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2012 Volume 28 Issue 4
2012, 28(04):
Abstract:
2012, 28(04): 739-750
doi: 10.3866/PKU.WHXB201112222
Abstract:
Chemosensors have developed quickly because they are widely used in biology. Compared to organic fluorescent chemosensors, phosphorescent chemosensors based on heavy metal complexes have attracted great attention because of distinctive merits such as relatively long lifetimes and significant Stokes shifts. Iridium complexes had been successfully used as phosphorescent chemosensors because of their relatively short excited state lifetime, high photoluminescence efficiency, and wide range emission colors that can be tuned by the coordinated ligands. In this review, we have summarized the applications of iridium complexes in cation, anion, oxygen, amino acid, and pH sensors. Furthermore, the advantages and disadvantages of these chemosensors have been compared to others. Finally, some prospects for future study are proposed.
Chemosensors have developed quickly because they are widely used in biology. Compared to organic fluorescent chemosensors, phosphorescent chemosensors based on heavy metal complexes have attracted great attention because of distinctive merits such as relatively long lifetimes and significant Stokes shifts. Iridium complexes had been successfully used as phosphorescent chemosensors because of their relatively short excited state lifetime, high photoluminescence efficiency, and wide range emission colors that can be tuned by the coordinated ligands. In this review, we have summarized the applications of iridium complexes in cation, anion, oxygen, amino acid, and pH sensors. Furthermore, the advantages and disadvantages of these chemosensors have been compared to others. Finally, some prospects for future study are proposed.
2012, 28(04): 751-758
doi: 10.3866/PKU.WHXB201202022
Abstract:
Molecular docking technology is an effective approach for prediction of intermolecular interactions and recognition. The design of a scoring function for selecting near-native structures is very important for successful prediction of complex structures. In this article, the main computational methods for scoring items in protein-protein docking, such as geometric complementarity, contact area, van der Waals' interaction, electrostatic interaction, and statistical pair propensity potential, are reviewed. Including our work, we introduce commonly used scoring schemes and some strategies in screening decoys based on the information for protein binding sites. The characteristic scoring functions in the commonly used docking programs are compared and summarized. The major problems in the existing scoring function in protein-protein docking are discussed along with prospect for future research.
Molecular docking technology is an effective approach for prediction of intermolecular interactions and recognition. The design of a scoring function for selecting near-native structures is very important for successful prediction of complex structures. In this article, the main computational methods for scoring items in protein-protein docking, such as geometric complementarity, contact area, van der Waals' interaction, electrostatic interaction, and statistical pair propensity potential, are reviewed. Including our work, we introduce commonly used scoring schemes and some strategies in screening decoys based on the information for protein binding sites. The characteristic scoring functions in the commonly used docking programs are compared and summarized. The major problems in the existing scoring function in protein-protein docking are discussed along with prospect for future research.
2012, 28(04): 759-765
doi: 10.3866/PKU.WHXB201202023
Abstract:
The structural and vibrational dynamics of the non-bridged C≡O stretching vibrations of two different tautomers of dimeric π-cyclopentadienyldicarbonyliron [CpFe(CO)2]2 in CH2Cl2 were examined using steady-state and femtosecond infrared pump-probe methods at 5-μm wavelength. The two main species in [CpFe(CO)2]2 had a cis:trans molar ratio of 1.7, and showed different vibrational and rotational relaxation dynamics. Both species showed biexponential decay in their two C≡O stretching vibrational excited-state populations, with a fast component (<1 ps) and a slow component (20 ps). The former was believed to be related to the rapid dephasing processes of the coherent state caused by broadband excitation, while the latter was the typical lifetime for the C≡O stretching vibrational excited state. Having a significant permanent dipole, the cis structure could interact strongly with solvent, resulting in relatively slower rotational dynamics. Our work demonstrated that the frequency and vibrational-rotational dynamics of the non-bridged C≡O stretching vibrations were very sensitive to both molecular structures and the solvent.
The structural and vibrational dynamics of the non-bridged C≡O stretching vibrations of two different tautomers of dimeric π-cyclopentadienyldicarbonyliron [CpFe(CO)2]2 in CH2Cl2 were examined using steady-state and femtosecond infrared pump-probe methods at 5-μm wavelength. The two main species in [CpFe(CO)2]2 had a cis:trans molar ratio of 1.7, and showed different vibrational and rotational relaxation dynamics. Both species showed biexponential decay in their two C≡O stretching vibrational excited-state populations, with a fast component (<1 ps) and a slow component (20 ps). The former was believed to be related to the rapid dephasing processes of the coherent state caused by broadband excitation, while the latter was the typical lifetime for the C≡O stretching vibrational excited state. Having a significant permanent dipole, the cis structure could interact strongly with solvent, resulting in relatively slower rotational dynamics. Our work demonstrated that the frequency and vibrational-rotational dynamics of the non-bridged C≡O stretching vibrations were very sensitive to both molecular structures and the solvent.
2012, 28(04): 766-772
doi: 10.3866/PKU.WHXB201202021
Abstract:
High signal to noise (S/N) ratio Raman spectra of NH4NO3 droplets deposited on a quartz substrate were obtained from dilute to supersaturated states by reducing the relative humidity (RH) of the environment, allowing for accurate control over the concentration of solute within the droplet. When the RH was reduced from 72.1% to 37.9%, the peak position of the v1-NO3- band of the NH4NO3 droplet did not shift from its original position at 1048 cm-1 and a similar full width at half-maximum (FWHM) of 10 cm-1 was also observed. It was concluded that the replacement of H2O molecules hydrogen-bonded with the O atoms of NO3- with NH4+ ions leaves the frequency of v1-NO3- relatively unchanged, indicating that both H2O and NH4+ forming hydrogen bonds have the same strength. From component band analysis in the spectral range of 2500-4000 cm-1, six peaks at 2890, 3090, 3140, 3220, 3402, 3507 cm-1 were identified and assigned. The first four components were assigned to the second overtone of NH4+ umbrella bending, the combination band of NH4+ umbrella bending and rocking vibrations, the NH4+ symmetric stretching vibration, and the NH4+ antisymmetric stretching vibration. The latter two peaks originated from strong and weak hydrogen bonds. The signature of the strong hydrogen bonding component was observed to decrease in intensity with the decrease in RH over the full range from 72.1% to 37.9%, while the signature of the weak hydrogen bonding component was shown to increase as the RH was reduced. The observed trend in the hydrogen bonding component resulted from the interactions between NH4+ and NO3- .
High signal to noise (S/N) ratio Raman spectra of NH4NO3 droplets deposited on a quartz substrate were obtained from dilute to supersaturated states by reducing the relative humidity (RH) of the environment, allowing for accurate control over the concentration of solute within the droplet. When the RH was reduced from 72.1% to 37.9%, the peak position of the v1-NO3- band of the NH4NO3 droplet did not shift from its original position at 1048 cm-1 and a similar full width at half-maximum (FWHM) of 10 cm-1 was also observed. It was concluded that the replacement of H2O molecules hydrogen-bonded with the O atoms of NO3- with NH4+ ions leaves the frequency of v1-NO3- relatively unchanged, indicating that both H2O and NH4+ forming hydrogen bonds have the same strength. From component band analysis in the spectral range of 2500-4000 cm-1, six peaks at 2890, 3090, 3140, 3220, 3402, 3507 cm-1 were identified and assigned. The first four components were assigned to the second overtone of NH4+ umbrella bending, the combination band of NH4+ umbrella bending and rocking vibrations, the NH4+ symmetric stretching vibration, and the NH4+ antisymmetric stretching vibration. The latter two peaks originated from strong and weak hydrogen bonds. The signature of the strong hydrogen bonding component was observed to decrease in intensity with the decrease in RH over the full range from 72.1% to 37.9%, while the signature of the weak hydrogen bonding component was shown to increase as the RH was reduced. The observed trend in the hydrogen bonding component resulted from the interactions between NH4+ and NO3- .
2012, 28(04): 773-780
doi: 10.3866/PKU.WHXB201202132
Abstract:
With a view to understanding the argument of phase-transition mechanisms of D- and L-alanine at around 270 K, the temperature dependence of heat capacity measurements was investigated, for single crystals, ground powders, and polycrystalline products, using differential scanning calorimetry (DSC). The Cp (heat capacity under constant pressure) values of D- and L-alanine were calibrated with standard sapphire by the triple-curve method; these values coincide with the standard Cp values in the literature. Endothermic transition peaks were observed at Tc=272.02 K, ΔH=1.87 J·mol-1 and Tc=271.85 K, ΔH=1.46 J·mol-1 for D- and L- alanine, respectively, and Tc=273.59 K, ΔH=1.75 J·mol-1 and Tc=273.76 K, ΔH=1.57 J·mol-1 for the reference crystals D- and L-valine, respectively. The energy differences of 0.41 J· mol-1 for D-and L-alanine and 0.18 J·mol-1 for D- and L-valine, which were observed from pre-aligned molecules in the single crystals and vanished in the ground powders and polycrystalline products, show that the phase transition is related to the crystal lattice. Neutron diffraction results exclude the possibility of a D→L configuration change, and show that the hydrogen bonds run antiparallel to the c-axis in the D- and Lcrystals. Polarized Raman vibrational spectroscopy shows that the transition mechanism may be related to the electronic orbital angular momentum and magnetic dipole moments of N+H…O- in the crystals. External magnetic fields, H=+1, -1 T, were applied parallel to the c(z)-axis of the D- and L-alanine crystalline lattices, respectively. The DC-magnetic susceptibilities show electron spin-flip transitions at around 270 K in D- and L-alanine. The spin is“up”or“down”relative to the direction of N+H…O- bond along the c(z)-axis. Based on spin rigidity and magnetic anisotropy, the results help to explain the discrepancies among heat capacity and magnetic susceptibility data for single crystals and polycrystalline powders of D- and L-alanine.
With a view to understanding the argument of phase-transition mechanisms of D- and L-alanine at around 270 K, the temperature dependence of heat capacity measurements was investigated, for single crystals, ground powders, and polycrystalline products, using differential scanning calorimetry (DSC). The Cp (heat capacity under constant pressure) values of D- and L-alanine were calibrated with standard sapphire by the triple-curve method; these values coincide with the standard Cp values in the literature. Endothermic transition peaks were observed at Tc=272.02 K, ΔH=1.87 J·mol-1 and Tc=271.85 K, ΔH=1.46 J·mol-1 for D- and L- alanine, respectively, and Tc=273.59 K, ΔH=1.75 J·mol-1 and Tc=273.76 K, ΔH=1.57 J·mol-1 for the reference crystals D- and L-valine, respectively. The energy differences of 0.41 J· mol-1 for D-and L-alanine and 0.18 J·mol-1 for D- and L-valine, which were observed from pre-aligned molecules in the single crystals and vanished in the ground powders and polycrystalline products, show that the phase transition is related to the crystal lattice. Neutron diffraction results exclude the possibility of a D→L configuration change, and show that the hydrogen bonds run antiparallel to the c-axis in the D- and Lcrystals. Polarized Raman vibrational spectroscopy shows that the transition mechanism may be related to the electronic orbital angular momentum and magnetic dipole moments of N+H…O- in the crystals. External magnetic fields, H=+1, -1 T, were applied parallel to the c(z)-axis of the D- and L-alanine crystalline lattices, respectively. The DC-magnetic susceptibilities show electron spin-flip transitions at around 270 K in D- and L-alanine. The spin is“up”or“down”relative to the direction of N+H…O- bond along the c(z)-axis. Based on spin rigidity and magnetic anisotropy, the results help to explain the discrepancies among heat capacity and magnetic susceptibility data for single crystals and polycrystalline powders of D- and L-alanine.
2012, 28(04): 781-786
doi: 10.3866/PKU.WHXB201202151
Abstract:
Aluminum nanopowders (nmAl) coated with oleic acid (OA) were obtained under nitrogen atmosphere, and their surface morphologies and structures were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The thermal decomposition reaction kinetics of composite systems, nmAl/hexogen (RDX) and (nmAl + OA)/RDX, were investigated using differential scanning calorimetry (DSC). Their kinetic parameters and kinetic equations were obtained. The results showed that most of the OA adsorbed on the aluminum nanopowder surface by physical adsorption. Only a small amount of OA reacted with the surface aluminum atoms and adhered to the surface via chemical bonds. Compared with the nmAl/RDX composite, the peak temperatures for the (nmAl+OA)/RDX composite at multiple heating rates were lower. The apparent activation energy (Ea) and pre-exponential factor (A) of the main decomposition reaction were 141.18 kJ·mol-1 and 1012.57 s-1. The reaction mechanism fits a three-dimensional diffusion mechanism and obeys the Jander equation with n= 1/2. The kinetic equation can be expressed as: dα/dt=1013.35(1-α)2/3[1-(1-α)1/3]1/2e-16981.0/T.
Aluminum nanopowders (nmAl) coated with oleic acid (OA) were obtained under nitrogen atmosphere, and their surface morphologies and structures were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The thermal decomposition reaction kinetics of composite systems, nmAl/hexogen (RDX) and (nmAl + OA)/RDX, were investigated using differential scanning calorimetry (DSC). Their kinetic parameters and kinetic equations were obtained. The results showed that most of the OA adsorbed on the aluminum nanopowder surface by physical adsorption. Only a small amount of OA reacted with the surface aluminum atoms and adhered to the surface via chemical bonds. Compared with the nmAl/RDX composite, the peak temperatures for the (nmAl+OA)/RDX composite at multiple heating rates were lower. The apparent activation energy (Ea) and pre-exponential factor (A) of the main decomposition reaction were 141.18 kJ·mol-1 and 1012.57 s-1. The reaction mechanism fits a three-dimensional diffusion mechanism and obeys the Jander equation with n= 1/2. The kinetic equation can be expressed as: dα/dt=1013.35(1-α)2/3[1-(1-α)1/3]1/2e-16981.0/T.
2012, 28(04): 787-791
doi: 10.3866/PKU.WHXB201202161
Abstract:
The ignition delay times of gas-phase kerosene/air mixtures were measured behind reflected shock waves, using side-wall pressure and CH* emission measurements in a heated shock tube. The experiments were performed over the temperature range of 1100-1500 K, at pressures of 2.0×105 and 4.0× 105 Pa, and for equivalence ratios (Φ) of 0.2, 1.0, and 2.0. The effects of temperature, pressure, and equivalence ratio on the ignition delay time were investigated. The global activation energy for kerosene/air varies significantly when the equivalence ratio changes from 0.2 to 1.0, whereas the global activation energy at an equivalence ratio of 1.0 is almost the same as that at 2.0. Three correlations for the ignition delay time under three different equivalence ratios were deduced. The current data were compared with available kinetic mechanisms, and were found to be in od agreement with the predictions of Honnet et al. Chemical mechanism sensitivity analyses for different equivalence ratios were performed; the results showed that the ignition sensitivity at an equivalence ratio of 0.2 is quite different from those at 1.0 and 2.0.
The ignition delay times of gas-phase kerosene/air mixtures were measured behind reflected shock waves, using side-wall pressure and CH* emission measurements in a heated shock tube. The experiments were performed over the temperature range of 1100-1500 K, at pressures of 2.0×105 and 4.0× 105 Pa, and for equivalence ratios (Φ) of 0.2, 1.0, and 2.0. The effects of temperature, pressure, and equivalence ratio on the ignition delay time were investigated. The global activation energy for kerosene/air varies significantly when the equivalence ratio changes from 0.2 to 1.0, whereas the global activation energy at an equivalence ratio of 1.0 is almost the same as that at 2.0. Three correlations for the ignition delay time under three different equivalence ratios were deduced. The current data were compared with available kinetic mechanisms, and were found to be in od agreement with the predictions of Honnet et al. Chemical mechanism sensitivity analyses for different equivalence ratios were performed; the results showed that the ignition sensitivity at an equivalence ratio of 0.2 is quite different from those at 1.0 and 2.0.
2012, 28(04): 792-798
doi: 10.3866/PKU.WHXB201201171
Abstract:
A systematic study of series of non-hydrated and hydrated Cn/m uranyl carbonate complexes (n is number of carbonate ligands, and m is number of water molecules) in the aqueous phase was carried out using relativistic density functional theory. The conductor-like screening model was used to calculate solvent effects. The zeroth-order regular approximation was used to account for scalar relativistic effects and spin-orbit coupling relativistic effects. Time-dependent density functional theory with the inclusion of spin-orbit coupling relativistic effects was used to calculate electronic transitions using the statistically averaged orbital potentials. The results indicate that carbonate ligands play an important role in the geometric and electronic transition properties of the complex. The stability of the C3/0 carbonate complex in the aqueous phase may be attributed to the involvement of 5f components in the highest occupied bonding orbital. The addition of carbonate ligands caused a blue shift in the maximum wavelength and high intensity absorptions in the near visible region.
A systematic study of series of non-hydrated and hydrated Cn/m uranyl carbonate complexes (n is number of carbonate ligands, and m is number of water molecules) in the aqueous phase was carried out using relativistic density functional theory. The conductor-like screening model was used to calculate solvent effects. The zeroth-order regular approximation was used to account for scalar relativistic effects and spin-orbit coupling relativistic effects. Time-dependent density functional theory with the inclusion of spin-orbit coupling relativistic effects was used to calculate electronic transitions using the statistically averaged orbital potentials. The results indicate that carbonate ligands play an important role in the geometric and electronic transition properties of the complex. The stability of the C3/0 carbonate complex in the aqueous phase may be attributed to the involvement of 5f components in the highest occupied bonding orbital. The addition of carbonate ligands caused a blue shift in the maximum wavelength and high intensity absorptions in the near visible region.
Factor Group Analysis of Molecular Vibrational Modes of Graphene and Density Functional Calculations
2012, 28(04): 799-804
doi: 10.3866/PKU.WHXB201202012
Abstract:
The molecular vibrational modes of graphene were analyzed theoretically by factor group analysis. The molecular vibrational modes of graphene and the spectral characteristics of each vibrational mode were calculated successfully. The molecular vibrational frequency and mode of graphene were also calculated by first-principles density functional theory based on establishment of the graphene Bravais crystal unit cell. The number of vibrational modes and corresponding vibrational frequency spectral properties calculated were consistent with the results obtained using factor group analysis. The above calculations and systematic comparison between the infrared and Raman spectra of graphene and graphite were used to determine why the infrared active vibrational modes A2u and E1u with D6h point group did not appear on the experimental infrared spectrum of graphene.
The molecular vibrational modes of graphene were analyzed theoretically by factor group analysis. The molecular vibrational modes of graphene and the spectral characteristics of each vibrational mode were calculated successfully. The molecular vibrational frequency and mode of graphene were also calculated by first-principles density functional theory based on establishment of the graphene Bravais crystal unit cell. The number of vibrational modes and corresponding vibrational frequency spectral properties calculated were consistent with the results obtained using factor group analysis. The above calculations and systematic comparison between the infrared and Raman spectra of graphene and graphite were used to determine why the infrared active vibrational modes A2u and E1u with D6h point group did not appear on the experimental infrared spectrum of graphene.
2012, 28(04): 805-810
doi: 10.3866/PKU.WHXB201202072
Abstract:
The geometric configurations and electronic structures of AlnO2± (n=1-10) clusters were studied using the B3LYP density functional theory (DFT) at the 6-311G** level. The ground state structure, vibrational frequency, charge transfer, and molecular orbital of the doped clusters are discussed. The results showed that the ground states of the AlnO2± (n＞1) clusters were combinations of two smaller AlmO (m＜n) fragments and the Al clusters shared an Al atom or local structure of one Al4O2. Stability information for the AlnO2± clusters was obtained by analyzing the energy of the ground state structure.
The geometric configurations and electronic structures of AlnO2± (n=1-10) clusters were studied using the B3LYP density functional theory (DFT) at the 6-311G** level. The ground state structure, vibrational frequency, charge transfer, and molecular orbital of the doped clusters are discussed. The results showed that the ground states of the AlnO2± (n＞1) clusters were combinations of two smaller AlmO (m＜n) fragments and the Al clusters shared an Al atom or local structure of one Al4O2. Stability information for the AlnO2± clusters was obtained by analyzing the energy of the ground state structure.
2012, 28(04): 811-817
doi: 10.3866/PKU.WHXB201202082
Abstract:
The geometries, electronic structures, and bonding energies of coinage metal-ethylene complexes LM-C2H4 (L=[N{(Me)C(Ph)N}2]; M=Cu, Ag, Au) were investigated by Hartree-Fock, Møller- Plesset perturbation (MP2), second-order approximate coupled-cluster (CC2), and density functional theory (DFT) methods. The MP2, CC2, and DFT methods performed well in reproducing the experimental geometric features of LM-C2H4. The bonding in LM-C2H4 can be described as a synergistic combination of σ-donor and π-acceptor interactions between the LM and C2H4 π-system. Both σ-donor and π-acceptor contributions increased the C＝C bond length and decreased the C＝C bond strength by removing electron density from the bonding π orbital and increasing electron density in the anti-bonding π* orbital, respectively. The results of natural population analysis and energy decomposition analysis show that the LM→C2H4 back-donation contribution to the LM-C2H4 bonding is higher than that of the C2H4→LM donation, but this order is reversed in the M+-C2H4 systems. Therefore, it is not appropriate to use M+-C2H4 as a computational model for electronic structures studies of LM-C2H4. The effects of changing the metal on the structural and electronic properties, such as C＝C bond length, charge populations of C2H4, and LM-C2H4 interactions, were large. Compared with LCu and LAg, LAu had the strongest ability to accept and donate electrons. Consequently, it showed the maximum reduction in the π orbital electron density and increase in the π* orbital density. Therefore, activation of the C＝C bond by LAu was more effective than by LCu and LAg. However, the effects of electron donating or withdrawing ability of the auxiliary ligands on the above properties were small.
The geometries, electronic structures, and bonding energies of coinage metal-ethylene complexes LM-C2H4 (L=[N{(Me)C(Ph)N}2]; M=Cu, Ag, Au) were investigated by Hartree-Fock, Møller- Plesset perturbation (MP2), second-order approximate coupled-cluster (CC2), and density functional theory (DFT) methods. The MP2, CC2, and DFT methods performed well in reproducing the experimental geometric features of LM-C2H4. The bonding in LM-C2H4 can be described as a synergistic combination of σ-donor and π-acceptor interactions between the LM and C2H4 π-system. Both σ-donor and π-acceptor contributions increased the C＝C bond length and decreased the C＝C bond strength by removing electron density from the bonding π orbital and increasing electron density in the anti-bonding π* orbital, respectively. The results of natural population analysis and energy decomposition analysis show that the LM→C2H4 back-donation contribution to the LM-C2H4 bonding is higher than that of the C2H4→LM donation, but this order is reversed in the M+-C2H4 systems. Therefore, it is not appropriate to use M+-C2H4 as a computational model for electronic structures studies of LM-C2H4. The effects of changing the metal on the structural and electronic properties, such as C＝C bond length, charge populations of C2H4, and LM-C2H4 interactions, were large. Compared with LCu and LAg, LAu had the strongest ability to accept and donate electrons. Consequently, it showed the maximum reduction in the π orbital electron density and increase in the π* orbital density. Therefore, activation of the C＝C bond by LAu was more effective than by LCu and LAg. However, the effects of electron donating or withdrawing ability of the auxiliary ligands on the above properties were small.
2012, 28(04): 818-822
doi: 10.3866/PKU.WHXB201201132
Abstract:
The reaction mechanism of 1,4-dimethoxybenzene (p-DMOB) as an overcharge protection additive for lithium ion batteries was determined by theoretical calculation of density functional theory (DFT) at the level of B3LYP/6-311+G(d,p) and MP2/6-311+G(d,p). It was found that p-DMOB is oxidized prior to the solvents, ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate, when the lithium ion battery is overcharged. The calculated oxidative potentials of p-DMOB by B3LYP and MP2 methods are well in agreement at 4.12 and 4.05 V (vs Li/Li+·), respectively. The initial oxidation of p-DMOB involves a one-electron transfer resulting in a radical cation p-DMOB+·. The corresponding energy variations were 701.24 and 728.27 kJ·mol-1 from B3LYP and MP2 calculations, respectively. The p-DMOB+· species then loses one proton forming a radical p-DMOB·through the breaking of a C―H bond on the benzene ring, with the corresponding energy variations of 1349.78 and 1810.99 kJ·mol-1 for B3LYP and MP2, respectively. The p-DMOB·species is unstable and copolymerizes forming an insulated polymer with the corresponding energy variations of -553.37 and -1331.20 kJ·mol-1 for B3LYP and MP2, respectively.
The reaction mechanism of 1,4-dimethoxybenzene (p-DMOB) as an overcharge protection additive for lithium ion batteries was determined by theoretical calculation of density functional theory (DFT) at the level of B3LYP/6-311+G(d,p) and MP2/6-311+G(d,p). It was found that p-DMOB is oxidized prior to the solvents, ethyl methyl carbonate, dimethyl carbonate, and ethylene carbonate, when the lithium ion battery is overcharged. The calculated oxidative potentials of p-DMOB by B3LYP and MP2 methods are well in agreement at 4.12 and 4.05 V (vs Li/Li+·), respectively. The initial oxidation of p-DMOB involves a one-electron transfer resulting in a radical cation p-DMOB+·. The corresponding energy variations were 701.24 and 728.27 kJ·mol-1 from B3LYP and MP2 calculations, respectively. The p-DMOB+· species then loses one proton forming a radical p-DMOB·through the breaking of a C―H bond on the benzene ring, with the corresponding energy variations of 1349.78 and 1810.99 kJ·mol-1 for B3LYP and MP2, respectively. The p-DMOB·species is unstable and copolymerizes forming an insulated polymer with the corresponding energy variations of -553.37 and -1331.20 kJ·mol-1 for B3LYP and MP2, respectively.
2012, 28(04): 823-830
doi: 10.3866/PKU.WHXB201202102
Abstract:
The lithium rich cathode materials xLi2MnO3·(1-x)Li[Ni1/3Mn1/3Co1/3]O2 (x=0.4, 0.5, 0.6) were successfully synthesized via sol-gel method with calcination in air. The transition metal acetate, lithium acetate, and citric acid were used as raw materials. The as-prepared materials were characterized by X-ray diffraction (XRD), scaning electron microscopy (SEM), and electrochemical tests. The material 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3]O2, which was obtained after calcination at 900 °C for 12 h, exhibited fine microstructures and od electrochemical performance. When cycled at 2.0-4.8 V with a current density of 20 mA·g-1 at room temperature, 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3]O2 delivered a initial discharge specific capacity of 260.0 mAh·g-1, and maintained a capacity of 244.7 mAh·g-1 after 40 cycles (capacity retention 94.12%).
The lithium rich cathode materials xLi2MnO3·(1-x)Li[Ni1/3Mn1/3Co1/3]O2 (x=0.4, 0.5, 0.6) were successfully synthesized via sol-gel method with calcination in air. The transition metal acetate, lithium acetate, and citric acid were used as raw materials. The as-prepared materials were characterized by X-ray diffraction (XRD), scaning electron microscopy (SEM), and electrochemical tests. The material 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3]O2, which was obtained after calcination at 900 °C for 12 h, exhibited fine microstructures and od electrochemical performance. When cycled at 2.0-4.8 V with a current density of 20 mA·g-1 at room temperature, 0.5Li2MnO3·0.5LiNi1/3Mn1/3Co1/3]O2 delivered a initial discharge specific capacity of 260.0 mAh·g-1, and maintained a capacity of 244.7 mAh·g-1 after 40 cycles (capacity retention 94.12%).
2012, 28(04): 831-836
doi: 10.3866/PKU.WHXB201202101
Abstract:
A novel high-performance PbO2 electrode modified with Bi3+ (Bi-PbO2) was prepared by electrodeposition. The microstructure and electrochemical properties of the modified electrode were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), fluorospectrophotometry (FP), Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS), and linear-sweep voltammetry (LSV). The results of SEM, EDS, XPS, XRD, and UV-Vis DRS show that insertion of Bi3+ , which is in the form of Bi2O3, into the PbO2 film can reduce its particle size, change its crystal cell parameters, and narrow its bandgap (Eg). FP analysis reveals that the electrocatalytic activity of the Bi-PbO2 electrode in the degradation of organic materials is higher than that of the PbO2 electrode because more hydroxyl radicals can be generated on its surface. Electrochemical performance tests show that the modified electrode has a more negative flat-band potential (Efb), larger active surface area, lower charge-transfer resistance, and higher oxygen-evolution potential; these characteristics promote the electrocatalytic activity of the Bi-PbO2 electrode in the decomposition of organic materials.
A novel high-performance PbO2 electrode modified with Bi3+ (Bi-PbO2) was prepared by electrodeposition. The microstructure and electrochemical properties of the modified electrode were investigated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), fluorospectrophotometry (FP), Mott-Schottky analysis, electrochemical impedance spectroscopy (EIS), and linear-sweep voltammetry (LSV). The results of SEM, EDS, XPS, XRD, and UV-Vis DRS show that insertion of Bi3+ , which is in the form of Bi2O3, into the PbO2 film can reduce its particle size, change its crystal cell parameters, and narrow its bandgap (Eg). FP analysis reveals that the electrocatalytic activity of the Bi-PbO2 electrode in the degradation of organic materials is higher than that of the PbO2 electrode because more hydroxyl radicals can be generated on its surface. Electrochemical performance tests show that the modified electrode has a more negative flat-band potential (Efb), larger active surface area, lower charge-transfer resistance, and higher oxygen-evolution potential; these characteristics promote the electrocatalytic activity of the Bi-PbO2 electrode in the decomposition of organic materials.
2012, 28(04): 837-842
doi: 10.3866/PKU.WHXB201202074
Abstract:
OMC/NiCo2O4 composite was prepared by co-precipitation with ordered mesoporous carbon (OMC) as a support. The crystalline structure and morphology of the composite were investigated by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). TEM images showed that NiCo2O4 was uniformly coated on the OMC. Cyclic voltammetry and galvanostatic charge-discharge were used to investigate the electrochemical performance of the OMC/ NiCo2O4 composite. The specific capacitances of the OMC/NiCo2O4 composite with a mass fraction of 40% NiCo2O4 were 577.0 F·g-1 at a current density of 1 A·g-1 and 470.8 F·g-1 at 8 A·g-1. The specific capacitance remains at 508.4 F·g-1 after 2000 cycles at a current density of 2 A·g-1, with a capacitance retention of 92.7%.
OMC/NiCo2O4 composite was prepared by co-precipitation with ordered mesoporous carbon (OMC) as a support. The crystalline structure and morphology of the composite were investigated by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectroscopy, and transmission electron microscopy (TEM). TEM images showed that NiCo2O4 was uniformly coated on the OMC. Cyclic voltammetry and galvanostatic charge-discharge were used to investigate the electrochemical performance of the OMC/ NiCo2O4 composite. The specific capacitances of the OMC/NiCo2O4 composite with a mass fraction of 40% NiCo2O4 were 577.0 F·g-1 at a current density of 1 A·g-1 and 470.8 F·g-1 at 8 A·g-1. The specific capacitance remains at 508.4 F·g-1 after 2000 cycles at a current density of 2 A·g-1, with a capacitance retention of 92.7%.
2012, 28(04): 843-849
doi: 10.3866/PKU.WHXB201202172
Abstract:
Control of the pore structures of carbon aerogels (CAs) was investigated by changing the sol-gel polymerization and activation conditions. The morphologies and physical properties of the CAs and KOH activated carbon aerogels (ACAs) were characterized by scanning electron microscopy (SEM) and N2 adsorption isotherms. The electrochemical performances of the CAs and ACAs as electrode materials were characterized using cyclic voltammetry (CV), a galvanostatic charge-discharge test, and electrochemical impedance spectroscopy (EIS). The results showed that the well developed threedimensional nano-network structures and the reasonable pore size distributions of the CAs have great effect on their electrochemical performance in supercapacitors. Because of abundant mesopores and a high specific surface area (1480 m2·g-1), the specific capacitance of a ACA electrode in 6 mol·L-1 KOH electrolyte was approximately 216 F·g-1 at a scan rate of 100 mV·s-1. A simple model was used to investigate the role of the pores in electrochemical performance.
Control of the pore structures of carbon aerogels (CAs) was investigated by changing the sol-gel polymerization and activation conditions. The morphologies and physical properties of the CAs and KOH activated carbon aerogels (ACAs) were characterized by scanning electron microscopy (SEM) and N2 adsorption isotherms. The electrochemical performances of the CAs and ACAs as electrode materials were characterized using cyclic voltammetry (CV), a galvanostatic charge-discharge test, and electrochemical impedance spectroscopy (EIS). The results showed that the well developed threedimensional nano-network structures and the reasonable pore size distributions of the CAs have great effect on their electrochemical performance in supercapacitors. Because of abundant mesopores and a high specific surface area (1480 m2·g-1), the specific capacitance of a ACA electrode in 6 mol·L-1 KOH electrolyte was approximately 216 F·g-1 at a scan rate of 100 mV·s-1. A simple model was used to investigate the role of the pores in electrochemical performance.
2012, 28(04): 850-856
doi: 10.3866/PKU.WHXB2012020111
Abstract:
The surface properties of TiO2-X (X=5, 10, 20, X=[NaOH] (in mol·L-1)) samples prepared by modification of hydrolyzed TiCl4 were studied. The surface-sensitized Ru(phen)2(PIBH) (Rup2P) (phen= phenanthroline, PIBH=pyridyl benzimidazole hybrid) film electrodes Rup2P/TiO2-5/ITO (indium tin oxide), Rup2P/TiO2-10/ITO, and Rup2P/TiO2-20/ITO were prepared. Among the three films, the photovoltaic properties of Rup2P/TiO2-10/ITO were the best and those of Rup2P/TiO2-5/ITO were the worst. The band structures, and properties on the surfaces of Rup2P and the three TiO2 samples were analyzed using absorption spectra, surface photovoltage spectra, photoluminescence spectra, and photocurrent action spectra. The photo-induced charge transfer process was studied by cyclic voltammetry under irradiation and photocurrent action spectra. The results revealed the oxygen vacancy at the TiO2 surface was very important for the photo-induced charge transfer process of Rup2P/TiO2-X/ITO. The photocurrent mechanism of Rup2P/TiO2-X/ITO is discussed.
The surface properties of TiO2-X (X=5, 10, 20, X=[NaOH] (in mol·L-1)) samples prepared by modification of hydrolyzed TiCl4 were studied. The surface-sensitized Ru(phen)2(PIBH) (Rup2P) (phen= phenanthroline, PIBH=pyridyl benzimidazole hybrid) film electrodes Rup2P/TiO2-5/ITO (indium tin oxide), Rup2P/TiO2-10/ITO, and Rup2P/TiO2-20/ITO were prepared. Among the three films, the photovoltaic properties of Rup2P/TiO2-10/ITO were the best and those of Rup2P/TiO2-5/ITO were the worst. The band structures, and properties on the surfaces of Rup2P and the three TiO2 samples were analyzed using absorption spectra, surface photovoltage spectra, photoluminescence spectra, and photocurrent action spectra. The photo-induced charge transfer process was studied by cyclic voltammetry under irradiation and photocurrent action spectra. The results revealed the oxygen vacancy at the TiO2 surface was very important for the photo-induced charge transfer process of Rup2P/TiO2-X/ITO. The photocurrent mechanism of Rup2P/TiO2-X/ITO is discussed.
2012, 28(04): 857-864
doi: 10.3866/PKU.WHXB201202204
Abstract:
Cu2S nanomaterials were prepared, and the influence of preparation conditions on the morphology and catalytic reduction of sodium polysulfide was investigated. The Cu2S photocathode prepared under optimal conditions was used as a quantum-dot-sensitized solar cell. For preparation of the Cu2S photocathodes, HCl pretreatment and reaction with sodium polysulfide were important processes. The Cu2S photocathodes had petal-like structures composed of nano-plates. The Cu2S photocathodes become rough and porous, which increased the surface area, as the HCl concentration increased and pretreatment time was prolonged. As a result, interfacial charge transfer resistance between the Cu2S electrodes and polysulfide electrolyte decreased. Because the reaction between Cu and sodium polysulfide is very fast, the reaction time should be controlled. Otherwise, the Cu2S film will fracture. For od catalytic performance of the Cu2S photocathodes, the best preparation conditions were 30% HCl, pretreatment time for 40 min, and reaction with sodium polysulfide for 10 s. The quantum-dot-sensitized solar cell showed a high photoelectric conversion efficiency of 4.01%.
Cu2S nanomaterials were prepared, and the influence of preparation conditions on the morphology and catalytic reduction of sodium polysulfide was investigated. The Cu2S photocathode prepared under optimal conditions was used as a quantum-dot-sensitized solar cell. For preparation of the Cu2S photocathodes, HCl pretreatment and reaction with sodium polysulfide were important processes. The Cu2S photocathodes had petal-like structures composed of nano-plates. The Cu2S photocathodes become rough and porous, which increased the surface area, as the HCl concentration increased and pretreatment time was prolonged. As a result, interfacial charge transfer resistance between the Cu2S electrodes and polysulfide electrolyte decreased. Because the reaction between Cu and sodium polysulfide is very fast, the reaction time should be controlled. Otherwise, the Cu2S film will fracture. For od catalytic performance of the Cu2S photocathodes, the best preparation conditions were 30% HCl, pretreatment time for 40 min, and reaction with sodium polysulfide for 10 s. The quantum-dot-sensitized solar cell showed a high photoelectric conversion efficiency of 4.01%.
2012, 28(04): 865-870
doi: 10.3866/PKU.WHXB201202152
Abstract:
Visible-light-responsive WO3 porous films were synthesized via step-voltage anodization in NH4F/(NH4)2SO4 solution and calcined at various temperatures. The crystalline phase and surface morphology were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The as-anodized nanoporous films converted to a monoclinic phase with preferential orientation in the (020) planes, and the pore diameters of the films calcined below 450 °C were estimated to be in the region of 50-100 nm. The photocatalytic activity was evaluated via photodegradation of methyl orange. The film calcined at 450 °C showed the highest photocatalytic activity. Photoelectrochemical measurements showed that the incident photon-to-current conversion efficiency (IPCE) values of the film calcined at 450 ° C were 87.4% at 340 nm and 22.1% at 400 nm. Under visible light (λ ≥400 nm), the photocurrent density in 0.5 mol·L-1 H2SO4 solution at 1.2 V (vs Ag/AgCl (KCl saturated)) was 5.11 mA·cm-2. Electrochemical impedance spectroscopy (EIS) measurements showed that the film calcined at 450 °C exhibited the smallest interface charge transfer resistance and optimal electroconductivity. Perfect crystallinity, high porosity and low resistance can therefore be obtained by controlling the calcination temperature. A large surface area and a porous structure are important factors in affecting photocatalytic activity.
Visible-light-responsive WO3 porous films were synthesized via step-voltage anodization in NH4F/(NH4)2SO4 solution and calcined at various temperatures. The crystalline phase and surface morphology were characterized using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The as-anodized nanoporous films converted to a monoclinic phase with preferential orientation in the (020) planes, and the pore diameters of the films calcined below 450 °C were estimated to be in the region of 50-100 nm. The photocatalytic activity was evaluated via photodegradation of methyl orange. The film calcined at 450 °C showed the highest photocatalytic activity. Photoelectrochemical measurements showed that the incident photon-to-current conversion efficiency (IPCE) values of the film calcined at 450 ° C were 87.4% at 340 nm and 22.1% at 400 nm. Under visible light (λ ≥400 nm), the photocurrent density in 0.5 mol·L-1 H2SO4 solution at 1.2 V (vs Ag/AgCl (KCl saturated)) was 5.11 mA·cm-2. Electrochemical impedance spectroscopy (EIS) measurements showed that the film calcined at 450 °C exhibited the smallest interface charge transfer resistance and optimal electroconductivity. Perfect crystallinity, high porosity and low resistance can therefore be obtained by controlling the calcination temperature. A large surface area and a porous structure are important factors in affecting photocatalytic activity.
2012, 28(04): 871-876
doi: 10.3866/PKU.WHXB201202013
Abstract:
Nano-flocculent-Co3O4 modified multi-walled carbon nanotubes supported Pd nanoparticles (Pd-Co3O4/MWCNTs) with uniform dimensions were prepared by a facile hydrothermal method using Co(NO3)3·6H2O as the cobalt source, polyethylene glycol (PEG) 20000 as a surface active agent, and H2PdCl4 as the Pd precursor. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray powder diffraction. The Pd nanoparticles had a face-centered cubic crystal structure and were well dispersed on the external walls of the Co3O4/MWCNTs. The catalytic activity was studied by cyclic voltammetry and chronoamperometry toward methanol oxidation. The Pd-Co3O4/MWCNT catalysts had a large electrochemically active area, od electrocatalytic performance, and stability toward methanol oxidation in alkaline media. All the results suggest that Co3O4 will improve the electrocatalytic activity in direct methanol fuel cells.
Nano-flocculent-Co3O4 modified multi-walled carbon nanotubes supported Pd nanoparticles (Pd-Co3O4/MWCNTs) with uniform dimensions were prepared by a facile hydrothermal method using Co(NO3)3·6H2O as the cobalt source, polyethylene glycol (PEG) 20000 as a surface active agent, and H2PdCl4 as the Pd precursor. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray powder diffraction. The Pd nanoparticles had a face-centered cubic crystal structure and were well dispersed on the external walls of the Co3O4/MWCNTs. The catalytic activity was studied by cyclic voltammetry and chronoamperometry toward methanol oxidation. The Pd-Co3O4/MWCNT catalysts had a large electrochemically active area, od electrocatalytic performance, and stability toward methanol oxidation in alkaline media. All the results suggest that Co3O4 will improve the electrocatalytic activity in direct methanol fuel cells.
2012, 28(04): 877-884
doi: 10.3866/PKU.WHXB201202141
Abstract:
Based on the empirical formula for concentration change of a detected molecule on the surface of a electrode, an approximate mathematical model of improved chronoamperometry was established. The relationship between the working current and detection reagent concentration was analyzed qualitatively. Parameters for the electrode reaction and excitation potential were not included. To solve this problem, the Nernst equation and Fick's law were applied to construct an integral equation for the specific concentrations of the oxidant and reductant on the surface of the electrode. The current-time curve obtained numerically was used to investigate the relationship between the peak current and concentration of reagent, inertia time constant, standard potential of the reference electrode, initial value and steady state value of the voltage excitation. Using the improved chronoamperometry device, we studied the electrochemical behavior of K3[Fe(CN)6]. The experimental results showed that the simulation results from the numerical model were much closer to the actual situation than the empirical model. The experimental results also confirmed the parameter relationships that were derived using the model.
Based on the empirical formula for concentration change of a detected molecule on the surface of a electrode, an approximate mathematical model of improved chronoamperometry was established. The relationship between the working current and detection reagent concentration was analyzed qualitatively. Parameters for the electrode reaction and excitation potential were not included. To solve this problem, the Nernst equation and Fick's law were applied to construct an integral equation for the specific concentrations of the oxidant and reductant on the surface of the electrode. The current-time curve obtained numerically was used to investigate the relationship between the peak current and concentration of reagent, inertia time constant, standard potential of the reference electrode, initial value and steady state value of the voltage excitation. Using the improved chronoamperometry device, we studied the electrochemical behavior of K3[Fe(CN)6]. The experimental results showed that the simulation results from the numerical model were much closer to the actual situation than the empirical model. The experimental results also confirmed the parameter relationships that were derived using the model.
2012, 28(04): 885-891
doi: 10.3866/PKU.WHXB201202202
Abstract:
In the present study we report the micellization behavior of imipramine hydrochloride (IMP) in absence and presence of different concentrations of inorganic salts (LiCl, NaF, NaCl, NaBr, and KCl) and ureas (urea and thiourea) over the temperature range from 288.15 to 303.15 K. The critical micellization concentrations (cmc) of drug and drug+additive systems were determined by conductometric technique. With increasing temperature the cmc first increases then decreases. Maximum cmc values were obtained at 293.15 K with or without additives. In presence of inorganic salts the cmc value decreases which is explained on the basis of nature and ion size of the added ion. Urea and thiourea also decrease the cmc at low concentrations (0.2 mmol·L-1 urea and 0.1 mmol·L-1 thiourea), but, at higher concentrations, increase in cmc is observed. The related thermodynamic parameters are also evaluated and discussed.
In the present study we report the micellization behavior of imipramine hydrochloride (IMP) in absence and presence of different concentrations of inorganic salts (LiCl, NaF, NaCl, NaBr, and KCl) and ureas (urea and thiourea) over the temperature range from 288.15 to 303.15 K. The critical micellization concentrations (cmc) of drug and drug+additive systems were determined by conductometric technique. With increasing temperature the cmc first increases then decreases. Maximum cmc values were obtained at 293.15 K with or without additives. In presence of inorganic salts the cmc value decreases which is explained on the basis of nature and ion size of the added ion. Urea and thiourea also decrease the cmc at low concentrations (0.2 mmol·L-1 urea and 0.1 mmol·L-1 thiourea), but, at higher concentrations, increase in cmc is observed. The related thermodynamic parameters are also evaluated and discussed.
2012, 28(04): 892-896
doi: 10.3866/PKU.WHXB201202031
Abstract:
Uniform polymer microspheres were prepared through precipitation polymerization of pentaerythritol triacrylate (PETA) and styrene in ethanol or an ethanol-water mixture using azobisisobutyronitrile (AIBN) as initiator. The effects of the polymerization time, amount of PETA, and water content in the mixed solvent on the polymerization process and the microspheres were studied. Uniform microspheres were readily obtained when the amount of PETA was between 5% and 35% (mass fraction) relative to all monomers with a polymerization time of 6 h. When the mass fraction of PETA was <20%, the microspheres decreased in size and became more uniform as the PETA mass fraction increased. By contrast, when the PETA mass fraction was >20%, the microspheres size increased and the size distribution became larger as the PETA mass fraction increased. With the ethanol-water binary solvent mixture, the monomer conversion and microsphere yield increased compared with those obtained with pure ethanol. However, the water volume fraction needed to be kept below 30%, above which the uniformity of the microspheres was deteriorated. Based on the results, the mechanism of microsphere formation is discussed.
Uniform polymer microspheres were prepared through precipitation polymerization of pentaerythritol triacrylate (PETA) and styrene in ethanol or an ethanol-water mixture using azobisisobutyronitrile (AIBN) as initiator. The effects of the polymerization time, amount of PETA, and water content in the mixed solvent on the polymerization process and the microspheres were studied. Uniform microspheres were readily obtained when the amount of PETA was between 5% and 35% (mass fraction) relative to all monomers with a polymerization time of 6 h. When the mass fraction of PETA was <20%, the microspheres decreased in size and became more uniform as the PETA mass fraction increased. By contrast, when the PETA mass fraction was >20%, the microspheres size increased and the size distribution became larger as the PETA mass fraction increased. With the ethanol-water binary solvent mixture, the monomer conversion and microsphere yield increased compared with those obtained with pure ethanol. However, the water volume fraction needed to be kept below 30%, above which the uniformity of the microspheres was deteriorated. Based on the results, the mechanism of microsphere formation is discussed.
2012, 28(04): 897-902
doi: 10.3866/PKU.WHXB201202091
Abstract:
Polymeric ethosomes, formed from amphiphilic octadecyl quaternized carboxymethyl chitosan (OQCMC) with different degrees of quaternary substitution (DS), were prepared by the microemulsion (ME) method. These ethosomes could simultaneously encapsulate both the hydrophobic drug indomethacin (IMC) and the hydrophilic drug vincristine (VCR). The effects of the DS of the OQCMC and primary alcohols as cosurfactants on the phase diagram were elucidated. The prepared nanoparticles (NPs) were small ((52.40 ± 0.55) nm) and suitable as drug carriers for different drugs. The maximum drug loading efficiencies of VCR-loaded and IMC-loaded NPs were 22.7% and 20.1%, respectively. The drug loading capacities for co-delivery of VCR and IMC were 12.2% and 10.0% , respectively. OQCMC polymeric ethosomes were stable in aqueous solution and exhibited slow, steady drug release. Hydrophilic fluorescein isothiocyanate (FITC) and hydrophobic Nile Red were encapsulated by the OQCMC ME NPs and simultaneously delivered into HO8901 cells with green and red fluorescence, respectively. This co-delivery system may allow for temporally distinct classes of drugs for cancer therapy.
Polymeric ethosomes, formed from amphiphilic octadecyl quaternized carboxymethyl chitosan (OQCMC) with different degrees of quaternary substitution (DS), were prepared by the microemulsion (ME) method. These ethosomes could simultaneously encapsulate both the hydrophobic drug indomethacin (IMC) and the hydrophilic drug vincristine (VCR). The effects of the DS of the OQCMC and primary alcohols as cosurfactants on the phase diagram were elucidated. The prepared nanoparticles (NPs) were small ((52.40 ± 0.55) nm) and suitable as drug carriers for different drugs. The maximum drug loading efficiencies of VCR-loaded and IMC-loaded NPs were 22.7% and 20.1%, respectively. The drug loading capacities for co-delivery of VCR and IMC were 12.2% and 10.0% , respectively. OQCMC polymeric ethosomes were stable in aqueous solution and exhibited slow, steady drug release. Hydrophilic fluorescein isothiocyanate (FITC) and hydrophobic Nile Red were encapsulated by the OQCMC ME NPs and simultaneously delivered into HO8901 cells with green and red fluorescence, respectively. This co-delivery system may allow for temporally distinct classes of drugs for cancer therapy.
2012, 28(04): 903-908
doi: 10.3866/PKU.WHXB201202171
Abstract:
The self-assembly behavior of hydrophobically associating polyacrylamide (HAPAM) in salt solution was studied by static light scattering, dynamic light scattering, and atomic force microscopy (AFM). The apparent weight average molecular weight (Mw,a), root mean square radius of gyration (<Rg>), hydrodynamic radius (<Rh>), and the second virial coefficient (A2), were investigated. The ratio of <Rg> to <Rh> was used to determine the molecular shape of the polymer in salt solution. As the salt concentration increased, the polymer chain transformed from stretch to curl.
The self-assembly behavior of hydrophobically associating polyacrylamide (HAPAM) in salt solution was studied by static light scattering, dynamic light scattering, and atomic force microscopy (AFM). The apparent weight average molecular weight (Mw,a), root mean square radius of gyration (<Rg>), hydrodynamic radius (<Rh>), and the second virial coefficient (A2), were investigated. The ratio of <Rg> to <Rh> was used to determine the molecular shape of the polymer in salt solution. As the salt concentration increased, the polymer chain transformed from stretch to curl.
2012, 28(04): 909-916
doi: 10.3866/PKU.WHXB201201164
Abstract:
Dissipative particle dynamics simulations were performed to study the mesoscopic structures of both humidified Nafion and polyvinyl alcohol (PVA)/Nafion blend membranes. Simulation results show that a phase-segregated microstructure is formed in both humidified Nafion and PVA/Nafion blend membranes. In humidified Nafion membrane, water molecules and sulfonate groups form tubular shaped water clusters. As the water content is increased, the size of water cluster is enlarged and water clusters percolate to form a continuous water channel. In the PVA/Nafion blend membrane, PVA, water molecules, and sulfonate groups together form hydrophilic domains. The mesoscopic structure of the PVA/Nafion blend membrane is affected by both the PVA/Nafion blend ratio and the water content in the membrane. When the PVA mass fraction is relatively low, PVA is predominantly distributed along the sulfonate groups of Nafion and as the PVA mass fraction is increased, PVA alone forms a distinct phase in the membrane. When the water content in the membrane is relatively low, water molecules are predominantly dissolved in PVA and as the water content is increased, spherical water clusters emerge in the membrane. This work provides further guidance for the development of PVA modified Nafion membranes for direct methanol fuel cell applications.
Dissipative particle dynamics simulations were performed to study the mesoscopic structures of both humidified Nafion and polyvinyl alcohol (PVA)/Nafion blend membranes. Simulation results show that a phase-segregated microstructure is formed in both humidified Nafion and PVA/Nafion blend membranes. In humidified Nafion membrane, water molecules and sulfonate groups form tubular shaped water clusters. As the water content is increased, the size of water cluster is enlarged and water clusters percolate to form a continuous water channel. In the PVA/Nafion blend membrane, PVA, water molecules, and sulfonate groups together form hydrophilic domains. The mesoscopic structure of the PVA/Nafion blend membrane is affected by both the PVA/Nafion blend ratio and the water content in the membrane. When the PVA mass fraction is relatively low, PVA is predominantly distributed along the sulfonate groups of Nafion and as the PVA mass fraction is increased, PVA alone forms a distinct phase in the membrane. When the water content in the membrane is relatively low, water molecules are predominantly dissolved in PVA and as the water content is increased, spherical water clusters emerge in the membrane. This work provides further guidance for the development of PVA modified Nafion membranes for direct methanol fuel cell applications.
2012, 28(04): 917-922
doi: 10.3866/PKU.WHXB201201172
Abstract:
Composite films of 3-aminopropyltriethoxysilane (APTES)-SiO2-APTES were prepared on single-crystal silicon substrates using a self-assembly technique, and then their composition, structure, and tribological properties were characterized. The results showed that the composite films had a uniform and dense surface with an average roughness (Ra) of 0.963 nm and a contact angle of 63°. The atomic force microscopy (AFM) and transmission electron microscopy (TEM) observations revealed that, in the middle layer of the composite film, silica particles of 20-50 nm in diameter were uniformly deposited on the APTES layer. Compared to the APTES self-assembled monolayers (SAMs), the APTES-SiO2-APTES composite films exhibited a smaller friction coefficient and a longer wear life due to the introduction of the silica nano-particles.
Composite films of 3-aminopropyltriethoxysilane (APTES)-SiO2-APTES were prepared on single-crystal silicon substrates using a self-assembly technique, and then their composition, structure, and tribological properties were characterized. The results showed that the composite films had a uniform and dense surface with an average roughness (Ra) of 0.963 nm and a contact angle of 63°. The atomic force microscopy (AFM) and transmission electron microscopy (TEM) observations revealed that, in the middle layer of the composite film, silica particles of 20-50 nm in diameter were uniformly deposited on the APTES layer. Compared to the APTES self-assembled monolayers (SAMs), the APTES-SiO2-APTES composite films exhibited a smaller friction coefficient and a longer wear life due to the introduction of the silica nano-particles.
2012, 28(04): 923-927
doi: 10.3866/PKU.WHXB201202081
Abstract:
Platinum nanoparticles (d=2.0 nm) were obtained by decomposition of Pt2(dba)3 (dba: dibenzalacetone) and captured by active carbon modified with Fe to prepare a Pt-Fe/C catalyst. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectrometry (EDS) were used to characterize the size, distribution, electronic state of the Pt and Fe nanoparticles, and surface elements of the catalysts. The catalysts selectively hydrogenated cinnamaldehyde (CAL) to cinnamyl alcohol (COL), and the activity was more than one time that of a Pt/C catalyst prepared by the impregnation method. The 1% (w, mass fraction)Pt-1.5% (w)Fe/C catalyst exhibited the highest activity and selectivity at 60 °C, 2.5 h, and 4.0 MPa H2. The conversion for CAL was 99.2%, and the selectivity of CAL to COL was 85.0%.
Platinum nanoparticles (d=2.0 nm) were obtained by decomposition of Pt2(dba)3 (dba: dibenzalacetone) and captured by active carbon modified with Fe to prepare a Pt-Fe/C catalyst. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray spectrometry (EDS) were used to characterize the size, distribution, electronic state of the Pt and Fe nanoparticles, and surface elements of the catalysts. The catalysts selectively hydrogenated cinnamaldehyde (CAL) to cinnamyl alcohol (COL), and the activity was more than one time that of a Pt/C catalyst prepared by the impregnation method. The 1% (w, mass fraction)Pt-1.5% (w)Fe/C catalyst exhibited the highest activity and selectivity at 60 °C, 2.5 h, and 4.0 MPa H2. The conversion for CAL was 99.2%, and the selectivity of CAL to COL was 85.0%.
2012, 28(04): 928-934
doi: 10.3866/PKU.WHXB201202073
Abstract:
The effects of Mg addition on the catalytic performance of PtNa/Sn-ZSM-5 in propane dehydrogenation was investigated using catalytic reaction performance tests and physicochemical characterizations such as X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed oxidation (O2-TPO). It was found that addition of appropriate amounts of Mg (0.3% and 0.5%, mass fraction) promoted the dispersion of metallic particles and decreased carbon deposition. In these cases, the presence of Mg in the PtMgNa/Sn-ZSM-5 catalyst could inhibit reduction of Sn species, thus more Sn could exist in oxidized states, which is advantageous to the reaction. However, when the content of Mg was excessive, the metallic particles were not well distributed and the particles agglomerated more easily. Moreover, the reduction of Sn species at high temperatures is relatively easy, which is disadvantageous to the reaction. In our experiments, the addition of 0.5% Mg to the PtNa/Sn-ZSM-5 catalyst gave the best catalytic performance. After reaction for 7 h, higher than 95% selectivity toward propene was achieved with a corresponding propane conversion value of 38.7%.
The effects of Mg addition on the catalytic performance of PtNa/Sn-ZSM-5 in propane dehydrogenation was investigated using catalytic reaction performance tests and physicochemical characterizations such as X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), NH3 temperature-programmed desorption (NH3-TPD), H2 temperature-programmed reduction (H2-TPR), and O2 temperature-programmed oxidation (O2-TPO). It was found that addition of appropriate amounts of Mg (0.3% and 0.5%, mass fraction) promoted the dispersion of metallic particles and decreased carbon deposition. In these cases, the presence of Mg in the PtMgNa/Sn-ZSM-5 catalyst could inhibit reduction of Sn species, thus more Sn could exist in oxidized states, which is advantageous to the reaction. However, when the content of Mg was excessive, the metallic particles were not well distributed and the particles agglomerated more easily. Moreover, the reduction of Sn species at high temperatures is relatively easy, which is disadvantageous to the reaction. In our experiments, the addition of 0.5% Mg to the PtNa/Sn-ZSM-5 catalyst gave the best catalytic performance. After reaction for 7 h, higher than 95% selectivity toward propene was achieved with a corresponding propane conversion value of 38.7%.
2012, 28(04): 935-941
doi: 10.3866/PKU.WHXB201202133
Abstract:
The reaction pathway for reforming coke oven gas (COG) in an oxygen permeation membrane was analyzed. Through the reforming experiments of H2+N2, CH4+N2, CO+N2, H2+CH4+N2 mixtures, with or without a catalyst and the catalyst bed, the reaction scheme is proposed: H2 in COG is absorbed and dissociates on Ni particle on catalyst, the H* of dissociation migrates to high active site (“triphase boundary”) and reacts with diffused oxygen or lattice oxygen on film surface to form H2O. The CH4 also could be dissociated on active metal surface to form CH3* and H*. The H2O formed reacts with the C species to form H2 and CO. At last the residual H2O reacts with the residual CH4 on the catalyst bed to form H2 and CO.
The reaction pathway for reforming coke oven gas (COG) in an oxygen permeation membrane was analyzed. Through the reforming experiments of H2+N2, CH4+N2, CO+N2, H2+CH4+N2 mixtures, with or without a catalyst and the catalyst bed, the reaction scheme is proposed: H2 in COG is absorbed and dissociates on Ni particle on catalyst, the H* of dissociation migrates to high active site (“triphase boundary”) and reacts with diffused oxygen or lattice oxygen on film surface to form H2O. The CH4 also could be dissociated on active metal surface to form CH3* and H*. The H2O formed reacts with the C species to form H2 and CO. At last the residual H2O reacts with the residual CH4 on the catalyst bed to form H2 and CO.
2012, 28(04): 942-948
doi: 10.3866/PKU.WHXB201202201
Abstract:
Two novel 1,3-dithiole-2-thione-4,5-dithiolate compounds, benzyltriethylamine bis(2-thioxo-1,3- dithiole-4,5-dithiolato) aurate(III) (BTEAADT) and benzyltriethylamine bis(2-thioxo-1,3-dithiole-4,5- dithiolato) nickel(III) (BTEANDT), were prepared and their optical nonlinearities in acetonitrile solutions at 532 and 1064 nm were investigated using the Z-scan technique with picosecond laser pulses. The Z-scan curves revealed that BTEAADT exhibited mainly reverse saturable absorption at 532 nm, negligible nonlinear absorption at 1064 nm, and a self-defocusing effect at both wavelengths, which meant that the third-order nonlinear refractive index was negative. BTEANDT exhibited saturable absorption at 1064 nm, negligible nonlinear absorption at 532 nm, and a self-focusing effect at both wavelengths, which meant that the third-order nonlinear refractive index was positive. The reason for these different phenomena was analyzed. The third-order nonlinear refractive index, the third-order nonlinear absorption coefficient, the third-order nonlinear susceptibility, and the hyperpolarizability were obtained at 532 and 1064 nm. The nonlinear refractive indices were -1.685×10-18 m2·W-1 at 532 nm and -1.459×10-18 m2·W-1 at 1064 nm for BTEAADT and 1.452×10-18 m2·W-1 at 532 nm and 7.311×10-18 m2·W-1 at 1064 nm for BETANDT. The magnitudes of the third-order nonlinear absorption coefficient, the third-order nonlinear susceptibility, and the hyperpolarizability were 10-11 m·W-1, 10-13 esu, and 10-31 esu, respectively. All these results suggest that these materials are promising candidates for application in the nonlinear optical area.
Two novel 1,3-dithiole-2-thione-4,5-dithiolate compounds, benzyltriethylamine bis(2-thioxo-1,3- dithiole-4,5-dithiolato) aurate(III) (BTEAADT) and benzyltriethylamine bis(2-thioxo-1,3-dithiole-4,5- dithiolato) nickel(III) (BTEANDT), were prepared and their optical nonlinearities in acetonitrile solutions at 532 and 1064 nm were investigated using the Z-scan technique with picosecond laser pulses. The Z-scan curves revealed that BTEAADT exhibited mainly reverse saturable absorption at 532 nm, negligible nonlinear absorption at 1064 nm, and a self-defocusing effect at both wavelengths, which meant that the third-order nonlinear refractive index was negative. BTEANDT exhibited saturable absorption at 1064 nm, negligible nonlinear absorption at 532 nm, and a self-focusing effect at both wavelengths, which meant that the third-order nonlinear refractive index was positive. The reason for these different phenomena was analyzed. The third-order nonlinear refractive index, the third-order nonlinear absorption coefficient, the third-order nonlinear susceptibility, and the hyperpolarizability were obtained at 532 and 1064 nm. The nonlinear refractive indices were -1.685×10-18 m2·W-1 at 532 nm and -1.459×10-18 m2·W-1 at 1064 nm for BTEAADT and 1.452×10-18 m2·W-1 at 532 nm and 7.311×10-18 m2·W-1 at 1064 nm for BETANDT. The magnitudes of the third-order nonlinear absorption coefficient, the third-order nonlinear susceptibility, and the hyperpolarizability were 10-11 m·W-1, 10-13 esu, and 10-31 esu, respectively. All these results suggest that these materials are promising candidates for application in the nonlinear optical area.
2012, 28(04): 949-956
doi: 10.3866/PKU.WHXB201201163
Abstract:
The luminescent properties of bis[(4,6-difluorophenyl)-pyridinato-N,C2']c(picolinate)iridium(III) (FIrpic) dependence on the doping concentrations and different annealing treatments were investigated. The color of emission from thin films and organic light emitting diodes (OELDs) could be adjusted from blue to yellow-green by controlling the FIrpic doping concentration. There was od spectral overlap from 440 to 480 nm between the FIrpic photoluminescence (PL) spectra and its absorption spectra. The 476 nm emission intensity decreased as the FIrpic doping concentration increased, and this effect could be attributed to FIrpic self-absorption. The PL and electroluminescence (EL) spectra were measured under different excitation power densities and in different doping concentrations, respectively. The intensity of emission peak at 530 nm was enhanced as the excitation power density or FIrpic doping concentration increased. This suggests that the emission peak at 530 nm originates from the excimer emission between FIrpic molecules. The morphologies of the thin film and changes in the EL spectra were analyzed before and after annealing treatment. This demonstrated that FIrpic molecular aggregation promoted by annealing treatment could increase the intensity of excimer emission between FIrpic molecules. The emission color of OLEDs could be adjusted from blue to yellow-green by changing the FIrpic doping concentration, optimizing the device structure, and using annealing treatment on the devices.
The luminescent properties of bis[(4,6-difluorophenyl)-pyridinato-N,C2']c(picolinate)iridium(III) (FIrpic) dependence on the doping concentrations and different annealing treatments were investigated. The color of emission from thin films and organic light emitting diodes (OELDs) could be adjusted from blue to yellow-green by controlling the FIrpic doping concentration. There was od spectral overlap from 440 to 480 nm between the FIrpic photoluminescence (PL) spectra and its absorption spectra. The 476 nm emission intensity decreased as the FIrpic doping concentration increased, and this effect could be attributed to FIrpic self-absorption. The PL and electroluminescence (EL) spectra were measured under different excitation power densities and in different doping concentrations, respectively. The intensity of emission peak at 530 nm was enhanced as the excitation power density or FIrpic doping concentration increased. This suggests that the emission peak at 530 nm originates from the excimer emission between FIrpic molecules. The morphologies of the thin film and changes in the EL spectra were analyzed before and after annealing treatment. This demonstrated that FIrpic molecular aggregation promoted by annealing treatment could increase the intensity of excimer emission between FIrpic molecules. The emission color of OLEDs could be adjusted from blue to yellow-green by changing the FIrpic doping concentration, optimizing the device structure, and using annealing treatment on the devices.
2012, 28(04): 957-962
doi: 10.3866/PKU.WHXB201202203
Abstract:
The mechanism of photochemical reactions of pyrenetetrasulfonate (PyTS) in aqueous solution was studied using laser flash photolysis-transient absorption spectrum techniques under irradiation at 355 nm. The characteristic absorption peaks of the excited singlet (PyTS1*) at 260 nm, the excited triplet (PyTS3*) at 300 nm, and the anion radical (PyTS-·) at 330 nm were first confirmed. Self-quenching and reaction with PyTS were regarded as the main decay channels for hydrated electrons (eaq-), and the pseudo-first-order rate constant of hydrated electrons with PyTS was determined to be 2.7× 105 s-1. The quantum yield of eaq- generated via two-photon ionization of PyTS was computed to be 3.2×10-2 under these conditions.
The mechanism of photochemical reactions of pyrenetetrasulfonate (PyTS) in aqueous solution was studied using laser flash photolysis-transient absorption spectrum techniques under irradiation at 355 nm. The characteristic absorption peaks of the excited singlet (PyTS1*) at 260 nm, the excited triplet (PyTS3*) at 300 nm, and the anion radical (PyTS-·) at 330 nm were first confirmed. Self-quenching and reaction with PyTS were regarded as the main decay channels for hydrated electrons (eaq-), and the pseudo-first-order rate constant of hydrated electrons with PyTS was determined to be 2.7× 105 s-1. The quantum yield of eaq- generated via two-photon ionization of PyTS was computed to be 3.2×10-2 under these conditions.
2012, 28(04): 963-970
doi: 10.3866/PKU.WHXB201202162
Abstract:
In the wavelength range 260-325 nm, we obtained mass-resolved dissociation spectra of OCS+ via A2П3/2←X2П3/2 (000) and A2П1/2←X2П1/2 (000, 001) transitions by preparing OCS+ (X2П) ions via [3+1] resonance enhanced multiphoton ionization (REMPI) of OCS molecules at 423, 420, 412.2, and 408.4 nm. The mass-resolved dissociation spectra of OCS+ via A2П1/2←X2П1/2 (001) were observed for the first time. The spectroscopic constants T0=31411.3 cm-1 and v1=814.3 cm-1 for the OCS+ (A2П3/2) state were deduced from the A2П3/2←X2П3/2 (000) photodissociation spectra, and the spectroscopic constants v1=816 cm-1, v2=(380.4± 2.8) cm-1, and v3=(2052.7±5.1) cm-1 for the OCS+ (A2П1/2) state were deduced from the A2П1/2←X2П1/2 (000) spectra. The spectroscopic constant v1=786.4 cm-1 was deduced from the A2П1/2←X2П1/2 (001) photodissociation spectra. The results show that the C－O stretching mode excitation of X2П1/2 can affect the C－S stretching mode vibration of the A2П1/2 state via A2П1/2←X2П1/2 (001) transitions. Bands involving the bending v2 mode excitation of A2П, such as A2П1/2 (020, 120, 021, …), were observed for the A2П1/2←X2П1/2 (000, 001) transitions, but were not observed for the A2П3/2 (υ1υ2υ3) ←X2П3/2 (000) transitions in the photodissociation spectra. The reason for this dependence of the bending v2 mode excitation of A2П on the spin-orbit splitting of the 2П state can be attributed to the Fermi resonance and Renner-Teller effect of OCS+ (A2П).
In the wavelength range 260-325 nm, we obtained mass-resolved dissociation spectra of OCS+ via A2П3/2←X2П3/2 (000) and A2П1/2←X2П1/2 (000, 001) transitions by preparing OCS+ (X2П) ions via [3+1] resonance enhanced multiphoton ionization (REMPI) of OCS molecules at 423, 420, 412.2, and 408.4 nm. The mass-resolved dissociation spectra of OCS+ via A2П1/2←X2П1/2 (001) were observed for the first time. The spectroscopic constants T0=31411.3 cm-1 and v1=814.3 cm-1 for the OCS+ (A2П3/2) state were deduced from the A2П3/2←X2П3/2 (000) photodissociation spectra, and the spectroscopic constants v1=816 cm-1, v2=(380.4± 2.8) cm-1, and v3=(2052.7±5.1) cm-1 for the OCS+ (A2П1/2) state were deduced from the A2П1/2←X2П1/2 (000) spectra. The spectroscopic constant v1=786.4 cm-1 was deduced from the A2П1/2←X2П1/2 (001) photodissociation spectra. The results show that the C－O stretching mode excitation of X2П1/2 can affect the C－S stretching mode vibration of the A2П1/2 state via A2П1/2←X2П1/2 (001) transitions. Bands involving the bending v2 mode excitation of A2П, such as A2П1/2 (020, 120, 021, …), were observed for the A2П1/2←X2П1/2 (000, 001) transitions, but were not observed for the A2П3/2 (υ1υ2υ3) ←X2П3/2 (000) transitions in the photodissociation spectra. The reason for this dependence of the bending v2 mode excitation of A2П on the spin-orbit splitting of the 2П state can be attributed to the Fermi resonance and Renner-Teller effect of OCS+ (A2П).
2012, 28(04): 971-977
doi: 10.3866/PKU.WHXB201112201
Abstract:
To obtain more structural information of polypeptides, glycine pentapeptide (simplified as GGGGG or G5) was chosen as a model to investigate the impact of alkali metal ions on the dissociation of GGGGG in the gas phase. Stoichiometric G5 and alkali metal salt solutions, including Li + , Na+ , K+ , Rb+ , were mixed, respectively, and then the solutions were left to stand at room temperature for 10 h to reach equilibrium. The mass spectrometric results indicated that the alkali metal ions and G5 could form 1:1 or 2: 1 non-covalent complexes in solution. The energy of the collision induced dissociation (CID) was 25 eV. The gas phase CID results demonstrate that in the 1:1 complexes, the extent of fragmentation decreases according to the order: Li+, Na+, K+, Rb+. Moreover, the unusual c, z ions were observed in the Rb+ complex. In the 2:1 non-covalent complexes, the extent of fragmentation increases according to the order: Li+ , Na+ , K+, Rb+. The gas phase dissociation of the Na+, K+, Rb+ 2:1 complexes are easier than their 1:1 complexes. Except for Li + , the activation abilities of the double metal ions to G5 are stronger than that of the single metal ion to G5, which can induce more dissection sites in the glycine pentapeptide and lead to the formation of more kinds of fragment ions.
To obtain more structural information of polypeptides, glycine pentapeptide (simplified as GGGGG or G5) was chosen as a model to investigate the impact of alkali metal ions on the dissociation of GGGGG in the gas phase. Stoichiometric G5 and alkali metal salt solutions, including Li + , Na+ , K+ , Rb+ , were mixed, respectively, and then the solutions were left to stand at room temperature for 10 h to reach equilibrium. The mass spectrometric results indicated that the alkali metal ions and G5 could form 1:1 or 2: 1 non-covalent complexes in solution. The energy of the collision induced dissociation (CID) was 25 eV. The gas phase CID results demonstrate that in the 1:1 complexes, the extent of fragmentation decreases according to the order: Li+, Na+, K+, Rb+. Moreover, the unusual c, z ions were observed in the Rb+ complex. In the 2:1 non-covalent complexes, the extent of fragmentation increases according to the order: Li+ , Na+ , K+, Rb+. The gas phase dissociation of the Na+, K+, Rb+ 2:1 complexes are easier than their 1:1 complexes. Except for Li + , the activation abilities of the double metal ions to G5 are stronger than that of the single metal ion to G5, which can induce more dissection sites in the glycine pentapeptide and lead to the formation of more kinds of fragment ions.
2012, 28(04): 978-984
doi: 10.3866/PKU.WHXB201202142
Abstract:
Dissipative particle dynamics (DPD) simulation technique is used to elucidate the microphase separation behavior of block copolymers in nanodroplets. The simulation is performed by relaxing disordered copolymer nanodroplets in a solvent bath. Microphase separation is then carried out inside the nanodroplet, which allows block copolymers self-assemble into many new morphologies differing from those formed in pure melts or in solution. These patterned structures depend on the volume ratio of solvophilic/solvophobic blocks (RH/T). As the value of RH/T increases, the following structures are formed: plum-pudding microsphere, volleyball-like structure, multilamellar vesicle, cage-like structure, nanorods, and discrete micelles. Density analysis is performed to characterize the onion's structure. At high RH/T values, block copolymers exhibit mainly solvophilicity and form swollen loose structures or small micelles suspended in the solvent. The simulation results are in od agreement with experimental and theoretical results.
Dissipative particle dynamics (DPD) simulation technique is used to elucidate the microphase separation behavior of block copolymers in nanodroplets. The simulation is performed by relaxing disordered copolymer nanodroplets in a solvent bath. Microphase separation is then carried out inside the nanodroplet, which allows block copolymers self-assemble into many new morphologies differing from those formed in pure melts or in solution. These patterned structures depend on the volume ratio of solvophilic/solvophobic blocks (RH/T). As the value of RH/T increases, the following structures are formed: plum-pudding microsphere, volleyball-like structure, multilamellar vesicle, cage-like structure, nanorods, and discrete micelles. Density analysis is performed to characterize the onion's structure. At high RH/T values, block copolymers exhibit mainly solvophilicity and form swollen loose structures or small micelles suspended in the solvent. The simulation results are in od agreement with experimental and theoretical results.
2012, 28(04): 985-992
doi: 10.3866/PKU.WHXB201202071
Abstract:
Mesoporous silica SBA-15-like materials with large pores were synthesized using tri-block copolymer P123 as a structure-directing agent, tetramethoxysilane as the silicon source, and different organic solvents as swelling agents. The resulting materials were characterized by powder X-ray diffraction (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The results showed that the introduction of swelling agents effectively enlarged the pore diameter and pore volume of the SBA-15 materials, and pore swelling with isooctane was larger than that with CCl4. When modified with tetraethylenepentamine (TEPA), all of these composite materials exhibited excellent adsorption capacities for CO2. The adsorption capacity of CO2 was independent of the pore structure, if the template was removed before modification with TEPA. By contrast, the adsorption capacity increased with the pore diameter when the as-synthesized mesoporous material was modified with TEPA. The effects of temperature and pressure on the CO2 adsorption capacity were investigated using adsorption isotherms and CO2 temperature-programmed desorption (TPD). With CO2 adsorption at higher temperature, the composite materials showed different adsorption capacities with pressure variation. As a result, the adsorption and separation of CO2 on these TEPA modified mesoporous materials in ambient air flow can be realized via pressure swing adsorption.
Mesoporous silica SBA-15-like materials with large pores were synthesized using tri-block copolymer P123 as a structure-directing agent, tetramethoxysilane as the silicon source, and different organic solvents as swelling agents. The resulting materials were characterized by powder X-ray diffraction (XRD), N2 adsorption-desorption, scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy. The results showed that the introduction of swelling agents effectively enlarged the pore diameter and pore volume of the SBA-15 materials, and pore swelling with isooctane was larger than that with CCl4. When modified with tetraethylenepentamine (TEPA), all of these composite materials exhibited excellent adsorption capacities for CO2. The adsorption capacity of CO2 was independent of the pore structure, if the template was removed before modification with TEPA. By contrast, the adsorption capacity increased with the pore diameter when the as-synthesized mesoporous material was modified with TEPA. The effects of temperature and pressure on the CO2 adsorption capacity were investigated using adsorption isotherms and CO2 temperature-programmed desorption (TPD). With CO2 adsorption at higher temperature, the composite materials showed different adsorption capacities with pressure variation. As a result, the adsorption and separation of CO2 on these TEPA modified mesoporous materials in ambient air flow can be realized via pressure swing adsorption.
