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2005 Volume 21 Issue 8
2005, 21(08): 825-828
doi: 10.3866/PKU.WHXB20050801
Abstract:
Pinhole-free Au core Pd shell (Au@Pd) nanoparticles with controllable size were synthesized, and the optical properties of the nanoparticles can be tuned by varying the size of the core and the thickness of the shell. The Au@Pd nanoparticles were characterized with TEM, HRTEM, UV-Vis absorption spectroscopy and SERS. Through a systematic study of the dependence of SERS activity of Au@Pd nanoparticles on the thickness of the Pd shell, it was found that the SERS activity of the Au@Pd nanoparticles is much higher than the massive Pd electrode roughened using electrochemical method, which is owing to the long-range effect of the enhanced electromagnetic field of the Au core.
Pinhole-free Au core Pd shell (Au@Pd) nanoparticles with controllable size were synthesized, and the optical properties of the nanoparticles can be tuned by varying the size of the core and the thickness of the shell. The Au@Pd nanoparticles were characterized with TEM, HRTEM, UV-Vis absorption spectroscopy and SERS. Through a systematic study of the dependence of SERS activity of Au@Pd nanoparticles on the thickness of the Pd shell, it was found that the SERS activity of the Au@Pd nanoparticles is much higher than the massive Pd electrode roughened using electrochemical method, which is owing to the long-range effect of the enhanced electromagnetic field of the Au core.
2005, 21(08): 829-833
doi: 10.3866/PKU.WHXB20050802
Abstract:
Base on the nonequilibrium solvation theory, the numerical calculation formulas for the conductor-like-screening-model (COSMO) have been established. Some new routines have been coded and added into the COSMO module in HONDO99 package, and accordingly the solvent reorganization energy has been evaluated for electron transfer in the radical cations [(CH2)2C]+—(CH2)n—C(CH2)2(n＝1～13).The numerical results indicate a od linear relationship between the reorganization energy and the reciprocal of the electron transfer distance. According to the numerical results, the sphere radius of the donor (or acceptor) has been fitted with the novel two-sphere model. The value is consistent with that by other methods.
Base on the nonequilibrium solvation theory, the numerical calculation formulas for the conductor-like-screening-model (COSMO) have been established. Some new routines have been coded and added into the COSMO module in HONDO99 package, and accordingly the solvent reorganization energy has been evaluated for electron transfer in the radical cations [(CH2)2C]+—(CH2)n—C(CH2)2(n＝1～13).The numerical results indicate a od linear relationship between the reorganization energy and the reciprocal of the electron transfer distance. According to the numerical results, the sphere radius of the donor (or acceptor) has been fitted with the novel two-sphere model. The value is consistent with that by other methods.
2005, 21(08): 834-839
doi: 10.3866/PKU.WHXB20050803
Abstract:
In order to study the third-order nonlinear optical properties of porphyrin, the nonlinear refractive indexes of two kinds of chiral zinc porphyrin complexes Zn(o-BocTyr)TAPP(host 1) and Zn(p-BocTyr)TAPP(host 2) were measured with nanosecond laser pulses at 532 nm by Z-scan techniques. And then, molecular recognition was studied between hosts and imidazole (Im) derivatives. The conformational searching of chiral zinc porphyrins with imidazole derivatives was studied by simulated annealing method on the basis of Tripos force field. The results illuminate:(1) these compounds showed very strong reverse saturable absorption and self-defocusing effect, (2) because of the different positions of the side chain, hosts had different polarized degrees, host 1 gave the larger nonlinear refractive index n2(－9.85×10-9 esu), (3) the aryl-aryl stacking interaction existed between the phenyl ring in side chain and porphyrin plane, (4) the coordinated orientation in which imidazole and 2-methylimidazole (2-MeIm) reacted to host 1 were studied. Imidazole coordinated to host 1 from the side with latral chain because the conformation had the lower energy, 2-methylimidazole coordinated to host 1 from the side without lateral chain, but host 2 had no coordination selectivity. The molecular recognition of this host and guest system was calculated by quantum chemistry. Experimental essence was further discussed by theoretical calculation.
In order to study the third-order nonlinear optical properties of porphyrin, the nonlinear refractive indexes of two kinds of chiral zinc porphyrin complexes Zn(o-BocTyr)TAPP(host 1) and Zn(p-BocTyr)TAPP(host 2) were measured with nanosecond laser pulses at 532 nm by Z-scan techniques. And then, molecular recognition was studied between hosts and imidazole (Im) derivatives. The conformational searching of chiral zinc porphyrins with imidazole derivatives was studied by simulated annealing method on the basis of Tripos force field. The results illuminate:(1) these compounds showed very strong reverse saturable absorption and self-defocusing effect, (2) because of the different positions of the side chain, hosts had different polarized degrees, host 1 gave the larger nonlinear refractive index n2(－9.85×10-9 esu), (3) the aryl-aryl stacking interaction existed between the phenyl ring in side chain and porphyrin plane, (4) the coordinated orientation in which imidazole and 2-methylimidazole (2-MeIm) reacted to host 1 were studied. Imidazole coordinated to host 1 from the side with latral chain because the conformation had the lower energy, 2-methylimidazole coordinated to host 1 from the side without lateral chain, but host 2 had no coordination selectivity. The molecular recognition of this host and guest system was calculated by quantum chemistry. Experimental essence was further discussed by theoretical calculation.
2005, 21(08): 840-845
doi: 10.3866/PKU.WHXB20050804
Abstract:
xKNO3-Ce0.5Zr0.5O2 catalysts were prepared by incipient-wetness impregnation method, and the catalytic activities for the soot combustion were studied using TPO. XRD, BET, FT-IR and XPS were used to investigate the influences of KNO3 concentration on the catalytic activities for soot combustion. It was found that the KNO3 had great effect on the surface area and the chemical environment. Compare with Ce0.5Zr0.5O2, the catalytic activities of xKNO3-Ce0.5Zr0.5O2 for soot combustion were improved significantly; the catalyst with x=0.5 had the best catalytic performance, on which Ti and Tp were 290 ℃ and 360 ℃, respectively. The results suggested that the formation of K2CO3 and molten KNO3 phase during the reaction course promoted the catalytic activities obviously.
xKNO3-Ce0.5Zr0.5O2 catalysts were prepared by incipient-wetness impregnation method, and the catalytic activities for the soot combustion were studied using TPO. XRD, BET, FT-IR and XPS were used to investigate the influences of KNO3 concentration on the catalytic activities for soot combustion. It was found that the KNO3 had great effect on the surface area and the chemical environment. Compare with Ce0.5Zr0.5O2, the catalytic activities of xKNO3-Ce0.5Zr0.5O2 for soot combustion were improved significantly; the catalyst with x=0.5 had the best catalytic performance, on which Ti and Tp were 290 ℃ and 360 ℃, respectively. The results suggested that the formation of K2CO3 and molten KNO3 phase during the reaction course promoted the catalytic activities obviously.
2005, 21(08): 846-851
doi: 10.3866/PKU.WHXB20050805
Abstract:
The binding of a series of square planar Pt(II) adducts on the Watson-Crick base pair AT and GC was investigated using advanced quantum chemical method. The result showed that the AT base pair was mainly influenced by electrostatic effect, the GC base pair was influenced by both electrostatic and polarization effect. The platinated purine and pyrimidine base pair was moderately strengthened, whereas interaction between the purine and pyrimidine base pair was slightly influenced compared with that of the isolated one. Further calculations on the Pd(II) and Ni(II) analogs showed a similar trend. The natural bonding orbital (NBO) analysis of the second-order perturbative energy ΔE2 well predicated strength of the H-bond in the base pair.
The binding of a series of square planar Pt(II) adducts on the Watson-Crick base pair AT and GC was investigated using advanced quantum chemical method. The result showed that the AT base pair was mainly influenced by electrostatic effect, the GC base pair was influenced by both electrostatic and polarization effect. The platinated purine and pyrimidine base pair was moderately strengthened, whereas interaction between the purine and pyrimidine base pair was slightly influenced compared with that of the isolated one. Further calculations on the Pd(II) and Ni(II) analogs showed a similar trend. The natural bonding orbital (NBO) analysis of the second-order perturbative energy ΔE2 well predicated strength of the H-bond in the base pair.
2005, 21(08): 852-856
doi: 10.3866/PKU.WHXB20050806
Abstract:
p-hydroxymandelate synthase (HMS) and 4-hydroxyphenylpyruvate dioxygenase (HPPD) are highhomology and share the same substrate, p-hydroxyphenylpyruvate(HPP). Using HPPD as a structural template, the 3D structure of HMS was built by homology modeling. Rational analysis of the modeled structure was performed. Subsequently, docking calculations of HPPD and HMS with the substrate HPP were conducted. A comparison of the binding mode of these two enzymes with HPP was made. While the three residues that coordinate to Fe2+, His, His and Glu, are important for the tight binding of both enzymes with the substrate, the conserved residues near the substrate, Leu228, Pro243, Asn245 and Phe364 in HPPD(1T47) and Met187, Thr202 and Ile204 in HMS, play a crucial role in determination of the reaction pathway. This may provide a starting point for the understanding of their difference in catalytic function.
p-hydroxymandelate synthase (HMS) and 4-hydroxyphenylpyruvate dioxygenase (HPPD) are highhomology and share the same substrate, p-hydroxyphenylpyruvate(HPP). Using HPPD as a structural template, the 3D structure of HMS was built by homology modeling. Rational analysis of the modeled structure was performed. Subsequently, docking calculations of HPPD and HMS with the substrate HPP were conducted. A comparison of the binding mode of these two enzymes with HPP was made. While the three residues that coordinate to Fe2+, His, His and Glu, are important for the tight binding of both enzymes with the substrate, the conserved residues near the substrate, Leu228, Pro243, Asn245 and Phe364 in HPPD(1T47) and Met187, Thr202 and Ile204 in HMS, play a crucial role in determination of the reaction pathway. This may provide a starting point for the understanding of their difference in catalytic function.
2005, 21(08): 857-861
doi: 10.3866/PKU.WHXB20050807
Abstract:
A kind of multi-functional polymer P1 containing terbium complex was synthesized by free radical polymerization. The chemical composition was analyzed by elemental analysis and XPS, and the structure was confirmed. The fluorescence property was investigated in solid state. The result indicated that the dominant emission was from 5D4→7F5 of the terbium complex at about 543 nm and with a bandwidth of less than 10 nm, a pure green light. The electrochemical property was studied, and the HOMO and LUMO energy levels were obtained by cyclic voltammetry (CV) methods. The CV result indicated that the HOMO and LUMO energy levels of P1 matched well the respective work function of ITO(－4.80 eV) and Ca(－2.89 eV). The CV result also revealed that the polymer P1 had the ability to balance the hole transport and electron transport.
A kind of multi-functional polymer P1 containing terbium complex was synthesized by free radical polymerization. The chemical composition was analyzed by elemental analysis and XPS, and the structure was confirmed. The fluorescence property was investigated in solid state. The result indicated that the dominant emission was from 5D4→7F5 of the terbium complex at about 543 nm and with a bandwidth of less than 10 nm, a pure green light. The electrochemical property was studied, and the HOMO and LUMO energy levels were obtained by cyclic voltammetry (CV) methods. The CV result indicated that the HOMO and LUMO energy levels of P1 matched well the respective work function of ITO(－4.80 eV) and Ca(－2.89 eV). The CV result also revealed that the polymer P1 had the ability to balance the hole transport and electron transport.
2005, 21(08): 862-866
doi: 10.3866/PKU.WHXB20050808
Abstract:
The interaction between Tween-20 and BSA was studied by surface tension and isothermal titration microcalorimetry. The results show that there is a weak interaction between Tween-20 and BSA and the Tween-20 molecules can replace BSA molecules adsorbed on the surface. A competition adsorption between Tween-20 and BSA occurred at the surface of mixed solution. The tendency of change of the properties of the BSA/Tween-20 mixed system with temperature is similar to that of the single non-ionic surfactant. In the range of BSA concentration from 3.7×10-5 kg•L-1 to 1.1×10-5 kg•L-1, the cmc of Tween-20 does not change with BSA concentrations. When the amount of Tween-20 is fixed, the thermal effects of the interaction between BSA and Tween-20 does not depend on the BSA concentration. The thermodynamic parameters of the mixed solutions in the presence or absence of BSA indicate that the cmc of Tween-20 decreases and the value of entropy change of the system increases in the presence of BSA in solution.
The interaction between Tween-20 and BSA was studied by surface tension and isothermal titration microcalorimetry. The results show that there is a weak interaction between Tween-20 and BSA and the Tween-20 molecules can replace BSA molecules adsorbed on the surface. A competition adsorption between Tween-20 and BSA occurred at the surface of mixed solution. The tendency of change of the properties of the BSA/Tween-20 mixed system with temperature is similar to that of the single non-ionic surfactant. In the range of BSA concentration from 3.7×10-5 kg•L-1 to 1.1×10-5 kg•L-1, the cmc of Tween-20 does not change with BSA concentrations. When the amount of Tween-20 is fixed, the thermal effects of the interaction between BSA and Tween-20 does not depend on the BSA concentration. The thermodynamic parameters of the mixed solutions in the presence or absence of BSA indicate that the cmc of Tween-20 decreases and the value of entropy change of the system increases in the presence of BSA in solution.
2005, 21(08): 867-872
doi: 10.3866/PKU.WHXB20050809
Abstract:
Atomic force microscopy (AFM) has been used to image arrays of molecules at the surface of DL-valine crystals. AFM images of DL-valine show that D- and L- molecular pairs formed from a DL-racemic mixture are exclusively homochiral. There are two different conclusions about the crystal structure of DL-valine with the data of X-ray crystallography. First, the structure of DL-valine was solved in the monoclinic space group P21/c. Second, the crystal structure of DL-valine has been refined in the centrosymmetric space group and indicated a triclinic rather than a monoclinic space group. The present work emphasizes to solve the contradicting observations of space group and to provide direct evidence for chiral recognition at molecular level. DL-valine molecules {001} are all in zwitterionic form with the isopropyl groups close to the surface and methyl groups on the top site, showing an ordered molecular morphology of triclinic unit cells, which are in fair agreement with the X-ray diffraction data. The application of AFM to the investigation of protein′s origins and a molecular-level illustration of chiral recognition at a periodic 2D surface structure of racemic crystals is discussed.
Atomic force microscopy (AFM) has been used to image arrays of molecules at the surface of DL-valine crystals. AFM images of DL-valine show that D- and L- molecular pairs formed from a DL-racemic mixture are exclusively homochiral. There are two different conclusions about the crystal structure of DL-valine with the data of X-ray crystallography. First, the structure of DL-valine was solved in the monoclinic space group P21/c. Second, the crystal structure of DL-valine has been refined in the centrosymmetric space group and indicated a triclinic rather than a monoclinic space group. The present work emphasizes to solve the contradicting observations of space group and to provide direct evidence for chiral recognition at molecular level. DL-valine molecules {001} are all in zwitterionic form with the isopropyl groups close to the surface and methyl groups on the top site, showing an ordered molecular morphology of triclinic unit cells, which are in fair agreement with the X-ray diffraction data. The application of AFM to the investigation of protein′s origins and a molecular-level illustration of chiral recognition at a periodic 2D surface structure of racemic crystals is discussed.
2005, 21(08): 873-877
doi: 10.3866/PKU.WHXB20050810
Abstract:
By measuring the gel fraction and GPC spectra of irradiated polydimethylsiloxane (PDMS) samples, the radiation effect of PDMS in latex form was investigated. Results showed that the •OH radical could not only initiate the radiation crosslinking of PDMS latex, but also accelerate the scission of PDMS molecular chain. For the PDMS latex without additives, the effect of •OH on the crosslinking behavior is not obvious. However, the addition of H2O2 or KIO4 or N2O which could increase the concentration of •OH would enhance the radiation degradation of PDMS. Moreover, with the increase of absorbed dose, the degradation is more predominant to lead to the drop of gel fraction. Particularly, in the presence of crosslinking sensitizer-trimethylol propane trimethacrylate (TMPTMA), when the dose was above 40 kGy, the excess •OH radical accelerated remarkably the degradation of PDMS chain which resulted in the narrow polydispersity of molecular weight and increase in content of PDMS with low molecular weight, and decrease of gel fraction, comparing with those of irradiated PDMS latex without TMPTMA. This suggested that the synergetic interaction perhaps existed between TMPTMA and excess •OH radical. This might be attributed to that the •OH radicals react with TMPTMA firstly, the resulted product might accelerate the degradation of PDMS.
By measuring the gel fraction and GPC spectra of irradiated polydimethylsiloxane (PDMS) samples, the radiation effect of PDMS in latex form was investigated. Results showed that the •OH radical could not only initiate the radiation crosslinking of PDMS latex, but also accelerate the scission of PDMS molecular chain. For the PDMS latex without additives, the effect of •OH on the crosslinking behavior is not obvious. However, the addition of H2O2 or KIO4 or N2O which could increase the concentration of •OH would enhance the radiation degradation of PDMS. Moreover, with the increase of absorbed dose, the degradation is more predominant to lead to the drop of gel fraction. Particularly, in the presence of crosslinking sensitizer-trimethylol propane trimethacrylate (TMPTMA), when the dose was above 40 kGy, the excess •OH radical accelerated remarkably the degradation of PDMS chain which resulted in the narrow polydispersity of molecular weight and increase in content of PDMS with low molecular weight, and decrease of gel fraction, comparing with those of irradiated PDMS latex without TMPTMA. This suggested that the synergetic interaction perhaps existed between TMPTMA and excess •OH radical. This might be attributed to that the •OH radicals react with TMPTMA firstly, the resulted product might accelerate the degradation of PDMS.
2005, 21(08): 878-882
doi: 10.3866/PKU.WHXB20050811
Abstract:
A self-consistent field theory for α,ω branched copolymers is developed, which can be extended to copolymers with any topological architecture. By solving the self-consistent field equation set numerically, ordered morphologies of α,ω branched copolymers with H shaped, π shaped and heteroarm architectures are simulated. Lamellae and hexa nal lattice phases obtained for H shaped and π shaped respectively are consistent with the experiments. Furthermore, self-assembly of heteroarm-α,ωbranched copolymers((AB)C(AB)) are investigated, and six stable microphases are uncovered. It is found that microphase morphologies are determined by the composition of three species. And variation of volume fractions for side chains will not change the ordered structure if composition is fixed. Also, simulation reveals that the junction points lie on the microphase interfaces.
A self-consistent field theory for α,ω branched copolymers is developed, which can be extended to copolymers with any topological architecture. By solving the self-consistent field equation set numerically, ordered morphologies of α,ω branched copolymers with H shaped, π shaped and heteroarm architectures are simulated. Lamellae and hexa nal lattice phases obtained for H shaped and π shaped respectively are consistent with the experiments. Furthermore, self-assembly of heteroarm-α,ωbranched copolymers((AB)C(AB)) are investigated, and six stable microphases are uncovered. It is found that microphase morphologies are determined by the composition of three species. And variation of volume fractions for side chains will not change the ordered structure if composition is fixed. Also, simulation reveals that the junction points lie on the microphase interfaces.
2005, 21(08): 883-887
doi: 10.3866/PKU.WHXB20050812
Abstract:
The non-α-position metabolites of nitrosamines play an important role in chemical carcinogenesis. Ab initio computations are carried out to study the reactivity of β- and γ-position metabolites of methylakylnitrosamines. Taking N-methyl-N-nitroso-2-(sulfate)ethylamine(Ⅰ), N-methyl-N-nitroso-2- (phosphate)ethylamine(Ⅱ), N-methyl- N-nitroso-2-(glucuronate)ethylamine(Ⅲ), N-methyl-N-nitroso-3- (sulfate)-propylamine (Ⅳ), N-methyl- N-nitroso-3- (phosphate)propylamine (Ⅴ), and N-methyl-N-nitroso-3- (glucuronate)propylamine (Ⅵ) as models, we investigate their reactivity with the anchimeric assistant process of the N-nitroso groups. Full geometric structure optimization has been done for all reactants, intermediates and transition states. The activation energies, vibrational frequencies and IRC are also obtained. All computations are performed at RHF/6-31G(d) and MP2/6-31G(d) levels. The results show that the reactivity of the sulfates (Ⅰand Ⅳ) are obviously higher than those of the phosphates (Ⅱ and Ⅴ) and the glucuronates (Ⅲ and Ⅵ). And these data indicate that the anchimeric assistance is much more efficient when the leaving group is on the β-carbon than on the γ-carbon.
The non-α-position metabolites of nitrosamines play an important role in chemical carcinogenesis. Ab initio computations are carried out to study the reactivity of β- and γ-position metabolites of methylakylnitrosamines. Taking N-methyl-N-nitroso-2-(sulfate)ethylamine(Ⅰ), N-methyl-N-nitroso-2- (phosphate)ethylamine(Ⅱ), N-methyl- N-nitroso-2-(glucuronate)ethylamine(Ⅲ), N-methyl-N-nitroso-3- (sulfate)-propylamine (Ⅳ), N-methyl- N-nitroso-3- (phosphate)propylamine (Ⅴ), and N-methyl-N-nitroso-3- (glucuronate)propylamine (Ⅵ) as models, we investigate their reactivity with the anchimeric assistant process of the N-nitroso groups. Full geometric structure optimization has been done for all reactants, intermediates and transition states. The activation energies, vibrational frequencies and IRC are also obtained. All computations are performed at RHF/6-31G(d) and MP2/6-31G(d) levels. The results show that the reactivity of the sulfates (Ⅰand Ⅳ) are obviously higher than those of the phosphates (Ⅱ and Ⅴ) and the glucuronates (Ⅲ and Ⅵ). And these data indicate that the anchimeric assistance is much more efficient when the leaving group is on the β-carbon than on the γ-carbon.
2005, 21(08): 888-892
doi: 10.3866/PKU.WHXB20050813
Abstract:
Combining surface plasmon resonance (SPR) and spatial phase modulation, a real-time SPR sensing chip was illuminated with a collimated parallel light beam. A Wollaston prism was introduced into the detection light path, causing the p- and s-polarization components to interfere with each other. The information of biochemical reactions could be obtained by extracting the phase change from the interference patterns. The sensor chips, on which the Au film was 30 nm and 40 nm, experimented with 50% and 20% alcohol solutions respectively to obtain SPR array graph. Subsequently, two proteins, rabbit IgG as positive sample and Bovine Serum Albumin (BSA) as negative control, reacted with the mixed solution of 0.2 mL at-anti-rabbit IgG sample and 1.8 mL deionized water, using Au film of 30 nm. The reaction diagram was also attained. The experimental results indicated that, with the merits of high noise resistance, high sensitivity, unlabelled and real-time detection, this SPR method could meet the requirement of protein micro-array detection.
Combining surface plasmon resonance (SPR) and spatial phase modulation, a real-time SPR sensing chip was illuminated with a collimated parallel light beam. A Wollaston prism was introduced into the detection light path, causing the p- and s-polarization components to interfere with each other. The information of biochemical reactions could be obtained by extracting the phase change from the interference patterns. The sensor chips, on which the Au film was 30 nm and 40 nm, experimented with 50% and 20% alcohol solutions respectively to obtain SPR array graph. Subsequently, two proteins, rabbit IgG as positive sample and Bovine Serum Albumin (BSA) as negative control, reacted with the mixed solution of 0.2 mL at-anti-rabbit IgG sample and 1.8 mL deionized water, using Au film of 30 nm. The reaction diagram was also attained. The experimental results indicated that, with the merits of high noise resistance, high sensitivity, unlabelled and real-time detection, this SPR method could meet the requirement of protein micro-array detection.
2005, 21(08): 893-897
doi: 10.3866/PKU.WHXB20050814
Abstract:
The transition metal ions incorporation reactions into 5, 10, 15, 20-tetrakis (pentafluorophenyl)porphyrin(H2tpfpp) to form the metal porphyrin complexes M(tpfpp) (M= Co, Ni, Zn) have been kinetically investigated using diaquabis(1, 1, 1, 5, 5, 5-hexafluoropentane-2, 4-dionato) metal compounds [M(hfac)2(H2O)2] in supercritical carbon dioxide (scCO2) medium in a spectrophotometric cell. The reactions are first order with respect to H2tpfpp under the conditions where [M(hfac)2(H2O)2] is in large excess relative to H2tpfpp. The saturation dependence of the conditional first-order rate constants as a function of the mole fraction of the excess metal compounds [M(hfac)2(H2O)2] is observed for the reaction systems [Co(hfac)2(H2O)2+H2tpfpp] and [Ni(hfac)2(H2O)2+H2tpfpp], and the linear dependence is observed for the reaction system [Zn(hfac)2(H2O)2+H2tpfpp]. The mechanisms are discussed and the thermodynamic and kinetic parameters for the reactions are obtained.
The transition metal ions incorporation reactions into 5, 10, 15, 20-tetrakis (pentafluorophenyl)porphyrin(H2tpfpp) to form the metal porphyrin complexes M(tpfpp) (M= Co, Ni, Zn) have been kinetically investigated using diaquabis(1, 1, 1, 5, 5, 5-hexafluoropentane-2, 4-dionato) metal compounds [M(hfac)2(H2O)2] in supercritical carbon dioxide (scCO2) medium in a spectrophotometric cell. The reactions are first order with respect to H2tpfpp under the conditions where [M(hfac)2(H2O)2] is in large excess relative to H2tpfpp. The saturation dependence of the conditional first-order rate constants as a function of the mole fraction of the excess metal compounds [M(hfac)2(H2O)2] is observed for the reaction systems [Co(hfac)2(H2O)2+H2tpfpp] and [Ni(hfac)2(H2O)2+H2tpfpp], and the linear dependence is observed for the reaction system [Zn(hfac)2(H2O)2+H2tpfpp]. The mechanisms are discussed and the thermodynamic and kinetic parameters for the reactions are obtained.
2005, 21(08): 898-902
doi: 10.3866/PKU.WHXB20050815
Abstract:
Using density functional theory(DFT), the double-bond isomerization of 1-butene to trans-2-butene over zeolites is investigated with a 3T cluster model simulating zeolite. At the B3LYP/6-31G(d, p) level, the complete geometry optimization and the activation energy calculation are performed with a EZP correction. It is found that the process include three steps, physical adsorption→chemical reaction→physical desorption. Firstly, the OH group of the acidic site of zeolite adsorbs the double-bond of 1-butene and forms a π-complex. Secondly, the double-bond isomerization reaction shows a concerted mechanism and yields the adsorbed trans-2-butene. Lastly, trans-2-butene is produced by desorption and the zeolite active site is restored. The calculated apparent activation energy is 57.1 kJ•mol-1, which is in agreement with the experimental data.
Using density functional theory(DFT), the double-bond isomerization of 1-butene to trans-2-butene over zeolites is investigated with a 3T cluster model simulating zeolite. At the B3LYP/6-31G(d, p) level, the complete geometry optimization and the activation energy calculation are performed with a EZP correction. It is found that the process include three steps, physical adsorption→chemical reaction→physical desorption. Firstly, the OH group of the acidic site of zeolite adsorbs the double-bond of 1-butene and forms a π-complex. Secondly, the double-bond isomerization reaction shows a concerted mechanism and yields the adsorbed trans-2-butene. Lastly, trans-2-butene is produced by desorption and the zeolite active site is restored. The calculated apparent activation energy is 57.1 kJ•mol-1, which is in agreement with the experimental data.
2005, 21(08): 903-908
doi: 10.3866/PKU.WHXB20050816
Abstract:
The adsorption of benzene on Cu(100) was analyzed using the first-principle density functional theoretical (DFT) slab calculation. In three optimized adsorption modes the benzene molecules were parallel to the surface and the carbon rings were distorted. The calculated results showed that interaction between the substrate and benzene molecule was relatively strong chemisorption. The hollow site was the most favorable adsorpion site of benzene on Cu(100) surface, followed by the bridge one. The top site was the least stable. The C—C bond was elongated in comparison with the free benzene molecule while the variation of C—H length was small. The hydrogen atoms bent away from the solid surface, but they bent toward the solid surface in the top site. Electron transference was found from benzene to Cu substrate.
The adsorption of benzene on Cu(100) was analyzed using the first-principle density functional theoretical (DFT) slab calculation. In three optimized adsorption modes the benzene molecules were parallel to the surface and the carbon rings were distorted. The calculated results showed that interaction between the substrate and benzene molecule was relatively strong chemisorption. The hollow site was the most favorable adsorpion site of benzene on Cu(100) surface, followed by the bridge one. The top site was the least stable. The C—C bond was elongated in comparison with the free benzene molecule while the variation of C—H length was small. The hydrogen atoms bent away from the solid surface, but they bent toward the solid surface in the top site. Electron transference was found from benzene to Cu substrate.
2005, 21(08): 909-914
doi: 10.3866/PKU.WHXB20050817
Abstract:
In order to examine the effects of water contents on structure relaxation parameters of glycerol aqueous glasses, heat capacity and glass transition temperature of five aqueous solutions (60%, 70%, 80%, 90%, and 100%) were determined using the differential scanning calorimetry (DSC). Structure relaxation behaviors of glycerol aqueous glasses were investigated in the term of Tool-Narayanaswamy-Monihan (TNM) model parameters. The structure relaxation time was found to decrease as the water content increased. Curve-fitting results indicated that the apparent activation energy and non-exponential parameter decreased while non-linear parameter and pre-exponential parameter increased as the water content increased.
In order to examine the effects of water contents on structure relaxation parameters of glycerol aqueous glasses, heat capacity and glass transition temperature of five aqueous solutions (60%, 70%, 80%, 90%, and 100%) were determined using the differential scanning calorimetry (DSC). Structure relaxation behaviors of glycerol aqueous glasses were investigated in the term of Tool-Narayanaswamy-Monihan (TNM) model parameters. The structure relaxation time was found to decrease as the water content increased. Curve-fitting results indicated that the apparent activation energy and non-exponential parameter decreased while non-linear parameter and pre-exponential parameter increased as the water content increased.
2005, 21(08): 915-919
doi: 10.3866/PKU.WHXB20050818
Abstract:
CoxCu1－x granular films were prepared by electrodeposition at room temperature on semiconductor Si substrate. XRD result revealed that the as-deposited films formed a single phase metastable fcc alloy structure. Pure Co fcc diffraction peaks were observed in XRD pattern of the annealed sample, indicating phase separation occurred upon annealing. TEM characterization also confirmed the precipitation of the magnetic Co particles from the Cu-rich matrix. The giant magnetoresistance(GMR) of the films was improved after annealing. The maximum MR ratio of 8.21% was obtained for Co0.20Cu0.80 thin film after annealing at 450 ℃ for 1 h. Hysteresis loops of the as-deposited and annealed samples indicated the change from superparamagnetic to ferromagnetic contribution to the GMR effect. The values of coercivity(Hc), remanent magnetization(Mr), saturation magnetization(Ms) increased with annealing temperature. The effect of supperparamagnetic particles resulted the difference between GMR－H and M－H curves.
CoxCu1－x granular films were prepared by electrodeposition at room temperature on semiconductor Si substrate. XRD result revealed that the as-deposited films formed a single phase metastable fcc alloy structure. Pure Co fcc diffraction peaks were observed in XRD pattern of the annealed sample, indicating phase separation occurred upon annealing. TEM characterization also confirmed the precipitation of the magnetic Co particles from the Cu-rich matrix. The giant magnetoresistance(GMR) of the films was improved after annealing. The maximum MR ratio of 8.21% was obtained for Co0.20Cu0.80 thin film after annealing at 450 ℃ for 1 h. Hysteresis loops of the as-deposited and annealed samples indicated the change from superparamagnetic to ferromagnetic contribution to the GMR effect. The values of coercivity(Hc), remanent magnetization(Mr), saturation magnetization(Ms) increased with annealing temperature. The effect of supperparamagnetic particles resulted the difference between GMR－H and M－H curves.
2005, 21(08): 920-924
doi: 10.3866/PKU.WHXB20050819
Abstract:
The effects of nanometer CuO additive on the performance of La-rich AB5 type hydrogen storage alloy electrodes(HSAE) have been studied. The change of storage capacity and mass of the electrodes with CuO additive has been investigated, and the electrochemical performances of the electrodes have been tested. Cyclic voltammograms (CV) and SEM results indicated that CuO is reduced during first charging process and copper particleis deposited on the surface of the alloy. Electrochemical testing results showed that the electrode with additive has better rate capability and cycle performance. Electrochemical impedance spectroscopy(EIS) analysis indicated that the electrode with additive CuO has higher activity and electrical conductivity, and lower ohmic and electrochemical impedance, which helps to improve the electrochemical properties of the electrode. Therefore the hydrogen storage alloy electrode with nanometer CuO would well meet the requirement for power sources of electric vehicles.
The effects of nanometer CuO additive on the performance of La-rich AB5 type hydrogen storage alloy electrodes(HSAE) have been studied. The change of storage capacity and mass of the electrodes with CuO additive has been investigated, and the electrochemical performances of the electrodes have been tested. Cyclic voltammograms (CV) and SEM results indicated that CuO is reduced during first charging process and copper particleis deposited on the surface of the alloy. Electrochemical testing results showed that the electrode with additive has better rate capability and cycle performance. Electrochemical impedance spectroscopy(EIS) analysis indicated that the electrode with additive CuO has higher activity and electrical conductivity, and lower ohmic and electrochemical impedance, which helps to improve the electrochemical properties of the electrode. Therefore the hydrogen storage alloy electrode with nanometer CuO would well meet the requirement for power sources of electric vehicles.
2005, 21(08): 925-928
doi: 10.3866/PKU.WHXB20050820
Abstract:
The nanostructure studies have been performed to the fluorescent and liquid-crystal molecule (2,5-bis-[2-(3,4-bis-dodecyloxy-phenyl)-vinyl]-3,6-dimethyl-pyrazine(BPDP12)) on highly oriented pyrolytic graphite (HOPG) using scanning tunneling microscopy (STM). The well-organized 2-D monolayer images reveal two kinds of configurations. The structure (I) is a stable and closely packed arrangement, in which all the conjugated cores are parallel to each other and the alkyl chains of the molecules interdigitate over the full length；while the structure (II) is an unstable and unclosely packed arrangement, in which all the conjugated cores are separated by the alkyl chains. The formation of above two structures owes to the competition between the stronger intermolecular π-π interactions and the van der Waals forces of alkyl chains during the self-assembly.
The nanostructure studies have been performed to the fluorescent and liquid-crystal molecule (2,5-bis-[2-(3,4-bis-dodecyloxy-phenyl)-vinyl]-3,6-dimethyl-pyrazine(BPDP12)) on highly oriented pyrolytic graphite (HOPG) using scanning tunneling microscopy (STM). The well-organized 2-D monolayer images reveal two kinds of configurations. The structure (I) is a stable and closely packed arrangement, in which all the conjugated cores are parallel to each other and the alkyl chains of the molecules interdigitate over the full length；while the structure (II) is an unstable and unclosely packed arrangement, in which all the conjugated cores are separated by the alkyl chains. The formation of above two structures owes to the competition between the stronger intermolecular π-π interactions and the van der Waals forces of alkyl chains during the self-assembly.
2005, 21(08): 929-933
doi: 10.3866/PKU.WHXB20050821
Abstract:
The kinetics of trace Ir(III) catalyzed oxidation of tetrahydrofurfuryl alcohol(THFA) by Ce(IV) in aqueous sulphuric acid medium was studied by titrimetric technique of redox in the temperature range of 298~313 K. The order was found to be unity with respect to both Ce(IV) and Ir(III), and for tetrahydrofurfuryl alcohol the apparent reaction order was a positive fraction. It was found that the pseudo first order ([THFA]>>[Ce(IV)]) rate constant, kobs, increased with the increase of [H＋] but decreased with the increase of [HSO4－]. Under the protection of nitrogen, however, the reaction system could induce polymerization of acrylonitrile, indicating the generation of free radicals. A reasonable mechanism involving a preequilibrium was proposed. From the relation between kobs and [HSO4－], Ce(SO4)2 was found to be the kinetically active species. The equilibrium constants and rate constants of the rate-determining step along with the activation parameters were evaluated.
The kinetics of trace Ir(III) catalyzed oxidation of tetrahydrofurfuryl alcohol(THFA) by Ce(IV) in aqueous sulphuric acid medium was studied by titrimetric technique of redox in the temperature range of 298~313 K. The order was found to be unity with respect to both Ce(IV) and Ir(III), and for tetrahydrofurfuryl alcohol the apparent reaction order was a positive fraction. It was found that the pseudo first order ([THFA]>>[Ce(IV)]) rate constant, kobs, increased with the increase of [H＋] but decreased with the increase of [HSO4－]. Under the protection of nitrogen, however, the reaction system could induce polymerization of acrylonitrile, indicating the generation of free radicals. A reasonable mechanism involving a preequilibrium was proposed. From the relation between kobs and [HSO4－], Ce(SO4)2 was found to be the kinetically active species. The equilibrium constants and rate constants of the rate-determining step along with the activation parameters were evaluated.
2005, 21(08): 934-938
doi: 10.3866/PKU.WHXB20050822
Abstract:
Li1.02CraCobLacMn2－a－b－cFyO4－y (a,b,c＝0, 0.01, 0.02; y＝0, 0.02) doped with several ions (anion-cation) was prepared by solid-state reaction method. X-ray diffraction showed that all the samples had perfect spinel strucure. The results of the charge/discharge curves showed that multiple doping spinel Li1.02Cr0.01Co0.02La0.01Mn1.96F0.02O3.98 had better performance than those undoped or cation-doped materials according to the inhibition of decline of reversible capacity of spinel at 25 ℃. Besides that, the multiple doping spinel also had ideal discharge capacity. And the cycle performance(120.1～113.5 mAh•g-1) was improved so obviously that 94.5% of the initial capacity was preserved after 80 cycles. Meanwhile, the elevated temperature(55 ℃) perforance of the material was improved. With the spinel Li1.02CraCobLacMn2－a－b－cFyO4－y as working electrode, Li as counter electrode and reference electrode, electro-chemical impedance tests showed that this material possessed od charge/discharge reversible capability and had the lowest impedance on the stage of charge/discharge.
Li1.02CraCobLacMn2－a－b－cFyO4－y (a,b,c＝0, 0.01, 0.02; y＝0, 0.02) doped with several ions (anion-cation) was prepared by solid-state reaction method. X-ray diffraction showed that all the samples had perfect spinel strucure. The results of the charge/discharge curves showed that multiple doping spinel Li1.02Cr0.01Co0.02La0.01Mn1.96F0.02O3.98 had better performance than those undoped or cation-doped materials according to the inhibition of decline of reversible capacity of spinel at 25 ℃. Besides that, the multiple doping spinel also had ideal discharge capacity. And the cycle performance(120.1～113.5 mAh•g-1) was improved so obviously that 94.5% of the initial capacity was preserved after 80 cycles. Meanwhile, the elevated temperature(55 ℃) perforance of the material was improved. With the spinel Li1.02CraCobLacMn2－a－b－cFyO4－y as working electrode, Li as counter electrode and reference electrode, electro-chemical impedance tests showed that this material possessed od charge/discharge reversible capability and had the lowest impedance on the stage of charge/discharge.
2005, 21(08): 939-943
doi: 10.3866/PKU.WHXB20050823
Abstract:
The surface adsorption and micelle formation of the mixed anionic Gemini surfactant (C9pPHCNa) and cationic conventional surfactant (C10TABr) aqueous solutions have been investigated by surface tension method. The synergism occurred in the mixed systems and yielded maximum synergism at the mole fraction of C9pPHCNa in the bulk (α1) equaling to 0.33, where the two components equal electricity mixing in solution. The corresponding minimum values of the critical micelle concentration (cmcT), the surface tension (γcmc) and the total concentration required to reduce 20 mN•m-1 surface tension of water (c20,T) are respectively 0.60 mmol•L-1, 23.5 mN•m-1 and 1.58×10-5 mol•L-1. Over the range of α1 studied, the molar compositions of C9pPHCNa and C10TABr both in the micelle and on the surface are close each other, which reflects strong interaction between the molecules.
The surface adsorption and micelle formation of the mixed anionic Gemini surfactant (C9pPHCNa) and cationic conventional surfactant (C10TABr) aqueous solutions have been investigated by surface tension method. The synergism occurred in the mixed systems and yielded maximum synergism at the mole fraction of C9pPHCNa in the bulk (α1) equaling to 0.33, where the two components equal electricity mixing in solution. The corresponding minimum values of the critical micelle concentration (cmcT), the surface tension (γcmc) and the total concentration required to reduce 20 mN•m-1 surface tension of water (c20,T) are respectively 0.60 mmol•L-1, 23.5 mN•m-1 and 1.58×10-5 mol•L-1. Over the range of α1 studied, the molar compositions of C9pPHCNa and C10TABr both in the micelle and on the surface are close each other, which reflects strong interaction between the molecules.
2005, 21(08): 944-948
doi: 10.3866/PKU.WHXB20050824
Abstract:
Transparent ZnO sols have been prepared by sol-gel method and deposited on aluminum foil substrates by dip-coating method, and then calcinated at 500 ℃ to obtain visible-light response nano-sized ZnO film photocatalysts. The films have been applied in photocatalytic degradation of methyl orange as model of organic pollutant under visible-light irradiation. The results show that the degradation of methyl orange reaches 96.3% by using a piece of ZnO/Al thin film as photocatalyst with an efficient irradiation area of 200 cm2, which is higher than that of ZnO/glass film. The films have been characterized by means of scanning electron microscopy and atomic force microscope, which indicated that photocatalytic activity of porous ZnO films should be higher than that of compact cumulate ZnO films；and the ZnO/Al film with high visible light response is formed by a layer of ZnO nano-sized particles with average diameter of 52.2 nm. The results suggest that the ZnO-supported commercial aluminum foil is a promising and efficient thin film catalyst to degrade organic pollutants under visible light irradiation.
Transparent ZnO sols have been prepared by sol-gel method and deposited on aluminum foil substrates by dip-coating method, and then calcinated at 500 ℃ to obtain visible-light response nano-sized ZnO film photocatalysts. The films have been applied in photocatalytic degradation of methyl orange as model of organic pollutant under visible-light irradiation. The results show that the degradation of methyl orange reaches 96.3% by using a piece of ZnO/Al thin film as photocatalyst with an efficient irradiation area of 200 cm2, which is higher than that of ZnO/glass film. The films have been characterized by means of scanning electron microscopy and atomic force microscope, which indicated that photocatalytic activity of porous ZnO films should be higher than that of compact cumulate ZnO films；and the ZnO/Al film with high visible light response is formed by a layer of ZnO nano-sized particles with average diameter of 52.2 nm. The results suggest that the ZnO-supported commercial aluminum foil is a promising and efficient thin film catalyst to degrade organic pollutants under visible light irradiation.
