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2006 Volume 22 Issue 10
2006, 22(10): 1175-1180
doi: 10.3866/PKU.WHXB20061001
Abstract:
ZnO-CNTs nanocomposites were successfully synthesized by sol method using Zn(CH3COO)2•2H2O and treated multiwalled carbon nanotubes (CNTs) as raw materials and diethyleneglycol (DEG) as regent. The samples were determined by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared (IR) absorbence, and photoluminescence (PL) spectrum. TEM and SEM images indicated that the coating layer was composed of ZnO nanoparticles with size less than 25 nm. The effects of various experimental conditions, such as reaction duration and reaction temperature on the obtained composites were investigated as well. Finally, PL function and possible formation mechanism of ZnO-CNTs nanocomposites were proposed. The PL spectra of ZnO-CNTs nanocomposites showed obvious blue-shifts compared with that of pure ZnO nanomaterial.
ZnO-CNTs nanocomposites were successfully synthesized by sol method using Zn(CH3COO)2•2H2O and treated multiwalled carbon nanotubes (CNTs) as raw materials and diethyleneglycol (DEG) as regent. The samples were determined by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared (IR) absorbence, and photoluminescence (PL) spectrum. TEM and SEM images indicated that the coating layer was composed of ZnO nanoparticles with size less than 25 nm. The effects of various experimental conditions, such as reaction duration and reaction temperature on the obtained composites were investigated as well. Finally, PL function and possible formation mechanism of ZnO-CNTs nanocomposites were proposed. The PL spectra of ZnO-CNTs nanocomposites showed obvious blue-shifts compared with that of pure ZnO nanomaterial.
2006, 22(10): 1181-1184
doi: 10.1016/S1872-1508(06)60054-5
Abstract:
A series of Ni-Fe oxides with high specific area and Ce0.8Sm0.2O1.9 (SDC) electrolyte were prepared using the nitrate-citric acid method. On the basis of Ni-Fe oxides and Ce0.8Sm0.2O1.9 electrolyte, Ni-Fe/SDC composite anode materials were prepared. Meanwhile, their microstructure and other performance-related parameters were also tested. The results showed that the thermal expansion of the composite anode materials matched well with that of the SDC electrolyte. Furthermore, the single cell, using hydrogen fuel and the composite materials as the anode of solid oxides fuel cell (SOFC), showed an excellent electrochemical performance with hydrogen fuel. At 700 ℃, the maximal power density was 90.6 mW•cm−2.
A series of Ni-Fe oxides with high specific area and Ce0.8Sm0.2O1.9 (SDC) electrolyte were prepared using the nitrate-citric acid method. On the basis of Ni-Fe oxides and Ce0.8Sm0.2O1.9 electrolyte, Ni-Fe/SDC composite anode materials were prepared. Meanwhile, their microstructure and other performance-related parameters were also tested. The results showed that the thermal expansion of the composite anode materials matched well with that of the SDC electrolyte. Furthermore, the single cell, using hydrogen fuel and the composite materials as the anode of solid oxides fuel cell (SOFC), showed an excellent electrochemical performance with hydrogen fuel. At 700 ℃, the maximal power density was 90.6 mW•cm−2.
2006, 22(10): 1185-1190
doi: 10.3866/PKU.WHXB20061003
Abstract:
Composites—sulfonated polyphenylacetylene/multiwalled carbon nanotubes (SPPA/MWNT) were prepared by mixing SPPA with MWNT in an ultrasonic bath. The conductive mechanism of SPPA/MWNT was studied by four-probe, field emission scanning electron microscope (FESEM), UV-Vis, XPS, and XRD. The results showed that there were two obvious increases of electrical conductivity, the dopant (MWNT) had a low percolation threshod, the MWNT was discontinuously dispersed in the composites when reaching the percolation threshold, and the resistance of the composites showed a negative temperature coefficient (NTC). XPS、UV-Vis, and XRD results indicated that SPPA was doped by the carbon atom of MWNT in the composites. The conductive mechanism of the composites was inferred as follows: there were two kinds of conductive networks, one was formed by doped SPPA contacting with each other , the other was formed by MWNT contacting with each other, since the conjugated polymer (SPPA) can be not only filled by MWNT, but also be doped by the carbon atoms of the MWNT.
Composites—sulfonated polyphenylacetylene/multiwalled carbon nanotubes (SPPA/MWNT) were prepared by mixing SPPA with MWNT in an ultrasonic bath. The conductive mechanism of SPPA/MWNT was studied by four-probe, field emission scanning electron microscope (FESEM), UV-Vis, XPS, and XRD. The results showed that there were two obvious increases of electrical conductivity, the dopant (MWNT) had a low percolation threshod, the MWNT was discontinuously dispersed in the composites when reaching the percolation threshold, and the resistance of the composites showed a negative temperature coefficient (NTC). XPS、UV-Vis, and XRD results indicated that SPPA was doped by the carbon atom of MWNT in the composites. The conductive mechanism of the composites was inferred as follows: there were two kinds of conductive networks, one was formed by doped SPPA contacting with each other , the other was formed by MWNT contacting with each other, since the conjugated polymer (SPPA) can be not only filled by MWNT, but also be doped by the carbon atoms of the MWNT.
2006, 22(10): 1191-1195
doi: 10.3866/PKU.WHXB20061004
Abstract:
The gas phase reaction mechanism of Br2+Cl2=2BrCl had been investigated by (U)MP2 at 6-311G* level, and a series of four-centered and three-centered transition states were obtained. Comparing the activation energies of three reaction paths, the result was achieved as follows: the minimum activation energy of the bimolecular elementary reaction Br2+Cl2=2BrCl was less than the dissociation energies of Br2 and Cl2. It was thus theoretically proved that the titled reaction occurred more easily in the bimolecular form without light initiation. However, if the reaction system was initiated by light, the titled reaction was completed quickly through the reaction path of Br atom reacting with Cl2 or Cl atom reacting with Br2. The theoretical result was further verified by determination of the absorbency (with or without light initiation) at 412 nm.
The gas phase reaction mechanism of Br2+Cl2=2BrCl had been investigated by (U)MP2 at 6-311G* level, and a series of four-centered and three-centered transition states were obtained. Comparing the activation energies of three reaction paths, the result was achieved as follows: the minimum activation energy of the bimolecular elementary reaction Br2+Cl2=2BrCl was less than the dissociation energies of Br2 and Cl2. It was thus theoretically proved that the titled reaction occurred more easily in the bimolecular form without light initiation. However, if the reaction system was initiated by light, the titled reaction was completed quickly through the reaction path of Br atom reacting with Cl2 or Cl atom reacting with Br2. The theoretical result was further verified by determination of the absorbency (with or without light initiation) at 412 nm.
2006, 22(10): 1196-1200
doi: 10.3866/PKU.WHXB20061005
Abstract:
The structures of the Au(I) complexes were fully optimized by using the MP2 method for the ground states and the CIS method for the excited states. In the ground states, it is clear that the molecule distances show a tendency of shortening towards middle; the modification effect of Au(I) weakens the bonding inside the ligand; with the lengthening of molecules, the bonding between the metal and ligand is weakened. In the excited states, the bonding effect between metal and ligand is weakened because of the electron transitions, which becomes clear with the lengthening of molecules. The results showed that the fluorescences of the Au(I) complexes have an inimitable nature, and the —AuPH3 has more ionic nature than —H.
The structures of the Au(I) complexes were fully optimized by using the MP2 method for the ground states and the CIS method for the excited states. In the ground states, it is clear that the molecule distances show a tendency of shortening towards middle; the modification effect of Au(I) weakens the bonding inside the ligand; with the lengthening of molecules, the bonding between the metal and ligand is weakened. In the excited states, the bonding effect between metal and ligand is weakened because of the electron transitions, which becomes clear with the lengthening of molecules. The results showed that the fluorescences of the Au(I) complexes have an inimitable nature, and the —AuPH3 has more ionic nature than —H.
2006, 22(10): 1201-1205
doi: 10.3866/PKU.WHXB20061006
Abstract:
Ordered mesoporous molecular sieves SBA-15 were synthesized by hydrothermal reaction with TEOS as the source of inorganic silica and tri-block copolymer P123 as the template in strong acid media with HCl. Characteristics of the structure and micro-morphology of the synthesized samples were investigated by means of XRD, SEM, TEM, and N2 adsorption-desorption analysis. The results indicated that HCl played a role of catalyst in the synthesizing process. It could enhance the formation of hexa nal ordered arrangement of the surfactant micelles. HCl could reduce the number of micropores. Apporpriate amount of HCl was favourable to form the thermally stable SBA-15 with the morphology of pearl-like chains.
Ordered mesoporous molecular sieves SBA-15 were synthesized by hydrothermal reaction with TEOS as the source of inorganic silica and tri-block copolymer P123 as the template in strong acid media with HCl. Characteristics of the structure and micro-morphology of the synthesized samples were investigated by means of XRD, SEM, TEM, and N2 adsorption-desorption analysis. The results indicated that HCl played a role of catalyst in the synthesizing process. It could enhance the formation of hexa nal ordered arrangement of the surfactant micelles. HCl could reduce the number of micropores. Apporpriate amount of HCl was favourable to form the thermally stable SBA-15 with the morphology of pearl-like chains.
2006, 22(10): 1206-1211
doi: 10.1016/S1872-1508(06)60055-7
Abstract:
The crystal of [Cu(HCOO)2(H2O)2]∞ (polymer 1) has been synthesized and cultured using the hydrothermal method. The thermal decomposition mechanisms and the associated kinetics of polymer 1 have been investigated based on the TG-DTG and DSC analyses. The most probable kinetic model function of the endothermic process was suggested by comparison of the kinetic parameters obtained from the analysis of the DSC curves by Kissinger′s, Ozawa′s, integral, and differential methods. The crystal of polymer 1 was characterized by X-ray single crystal diffraction, elemental analysis, and FTIR spectroscopy techniques. The coordination polymer crystallizes in monoclinic system, P21/c space group with crystal parameters of a=0.8533(2) nm, b=0.7151(2) nm, c=0.9463(2) nm, β=96.94(0)°, V=0.5732(2) nm3, Z=4, and Dc=2.197 g•cm−3. In the coordination polymer, with the formates as space linkers, two types of copper centers are joined together to form three-dimensional frameworks.
The crystal of [Cu(HCOO)2(H2O)2]∞ (polymer 1) has been synthesized and cultured using the hydrothermal method. The thermal decomposition mechanisms and the associated kinetics of polymer 1 have been investigated based on the TG-DTG and DSC analyses. The most probable kinetic model function of the endothermic process was suggested by comparison of the kinetic parameters obtained from the analysis of the DSC curves by Kissinger′s, Ozawa′s, integral, and differential methods. The crystal of polymer 1 was characterized by X-ray single crystal diffraction, elemental analysis, and FTIR spectroscopy techniques. The coordination polymer crystallizes in monoclinic system, P21/c space group with crystal parameters of a=0.8533(2) nm, b=0.7151(2) nm, c=0.9463(2) nm, β=96.94(0)°, V=0.5732(2) nm3, Z=4, and Dc=2.197 g•cm−3. In the coordination polymer, with the formates as space linkers, two types of copper centers are joined together to form three-dimensional frameworks.
2006, 22(10): 1212-1216
doi: 10.3866/PKU.WHXB20061008
Abstract:
Fe3+-modified SnO2 nanoparticles were directly prepared by hydrothermal method, and were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscopy, and UV-Vis diffuse reflectance spectra (DRS). It was found that rutile phase was directly synthesized without calcination. The Fe3+-modified SnO2 nanoparticles were well dispersed with narrow size distribution. The crystalline size of SnO2 decreased from 6.0 to 3.8 nm when the Fe3+ content increased from 0 to 20%. The specific surface area of pure SnO2 was 206.1 m2•g−1, and it increased to 259.8 m2•g−1 when Fe content was 15%. A considerable red shift in the absorbing band edge was observed as increase of Fe3+ content. XRD and DRS proved that Fe3+ and SnO2 formed solid solution nanoparticles.
Fe3+-modified SnO2 nanoparticles were directly prepared by hydrothermal method, and were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared (FT-IR) spectroscopy, and UV-Vis diffuse reflectance spectra (DRS). It was found that rutile phase was directly synthesized without calcination. The Fe3+-modified SnO2 nanoparticles were well dispersed with narrow size distribution. The crystalline size of SnO2 decreased from 6.0 to 3.8 nm when the Fe3+ content increased from 0 to 20%. The specific surface area of pure SnO2 was 206.1 m2•g−1, and it increased to 259.8 m2•g−1 when Fe content was 15%. A considerable red shift in the absorbing band edge was observed as increase of Fe3+ content. XRD and DRS proved that Fe3+ and SnO2 formed solid solution nanoparticles.
2006, 22(10): 1217-1221
doi: 10.1016/S1872-1508(06)60056-9
Abstract:
The thermochemical properties of reaction N++H2→NH++H have been computed under Titan′s atmosphere conditions. It is observed that this reaction is an endothermic reaction and cannot proceed forward spontaneously under low temperature. The rate for this reaction at 300 K has been calculated as k=4.16×10−10 cm3•mol−1•s−1. The reaction barrier is 109.847 kJ•mol−1 at 298.15 K, which is probably too high to allow this reaction to occur in the atmosphere of Titan. The kinetic properties of the reaction are calculated at a pressure of 90 Pa and a temperature ranging from 1 to 5000 K. It is found that this reaction has very low reaction rate under low temperature in Titan′s atmosphere and that the rate decreases drastically with decreasing temperature. This result should be applicable to interstellar place of the low temperature values. The results are compared with those obtained from experiments.
The thermochemical properties of reaction N++H2→NH++H have been computed under Titan′s atmosphere conditions. It is observed that this reaction is an endothermic reaction and cannot proceed forward spontaneously under low temperature. The rate for this reaction at 300 K has been calculated as k=4.16×10−10 cm3•mol−1•s−1. The reaction barrier is 109.847 kJ•mol−1 at 298.15 K, which is probably too high to allow this reaction to occur in the atmosphere of Titan. The kinetic properties of the reaction are calculated at a pressure of 90 Pa and a temperature ranging from 1 to 5000 K. It is found that this reaction has very low reaction rate under low temperature in Titan′s atmosphere and that the rate decreases drastically with decreasing temperature. This result should be applicable to interstellar place of the low temperature values. The results are compared with those obtained from experiments.
2006, 22(10): 1222-1226
doi: 10.3866/PKU.WHXB20061010
Abstract:
The corrosion behaviour of pure magnesium in Hank′s simulated body fluid (SBF) was investigated. It was found that the polarization of Mg in the SBF solution was similar to that in a NaCl aqueous solution. However, AC impedance analysis suggested that the detailed dissolution steps involved in the corrosion of Mg in the SBF could be different in terms of their rates or contributions to corrosion damage of Mg. Moreover, the corrosion rate of Mg in the SBF solution was found to be increasing with time and significant hydrogen evolution and alkalization of the SBF solution resulting from corrosion of Mg were measured in the study. The results suggested that after some proper measures are taken to retard corrosion reaction, Mg can be successfully employed as a degradable and absorbable implant material.
The corrosion behaviour of pure magnesium in Hank′s simulated body fluid (SBF) was investigated. It was found that the polarization of Mg in the SBF solution was similar to that in a NaCl aqueous solution. However, AC impedance analysis suggested that the detailed dissolution steps involved in the corrosion of Mg in the SBF could be different in terms of their rates or contributions to corrosion damage of Mg. Moreover, the corrosion rate of Mg in the SBF solution was found to be increasing with time and significant hydrogen evolution and alkalization of the SBF solution resulting from corrosion of Mg were measured in the study. The results suggested that after some proper measures are taken to retard corrosion reaction, Mg can be successfully employed as a degradable and absorbable implant material.
2006, 22(10): 1227-1232
doi: 10.1016/S1872-1508(06)60057-0
Abstract:
A new electroactive polynuclear inorganic compound of rare earth metal, gadolinium hexacyanoferrate (GdHCF), was prepared and characterized using the techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), UV-Vis spectrometry, X-ray photoelectron spectroscopy (XPS), ICP atomic emission spectoscopy, and EDX. The results of ICP atomic emission spectroscopy, EDX, and TGA indicated that the prepared GdHCF sample had a stoichiometry of NaGdFe(CN)6•12H2O (when GdHCF was prepared in NaCl solution). The FTIR spectrum of GdHCF showed that there were two types of water molecules in the structure of GdHCF: one was the interstitial water (5 H2O), which resulted from the association of water due to H-bonding, and the other was water coordinated with Gd (7 H2O). The results obtained using XPS showed that the oxidation state of Fe and Gd in the GdHCF sample was +2 and +3, respectively. GdHCF was immobilized on the surface of spectroscopically pure graphite (SG) electrode forming the GdHCF/SG electrode, and the solid-state electrochemistry of the resultant electrode was studied using cyclic voltammetry. The cyclic voltammetric results indicated that the GdHCF/SG electrode exhibited a pair of welldefined and stable redox peaks with the formal potential of E0′=(197±3) mV. The effects of the concentration of the supporting electrolyte on the electrochemical characteristics of GdHCF were studied, and the results showed that the value of E0′ increased linearly with the activity of the cationic ion of the supporting electrolyte (lgaNa+), with a slope of 54.1 mV, which may become a novel method for determining the activity of Na+ in solution. Further experimental results indicated that GdHCF had electrocatalytic activities toward the oxidation of dopamine (DA), and ascorbic acid (AA), and the electro- catalytic current increased linearly with the concentration of DA (or AA) in the range of 1.0~10.0 mmol•L−1 (for DA) or 0.5~20.0 mmol•L−1 (for AA).
A new electroactive polynuclear inorganic compound of rare earth metal, gadolinium hexacyanoferrate (GdHCF), was prepared and characterized using the techniques of FTIR spectroscopy, thermogravimetric analysis (TGA), UV-Vis spectrometry, X-ray photoelectron spectroscopy (XPS), ICP atomic emission spectoscopy, and EDX. The results of ICP atomic emission spectroscopy, EDX, and TGA indicated that the prepared GdHCF sample had a stoichiometry of NaGdFe(CN)6•12H2O (when GdHCF was prepared in NaCl solution). The FTIR spectrum of GdHCF showed that there were two types of water molecules in the structure of GdHCF: one was the interstitial water (5 H2O), which resulted from the association of water due to H-bonding, and the other was water coordinated with Gd (7 H2O). The results obtained using XPS showed that the oxidation state of Fe and Gd in the GdHCF sample was +2 and +3, respectively. GdHCF was immobilized on the surface of spectroscopically pure graphite (SG) electrode forming the GdHCF/SG electrode, and the solid-state electrochemistry of the resultant electrode was studied using cyclic voltammetry. The cyclic voltammetric results indicated that the GdHCF/SG electrode exhibited a pair of welldefined and stable redox peaks with the formal potential of E0′=(197±3) mV. The effects of the concentration of the supporting electrolyte on the electrochemical characteristics of GdHCF were studied, and the results showed that the value of E0′ increased linearly with the activity of the cationic ion of the supporting electrolyte (lgaNa+), with a slope of 54.1 mV, which may become a novel method for determining the activity of Na+ in solution. Further experimental results indicated that GdHCF had electrocatalytic activities toward the oxidation of dopamine (DA), and ascorbic acid (AA), and the electro- catalytic current increased linearly with the concentration of DA (or AA) in the range of 1.0~10.0 mmol•L−1 (for DA) or 0.5~20.0 mmol•L−1 (for AA).
2006, 22(10): 1233-1237
doi: 10.1016/S1872-1508(06)60058-2
Abstract:
Using trimethylphosphine(TMP) and d5-pyridine (deuterated pyridine) as the basic probe molecules, the concentrations of Brönsted acid sites on both HY zeolite and dealuminated HY zeolite have been quantitatively determined using solid-state 1H and 31P magic-angle spinning(MAS) NMR. After the adsorption of the probe molecules, the concentration of Brönsted acid sites on the dealuminated HY zeolite increases by about 25%, whereas the parent HY sample remains almost unchanged. The increase in the concentration of Brönsted acid sites is due to the appearance of base-induced Brönsted acid sites in the dealuminated HY zeolite. The terminal SiOH in the vicinity of the aluminum atom is “induced” to form a bridging hydroxyl group (SiOHAl) in the presence of the basic probe molecules. The mechanism of formation of the induced Brönsted acid sites has also been discussed.
Using trimethylphosphine(TMP) and d5-pyridine (deuterated pyridine) as the basic probe molecules, the concentrations of Brönsted acid sites on both HY zeolite and dealuminated HY zeolite have been quantitatively determined using solid-state 1H and 31P magic-angle spinning(MAS) NMR. After the adsorption of the probe molecules, the concentration of Brönsted acid sites on the dealuminated HY zeolite increases by about 25%, whereas the parent HY sample remains almost unchanged. The increase in the concentration of Brönsted acid sites is due to the appearance of base-induced Brönsted acid sites in the dealuminated HY zeolite. The terminal SiOH in the vicinity of the aluminum atom is “induced” to form a bridging hydroxyl group (SiOHAl) in the presence of the basic probe molecules. The mechanism of formation of the induced Brönsted acid sites has also been discussed.
2006, 22(10): 1238-1242
doi: 10.3866/PKU.WHXB20061013
Abstract:
Pt/nanoTiO2-CNT complex catalysts were prepared by direct hydrolysis of Ti(OEt)4 and electrochemical scan electrodepositing method. The results of XRD and SEM showed that the nanoTiO2 (anatase) and Pt nanoparticles (size about 5~10 nm) were dispersed uniformly on CNT film surface. The electrocatalytic activity of Pt/nanoTiO2-CNT electrode was investigated by cyclic voltammetry and chronopotentiogram. The results indicated that Pt/nanoTiO2-CNT electrode (Pt loading was 0.32 mg•cm−2) exhibited high electrochemical activity surface area (51.8 m2•g−1) and very high electrocatalytic activity and stability for the electro-oxidation of ethanol at room temperature in atmosphere pressure. The oxidation peak potentials of ethanol were 0.59, 0.96, and 0.24 V, and the corresponding oxidation peak current sdensities were −115, −113, and −75 mA•cm−2. The high electrocatalytic activity and od stability can be attributed to the synergistic catalytic effect among nanocomposite.
Pt/nanoTiO2-CNT complex catalysts were prepared by direct hydrolysis of Ti(OEt)4 and electrochemical scan electrodepositing method. The results of XRD and SEM showed that the nanoTiO2 (anatase) and Pt nanoparticles (size about 5~10 nm) were dispersed uniformly on CNT film surface. The electrocatalytic activity of Pt/nanoTiO2-CNT electrode was investigated by cyclic voltammetry and chronopotentiogram. The results indicated that Pt/nanoTiO2-CNT electrode (Pt loading was 0.32 mg•cm−2) exhibited high electrochemical activity surface area (51.8 m2•g−1) and very high electrocatalytic activity and stability for the electro-oxidation of ethanol at room temperature in atmosphere pressure. The oxidation peak potentials of ethanol were 0.59, 0.96, and 0.24 V, and the corresponding oxidation peak current sdensities were −115, −113, and −75 mA•cm−2. The high electrocatalytic activity and od stability can be attributed to the synergistic catalytic effect among nanocomposite.
2006, 22(10): 1243-1247
doi: 10.3866/PKU.WHXB20061014
Abstract:
The ABEEM/MM (atom-bond electronegativity equalization fused into molecular mechanic) fluctuating charge model was applied to simulate five realistic cyclic peptides. In the ABEEM/MM model, comparing to the classical force field with fixed charge electrostatic potential, the partial charges were allowed to fluctuate in the same molecule in response to the environment. The important non-atomic-center charge sites (chemical bond and lone pair) were added into this model to describe the charge population reasonably. The CPU time was not longer than that in other polarized force fields. The relevant structural information was analyzed, such as the root-mean-square deviation of the atomic coordinate shift, the deviation of hydrogen bond lengths and the deviation of dihedral angle of five cyclic peptides from the corresponding experimental data, whose values are 0.009 nm, 0.013 nm, and 5.16° respectively. The ABEEM/MM model could well reproduce the experimental structures of realistic peptides. All in all, the results from the ABEEM/MM model present higher accuracy than those from other force fields. It is proved to be suitable to explore and simulate the realistic protein systems.
The ABEEM/MM (atom-bond electronegativity equalization fused into molecular mechanic) fluctuating charge model was applied to simulate five realistic cyclic peptides. In the ABEEM/MM model, comparing to the classical force field with fixed charge electrostatic potential, the partial charges were allowed to fluctuate in the same molecule in response to the environment. The important non-atomic-center charge sites (chemical bond and lone pair) were added into this model to describe the charge population reasonably. The CPU time was not longer than that in other polarized force fields. The relevant structural information was analyzed, such as the root-mean-square deviation of the atomic coordinate shift, the deviation of hydrogen bond lengths and the deviation of dihedral angle of five cyclic peptides from the corresponding experimental data, whose values are 0.009 nm, 0.013 nm, and 5.16° respectively. The ABEEM/MM model could well reproduce the experimental structures of realistic peptides. All in all, the results from the ABEEM/MM model present higher accuracy than those from other force fields. It is proved to be suitable to explore and simulate the realistic protein systems.
2006, 22(10): 1248-1252
doi: 10.3866/PKU.WHXB20061015
Abstract:
Using a home-made in situ electrochemical cell of electrochemical impedance spectroscop(EIS), the impedance behaviors of the titanium/MG63 cells interface were measured to elucidate the interfacial structure and to monitor the interactions of biomaterials and living cells in a physiological condition. The in situ electrochemical cell was designed to detect the dynamic EIS behavior of living cells growing on a tiatanium surface. A three-well design of electrochemical cell was used to decrease system error and a home-made Ag/AgCl electrode was introduced as a reference electrode to eliminate the distortion phenomena in high frequency range. The EIS spectra and its time dependency of titanium/MG63 cells interface showed that the polarization resistance was increased with the decreasing of CPE constant (Y0) and a new time constant in high frequency range was detected. It suggested that the adhesion and growth activities of the living cells on the biomaterial surface may influence the surface status and the structure of the double layer at the interface, and thus alter its electrochemical characteristics.
Using a home-made in situ electrochemical cell of electrochemical impedance spectroscop(EIS), the impedance behaviors of the titanium/MG63 cells interface were measured to elucidate the interfacial structure and to monitor the interactions of biomaterials and living cells in a physiological condition. The in situ electrochemical cell was designed to detect the dynamic EIS behavior of living cells growing on a tiatanium surface. A three-well design of electrochemical cell was used to decrease system error and a home-made Ag/AgCl electrode was introduced as a reference electrode to eliminate the distortion phenomena in high frequency range. The EIS spectra and its time dependency of titanium/MG63 cells interface showed that the polarization resistance was increased with the decreasing of CPE constant (Y0) and a new time constant in high frequency range was detected. It suggested that the adhesion and growth activities of the living cells on the biomaterial surface may influence the surface status and the structure of the double layer at the interface, and thus alter its electrochemical characteristics.
2006, 22(10): 1253-1259
doi: 10.1016/S1872-1508(06)60059-4
Abstract:
Structure, electronic state, and energy of semiconductor binary micro-clusters, GaxPy and GaxPy−, having eight atoms have been computed using density functional theory (DFT) method. Structural optimization and frequency analysis are performed at the B3LYP/6-311+G(2df) level. The charged-induced structural changes of these anions have been discussed. The strong Ga—P bond is favored over the P—P bond in GaxPy−(x+y=8), in comparison with the corresponding neutral cluster. The calculations predict the existence of previously unknown isomers (i.e. G a1P7−、Ga2P6−、Ga3P5−、Ga6P2−, and Ga7P1−). Among different GaxPy and GaxPy− (x+y=8) clusters, Ga4P4 and Ga4P4− are more stable. Two types of energy separations are reported in this study, adiabatic electron affinities (ΔEAEA) and vertical detachment energies (ΔEVDE), wherever applicalde, and are compared with those described in other published data in the literature. Adiabatic electron affinities for Ga4P4 and Ga5P3 are in od agreement with those obtained in the experiments. Mulliken population analyses indicate that the bonding in GaP clusters is of a mixed type.
Structure, electronic state, and energy of semiconductor binary micro-clusters, GaxPy and GaxPy−, having eight atoms have been computed using density functional theory (DFT) method. Structural optimization and frequency analysis are performed at the B3LYP/6-311+G(2df) level. The charged-induced structural changes of these anions have been discussed. The strong Ga—P bond is favored over the P—P bond in GaxPy−(x+y=8), in comparison with the corresponding neutral cluster. The calculations predict the existence of previously unknown isomers (i.e. G a1P7−、Ga2P6−、Ga3P5−、Ga6P2−, and Ga7P1−). Among different GaxPy and GaxPy− (x+y=8) clusters, Ga4P4 and Ga4P4− are more stable. Two types of energy separations are reported in this study, adiabatic electron affinities (ΔEAEA) and vertical detachment energies (ΔEVDE), wherever applicalde, and are compared with those described in other published data in the literature. Adiabatic electron affinities for Ga4P4 and Ga5P3 are in od agreement with those obtained in the experiments. Mulliken population analyses indicate that the bonding in GaP clusters is of a mixed type.
2006, 22(10): 1260-1265
doi: 10.1016/S1872-1508(06)60060-0
Abstract:
Kinetics of the reaction of ozone with propylene under real atmospheric environmental conditions with an ozone concentration of ca 6.6×10−8 has been investigated in a self-made Teflon Chamber. Using Model 49C-O3 Analyzer and GC-FID, reaction rate constants at temperature range of 282~314 K are determined by an absolute rate technique in terms of measurement of ozone concentrations. Results show that the reaction rate constant is 6.73×10−18 cm3•molecule−1•s−1 for the initial ozone concentration of 6.61×10−8 and the temperature of 282 K. According to the reaction rate constants under different temperatures, the Arrhenius equation of k2=(5.8±1.2)×10−15e(−1907±53)/T is obtained. Compared with the results reported by other researchers, although the rate constants obtained in this study are systematically underestimated and the activation energy of the reaction overestimated, the results are satisfactory. For example, the largest relative error is only 11% and 5% for the rate constant and activation energy, respectively. These demonstrate that the research equipment used in this study is reliable under real atmospheric conditions and can be used to do further studies related to ozone reactions.
Kinetics of the reaction of ozone with propylene under real atmospheric environmental conditions with an ozone concentration of ca 6.6×10−8 has been investigated in a self-made Teflon Chamber. Using Model 49C-O3 Analyzer and GC-FID, reaction rate constants at temperature range of 282~314 K are determined by an absolute rate technique in terms of measurement of ozone concentrations. Results show that the reaction rate constant is 6.73×10−18 cm3•molecule−1•s−1 for the initial ozone concentration of 6.61×10−8 and the temperature of 282 K. According to the reaction rate constants under different temperatures, the Arrhenius equation of k2=(5.8±1.2)×10−15e(−1907±53)/T is obtained. Compared with the results reported by other researchers, although the rate constants obtained in this study are systematically underestimated and the activation energy of the reaction overestimated, the results are satisfactory. For example, the largest relative error is only 11% and 5% for the rate constant and activation energy, respectively. These demonstrate that the research equipment used in this study is reliable under real atmospheric conditions and can be used to do further studies related to ozone reactions.
2006, 22(10): 1266-1271
doi: 10.1016/S1872-1508(06)60061-2
Abstract:
The mechanisms of the reactions of the radicals (•OH and •NO2) derived from peroxynitrous acid with phenol have been studied using density functional theory (DFT) at the B3LYP/6-311++G(d, p)//B3LYP/6-311G(d, p) level. The geometries of all the molecules were optimized, and the harmonic vibration frequencies and the energies were calculated as well. The calculation results show that the primary products of the reaction of peroxynitrous acid and phenol are o-hydroxyphenol and p-hydroxyphenol, due to their relatively lower activation barriers. The conclusion is in od agreement with the corresponding experimental data. In addition, the effects of solvents on these reactions were also investigated. The results suggest that polar solvents can reduce the activation energy and hence facillate the occurrence of reactions.
The mechanisms of the reactions of the radicals (•OH and •NO2) derived from peroxynitrous acid with phenol have been studied using density functional theory (DFT) at the B3LYP/6-311++G(d, p)//B3LYP/6-311G(d, p) level. The geometries of all the molecules were optimized, and the harmonic vibration frequencies and the energies were calculated as well. The calculation results show that the primary products of the reaction of peroxynitrous acid and phenol are o-hydroxyphenol and p-hydroxyphenol, due to their relatively lower activation barriers. The conclusion is in od agreement with the corresponding experimental data. In addition, the effects of solvents on these reactions were also investigated. The results suggest that polar solvents can reduce the activation energy and hence facillate the occurrence of reactions.
2006, 22(10): 1272-1276
doi: 10.1016/S1872-1508(06)60062-4
Abstract:
Highly dispersed supported ionic liquid-phase palladium catalyst was prepared and its catalytic performances for carbonylation of aryl halide were investigated. Active-carbon supported ionic liquid-phase palladium catalyst was characterized by XRD, high-resolution TEM (HRTEM), and XPS. The results showed that the active-carbon supported ionic liquid-phase palladium catalyst was reduced to zero valence and that the average particle diameter of the Pd crystallites was less than 5 nm. A thin ionic liquid film was observed on the surface of the catalyst. The results indicated that the supported ionic liquid-phase palladium catalyst exhibited higher activity in the carbonylation of aryl halides compared with the correspording organic-ionic liquid biphasic system. Under the optimum reaction conditions: 140 ℃, pCO=4.0 MPa, n(PhI):n(Pd)=10528:1, the turnover frequency(TOF) of 4926 h−1 was achieved for ethyl benzoate, with the conversion of 99.3%, and the selectivity for forming ethyl benzoate was more than 99%.
Highly dispersed supported ionic liquid-phase palladium catalyst was prepared and its catalytic performances for carbonylation of aryl halide were investigated. Active-carbon supported ionic liquid-phase palladium catalyst was characterized by XRD, high-resolution TEM (HRTEM), and XPS. The results showed that the active-carbon supported ionic liquid-phase palladium catalyst was reduced to zero valence and that the average particle diameter of the Pd crystallites was less than 5 nm. A thin ionic liquid film was observed on the surface of the catalyst. The results indicated that the supported ionic liquid-phase palladium catalyst exhibited higher activity in the carbonylation of aryl halides compared with the correspording organic-ionic liquid biphasic system. Under the optimum reaction conditions: 140 ℃, pCO=4.0 MPa, n(PhI):n(Pd)=10528:1, the turnover frequency(TOF) of 4926 h−1 was achieved for ethyl benzoate, with the conversion of 99.3%, and the selectivity for forming ethyl benzoate was more than 99%.
2006, 22(10): 1277-1280
doi: 10.3866/PKU.WHXB20061020
Abstract:
The dilution enthalpies of myo-inositol in water and in aqueous sodium halide solutions have been determined with flow-mix-isothermal microcalorimetry at 298.15 K. The enthalpic interaction coefficients in the range of sodium halide solutions have been calculated according to the McMillan-Mayer theory. The results show that enthalpic pairwise interaction coefficients (h2) of myo-inositol are negative in aqueous sodium halide solutions and absolute values of h2 increase with elongation of radius of halogen anion.
The dilution enthalpies of myo-inositol in water and in aqueous sodium halide solutions have been determined with flow-mix-isothermal microcalorimetry at 298.15 K. The enthalpic interaction coefficients in the range of sodium halide solutions have been calculated according to the McMillan-Mayer theory. The results show that enthalpic pairwise interaction coefficients (h2) of myo-inositol are negative in aqueous sodium halide solutions and absolute values of h2 increase with elongation of radius of halogen anion.
2006, 22(10): 1281-1286
doi: 10.3866/PKU.WHXB20061021
Abstract:
A transient analysis method, based on the coulostatic impulse technique, is developed. This method can compute the polarization resistance and Tafel slopes by analyzing the coulostatically-induced transients with different amplitude over-potential decay and, on the ground of their knowledge, evaluate the corrosion current, icorr. The experimental application concerns the behavior of carbon steel in natural seawater. Experimental results for carbon steel exposed to natural seawater show od agreement between the proposed method and the steady-state polarization curves method with concentration polarization consideration. Additionally, the cathodic Tafel slopes obtained by the coulostatic strong polarization integral (CSPI) method are closer to the theoretical values associated with the oxygen reduction reaction. Therefore, the coulostatic method is very useful in evaluation of the electrochemical corrosion parameters in mixture controlled systems, which enable us to minimize the effect of concentration polarization.
A transient analysis method, based on the coulostatic impulse technique, is developed. This method can compute the polarization resistance and Tafel slopes by analyzing the coulostatically-induced transients with different amplitude over-potential decay and, on the ground of their knowledge, evaluate the corrosion current, icorr. The experimental application concerns the behavior of carbon steel in natural seawater. Experimental results for carbon steel exposed to natural seawater show od agreement between the proposed method and the steady-state polarization curves method with concentration polarization consideration. Additionally, the cathodic Tafel slopes obtained by the coulostatic strong polarization integral (CSPI) method are closer to the theoretical values associated with the oxygen reduction reaction. Therefore, the coulostatic method is very useful in evaluation of the electrochemical corrosion parameters in mixture controlled systems, which enable us to minimize the effect of concentration polarization.
2006, 22(10): 1287-1290
doi: 10.3866/PKU.WHXB20061022
Abstract:
The dissolution kinetics of calcined ulexite in ammonium chloride solutions at high solid-to-liquid ratios were investigated. In the experiments, calcination temperature, solution concentration, reaction temperature, and pre-hydration were chosen as parameters. It was observed that the dissolution rate increased with increasing calcination temperature, solution concentration, and reaction temperature, whereas it was not affected by pre-hydration. Employing graphical and statistic methods, the dissolution rate, based on homogeneous reaction model, can be given as: (1−X(B2O3))−1−1=k(c(NH4Cl))1.982t. The activation energy for the dissolution of the ulexite sample calcined at 160 ℃ was found to be 84.04 kJ•mol−1.
2006, 22(10): 1291-1295
doi: 10.3866/PKU.WHXB20061023
Abstract:
ZnGa2O4:Cr3+ red phosphors were synthesized by citric-gel method. Typical spinel-phase ZnGa2O4 could be attained after calcined at 1000 ℃ in air ambient. According to the results of XPS and EPR, it could be deduced that Cr3+ ions were dominant in the lattice and it could not be oxidized to Cr5+ or Cr6+ after calcined in air. The emission of Cr3+ at 695 nm is originated from the transition of 2E-4A2. And due to the large overlap between absorption band of Cr3+ and emission band of the host, Cr3+ could obtain the excitation energy from the host via the effective energy transfer. The electroluminescent device was fabricated by screen printing utilizing ZnGa2O4:Cr3+ as the phosphor layer. Luminance (L) versus voltage (V) of the device match the well-known equation of L=L0exp(−bV−1/2) and the luminance increase proportionally with frequency due to the increase of excitation probability of host lattice or Cr3+ centers. The diagram of charge density (Q) versus applied voltage (V) is based on a conventional Sawyer-Tower circuit. At 280 V and 1000 Hz, the luminance and luminous efficiency of the fabricated powder EL device are about 1.0 cd•m−2 and 13 lm•W−1, respectively.
ZnGa2O4:Cr3+ red phosphors were synthesized by citric-gel method. Typical spinel-phase ZnGa2O4 could be attained after calcined at 1000 ℃ in air ambient. According to the results of XPS and EPR, it could be deduced that Cr3+ ions were dominant in the lattice and it could not be oxidized to Cr5+ or Cr6+ after calcined in air. The emission of Cr3+ at 695 nm is originated from the transition of 2E-4A2. And due to the large overlap between absorption band of Cr3+ and emission band of the host, Cr3+ could obtain the excitation energy from the host via the effective energy transfer. The electroluminescent device was fabricated by screen printing utilizing ZnGa2O4:Cr3+ as the phosphor layer. Luminance (L) versus voltage (V) of the device match the well-known equation of L=L0exp(−bV−1/2) and the luminance increase proportionally with frequency due to the increase of excitation probability of host lattice or Cr3+ centers. The diagram of charge density (Q) versus applied voltage (V) is based on a conventional Sawyer-Tower circuit. At 280 V and 1000 Hz, the luminance and luminous efficiency of the fabricated powder EL device are about 1.0 cd•m−2 and 13 lm•W−1, respectively.
2006, 22(10): 1296-1299
doi: 10.3866/PKU.WHXB20061024
Abstract:
Patterned DR(diazoresin)/PAA(polyacrylic acid) SA(self-assembly) film was used as template on which a patterned DNA film was prepared by alternate deposition of DNA and PDDA(polydimethyldiallylammonium chloride). Then a patterned Ag film was obtained by means of Ag electroless deposition in the DNA patterned film. After surface modification with n-dodecanethiol the patterned Ag film, which exhibits obvious microstructure and nanostrucutre, will possess super hydrophobic properties and the contact angle of water on this surface can reach to about 168°.
Patterned DR(diazoresin)/PAA(polyacrylic acid) SA(self-assembly) film was used as template on which a patterned DNA film was prepared by alternate deposition of DNA and PDDA(polydimethyldiallylammonium chloride). Then a patterned Ag film was obtained by means of Ag electroless deposition in the DNA patterned film. After surface modification with n-dodecanethiol the patterned Ag film, which exhibits obvious microstructure and nanostrucutre, will possess super hydrophobic properties and the contact angle of water on this surface can reach to about 168°.
2006, 22(10): 1300-1304
doi: 10.1016/S1872-1508(06)60063-6
Abstract:
Growth of polyoxomolybdate (POM) clusters and the main role of penta nal {(Mo)Mo5}-type building blocks in the construction principle for nanoscale inorganic polyoxomolybdate compounds were introduced. The peculiar self-assembly of the nanoscale inorganic ions in aqueous solutions was reviewed. The concepts of “second organized structures” of nanoscale inorganic molybdenum compounds and the mixtures of POMs/surfactants were proposed.
