SnO2/C might be changed due to the addition of Ni. The activity of Pt-Ni-SnO2/C for EOR was found to be higher than that of Pt/C, Pt-Ni/C and Pt-SnO2/C catalysts. The incorporation of Ni and SnO2 did not significantly improve C-C bond breaking for complete oxidation of ethanol, but the synergy under the low potential (0.1 V) to strengthen the further oxidation of acetaldehyde, generate the acetic acid.
A series of Pt/C, Pt-Ni1/3/C, Pt-SnO2/C and Pt-Nix-SnO2/C (x=1/4, 1/3, 2/3, 1) anode electro-catalysts have been synthesized by an improved Bönnemann method. The crystal structure, surface morphology and surface electronic structure were characterizated by X-ray diffraction (XRD), high resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The electro-catalytic activities were characterizated by linear sweep voltammetry (LSV) and amperometric current density-time (j-t) curve techniques for ethanol oxidation reaction (EOR). In situ spectroelectrochemical studies have been used to identity adsorbed reaction intermediates and products (in situ Fourier transform infrared spectroscopy, FT-IR). XRD and HR-TEM analysis revealed two phases in the ternary Pt-Ni-SnO2/C catalyst:Pt-Ni alloys and SnO2. XPS results show that the electronic structure of the Pt in Pt-Ni1/3-SnO2/C might be changed due to the addition of Ni. The activity of Pt-Ni-SnO2/C for EOR was found to be higher than that of Pt/C, Pt-Ni/C and Pt-SnO2/C catalysts. The incorporation of Ni and SnO2 did not significantly improve C-C bond breaking for complete oxidation of ethanol, but the synergy under the low potential (0.1 V) to strengthen the further oxidation of acetaldehyde, generate the acetic acid.
2017, 33(3): 573-581
doi: 10.3866/PKU.WHXB201612122
Abstract:
This paper describes the sensing properties of a potentiometric sensor based on a palladium oxide (PdO) electrode. Our investigation of the sensing mechanism is also discussed. We studied carbon monoxide (CO) sensing performance of a PdO electrode doped with Mg, Ni, and La, printed on zirconia. The results indicated that defects on the surface of PdO, which allow adsorption of CO, can effectively enhance the sensitivity of the sensors. To explore the source of the signal, a PdO-based electrode was printed on an alumina disc and a zeolite pellet for CO detection at 450℃. Notably the zeolite coupled with the PdO-based electrode to generate potentiometric responses to changes in CO concentration. According to the resistance and impedance measurements, the response to CO was ascribed to the changing interfacial potential between the PdO electrode and electrolyte. A model based on an electrochemical double layer between the PdO and electrolyte was determined to explain the behavior of the potentiometric sensor. It may be possible to harness these effects at PdO electrodes for the development of electrochemical sensors.
This paper describes the sensing properties of a potentiometric sensor based on a palladium oxide (PdO) electrode. Our investigation of the sensing mechanism is also discussed. We studied carbon monoxide (CO) sensing performance of a PdO electrode doped with Mg, Ni, and La, printed on zirconia. The results indicated that defects on the surface of PdO, which allow adsorption of CO, can effectively enhance the sensitivity of the sensors. To explore the source of the signal, a PdO-based electrode was printed on an alumina disc and a zeolite pellet for CO detection at 450℃. Notably the zeolite coupled with the PdO-based electrode to generate potentiometric responses to changes in CO concentration. According to the resistance and impedance measurements, the response to CO was ascribed to the changing interfacial potential between the PdO electrode and electrolyte. A model based on an electrochemical double layer between the PdO and electrolyte was determined to explain the behavior of the potentiometric sensor. It may be possible to harness these effects at PdO electrodes for the development of electrochemical sensors.
2017, 33(3): 582-589
doi: 10.3866/PKU.WHXB201611292
Abstract:
A hybrid molecule having a molecular structure of cholesterol-polyoxometalate-cholesterol, was created by covalently connecting two cholesterol molecules onto the two sides of an organically modified Anderson-type polyoxometalate (POM). This hybrid molecule could self-assemble into highly ordered hexagonally packed cylinders in a bulk sample. The POM cluster of the hybrid molecule dissolved well in N,N-dimethylformamide (DMF) solvent and cholesterol moieties had appropriate solubility in toluene. In mixed DMF/toluene solvents, the hybrid molecule self-assembled into fibril-shaped aggregates. These aggregates further twisted around each other to form the three-dimensional network structures. These formations were attributed to the solubility difference between the POM cluster and cholesterol moieties, van der Waals interactions among the cholesterol moieties, and electrostatic interactions among the POM clusters. Within the fibrous structure, the POM cluster and cholesterol moieties in the hybrid molecule assembled into a well-organized structure with alternatively arranged POM layer and cholesterol layer. The results described herein has potential application value toward design, assembly, and application of nanomaterials.
A hybrid molecule having a molecular structure of cholesterol-polyoxometalate-cholesterol, was created by covalently connecting two cholesterol molecules onto the two sides of an organically modified Anderson-type polyoxometalate (POM). This hybrid molecule could self-assemble into highly ordered hexagonally packed cylinders in a bulk sample. The POM cluster of the hybrid molecule dissolved well in N,N-dimethylformamide (DMF) solvent and cholesterol moieties had appropriate solubility in toluene. In mixed DMF/toluene solvents, the hybrid molecule self-assembled into fibril-shaped aggregates. These aggregates further twisted around each other to form the three-dimensional network structures. These formations were attributed to the solubility difference between the POM cluster and cholesterol moieties, van der Waals interactions among the cholesterol moieties, and electrostatic interactions among the POM clusters. Within the fibrous structure, the POM cluster and cholesterol moieties in the hybrid molecule assembled into a well-organized structure with alternatively arranged POM layer and cholesterol layer. The results described herein has potential application value toward design, assembly, and application of nanomaterials.
2017, 33(3): 590-601
doi: 10.3866/PKU.WHXB201611241
Abstract:
A series of p-n coupled p-CoFe2O4/n-CdS photocatalysts were prepared by a hydrothermal method. The structure and properties of p-CoFe2O4/n-CdS were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), transmission electron microscopy (TEM) and the electrochemical workstation. The photocatalytic activities of p-CoFe2O4/nCdS were evaluated by photocatalytic hydrogen production under visible light irradiation. The effects of photocorrosion of CdS in p-CoFe2O4/n-CdS were investigated by analyzing the cadmium concentration of the supernatant collected after the photocatalytic reactions. The mechanism of the catalytic activity enhancement, effects of reaction conditions on the photocatalytic hydrogen evolution rate, and cadmium leakage resistance are discussed. The results show that p-CoFe2O4/n-CdS exhibits higher photocatalytic activity attributed to stronger light absorption by the two types of narrow band gap semiconductor CoFe2O4 and CdS, the formation of a "forest-like" structure of CdS and rapid electron transfer from CoFe2O4 to CdS, resulting from band overlap and an inner electric field in p-CoFe2O4/n-CdS, to reduce the probability of electron/hole pair recombination. Both the separation efficiency of photo-generated electron-hole pairs and the adsorption performance of photocatalysts had an important influence on the hydrogen production rate. The pH of the CH3OH aqueous solution influenced the separation efficiency of photogenerated electron-hole pairs and the adsorption properties of the photocatalyst. p-CoFe2O4/n-CdS also exhibited resistance against cadmium leakage under light irradiation owing to the presence of methanol in the reaction solution, the band overlap of the semiconductors and the inner electric field in p-CoFe2O4/n-CdS. The band overlap and inner electric field had the most influence on the cadmium leakage resistance.
A series of p-n coupled p-CoFe2O4/n-CdS photocatalysts were prepared by a hydrothermal method. The structure and properties of p-CoFe2O4/n-CdS were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), transmission electron microscopy (TEM) and the electrochemical workstation. The photocatalytic activities of p-CoFe2O4/nCdS were evaluated by photocatalytic hydrogen production under visible light irradiation. The effects of photocorrosion of CdS in p-CoFe2O4/n-CdS were investigated by analyzing the cadmium concentration of the supernatant collected after the photocatalytic reactions. The mechanism of the catalytic activity enhancement, effects of reaction conditions on the photocatalytic hydrogen evolution rate, and cadmium leakage resistance are discussed. The results show that p-CoFe2O4/n-CdS exhibits higher photocatalytic activity attributed to stronger light absorption by the two types of narrow band gap semiconductor CoFe2O4 and CdS, the formation of a "forest-like" structure of CdS and rapid electron transfer from CoFe2O4 to CdS, resulting from band overlap and an inner electric field in p-CoFe2O4/n-CdS, to reduce the probability of electron/hole pair recombination. Both the separation efficiency of photo-generated electron-hole pairs and the adsorption performance of photocatalysts had an important influence on the hydrogen production rate. The pH of the CH3OH aqueous solution influenced the separation efficiency of photogenerated electron-hole pairs and the adsorption properties of the photocatalyst. p-CoFe2O4/n-CdS also exhibited resistance against cadmium leakage under light irradiation owing to the presence of methanol in the reaction solution, the band overlap of the semiconductors and the inner electric field in p-CoFe2O4/n-CdS. The band overlap and inner electric field had the most influence on the cadmium leakage resistance.
2017, 33(3): 602-610
doi: 10.3866/PKU.WHXB201611251
Abstract:
Anatase TiO2 nanospindles containing 89% exposed {101} facets (TiO2-101) and nanosheets with 77% exposed {001} facets (TiO2-001) were hydrothermally synthesized and used as supports for Pd catalysts. The effects of the TiO2 materials on the catalytic performance of Pd/TiO2-101 and Pd/TiO2-001 catalysts were investigated in the selective hydrogenation of acetylene to polymer-grade ethylene. The Pd/TiO2-101 catalyst exhibited enhanced performance in terms of acetylene conversion and ethylene yield. To understand these effects, the catalysts were characterized by H2 temperature-programmed desorption (H2-TPD), H2 temperatureprogrammed reduction (H2-TPR), transmission electron microscopy (TEM), pulse CO chemisorption, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The TEM and CO chemisorption results confirmed that Pd nanoparticles (NPs) on the TiO2-101 support had a smaller average particle size (1.53 nm) and a higher dispersion (15.95%) than those on the TiO2-001 support (average particle size of 4.36 nm and dispersion of 9.06%). The smaller particle size and higher dispersion of Pd on the Pd/TiO2-101 catalyst provided more reaction active sites, which contributed to the improved catalytic activity of this supported catalyst.
Anatase TiO2 nanospindles containing 89% exposed {101} facets (TiO2-101) and nanosheets with 77% exposed {001} facets (TiO2-001) were hydrothermally synthesized and used as supports for Pd catalysts. The effects of the TiO2 materials on the catalytic performance of Pd/TiO2-101 and Pd/TiO2-001 catalysts were investigated in the selective hydrogenation of acetylene to polymer-grade ethylene. The Pd/TiO2-101 catalyst exhibited enhanced performance in terms of acetylene conversion and ethylene yield. To understand these effects, the catalysts were characterized by H2 temperature-programmed desorption (H2-TPD), H2 temperatureprogrammed reduction (H2-TPR), transmission electron microscopy (TEM), pulse CO chemisorption, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The TEM and CO chemisorption results confirmed that Pd nanoparticles (NPs) on the TiO2-101 support had a smaller average particle size (1.53 nm) and a higher dispersion (15.95%) than those on the TiO2-001 support (average particle size of 4.36 nm and dispersion of 9.06%). The smaller particle size and higher dispersion of Pd on the Pd/TiO2-101 catalyst provided more reaction active sites, which contributed to the improved catalytic activity of this supported catalyst.
2017, 33(3): 611-619
doi: 10.3866/PKU.WHXB201611102
Abstract:
In this work, graphitic carbon nitride (g-C3N4) with large surface area and many nitrogen vacancies was synthesized by introducing ionic liquid[Bmim]Br as a solvent into the solvothermal post-treatment. X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), temperature-programmed desorption of N2 (N2-TPD), and photoluminescence (PL) spectroscopy were used to characterize the prepared catalysts. The morphology of the as-prepared g-C3N4 was markedly changed from an orderless layered structure to nanoparticles with a uniform size distribution of around 30-40 nm after the introduction of[Bmim]Br, leading an increase in surface area from 8.6 to 37.9 m2·g-1. N2-TPD, photoluminescence spectra, and density functional theory (DFT) simulations indicated that the nitrogen vacancies not only trapped the photogenerated electrons to enhance their separation rate, but also served as active sites for the adsorption and activation of N2 molecules. The increased surface area of the as-prepared g-C3N4 meant that more nitrogen vacancies were exposed on the surface, leading to a markedly promoted nitrogen photofixation ability. The possible reaction mechanism is proposed.
In this work, graphitic carbon nitride (g-C3N4) with large surface area and many nitrogen vacancies was synthesized by introducing ionic liquid[Bmim]Br as a solvent into the solvothermal post-treatment. X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), temperature-programmed desorption of N2 (N2-TPD), and photoluminescence (PL) spectroscopy were used to characterize the prepared catalysts. The morphology of the as-prepared g-C3N4 was markedly changed from an orderless layered structure to nanoparticles with a uniform size distribution of around 30-40 nm after the introduction of[Bmim]Br, leading an increase in surface area from 8.6 to 37.9 m2·g-1. N2-TPD, photoluminescence spectra, and density functional theory (DFT) simulations indicated that the nitrogen vacancies not only trapped the photogenerated electrons to enhance their separation rate, but also served as active sites for the adsorption and activation of N2 molecules. The increased surface area of the as-prepared g-C3N4 meant that more nitrogen vacancies were exposed on the surface, leading to a markedly promoted nitrogen photofixation ability. The possible reaction mechanism is proposed.
2017, 33(3): 620-626
doi: 10.3866/PKU.WHXB201612011
Abstract:
Enzyme-catalyzed reactions are a prominent field of research in green chemistry. Laccase is a multicopper oxidase, which we used to study the oxidation of catechol. A mechanism for this ring-opening reaction is also proposed. A o-benzosemiquinone radical was the initial nascent product of catechol oxidation during the catalytic reaction. This radical underwent two reaction pathways:(1) formation of an intramolecular adduct, which gave a carbon-centered furan-derived radical trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO); (2) formation of an intermolecular adduct producing dimeric and trimeric oligomers, as resolved by mass spectrometry. Products of the furan-like intermediate were also characterized by 1H-NMR. Simultaneously, a hydroxyl radical (·OH) originating from the water solvent was identified by 17O-isotope tracing. The kinetics of this radical were also evident with substrates including 3-and 4-methyl catechol, but not with resorcinol and hydroquinone isomers, 3-and 4-nitro catechol, and 2,3-dihydroxynaphthalene. The mechanism of selective activation and ring-opening at the C4-C5 site is discussed. This reaction is distinct from intra-and extra-diol ringcleavages catalyzed by catechol dioxygenase. These results are meaningful for mimicking laccase catalysis to further protein design.
Enzyme-catalyzed reactions are a prominent field of research in green chemistry. Laccase is a multicopper oxidase, which we used to study the oxidation of catechol. A mechanism for this ring-opening reaction is also proposed. A o-benzosemiquinone radical was the initial nascent product of catechol oxidation during the catalytic reaction. This radical underwent two reaction pathways:(1) formation of an intramolecular adduct, which gave a carbon-centered furan-derived radical trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO); (2) formation of an intermolecular adduct producing dimeric and trimeric oligomers, as resolved by mass spectrometry. Products of the furan-like intermediate were also characterized by 1H-NMR. Simultaneously, a hydroxyl radical (·OH) originating from the water solvent was identified by 17O-isotope tracing. The kinetics of this radical were also evident with substrates including 3-and 4-methyl catechol, but not with resorcinol and hydroquinone isomers, 3-and 4-nitro catechol, and 2,3-dihydroxynaphthalene. The mechanism of selective activation and ring-opening at the C4-C5 site is discussed. This reaction is distinct from intra-and extra-diol ringcleavages catalyzed by catechol dioxygenase. These results are meaningful for mimicking laccase catalysis to further protein design.
2017, 33(3): 627-632
doi: 10.3866/PKU.WHXB201612051
Abstract:
Corannulene (COR) is considered a promising molecular building block for organic electronics owing to its intriguing geometrical and electronic properties. Intensive research efforts have been devoted to understanding the assembly behavior and electronic structure of COR and its derivatives on various metal surfaces via low-temperature scanning tunneling microscopy (LT-STM). Here we report the formation of binary molecular networks of copper hexadecafluorophthalocyanine (F16CuPc)-COR self-assembled on the highly oriented pyrolytic graphite (HOPG) and Ag(111) substrates. Intermolecular hydrogen bonding between F16CuPc and COR facilitates the formation of binary molecular networks on HOPG and further induces a preference for bowl-down configured COR molecules. This observed configuration preference disappears on Ag(111) substrate, where COR molecules lie on the substrate with their bowl openings pointing up and down randomly. We propose that strong interfacial interactions between the molecule and Ag(111) surface constrain the bowl inversion of the COR molecule, which thus retains its initial configuration upon adsorption.
Corannulene (COR) is considered a promising molecular building block for organic electronics owing to its intriguing geometrical and electronic properties. Intensive research efforts have been devoted to understanding the assembly behavior and electronic structure of COR and its derivatives on various metal surfaces via low-temperature scanning tunneling microscopy (LT-STM). Here we report the formation of binary molecular networks of copper hexadecafluorophthalocyanine (F16CuPc)-COR self-assembled on the highly oriented pyrolytic graphite (HOPG) and Ag(111) substrates. Intermolecular hydrogen bonding between F16CuPc and COR facilitates the formation of binary molecular networks on HOPG and further induces a preference for bowl-down configured COR molecules. This observed configuration preference disappears on Ag(111) substrate, where COR molecules lie on the substrate with their bowl openings pointing up and down randomly. We propose that strong interfacial interactions between the molecule and Ag(111) surface constrain the bowl inversion of the COR molecule, which thus retains its initial configuration upon adsorption.
2017, 33(3): 633-641
doi: 10.3866/PKU.WHXB201612052
Abstract:
Hemagglutinin (HA) is a glycoprotein located on the surface of the avian influenza A viruses. HA plays a key role in the infection process, binding to receptors on the host cell surface and mediating the fusion between viral and host endosomal membranes. In nature, influenza A virus undergoes continuous variation, particularly the amino acid sequence at the receptor binding site of HA. When the binding ability of HA variants towards human receptors becomes strong, influenza A virus can infect humans. To prevent the influenza A virus from infecting humans, proper assessments of the infectious risk posed are urgently needed. Screening of high risk virus strains by analyzing the binding ability of HA variants for human receptors through a high-throughput method would be particularly useful. In this study, we used H7 (a subtype of HA) as a subject and developed a molecular docking based theoretical calculation method to evaluate the affinity of HA variants for human receptors. The results showed that the binding affinity of H7 for human receptors is lower than that of H1, which shows a strong ability to infect humans. This result suggests that strains of the H7 subtype are generally weakly infectious in humans. Nevertheless, the calculation results also showed that some newly-found virus strains of the H7N9 subtype have a high binding affinity for human receptors, suggesting that the H7N9 subtype might include strains with a high risk for infecting humans. These results are consistent with the actual occurrence of the 2013 H7N9 epidemic. Our method may be used to rapidly predict the affinity of HA for human receptors and provides a theoretical basis for the risk assessment of the infectiousness of influenza A virus toward humans.
Hemagglutinin (HA) is a glycoprotein located on the surface of the avian influenza A viruses. HA plays a key role in the infection process, binding to receptors on the host cell surface and mediating the fusion between viral and host endosomal membranes. In nature, influenza A virus undergoes continuous variation, particularly the amino acid sequence at the receptor binding site of HA. When the binding ability of HA variants towards human receptors becomes strong, influenza A virus can infect humans. To prevent the influenza A virus from infecting humans, proper assessments of the infectious risk posed are urgently needed. Screening of high risk virus strains by analyzing the binding ability of HA variants for human receptors through a high-throughput method would be particularly useful. In this study, we used H7 (a subtype of HA) as a subject and developed a molecular docking based theoretical calculation method to evaluate the affinity of HA variants for human receptors. The results showed that the binding affinity of H7 for human receptors is lower than that of H1, which shows a strong ability to infect humans. This result suggests that strains of the H7 subtype are generally weakly infectious in humans. Nevertheless, the calculation results also showed that some newly-found virus strains of the H7N9 subtype have a high binding affinity for human receptors, suggesting that the H7N9 subtype might include strains with a high risk for infecting humans. These results are consistent with the actual occurrence of the 2013 H7N9 epidemic. Our method may be used to rapidly predict the affinity of HA for human receptors and provides a theoretical basis for the risk assessment of the infectiousness of influenza A virus toward humans.
