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2004 Volume 20 Issue 5
2004, 20(05): 449-453
doi: 10.3866/PKU.WHXB20040501
Abstract:
The formation of stable Langmuir films on the aqueous AgNO3 subphase of 2-alkyl benzimidazoles (BzCn) with various chain lengths (from C5 to C15) and the layer structures of the transferred films were described. From the surface pressure-area isotherm, it has been found that the true monolayer could be formed for the short chain derivatives, while multilayer structures for the long ones. All of the Langmuir films could be transferred to solid substrate. The measurement of the UV spectra of the transferred LB films confirmed the coordination between benzimidazole group and Ag(I) ion in the Langmuir films. The effect of the length of alkyl chains on the structure of the transferred LB films was revealed by application of atomic force microscopy, FT-IR spectra and X-ray diffraction (XRD) measurement. It showed that except for BzC15, a regular layer structure was formed. Characterization of the morphology points to the formation of the neat LB film for the short derivatives and multilayer structure for BzC15.
The formation of stable Langmuir films on the aqueous AgNO3 subphase of 2-alkyl benzimidazoles (BzCn) with various chain lengths (from C5 to C15) and the layer structures of the transferred films were described. From the surface pressure-area isotherm, it has been found that the true monolayer could be formed for the short chain derivatives, while multilayer structures for the long ones. All of the Langmuir films could be transferred to solid substrate. The measurement of the UV spectra of the transferred LB films confirmed the coordination between benzimidazole group and Ag(I) ion in the Langmuir films. The effect of the length of alkyl chains on the structure of the transferred LB films was revealed by application of atomic force microscopy, FT-IR spectra and X-ray diffraction (XRD) measurement. It showed that except for BzC15, a regular layer structure was formed. Characterization of the morphology points to the formation of the neat LB film for the short derivatives and multilayer structure for BzC15.
2004, 20(05): 454-458
doi: 10.3866/PKU.WHXB20040502
Abstract:
According to the theory on eletrocystallization of metal, the growth mechanism of polyaniline nanotubules in alumina template was studied by electrochemical methods, such as chronoamperometry, cyclic voltammetry. It was found that a chain monolayer of polyaniline crystal cell was formed by the two-dimensional instantaneous nucleation-growth without diffusion control during the initial stage of eletropolymerization, and after forming the monolayer, the growing process of polyaniline tubules was controlled by diffusion instead. The results of XRD showed that the eletrosynthesized polyaniline structure is composed of both the crystalline phase and the amorphous phase, consistent with the electrochemical experiment results. Meanwhile, it is possible that the cystallization of polymer can be studied by electrochemical methods with the theory on eletrocystalization of metal.
According to the theory on eletrocystallization of metal, the growth mechanism of polyaniline nanotubules in alumina template was studied by electrochemical methods, such as chronoamperometry, cyclic voltammetry. It was found that a chain monolayer of polyaniline crystal cell was formed by the two-dimensional instantaneous nucleation-growth without diffusion control during the initial stage of eletropolymerization, and after forming the monolayer, the growing process of polyaniline tubules was controlled by diffusion instead. The results of XRD showed that the eletrosynthesized polyaniline structure is composed of both the crystalline phase and the amorphous phase, consistent with the electrochemical experiment results. Meanwhile, it is possible that the cystallization of polymer can be studied by electrochemical methods with the theory on eletrocystalization of metal.
Effect of Permanent Charge on the Intrinsic Ionization Constant of Zn-Al Hydrotalcite-like Compounds
2004, 20(05): 459-462
doi: 10.3866/PKU.WHXB20040503
Abstract:
Potentiometric titration (PT) method was often used to determine the point of zero net proton charge (pHPZNPC) and intrinsic ionization constant (pKa2int ) of oxide. Extensive studies on the interrelation of and pHPZNPC of various oxides had shown that pKa2int =0.827pHPZNPC＋4.478.From that we can know that different metal had different affinity to H＋ or OH－,however the study on the permanent charged materials such as hydrotalcite-like compounds (HTlc) and clays was rare. The study focused on the influence of permanent charge on the intrinsic ionization constant (pKa2int) had not been reported yet. In our research, potentiometric titration method was used to determine the point of zero net charge (pHPZNC), and potentiometric titration data at pHPZNC was used to calculate pKa2int and the free energy of proton adsorption (G0ads,2) of Zn-Al HTlc samples for the first time. The theoretical permanent charge density (σp) of the HTlc sample was calculated from the crystal structure of Zn-Al HTlc according to the chemical analysis results. The influence of σp on the pKa2int and G0ads,2 was examined. The results showed that pKa2int and G0ads,2 of Zn-Al HTlc decreased with the increase of σp, indicating that protonation decreased with the increase of σp. It was found that pKa2int and pHPZNC had the relationship: pKa2int =1.372 pHPZNC－3.328.
Potentiometric titration (PT) method was often used to determine the point of zero net proton charge (pHPZNPC) and intrinsic ionization constant (pKa2int ) of oxide. Extensive studies on the interrelation of and pHPZNPC of various oxides had shown that pKa2int =0.827pHPZNPC＋4.478.From that we can know that different metal had different affinity to H＋ or OH－,however the study on the permanent charged materials such as hydrotalcite-like compounds (HTlc) and clays was rare. The study focused on the influence of permanent charge on the intrinsic ionization constant (pKa2int) had not been reported yet. In our research, potentiometric titration method was used to determine the point of zero net charge (pHPZNC), and potentiometric titration data at pHPZNC was used to calculate pKa2int and the free energy of proton adsorption (G0ads,2) of Zn-Al HTlc samples for the first time. The theoretical permanent charge density (σp) of the HTlc sample was calculated from the crystal structure of Zn-Al HTlc according to the chemical analysis results. The influence of σp on the pKa2int and G0ads,2 was examined. The results showed that pKa2int and G0ads,2 of Zn-Al HTlc decreased with the increase of σp, indicating that protonation decreased with the increase of σp. It was found that pKa2int and pHPZNC had the relationship: pKa2int =1.372 pHPZNC－3.328.
2004, 20(05): 463-467
doi: 10.3866/PKU.WHXB20040504
Abstract:
The basic electrolyte solution of flash palladium plating contains of 4 g•L－1 Pd(NH3)2Cl2 and 104 g•L－1 NH4H2PO4. In the solution with or without additive the electrodeposition and electrocrystallization behaviors of palladium on glassy carbon(GC)electrode were studied by means of polarization curve, cyclic voltammetry and potentiostatic current transient. The results showed that the additive hindered the electrodeposition of palladium. The exchange current density of palladium on GC electrode was very low. The electrodeposition of palladium proceeded a nucleation. Its electrocrystallization mechanism in the electrolyte solution without additive was in tendency to nucleate progressively in three dimensions while in the electrolyte solution containing additive it was in tendency to nucleate instantaneously in three dimensions.
The basic electrolyte solution of flash palladium plating contains of 4 g•L－1 Pd(NH3)2Cl2 and 104 g•L－1 NH4H2PO4. In the solution with or without additive the electrodeposition and electrocrystallization behaviors of palladium on glassy carbon(GC)electrode were studied by means of polarization curve, cyclic voltammetry and potentiostatic current transient. The results showed that the additive hindered the electrodeposition of palladium. The exchange current density of palladium on GC electrode was very low. The electrodeposition of palladium proceeded a nucleation. Its electrocrystallization mechanism in the electrolyte solution without additive was in tendency to nucleate progressively in three dimensions while in the electrolyte solution containing additive it was in tendency to nucleate instantaneously in three dimensions.
2004, 20(05): 468-471
doi: 10.3866/PKU.WHXB20040505
Abstract:
The SVRT (semirigid vibrating rotor target) model is applied to study the reaction of D＋CH4 using time-dependent wave packet method based on the PES of Jordan and Gilbert. The total reaction probabilities, cross-sections and rate constants of different initial rovibrational states are calculated. The comparison and discussion are carried out between the calculated results for D＋CH4 and that for H＋CH4.The energy dependence of the calculated reaction probability shows oscillatory structures, similar to those observed in the reactions H＋H2, H＋CH4 etc. We have also studied the influence of internal energy of the reactant molecule (CH4) on the reaction probability. The excitation of the H－CH3 stretching vibration gives significant enhancement of reaction probability and the reaction threshold decreases with the enhancement of the vibrational excitation. And the reaction probability also rises significantly with the enhancement of rotational quantum number j but the reaction threshold has no change.
The SVRT (semirigid vibrating rotor target) model is applied to study the reaction of D＋CH4 using time-dependent wave packet method based on the PES of Jordan and Gilbert. The total reaction probabilities, cross-sections and rate constants of different initial rovibrational states are calculated. The comparison and discussion are carried out between the calculated results for D＋CH4 and that for H＋CH4.The energy dependence of the calculated reaction probability shows oscillatory structures, similar to those observed in the reactions H＋H2, H＋CH4 etc. We have also studied the influence of internal energy of the reactant molecule (CH4) on the reaction probability. The excitation of the H－CH3 stretching vibration gives significant enhancement of reaction probability and the reaction threshold decreases with the enhancement of the vibrational excitation. And the reaction probability also rises significantly with the enhancement of rotational quantum number j but the reaction threshold has no change.
2004, 20(05): 472-477
doi: 10.3866/PKU.WHXB20040506
Abstract:
The kinetics of oxygen reduction over Sm0.5Sr0.5CoO3- La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (SSC-LSGMC5) cathode was investigated using polarization and AC(alternating current) impedance. Two arcs were observed in the impedance spectra of SSC-LSGMC5 at near equilibrium conditions. The conductivities of the high frequency arcs had no dependency on oxygen partial pressures (pO2), and showed an activation energy about (1.0～1.1)×102 kJ•mol－1. The dependency of the conductivities of the low frequency arcs decreased from 0.6 to 0.4 with the decrease in temperature 1073～873 K，accordingly,the activation energies increased from 1.3×102 to 1.6×102 kJ•mol－1 with the increase in (2×104～1×105 Pa). The high frequency arcs could be related to the transfer of oxygen ions across the electrode/electrolyte interface, while the low frequency arcs could correspond to the diffusion of oxygen atoms from the electrode surface to the three-phase boundary. The polarization curves of SSC-LSGMC5 agreed well with the Butler-Volmer equation. The anodic and cathodic charge transfer coefficients were all about 1 and the pO2 dependency of the exchange current density was around 0.25, suggesting a rate-determining step of charge transfer. The mechanism of oxygen reduction over SSC-LSGMC5 depended strongly on the over-potential and reaction temperature.
The kinetics of oxygen reduction over Sm0.5Sr0.5CoO3- La0.8Sr0.2Ga0.8Mg0.15Co0.05O3 (SSC-LSGMC5) cathode was investigated using polarization and AC(alternating current) impedance. Two arcs were observed in the impedance spectra of SSC-LSGMC5 at near equilibrium conditions. The conductivities of the high frequency arcs had no dependency on oxygen partial pressures (pO2), and showed an activation energy about (1.0～1.1)×102 kJ•mol－1. The dependency of the conductivities of the low frequency arcs decreased from 0.6 to 0.4 with the decrease in temperature 1073～873 K，accordingly,the activation energies increased from 1.3×102 to 1.6×102 kJ•mol－1 with the increase in (2×104～1×105 Pa). The high frequency arcs could be related to the transfer of oxygen ions across the electrode/electrolyte interface, while the low frequency arcs could correspond to the diffusion of oxygen atoms from the electrode surface to the three-phase boundary. The polarization curves of SSC-LSGMC5 agreed well with the Butler-Volmer equation. The anodic and cathodic charge transfer coefficients were all about 1 and the pO2 dependency of the exchange current density was around 0.25, suggesting a rate-determining step of charge transfer. The mechanism of oxygen reduction over SSC-LSGMC5 depended strongly on the over-potential and reaction temperature.
Fluorescence Probe Studies on the Conformation Behavior of P(DEAM-co-MAA) in Dilute Aqueous Solution
2004, 20(05): 478-482
doi: 10.3866/PKU.WHXB20040507
Abstract:
The conformation behavior of N,N-diethylacrylamide (DEAM) and methacrylic acid (MAA) copolymer P(DEAM-co-MAA) was investigated by fluorescence probe technique and UV transmittance measurements. The results demonstrated that the conformation behavior of P(DEAM-co-MAA) in dilute aqueous solution is similar to that of PMAA, showing hypercoiled conformation and forming hydrophobic microdomain when the molar fraction of DEAM in P(DEAM-co-MAA) is less than 8.00％ and the solution pH is less than 6;but the conformation of P(DEAM-co-MAA) in dilute aqueous solution shows a loose extended form due to polymer dilution effect in all of pH range when the molar fraction of DEAM in P(DEAM-co-MAA) is higher than 8.00％.The effect of DEAM contents and pH on the conformation of P(DEAM-co-MAA) may find some uses in the design and synthesis of novel sensitive gels.
The conformation behavior of N,N-diethylacrylamide (DEAM) and methacrylic acid (MAA) copolymer P(DEAM-co-MAA) was investigated by fluorescence probe technique and UV transmittance measurements. The results demonstrated that the conformation behavior of P(DEAM-co-MAA) in dilute aqueous solution is similar to that of PMAA, showing hypercoiled conformation and forming hydrophobic microdomain when the molar fraction of DEAM in P(DEAM-co-MAA) is less than 8.00％ and the solution pH is less than 6;but the conformation of P(DEAM-co-MAA) in dilute aqueous solution shows a loose extended form due to polymer dilution effect in all of pH range when the molar fraction of DEAM in P(DEAM-co-MAA) is higher than 8.00％.The effect of DEAM contents and pH on the conformation of P(DEAM-co-MAA) may find some uses in the design and synthesis of novel sensitive gels.
2004, 20(05): 483-487
doi: 10.3866/PKU.WHXB20040508
Abstract:
The reaction mechanisms and molecular dynamics of the multi-channel reaction H＋CH2CO which might occur through four channels depending on the different initial reaction positions of the reactants CH2CO are detailedly studied. All the calculations are performed at the UQCISD/6-311G (d,p) and G2 theory level. Every transition state is confirmed by the numbers of virtual frequency and the intrinsic reaction coordinate (IRC) paths. The computational results suggest that the reaction channel of forming CH3＋CO through an intermediate is the dominant one. This channel is an exothermic reaction whose enthalpy changes are －146.07 kJ•mol－1 and the calculated potential barrier of the rate-determining step is 55.09 kJ•mol－1. The obtained reaction potential profile can qualitatively explain the experimental coexistence phenomena of the primary products and the other minor products.
The reaction mechanisms and molecular dynamics of the multi-channel reaction H＋CH2CO which might occur through four channels depending on the different initial reaction positions of the reactants CH2CO are detailedly studied. All the calculations are performed at the UQCISD/6-311G (d,p) and G2 theory level. Every transition state is confirmed by the numbers of virtual frequency and the intrinsic reaction coordinate (IRC) paths. The computational results suggest that the reaction channel of forming CH3＋CO through an intermediate is the dominant one. This channel is an exothermic reaction whose enthalpy changes are －146.07 kJ•mol－1 and the calculated potential barrier of the rate-determining step is 55.09 kJ•mol－1. The obtained reaction potential profile can qualitatively explain the experimental coexistence phenomena of the primary products and the other minor products.
2004, 20(05): 488-493
doi: 10.3866/PKU.WHXB20040509
Abstract:
GABAA receptor is the major neurotransmitter system in the central nervous system(CNS) and elicits a wide range of neuronal physiological activities. Since anxiolytic/anticonvulsant agents have been employed widely in clinic, the receptor sites for the benzodiazepine are of prime importance. Studies on quantitative structure-activity relationship with CoMFA for the binding affinities of a series of imidazobenzodiazepines at five recombinant receptor subtypes were carried out successfully, and a od crossvalidated correlation was obtained for each receptor subtype. Then a set of non-cross-validated PLS models was built and permitted demonstration of high predictability for the affinities of the six ligands in the test set selected in random at all five receptor subtypes. The modals can help design high affinitiy ligands on the GABAA/BZ receptor and understand the GABAA receptor modal.
GABAA receptor is the major neurotransmitter system in the central nervous system(CNS) and elicits a wide range of neuronal physiological activities. Since anxiolytic/anticonvulsant agents have been employed widely in clinic, the receptor sites for the benzodiazepine are of prime importance. Studies on quantitative structure-activity relationship with CoMFA for the binding affinities of a series of imidazobenzodiazepines at five recombinant receptor subtypes were carried out successfully, and a od crossvalidated correlation was obtained for each receptor subtype. Then a set of non-cross-validated PLS models was built and permitted demonstration of high predictability for the affinities of the six ligands in the test set selected in random at all five receptor subtypes. The modals can help design high affinitiy ligands on the GABAA/BZ receptor and understand the GABAA receptor modal.
2004, 20(05): 494-497
doi: 10.3866/PKU.WHXB20040510
Abstract:
This paper presents the normal-mode analytical approach of Fumi-Tosi ionic liquid based on molecular dynamics simulation. We replace the Lennard-Jones potential with the Fumi-Tosi potential (including the long-range potential) and handle the long-range Coulomb interaction using the equivalent Coulomb potential. The computation methods of the elements of Hessian matrix and the eigenvalues of Hessian matrix are discussed. It is shown that the Hessian matrix and the density of states can be obtained reasonably using the equivalent Coulomb potential in the form of the complementary error function.The numerical results of the configuration-averaged densities of states in liquid RbCl show that they have similar characteristics to those in Lennard-Jones liquids.
This paper presents the normal-mode analytical approach of Fumi-Tosi ionic liquid based on molecular dynamics simulation. We replace the Lennard-Jones potential with the Fumi-Tosi potential (including the long-range potential) and handle the long-range Coulomb interaction using the equivalent Coulomb potential. The computation methods of the elements of Hessian matrix and the eigenvalues of Hessian matrix are discussed. It is shown that the Hessian matrix and the density of states can be obtained reasonably using the equivalent Coulomb potential in the form of the complementary error function.The numerical results of the configuration-averaged densities of states in liquid RbCl show that they have similar characteristics to those in Lennard-Jones liquids.
2004, 20(05): 498-502
doi: 10.3866/PKU.WHXB20040511
Abstract:
The correlation relationships among amino acid residues in protein structures are studied. Some residue pairs have larger correlation coefficients and they are not independent of protein structural classes. The correlation relationships of amino acid residues are the earmarks of protein structural classes and have special physical and chemical causes. These correlation relationships are used in the predictions of protein structures for α,β,α/β, and α＋β protein classes, in total 204 proteins. The prediction accuracy are 94％ (α-proteins),89％ (β-proteins),79％ ((α/β)-proteins) and 89％ ((α＋β)-proteins),higher than the results of the simple distance method and the Euclidean distance method.
The correlation relationships among amino acid residues in protein structures are studied. Some residue pairs have larger correlation coefficients and they are not independent of protein structural classes. The correlation relationships of amino acid residues are the earmarks of protein structural classes and have special physical and chemical causes. These correlation relationships are used in the predictions of protein structures for α,β,α/β, and α＋β protein classes, in total 204 proteins. The prediction accuracy are 94％ (α-proteins),89％ (β-proteins),79％ ((α/β)-proteins) and 89％ ((α＋β)-proteins),higher than the results of the simple distance method and the Euclidean distance method.
2004, 20(05): 503-506
doi: 10.3866/PKU.WHXB20040512
Abstract:
Molecular structures of fourteen 6-thioxanthine tautomers were calculated by the B3LYP /6-311G** method, both in gas and aqueous phases, with full geometry optimization. The Onsager solvate theory model was employed for aqueous solution calculations. The structure, total energy, standard enthalpy, standard entropy and standard Gibbs free energy were obtained. The calculations show that 6-thioxanthine exists predominantly as the thione forms in the gas and aqueous phases. The thione-N7(H) isomer is more stable than the thione-N9(H) isomer in the gas and aqueous phase. The results are in od agreement with available experimental results. The entropy effect on the Gibbs free energies of 6-thioxanthine base is very small and there is little significance for the tautomeric equilibria of the base. The enthalpic term is dominant in the determination of tautomeric equilibria. The Gibbs free energies of solvation are well correlated with the dipole moments of 6-thioxanthine tautomers.
Molecular structures of fourteen 6-thioxanthine tautomers were calculated by the B3LYP /6-311G** method, both in gas and aqueous phases, with full geometry optimization. The Onsager solvate theory model was employed for aqueous solution calculations. The structure, total energy, standard enthalpy, standard entropy and standard Gibbs free energy were obtained. The calculations show that 6-thioxanthine exists predominantly as the thione forms in the gas and aqueous phases. The thione-N7(H) isomer is more stable than the thione-N9(H) isomer in the gas and aqueous phase. The results are in od agreement with available experimental results. The entropy effect on the Gibbs free energies of 6-thioxanthine base is very small and there is little significance for the tautomeric equilibria of the base. The enthalpic term is dominant in the determination of tautomeric equilibria. The Gibbs free energies of solvation are well correlated with the dipole moments of 6-thioxanthine tautomers.
2004, 20(05): 507-511
doi: 10.3866/PKU.WHXB20040513
Abstract:
The TiO2 thin films from dip-coating system were magnetron sputtered on with WOx, and can be activated by visible-light in gaseous dimethyl benzene photocatalytic degradation. The mechanism of its visible-light activity was investigated by UV-Vis absorption spectra and X-ray photoemission. UV-Vis absorption spectra showed its visible-light response expanding and having strong absorption with respect to the pure TiO2 film. XPS indicated the formation of W impurity energy level and Ti defect energy level, which was the main reason for the absorption in the visible-light range and the perquisite to have visible-light activity; and made Fermi level upper moved, free carriers more and photocatalytic efficiency enhanced.
The TiO2 thin films from dip-coating system were magnetron sputtered on with WOx, and can be activated by visible-light in gaseous dimethyl benzene photocatalytic degradation. The mechanism of its visible-light activity was investigated by UV-Vis absorption spectra and X-ray photoemission. UV-Vis absorption spectra showed its visible-light response expanding and having strong absorption with respect to the pure TiO2 film. XPS indicated the formation of W impurity energy level and Ti defect energy level, which was the main reason for the absorption in the visible-light range and the perquisite to have visible-light activity; and made Fermi level upper moved, free carriers more and photocatalytic efficiency enhanced.
2004, 20(05): 512-517
doi: 10.3866/PKU.WHXB20040514
Abstract:
The prediction of human intestinal absorption is a major al in the design, optimization, and selection of candidates for the development of oral drugs. A computerized method (VolSurf/GRID) was used as a novel tool for predicting human intestinal absorption of test compound, and for determining the critical molecular properties needed for human intestinal absorption. The tested molecules consisted of 112 diverse drug-like compounds. Partial least squares discriminant analysis was used to correlate the experimental data with the theoretical molecular properties of human intestinal absorption. There was high consistency between two built models. A od correlation (r2=0.82, q2=0.67) between the molecular properties and the experimental data demonstrated that human intestinal absorption could be predicted from the three-dimensional molecular structure of a compound. Favorable structural properties identified for the potent intestinal absorption drugs included strong imbalance between the center of mass of a molecule and the barycenter of its hydrophilic and hydrophobic regions and a definitive hydrophobic region as well as less hydrogen bond donors on the molecule.
The prediction of human intestinal absorption is a major al in the design, optimization, and selection of candidates for the development of oral drugs. A computerized method (VolSurf/GRID) was used as a novel tool for predicting human intestinal absorption of test compound, and for determining the critical molecular properties needed for human intestinal absorption. The tested molecules consisted of 112 diverse drug-like compounds. Partial least squares discriminant analysis was used to correlate the experimental data with the theoretical molecular properties of human intestinal absorption. There was high consistency between two built models. A od correlation (r2=0.82, q2=0.67) between the molecular properties and the experimental data demonstrated that human intestinal absorption could be predicted from the three-dimensional molecular structure of a compound. Favorable structural properties identified for the potent intestinal absorption drugs included strong imbalance between the center of mass of a molecule and the barycenter of its hydrophilic and hydrophobic regions and a definitive hydrophobic region as well as less hydrogen bond donors on the molecule.
2004, 20(05): 518-523
doi: 10.3866/PKU.WHXB20040515
Abstract:
A novel organic disulfide, 2,2’-diaminophenyloxydisulfide(DAPOD), has been proposed as a material of energy storage. The electrochemical study of this disulfide-thiolate redox couple has been studied on platinum, ld, glassy carbon or graphite electrode in AN/THF solution containing DAPOD and LiClO4 supporting electrolytes by potential cyclic sweep voltammetry, potential linear sweep voltammetry and rotating disk electrode technique. The CV results imply that the redox reactions of DAPOD are chemically reversible, yet kinetically hindered. The slow electrode kinetics indicates that the introduction of electrocatalysis to assist the electrode reaction may be effective in providing better performance. The observed reaction orders for DAPOD are 0.5 in the cathodic direction and 1 in the anodic direction. These results show that two electrons are involved in redox reaction of DAPOD, and that the reduction of the organodisulfide to the corresponding thiolate anions proceeds in two steps: the first step, chemical reaction, is at equilibrium, while the second step, charge-transfer reaction, is rate determining step. The kinetic constants such as transfer coefficients, exchange current, equilibrium potential and standard rate constant were determined. The electrochemical behavior of DAPOD at different electrode materials indicates that the graphite electrode demonstrates the electrocatalytic action to the electrode kinetics of DAPOD.
A novel organic disulfide, 2,2’-diaminophenyloxydisulfide(DAPOD), has been proposed as a material of energy storage. The electrochemical study of this disulfide-thiolate redox couple has been studied on platinum, ld, glassy carbon or graphite electrode in AN/THF solution containing DAPOD and LiClO4 supporting electrolytes by potential cyclic sweep voltammetry, potential linear sweep voltammetry and rotating disk electrode technique. The CV results imply that the redox reactions of DAPOD are chemically reversible, yet kinetically hindered. The slow electrode kinetics indicates that the introduction of electrocatalysis to assist the electrode reaction may be effective in providing better performance. The observed reaction orders for DAPOD are 0.5 in the cathodic direction and 1 in the anodic direction. These results show that two electrons are involved in redox reaction of DAPOD, and that the reduction of the organodisulfide to the corresponding thiolate anions proceeds in two steps: the first step, chemical reaction, is at equilibrium, while the second step, charge-transfer reaction, is rate determining step. The kinetic constants such as transfer coefficients, exchange current, equilibrium potential and standard rate constant were determined. The electrochemical behavior of DAPOD at different electrode materials indicates that the graphite electrode demonstrates the electrocatalytic action to the electrode kinetics of DAPOD.
2004, 20(05): 524-528
doi: 10.3866/PKU.WHXB20040516
Abstract:
The temperature-programmed desorption (TPD) and temperature-programmed surface reaction (TPSR) were studied by in situ mass spectrographic analysis. The results showed that methanol exists on the reactive surface of catalysts as molecular state and that adsorbed formate is one of intermediate species for the steam reforming of methanol (SRM).When the concentration of methanol among gas mixture is higher then 5.4％,0.37％ and 0.17％ for catalyst CuO, CuO-ZnO and CuO-ZnO-ZrO2, respectively, adsorbed formate decomposes into CO2 and H2,and conversely,CO,CO2 and H2 are products of formate decomposition.
The temperature-programmed desorption (TPD) and temperature-programmed surface reaction (TPSR) were studied by in situ mass spectrographic analysis. The results showed that methanol exists on the reactive surface of catalysts as molecular state and that adsorbed formate is one of intermediate species for the steam reforming of methanol (SRM).When the concentration of methanol among gas mixture is higher then 5.4％,0.37％ and 0.17％ for catalyst CuO, CuO-ZnO and CuO-ZnO-ZrO2, respectively, adsorbed formate decomposes into CO2 and H2,and conversely,CO,CO2 and H2 are products of formate decomposition.
2004, 20(05): 529-534
doi: 10.3866/PKU.WHXB20040517
Abstract:
Chiral Salen ligand(H3L) and zinc(II) dinuclear complex(host) were synthesized, which were characterized by elemental analysis, 1H NMR, UV-Vis, FT-IR and CD spectra. Molecular recognition behavior of the host for imidazoles and amino acid esters was studied. The binding constants between host and guest were measured, and it shows that the binding constants decrease in the orders of K(Im) >K(2-MeIm) >K(2-Et-4-MeIm) (imidazoles) and K(LeuOCH3) >K(ValOCH3) >K(AlaOCH3) >K(SerOCH3) (amino acid esters), and the coordination number is 2. The enthalpy-entropy compensation existed in host-guest system. By studying the binding constants between the host and amino acid esters, we find that the enantiosel selectivity decreases as the temperature increases. The studies of circular dichroism spectra of hostguest system show that the recognition behavior is different for various guests.
Chiral Salen ligand(H3L) and zinc(II) dinuclear complex(host) were synthesized, which were characterized by elemental analysis, 1H NMR, UV-Vis, FT-IR and CD spectra. Molecular recognition behavior of the host for imidazoles and amino acid esters was studied. The binding constants between host and guest were measured, and it shows that the binding constants decrease in the orders of K(Im) >K(2-MeIm) >K(2-Et-4-MeIm) (imidazoles) and K(LeuOCH3) >K(ValOCH3) >K(AlaOCH3) >K(SerOCH3) (amino acid esters), and the coordination number is 2. The enthalpy-entropy compensation existed in host-guest system. By studying the binding constants between the host and amino acid esters, we find that the enantiosel selectivity decreases as the temperature increases. The studies of circular dichroism spectra of hostguest system show that the recognition behavior is different for various guests.
2004, 20(05): 535-539
doi: 10.3866/PKU.WHXB20040518
Abstract:
The reactions of NCO with SO2 or CS2 in gas phase under total pressure of 2660 Pa and 298 K were studied by laser photolysis/laser induced fluorescence (LP/LIF).The NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of the produced CH in the photolysis reaction with NO. The relative concentration of ground states NCO radicals were monitored by time resolved LIF spectra. From the results of time resolved measurements on the NCO radicals, the bimolecular rate constants for the reactions of NCO with SO2 and CS2 were obtained as (1.8±0.3)×10－11 and (3.1±0.4)×10－12 cm3•molecule－1•s－1, respectively. In addition, the two reactions were studied using ab initio calculations at the B3LYP/6-31＋G(d) level. The results show that both are addition reactions and have the similar mechanism in which N atom of NCO radical attacks the central atom of SO2 or CS2 to form addition product.
The reactions of NCO with SO2 or CS2 in gas phase under total pressure of 2660 Pa and 298 K were studied by laser photolysis/laser induced fluorescence (LP/LIF).The NCO radicals were produced by laser photolysis of CHBr3 at 266 nm followed by the reaction of the produced CH in the photolysis reaction with NO. The relative concentration of ground states NCO radicals were monitored by time resolved LIF spectra. From the results of time resolved measurements on the NCO radicals, the bimolecular rate constants for the reactions of NCO with SO2 and CS2 were obtained as (1.8±0.3)×10－11 and (3.1±0.4)×10－12 cm3•molecule－1•s－1, respectively. In addition, the two reactions were studied using ab initio calculations at the B3LYP/6-31＋G(d) level. The results show that both are addition reactions and have the similar mechanism in which N atom of NCO radical attacks the central atom of SO2 or CS2 to form addition product.
2004, 20(05): 540-545
doi: 10.3866/PKU.WHXB20040519
Abstract:
Most biomolecules are chiral, but only one enantiomeric form occurs in nature. Life is based on L-amino acids and D-sugars rather than the D-amino acids and L-sugars. The homochirality is a hallmark of life, which remains a puzzle for theories of the chemical origin of life. This broken symmetry is believed to be a feature of fundamental physics, a result of symmetry breaking by the weak force, which makes one enantiomer slightly more stable than the other. The natural L-amino acids, L-alanine and L-valine were found to be more stable than their D-amino acids. For glyceraldehydes (n=3), the parent of the higher sugars, the D form is PVED-stabilized by about 10－17 kT. D-oxyribose is also PVED-stabilized in the C2-endo form found in DNA. It has recently become recognized that homochirality is not just a consequence of life. This is because life and self-organization seem to require polymers and polymerization do not in racemic solution. It is found that polymerization to give stereoregular biopolymers, in particular poly-D-ribonucleotides and poly-L-peptides, proceeds efficiently only in almost homochiral monomer solutions. In racemic solution, addition of the “wrong” hand to the growing chain tends to terminate the polymerization. The weak force appears to predict hand whatever came first. For nucleic acids, D-glyceraldehyde and α-D-ribose are more stable and the right-hand helical backbone of DNA is also PVED-stabilized. For proteins, the L-amino acids are more stable. In 1991 Abdus Salam proposed a hypothesis:the subtle energy difference(PVED) of chiral molecules induced by Z0 interactions combined with Bose condensation may cause homochirality among nineteen amino acids (excluding the achiral glycine). This is a consequence of secondorder phase transition at a critical temperature Tc, which is analo us to that of BCS(Bardeen-Cooper-Schrieffer) superconductivity. The value of temperature Tc is estimated to be around 250 K deduced from Ginzberg -Landau equation. To verify the Salam hypothesis, one may lower the temperature while measuring the optical activity when polarized light is shone upon a particular amino acid. If the polarization vectors get rotated, it can be said that the “phase transition” has taken place. Chiral molecules are characterized by a natural optical activity. The difficulty of the experiment is how to measure the rotation angle of monoclinic crystals of valine enantiomers. In this paper natural optical rotation in biaxial crystal of monoclinic valine is studied by projecting He-Ne laser light along one of the optic axes, b axis. The other two principal axes of refractive index ellipsoid, a and c are to be determined. Here we design a method to eliminate the effect of ellipticity induced by the crystal anisotropy. The temperature dependence of the natural optical rotation angle of D-valine, L-valine and DL-valine can thus be determined. The obtained results provide a direct evidence of the Salam hypothesis.
Most biomolecules are chiral, but only one enantiomeric form occurs in nature. Life is based on L-amino acids and D-sugars rather than the D-amino acids and L-sugars. The homochirality is a hallmark of life, which remains a puzzle for theories of the chemical origin of life. This broken symmetry is believed to be a feature of fundamental physics, a result of symmetry breaking by the weak force, which makes one enantiomer slightly more stable than the other. The natural L-amino acids, L-alanine and L-valine were found to be more stable than their D-amino acids. For glyceraldehydes (n=3), the parent of the higher sugars, the D form is PVED-stabilized by about 10－17 kT. D-oxyribose is also PVED-stabilized in the C2-endo form found in DNA. It has recently become recognized that homochirality is not just a consequence of life. This is because life and self-organization seem to require polymers and polymerization do not in racemic solution. It is found that polymerization to give stereoregular biopolymers, in particular poly-D-ribonucleotides and poly-L-peptides, proceeds efficiently only in almost homochiral monomer solutions. In racemic solution, addition of the “wrong” hand to the growing chain tends to terminate the polymerization. The weak force appears to predict hand whatever came first. For nucleic acids, D-glyceraldehyde and α-D-ribose are more stable and the right-hand helical backbone of DNA is also PVED-stabilized. For proteins, the L-amino acids are more stable. In 1991 Abdus Salam proposed a hypothesis:the subtle energy difference(PVED) of chiral molecules induced by Z0 interactions combined with Bose condensation may cause homochirality among nineteen amino acids (excluding the achiral glycine). This is a consequence of secondorder phase transition at a critical temperature Tc, which is analo us to that of BCS(Bardeen-Cooper-Schrieffer) superconductivity. The value of temperature Tc is estimated to be around 250 K deduced from Ginzberg -Landau equation. To verify the Salam hypothesis, one may lower the temperature while measuring the optical activity when polarized light is shone upon a particular amino acid. If the polarization vectors get rotated, it can be said that the “phase transition” has taken place. Chiral molecules are characterized by a natural optical activity. The difficulty of the experiment is how to measure the rotation angle of monoclinic crystals of valine enantiomers. In this paper natural optical rotation in biaxial crystal of monoclinic valine is studied by projecting He-Ne laser light along one of the optic axes, b axis. The other two principal axes of refractive index ellipsoid, a and c are to be determined. Here we design a method to eliminate the effect of ellipticity induced by the crystal anisotropy. The temperature dependence of the natural optical rotation angle of D-valine, L-valine and DL-valine can thus be determined. The obtained results provide a direct evidence of the Salam hypothesis.
2004, 20(05): 546-549
doi: 10.3866/PKU.WHXB20040520
Abstract:
Activated carbon nanotubes were obtained by the activation of carbon nanotubes using KOH as activator at high temperature. The specific surface area and pore volume of the obtained activated carbon nanotubes were 3 and 1.5 times as large as that of the pristine carbon nanotubes, respectively. The two kinds of carbon nanotubes were used as the electrode materials of electrochemical supercapacitors and the simulated electrochemical supercapacitors were assembled in the glove box filled with ar n air. The electrochemical capacitance of the activated carbon nanotubes was twice as large as that of the pristine carbon nanotubes by test under constant current chargingdischarging. So, the activated carbon nanotubes with a short cut length and rough tube surface are more suitable in using as the electrode materials of electrochemical supercapacitors than the normal carbon nanotubes.
Activated carbon nanotubes were obtained by the activation of carbon nanotubes using KOH as activator at high temperature. The specific surface area and pore volume of the obtained activated carbon nanotubes were 3 and 1.5 times as large as that of the pristine carbon nanotubes, respectively. The two kinds of carbon nanotubes were used as the electrode materials of electrochemical supercapacitors and the simulated electrochemical supercapacitors were assembled in the glove box filled with ar n air. The electrochemical capacitance of the activated carbon nanotubes was twice as large as that of the pristine carbon nanotubes by test under constant current chargingdischarging. So, the activated carbon nanotubes with a short cut length and rough tube surface are more suitable in using as the electrode materials of electrochemical supercapacitors than the normal carbon nanotubes.
2004, 20(05): 550-553
doi: 10.3866/PKU.WHXB20040521
Abstract:
The effects of Zr in CuO-ZnO-ZrO2 catalysts on the diameter of CuO and ZnO ,BET surface area of the catalysts as well as the catalytic activity have been studied by XRD,TEM,BET and the evaluation of catalytic activity for steam reforming of methanol (SRM).The results indicated that the diameter of catalyst particle was lowered from 15 to 10 nm (the average diameters of CuO and ZnO were lowered from 7.7 and 10.4 nm to 3.9 and 8.7 nm, respectively),the BET surface area was increased from 60 to 78 m2•g－1 due to the existence of Zr. The conversion of methanol and the sensitivity of both hydrogen and carbon dioxide over Cu-ZnO-ZrO2 catalysts in SRM reaction were changed along with content of Zr in the catalysts. The conversion of methanol of 51.6％ and the sensitivity of both hydrogen and carbon dioxide of 100％ (content of CO and CH4 was lower than 10－4(φ)and can not be detected by 102GC) were obtained under the following reaction conditions: Zr content of 24.0％(w) in the catalyst, reaction temperature of 220 ℃ and mole ratio of water to methanol of 1.3. These results have important significance in the application of steam reformer of methanol for methanol fuel cell.
The effects of Zr in CuO-ZnO-ZrO2 catalysts on the diameter of CuO and ZnO ,BET surface area of the catalysts as well as the catalytic activity have been studied by XRD,TEM,BET and the evaluation of catalytic activity for steam reforming of methanol (SRM).The results indicated that the diameter of catalyst particle was lowered from 15 to 10 nm (the average diameters of CuO and ZnO were lowered from 7.7 and 10.4 nm to 3.9 and 8.7 nm, respectively),the BET surface area was increased from 60 to 78 m2•g－1 due to the existence of Zr. The conversion of methanol and the sensitivity of both hydrogen and carbon dioxide over Cu-ZnO-ZrO2 catalysts in SRM reaction were changed along with content of Zr in the catalysts. The conversion of methanol of 51.6％ and the sensitivity of both hydrogen and carbon dioxide of 100％ (content of CO and CH4 was lower than 10－4(φ)and can not be detected by 102GC) were obtained under the following reaction conditions: Zr content of 24.0％(w) in the catalyst, reaction temperature of 220 ℃ and mole ratio of water to methanol of 1.3. These results have important significance in the application of steam reformer of methanol for methanol fuel cell.
2004, 20(05): 554-556
doi: 10.3866/PKU.WHXB20040522
Abstract:
Silver nanoparticles were synthesized in a room temperature ionic liquid via chemical reduction under ambient conditions. X-ray power diffraction, transmission electron microscopy, thermal analysis and FT-IR were used to characterize the structure of the Ag nanoparticles. The results indicate that the mean diameter of the namoparticles is about 20 nm and the surface of the Ag nanoparticles was modified with the room temperature ionic liquid. So we conclude that the room temperature ionic liquid is not only used as reaction medium but also as stabilizing agent to prevent the silver nanoparticles aggregating. The proposed formation mechanisms of silver nanoparticles are discussed.
Silver nanoparticles were synthesized in a room temperature ionic liquid via chemical reduction under ambient conditions. X-ray power diffraction, transmission electron microscopy, thermal analysis and FT-IR were used to characterize the structure of the Ag nanoparticles. The results indicate that the mean diameter of the namoparticles is about 20 nm and the surface of the Ag nanoparticles was modified with the room temperature ionic liquid. So we conclude that the room temperature ionic liquid is not only used as reaction medium but also as stabilizing agent to prevent the silver nanoparticles aggregating. The proposed formation mechanisms of silver nanoparticles are discussed.
2004, 20(05): 557-560
doi: 10.3866/PKU.WHXB20040523
Abstract:
A novel plasma reactor with rotary multi-tip electrode and a fixed concentric cylinder electrode has been developed in order to use in CH4 discharge and to produce unsaturated C2 hydrocarbons.CH4 coupling in the presence of H2 has been investigated to evaluate the plasma reactor. In the reactor, flowing reactants run crisscross through the circular plasma zone between the two electrodes. No substantial amount of coke is observed on surface of the rotary multi-tip and fixed cylinder electrodes after a long time of the continuous reaction at about 40 V of supplied voltage under 20 kHz of pulse frequency discharge plasmas. The rotary multi-tip electrode process is possessed of higher CH4 conversion and higher C2 hydrocarbons single pass yield and higher energy efficiency than the plasma processes using fixed wire-plate electrodes under the same conditions.
A novel plasma reactor with rotary multi-tip electrode and a fixed concentric cylinder electrode has been developed in order to use in CH4 discharge and to produce unsaturated C2 hydrocarbons.CH4 coupling in the presence of H2 has been investigated to evaluate the plasma reactor. In the reactor, flowing reactants run crisscross through the circular plasma zone between the two electrodes. No substantial amount of coke is observed on surface of the rotary multi-tip and fixed cylinder electrodes after a long time of the continuous reaction at about 40 V of supplied voltage under 20 kHz of pulse frequency discharge plasmas. The rotary multi-tip electrode process is possessed of higher CH4 conversion and higher C2 hydrocarbons single pass yield and higher energy efficiency than the plasma processes using fixed wire-plate electrodes under the same conditions.
