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2005 Volume 21 Issue 9
2005, 21(09): 949-951
doi: 10.3866/PKU.WHXB20050901
Abstract:
The adsorption of metal-organic complex molecule ([Cu2(μ-O)(dptap)4(NO3)2], where dptap represents 2-(2-pyridylimino)-2H-1,2,4-thia-diazolo[2,3-a] pyridine) on Au(111) surface is studied by STM. STM results show coexistence of undissociative and dissociative adsorption of the molecule. The former shows regular arrangements of the molecule, while the latter gives a (√3×√3)R30°Cu adlayer structure. The possible origin of the coexistence of undissociative and dissociative adsorption is discussed.
The adsorption of metal-organic complex molecule ([Cu2(μ-O)(dptap)4(NO3)2], where dptap represents 2-(2-pyridylimino)-2H-1,2,4-thia-diazolo[2,3-a] pyridine) on Au(111) surface is studied by STM. STM results show coexistence of undissociative and dissociative adsorption of the molecule. The former shows regular arrangements of the molecule, while the latter gives a (√3×√3)R30°Cu adlayer structure. The possible origin of the coexistence of undissociative and dissociative adsorption is discussed.
2005, 21(09): 952-956
doi: 10.3866/PKU.WHXB20050902
Abstract:
In order to investigate the tautomerism of 5-fluorouracil (5-FU) induced by proton transfer, we describe a study of structural tautomer interconversion using density functional theory (DFT) calculations at B3LYP/6-311++G(d, p) level of the theory. Thirty-eight geometries including fifteen transition states with and without water molecule were studied. The calculated results indicate that there are two absolutely opposite regions in the vicinity of 5-FU. In one of the regions, water molecules can assist the tautomerism from 5-FU to its enol form (5-FU*), whereas in another region, water molecules can protect 5-FU from tautomerizing to 5-FU*. Furthermore, compared with the tautomerizing processes of uracil, the probability of 5-FU to tautomerize to its enol form is much higher. Based on such facts, the reason why 5-FU is an effective anticancer medicament but with some of toxicity is explained to some extent.
In order to investigate the tautomerism of 5-fluorouracil (5-FU) induced by proton transfer, we describe a study of structural tautomer interconversion using density functional theory (DFT) calculations at B3LYP/6-311++G(d, p) level of the theory. Thirty-eight geometries including fifteen transition states with and without water molecule were studied. The calculated results indicate that there are two absolutely opposite regions in the vicinity of 5-FU. In one of the regions, water molecules can assist the tautomerism from 5-FU to its enol form (5-FU*), whereas in another region, water molecules can protect 5-FU from tautomerizing to 5-FU*. Furthermore, compared with the tautomerizing processes of uracil, the probability of 5-FU to tautomerize to its enol form is much higher. Based on such facts, the reason why 5-FU is an effective anticancer medicament but with some of toxicity is explained to some extent.
2005, 21(09): 957-960
doi: 10.3866/PKU.WHXB20050903
Abstract:
The solid diffusion coefficient of lithium-ion in spinel LiMn2O4 cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. Results show that there are two minimum peaks in the curves of the solid diffusion coefficient (D) vs voltage (E) at 3.95 V and 4.12 V in the voltage range from 3.85 V to 4.30 V. The curves of lgD－E for the first 20 cycles show that the two minimum peaks are gradually flatted out and the values of solid diffusion coefficient tend to increase when the cycling number increases. The results suggest that LiMn2O4 cathode material has the ability of self-diffusion-enhance during intercalation/deintercalation of lithium-ion.
The solid diffusion coefficient of lithium-ion in spinel LiMn2O4 cathode material has been investigated by the capacity intermittent titration technique (CITT) at different voltages and at different charge/discharge cycles. Results show that there are two minimum peaks in the curves of the solid diffusion coefficient (D) vs voltage (E) at 3.95 V and 4.12 V in the voltage range from 3.85 V to 4.30 V. The curves of lgD－E for the first 20 cycles show that the two minimum peaks are gradually flatted out and the values of solid diffusion coefficient tend to increase when the cycling number increases. The results suggest that LiMn2O4 cathode material has the ability of self-diffusion-enhance during intercalation/deintercalation of lithium-ion.
2005, 21(09): 961-966
doi: 10.3866/PKU.WHXB20050904
Abstract:
The gas phase reaction mechanism of Cl2+2HI=2HCl+I2 has been investigated by MP2/3-21G**, CCSD(T) /3-21G**//MP2/3-21G** and B3LYP/3-21G** levels respectively, and a series of four-centred and three-centred transition states have been obtained. The following result is achieved by comparing the activation energies of six reaction paths. The activation energies of the bimolecular elementary reactions Cl2+HIHCl+ICl and ICl+HII2+HCl are lower than the dissociation energies of Cl2, HI, and ICl. It is thus theoretically proved that the titled reaction occurs more easily in the bimolecular form with two intermediate steps. And finally the transition state calculated from MP2/3-21G** method is validated by intrinsic reaction coordinate (IRC).
The gas phase reaction mechanism of Cl2+2HI=2HCl+I2 has been investigated by MP2/3-21G**, CCSD(T) /3-21G**//MP2/3-21G** and B3LYP/3-21G** levels respectively, and a series of four-centred and three-centred transition states have been obtained. The following result is achieved by comparing the activation energies of six reaction paths. The activation energies of the bimolecular elementary reactions Cl2+HIHCl+ICl and ICl+HII2+HCl are lower than the dissociation energies of Cl2, HI, and ICl. It is thus theoretically proved that the titled reaction occurs more easily in the bimolecular form with two intermediate steps. And finally the transition state calculated from MP2/3-21G** method is validated by intrinsic reaction coordinate (IRC).
2005, 21(09): 967-970
doi: 10.3866/PKU.WHXB20050905
Abstract:
Fluorite-type rare earth complex oxides of (Ce0.8La0.2)1－xCaxO2－δwere prepared by a sol-gel process. Crystalstructure and microstructure of the product were characterized by X-ray diffraction (XRD), transmisson electronmicroscopy (TEM) and scanning electron microscopy (SEM). Electrical conductivity measurements performed in N2/H2 over the temperature range of 400 to 800 ℃ showed that conductivity was enhanced by extrinsic doping. Ammonia was synthesized from nitrogen and hydrogen under atmospheric pressure in a solid state proton conducting cell reactor, and the optimal temperature determined in the ammonia production was 650 ℃. The effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) explained the effect of imposed potential on the rate of NH3 synthesis. The rates of evolution of ammonia were 7.2×10－9 mol•s-1•cm-2 and 7.5×10－9 mol•s-1•cm-2 for Ce0.8La0.2O2－δ and (Ce0.8La0.2)0.975Ca0.025O2－δrespectively at 650 ℃.
Fluorite-type rare earth complex oxides of (Ce0.8La0.2)1－xCaxO2－δwere prepared by a sol-gel process. Crystalstructure and microstructure of the product were characterized by X-ray diffraction (XRD), transmisson electronmicroscopy (TEM) and scanning electron microscopy (SEM). Electrical conductivity measurements performed in N2/H2 over the temperature range of 400 to 800 ℃ showed that conductivity was enhanced by extrinsic doping. Ammonia was synthesized from nitrogen and hydrogen under atmospheric pressure in a solid state proton conducting cell reactor, and the optimal temperature determined in the ammonia production was 650 ℃. The effect of non-Faradaic electrochemical modification of catalytic activity (NEMCA) explained the effect of imposed potential on the rate of NH3 synthesis. The rates of evolution of ammonia were 7.2×10－9 mol•s-1•cm-2 and 7.5×10－9 mol•s-1•cm-2 for Ce0.8La0.2O2－δ and (Ce0.8La0.2)0.975Ca0.025O2－δrespectively at 650 ℃.
2005, 21(09): 971-976
doi: 10.3866/PKU.WHXB20050906
Abstract:
The kinetics for photocatalytic degradation reaction of methyl red, an azo dye, was investigated in a photoelectrochemical (PEC) cell, with titania thin film loaded on titanium as photoanode. The results showed that the degradation of methyl red was accelerated in PEC cell due to a reduced recombination of photogenerated carriers by the separation of the anodic and cathodic reactions. Under the same condition, an increase in photocurrent for PEC cell will suggest an improved rate of degradation. A thin SnO2 film was applied as an interlayer between the substrate and the TiO2 coating to obtain the assembled photoanodes, Ti/SnO2/TiO2, leading to a more separation efficiency of photogenerated carriers. Meanwhile, the photocatalytic activities of the electrodes were estimated by the electrochemical impedance spectroscopy (EIS).
The kinetics for photocatalytic degradation reaction of methyl red, an azo dye, was investigated in a photoelectrochemical (PEC) cell, with titania thin film loaded on titanium as photoanode. The results showed that the degradation of methyl red was accelerated in PEC cell due to a reduced recombination of photogenerated carriers by the separation of the anodic and cathodic reactions. Under the same condition, an increase in photocurrent for PEC cell will suggest an improved rate of degradation. A thin SnO2 film was applied as an interlayer between the substrate and the TiO2 coating to obtain the assembled photoanodes, Ti/SnO2/TiO2, leading to a more separation efficiency of photogenerated carriers. Meanwhile, the photocatalytic activities of the electrodes were estimated by the electrochemical impedance spectroscopy (EIS).
2005, 21(09): 977-982
doi: 10.3866/PKU.WHXB20050907
Abstract:
Galvanostatic oxidation of glucose, galactose and ethanol at platinum electrodes in 0.5 mol•L-1 aqueous NaOH and accompanying potential oscillation behaviors were comparatively studied by the electrochemical quartz crystal microbalance(EQCM) method. The EQCM-frequency oscillation was synchronously observed for the two saccharide systems during their potential oscillations, but it was negligibly small for the ethanol system, and the responses of the motional resistance were minor for all systems, suggesting that the mass effect verned the EQCM frequency responses. Although glucose and galactose are very similar in chemical structure and the amplitude for potential or frequency oscillation was roughly equivalent for both systems, the wave numbers and periods were obviously different from each other, implying that the electrochemical oscillation possesses high molecular recognition between the two systems. Related oscillation mechanism, the effect of NaOH concentration on oscillation, and the electrochemical process of platinum electrode in aqueous NaOH were also discussed. It was concluded that the platinum oxide formed here was mainly PtO2-3H2Oad, and the potential oscillations for the two saccharide systems were accompanied with the adsorption/desorption of anions of saccharic acids at high/low potentials on platinum.
Galvanostatic oxidation of glucose, galactose and ethanol at platinum electrodes in 0.5 mol•L-1 aqueous NaOH and accompanying potential oscillation behaviors were comparatively studied by the electrochemical quartz crystal microbalance(EQCM) method. The EQCM-frequency oscillation was synchronously observed for the two saccharide systems during their potential oscillations, but it was negligibly small for the ethanol system, and the responses of the motional resistance were minor for all systems, suggesting that the mass effect verned the EQCM frequency responses. Although glucose and galactose are very similar in chemical structure and the amplitude for potential or frequency oscillation was roughly equivalent for both systems, the wave numbers and periods were obviously different from each other, implying that the electrochemical oscillation possesses high molecular recognition between the two systems. Related oscillation mechanism, the effect of NaOH concentration on oscillation, and the electrochemical process of platinum electrode in aqueous NaOH were also discussed. It was concluded that the platinum oxide formed here was mainly PtO2-3H2Oad, and the potential oscillations for the two saccharide systems were accompanied with the adsorption/desorption of anions of saccharic acids at high/low potentials on platinum.
2005, 21(09): 983-987
doi: 10.3866/PKU.WHXB20050908
Abstract:
Monolayers and multilayers of copper tetrakis (12-alkyloxycarbonyl)phthalocyanine (CuC12Pc), CuC12Pc mixed with octadecylammonium (ODA) and CuC12Pc mixed with arachic acid (AA) were prepared by Langmuir-Blodgett (LB) technique and their configurations were also studied. The results showed that the compounds form uniform and stable bilayer Langmuir films. Meanwhile, the LB films could be formed very well. The morphology and structure of mixed LB films were observed using AFM, which demonstrated that the configuration of mixed film showed net-like aggregates in the mixture of CuC12Pc/AA, but long island-like aggregates in the mixture of CuC12Pc/ODA. UV-Vis absorption spectra also indicated the reason of different aggregations of the CuC12Pc molecule formed in mixed LB films.
Monolayers and multilayers of copper tetrakis (12-alkyloxycarbonyl)phthalocyanine (CuC12Pc), CuC12Pc mixed with octadecylammonium (ODA) and CuC12Pc mixed with arachic acid (AA) were prepared by Langmuir-Blodgett (LB) technique and their configurations were also studied. The results showed that the compounds form uniform and stable bilayer Langmuir films. Meanwhile, the LB films could be formed very well. The morphology and structure of mixed LB films were observed using AFM, which demonstrated that the configuration of mixed film showed net-like aggregates in the mixture of CuC12Pc/AA, but long island-like aggregates in the mixture of CuC12Pc/ODA. UV-Vis absorption spectra also indicated the reason of different aggregations of the CuC12Pc molecule formed in mixed LB films.
2005, 21(09): 988-992
doi: 10.3866/PKU.WHXB20050909
Abstract:
The thermal decomposition kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) has been investigated by means of non-isothermal TG-DTA with various heating rates of 5.0, 10.0, 15.0, and 20.0 K•min-1. The result shows that the decomposition process of PHBV is composed of three stages：initial stage, medium stage, and end stage. The most probable kinetic function of the initial stage is the Avrami-Erofeev equation with n=1/2, and the corresponding machanism is controlled by random nuclear producing and growing process. The apparent activation energy (Ea(β→0)) and the pre-exponential constant(A(β→0)) are 69.44 kJ•mol-1 and 106.27 s-1 respectively. The most probable kinetic function of the medium stage is the Avrami-Erofeev equation with n=2/5, and the corresponding machanism is the same with the previous stage. The apparent activation energy (Ea(β→0)) and the pre-exponential constant (A(β→0)) are 117.64 kJ•mol-1 and 1011.48 s-1 respectively. The most probable kinetic function of the end stage is the exponential function with n=1/3, and the corresponding mechanism follows Mampel Power theorem. The apparent activation energy(Ea(β→0)) and the pre-exponential constant (A(β→0)) are 116.64 kJ•mol-1 and 108.68 s-1 respectively.
The thermal decomposition kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)(PHBV) has been investigated by means of non-isothermal TG-DTA with various heating rates of 5.0, 10.0, 15.0, and 20.0 K•min-1. The result shows that the decomposition process of PHBV is composed of three stages：initial stage, medium stage, and end stage. The most probable kinetic function of the initial stage is the Avrami-Erofeev equation with n=1/2, and the corresponding machanism is controlled by random nuclear producing and growing process. The apparent activation energy (Ea(β→0)) and the pre-exponential constant(A(β→0)) are 69.44 kJ•mol-1 and 106.27 s-1 respectively. The most probable kinetic function of the medium stage is the Avrami-Erofeev equation with n=2/5, and the corresponding machanism is the same with the previous stage. The apparent activation energy (Ea(β→0)) and the pre-exponential constant (A(β→0)) are 117.64 kJ•mol-1 and 1011.48 s-1 respectively. The most probable kinetic function of the end stage is the exponential function with n=1/3, and the corresponding mechanism follows Mampel Power theorem. The apparent activation energy(Ea(β→0)) and the pre-exponential constant (A(β→0)) are 116.64 kJ•mol-1 and 108.68 s-1 respectively.
2005, 21(09): 993-996
doi: 10.3866/PKU.WHXB20050910
Abstract:
The characteristics of the formation of micro-droplets were investigated in a humidity-controlled chamber. The results showed that the micro-droplets formation had a close relation with the atmospheric corrosion of metal based on the pH and potential distributions of micro-droplets. Micro-droplets could only appear on high potential area in a corrosive combination of metals and salt particles. Meanwhile, a high value of pH was found in the areas covered with micro-droplets. The formation of micro-droplets needed two premises, one was that the relative humidity should be over the saturated relative humidity of main-droplet, the other was that the metal substrate could be eroded under the main-droplet.
The characteristics of the formation of micro-droplets were investigated in a humidity-controlled chamber. The results showed that the micro-droplets formation had a close relation with the atmospheric corrosion of metal based on the pH and potential distributions of micro-droplets. Micro-droplets could only appear on high potential area in a corrosive combination of metals and salt particles. Meanwhile, a high value of pH was found in the areas covered with micro-droplets. The formation of micro-droplets needed two premises, one was that the relative humidity should be over the saturated relative humidity of main-droplet, the other was that the metal substrate could be eroded under the main-droplet.
2005, 21(09): 997-1000
doi: 10.3866/PKU.WHXB20050911
Abstract:
CuO species and thermal solid-solid interaction in CuO(w,%)/ CeO2-Al2O3 catalysts prepared by an impregnation method are characterized by in-situ XRD, Raman spectroscopy and H2-TPR techniques. Experiment results show that CuO presents as highly dispersed and bulk CuO on the surface of CuO(33.3%)/CeO2-Al2O3 calcined at 300 ℃. At high temperatures CuO can be transferred from the surface into the internal layer of CeO2 and the transference of CuO increases with increasing the calcination temperature. Some of CuO that exists in the internal layer of CeO2 presents as bulk CuO, some of that interacts with the support Al2O3 to produce CuAl2O4. The calcination temperature also promotes the CuO-Al2O3 interaction. It shows that the existence of different CuO species can be effectively confirmed by in-situ XRD, Raman spectroscopy and H2-TPR techniques.
CuO species and thermal solid-solid interaction in CuO(w,%)/ CeO2-Al2O3 catalysts prepared by an impregnation method are characterized by in-situ XRD, Raman spectroscopy and H2-TPR techniques. Experiment results show that CuO presents as highly dispersed and bulk CuO on the surface of CuO(33.3%)/CeO2-Al2O3 calcined at 300 ℃. At high temperatures CuO can be transferred from the surface into the internal layer of CeO2 and the transference of CuO increases with increasing the calcination temperature. Some of CuO that exists in the internal layer of CeO2 presents as bulk CuO, some of that interacts with the support Al2O3 to produce CuAl2O4. The calcination temperature also promotes the CuO-Al2O3 interaction. It shows that the existence of different CuO species can be effectively confirmed by in-situ XRD, Raman spectroscopy and H2-TPR techniques.
2005, 21(09): 1001-1005
doi: 10.3866/PKU.WHXB20050912
Abstract:
Thermodynamics and Kinetics of MC2O4 (M=Mn, Fe, Co, Ni, Cu, Zn) were studied in N2 or O2 using DSC and TGA techniques. In N2, the dehydration temprature Tde and enthalpy of dehydration ΔdeHm show “Two Group Domino Effect” along with atomic number Zre；ΔdeHm fluctuates in the range of (96.46±7.00) kJ•mol-1；the decomposition temperature Td of MC2O4•2H2O (M=Mn, Fe, Ni) and enthalpy have very od linearity along with atomic number Zre. When forming oxide MO in oxygen, decomposition enthalpy of MC2O4 (M=Co, Ni, Cu) shows a beeline along with atomic number Zre. All the reactions, except the dehydration of NiC2O4•2H2O and the decomposition FeC2O4, belong to the same mechanism of random nucleation and growth, with integral form , and differential form .
Thermodynamics and Kinetics of MC2O4 (M=Mn, Fe, Co, Ni, Cu, Zn) were studied in N2 or O2 using DSC and TGA techniques. In N2, the dehydration temprature Tde and enthalpy of dehydration ΔdeHm show “Two Group Domino Effect” along with atomic number Zre；ΔdeHm fluctuates in the range of (96.46±7.00) kJ•mol-1；the decomposition temperature Td of MC2O4•2H2O (M=Mn, Fe, Ni) and enthalpy have very od linearity along with atomic number Zre. When forming oxide MO in oxygen, decomposition enthalpy of MC2O4 (M=Co, Ni, Cu) shows a beeline along with atomic number Zre. All the reactions, except the dehydration of NiC2O4•2H2O and the decomposition FeC2O4, belong to the same mechanism of random nucleation and growth, with integral form , and differential form .
2005, 21(09): 1006-1010
doi: 10.3866/PKU.WHXB20050913
Abstract:
Ordered intermetallic PtSb was synthesized by arc-melting and then sintering treatment. The electro-oxidation of liquid ethanol on PtSb was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results were compared with those at a polycrystalline platinum electrode surface. It was found that at the PtSb surface the onset potential for ethanol oxidation was shifted negatively over 200 mV and the current density at PtSb electrode was about six fold as that at Pt electrode. XRD and XPS technologies were used to investigate the crystal structure and electron effect. The results of electrochemical test and ex-site FT-IR test suggested that ethanol decomposition on PtSb favors the reactive intermediate route and the CO intermediate has less effect on PtSb than on Pt. Part of the dynamic parameters of the electrocatalytic oxidation of ethanol on Pt and PtSb electrodes were obtained through the cyclic voltammetry of different scanning speed. The electron exchange coefficient (α) for C2H5OH oxidation on PtSb electrode was much higher than that on Pt electrode.
Ordered intermetallic PtSb was synthesized by arc-melting and then sintering treatment. The electro-oxidation of liquid ethanol on PtSb was investigated at room temperature by cyclic voltammetry and chronoamperometry. The results were compared with those at a polycrystalline platinum electrode surface. It was found that at the PtSb surface the onset potential for ethanol oxidation was shifted negatively over 200 mV and the current density at PtSb electrode was about six fold as that at Pt electrode. XRD and XPS technologies were used to investigate the crystal structure and electron effect. The results of electrochemical test and ex-site FT-IR test suggested that ethanol decomposition on PtSb favors the reactive intermediate route and the CO intermediate has less effect on PtSb than on Pt. Part of the dynamic parameters of the electrocatalytic oxidation of ethanol on Pt and PtSb electrodes were obtained through the cyclic voltammetry of different scanning speed. The electron exchange coefficient (α) for C2H5OH oxidation on PtSb electrode was much higher than that on Pt electrode.
2005, 21(09): 1011-1016
doi: 10.3866/PKU.WHXB20050914
Abstract:
A series of M -ZrO2 composites with various compositions were prepared by co-precipitation with NH4OH from mixed aqueous solution of nitrates and calcination at 500 ℃ and 600 ℃ respectively. The samples were characterized by XRD, XPS, BET, TEM, EXAFS and DTA measurements. The results exhibit that M tends to dissolve into the bulk phase of ZrO2 to form solid solution as Mg/Zr molar ratio is lower than 1. After the dissolution reaches saturation, M starts to disperse onto the surface of the solid solution, and at the same time the separate crystalline phase of M appears. However, when the content of M is high, ZrO2 does not dissolve into the bulk phase of M and not form the separate crystalline phase of ZrO2, but disperses onto the surface of the crystallite of M . And the properties of the surfaces of the samples were obviously affected by the dispersion of ZrO2. These results suggest that in the samples prepared by co-precipitation, one component can disperse as a monolayer onto the surface of the separate crystalline phase of the other component or the solid solutions composed of the two components in a certain content range. This phenomenon might exist in many binary oxide systems and deserves much more attention.
A series of M -ZrO2 composites with various compositions were prepared by co-precipitation with NH4OH from mixed aqueous solution of nitrates and calcination at 500 ℃ and 600 ℃ respectively. The samples were characterized by XRD, XPS, BET, TEM, EXAFS and DTA measurements. The results exhibit that M tends to dissolve into the bulk phase of ZrO2 to form solid solution as Mg/Zr molar ratio is lower than 1. After the dissolution reaches saturation, M starts to disperse onto the surface of the solid solution, and at the same time the separate crystalline phase of M appears. However, when the content of M is high, ZrO2 does not dissolve into the bulk phase of M and not form the separate crystalline phase of ZrO2, but disperses onto the surface of the crystallite of M . And the properties of the surfaces of the samples were obviously affected by the dispersion of ZrO2. These results suggest that in the samples prepared by co-precipitation, one component can disperse as a monolayer onto the surface of the separate crystalline phase of the other component or the solid solutions composed of the two components in a certain content range. This phenomenon might exist in many binary oxide systems and deserves much more attention.
2005, 21(09): 1017-1021
doi: 10.3866/PKU.WHXB20050915
Abstract:
A method based on threshold to denoise coulostatic response signal in wavelet domain was presented. The results of this method were compared with data smoothing in time domain and classical low pass filtering in the Fourier domain. The choice of wavelet decomposition levels was also discussed in this work. By using wavelet transform, coulostatic signal extraction from noisy data could be done both in time and frequency domains. The precision of curve fitting in time domain and reliability of spectral analysis could be improved respectively by the proposed method. Practically, this method was effective when the decomposition levels were from 5 to 7.
A method based on threshold to denoise coulostatic response signal in wavelet domain was presented. The results of this method were compared with data smoothing in time domain and classical low pass filtering in the Fourier domain. The choice of wavelet decomposition levels was also discussed in this work. By using wavelet transform, coulostatic signal extraction from noisy data could be done both in time and frequency domains. The precision of curve fitting in time domain and reliability of spectral analysis could be improved respectively by the proposed method. Practically, this method was effective when the decomposition levels were from 5 to 7.
2005, 21(09): 1022-1027
doi: 10.3866/PKU.WHXB20050916
Abstract:
An exact three-dimensional time-dependent quantum wave packet was employed to calculate the O(3P) + HBr(DBr) reaction using a generalized London-Ering-Polanyi-Sato(LEPS) potential energy surface. The results showed that vibrational excitation is effective for the reaction, and rotational excitation has an orientational effect in definite energy range. The rate constants and the reaction cross sections for the title reactions have been computed, the calculated rate constants kO+HBr agreed well with experimental data. By comparing with relevant results, it can be found that the kinetic isotopic effects of the reaction are relatively obvious.
An exact three-dimensional time-dependent quantum wave packet was employed to calculate the O(3P) + HBr(DBr) reaction using a generalized London-Ering-Polanyi-Sato(LEPS) potential energy surface. The results showed that vibrational excitation is effective for the reaction, and rotational excitation has an orientational effect in definite energy range. The rate constants and the reaction cross sections for the title reactions have been computed, the calculated rate constants kO+HBr agreed well with experimental data. By comparing with relevant results, it can be found that the kinetic isotopic effects of the reaction are relatively obvious.
2005, 21(09): 1028-1035
doi: 10.3866/PKU.WHXB20050917
Abstract:
Based on the electrostatic effects of the alkyl R and the substituent X, combining the polarizability effect index PEI(R) of alkyl R and the electronegativity χX of substituent X, the interaction of R and X in monosubstituted alkane RX was quantified. It was taken as the parameters that the eigenvalues (X1CC and X1CH) of the orbital-connecting matrices of Ci—Cj and Ci—H bonds together with the interaction of R and X in RX. A general expression to estimate the enthalpies of formation ΔfH0(RX, l) for monosubstituted alkanes RX (where, X=Cl, Br, I, OH, SH, NO2, CN, NH2, CHO and COOH) in liquid-phase was established： ΔfH0(RX, l)＝－39.5001ΣX1CC＋33.5508NCC－0.0789ΣX1CH－25.7087NCH＋0.1557ΣSij＋0.9976H(X)－ 27.6642 PEI(R)×χX＋31.5043χX Where the NCC and NCH are the numbers of C—C and C—H bonds in the RX molecule respectively, the H(X) is the contribution of the substituent X to theΔfH0(RX, l). The equation can be used to predict the enthalpy of formation well for RX in liquid-phase with a correlation coefficient R=0.9999 and a standard derivation SD=2.87 kJ•mol-1. What is more, each of the items in the equation has its explicit physical meaning. The obtained equation can help us further understand the correlation between molecular structures and their properties. The stability of the above equation was tested by the leave-one-out cross-validation method. The research result shows that the famous Luo's equation is a specific expression of the above equation, which can be regarded as a od progress in this field of Luo's research. This work maybe explores a novel way to investigate the interaction of the substituents in more complex compounds.
Based on the electrostatic effects of the alkyl R and the substituent X, combining the polarizability effect index PEI(R) of alkyl R and the electronegativity χX of substituent X, the interaction of R and X in monosubstituted alkane RX was quantified. It was taken as the parameters that the eigenvalues (X1CC and X1CH) of the orbital-connecting matrices of Ci—Cj and Ci—H bonds together with the interaction of R and X in RX. A general expression to estimate the enthalpies of formation ΔfH0(RX, l) for monosubstituted alkanes RX (where, X=Cl, Br, I, OH, SH, NO2, CN, NH2, CHO and COOH) in liquid-phase was established： ΔfH0(RX, l)＝－39.5001ΣX1CC＋33.5508NCC－0.0789ΣX1CH－25.7087NCH＋0.1557ΣSij＋0.9976H(X)－ 27.6642 PEI(R)×χX＋31.5043χX Where the NCC and NCH are the numbers of C—C and C—H bonds in the RX molecule respectively, the H(X) is the contribution of the substituent X to theΔfH0(RX, l). The equation can be used to predict the enthalpy of formation well for RX in liquid-phase with a correlation coefficient R=0.9999 and a standard derivation SD=2.87 kJ•mol-1. What is more, each of the items in the equation has its explicit physical meaning. The obtained equation can help us further understand the correlation between molecular structures and their properties. The stability of the above equation was tested by the leave-one-out cross-validation method. The research result shows that the famous Luo's equation is a specific expression of the above equation, which can be regarded as a od progress in this field of Luo's research. This work maybe explores a novel way to investigate the interaction of the substituents in more complex compounds.
2005, 21(09): 1036-1041
doi: 10.3866/PKU.WHXB20050918
Abstract:
The mixtures of [bmim][BF4]+water are studied by molecular dynamics simulation. The radial distribution function (RDF), local composition, as well as Kirkwood-Buff integration between different components are obtained. The simulation results show that the RDFs change regularly with the concentrations. The interaction manner between the different components can be understood more clearly through the association factor. In addition, the partial molar properties and the derivatives of activity coefficients were estimated by Kirkwood-Buff theory, which can provide valuable information of the mixture.
The mixtures of [bmim][BF4]+water are studied by molecular dynamics simulation. The radial distribution function (RDF), local composition, as well as Kirkwood-Buff integration between different components are obtained. The simulation results show that the RDFs change regularly with the concentrations. The interaction manner between the different components can be understood more clearly through the association factor. In addition, the partial molar properties and the derivatives of activity coefficients were estimated by Kirkwood-Buff theory, which can provide valuable information of the mixture.
2005, 21(09): 1042-1045
doi: 10.3866/PKU.WHXB20050919
Abstract:
Tt was found that N-diisopropyloxyphosphoryl alanine (DIPP-Ala) could form adduct with hen egg white lysozyme (HEWL) as shown in electrospray ionization mass spectroscopy (ESI-MS), but the non-phosphorylated alanine couldn’t. The capability for formation of DIPP-Ala dimmer was more stronger than that of alanine. It suggested that a specific non-covalent complex was formed in the solution phase and could be transferred to the gas phase via electrospray ionization (ESI). The results implied that phosphorylated alanine possessed relatively stronger affinities for protein and formed non-covalent complexes with protein more easily than alanine. Using Tripos force field, molecular mechanics calculation on DIPP-Ala dimmer showed that such non-covalent adduct formation was due to the inter-molecular hydrogen bond.
Tt was found that N-diisopropyloxyphosphoryl alanine (DIPP-Ala) could form adduct with hen egg white lysozyme (HEWL) as shown in electrospray ionization mass spectroscopy (ESI-MS), but the non-phosphorylated alanine couldn’t. The capability for formation of DIPP-Ala dimmer was more stronger than that of alanine. It suggested that a specific non-covalent complex was formed in the solution phase and could be transferred to the gas phase via electrospray ionization (ESI). The results implied that phosphorylated alanine possessed relatively stronger affinities for protein and formed non-covalent complexes with protein more easily than alanine. Using Tripos force field, molecular mechanics calculation on DIPP-Ala dimmer showed that such non-covalent adduct formation was due to the inter-molecular hydrogen bond.
2005, 21(09): 1046-1049
doi: 10.3866/PKU.WHXB20050920
Abstract:
The isothermal solubility, density, and refractive index of the ternary system RbNO3-C2H5OH-H2O at 25 and 50 ℃ have been investigated using phase equilibrium. The compositions of the liquid and solid phases at equilibrium states were determined, and the phase diagrams were obtained. Three empirical formulae were used to correlate the solubility, density, and refractive index. No demixing phenomena were observed in the involved range of temperatures and compositions. The equilibrium solid phases at different temperatures were all simple rubidium nitrate. No new compounds were found.
The isothermal solubility, density, and refractive index of the ternary system RbNO3-C2H5OH-H2O at 25 and 50 ℃ have been investigated using phase equilibrium. The compositions of the liquid and solid phases at equilibrium states were determined, and the phase diagrams were obtained. Three empirical formulae were used to correlate the solubility, density, and refractive index. No demixing phenomena were observed in the involved range of temperatures and compositions. The equilibrium solid phases at different temperatures were all simple rubidium nitrate. No new compounds were found.
2005, 21(09): 1050-1054
doi: 10.3866/PKU.WHXB20050921
Abstract:
Carbon nanotubes electrodes were prepared in the holes of glass directly by microwave plasma chemical vapor deposition. During the process of carbon nanotubes growth, the negative bias imposed on the substrate could improve the alignment of carbon nanotubes. The electrochemical behavior of CuSO4 at the carbon nanotubes electrode was investigated. Compared to graphite electrode, carbon nanotubes had excellent electrochemical behavior for the analysis of Cu2+. The current had linearship with the Cu2+ concentration in the range of 0.01~0.30 mmol•L-1, and the correlation coefficient was 0.9975. Because carbon nanotubes were integrated directly on the substrate, the stable response to Cu2+ solution showed that the carbon nanotubes electrodes had long-term stability.
Carbon nanotubes electrodes were prepared in the holes of glass directly by microwave plasma chemical vapor deposition. During the process of carbon nanotubes growth, the negative bias imposed on the substrate could improve the alignment of carbon nanotubes. The electrochemical behavior of CuSO4 at the carbon nanotubes electrode was investigated. Compared to graphite electrode, carbon nanotubes had excellent electrochemical behavior for the analysis of Cu2+. The current had linearship with the Cu2+ concentration in the range of 0.01~0.30 mmol•L-1, and the correlation coefficient was 0.9975. Because carbon nanotubes were integrated directly on the substrate, the stable response to Cu2+ solution showed that the carbon nanotubes electrodes had long-term stability.
2005, 21(09): 1055-1058
doi: 10.3866/PKU.WHXB20050922
Abstract:
Small-angle X-ray scattering (SAXS) is utilized to study the ordering of AOT/water lamellar phase. As increasing surfactant concentration, temperature or adding cosurfactant in certain range, the arrangement of hydrocarbon chains will change from sparse to dense which results in the structural transformation of lamellar phase from “flexible” to “planar” bilayers. The possible mechanism is proposed based on shape factor and molecular interactions. Molecular simulations are also carried out to testify the obtained results.
Small-angle X-ray scattering (SAXS) is utilized to study the ordering of AOT/water lamellar phase. As increasing surfactant concentration, temperature or adding cosurfactant in certain range, the arrangement of hydrocarbon chains will change from sparse to dense which results in the structural transformation of lamellar phase from “flexible” to “planar” bilayers. The possible mechanism is proposed based on shape factor and molecular interactions. Molecular simulations are also carried out to testify the obtained results.
2005, 21(09): 1059-1062
doi: 10.3866/PKU.WHXB20050923
Abstract:
In order to investigate the spectral properties of the Cr3+ in Ca3Al2Ge3O12: garnet, the polycrystal material Ca3Al2Ge3O12:Cr3+ was synthesized; its X-ray diffraction patterns, diffuse reflection spectra, excitation and emission spectra were measured. The spectral properties of the material were discussed and the crystal field strength (Dq/B), Stokes displacements(ΔEs) along with Huang-Rhys factors(S) were calculated. Under the excitation of 450 nm light, the emission spectrum of Cr3+ in Ca3Al2Ge3O12 garnet at room temperature mainly consists of three broad bands with weak R line. Three broad bands correspond to 4T1-4A2, 4T2-4A2, and 2T2-4A2 transitions of Cr3+ ions, respectively. The R line becomes stronger and sharper at low temperature of 30 K. The calculated results showed Dq/B=2.43, ΔEs=1884 cm-1 and S=5.21, indicating that Cr3+ ions in Ca3Al2Ge3O12: garnet locate at weaker crystal field strength and the coupling between the electrons and the phonons is strong. The results imply that Ca3Al2Ge3O12:Cr3+ would be a promising material for tunable laser.
2005, 21(09): 1063-1066
doi: 10.3866/PKU.WHXB20050924
Abstract:
The far-infrared spectra of 2,2′-biphenol(2BP) and 4,4′-biphenol(4BP) in the frequency range between 0.1 and 1.6 THz were measured by terahertz time-domain spectroscopy at 295 K. We observed distinct differences between the two isomers. 2BP has an absorption band at 1.45 THz while 4BP shows no peaks through all experimental frequency range. To investigate the relationship between the THz spectra and the low-energy modes of the molecules, quantum chemical calculations with full geometry optimizations and frequency analysis of the optimized structures were performed using the Gaussian 03 program package. The structure analyses with AM1 show that the hydroxyl groups in 2BP can form intramolecular hydrogen bond. The origin of the observed absorption at 1.45 THz is assigned to the low-frequency torsions of the two-phenyl rings which contain the hydrogen bond.
The far-infrared spectra of 2,2′-biphenol(2BP) and 4,4′-biphenol(4BP) in the frequency range between 0.1 and 1.6 THz were measured by terahertz time-domain spectroscopy at 295 K. We observed distinct differences between the two isomers. 2BP has an absorption band at 1.45 THz while 4BP shows no peaks through all experimental frequency range. To investigate the relationship between the THz spectra and the low-energy modes of the molecules, quantum chemical calculations with full geometry optimizations and frequency analysis of the optimized structures were performed using the Gaussian 03 program package. The structure analyses with AM1 show that the hydroxyl groups in 2BP can form intramolecular hydrogen bond. The origin of the observed absorption at 1.45 THz is assigned to the low-frequency torsions of the two-phenyl rings which contain the hydrogen bond.
