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2008 Volume 24 Issue 10
2008, 24(10):
Abstract:
2008, 24(10): 1739-1744
doi: 10.1016/S1872-1508(08)60069-8
Abstract:
Dissociative adsorption and electrooxidation of dimethyl ether (DME) on a platinumelectrode in different pH solutions were studied using cyclic voltammetry (CV) and in situ FTIR reflection spectroscopy. The coverage of the dissociative adsorbed species was measured about 70% from hydrogen adsorption-desorption region (0.05-0.35 V(vs RHE)) of steady-state voltammogram recorded in 0.1 mol·L-1 H2SO4 solution. It was found that the electrochemical reactivity of DME was pH dependent, i.e., the larger the pH value was, the less the reactivity of DME would be. No perceptible reactivity of DME in 0.1 mol·L-1NaOHsolution could be detected. It was revealed that the protonation of the oxygen atom in the C—O—C bond played a key role in the electrooxidation of DME. In situ FTIR spectroscopic results illustrated that linearly bonded CO (COL) species determined at low potential region were derived from the dissociative adsorption of DME and behaved as‘poisoning’intermediate. The COL species could be oxidized to CO2 at potential higher than 0.55 V (vs RHE), and in the potential range from 0.75 to 1.00 V (vs RHE) DME was oxidized simultaneously via HCOOH species that were identified as the reactive intermediates.
Dissociative adsorption and electrooxidation of dimethyl ether (DME) on a platinumelectrode in different pH solutions were studied using cyclic voltammetry (CV) and in situ FTIR reflection spectroscopy. The coverage of the dissociative adsorbed species was measured about 70% from hydrogen adsorption-desorption region (0.05-0.35 V(vs RHE)) of steady-state voltammogram recorded in 0.1 mol·L-1 H2SO4 solution. It was found that the electrochemical reactivity of DME was pH dependent, i.e., the larger the pH value was, the less the reactivity of DME would be. No perceptible reactivity of DME in 0.1 mol·L-1NaOHsolution could be detected. It was revealed that the protonation of the oxygen atom in the C—O—C bond played a key role in the electrooxidation of DME. In situ FTIR spectroscopic results illustrated that linearly bonded CO (COL) species determined at low potential region were derived from the dissociative adsorption of DME and behaved as‘poisoning’intermediate. The COL species could be oxidized to CO2 at potential higher than 0.55 V (vs RHE), and in the potential range from 0.75 to 1.00 V (vs RHE) DME was oxidized simultaneously via HCOOH species that were identified as the reactive intermediates.
2008, 24(10): 1745-1750
doi: 10.1016/S1872-1508(08)60070-4
Abstract:
Mj HSP16.5 is a small heat shock protein (sHSP) from the hyperthermophilic methanoarchaeon, Methanococcus jannaschii (Mj), which lives at the environment of high temperature up to 94 ℃. The structural data showed that Mj HSP16.5 was a 24-mer that formed a hollow sphere with octahedral symmetry. Mj HSP16.5 was very stable at pH 7 that it maintained the 24-mer structure even at 85 ℃. In the present study, we investigated the unfolding process of Mj HSP16.5 in the presence of denaturants using several techniques, including circular dichroism (CD), dynamic light scattering (DLS), fluorescence spectroscopy, and size exclusive chromatography (SEC). We found that 8 mol·L-1 urea had no obvious effect on the structure of Mj HSP16.5 at pH 7. The unfolding of Mj HSP16.5 at pH 7 in the presence of guanidine hydrochloride (GdHCl) showed hierarchical behavior. Three significant transitions were observed around 2.0, 3.0, and 6.0 mol·L-1 GdHCl at pH 7. ANS (8-anilino-1-naphthalenesulfonic acid) titration results showed that the binding ability of Mj HSP16.5 to ANS decreased gradually as the concentration of GdHCl increased until around 2.0 mol·L-1 GdHCl, indicating surface hydrophobic area change, and this first transition was companioned with precipitation of Mj HSP16.5. Acrylamide quenching of fluorescence showed that the Stern-Volmer constant changed at about 3.0 mol·L -1 GdHCl, indicating changes of the dimeric interface, and this phase transition was companioned with oli meric state change from 24-mer to small oli mers (4-mer to 8-mer). The last unfolding phase started around 5.0 mol·L-1GdHCl, with a midpoint of 6.1 mol·L-1 GdHCl, and Mj HSP16.5 was completely unfolded at 7.0 mol·L -1 GdHCl. We also found that Mj HSP16.5 could be quite easily unfolded at pH 3, where it could be completely unfolded in 4.0 mol·L-1 GdHCl.
Mj HSP16.5 is a small heat shock protein (sHSP) from the hyperthermophilic methanoarchaeon, Methanococcus jannaschii (Mj), which lives at the environment of high temperature up to 94 ℃. The structural data showed that Mj HSP16.5 was a 24-mer that formed a hollow sphere with octahedral symmetry. Mj HSP16.5 was very stable at pH 7 that it maintained the 24-mer structure even at 85 ℃. In the present study, we investigated the unfolding process of Mj HSP16.5 in the presence of denaturants using several techniques, including circular dichroism (CD), dynamic light scattering (DLS), fluorescence spectroscopy, and size exclusive chromatography (SEC). We found that 8 mol·L-1 urea had no obvious effect on the structure of Mj HSP16.5 at pH 7. The unfolding of Mj HSP16.5 at pH 7 in the presence of guanidine hydrochloride (GdHCl) showed hierarchical behavior. Three significant transitions were observed around 2.0, 3.0, and 6.0 mol·L-1 GdHCl at pH 7. ANS (8-anilino-1-naphthalenesulfonic acid) titration results showed that the binding ability of Mj HSP16.5 to ANS decreased gradually as the concentration of GdHCl increased until around 2.0 mol·L-1 GdHCl, indicating surface hydrophobic area change, and this first transition was companioned with precipitation of Mj HSP16.5. Acrylamide quenching of fluorescence showed that the Stern-Volmer constant changed at about 3.0 mol·L -1 GdHCl, indicating changes of the dimeric interface, and this phase transition was companioned with oli meric state change from 24-mer to small oli mers (4-mer to 8-mer). The last unfolding phase started around 5.0 mol·L-1GdHCl, with a midpoint of 6.1 mol·L-1 GdHCl, and Mj HSP16.5 was completely unfolded at 7.0 mol·L -1 GdHCl. We also found that Mj HSP16.5 could be quite easily unfolded at pH 3, where it could be completely unfolded in 4.0 mol·L-1 GdHCl.
2008, 24(10): 1751-1755
doi: 10.1016/S1872-1508(08)60071-6
Abstract:
Pure TiO2 and La-doped TiO2 were prepared by the sol-gel method. Au was supported on TiO2 by the deposition-precipitation (DP) method, and its catalytic activity for CO oxidation was tested. The results showed that doping La in Au/TiO2 could improve its catalytic activity obviously for CO oxidation. The analyses of X-ray diffraction (XRD), temperature-programmed desorption (TPD), and Brunauer-Emmett-Teller (BET) surface area further showed that the presence of La in TiO2 not only increased its surface area and restrained the growth of TiO2 crystallites, but could also enhance the microstrain of TiO2. In terms of O2-TPD, a new adsorbed species O- appeared on the surface of La-doped TiO2. The results of in-situ Fourier transform-infrared (FT-IR) spectroscopy illustrated that the high activity of Au/La2O3-TiO2 was attributed to the presence of La promoting the reactivity of CO adsorbed on the Au site and the formation of the second active site on the surface of TiO2.
Pure TiO2 and La-doped TiO2 were prepared by the sol-gel method. Au was supported on TiO2 by the deposition-precipitation (DP) method, and its catalytic activity for CO oxidation was tested. The results showed that doping La in Au/TiO2 could improve its catalytic activity obviously for CO oxidation. The analyses of X-ray diffraction (XRD), temperature-programmed desorption (TPD), and Brunauer-Emmett-Teller (BET) surface area further showed that the presence of La in TiO2 not only increased its surface area and restrained the growth of TiO2 crystallites, but could also enhance the microstrain of TiO2. In terms of O2-TPD, a new adsorbed species O- appeared on the surface of La-doped TiO2. The results of in-situ Fourier transform-infrared (FT-IR) spectroscopy illustrated that the high activity of Au/La2O3-TiO2 was attributed to the presence of La promoting the reactivity of CO adsorbed on the Au site and the formation of the second active site on the surface of TiO2.
2008, 24(10): 1756-1760
doi: 10.3866/PKU.WHXB20081004
Abstract:
The structures of some energetic azo-compounds, e.g. azobenzene derivatives, azofurazan, azotriazine, and azotetrazine, were optimized using density functional theory at B3LYP/6-31G* level. A second-order Mφller-Plesset perturbation theory (MP2) calculation with 6-31G* basis set was carried out in order to obtain more precise relative energy between the trans-and cis-isomers of azo-compounds. It was found that a correlation existed between the relative energy and the sensitivity for these energetic azo-compounds. The higher the relative energy is, the lower the sensitivity of the azo-compound is. The relative energy could be regarded as one of the parameters that evaluated the sensitivity of energetic azo-compounds. Furthermore, by analyzing the mechanism of how the trans-cis isomerization process influences the sensitivity, we proposed that the energetic azo-compound owned the characteristic of self-desensitivity.
The structures of some energetic azo-compounds, e.g. azobenzene derivatives, azofurazan, azotriazine, and azotetrazine, were optimized using density functional theory at B3LYP/6-31G* level. A second-order Mφller-Plesset perturbation theory (MP2) calculation with 6-31G* basis set was carried out in order to obtain more precise relative energy between the trans-and cis-isomers of azo-compounds. It was found that a correlation existed between the relative energy and the sensitivity for these energetic azo-compounds. The higher the relative energy is, the lower the sensitivity of the azo-compound is. The relative energy could be regarded as one of the parameters that evaluated the sensitivity of energetic azo-compounds. Furthermore, by analyzing the mechanism of how the trans-cis isomerization process influences the sensitivity, we proposed that the energetic azo-compound owned the characteristic of self-desensitivity.
2008, 24(10): 1761-1766
doi: 10.1016/S1872-1508(08)60072-8
Abstract:
YFeO3 was prepared by coprecipitation method and citric acid method, and TiO2/YFeO3 heterosystem photocatalysts were synthesized by loading TiO2 sol on the surface of YFeO3 via sol-gel method. Their photocatalytic activities were evaluated by the decomposition of gaseous benzene under UV light illumination. The prepared photocatalysts were characterized by nitrogen adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy. Results revealed that the heterosystem photocatalysts prepared by coprecipitation method showed higher activity, and the maximumconversion of benzene could reach 44.7% within 180 min. The YFeO3 samples prepared fromcoprecipitation method and citric acid method were absolutely in orthorhombic phase. The deposited titania was dispersed on the surface of carrier and a certain interaction existed between TiO2 and YFeO3. The two heterosystemphotocatalysts had narrow band-gap energies.
YFeO3 was prepared by coprecipitation method and citric acid method, and TiO2/YFeO3 heterosystem photocatalysts were synthesized by loading TiO2 sol on the surface of YFeO3 via sol-gel method. Their photocatalytic activities were evaluated by the decomposition of gaseous benzene under UV light illumination. The prepared photocatalysts were characterized by nitrogen adsorption-desorption, X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy. Results revealed that the heterosystem photocatalysts prepared by coprecipitation method showed higher activity, and the maximumconversion of benzene could reach 44.7% within 180 min. The YFeO3 samples prepared fromcoprecipitation method and citric acid method were absolutely in orthorhombic phase. The deposited titania was dispersed on the surface of carrier and a certain interaction existed between TiO2 and YFeO3. The two heterosystemphotocatalysts had narrow band-gap energies.
2008, 24(10): 1767-1772
doi: 10.3866/PKU.WHXB20081006
Abstract:
Photoionization and photodissociation of diethylzinc (ZnC4H10) were performed using vacuum ultraviolet (VUV) synchrotron radiation and a time-of-flight mass spectrometer (TOF-MS). The photoionization mass spectra of all the observed ions fromdiethylzinc and their photoionization efficiency (PIE) curves with the photon energy from8 to 22 eV were measured. From their PIE curves, the ionization potential (IP) of ZnC4H10 (IP=8.20±0.05 eV) and appearance potentials of fragment ions (ZnC2H5+, ZnH+, Zn+, C2H5+, C2H3+, etc.) were obtained. According to the gas phase energetic data from references, the formation enthalpies of chief ions were evaluated and their possible channels of dissociative photoionization as well as their branch rates were discussed. The results indicated that the chief channels were the simple cleavage of Zn—C bond in the parent ions to form fragmental ions C2H5+ and ZnC2H5+ which further dissociated to Zn+ ion. More than 75%of the total production ions belonged to Zn-containing ions.
Photoionization and photodissociation of diethylzinc (ZnC4H10) were performed using vacuum ultraviolet (VUV) synchrotron radiation and a time-of-flight mass spectrometer (TOF-MS). The photoionization mass spectra of all the observed ions fromdiethylzinc and their photoionization efficiency (PIE) curves with the photon energy from8 to 22 eV were measured. From their PIE curves, the ionization potential (IP) of ZnC4H10 (IP=8.20±0.05 eV) and appearance potentials of fragment ions (ZnC2H5+, ZnH+, Zn+, C2H5+, C2H3+, etc.) were obtained. According to the gas phase energetic data from references, the formation enthalpies of chief ions were evaluated and their possible channels of dissociative photoionization as well as their branch rates were discussed. The results indicated that the chief channels were the simple cleavage of Zn—C bond in the parent ions to form fragmental ions C2H5+ and ZnC2H5+ which further dissociated to Zn+ ion. More than 75%of the total production ions belonged to Zn-containing ions.
2008, 24(10): 1773-1779
doi: 10.3866/PKU.WHXB20081007
Abstract:
The samples containing nickel phosphide precursors were synthesized by co-impregnation method using mesoporous molecular sieve SBA-15 as support, nickel nitrate as nickel source, and (NH4)2HPO4 as phosphorus source. Then, the Ni2P/SBA-15 catalysts with different Ni2P contents were prepared by temperature-programmed reduction method in H2 flow. The structure of the catalysts was characterized using X-ray diffraction (XRD), N2 adsorption/desorption, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) techniques. The catalytic performances of hydrodesulfurization (HDS) were evaluated in a fixed-bed micro-reactor using thiophene and dibenzothiophene (DBT) as the model compounds. The results indicated that the mesoporous structure of SBA-15 was still preserved in the Ni2P/SBA-15 catalysts. The active component Ni2P was well dispersed on the surface of the catalysts. The BET surface area, pore volume, and pore diameter decreased obviously with the increase of Ni2P loading. The Ni2P/SBA-15 catalysts had the better catalytic performance at 320 ℃ when Ni2P loading was from 15% to 25% (w, mass fraction) . All of the catalysts showed an excellent deep HDS performance when reaction temperature was higher than 360 ℃. The mechanism of the HDS of DBT was the main direct desulfurization (DDS) over the Ni2P/SBA-15 catalysts.
The samples containing nickel phosphide precursors were synthesized by co-impregnation method using mesoporous molecular sieve SBA-15 as support, nickel nitrate as nickel source, and (NH4)2HPO4 as phosphorus source. Then, the Ni2P/SBA-15 catalysts with different Ni2P contents were prepared by temperature-programmed reduction method in H2 flow. The structure of the catalysts was characterized using X-ray diffraction (XRD), N2 adsorption/desorption, transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) techniques. The catalytic performances of hydrodesulfurization (HDS) were evaluated in a fixed-bed micro-reactor using thiophene and dibenzothiophene (DBT) as the model compounds. The results indicated that the mesoporous structure of SBA-15 was still preserved in the Ni2P/SBA-15 catalysts. The active component Ni2P was well dispersed on the surface of the catalysts. The BET surface area, pore volume, and pore diameter decreased obviously with the increase of Ni2P loading. The Ni2P/SBA-15 catalysts had the better catalytic performance at 320 ℃ when Ni2P loading was from 15% to 25% (w, mass fraction) . All of the catalysts showed an excellent deep HDS performance when reaction temperature was higher than 360 ℃. The mechanism of the HDS of DBT was the main direct desulfurization (DDS) over the Ni2P/SBA-15 catalysts.
2008, 24(10): 1780-1784
doi: 10.3866/PKU.WHXB20081008
Abstract:
Two-photon absorption (TPA) properties of multibranch chromophores with nitrogen coupling center, N-[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl]-N,N-diphenylamine (BPODPA), N,N-bis[4-{2(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl]-N-phenylamine (BBPOPA) and N,N,N-tris[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl] amine (TBPOA), were measured by nonlinear transmission method. Single photon excited fluorescence and two-photon excited fluorescence (TPEF) of the chromophores were studied. The effect of dendronization on the TPA and TPEF characters of triphenylamine-based chromophores was investigated. When pumped with 800 nm laser irradiation, chromophores BPODPA, BBPOPA, and TBPOA showed strong two-photon excited blue green fluorescence at 502, 515, and 518 nm, respectively. These multibranched chromophores showed large TPA cross-section. The enhanced two-photon absorption found in these chromophores was attributed to the fact that the multibranched chromophores had both an extended π-conjugated system and an increased intramolecular cooperative effect compared to the one-branched chromophore.
Two-photon absorption (TPA) properties of multibranch chromophores with nitrogen coupling center, N-[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl]-N,N-diphenylamine (BPODPA), N,N-bis[4-{2(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl]-N-phenylamine (BBPOPA) and N,N,N-tris[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl] amine (TBPOA), were measured by nonlinear transmission method. Single photon excited fluorescence and two-photon excited fluorescence (TPEF) of the chromophores were studied. The effect of dendronization on the TPA and TPEF characters of triphenylamine-based chromophores was investigated. When pumped with 800 nm laser irradiation, chromophores BPODPA, BBPOPA, and TBPOA showed strong two-photon excited blue green fluorescence at 502, 515, and 518 nm, respectively. These multibranched chromophores showed large TPA cross-section. The enhanced two-photon absorption found in these chromophores was attributed to the fact that the multibranched chromophores had both an extended π-conjugated system and an increased intramolecular cooperative effect compared to the one-branched chromophore.
2008, 24(10): 1785-1789
doi: 10.3866/PKU.WHXB20081009
Abstract:
The microenvironment of carboxylic acid terminated dendrimers (Gn, n=1-4) was studied by using pyrene and anthracene as probes. The results of fluorescence spectra of pyrene indicated that dendrimers G1-G3 adopted an open structure, and G4 took a more close spherical shape which showed better encapsulation capability. The results of fluorescence spectra of (9-anthrymethyl) trimethylammonium(An) in G2 potassiumaqueous solution indicated that G2 could encapsulate more than two An molecules, and the hydrophobic anthracene moiety and the hydrophilic cation portion of An encapsulated within G2 were located in the interior and the periphery of the dendrimer, respectively.
The microenvironment of carboxylic acid terminated dendrimers (Gn, n=1-4) was studied by using pyrene and anthracene as probes. The results of fluorescence spectra of pyrene indicated that dendrimers G1-G3 adopted an open structure, and G4 took a more close spherical shape which showed better encapsulation capability. The results of fluorescence spectra of (9-anthrymethyl) trimethylammonium(An) in G2 potassiumaqueous solution indicated that G2 could encapsulate more than two An molecules, and the hydrophobic anthracene moiety and the hydrophilic cation portion of An encapsulated within G2 were located in the interior and the periphery of the dendrimer, respectively.
2008, 24(10): 1790-1796
doi: 10.1016/S1872-1508(08)60073-X
Abstract:
This study investigated the coaxial electrospinning process of silver filling in TiO2 ultrafine hollow fibers using polyvinyl pyrrolidone (PVP) sol/titanium n-butyloxide (Ti(OC4H9)4) and PVP sol/silver nanoparticles as pore-directing agents. The bicomponent fibers were heat treated at 200 ℃ and calcined at 600 ℃. Silver particles having diameters of 5 to 40 nm were deposited on the inner surface of the long hollow TiO2 nanofibers (outer diameter of 150-300 nm) with mesoporous walls (thickness of 10-20 nm). The morphological structure of the filled ultrafine hollowfibers has been studied by means of infrared (IR) spectrum, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. Compared with other nanostructured TiO2 materials, such as mesoporous Ag-TiO2 blending fibers, TiO2 hollow nanofibers, TiO2 nanofibers, and TiO2 powders, the silver filled TiO2 hollow fibers exhibited a higher photocatalytic activity toward the degradation of methylene blue.
This study investigated the coaxial electrospinning process of silver filling in TiO2 ultrafine hollow fibers using polyvinyl pyrrolidone (PVP) sol/titanium n-butyloxide (Ti(OC4H9)4) and PVP sol/silver nanoparticles as pore-directing agents. The bicomponent fibers were heat treated at 200 ℃ and calcined at 600 ℃. Silver particles having diameters of 5 to 40 nm were deposited on the inner surface of the long hollow TiO2 nanofibers (outer diameter of 150-300 nm) with mesoporous walls (thickness of 10-20 nm). The morphological structure of the filled ultrafine hollowfibers has been studied by means of infrared (IR) spectrum, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The diameters and wall thicknesses of the hollow fibers could be tuned by adjusting the electrospinning parameters. Compared with other nanostructured TiO2 materials, such as mesoporous Ag-TiO2 blending fibers, TiO2 hollow nanofibers, TiO2 nanofibers, and TiO2 powders, the silver filled TiO2 hollow fibers exhibited a higher photocatalytic activity toward the degradation of methylene blue.
2008, 24(10): 1797-1802
doi: 10.3866/PKU.WHXB20081011
Abstract:
Geometry optimizations and frequency calculations of three (C^N)PtIIQtype complexes in the ground state were performed at the level of B3LYP/LANL2DZ, and their absorption properties in dichloromethane (CH2Cl2) media were calculated by using time-dependent density functional theory (TD-DFT) associated with the polarized continuum model (PCM). The optimized structures and calculated absorption spectra were in reasonable agreement with experimental data. All the complexes had relative strong absorption and broad absorption bands in visible region. The lowest-energy absorption bands of (C^N)PtIIQ type complexes exhibited ILCT (intra-ligand charge transfer) mixed with partially MLCT (metal-to-ligand charge transfer) characteristic, and showed different transition mechanisms compared with those of PtIIQ2 type complexes, whose lowest energy absorption bands were usually dominated by ILCT transitions.
Geometry optimizations and frequency calculations of three (C^N)PtIIQtype complexes in the ground state were performed at the level of B3LYP/LANL2DZ, and their absorption properties in dichloromethane (CH2Cl2) media were calculated by using time-dependent density functional theory (TD-DFT) associated with the polarized continuum model (PCM). The optimized structures and calculated absorption spectra were in reasonable agreement with experimental data. All the complexes had relative strong absorption and broad absorption bands in visible region. The lowest-energy absorption bands of (C^N)PtIIQ type complexes exhibited ILCT (intra-ligand charge transfer) mixed with partially MLCT (metal-to-ligand charge transfer) characteristic, and showed different transition mechanisms compared with those of PtIIQ2 type complexes, whose lowest energy absorption bands were usually dominated by ILCT transitions.
2008, 24(10): 1803-1810
doi: 10.3866/PKU.WHXB20081012
Abstract:
The complex model structure of human immunodeficiency virus-1 (HIV-1) DNA with integrase (IN) dimer (IN2) was refined through molecular dynamics (MD) simulation, and the viral DNAconformational change was explored after binding with IN2. The result showed that the viral DNA could be divided into five regions (i.e. non-binding region, high-affinity region 1, weak-affinity region, high-affinity region 2, and reaction region) according to the binding power with IN2. The partition rationality for viral DNA was confirmed through binding free energy computation. Compared with the viral DNA before binding with IN2, some big conformational changes occurred for the bases in the four binding regions other than the non-binding region for the viral DNA complexed with IN2. The obvious deviation from standard B-DNA in the viral DNA main chain of the complex and the broading of the minor groove in the binding site were both the structural basis for the recognition of viral DNA with IN. The simulation results basically agreed with experimental data, which provided some structural information for the drug design based on the structure of HIV-1 IN.
The complex model structure of human immunodeficiency virus-1 (HIV-1) DNA with integrase (IN) dimer (IN2) was refined through molecular dynamics (MD) simulation, and the viral DNAconformational change was explored after binding with IN2. The result showed that the viral DNA could be divided into five regions (i.e. non-binding region, high-affinity region 1, weak-affinity region, high-affinity region 2, and reaction region) according to the binding power with IN2. The partition rationality for viral DNA was confirmed through binding free energy computation. Compared with the viral DNA before binding with IN2, some big conformational changes occurred for the bases in the four binding regions other than the non-binding region for the viral DNA complexed with IN2. The obvious deviation from standard B-DNA in the viral DNA main chain of the complex and the broading of the minor groove in the binding site were both the structural basis for the recognition of viral DNA with IN. The simulation results basically agreed with experimental data, which provided some structural information for the drug design based on the structure of HIV-1 IN.
2008, 24(10): 1811-1816
doi: 10.1016/S1872-1508(08)60074-1
Abstract:
The regioselectivity of Diels-Alder cycloaddition of 1,3-butadiene to C59XH (X=N, B) has been studied theoretically by means of the semiempirical AM1 and DFT (B3LYP/6-31G*) methods. The mechanisms of the cycloaddition on some selected 6—6 bonds of C59XH (X=N, B) have been analyzed. For C59NH, the activation energies become lower with the addition site increasingly farther fromthe N atom; however, they are all higher than that of the reaction of 1,3-butadiene with C60. In contrast to C59NH, for the cycloaddition to C59BH, the activation energies corresponding to 2,12/r-and 2,12/f-transition states, in which the addition sites are the nearest ones to the B atom, are the lowest ones,and are lower than that of the reaction of 1,3-butadiene with C60 by over 18 kJ·mol-1, and the products corresponding to these two transition states are the most stable ones. The different electronic natures ofNandB atoms results in different effects on the Diels-Alder reactions of 1,3-butadiene with C59NH and C59BH; the former makes the reactivity of C59NH reduced and the latter makes the reactivity of C59BH enhanced, relative to that of C60.
The regioselectivity of Diels-Alder cycloaddition of 1,3-butadiene to C59XH (X=N, B) has been studied theoretically by means of the semiempirical AM1 and DFT (B3LYP/6-31G*) methods. The mechanisms of the cycloaddition on some selected 6—6 bonds of C59XH (X=N, B) have been analyzed. For C59NH, the activation energies become lower with the addition site increasingly farther fromthe N atom; however, they are all higher than that of the reaction of 1,3-butadiene with C60. In contrast to C59NH, for the cycloaddition to C59BH, the activation energies corresponding to 2,12/r-and 2,12/f-transition states, in which the addition sites are the nearest ones to the B atom, are the lowest ones,and are lower than that of the reaction of 1,3-butadiene with C60 by over 18 kJ·mol-1, and the products corresponding to these two transition states are the most stable ones. The different electronic natures ofNandB atoms results in different effects on the Diels-Alder reactions of 1,3-butadiene with C59NH and C59BH; the former makes the reactivity of C59NH reduced and the latter makes the reactivity of C59BH enhanced, relative to that of C60.
2008, 24(10): 1817-1823
doi: 10.3866/PKU.WHXB20081014
Abstract:
Three different calciumoxide catalysts were synthesized fromdifferent precursors and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed desorption (TPD). They were used as catalysts in the transesterification of soybean oil (SBO) for the production of fatty acid methyl esters (FAME), namely biodiesel. Calciumoxide fromcalcite (Cal(N)) showed the highest activity towards the transesterification of SBO. The transesterification activity of CaO was found to be highly related to the basicity of the catalysts. The catalytic activity of CaO greatly decreased when CaO was exposed to CO2. (Raman spectroscopic studies demonstrated that the formation of CaCO3 and Ca(OH)2 on the surface of CaO when CaO was exposed to room air prevented CaO from participating in the transesterification of SBO). The degree of poisoning was highly dependent on the type of precursors with Cal(N) more resistant to CO2 poisoning than CaO from ara nite (Ara(N)). Deactivated CaO catalysts could be partially regenerated. A mechanism was proposed to explain the poisoning and regenerating processes. Furthermore, whether the solid phase of CaO or dissolved CaO was the active species in the transesterification of SBO was also investigated.
Three different calciumoxide catalysts were synthesized fromdifferent precursors and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and temperature-programmed desorption (TPD). They were used as catalysts in the transesterification of soybean oil (SBO) for the production of fatty acid methyl esters (FAME), namely biodiesel. Calciumoxide fromcalcite (Cal(N)) showed the highest activity towards the transesterification of SBO. The transesterification activity of CaO was found to be highly related to the basicity of the catalysts. The catalytic activity of CaO greatly decreased when CaO was exposed to CO2. (Raman spectroscopic studies demonstrated that the formation of CaCO3 and Ca(OH)2 on the surface of CaO when CaO was exposed to room air prevented CaO from participating in the transesterification of SBO). The degree of poisoning was highly dependent on the type of precursors with Cal(N) more resistant to CO2 poisoning than CaO from ara nite (Ara(N)). Deactivated CaO catalysts could be partially regenerated. A mechanism was proposed to explain the poisoning and regenerating processes. Furthermore, whether the solid phase of CaO or dissolved CaO was the active species in the transesterification of SBO was also investigated.
2008, 24(10): 1824-1830
doi: 10.3866/PKU.WHXB20081015
Abstract:
TraPPE-UA and OPLS-AA force fields were used to investigate the applications of the Gibbs ensemble Monte Carlo (GEMC) method and the Gibbs-Duhemintegration (GDI) method in predicting the vapor-liquid equilibrium properties. It was found that the GDI method was much faster than the GEMC method if all-atom force field was employed. Based on the calculation results, the two methods could be viewed as complementary to the problem of vapor liquid coexistence. The calculated liquid densities, enthalpies of vaporization, critical temperatures, and critical densities by the two methods were very close to each other for a given force field. If the force field caused errors in the calculated heats of vaporization, the calculated vapor pressures and densities by the two methods were clearly different, which also led to difference in the predicted critical pressure.
TraPPE-UA and OPLS-AA force fields were used to investigate the applications of the Gibbs ensemble Monte Carlo (GEMC) method and the Gibbs-Duhemintegration (GDI) method in predicting the vapor-liquid equilibrium properties. It was found that the GDI method was much faster than the GEMC method if all-atom force field was employed. Based on the calculation results, the two methods could be viewed as complementary to the problem of vapor liquid coexistence. The calculated liquid densities, enthalpies of vaporization, critical temperatures, and critical densities by the two methods were very close to each other for a given force field. If the force field caused errors in the calculated heats of vaporization, the calculated vapor pressures and densities by the two methods were clearly different, which also led to difference in the predicted critical pressure.
2008, 24(10): 1831-1838
doi: 10.3866/PKU.WHXB20081016
Abstract:
The corrosion behavior of anodized AZ91D magnesium alloy in neutral 1%(w) NaCl aqueous solution was investigated by salt spray test, polarization curve, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and scanning electron microscope (SEM). The results showed that the corrosion behavior of Mg alloy presented characteristic changes due to anodization. For example, the unsealed anodic film could be sustained in 5% NaCl salt spray beyond 200 h, Ecorr of anodized magnesium alloy shifted up and the inductive period for pitting corrosion was obviously prolonged, and the impedance modules in high frequency of anodized alloy were several thousand times those of unanodized alloy. All these proved that anodization process made the alloy gain excellent property of anti-corrosion. The evolution of fractal dimension (Df) was first utilized to depict the corrosion process of anodized AZ91D magnesium alloy and shown as rapid increasing in the initial, fluctuating in the medium and decreasing in the last. This evolution was related with the three different corrosion stages of anodized AZ91D magnesiumalloy in 1%NaCl solution.
The corrosion behavior of anodized AZ91D magnesium alloy in neutral 1%(w) NaCl aqueous solution was investigated by salt spray test, polarization curve, electrochemical impedance spectroscopy (EIS), electrochemical noise (EN) and scanning electron microscope (SEM). The results showed that the corrosion behavior of Mg alloy presented characteristic changes due to anodization. For example, the unsealed anodic film could be sustained in 5% NaCl salt spray beyond 200 h, Ecorr of anodized magnesium alloy shifted up and the inductive period for pitting corrosion was obviously prolonged, and the impedance modules in high frequency of anodized alloy were several thousand times those of unanodized alloy. All these proved that anodization process made the alloy gain excellent property of anti-corrosion. The evolution of fractal dimension (Df) was first utilized to depict the corrosion process of anodized AZ91D magnesium alloy and shown as rapid increasing in the initial, fluctuating in the medium and decreasing in the last. This evolution was related with the three different corrosion stages of anodized AZ91D magnesiumalloy in 1%NaCl solution.
2008, 24(10): 1839-1844
doi: 10.3866/PKU.WHXB20081017
Abstract:
By using Insight II/Affinity, molecular docking study on taxotere binding to αβ-tubulin was performed, and then a computational approach with B3LYP/6-31G was used to study the interactions of taxotere with αβ-tubulin. Optimum conformation 5 with binding energy of -190.53 kJ·mol-1 was obtained from ten conformations which were produced in the molecular docking process. The conformation 5 provides an interaction model for the binding of taxotere to αβ-tubulin, which shows herein both the hydrophobic and hydrogen bond interactions in the active site. The hydrophobic groups of tubulin are present in the bottomof active site, and forma hydrophobic space with the phenyl in both C13 side chain and C2—OBz group of taxotere. Six hydrogen bond interactions are found in the interaction model, which are located A and B binding sites respectively. Three hydrogen bond interactions between polarity group in C13 side chain and ASP26 and ARG369 in β-tubulin are found in the A site, and the other three hydrogen bond interactions between the polarity group in the cycle of taxotere and THR276, ARG278 and GLN282 in β-tubulin are found in B site. As a whole, hydrogen bond interactions in the upside of active site strengthen the interaction between taxotere and αβ-tubulin and prevent taxotere fromfalling off αβ-tubulin.
By using Insight II/Affinity, molecular docking study on taxotere binding to αβ-tubulin was performed, and then a computational approach with B3LYP/6-31G was used to study the interactions of taxotere with αβ-tubulin. Optimum conformation 5 with binding energy of -190.53 kJ·mol-1 was obtained from ten conformations which were produced in the molecular docking process. The conformation 5 provides an interaction model for the binding of taxotere to αβ-tubulin, which shows herein both the hydrophobic and hydrogen bond interactions in the active site. The hydrophobic groups of tubulin are present in the bottomof active site, and forma hydrophobic space with the phenyl in both C13 side chain and C2—OBz group of taxotere. Six hydrogen bond interactions are found in the interaction model, which are located A and B binding sites respectively. Three hydrogen bond interactions between polarity group in C13 side chain and ASP26 and ARG369 in β-tubulin are found in the A site, and the other three hydrogen bond interactions between the polarity group in the cycle of taxotere and THR276, ARG278 and GLN282 in β-tubulin are found in B site. As a whole, hydrogen bond interactions in the upside of active site strengthen the interaction between taxotere and αβ-tubulin and prevent taxotere fromfalling off αβ-tubulin.
2008, 24(10): 1845-1849
doi: 10.3866/PKU.WHXB20081018
Abstract:
By using first-principles plane-wave normconserving pseudopotential method of density functional theory, the structures and thermodynamic properties of 3C-SiC were investigated. The calculated lattice parameters, bulk modulus, the first order pressure derivative of bulk modulus, and elastic constants are consistent with the experimental data and those calculated by others. Through the quasi-harmonic Debye model, Debye temperature and heat capacity under different temperatures and pressures were successfully obtained. It is shown that when the temperature is constant, the Debye temperature increases almost linearly with applied pressures, while the heat capacity shows an opposite trend. The relative lattice parameters and relative volume, the bulk modulus, thermal expansion versus temperature and pressure were also investigated.
By using first-principles plane-wave normconserving pseudopotential method of density functional theory, the structures and thermodynamic properties of 3C-SiC were investigated. The calculated lattice parameters, bulk modulus, the first order pressure derivative of bulk modulus, and elastic constants are consistent with the experimental data and those calculated by others. Through the quasi-harmonic Debye model, Debye temperature and heat capacity under different temperatures and pressures were successfully obtained. It is shown that when the temperature is constant, the Debye temperature increases almost linearly with applied pressures, while the heat capacity shows an opposite trend. The relative lattice parameters and relative volume, the bulk modulus, thermal expansion versus temperature and pressure were also investigated.
2008, 24(10): 1850-1858
doi: 10.3866/PKU.WHXB20081019
Abstract:
Using the first-principles method, the configurations and electronic structures for the adsorption of CO molecule on TiC(001) surface were investigated in details with a slab model. Our results showed that the CO molecule tended to occupy the atop site of the surface Ti atom through its C ending, and the predicted adsorption energy, the positions of CO valence levels and the red shift of C—O stretching frequency were in agreement with the experimental observations. By analyzing the band structures and Mvlliken population, when CO molecule was adsorbed by C ending, the compositions and energy levels of the corresponding 5σ and 2π-states changed obviously with respect to CO in gas-phase , especially for the case that CO sited at the bridge site between two neighbor Ti atoms. Furthermore, the role of the surface state during the CO adsorption was discussed.
Using the first-principles method, the configurations and electronic structures for the adsorption of CO molecule on TiC(001) surface were investigated in details with a slab model. Our results showed that the CO molecule tended to occupy the atop site of the surface Ti atom through its C ending, and the predicted adsorption energy, the positions of CO valence levels and the red shift of C—O stretching frequency were in agreement with the experimental observations. By analyzing the band structures and Mvlliken population, when CO molecule was adsorbed by C ending, the compositions and energy levels of the corresponding 5σ and 2π-states changed obviously with respect to CO in gas-phase , especially for the case that CO sited at the bridge site between two neighbor Ti atoms. Furthermore, the role of the surface state during the CO adsorption was discussed.
2008, 24(10): 1859-1863
doi: 10.3866/PKU.WHXB20081020
Abstract:
Benzoxazinone derivatives have recently been reported as a type of compounds with potential antiplatelet activity. On the basis of published papers, comparative molecular field analysis (CoMFA) and comparative molecular similiarity indices analysis (CoMSIA) were used to gain insight into the three dimensional quantitative structure activity relationships (3D-QSAR) of benzoxazinone derivatives. The coefficients of cross-validation Q2 and non cross-validation R2 for CoMFA model established in this study were 0.703 and 0.994, respectively, and for CoMSIA model were 0.847 and 0.992. The results indicated that the two models had od predictability. The 3D contour maps suggested that the electrostatic effect of 8-substituted group R1 and the steric effect in the 2-substituted group R2 with moderate volume played major roles. Six compounds with new activities were designed on the basis of these conclusions.
Benzoxazinone derivatives have recently been reported as a type of compounds with potential antiplatelet activity. On the basis of published papers, comparative molecular field analysis (CoMFA) and comparative molecular similiarity indices analysis (CoMSIA) were used to gain insight into the three dimensional quantitative structure activity relationships (3D-QSAR) of benzoxazinone derivatives. The coefficients of cross-validation Q2 and non cross-validation R2 for CoMFA model established in this study were 0.703 and 0.994, respectively, and for CoMSIA model were 0.847 and 0.992. The results indicated that the two models had od predictability. The 3D contour maps suggested that the electrostatic effect of 8-substituted group R1 and the steric effect in the 2-substituted group R2 with moderate volume played major roles. Six compounds with new activities were designed on the basis of these conclusions.
2008, 24(10): 1864-1868
doi: 10.3866/PKU.WHXB20081021
Abstract:
Flower-like indium nanostructures with an average diameter of about 450 nm were successfully synthesized through an ultrasonic dispersion method in ployol system, and were characterized by TEM, XRD, and TG/DTA. The results indicated that these flower-like indium nanoparticles were built from nanopetals and nanorods, and possessed the same crystal structure as bulk indium. Their tribological property as additives in lubricant oil was evaluated on a four-ball tester, and tribological results showed that the as-obtained flower-like indium nanoparticles had an excellent ability in friction-reducing and antiwear.
Flower-like indium nanostructures with an average diameter of about 450 nm were successfully synthesized through an ultrasonic dispersion method in ployol system, and were characterized by TEM, XRD, and TG/DTA. The results indicated that these flower-like indium nanoparticles were built from nanopetals and nanorods, and possessed the same crystal structure as bulk indium. Their tribological property as additives in lubricant oil was evaluated on a four-ball tester, and tribological results showed that the as-obtained flower-like indium nanoparticles had an excellent ability in friction-reducing and antiwear.
2008, 24(10): 1869-1874
doi: 10.3866/PKU.WHXB20081022
Abstract:
N-glucose ethylenediamine triacetic acid (GED3A) was used to modify the surface of carbonyl iron (CI) particles for preparing composite magnetic particles (CMPs) and aqueous magnetorheologic (MR) fluids. The properties of the obtained CMPs, including morphology, magnetic property, and anti-oxidation ability, were characterized by scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The magnetorheologic properties of aqueous MR fluids were measured using a commercial rheometer equipped with a magnetic field supplier and controller. Meanwhile, the dispersion stability and the anti-oxidation ability of the prepared aqueous MR fluids were also analyzed via stability test, air oxidation test, and acid corrosion test, respectively. The results are shown in below. (i) The CMPs possess better soft magnetic properties (magnetic saturation (Ms ): 182.2 emu·g-1, coercivity (Hc ): 4.17 Oe, remanence (Mr): 0.1944 emu·g-1. (ii) Compared with the aqueous MR fluid based on CI particles, the dispersion stability, anti-oxidation ability, and magnetorheological effect of the aqueous MR fluid based on the CMPs were substantially improved. The sedimentation ratio dropped by about 24.4%; and in the range of 0.02-0.10 mol·L-1 of acids, the anti-oxidation ability increased by 92.6%-95.7%for HCl, and 86.1%-93.8%for HNO3.
N-glucose ethylenediamine triacetic acid (GED3A) was used to modify the surface of carbonyl iron (CI) particles for preparing composite magnetic particles (CMPs) and aqueous magnetorheologic (MR) fluids. The properties of the obtained CMPs, including morphology, magnetic property, and anti-oxidation ability, were characterized by scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The magnetorheologic properties of aqueous MR fluids were measured using a commercial rheometer equipped with a magnetic field supplier and controller. Meanwhile, the dispersion stability and the anti-oxidation ability of the prepared aqueous MR fluids were also analyzed via stability test, air oxidation test, and acid corrosion test, respectively. The results are shown in below. (i) The CMPs possess better soft magnetic properties (magnetic saturation (Ms ): 182.2 emu·g-1, coercivity (Hc ): 4.17 Oe, remanence (Mr): 0.1944 emu·g-1. (ii) Compared with the aqueous MR fluid based on CI particles, the dispersion stability, anti-oxidation ability, and magnetorheological effect of the aqueous MR fluid based on the CMPs were substantially improved. The sedimentation ratio dropped by about 24.4%; and in the range of 0.02-0.10 mol·L-1 of acids, the anti-oxidation ability increased by 92.6%-95.7%for HCl, and 86.1%-93.8%for HNO3.
2008, 24(10): 1875-1878
doi: 10.3866/PKU.WHXB20081023
Abstract:
Defect-free zeolite NaA membranes were coated onto the surface of spherical Pt/Al2O3 particles using a two-step hydrothermal method. The structure and morphology of the synthesized composite catalysts were characterized using XRD and SEM techniques, respectively. The results indicated a layer of compact and uniform NaA molecular sieve membrane with a thickness of about 20 滋m was coated on the spherical Pt/Al2O3 particles after the two-step hydrothermal synthesis. The prepared NaA membrane coated catalysts were used in the oxidation of a mixture of CO and C2H4 to study the reactant selectivity over the coated zeolite NaA membranes. Under the optimized conditions, the oxidation selectivity for CO over C2H4 on the composite catalyst was as high as 96%. The feasible application of this composite membrane coated catalyst to the selective removal of CO in the presence of C2H4 was anticipated.
Defect-free zeolite NaA membranes were coated onto the surface of spherical Pt/Al2O3 particles using a two-step hydrothermal method. The structure and morphology of the synthesized composite catalysts were characterized using XRD and SEM techniques, respectively. The results indicated a layer of compact and uniform NaA molecular sieve membrane with a thickness of about 20 滋m was coated on the spherical Pt/Al2O3 particles after the two-step hydrothermal synthesis. The prepared NaA membrane coated catalysts were used in the oxidation of a mixture of CO and C2H4 to study the reactant selectivity over the coated zeolite NaA membranes. Under the optimized conditions, the oxidation selectivity for CO over C2H4 on the composite catalyst was as high as 96%. The feasible application of this composite membrane coated catalyst to the selective removal of CO in the presence of C2H4 was anticipated.
2008, 24(10): 1879-1883
doi: 10.3866/PKU.WHXB20081024
Abstract:
The π-conjugated polymers and oli mers containing bridged biphenyl were important luminescent materials with wide gap. The luminescent property of these materials was relative to the twisted angle between two benzene rings of the bridged biphenyl. The crystal structures of a series of seven-member heterocycle bridged biphenyls were determined by X-ray diffraction. The effect of the bridged atom, the substituent groups in 6,6-position and hydrogen bond (between bridged oxygen atom and hydrogen atom in 2,2’-position of the center biphenyl) on conformation of the bridged biphenyls was discussed.When the bridged bond (—CH2—O—CH2—) changed to—CH2—S—CH2—, the twisted angle between two benzene rings increased by about 12°. The twisted angle also could be influenced by 6,6-substitaent groups, and the twisted angle might increase by about 5°. The hydrogen bond between bridged oxygen atom and hydrogen atom in 2,2’-position of the center biphenyl didn’t affect the conformation of the bridged biphenyls. The bridged atom played an important role for the conformation of the bridged biphenyl of seven-member heterocyle, and the twisted angle also could be influenced lightly by 6,6-substituent groups.
The π-conjugated polymers and oli mers containing bridged biphenyl were important luminescent materials with wide gap. The luminescent property of these materials was relative to the twisted angle between two benzene rings of the bridged biphenyl. The crystal structures of a series of seven-member heterocycle bridged biphenyls were determined by X-ray diffraction. The effect of the bridged atom, the substituent groups in 6,6-position and hydrogen bond (between bridged oxygen atom and hydrogen atom in 2,2’-position of the center biphenyl) on conformation of the bridged biphenyls was discussed.When the bridged bond (—CH2—O—CH2—) changed to—CH2—S—CH2—, the twisted angle between two benzene rings increased by about 12°. The twisted angle also could be influenced by 6,6-substitaent groups, and the twisted angle might increase by about 5°. The hydrogen bond between bridged oxygen atom and hydrogen atom in 2,2’-position of the center biphenyl didn’t affect the conformation of the bridged biphenyls. The bridged atom played an important role for the conformation of the bridged biphenyl of seven-member heterocyle, and the twisted angle also could be influenced lightly by 6,6-substituent groups.
2008, 24(10): 1884-1890
doi: 10.3866/PKU.WHXB20081025
Abstract:
A new compound, barium nicotinate trihydrate, was synthesized by the method of room temperature solid phase synthesis and ball grinder. FTIR, chemical and elemental analyses, and X-ray powder diffraction techniques were applied to characterize the structure and composition of the complex. Low-temperature heat capacities of the solid coordination compound were measured by a precision automated adiabatic calorimeter over the temperature range from78 to 400 K. A phase transition process occurred in the temperature range of 312-332 K in the heat capacity curve, and the peak temperature, molar enthalpy and entropy of the solid-to-solid phase transition of the complex were determined to be as follows: Ttrs=(327.097±1.082) K, ⊿trsHm=(16.793±0.084) kJ·mol-1 and ⊿trsSm=(51.340±0.164) J·K-1·mol-1. The experimental values of the molar heat capacities in the temperature regions of 78-311 K and 333 -400 K were respectively fitted to two polynomial equations. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature of 298.15 K were calculated and tabulated at an interval of 5 K. In accordance with Hess law, a thermochemical cycle was designed, the reaction enthalpy of the solid phase reaction was determined as ⊿rH0m
=-(84.12±0.38) kJ·mol-1, and the standard molar enthalpy of formation of the complex was calculated as ⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1 by using an isoperibol solution-reaction calorimeter.
A new compound, barium nicotinate trihydrate, was synthesized by the method of room temperature solid phase synthesis and ball grinder. FTIR, chemical and elemental analyses, and X-ray powder diffraction techniques were applied to characterize the structure and composition of the complex. Low-temperature heat capacities of the solid coordination compound were measured by a precision automated adiabatic calorimeter over the temperature range from78 to 400 K. A phase transition process occurred in the temperature range of 312-332 K in the heat capacity curve, and the peak temperature, molar enthalpy and entropy of the solid-to-solid phase transition of the complex were determined to be as follows: Ttrs=(327.097±1.082) K, ⊿trsHm=(16.793±0.084) kJ·mol-1 and ⊿trsSm=(51.340±0.164) J·K-1·mol-1. The experimental values of the molar heat capacities in the temperature regions of 78-311 K and 333 -400 K were respectively fitted to two polynomial equations. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature of 298.15 K were calculated and tabulated at an interval of 5 K. In accordance with Hess law, a thermochemical cycle was designed, the reaction enthalpy of the solid phase reaction was determined as ⊿rH0m
=-(84.12±0.38) kJ·mol-1, and the standard molar enthalpy of formation of the complex was calculated as ⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1 by using an isoperibol solution-reaction calorimeter.
2008, 24(10): 1891-1896
doi: 10.3866/PKU.WHXB20081026
Abstract:
Structures, electronic and magnetic properties of FMBen (FM=Fe, Co, Ni; n=1 -12) have been investigated by generalized gradient approximation of density functional theory. It is different from the magic number of Ben+1 (n=1-12) in view of the electronic shell model, and the strong stability of FMBen is explained by the geometric model. In contrast with Ben+1 (n=1-12) clusters, it is found that the doped ferromagnetic element is capped on host clusters and remains on the surface of host clusters; the doped atoms increase the stability of beryllium clusters. The calculated second-order difference of energies shows that FeBe5 and FeBe10, CoBe5 and CoBe10, NiBe4 and NiBe10 are the most stable ones among the studied clusters. The magnetic moments of FMBen show different rules with different doped atoms.
Structures, electronic and magnetic properties of FMBen (FM=Fe, Co, Ni; n=1 -12) have been investigated by generalized gradient approximation of density functional theory. It is different from the magic number of Ben+1 (n=1-12) in view of the electronic shell model, and the strong stability of FMBen is explained by the geometric model. In contrast with Ben+1 (n=1-12) clusters, it is found that the doped ferromagnetic element is capped on host clusters and remains on the surface of host clusters; the doped atoms increase the stability of beryllium clusters. The calculated second-order difference of energies shows that FeBe5 and FeBe10, CoBe5 and CoBe10, NiBe4 and NiBe10 are the most stable ones among the studied clusters. The magnetic moments of FMBen show different rules with different doped atoms.
2008, 24(10): 1897-1901
doi: 10.3866/PKU.WHXB20081027
Abstract:
Nonlinear dynamics of the hydrogen peroxide-sulfide reaction was investigated in a continuous flow stirred tank reactor (CSTR), in which various complex oscillations including 11 type, 12 type, mixed-mode and damped oscillations were observed. Perturbation experiments showed that the delay effect of hydrogen ions depended on the oscillatory phase at which the perturbation was applied. Numerical simulations were carried out with a model which was developed thoroughly based on changing oxidation states of sulfur. The calculation qualitatively reproduced the various complex oscillations seen in experiments, suggesting that complex dynamical behaviors could be driven by sulfur (-II) oxidation.
Nonlinear dynamics of the hydrogen peroxide-sulfide reaction was investigated in a continuous flow stirred tank reactor (CSTR), in which various complex oscillations including 11 type, 12 type, mixed-mode and damped oscillations were observed. Perturbation experiments showed that the delay effect of hydrogen ions depended on the oscillatory phase at which the perturbation was applied. Numerical simulations were carried out with a model which was developed thoroughly based on changing oxidation states of sulfur. The calculation qualitatively reproduced the various complex oscillations seen in experiments, suggesting that complex dynamical behaviors could be driven by sulfur (-II) oxidation.
2008, 24(10): 1902-1906
doi: 10.3866/PKU.WHXB20081028
Abstract:
A new compound, N-(9-anthracylmethyl)-L-histidine (1), was synthesized and characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS), 1H-NMR, and 13C-NMR, etc. The effects of pH values and metal ions on the fluorescent intensity of compound 1 were studied. In neutral aqueous solutions, the fluorescence intensity of compound 1 increased upon addition of Zn2+ or Cd2+, while other metal ions (Pb2+, Co2+, Hg2+, Ni2+, and Cu2+) quenched the fluorescence. Among these metal ions, Cu2+ and Ni2+ had the strongest quenching capacity. They both formed a stable complex with compound 1 (1:2 molar ratio), and the complex constants were 2.88×106 and 1.12×106 L2·mol-2, respectively. The experimental results showed that static quenching was involved in adding Cu2+ or Ni2+ in aqueous solution of compound 1. On the basis of these studies, a NOR fluorescent molecular logic gate was fabricated with Cu2+ and Ni2+ as two inputs and with emission of anthracene as the output.
A new compound, N-(9-anthracylmethyl)-L-histidine (1), was synthesized and characterized by elemental analysis, electrospray ionization mass spectrometry (ESI-MS), 1H-NMR, and 13C-NMR, etc. The effects of pH values and metal ions on the fluorescent intensity of compound 1 were studied. In neutral aqueous solutions, the fluorescence intensity of compound 1 increased upon addition of Zn2+ or Cd2+, while other metal ions (Pb2+, Co2+, Hg2+, Ni2+, and Cu2+) quenched the fluorescence. Among these metal ions, Cu2+ and Ni2+ had the strongest quenching capacity. They both formed a stable complex with compound 1 (1:2 molar ratio), and the complex constants were 2.88×106 and 1.12×106 L2·mol-2, respectively. The experimental results showed that static quenching was involved in adding Cu2+ or Ni2+ in aqueous solution of compound 1. On the basis of these studies, a NOR fluorescent molecular logic gate was fabricated with Cu2+ and Ni2+ as two inputs and with emission of anthracene as the output.
2008, 24(10): 1907-1911
doi: 10.3866/PKU.WHXB20081029
Abstract:
The influence of wire radius (0.04-0.82 mm) on the corrosion behavior of copper wires was investigated in naturally aerated 0.5 mol·L-1 NaCl solution (pH=7.4), by means of polarization and electrochemical impedance spectroscopy method. The results showed that the mass transfer process was significantly accelerated by non-linear diffusion when radius of copper wire was less than the thickness of diffusion layer (0.56 mm), and consequently, the cathodic and anodic reaction rates controlled by diffusion, as well as the corrosion current density, increased rapidly. It showed that the influence was accelerated with the decrease of wire radius. By comparing cathodic oxygen reduction reaction of platinum and stainless steel wires, the same results were obtained. Therefore, the size effect on corrosion behavior of copper wires is a widespread phenomenon.
The influence of wire radius (0.04-0.82 mm) on the corrosion behavior of copper wires was investigated in naturally aerated 0.5 mol·L-1 NaCl solution (pH=7.4), by means of polarization and electrochemical impedance spectroscopy method. The results showed that the mass transfer process was significantly accelerated by non-linear diffusion when radius of copper wire was less than the thickness of diffusion layer (0.56 mm), and consequently, the cathodic and anodic reaction rates controlled by diffusion, as well as the corrosion current density, increased rapidly. It showed that the influence was accelerated with the decrease of wire radius. By comparing cathodic oxygen reduction reaction of platinum and stainless steel wires, the same results were obtained. Therefore, the size effect on corrosion behavior of copper wires is a widespread phenomenon.
2008, 24(10): 1912-1916
doi: 10.3866/PKU.WHXB20081030
Abstract:
Ternary Zn1-xCdxO single-crystal bramble-like nanostructures with an incorporation Cd molar ratio of about 6.7% were synthesized by thermal evaporation of Zn and Cd on an Si substrate using Au as catalyst. The as-grown Zn1-xCdxO nanobrambles had a fairly uniform trunk with a diameter of approximately 100 nm. The diameter and length of the two-sided nano-thorns were about 10 and 100 nm, respectively. Ultra-violet (UV) near-band-edge (NBE) emission of the Zn1-xCdxO nanobrambles was red-shifted from3.37 to 3.14 eV due to the direct modulation of band gap caused by Cd substitution. The oxygen partial pressure was deemed as the critical experimental parameter for the formation of the bramble-like Zn1-xCdxO nanostructures.
Ternary Zn1-xCdxO single-crystal bramble-like nanostructures with an incorporation Cd molar ratio of about 6.7% were synthesized by thermal evaporation of Zn and Cd on an Si substrate using Au as catalyst. The as-grown Zn1-xCdxO nanobrambles had a fairly uniform trunk with a diameter of approximately 100 nm. The diameter and length of the two-sided nano-thorns were about 10 and 100 nm, respectively. Ultra-violet (UV) near-band-edge (NBE) emission of the Zn1-xCdxO nanobrambles was red-shifted from3.37 to 3.14 eV due to the direct modulation of band gap caused by Cd substitution. The oxygen partial pressure was deemed as the critical experimental parameter for the formation of the bramble-like Zn1-xCdxO nanostructures.
2008, 24(10): 1917-1921
doi: 10.3866/PKU.WHXB20081031
Abstract:
Molecular dynamics simulations were used to investigate the interaction of DB921 with the DNA oli nucleotide d[CGCGAATTCGCG]2. A 7 ns MD calculation was performed to study the DB921-DNA complex and the results indicated that DB921 was inserted in the minor groove of DNA, binding to the region of duplex AATTC bases. A water molecule forms bifurcated pair of H-bonds between the N atom of benzimidazole ring and N3 atom of the adenine 5 in the DB921-DNA complex. This water molecule performs a key bridging role which induces a more favorable curvature configuration and matches well the DNA minor groove topology. Molecular dynamics studies complemented the structural analysis and offered a clear picture of the water-bridge, providing the theoretical guidance for the design of biologically active minor groove agents.
Molecular dynamics simulations were used to investigate the interaction of DB921 with the DNA oli nucleotide d[CGCGAATTCGCG]2. A 7 ns MD calculation was performed to study the DB921-DNA complex and the results indicated that DB921 was inserted in the minor groove of DNA, binding to the region of duplex AATTC bases. A water molecule forms bifurcated pair of H-bonds between the N atom of benzimidazole ring and N3 atom of the adenine 5 in the DB921-DNA complex. This water molecule performs a key bridging role which induces a more favorable curvature configuration and matches well the DNA minor groove topology. Molecular dynamics studies complemented the structural analysis and offered a clear picture of the water-bridge, providing the theoretical guidance for the design of biologically active minor groove agents.
2008, 24(10): 1922-1926
doi: 10.3866/PKU.WHXB20081032
Abstract:
ld nanowires with diameters (d) between 45 nmand 200 nmand with length/diameter ratio of 700 were prepared in ion-track templates with electrodeposition method. The morphology and crystal structure of the ld nanowires were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The 200 nm (d) ld nanowires preferred orientation along the [100] direction were formed at the deposition voltage of 1.5 V (without reference electrode). The optical properties of ld nanowire arrays embedded in ion-track templates were studied by UV-Vis spectrophotometer. There was a strong absorption peak at 539 nm for 45 nm (d) ld nanowire arrays. With the diameter of ld nanowires increasing, the absorption peak shifted to the longer wavelength. At last, the result was discussed combined with surface plasmon resonance of ld nanoparticles.
ld nanowires with diameters (d) between 45 nmand 200 nmand with length/diameter ratio of 700 were prepared in ion-track templates with electrodeposition method. The morphology and crystal structure of the ld nanowires were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The 200 nm (d) ld nanowires preferred orientation along the [100] direction were formed at the deposition voltage of 1.5 V (without reference electrode). The optical properties of ld nanowire arrays embedded in ion-track templates were studied by UV-Vis spectrophotometer. There was a strong absorption peak at 539 nm for 45 nm (d) ld nanowire arrays. With the diameter of ld nanowires increasing, the absorption peak shifted to the longer wavelength. At last, the result was discussed combined with surface plasmon resonance of ld nanoparticles.
2008, 24(10): 1927-1931
doi: 10.3866/PKU.WHXB20081033
Abstract:
Hollow MoS2 microspheres were synthesized via soft template method with polyethylene glycol (PEG) as template. The as-prepared samples were characterized with X-ray diffraction (XRD), infrared spectrometer (IR), and scanning electron microscopy (SEM). The results indicated that the as-prepared MoS2 was hollow microspheres with diameter of 2-7 μm and had poor crystallinity, which could be improved by calcination. There was strong organic-inorganic hybridization between polyethylene glycol and MoS2. Furthermore, both the concentration and molecular weight of polyethylene glycol had great effects on morphological control of the product. Based on the IR analysis of product, the formation mechanismof hollow MoS2 microspheres was discussed preliminarily.
Hollow MoS2 microspheres were synthesized via soft template method with polyethylene glycol (PEG) as template. The as-prepared samples were characterized with X-ray diffraction (XRD), infrared spectrometer (IR), and scanning electron microscopy (SEM). The results indicated that the as-prepared MoS2 was hollow microspheres with diameter of 2-7 μm and had poor crystallinity, which could be improved by calcination. There was strong organic-inorganic hybridization between polyethylene glycol and MoS2. Furthermore, both the concentration and molecular weight of polyethylene glycol had great effects on morphological control of the product. Based on the IR analysis of product, the formation mechanismof hollow MoS2 microspheres was discussed preliminarily.
2008, 24(10): 1932-1936
doi: 10.3866/PKU.WHXB20081034
Abstract:
CoFe2O4magnetic nanoparticles were dealt with nitric acid to forman ionization surface and to improve the dispersibility of CoFe2O4 nanoparticles greatly. Then polyaniline (PANI)/CoFe2O4 electromagnetic nanocomposites with different amounts of CoFe2O4 were synthesized by in-situ polymerization method. The morphologies, structures, and electromagnetic properties of the PANI/CoFe2O4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectra, four-probe electrometer, and vibrating sample magnetometer (VSM). The results indicated that the CoFe2O4 magnetic nanoparticles with diameter of about 25 nm were dispersed in the base of PANI and the bonding interaction existed between CoFe2O4 particles and polyaniline in the composites. The composites possessed both conductivity and magnetism. With increasing CoFe2O4 content, the conductivity of the composites decreased while the saturated magnetization (Ms) increased. Increasing CoFe2O4 content from 16.8%to 69.2%, the coercive force (Hc) of PANI/CoFe2O4 nanocomposites was higher than that of the CoFe2O4 nanoparticles and increased firstly and then decreased.
CoFe2O4magnetic nanoparticles were dealt with nitric acid to forman ionization surface and to improve the dispersibility of CoFe2O4 nanoparticles greatly. Then polyaniline (PANI)/CoFe2O4 electromagnetic nanocomposites with different amounts of CoFe2O4 were synthesized by in-situ polymerization method. The morphologies, structures, and electromagnetic properties of the PANI/CoFe2O4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform-infrared (FT-IR) spectra, four-probe electrometer, and vibrating sample magnetometer (VSM). The results indicated that the CoFe2O4 magnetic nanoparticles with diameter of about 25 nm were dispersed in the base of PANI and the bonding interaction existed between CoFe2O4 particles and polyaniline in the composites. The composites possessed both conductivity and magnetism. With increasing CoFe2O4 content, the conductivity of the composites decreased while the saturated magnetization (Ms) increased. Increasing CoFe2O4 content from 16.8%to 69.2%, the coercive force (Hc) of PANI/CoFe2O4 nanocomposites was higher than that of the CoFe2O4 nanoparticles and increased firstly and then decreased.
2008, 24(10): 1937-1940
doi: 10.3866/PKU.WHXB20081035
Abstract:
The electrochemical reduction of p-nitrophenol in sulfuric acid on copper electrode was investigated by in situ FTIR technique. Electroreduction of p-nitrophenol in sulfuric acid led to the formation of p-nitrosophenol first, which could be converted to trans-dimer of p-nitrosophenol, and then p-hydroxylamino phenol. Finally p-hydroxylamino phenol was reduced to p-aminophenol at low potential.
The electrochemical reduction of p-nitrophenol in sulfuric acid on copper electrode was investigated by in situ FTIR technique. Electroreduction of p-nitrophenol in sulfuric acid led to the formation of p-nitrosophenol first, which could be converted to trans-dimer of p-nitrosophenol, and then p-hydroxylamino phenol. Finally p-hydroxylamino phenol was reduced to p-aminophenol at low potential.
