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2006 Volume 22 Issue 4
2006, 22(04): 391-396
doi: 10.1016/S1872-1508(06)60010-7
Abstract:
The electronic and geometric structures of a series of isomeric complexes α-, β-, γ-, δ-, ε-[Ru(azpy)2Cl2](azpy = 2-phenylazopyridine) (1~5) have been systemically studied, using the density functional theory(DFT) method at the B3LYP/LanL2DZ level. In particular, the structure-activity relationship(SAR) of 1~3 reported recently to be well-known antitumors, was emphatically investigated. The computed results show that: (i) The main-body (azopyridine) planes of two conjugative ligands(azpy) in γ-[Ru(azpy)2Cl2](3) are almost located on the same plane, it must be advantageous to the conjugative ligand intercalating between DNA-base-pairs, whereas those in α- and β-[Ru(azpy)2Cl2](1 and 2) are almost intervertical and thus it must be unadvantageous to their DNA-binding affinities due to their greater steric hindrance. (ii) The energies (εL) of the lowest unoccupied molecular orbitals(LUMO) playing a main role in the electrophilic reaction, are in sequence of εL(2) >εL(1) >εL(3); The energy differences (ΔεL-H) between LUMOs and HOMOs, being closely relative to the reaction activity, are in sequence of ? ΔεL-H(3)<ΔεL-H(1)<ΔεL-H(2). (iii) The total dipole moments (µ) of the isomer, being closely relative to the hydrophobic parameter of the molecule, are in sequence of µ(2) >µ(1) >µ(3). (iv) The positive charges (QL) in the ligand azpy, being also relative to the ability to accept the electron from DNA, are in sequence of QL(3) >QL(1) >QL(2). In addition, based on the above theoretical analytic method, the heretofore unreported antimetastatic activities of the other two isomeric complexes δ-, ε-[Ru(azpy)2Cl2](4 and 5) have been predicted.
The electronic and geometric structures of a series of isomeric complexes α-, β-, γ-, δ-, ε-[Ru(azpy)2Cl2](azpy = 2-phenylazopyridine) (1~5) have been systemically studied, using the density functional theory(DFT) method at the B3LYP/LanL2DZ level. In particular, the structure-activity relationship(SAR) of 1~3 reported recently to be well-known antitumors, was emphatically investigated. The computed results show that: (i) The main-body (azopyridine) planes of two conjugative ligands(azpy) in γ-[Ru(azpy)2Cl2](3) are almost located on the same plane, it must be advantageous to the conjugative ligand intercalating between DNA-base-pairs, whereas those in α- and β-[Ru(azpy)2Cl2](1 and 2) are almost intervertical and thus it must be unadvantageous to their DNA-binding affinities due to their greater steric hindrance. (ii) The energies (εL) of the lowest unoccupied molecular orbitals(LUMO) playing a main role in the electrophilic reaction, are in sequence of εL(2) >εL(1) >εL(3); The energy differences (ΔεL-H) between LUMOs and HOMOs, being closely relative to the reaction activity, are in sequence of ? ΔεL-H(3)<ΔεL-H(1)<ΔεL-H(2). (iii) The total dipole moments (µ) of the isomer, being closely relative to the hydrophobic parameter of the molecule, are in sequence of µ(2) >µ(1) >µ(3). (iv) The positive charges (QL) in the ligand azpy, being also relative to the ability to accept the electron from DNA, are in sequence of QL(3) >QL(1) >QL(2). In addition, based on the above theoretical analytic method, the heretofore unreported antimetastatic activities of the other two isomeric complexes δ-, ε-[Ru(azpy)2Cl2](4 and 5) have been predicted.
2006, 22(04): 397-402
doi: 10.1016/S1872-1508(06)60011-9
Abstract:
In order to predict the antitumor activities of various epothilone analogues, a set of molecular descriptors, including electronic, topological, and geometric descriptors, and molecular shape indices (K-order moment shape indices), were calculated to characterize the structural and physicochemical properties for 150 compounds. The 30 descriptors selected with genetic al rithm were employed to establish the classification and prediction model of epothilone analogues by using support vector machine (SVM). This SVM system gives a total prediction accuracy of 83.3% by the leave-one-out method and that of 80.6% by the 5-fold cross-validation method. The present study indicates that K-order moment shape indices are useful for description of configuration isomers, and SVM is a facilitating tool in prediction of antitumor activity of epothilone analogues.
In order to predict the antitumor activities of various epothilone analogues, a set of molecular descriptors, including electronic, topological, and geometric descriptors, and molecular shape indices (K-order moment shape indices), were calculated to characterize the structural and physicochemical properties for 150 compounds. The 30 descriptors selected with genetic al rithm were employed to establish the classification and prediction model of epothilone analogues by using support vector machine (SVM). This SVM system gives a total prediction accuracy of 83.3% by the leave-one-out method and that of 80.6% by the 5-fold cross-validation method. The present study indicates that K-order moment shape indices are useful for description of configuration isomers, and SVM is a facilitating tool in prediction of antitumor activity of epothilone analogues.
2006, 22(04): 403-408
doi: 10.1016/S1872-1508(06)60012-0
Abstract:
The electrode process of concentrated V(IV)/V(V) species has been studied at a graphite electrode using cyclic voltammetry, linear polarization, and impedance techniques. The results have revealed that in H2SO4 solution below 2 mol•L-1 containing 2.0 mol•L-1 V(IV), the electrode process of V(IV)/V(V) is controlled by the electrochemical polarization and diffusion with poor reversibility. When the concentration of H2SO4 is above 2 mol•L-1, the electrode process of V(IV)/V(V) turns into the diffusion control with improvement of the reversibility. An increase in concentration of H2SO4 solution facilitates a decrease in impedance, whereas too high concentration of H2SO4 solution(>3 mol•L-1) results in a remarkable increase in the viscosity of solution leading to a large mass transportation polarization, and thus the impedance starts to increase a bit. In 3 mol•L-1 H2SO4 solution, the reversibility and kinetics of V(IV)/V(V) are improved gradually as well as the characteristics of impedance with increasing concentration of V(IV) solution. But, when the concentration of V(IV) solution exceeds 2.0 mol•L-1, the viscosity of the solution is so high that the mass transportation polarization increases considerably, resulting in the deterioration of electrochemical performance of V(IV)/V(V) species and an increase in impedance. Therefore, considering from standpoint of increasing the energy density and electrode kinetics comprehensively, the optimal concentration of H2SO4 is 3 mol•L-1 containing 1.5~2.0 mol•L-1 of V(IV).
The electrode process of concentrated V(IV)/V(V) species has been studied at a graphite electrode using cyclic voltammetry, linear polarization, and impedance techniques. The results have revealed that in H2SO4 solution below 2 mol•L-1 containing 2.0 mol•L-1 V(IV), the electrode process of V(IV)/V(V) is controlled by the electrochemical polarization and diffusion with poor reversibility. When the concentration of H2SO4 is above 2 mol•L-1, the electrode process of V(IV)/V(V) turns into the diffusion control with improvement of the reversibility. An increase in concentration of H2SO4 solution facilitates a decrease in impedance, whereas too high concentration of H2SO4 solution(>3 mol•L-1) results in a remarkable increase in the viscosity of solution leading to a large mass transportation polarization, and thus the impedance starts to increase a bit. In 3 mol•L-1 H2SO4 solution, the reversibility and kinetics of V(IV)/V(V) are improved gradually as well as the characteristics of impedance with increasing concentration of V(IV) solution. But, when the concentration of V(IV) solution exceeds 2.0 mol•L-1, the viscosity of the solution is so high that the mass transportation polarization increases considerably, resulting in the deterioration of electrochemical performance of V(IV)/V(V) species and an increase in impedance. Therefore, considering from standpoint of increasing the energy density and electrode kinetics comprehensively, the optimal concentration of H2SO4 is 3 mol•L-1 containing 1.5~2.0 mol•L-1 of V(IV).
2006, 22(04): 409-413
doi: 10.3866/PKU.WHXB20060404
Abstract:
Surfactant p-octyl polyethylene glycol phenyl ether (Triton X-100) or cetyltrimethylammonium bromide (CTAB) was mixed with n-hexane, n-hexanol, and water for preparing reverse microemulsion. The effects of H+ concentration in water phase, concentrations of surfactant and cosurfactant on the microemulsion conductivity were studied. The results demonstrated that increasing H+ concentration in water phase enhanced the conductivity of reverse microemulsion greatly. The conductivity of microemulsion could be increased by 1~2 orders of magnitude as the H+ concentration increased from 1 mol•L-1 to 10 mol•L-1. When the H+ concentration of water phase was 10 mol•L-1, the conductivity of microemulsion enhanced as the water volume increased. The conductivity of these microemulsion increased to about 3200 μS•cm-1 when the volume ratio of water to oil was 3:10. The conductivity of microemulsion was enhanced as the Triton X-100 concentration increased, while it decreased with the increase of the CTAB concentration. The conductivity of non-ionic microemulsion decreased with the increase of cosurfactant concentration, while the conductivity of ionic microemulsion showed a camel shape change with the cosurfactant concentration.
Surfactant p-octyl polyethylene glycol phenyl ether (Triton X-100) or cetyltrimethylammonium bromide (CTAB) was mixed with n-hexane, n-hexanol, and water for preparing reverse microemulsion. The effects of H+ concentration in water phase, concentrations of surfactant and cosurfactant on the microemulsion conductivity were studied. The results demonstrated that increasing H+ concentration in water phase enhanced the conductivity of reverse microemulsion greatly. The conductivity of microemulsion could be increased by 1~2 orders of magnitude as the H+ concentration increased from 1 mol•L-1 to 10 mol•L-1. When the H+ concentration of water phase was 10 mol•L-1, the conductivity of microemulsion enhanced as the water volume increased. The conductivity of these microemulsion increased to about 3200 μS•cm-1 when the volume ratio of water to oil was 3:10. The conductivity of microemulsion was enhanced as the Triton X-100 concentration increased, while it decreased with the increase of the CTAB concentration. The conductivity of non-ionic microemulsion decreased with the increase of cosurfactant concentration, while the conductivity of ionic microemulsion showed a camel shape change with the cosurfactant concentration.
2006, 22(04): 414-418
doi: 10.3866/PKU.WHXB20060405
Abstract:
The interactions of a series of novel cleavable esterquat Gemini surfactants, Cm-1H2m-1COOCH2CH2(CH3)2N+(CH2)n+N(CH3)2CH2CH2OOCCm-1H2m-1]•2Br-(symbolized II-m-n, m=10, 12; n=3, 4, 6), with sodium dodecyl sulphate (SDS) in aqueous solution have been investigated. The experimental results suggested that both II-10-n and II-12-n had evident synergism with SDS in mixed micelle formation and surface tension reduction in binary system. II-10-n manifested stronger synergistic interaction with SDS than II-12-n, which was attributed to the equal-chain length effect. The synergism in mixed micelle formation of II-m-n/SDS was found to become more intense increasingly with the increase of n. The equilibrium constant proof illustrated that the ratio of II-m-n to SDS existed in mixed micelles was approximately 1:1, which indicated that the mixed micelle was charged. Therefore the addition of NaBr could improve the surface activity of II-m-n/SDS mixtures and promote the formation of mixed micelles.
The interactions of a series of novel cleavable esterquat Gemini surfactants, Cm-1H2m-1COOCH2CH2(CH3)2N+(CH2)n+N(CH3)2CH2CH2OOCCm-1H2m-1]•2Br-(symbolized II-m-n, m=10, 12; n=3, 4, 6), with sodium dodecyl sulphate (SDS) in aqueous solution have been investigated. The experimental results suggested that both II-10-n and II-12-n had evident synergism with SDS in mixed micelle formation and surface tension reduction in binary system. II-10-n manifested stronger synergistic interaction with SDS than II-12-n, which was attributed to the equal-chain length effect. The synergism in mixed micelle formation of II-m-n/SDS was found to become more intense increasingly with the increase of n. The equilibrium constant proof illustrated that the ratio of II-m-n to SDS existed in mixed micelles was approximately 1:1, which indicated that the mixed micelle was charged. Therefore the addition of NaBr could improve the surface activity of II-m-n/SDS mixtures and promote the formation of mixed micelles.
2006, 22(04): 419-423
doi: 10.1016/S1872-1508(06)60013-2
Abstract:
Modification of conventional Pt/C electrocatalyst with silicomolybdic acid (SiMoA) was performed using electrochemical cyclic voltammetry method. The modified and unmodified catalysts were tested under identical conditions for the electrooxidation of CO, methanol, and ethanol. In the CO stripping experiments, the modified catalyst was characterized by significant shifts (80 and 60 mV) to lower onset potential and peak potentials for CO electrooxidation, suggesting better CO tolerant property of the modified catalyst. In the electrooxidation of methanol and ethanol, the modified catalyst was featured by significantly increased current densities due to reduced residence time of the reaction intermediates, showing significantly higher electrocatalytic activity for electrooxidation of alcohols.
Modification of conventional Pt/C electrocatalyst with silicomolybdic acid (SiMoA) was performed using electrochemical cyclic voltammetry method. The modified and unmodified catalysts were tested under identical conditions for the electrooxidation of CO, methanol, and ethanol. In the CO stripping experiments, the modified catalyst was characterized by significant shifts (80 and 60 mV) to lower onset potential and peak potentials for CO electrooxidation, suggesting better CO tolerant property of the modified catalyst. In the electrooxidation of methanol and ethanol, the modified catalyst was featured by significantly increased current densities due to reduced residence time of the reaction intermediates, showing significantly higher electrocatalytic activity for electrooxidation of alcohols.
2006, 22(04): 424-429
doi: 10.1016/S1872-1508(06)60014-4
Abstract:
N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) copolymer microspheres with various compositions were prepared by inverse suspension polymerization technique. The microgels thus prepared were employed as templates for the deposition of MS (M=Cu, Cd or Zn). In this way, a number of MS (M=Cu, Cd or Zn)-P(NIPAM-co-MAA) composite microspheres with different surface morphologies were prepared successfully. The effects of surfactants and the composition of the microgels upon the surface morphologies of the composite microspheres were studied in detail. It was demonstrated that the structures of the surfactants and the compositions of the microgels employed in the preparation have a great effect upon the surface morphologies of the composite microspheres. As for the model systems, the surface structures of the composite microspheres tend to be coarse with the structures of the surfactants becoming complex, or with their HLB (hydrophile-lipophile balance) values decreasing (Span-20, Span-80 and Span-85). Even so, the surface structures of the composite microspheres prepared in the presence of Span-85 are still highly ordered. It was also demonstrated that more fine surface structures were formed with increasing the MAA content in the template microgels. Thus, it may be concluded that the surface structures of the composite microspheres can be tailored to a certain extent by simply varying the types of surfactants, and changing the composition of monomer units in the template microgels.
N-isopropylacrylamide (NIPAM) and methacrylic acid (MAA) copolymer microspheres with various compositions were prepared by inverse suspension polymerization technique. The microgels thus prepared were employed as templates for the deposition of MS (M=Cu, Cd or Zn). In this way, a number of MS (M=Cu, Cd or Zn)-P(NIPAM-co-MAA) composite microspheres with different surface morphologies were prepared successfully. The effects of surfactants and the composition of the microgels upon the surface morphologies of the composite microspheres were studied in detail. It was demonstrated that the structures of the surfactants and the compositions of the microgels employed in the preparation have a great effect upon the surface morphologies of the composite microspheres. As for the model systems, the surface structures of the composite microspheres tend to be coarse with the structures of the surfactants becoming complex, or with their HLB (hydrophile-lipophile balance) values decreasing (Span-20, Span-80 and Span-85). Even so, the surface structures of the composite microspheres prepared in the presence of Span-85 are still highly ordered. It was also demonstrated that more fine surface structures were formed with increasing the MAA content in the template microgels. Thus, it may be concluded that the surface structures of the composite microspheres can be tailored to a certain extent by simply varying the types of surfactants, and changing the composition of monomer units in the template microgels.
2006, 22(04): 430-435
doi: 10.3866/PKU.WHXB20060408
Abstract:
A series of N-carboxyl appended pyridinium task-specific ionic liquids(TSILs) were synthesized and characterized by 1H NMR, 13C NMR, IR, and DSC. The miscibilities of these TSILs with conventional solvents were studied and the acid-dissociation constant pKa values of them were measured through titration. The pKa values of N-carboxyl appended TSILs were between 2.5 to 4.0 and increased with increasing alkyl chain length. The melting points of N-carboxyl appended TSILs were influenced extensively by the size of ions and hydrogen bonds formed between the ions, the smaller the anion size is, the higher the melt point is. With conventional organic solvents, the miscibilities of all synthesized N-carboxyl appended TSILs were the same and mainly determined by the substituted carboxyl. Contrary to common imidazolium ILs, N-carboxyl appended TSILs were immiscibe with acetone and dichloromethane. The physical properties of TSILs were mainly affected by the substituted group and could be adjusted with task-specified cation, changing the length of substituted group, or combining of the selected cation and anion.
A series of N-carboxyl appended pyridinium task-specific ionic liquids(TSILs) were synthesized and characterized by 1H NMR, 13C NMR, IR, and DSC. The miscibilities of these TSILs with conventional solvents were studied and the acid-dissociation constant pKa values of them were measured through titration. The pKa values of N-carboxyl appended TSILs were between 2.5 to 4.0 and increased with increasing alkyl chain length. The melting points of N-carboxyl appended TSILs were influenced extensively by the size of ions and hydrogen bonds formed between the ions, the smaller the anion size is, the higher the melt point is. With conventional organic solvents, the miscibilities of all synthesized N-carboxyl appended TSILs were the same and mainly determined by the substituted carboxyl. Contrary to common imidazolium ILs, N-carboxyl appended TSILs were immiscibe with acetone and dichloromethane. The physical properties of TSILs were mainly affected by the substituted group and could be adjusted with task-specified cation, changing the length of substituted group, or combining of the selected cation and anion.
2006, 22(04): 436-440
doi: 10.3866/PKU.WHXB20060409
Abstract:
The structure change of carbon nanotubes (CNTs) after heat treatment and the effect of CNTs treated at different temperatures in nitrogen ambient on the electrochemical properties of CNTs-LaNi5 electrodes were investigated. The thickness of CNTs after heat treatment is thinner, the number of layers is less and the outside diameter is smaller than those unheated of CNTs. So the deposition and release of hydrogen are easier. CNTs-LaNi5 electrodes were prepared by mixing CNTs and LaNi5 alloy in a mass ratio of 1:10. The CNTs-LaNi5 electrodes with CNTs treated at 800 ℃ in nitrogen has the best electrochemical hydrogen storage capacity with a highest capacity of 519.1 mAh•g-1 and a corresponding discharging plateau voltage of 1.19 V. From 500 ℃ to 800 ℃, the higher the temperature of the heat treatment is, the better the electrochemical hydrogen storage property of the electrode will be. However, CNTs-LaNi5 electrodes with CNTs treated at 900 ℃ has a lower capacity. This shows that the temperature of treatment is an important factor that influences electrochemical hydrogen storage performance of CNTs. Pure LaNi5 electrode has a discharge capacity of only 265.6 mAh•g-1 and a discharging plateau voltage of only 0.83 V, which are lower than those of all CNTs-LaNi5 electrodes treated at different temperatures in nitrogen ambient.
The structure change of carbon nanotubes (CNTs) after heat treatment and the effect of CNTs treated at different temperatures in nitrogen ambient on the electrochemical properties of CNTs-LaNi5 electrodes were investigated. The thickness of CNTs after heat treatment is thinner, the number of layers is less and the outside diameter is smaller than those unheated of CNTs. So the deposition and release of hydrogen are easier. CNTs-LaNi5 electrodes were prepared by mixing CNTs and LaNi5 alloy in a mass ratio of 1:10. The CNTs-LaNi5 electrodes with CNTs treated at 800 ℃ in nitrogen has the best electrochemical hydrogen storage capacity with a highest capacity of 519.1 mAh•g-1 and a corresponding discharging plateau voltage of 1.19 V. From 500 ℃ to 800 ℃, the higher the temperature of the heat treatment is, the better the electrochemical hydrogen storage property of the electrode will be. However, CNTs-LaNi5 electrodes with CNTs treated at 900 ℃ has a lower capacity. This shows that the temperature of treatment is an important factor that influences electrochemical hydrogen storage performance of CNTs. Pure LaNi5 electrode has a discharge capacity of only 265.6 mAh•g-1 and a discharging plateau voltage of only 0.83 V, which are lower than those of all CNTs-LaNi5 electrodes treated at different temperatures in nitrogen ambient.
2006, 22(04): 441-444
doi: 10.1016/S1872-1508(06)60015-6
Abstract:
A high-throughput method has been developed for screening and optimization of heterogeneous catalysts and reacting condition by judging from the change in color of reactants and products as well as indicators during reaction. As compared with other techniques, this method is simple and viable. In catalytic esterification, methyl orange is chosen as an indicator for screening the activities under various conditions. In the photocatalytic degradation of dyes, methyl orange and Rhodamine B are chosen as indicators for the catalytic reactions. Furthermore, the results obtained from high-throughput color-screening have been verified by GC and UV-Vis spectrometer, showing a od accordance between the color-screening and the GC, UV-Vis techniques.
A high-throughput method has been developed for screening and optimization of heterogeneous catalysts and reacting condition by judging from the change in color of reactants and products as well as indicators during reaction. As compared with other techniques, this method is simple and viable. In catalytic esterification, methyl orange is chosen as an indicator for screening the activities under various conditions. In the photocatalytic degradation of dyes, methyl orange and Rhodamine B are chosen as indicators for the catalytic reactions. Furthermore, the results obtained from high-throughput color-screening have been verified by GC and UV-Vis spectrometer, showing a od accordance between the color-screening and the GC, UV-Vis techniques.
2006, 22(04): 445-450
doi: 10.3866/PKU.WHXB20060411
Abstract:
The influence of hydrogen contamination on the atomic geometry of Ti(0001) surface have been studied by using the density-functional theory and the projector-augmented wave(PAW) method. Based on the optimized structural parameters of hcp Ti from the PAW total energy calculation, the surface relaxation, surface energy, and work function of clean Ti(0001) surface were calculated in the same way. The adsorption geometries and total energies of several coverages of hydrogen on Ti(0001) surface including p(1×1),p(1×2),3^1/2×3^1/2R30[deg], and p(2×2), were studied for the hcp and fcc site absorptions combined with the both sites occupation in p(1×1) structure. These results suggest that the Ti(0001) p(1×1)/H geometry has the largest energy gain among the above conformations, so under the condition of low coverage and low H2 pressure, the most possible conformation is p(1×1)-H adsorption. The shrink of Ti(0001) surface with H contamination was -3.7% from available experiments and this work yields -2.85% for hcp and -4.31% for fcc adsorption geometries, respectively. It is deduced that the most possible adsorption configuration for a hydrogen contaminated Ti(0001) surface is a mixture of hcp and fcc adsorptions. For a clean Ti(0001) surface the surface contraction is calculated to be near -7.0% while the experimental measurement predicted -4.9%. This observation implies that even for a “clean” Ti(0001) surface there is still about 13.6% surface area covered with hydrogen adsorption. These results reflect that the hydrogen contamination could affect the Ti(0001) surface structure dramatically. Furthermore the present study could yield a conclusion naturally that the shrink of the Ti(0001) surface will be reduced with the increase of H atom adsorption below 1.0 ML(monolayer).
The influence of hydrogen contamination on the atomic geometry of Ti(0001) surface have been studied by using the density-functional theory and the projector-augmented wave(PAW) method. Based on the optimized structural parameters of hcp Ti from the PAW total energy calculation, the surface relaxation, surface energy, and work function of clean Ti(0001) surface were calculated in the same way. The adsorption geometries and total energies of several coverages of hydrogen on Ti(0001) surface including p(1×1),p(1×2),3^1/2×3^1/2R30[deg], and p(2×2), were studied for the hcp and fcc site absorptions combined with the both sites occupation in p(1×1) structure. These results suggest that the Ti(0001) p(1×1)/H geometry has the largest energy gain among the above conformations, so under the condition of low coverage and low H2 pressure, the most possible conformation is p(1×1)-H adsorption. The shrink of Ti(0001) surface with H contamination was -3.7% from available experiments and this work yields -2.85% for hcp and -4.31% for fcc adsorption geometries, respectively. It is deduced that the most possible adsorption configuration for a hydrogen contaminated Ti(0001) surface is a mixture of hcp and fcc adsorptions. For a clean Ti(0001) surface the surface contraction is calculated to be near -7.0% while the experimental measurement predicted -4.9%. This observation implies that even for a “clean” Ti(0001) surface there is still about 13.6% surface area covered with hydrogen adsorption. These results reflect that the hydrogen contamination could affect the Ti(0001) surface structure dramatically. Furthermore the present study could yield a conclusion naturally that the shrink of the Ti(0001) surface will be reduced with the increase of H atom adsorption below 1.0 ML(monolayer).
2006, 22(04): 451-455
doi: 10.1016/S1872-1508(06)60016-8
Abstract:
The structure and infrared vibration of silica nanotubes with anhydrous structure(SiO2-NTs) and hydrogen-capped structure (SiO2-WNTs) have been investigated using the density-functional theory (DFT). It was found that the average binding energies were almost the same for SiO2-WNTs having same layer numbers or length. SiO2-WNTs are energetically more favorable than the SiO2-NTs and two-membered ring (2MR) molecular chains structure. IR spectrum of 4MR-WNTs was in well accord with the experimental data and the vibrations of oxygen atoms with directions parallel and normal to the axis of nanotubes show a strong size effect. The SiO2-WNTs would be considered as an appropriate structure model for one-dimensional silica nanotube.
The structure and infrared vibration of silica nanotubes with anhydrous structure(SiO2-NTs) and hydrogen-capped structure (SiO2-WNTs) have been investigated using the density-functional theory (DFT). It was found that the average binding energies were almost the same for SiO2-WNTs having same layer numbers or length. SiO2-WNTs are energetically more favorable than the SiO2-NTs and two-membered ring (2MR) molecular chains structure. IR spectrum of 4MR-WNTs was in well accord with the experimental data and the vibrations of oxygen atoms with directions parallel and normal to the axis of nanotubes show a strong size effect. The SiO2-WNTs would be considered as an appropriate structure model for one-dimensional silica nanotube.
2006, 22(04): 456-459
doi: 10.3866/PKU.WHXB20060413
Abstract:
1H NMR, 13C NMR, and 13C spin-lattice relaxation time(T1) of the mixtures of room temperature ionic liquid [C8mim][BF4] and acetone with different proportions have been studied by NMR. The results indicated that the interaction between the protons of the ring, the methyl and methylene next to the nitrogen of ionic liquids and the carbonyl oxygen of acetone weakened the strong interaction between the cation and anion of the ionic liquid, thus increased the motion and decreased the viscosity of the ionic liquid.
1H NMR, 13C NMR, and 13C spin-lattice relaxation time(T1) of the mixtures of room temperature ionic liquid [C8mim][BF4] and acetone with different proportions have been studied by NMR. The results indicated that the interaction between the protons of the ring, the methyl and methylene next to the nitrogen of ionic liquids and the carbonyl oxygen of acetone weakened the strong interaction between the cation and anion of the ionic liquid, thus increased the motion and decreased the viscosity of the ionic liquid.
2006, 22(04): 460-464
doi: 10.1016/S1872-1508(06)60017-X
Abstract:
The Photodissociation dynamics of C8H17Br with excitation laser at 234 nm has been studied using velocity map ion imaging. The relative quantum yields are obtained from (2+1) resonance-enhanced multiphoton ionization (REMPI) of the photofragment Br*(2P1/2) and Br(2P3/2). The velocity maps provide detail information on translational energy distributions and angle distributions. The probabilities of the individual pathways of the fragments are calculated from the relative quantum yield and angular distribution. The results indicate that a large fraction of the available energy translates into the internal energy of the fragments, which can be explained using the soft impulsive model. The relationship between the energy partition and the alkyl structure has been analysed.
The Photodissociation dynamics of C8H17Br with excitation laser at 234 nm has been studied using velocity map ion imaging. The relative quantum yields are obtained from (2+1) resonance-enhanced multiphoton ionization (REMPI) of the photofragment Br*(2P1/2) and Br(2P3/2). The velocity maps provide detail information on translational energy distributions and angle distributions. The probabilities of the individual pathways of the fragments are calculated from the relative quantum yield and angular distribution. The results indicate that a large fraction of the available energy translates into the internal energy of the fragments, which can be explained using the soft impulsive model. The relationship between the energy partition and the alkyl structure has been analysed.
Hydroformylation of Long-chain Olefins Catalyzed by Rhodium-Phosphine Complexes in New Ionic Liquids
2006, 22(04): 465-469
doi: 10.3866/PKU.WHXB20060415
Abstract:
Preparation and characterization of a series of halogen-free ionic liquids 1-alkyl-3-methyl-imidazolium p-tolusulfonate([Rmim][p-CH3C6H4SO3], R= n-butyl, n-octyl, n-dodecyl, n-cetyl) were reported. These halogen-free ionic liquids were applied as a reaction medium in the hydroformylation catalyzed by water-soluble rhodium complex HRh(CO)(TPPTS)3[TPPTS: P(m-C6H4SO3Na)3]. The results showed that the activity of the hydroformylation was related with the chain-length of R-group in ionic liquids [Rmim][p-CH3C6H4SO3] and decreased with the increase of chain-length of higher olefins. Compared with the halogen-containing anologues [Bmim]BF4 and [Bmim]PF6, the hydroformylation of higher olefins in ionic liquids [Rmim][p-CH3C6H4SO3] exhibited higher activity and selectivity for the aldehydes. Under moderate reaction conditions, the catalyst turnover frequency of 1-hexene hydroformylation as high as 2736 h-1 has been observed. Moreover, the products were conveniently separated from the catalyst by simple decantation and the rhodium-phosphine complexes immobilized in the ionic liquids could be reused several times without significant loss of activity and selectivity. The rhodium leaching into the organic product was lower than 0.1%.
Preparation and characterization of a series of halogen-free ionic liquids 1-alkyl-3-methyl-imidazolium p-tolusulfonate([Rmim][p-CH3C6H4SO3], R= n-butyl, n-octyl, n-dodecyl, n-cetyl) were reported. These halogen-free ionic liquids were applied as a reaction medium in the hydroformylation catalyzed by water-soluble rhodium complex HRh(CO)(TPPTS)3[TPPTS: P(m-C6H4SO3Na)3]. The results showed that the activity of the hydroformylation was related with the chain-length of R-group in ionic liquids [Rmim][p-CH3C6H4SO3] and decreased with the increase of chain-length of higher olefins. Compared with the halogen-containing anologues [Bmim]BF4 and [Bmim]PF6, the hydroformylation of higher olefins in ionic liquids [Rmim][p-CH3C6H4SO3] exhibited higher activity and selectivity for the aldehydes. Under moderate reaction conditions, the catalyst turnover frequency of 1-hexene hydroformylation as high as 2736 h-1 has been observed. Moreover, the products were conveniently separated from the catalyst by simple decantation and the rhodium-phosphine complexes immobilized in the ionic liquids could be reused several times without significant loss of activity and selectivity. The rhodium leaching into the organic product was lower than 0.1%.
2006, 22(04): 470-474
doi: 10.3866/PKU.WHXB20060416
Abstract:
The thin films of fluorescein grown on Ag(110) have been studied by the ultraviolet photoemission spectroscopy(UPS). Four emission features are located at 2.70, 3.80, 7.40, and 9.80 eV below the Fermi level, respectively. The angle-resolved ultraviolet photoemission spectroscopy(ARUPS) suggests that the triring plane of fluorescein is parallel to the substrate and the axis of the C=O orbit is close to the [1-10] azimuth.
The thin films of fluorescein grown on Ag(110) have been studied by the ultraviolet photoemission spectroscopy(UPS). Four emission features are located at 2.70, 3.80, 7.40, and 9.80 eV below the Fermi level, respectively. The angle-resolved ultraviolet photoemission spectroscopy(ARUPS) suggests that the triring plane of fluorescein is parallel to the substrate and the axis of the C=O orbit is close to the [1-10] azimuth.
2006, 22(04): 475-480
doi: 10.3866/PKU.WHXB20060417
Abstract:
The microstructure of cyhalothrin microemulsion was studied by means of conductivity measurement, and pseudo ternary phase diagrams were presented. The formation mechanism of cyhalothrin microemulsion was studied, with particular emphasis on the effects of molar fraction of sodium dodecylbenzene sulfonate(SDBS), electrolyte mass concentration and tempreture on cyhalothrin microemulsion. It has been found that: ①with the increase of molar fraction of SDBS, the areas of BC and O/W type microemulsion region increased first and decreased afterwards, while the W/O type decreased first and increased afterwards; ②with the increase of electrolyte mass concentration, the areas of W/O , BC and O/W type microemulsion region all increased first and decreased afterwards; ③with the increase of tempreture, the areas of BC and O/W type microemulsion region decreased, while the W/O type increased.
The microstructure of cyhalothrin microemulsion was studied by means of conductivity measurement, and pseudo ternary phase diagrams were presented. The formation mechanism of cyhalothrin microemulsion was studied, with particular emphasis on the effects of molar fraction of sodium dodecylbenzene sulfonate(SDBS), electrolyte mass concentration and tempreture on cyhalothrin microemulsion. It has been found that: ①with the increase of molar fraction of SDBS, the areas of BC and O/W type microemulsion region increased first and decreased afterwards, while the W/O type decreased first and increased afterwards; ②with the increase of electrolyte mass concentration, the areas of W/O , BC and O/W type microemulsion region all increased first and decreased afterwards; ③with the increase of tempreture, the areas of BC and O/W type microemulsion region decreased, while the W/O type increased.
2006, 22(04): 481-485
doi: 10.3866/PKU.WHXB20060418
Abstract:
Vinyl radical was generated by photolysing methyl vinyl ketone at 193 nm, then was photodissociated by another tunable laser in the 21180~21320 cm1 range. The dissociated H atom fragments were ionized and detected by resonance-enhanced multiphoton ionization (REMPI) processes. The ro-vibrational action spectra of the A2A″(µ′5,6,8=1)←X2A′(µ″=0) of vinyl radical were recorded by monitoring the H+ ion intensity with dissociation laser wavelength. The corresponding analyses were obtained with the aid of quantum chemical calculations and spectroscopic simulations, vibrational bands and main rotational transitions were definitely assigned. Additionally, the predissociative lifetime was derived from the simulated linewidth, and its dependence on the vibrational mode and rotational quantum number was discussed. The in-plane dissociation mechanism of the state predicted by theoretical studies was confirmed.
Vinyl radical was generated by photolysing methyl vinyl ketone at 193 nm, then was photodissociated by another tunable laser in the 21180~21320 cm1 range. The dissociated H atom fragments were ionized and detected by resonance-enhanced multiphoton ionization (REMPI) processes. The ro-vibrational action spectra of the A2A″(µ′5,6,8=1)←X2A′(µ″=0) of vinyl radical were recorded by monitoring the H+ ion intensity with dissociation laser wavelength. The corresponding analyses were obtained with the aid of quantum chemical calculations and spectroscopic simulations, vibrational bands and main rotational transitions were definitely assigned. Additionally, the predissociative lifetime was derived from the simulated linewidth, and its dependence on the vibrational mode and rotational quantum number was discussed. The in-plane dissociation mechanism of the state predicted by theoretical studies was confirmed.
2006, 22(04): 486-491
doi: 10.3866/PKU.WHXB20060419
Abstract:
A novel substituent descriptor based on the 17 different physicochemical parameters about the electronic, hydrophobic and steric properties of substituents is used to describe the chemical structures of 22 cyclic ureas and 22 N,N-dimethyl-2-bromo(substituted phenyl) ethylamine derivatives, respectively. The variables are reduced using stepwise multiple regression (SMR) method for the training set, and the statistical results indicate that the correlation coefficient square for the two series of compounds in the multiple linear regression and cross validation using leave one out (LOO) is 0.853, 0.960, 0.723 and 0.901, respectively. To validate the predictive power of resulting models, external validation are performed for two testing sets with Qext2 values of 0.7617 and 0.7653, respectively. The models obtained also shows that the anti-HIV activity of cyclic ureas is blocked by steric hindrance of ortho and para substituents and hydrophobicity of meta and para substituents, the biological activity of N,N-dimethyl-2-bromo (substituted phenyl) ethylamine derivatives may be improved by introducing the steric substituents and electronic supplying para substituents into phenyl ring.
A novel substituent descriptor based on the 17 different physicochemical parameters about the electronic, hydrophobic and steric properties of substituents is used to describe the chemical structures of 22 cyclic ureas and 22 N,N-dimethyl-2-bromo(substituted phenyl) ethylamine derivatives, respectively. The variables are reduced using stepwise multiple regression (SMR) method for the training set, and the statistical results indicate that the correlation coefficient square for the two series of compounds in the multiple linear regression and cross validation using leave one out (LOO) is 0.853, 0.960, 0.723 and 0.901, respectively. To validate the predictive power of resulting models, external validation are performed for two testing sets with Qext2 values of 0.7617 and 0.7653, respectively. The models obtained also shows that the anti-HIV activity of cyclic ureas is blocked by steric hindrance of ortho and para substituents and hydrophobicity of meta and para substituents, the biological activity of N,N-dimethyl-2-bromo (substituted phenyl) ethylamine derivatives may be improved by introducing the steric substituents and electronic supplying para substituents into phenyl ring.
2006, 22(04): 492-495
doi: 10.3866/PKU.WHXB20060420
Abstract:
Ce2(C2O4)3•10H2O powders with different morphologies were prepared by homogeneous precipitation method at different temperatures. The source materials were Ce(NO3)3•6H2O and dimethyl oxalate (DMO) with a molar ratio of 1:7.5. The phase, morphology and property of the products were characterized by XRD, TEM and TG-DTA. The results showed that the product was Ce2(C2O4)3•10H2O with a monoclinic structure, and the products′crystallization degree could be enhanced by increasing the reaction temperature. The reaction temperature had direct influences on the particle morphology and size. When the reaction temperatures were 30, 50, 65, 85 ℃, the morphologies were irregular, spherical, rice-like, sheet-like, respectively, indicating the reaction course to be temperature sensitive. The reaction mechanism actually related to nucleation velocity and growth rate of the grains, and it followed LaMer model and crystal distributions and control principle during the crystal formation.
Ce2(C2O4)3•10H2O powders with different morphologies were prepared by homogeneous precipitation method at different temperatures. The source materials were Ce(NO3)3•6H2O and dimethyl oxalate (DMO) with a molar ratio of 1:7.5. The phase, morphology and property of the products were characterized by XRD, TEM and TG-DTA. The results showed that the product was Ce2(C2O4)3•10H2O with a monoclinic structure, and the products′crystallization degree could be enhanced by increasing the reaction temperature. The reaction temperature had direct influences on the particle morphology and size. When the reaction temperatures were 30, 50, 65, 85 ℃, the morphologies were irregular, spherical, rice-like, sheet-like, respectively, indicating the reaction course to be temperature sensitive. The reaction mechanism actually related to nucleation velocity and growth rate of the grains, and it followed LaMer model and crystal distributions and control principle during the crystal formation.
2006, 22(04): 496-501
doi: 10.3866/PKU.WHXB20060421
Abstract:
The Krafft point and the critical micelle concentrations (cmc) at different temperatures for the surface active monomer, sodium 2-acrylamido-tetradecane (NaAMC14S), were determined. The copolymerizations of NaAMC14S and acrylamide (AM) were carried out in aqueous solution at above and below cmc of NaAMC14S, respectively. The compositions of the copolymers were characterized via conductometric titration method, the thermal behaviors of the copolymers were measured by DSC, and the properties of hydrophobic association of the copolymers were determined by using fluorescence probe technique. By the above investigations, the copolymerization mechanism was explored emphatically. The experiment results show that there are two kinds of copolymerization mechanisms depending on the concentrations of NaAMC14S. When the copolymerization of NaAMC14S and AM is performed above the critical micelle concentration of NaAMC14S, the copolymerization process keeps being a micro-block copolymerization mechanism, and a large compositional drift occurs during the copolymerization. Whereas when the copolymerization of NaAMC14S and AM is performed below the critical micelle concentration of NaAMC14S, the polymerization process is carried out in agreement with random copolymerization mechanism, and the variation of the copolymer composition with the conversion is slower. The DSC thermograms of the copolymers and the result determined by fluorescence probe technique confirm the above mechanisms.
The Krafft point and the critical micelle concentrations (cmc) at different temperatures for the surface active monomer, sodium 2-acrylamido-tetradecane (NaAMC14S), were determined. The copolymerizations of NaAMC14S and acrylamide (AM) were carried out in aqueous solution at above and below cmc of NaAMC14S, respectively. The compositions of the copolymers were characterized via conductometric titration method, the thermal behaviors of the copolymers were measured by DSC, and the properties of hydrophobic association of the copolymers were determined by using fluorescence probe technique. By the above investigations, the copolymerization mechanism was explored emphatically. The experiment results show that there are two kinds of copolymerization mechanisms depending on the concentrations of NaAMC14S. When the copolymerization of NaAMC14S and AM is performed above the critical micelle concentration of NaAMC14S, the copolymerization process keeps being a micro-block copolymerization mechanism, and a large compositional drift occurs during the copolymerization. Whereas when the copolymerization of NaAMC14S and AM is performed below the critical micelle concentration of NaAMC14S, the polymerization process is carried out in agreement with random copolymerization mechanism, and the variation of the copolymer composition with the conversion is slower. The DSC thermograms of the copolymers and the result determined by fluorescence probe technique confirm the above mechanisms.
2006, 22(04): 502-506
doi: 10.3866/PKU.WHXB20060422
Abstract:
The anionic surfactant SDS can control the current oscillation of nickel in 0.5 mol•L-1 HNO3/0.005 mol•L-1 Cl-/H2O system. During the current oscillation, differential capacitance and conductance oscillations are found at the nickel electrode. With the increase of SDS concentration, the amplitudes of the differential capacitance and conductance oscillations all decrease gradually. The functionary mechanism of SDS in the current oscillations and passivation processes is explained.
The anionic surfactant SDS can control the current oscillation of nickel in 0.5 mol•L-1 HNO3/0.005 mol•L-1 Cl-/H2O system. During the current oscillation, differential capacitance and conductance oscillations are found at the nickel electrode. With the increase of SDS concentration, the amplitudes of the differential capacitance and conductance oscillations all decrease gradually. The functionary mechanism of SDS in the current oscillations and passivation processes is explained.
2006, 22(04): 507-512
doi: 10.3866/PKU.WHXB20060423
Abstract:
A carbon-disk microelectrode was used to investigate the surface concentration profile of etchant Br2, which was electrogenerated on the Pt working electrode. The steady state reducing currents of Br2 at different distances away from the Pt electrode was measured. The concentration profile was estimated from the current-distance variation curves as a function of different sampling times. Experimentally determined concentration profiles are in od agreement with those estimated from the microetching results. The microelectrode technique has offered a od method to choose suitable etching solution for chemical micromachining.
A carbon-disk microelectrode was used to investigate the surface concentration profile of etchant Br2, which was electrogenerated on the Pt working electrode. The steady state reducing currents of Br2 at different distances away from the Pt electrode was measured. The concentration profile was estimated from the current-distance variation curves as a function of different sampling times. Experimentally determined concentration profiles are in od agreement with those estimated from the microetching results. The microelectrode technique has offered a od method to choose suitable etching solution for chemical micromachining.
2006, 22(04): 513-516
doi: 10.3866/PKU.WHXB20060424
Abstract:
Polymer-stabilized Au colloidal nanoparticles were prepared by microwave irradiation. Size of the Au particles varied from 5 nm to 120 nm along with different reactive conditions. Effects of the alcohol reducing agent and NaOH on particle size and shape were investigated. The prepared Au nanoparticles were characterized by transmission electron microscope (TEM) and ultraviolet-visible (UV-Vis) spectrophotometer. The Au nanoparticles prepared by microware irradiation have small particle size and od size distribution. The nanoparticle size and shape are highly dependent on the nature of the reducing agent and concentration of NaOH. Using UV-Vis spectra, it was found that the velocity of the formation of the Au nanoparticles in the reactive system with adding of NaOH was obviously faster and easier to form spherical particles than that without NaOH.
Polymer-stabilized Au colloidal nanoparticles were prepared by microwave irradiation. Size of the Au particles varied from 5 nm to 120 nm along with different reactive conditions. Effects of the alcohol reducing agent and NaOH on particle size and shape were investigated. The prepared Au nanoparticles were characterized by transmission electron microscope (TEM) and ultraviolet-visible (UV-Vis) spectrophotometer. The Au nanoparticles prepared by microware irradiation have small particle size and od size distribution. The nanoparticle size and shape are highly dependent on the nature of the reducing agent and concentration of NaOH. Using UV-Vis spectra, it was found that the velocity of the formation of the Au nanoparticles in the reactive system with adding of NaOH was obviously faster and easier to form spherical particles than that without NaOH.
