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2007 Volume 23 Issue 2
2007, 23(02): 139-144
doi: 10.1016/S1872-1508(07)60011-4
Abstract:
The microphase separation dynamics of triblock copolymer surfactant [(ethylene oxide)27(propylene oxide)61-(ethylene oxide)27](P104) in aqueous solution was simulated by a dynamic variant of mean-field density functional theory for Gaussian chains. Different morphologies depending on the simulation concentration and time were shown in low concentration (φ<35%). With the increase of the concentration, the self-assemble aggregates changed from spherical micelles, micellar clusters, to disk-like micelles. (1) In the spherical micellar region (5%-10%, φ), the result of the simulation was similar to that of the experiment in that micelle was a dense core consisting mainly of PPO and a hydrated PEO swollen corona. (2) Due to the coalescence among spherical micelles, larger micellar clusters are formed in a concentration ranging from 11% to 15%(φ). (3) Owing to the attractions between the PEO coronas of micellar clusters, series of disk-like micelles were found above the concentration 16%(φ). The order parameters showed that the phase separation of spherical micelles was easily formed, while the micellar cluster or disk-like micelles required a longer time to acquire steady equilibrium.
The microphase separation dynamics of triblock copolymer surfactant [(ethylene oxide)27(propylene oxide)61-(ethylene oxide)27](P104) in aqueous solution was simulated by a dynamic variant of mean-field density functional theory for Gaussian chains. Different morphologies depending on the simulation concentration and time were shown in low concentration (φ<35%). With the increase of the concentration, the self-assemble aggregates changed from spherical micelles, micellar clusters, to disk-like micelles. (1) In the spherical micellar region (5%-10%, φ), the result of the simulation was similar to that of the experiment in that micelle was a dense core consisting mainly of PPO and a hydrated PEO swollen corona. (2) Due to the coalescence among spherical micelles, larger micellar clusters are formed in a concentration ranging from 11% to 15%(φ). (3) Owing to the attractions between the PEO coronas of micellar clusters, series of disk-like micelles were found above the concentration 16%(φ). The order parameters showed that the phase separation of spherical micelles was easily formed, while the micellar cluster or disk-like micelles required a longer time to acquire steady equilibrium.
2007, 23(02): 145-151
doi: 10.1016/S1872-1508(07)60012-6
Abstract:
A CNT/ZnO nanocomplex was fabricated by attaching ZnO nanoparticles with various diameters to carbon nanotubes (CNTs). The as-prepared agglomerate ZnO nanoparticles were dispersed and positively charged by utilizing a cationic surfactant cetyltrimethylammonium bromide (CTAB). ZnO/CTAB micelles were subsequently anchored to the surface of CNTs by electrostatic interaction between carboxyl groups on the chemically oxidized nanotubes′ sidewalls and CTAB molecules. Different experimental conditions for the attachment were studied. The CNT/ZnO nanocomplex was characterized using structural and optical analysis methods. ZnO nanoparticles attached to the carbon nanotubes were found to be separated from each other maintaining characteristics of quantum dots Photoluminescence study showed that the emission of ZnO nanoparticles was quenched in the nanocomplex.
A CNT/ZnO nanocomplex was fabricated by attaching ZnO nanoparticles with various diameters to carbon nanotubes (CNTs). The as-prepared agglomerate ZnO nanoparticles were dispersed and positively charged by utilizing a cationic surfactant cetyltrimethylammonium bromide (CTAB). ZnO/CTAB micelles were subsequently anchored to the surface of CNTs by electrostatic interaction between carboxyl groups on the chemically oxidized nanotubes′ sidewalls and CTAB molecules. Different experimental conditions for the attachment were studied. The CNT/ZnO nanocomplex was characterized using structural and optical analysis methods. ZnO nanoparticles attached to the carbon nanotubes were found to be separated from each other maintaining characteristics of quantum dots Photoluminescence study showed that the emission of ZnO nanoparticles was quenched in the nanocomplex.
2007, 23(02): 152-156
doi: 10.1016/S1872-1508(07)60013-8
Abstract:
The reaction mechanism of C6F6-HNO2 aqueous solution was studied using laser flash photolysis-transient absorption spectrum technique under irradiation at 355 nm. The characteristic absorption peaks and the kinetic parameters of transient species were also investigated. The hydroxyl radical derived from the photolysis of HNO2 was added to hexafluorobenzene with a second-order rate constant of 1.8×109 L·mol-1·s-1 to form an adduct, C6F6…OH, which had absorption peaks at 250, 270, and 400 nm. The C6F6…OH adduct decayed by the elimination of HF to yield C6F5O· with an apparent first-order rate constant 6.1×105 s-1. In the presence of O2, C6F6…OH underwent a complex reaction with a rate constant of 2.8×106 L·mol-1·s-1 to form C6F6OHO2, which had the same absorption bands as C6F6…OH. The final products were identified using the GC-MS technique and the possible reaction pathways were also discussed.
The reaction mechanism of C6F6-HNO2 aqueous solution was studied using laser flash photolysis-transient absorption spectrum technique under irradiation at 355 nm. The characteristic absorption peaks and the kinetic parameters of transient species were also investigated. The hydroxyl radical derived from the photolysis of HNO2 was added to hexafluorobenzene with a second-order rate constant of 1.8×109 L·mol-1·s-1 to form an adduct, C6F6…OH, which had absorption peaks at 250, 270, and 400 nm. The C6F6…OH adduct decayed by the elimination of HF to yield C6F5O· with an apparent first-order rate constant 6.1×105 s-1. In the presence of O2, C6F6…OH underwent a complex reaction with a rate constant of 2.8×106 L·mol-1·s-1 to form C6F6OHO2, which had the same absorption bands as C6F6…OH. The final products were identified using the GC-MS technique and the possible reaction pathways were also discussed.
2007, 23(02): 157-161
doi: 10.3866/PKU.WHXB20070204
Abstract:
Ni catalysts supported on mesoporous alumina (Ni-Al2O3) were prepared by in-situ synthesis method and traditional impregnation method. The physical, chemical, and structure properties of synthesized catalysts were investigated by several measuring technologies (BET, TEM, XRD, TG). The experimental results showed that Ni-Al2O3 with high surface area(＞210 m2·g-1) and narrow pore size distribution(4 nm) could be synthesized by both in-situ synthesis method and impregnation method. In contrast to the impregnation method, the interaction between nickel ion and the carrier was stronger in Ni-Al2O3 synthesized by in-situ synthesis method, and the structure of pore showed to be organized in some degree.
Ni catalysts supported on mesoporous alumina (Ni-Al2O3) were prepared by in-situ synthesis method and traditional impregnation method. The physical, chemical, and structure properties of synthesized catalysts were investigated by several measuring technologies (BET, TEM, XRD, TG). The experimental results showed that Ni-Al2O3 with high surface area(＞210 m2·g-1) and narrow pore size distribution(4 nm) could be synthesized by both in-situ synthesis method and impregnation method. In contrast to the impregnation method, the interaction between nickel ion and the carrier was stronger in Ni-Al2O3 synthesized by in-situ synthesis method, and the structure of pore showed to be organized in some degree.
2007, 23(02): 162-168
doi: 10.3866/PKU.WHXB20070205
Abstract:
Kept the atomic ratios of M2+/M3+ at a constant of 3, series of hydrotalcite-like precursors with different Co contents CoxMg3-xAl-HT(x=0, 0.5, 1, 1.5, 2, 2.5, 3) were synthesized by co-precipitation methods. Mixed oxides CoxMg3-xAlO were derived from these precursors through calcination. XRD, BET, TG-DSC, and TPR techniques were used to study the influences of Co content on composition and structure of precursors and corresponding mixed oxides. The performances of N2O catalytic decomposition over CoxMg3-xAlO catalysts were investigated and the effect of reaction conditions, such as N2O concentration, space velocity, O2, and H2O, on catalytic activity were also studied in detail. The results showed that complete layer structure of hydrotalcite was formed in all precursors. After calcination, the main phase of the catalysts was Co-Al spinel. Moreover, Co introduction promoted the formation of spinel. Mg could improve thermal stability of the catalysts to some degree. Co content had important influence on the thermal stability, surface area, reducibility, and activity of the catalysts. With increase of Co content, surface area of the catalysts decreased, however, surface area was not an important factor in N2O catalytic decomposition. Two-stage reduction was observed in TPR tests of all Co-containing catalysts. The reduction process of Co was followed as the route: Co3+→Co2+→Co. Co2.5Mg0.5AlO catalyst calcined at 500 ℃ showed relatively od activity in N2O decomposition. Catalytic activity decreased with increase of calcination temperatures. N2O concentration, space velocity, and O2 had a little effect on activity in some sense, while H2O obviously influenced the activity of N2O catalytic decomposition.
Kept the atomic ratios of M2+/M3+ at a constant of 3, series of hydrotalcite-like precursors with different Co contents CoxMg3-xAl-HT(x=0, 0.5, 1, 1.5, 2, 2.5, 3) were synthesized by co-precipitation methods. Mixed oxides CoxMg3-xAlO were derived from these precursors through calcination. XRD, BET, TG-DSC, and TPR techniques were used to study the influences of Co content on composition and structure of precursors and corresponding mixed oxides. The performances of N2O catalytic decomposition over CoxMg3-xAlO catalysts were investigated and the effect of reaction conditions, such as N2O concentration, space velocity, O2, and H2O, on catalytic activity were also studied in detail. The results showed that complete layer structure of hydrotalcite was formed in all precursors. After calcination, the main phase of the catalysts was Co-Al spinel. Moreover, Co introduction promoted the formation of spinel. Mg could improve thermal stability of the catalysts to some degree. Co content had important influence on the thermal stability, surface area, reducibility, and activity of the catalysts. With increase of Co content, surface area of the catalysts decreased, however, surface area was not an important factor in N2O catalytic decomposition. Two-stage reduction was observed in TPR tests of all Co-containing catalysts. The reduction process of Co was followed as the route: Co3+→Co2+→Co. Co2.5Mg0.5AlO catalyst calcined at 500 ℃ showed relatively od activity in N2O decomposition. Catalytic activity decreased with increase of calcination temperatures. N2O concentration, space velocity, and O2 had a little effect on activity in some sense, while H2O obviously influenced the activity of N2O catalytic decomposition.
2007, 23(02): 169-172
doi: 10.3866/PKU.WHXB20070206
Abstract:
The geometric configurations, electronic structures, vibrational frequencies, and natural bond orbital (NBO) of BmN (m=2-9) clusters were studied using the B3LYP DFT method at 6-311G* level. The stabilities of the BmN (m=2-9) were analysized by means of energy difference, nucleus independent chemical shifts (NICS), and secondary energy differences of the ground state structures.
The geometric configurations, electronic structures, vibrational frequencies, and natural bond orbital (NBO) of BmN (m=2-9) clusters were studied using the B3LYP DFT method at 6-311G* level. The stabilities of the BmN (m=2-9) were analysized by means of energy difference, nucleus independent chemical shifts (NICS), and secondary energy differences of the ground state structures.
2007, 23(02): 173-176
doi: 10.1016/S1872-1508(07)60014-X
Abstract:
The interaction between the alkylbenzene sulfonate Gemini surfactant Ia and the conventional nonionic surfactant C10E6 was investigated. The critical micelle concentrations of different mixtures were measured by surface tension measurement in aqueous solution at different temperatures. The results suggested that the critical micelle concentration of different mixtures at any mole ratio was lower than that of either pure Ia or C10E6 surfactant, indicating synergetic behavior. The cmc values for pure Ia, C10E6 surfactant, and their different mixtures at any mole ratio increased with increasing temperature. And the interaction parameter β values for the mixed micelles were negative, showing attractive interaction between these surfactant molecules. The micelle aggregation number (N) was measured using a steady state fluorescence quenching method. The N values of the mixed surfactant system were larger than that of pure Ia but lower than pure C10E6 at all mole ratios. The micropolarity of micelles becomes small gradually with the increase of the mole ratio of the Gemini surfactant Ia.
The interaction between the alkylbenzene sulfonate Gemini surfactant Ia and the conventional nonionic surfactant C10E6 was investigated. The critical micelle concentrations of different mixtures were measured by surface tension measurement in aqueous solution at different temperatures. The results suggested that the critical micelle concentration of different mixtures at any mole ratio was lower than that of either pure Ia or C10E6 surfactant, indicating synergetic behavior. The cmc values for pure Ia, C10E6 surfactant, and their different mixtures at any mole ratio increased with increasing temperature. And the interaction parameter β values for the mixed micelles were negative, showing attractive interaction between these surfactant molecules. The micelle aggregation number (N) was measured using a steady state fluorescence quenching method. The N values of the mixed surfactant system were larger than that of pure Ia but lower than pure C10E6 at all mole ratios. The micropolarity of micelles becomes small gradually with the increase of the mole ratio of the Gemini surfactant Ia.
2007, 23(02): 177-180
doi: 10.3866/PKU.WHXB20070208
Abstract:
Terahertz time-domain spectroscopic technique was applied to investigate the optical properties of polyethylene-carbon black composites in the frequency range of 0.3-2.0 THz as a function of frequency and volume fraction of the carbon black. It is found that the absorption coefficient and the refractive index of the composite increased with increase of carbon black content. At the same carbon black concentration, the absorption coefficient increased and the refractive index decreased with increase of frequency. The experimental measurements were analyzed by using Debye theory of dipole relaxation under the assumption that carbon black particles dispersed in the polyethylene matrix behave like dipoles and contribute mainly to the dielectric loss.
Terahertz time-domain spectroscopic technique was applied to investigate the optical properties of polyethylene-carbon black composites in the frequency range of 0.3-2.0 THz as a function of frequency and volume fraction of the carbon black. It is found that the absorption coefficient and the refractive index of the composite increased with increase of carbon black content. At the same carbon black concentration, the absorption coefficient increased and the refractive index decreased with increase of frequency. The experimental measurements were analyzed by using Debye theory of dipole relaxation under the assumption that carbon black particles dispersed in the polyethylene matrix behave like dipoles and contribute mainly to the dielectric loss.
2007, 23(02): 181-186
doi: 10.3866/PKU.WHXB20070209
Abstract:
Using ammonium metatungstate (AMT) treated by spay drying as precursors, the tungsten carbides (WC) catalyst with meso-porosity was prepared by gas-solid reaction in the atmosphere of CH4/H2. The WC-supported nano platinum (Pt) catalyst was prepared by impregnation. SEM and XRD results showed that the average diameter of the Pt particles which were well dispersed on the surface of Pt/WC, was about 13.5 nm. The electro-catalytic properties and chemical stability of the Pt/WC powder microelectrode (PME) for the hydrogen evolution reaction in acid solution were investigated using the electrochemical techniques of cyclic voltammetry and linear sweep voltammetry. The results showed that the Pt/WC-PME exhibited an attractive catalytic activity in hydrogen evolution with parameter a in Tafel equation was 0.292 V, and the exchange current density of hydrogen evolution was 4.42 mA·cm-2. When the over-potential was 250 mV, the activation energy of hydrogen evolution was 26.20 kJ·mol-1.
Using ammonium metatungstate (AMT) treated by spay drying as precursors, the tungsten carbides (WC) catalyst with meso-porosity was prepared by gas-solid reaction in the atmosphere of CH4/H2. The WC-supported nano platinum (Pt) catalyst was prepared by impregnation. SEM and XRD results showed that the average diameter of the Pt particles which were well dispersed on the surface of Pt/WC, was about 13.5 nm. The electro-catalytic properties and chemical stability of the Pt/WC powder microelectrode (PME) for the hydrogen evolution reaction in acid solution were investigated using the electrochemical techniques of cyclic voltammetry and linear sweep voltammetry. The results showed that the Pt/WC-PME exhibited an attractive catalytic activity in hydrogen evolution with parameter a in Tafel equation was 0.292 V, and the exchange current density of hydrogen evolution was 4.42 mA·cm-2. When the over-potential was 250 mV, the activation energy of hydrogen evolution was 26.20 kJ·mol-1.
2007, 23(02): 187-191
doi: 10.3866/PKU.WHXB20070210
Abstract:
Proton exchange membrane is one of the key parts of direct methanol fuel cell (DMFC). Sulfonated poly(phthalazinones) membranes were prepared and the feasibility of applying these membranes in DMFC was studied. The thermal degradation temperature of sulfonated poly(phthalazinone ether sulfone keton) (SPPESK) membrane was about 100 ℃ lower than that of sulfonated poly(phthalazinone ether keton) (SPPEK) and sulfonated poly(phthalazinone ether sulfone) (SPPES) membranes with similar ion-exchange capacity (IEC). These new membranes showed high proton conductivity and their methanol permeability was lower than that of Nafion membrane. DMFC performance of these new membranes was also investigated. The DMFCs with sulfonated poly(phthalazinones) membranes showed higher open circuit voltage than that using Nafion membrane as electrolyte. However, the DMFC performance of these new membranes was lower than that of Nafion membrane at high current density.
Proton exchange membrane is one of the key parts of direct methanol fuel cell (DMFC). Sulfonated poly(phthalazinones) membranes were prepared and the feasibility of applying these membranes in DMFC was studied. The thermal degradation temperature of sulfonated poly(phthalazinone ether sulfone keton) (SPPESK) membrane was about 100 ℃ lower than that of sulfonated poly(phthalazinone ether keton) (SPPEK) and sulfonated poly(phthalazinone ether sulfone) (SPPES) membranes with similar ion-exchange capacity (IEC). These new membranes showed high proton conductivity and their methanol permeability was lower than that of Nafion membrane. DMFC performance of these new membranes was also investigated. The DMFCs with sulfonated poly(phthalazinones) membranes showed higher open circuit voltage than that using Nafion membrane as electrolyte. However, the DMFC performance of these new membranes was lower than that of Nafion membrane at high current density.
2007, 23(02): 192-197
doi: 10.1016/S1872-1508(07)60015-1
Abstract:
Quantum chemical calculations at the HF/6-31G* and B3LYP/6-31G* levels have been carried out on five explosive sensitizers: ethyl nitrate (EN), n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), and tetraethylene glycol dinitrate (TEGDN). Theoretical studies have yielded a wealth of quantum chemical information on the molecular geometries, electronic structures, and energies of the title compounds. On the basis of the Mulliken populations and bond lengths, the O2—N3 fission is acceptable. Charge distribution analysis indicated that the five nitrates produced NO2 gas during the dissociation of the O2—N3 weak bond. The relative thermal stability ordering of the five nitrates was estimated on the basis of the frontier orbital energy (EHOMO, ELUMO) and the energy gap (ΔE). The heats of formation (HOFs) of the five sensitizers, EN, IPN, NPN, EHN, and TEGDN, were calculated from the isodesmic reactions and were -155.972, -190.896, -175.279, -272.376, and -790.733 kJ·mol-1, respectively.
Quantum chemical calculations at the HF/6-31G* and B3LYP/6-31G* levels have been carried out on five explosive sensitizers: ethyl nitrate (EN), n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), and tetraethylene glycol dinitrate (TEGDN). Theoretical studies have yielded a wealth of quantum chemical information on the molecular geometries, electronic structures, and energies of the title compounds. On the basis of the Mulliken populations and bond lengths, the O2—N3 fission is acceptable. Charge distribution analysis indicated that the five nitrates produced NO2 gas during the dissociation of the O2—N3 weak bond. The relative thermal stability ordering of the five nitrates was estimated on the basis of the frontier orbital energy (EHOMO, ELUMO) and the energy gap (ΔE). The heats of formation (HOFs) of the five sensitizers, EN, IPN, NPN, EHN, and TEGDN, were calculated from the isodesmic reactions and were -155.972, -190.896, -175.279, -272.376, and -790.733 kJ·mol-1, respectively.
2007, 23(02): 198-205
doi: 10.1016/S1872-1508(07)60016-3
Abstract:
The binding affinity model of a peptide-major histocompatibility complex (MHC) was studied using the methods of partial least squares (PLS) and amino acid structure descriptors. Using these models, the predictive sets of 805 peptides are predicted for the binding affinity of the HLA-A*0201 complex, and the predictive accuracies of the two models are 66.8% and 65.5%, respectively. To test the robustness of the models, the outliers are eliminated, and it is proved that the robustness of the models is od. This shows that the models using the PLS and amino acid structure descriptors are feasible on predicting of CTL (cytotoxicy T lymphocyte) epitopes.
The binding affinity model of a peptide-major histocompatibility complex (MHC) was studied using the methods of partial least squares (PLS) and amino acid structure descriptors. Using these models, the predictive sets of 805 peptides are predicted for the binding affinity of the HLA-A*0201 complex, and the predictive accuracies of the two models are 66.8% and 65.5%, respectively. To test the robustness of the models, the outliers are eliminated, and it is proved that the robustness of the models is od. This shows that the models using the PLS and amino acid structure descriptors are feasible on predicting of CTL (cytotoxicy T lymphocyte) epitopes.
2007, 23(02): 206-211
doi: 10.3866/PKU.WHXB20070213
Abstract:
In order to examine the effects of water contents on glass transition and structure relaxation parameters of 1, 2-propanediol (PD) aqueous glasses, apparent specific heat capacity during glass transition processes of five PD aqueous solutions with high concentrations (60%, 70%, 80%, 90%, and 100%, w) were determined using the differential scanning calorimetry (DSC). Five cooling rates (1, 2, 5, 10, 20 K·min-1) and one heating rate (10 K·min-1) were used to obtain the glass transition and structure relaxation parameters. Water seemed to be no obvious plasticization effect on 1, 2-propanediol (compared to some “pure hydroxyl group” linear polyalcohol) since the glass transition temperatures of the aqueous solutions were only slightly decreased with the increasing of water content. The structure relaxation activation energies were found to decrease as the water content increased. A comparison of thermodynamic fragility(ΔCp) and dynamic fragility (Angell′s fragility) was present and no similar trend was found with the changing of the component, since the former increased first and decreased last. The calculating results of dynamic fragility indicated that 1, 2-propanediol aqueous solutions behaved as though they were “stronger” than the pure solute. The sizes of cooperative rearrangement region (CRR) discussed in the term of glass transition characteristic length were determined using Donth’s thermodynamic temperature fluctuant method. It was found that the sizes of CRR decreased as the water content increasing in 1,2-propanediol aqueous solutions.
In order to examine the effects of water contents on glass transition and structure relaxation parameters of 1, 2-propanediol (PD) aqueous glasses, apparent specific heat capacity during glass transition processes of five PD aqueous solutions with high concentrations (60%, 70%, 80%, 90%, and 100%, w) were determined using the differential scanning calorimetry (DSC). Five cooling rates (1, 2, 5, 10, 20 K·min-1) and one heating rate (10 K·min-1) were used to obtain the glass transition and structure relaxation parameters. Water seemed to be no obvious plasticization effect on 1, 2-propanediol (compared to some “pure hydroxyl group” linear polyalcohol) since the glass transition temperatures of the aqueous solutions were only slightly decreased with the increasing of water content. The structure relaxation activation energies were found to decrease as the water content increased. A comparison of thermodynamic fragility(ΔCp) and dynamic fragility (Angell′s fragility) was present and no similar trend was found with the changing of the component, since the former increased first and decreased last. The calculating results of dynamic fragility indicated that 1, 2-propanediol aqueous solutions behaved as though they were “stronger” than the pure solute. The sizes of cooperative rearrangement region (CRR) discussed in the term of glass transition characteristic length were determined using Donth’s thermodynamic temperature fluctuant method. It was found that the sizes of CRR decreased as the water content increasing in 1,2-propanediol aqueous solutions.
2007, 23(02): 212-216
doi: 10.1016/S1872-1508(07)60017-5
Abstract:
Amino acids are important biological compounds that played an essential role in the formation of peptides, the backbone of protein, in the prebiotic chemistry of the early Earth for the origin of life. To probe for a possible new origin of amino acids, density functional theory at the B3LYP/6-311++G(d, p) level has been carried out for important reactions between methaneimine, CH2NH, and the two isomers HNC/HCN via Strecker synthesis route, leading to the formation of aminoacetonitrile, H2NCH2CN, a precursor of glycine, both in the gas phase and on a model icy grain surface in the interstellar medium (ISM). This study shows the very feasible formation of H2NCH2CN among the CH2NH, HCN, HNC, and H2O molecules that are widespread in the interstellar dense molecular cloud before the Earth began and on the model icy grain surface in the ISM via Strecker synthesis route. This article discusses that H2NCH2CN might be prevalent throughout the Universe in the interstellar dense molecular cloud and then implies the importance of H2NCH2CN in the origin of amino acids and in the origin of life with respect to the “Primordial Soup”theory on the early Earth.
Amino acids are important biological compounds that played an essential role in the formation of peptides, the backbone of protein, in the prebiotic chemistry of the early Earth for the origin of life. To probe for a possible new origin of amino acids, density functional theory at the B3LYP/6-311++G(d, p) level has been carried out for important reactions between methaneimine, CH2NH, and the two isomers HNC/HCN via Strecker synthesis route, leading to the formation of aminoacetonitrile, H2NCH2CN, a precursor of glycine, both in the gas phase and on a model icy grain surface in the interstellar medium (ISM). This study shows the very feasible formation of H2NCH2CN among the CH2NH, HCN, HNC, and H2O molecules that are widespread in the interstellar dense molecular cloud before the Earth began and on the model icy grain surface in the ISM via Strecker synthesis route. This article discusses that H2NCH2CN might be prevalent throughout the Universe in the interstellar dense molecular cloud and then implies the importance of H2NCH2CN in the origin of amino acids and in the origin of life with respect to the “Primordial Soup”theory on the early Earth.
2007, 23(02): 217-222
doi: 10.3866/PKU.WHXB20070215
Abstract:
The gas-phase reaction mechanism of allyl anion with N2O was investigated at the MP2/6-31G(d,p) level of the MP2 theory. The single-point energies have also been refined at the CCSD(T)/6-31G(d,p) level to get more accurate energies using the MP2/6-31G(d,p) optimized geometries. The computational results indicated that the reaction involved three reaction pathways to produce cis-vinyl-diazomethyl anion, trans-vinyl-diazomethyl anion, and allenyl anion. The major competition channels of the reaction which produced cis-vinyl-diazomethyl anion, and trans-vinyl-diazomethyl anion all involved two steps of α-H migration. Furthermore, all these rate-determing steps are the second α-H migration and the barriers are 89.79 and 97.93 kJ·mol-1, respectively. Distinctly, allenyl anion was formed through one α-H and one β-H migration and its rate-determing step was the rotation of the N10—O11 and N9—C3 bonds around N—N bond. The rate coefficients of the rate-determining step of all the reaction channels have also been calculated using statistic thermodynamics and conventional transition state theory at 298 K.
The gas-phase reaction mechanism of allyl anion with N2O was investigated at the MP2/6-31G(d,p) level of the MP2 theory. The single-point energies have also been refined at the CCSD(T)/6-31G(d,p) level to get more accurate energies using the MP2/6-31G(d,p) optimized geometries. The computational results indicated that the reaction involved three reaction pathways to produce cis-vinyl-diazomethyl anion, trans-vinyl-diazomethyl anion, and allenyl anion. The major competition channels of the reaction which produced cis-vinyl-diazomethyl anion, and trans-vinyl-diazomethyl anion all involved two steps of α-H migration. Furthermore, all these rate-determing steps are the second α-H migration and the barriers are 89.79 and 97.93 kJ·mol-1, respectively. Distinctly, allenyl anion was formed through one α-H and one β-H migration and its rate-determing step was the rotation of the N10—O11 and N9—C3 bonds around N—N bond. The rate coefficients of the rate-determining step of all the reaction channels have also been calculated using statistic thermodynamics and conventional transition state theory at 298 K.
2007, 23(02): 223-227
doi: 10.1016/S1872-1508(07)60018-7
Abstract:
Novel polyurethane thiazole(PUT)/SiO2 nanocomposite material was prepared by hydrolysis and condensation of alkoxysilane dye, polyurethane (PU) containing alkoxysilane, and tetraethoxysiliane (TEOS) together using the sol-gel process. The structure and properties were characterized by IR, SEM, TEM, UV-Vis, and DSC-TGA measurements. The result showed that the organic phase connected with the inorganic phase by covalent bond without separation of phase in the material, and the content of thiazole chromophore with od nonlinearity in the material, the glassy temperature, and decomposed temperature of the material increase remarkably; thus, the material can be used to manufacture second-order nonlinear apparatus having fine performance.
Novel polyurethane thiazole(PUT)/SiO2 nanocomposite material was prepared by hydrolysis and condensation of alkoxysilane dye, polyurethane (PU) containing alkoxysilane, and tetraethoxysiliane (TEOS) together using the sol-gel process. The structure and properties were characterized by IR, SEM, TEM, UV-Vis, and DSC-TGA measurements. The result showed that the organic phase connected with the inorganic phase by covalent bond without separation of phase in the material, and the content of thiazole chromophore with od nonlinearity in the material, the glassy temperature, and decomposed temperature of the material increase remarkably; thus, the material can be used to manufacture second-order nonlinear apparatus having fine performance.
2007, 23(02): 228-231
doi: 10.3866/PKU.WHXB20070217
Abstract:
Using few-state model and DFT method, we calculate the nonlinear optical properties of three Benzothiazolyl-derivatives newly synthesized. The calculation results show that when the delocalization of the p electrons in the organic molecules increases the maximum absorption take place red-shift. When the conjugate chain has a longer size, the distribution of the increasing size of the conjugate chain on the increasing cross section is more important than the changing of pull-electron base. This kind of molecule has a better TPA characteristic.
Using few-state model and DFT method, we calculate the nonlinear optical properties of three Benzothiazolyl-derivatives newly synthesized. The calculation results show that when the delocalization of the p electrons in the organic molecules increases the maximum absorption take place red-shift. When the conjugate chain has a longer size, the distribution of the increasing size of the conjugate chain on the increasing cross section is more important than the changing of pull-electron base. This kind of molecule has a better TPA characteristic.
2007, 23(02): 232-236
doi: 10.3866/PKU.WHXB20070218
Abstract:
La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) precursor powder was prepared by a nitrate-glycine solution combustion method. The properties of LSCF powder were characterized by XRD, BET, FESEM, and dynamic laser scattering (DLS) method. The results showed that LSCF powder was in the perovskite structure with a specific surface area of 22.9 m2·g-1 and an average particle size of 175 nm. The results of non-isothermal sintering tests suggested that LSCF powder possessed od low-temperature sintering activity. The cell Ni-YSZ/YSZ/LSCF(YSZ: yttria stabilized zirconia) with the cathode sintered at 800 ℃ for 2 h demonstrated excellent generation performance with the maximum power density of 0.97 W·cm-2 and the power density of 0.83 W·cm-2 at 0.7 V under operation at 700 ℃. Low temperature processing of the interlayer-free LSCF cathode was beneficial to simplify the cell structure and manufacturing process and to improve the cell performance.
La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) precursor powder was prepared by a nitrate-glycine solution combustion method. The properties of LSCF powder were characterized by XRD, BET, FESEM, and dynamic laser scattering (DLS) method. The results showed that LSCF powder was in the perovskite structure with a specific surface area of 22.9 m2·g-1 and an average particle size of 175 nm. The results of non-isothermal sintering tests suggested that LSCF powder possessed od low-temperature sintering activity. The cell Ni-YSZ/YSZ/LSCF(YSZ: yttria stabilized zirconia) with the cathode sintered at 800 ℃ for 2 h demonstrated excellent generation performance with the maximum power density of 0.97 W·cm-2 and the power density of 0.83 W·cm-2 at 0.7 V under operation at 700 ℃. Low temperature processing of the interlayer-free LSCF cathode was beneficial to simplify the cell structure and manufacturing process and to improve the cell performance.
2007, 23(02): 237-241
doi: 10.3866/PKU.WHXB20070219
Abstract:
A ruthenium(II) complex of [Ru(bpy)2(Hfip)](ClO4)2 (bpy=2,2′-bipyridine, Hfip=2-(9H-fluoren-2-yl)-1H-imidazolo-[4,5-f]-[1,10]-phenanthrolin) was synthesized. The DNA binding properties of the complex were studied by means of electronic absorption and emission spectroscopic titrations, steady-state emission quenching by Fe(CN)4-6, viscosity measurements, DNA competitive binding with ethidium bromide, and thermal denaturation of DNA. The results indicated that the complex bound to calf-thymus DNA in an intercalative mode with a binding constant of 8.6×105 L·mol-1 in the presence of 50 mmol·L-1 NaCl solution.
A ruthenium(II) complex of [Ru(bpy)2(Hfip)](ClO4)2 (bpy=2,2′-bipyridine, Hfip=2-(9H-fluoren-2-yl)-1H-imidazolo-[4,5-f]-[1,10]-phenanthrolin) was synthesized. The DNA binding properties of the complex were studied by means of electronic absorption and emission spectroscopic titrations, steady-state emission quenching by Fe(CN)4-6, viscosity measurements, DNA competitive binding with ethidium bromide, and thermal denaturation of DNA. The results indicated that the complex bound to calf-thymus DNA in an intercalative mode with a binding constant of 8.6×105 L·mol-1 in the presence of 50 mmol·L-1 NaCl solution.
2007, 23(02): 242-246
doi: 10.1016/S1872-1508(07)60019-9
Abstract:
Rayleigh and Hyper-Rayleigh scatterings(HRS) from the nano-particle SnO2 were measured. It is found that as the concentration of the colloidal SnO2 or radiation power increases, the first- and second-order polarizabilities decrease. The radiation power dependencies of the first- and second-order polarizabilities show two domains: in high radiation power domain, the first- and second-order polarizabilities are approximately constant, in low radiation power domain, the first- and second-order polarizabilities increase sharply and become sensitive to the radiation power. The behavior of the concentration dependencies of the first- and second-order polarizabilities of colloidal SnO2 particles is similar to that of the radiation power dependence. A detailed mechanism explaining these phenomena has been discussed.
Rayleigh and Hyper-Rayleigh scatterings(HRS) from the nano-particle SnO2 were measured. It is found that as the concentration of the colloidal SnO2 or radiation power increases, the first- and second-order polarizabilities decrease. The radiation power dependencies of the first- and second-order polarizabilities show two domains: in high radiation power domain, the first- and second-order polarizabilities are approximately constant, in low radiation power domain, the first- and second-order polarizabilities increase sharply and become sensitive to the radiation power. The behavior of the concentration dependencies of the first- and second-order polarizabilities of colloidal SnO2 particles is similar to that of the radiation power dependence. A detailed mechanism explaining these phenomena has been discussed.
Effect of Oxyethylene Numbers on Surface Dilational Properties of Octylphenol polyoxyethylene ethers
2007, 23(02): 247-252
doi: 10.3866/PKU.WHXB20070221
Abstract:
The surface dilational viscoelasticities of octylphenol polyoxyethylene ethers solutions, TX-100(10 oxyethylene (EO), TX-102(12EO) and TX-165(16EO), were investigated by Langmuir trough method. The influences of polyoxyethylene numbers on surface dilational properties were expounded. It showed that the increase of polyoxyethylene numbers resulted in the increase of surface dilational modulus and elasticity, which may be attributed to the slower relaxation processes caused by the “flat-configuration” of the longer polyoxyethylene chain at the surface.
The surface dilational viscoelasticities of octylphenol polyoxyethylene ethers solutions, TX-100(10 oxyethylene (EO), TX-102(12EO) and TX-165(16EO), were investigated by Langmuir trough method. The influences of polyoxyethylene numbers on surface dilational properties were expounded. It showed that the increase of polyoxyethylene numbers resulted in the increase of surface dilational modulus and elasticity, which may be attributed to the slower relaxation processes caused by the “flat-configuration” of the longer polyoxyethylene chain at the surface.
2007, 23(02): 253-257
doi: 10.3866/PKU.WHXB20070222
Abstract:
Using surface tension method, the changes of surface activity and thermodynamic properties of a novel borate surfactant surfmer (BES) in aqueous solution were studied at different temperatures (288-313 K). The interaction of BES with sodium dodecylbenzene sulfonate (LAS) in 0.5 mol·L-1 aqueous NaCl solutions was also measured. The results showed that the critical micelle concentration(cmc) of BES at 298 K was 0.066 mmol·L-1, and γcmc was 29.2 mN·m-1. The micellization free energie (ΔG0m) was in the range of -22.4 - -25.8 kJ·mol-1 at the experimental temperatures, and the process of micellization of BES was mainly driven by the entropy. The mixed BES/LAS solution was a non-ideal system with negative deviation, and the average molecular interaction parameter βm was -3.48. When the molar fraction αBES of BES in bulk solution was 0.5, its molar fraction X1m in mixed micelles was 0.46, |βm| could reach the maximum, cmc of the mixed solution reached the minimum 0.017 mmol·L-1, and γcmc was 27.8 mN·m-1.
Using surface tension method, the changes of surface activity and thermodynamic properties of a novel borate surfactant surfmer (BES) in aqueous solution were studied at different temperatures (288-313 K). The interaction of BES with sodium dodecylbenzene sulfonate (LAS) in 0.5 mol·L-1 aqueous NaCl solutions was also measured. The results showed that the critical micelle concentration(cmc) of BES at 298 K was 0.066 mmol·L-1, and γcmc was 29.2 mN·m-1. The micellization free energie (ΔG0m) was in the range of -22.4 - -25.8 kJ·mol-1 at the experimental temperatures, and the process of micellization of BES was mainly driven by the entropy. The mixed BES/LAS solution was a non-ideal system with negative deviation, and the average molecular interaction parameter βm was -3.48. When the molar fraction αBES of BES in bulk solution was 0.5, its molar fraction X1m in mixed micelles was 0.46, |βm| could reach the maximum, cmc of the mixed solution reached the minimum 0.017 mmol·L-1, and γcmc was 27.8 mN·m-1.
2007, 23(02): 258-261
doi: 10.3866/PKU.WHXB20070223
Abstract:
Single-crystalline α-MnO2 and β-MnO2 nanorods were prepared directly by facile hydrothermal process at 150 ℃ and 220 ℃, respectively. The as-synthesized α-MnO2 and β-MnO2 nanorods were investigated by XRD, TEM, SEM, and EDS. The temperature was found to play important roles in controlling the synthesis of α-MnO2 and β-MnO2 nanorods.
Single-crystalline α-MnO2 and β-MnO2 nanorods were prepared directly by facile hydrothermal process at 150 ℃ and 220 ℃, respectively. The as-synthesized α-MnO2 and β-MnO2 nanorods were investigated by XRD, TEM, SEM, and EDS. The temperature was found to play important roles in controlling the synthesis of α-MnO2 and β-MnO2 nanorods.
2007, 23(02): 262-267
doi: 10.3866/PKU.WHXB20070224
Abstract:
By means of fluorescence and resonance light scattering spectrometries, the comparison of the interactions was made between metronidazole and bovine serum albumin(BSA). The apparent binding constant KA was found to be 2.22×104 L·mol-1 and the binding sits n to be 1.06±0.02 at 298 K by fluorescence quenching method. The quenching mechanism was discussed referring to metronidazole against the fluorescence and the resonance light scattering of BSA. The thermodynamic parameters of binding reaction were determined as follows: the molar change of enthalpy ΔrHm=6.42 kJ·mol-1, the molar change of Gibbs function ΔrGm=-23.0 kJ·mol-1, and the molar change of entropy ΔrSm=98.8 J·mol-1·K-1 at 298 K. The binding power between metronidazole and bovine serum albumin was also discussed. Furthermore, the binding distance of 3.16 nm was obtained between metronidazole and bovine serum albumin based on the mechanism of Forster non-radiation energy transfer. The effect of metronidazole on the conformation of BSA was analyzed by using the synchronous fluorescence spectroscopy.
By means of fluorescence and resonance light scattering spectrometries, the comparison of the interactions was made between metronidazole and bovine serum albumin(BSA). The apparent binding constant KA was found to be 2.22×104 L·mol-1 and the binding sits n to be 1.06±0.02 at 298 K by fluorescence quenching method. The quenching mechanism was discussed referring to metronidazole against the fluorescence and the resonance light scattering of BSA. The thermodynamic parameters of binding reaction were determined as follows: the molar change of enthalpy ΔrHm=6.42 kJ·mol-1, the molar change of Gibbs function ΔrGm=-23.0 kJ·mol-1, and the molar change of entropy ΔrSm=98.8 J·mol-1·K-1 at 298 K. The binding power between metronidazole and bovine serum albumin was also discussed. Furthermore, the binding distance of 3.16 nm was obtained between metronidazole and bovine serum albumin based on the mechanism of Forster non-radiation energy transfer. The effect of metronidazole on the conformation of BSA was analyzed by using the synchronous fluorescence spectroscopy.
2007, 23(02): 268-273
doi: 10.3866/PKU.WHXB20070225
Abstract:
RuOx-PdO/Ti electrode was prepared and used in the photoelectrochemical degradation of reactive brilliant red K-2BP. The effects of supporting electrolytes, such as NaCl, NaNO3, and Na2SO4, on the discoloration were studied. Several parameters altering the efficiency of the photoelectrochemical degradation were also investigated and optimized. It was found that under the optimal reaction conditions, that is, pH≈6.0, the NaCl concentration 0.02 mol·L-1, and current intensity 0.25 mA·cm-2, a color removal of 91.6% within 30 min could be obtained. The main cause of the discoloration could be attributed to a synergetic effect between electrochemical process and photochemical process, that is, to a synergetic effect between the active chlorine formed during the electrochemical treatment as well as the derived HO∙, O-, Cl∙ species under photo radiation and the photoelectrochemical degradation. The electrode performed well over a wide range of temperatures and initial concentrations of dye. This showed promise for the application of RuOx-PdO/Ti electrode in the treatment of dye-polluted water.
RuOx-PdO/Ti electrode was prepared and used in the photoelectrochemical degradation of reactive brilliant red K-2BP. The effects of supporting electrolytes, such as NaCl, NaNO3, and Na2SO4, on the discoloration were studied. Several parameters altering the efficiency of the photoelectrochemical degradation were also investigated and optimized. It was found that under the optimal reaction conditions, that is, pH≈6.0, the NaCl concentration 0.02 mol·L-1, and current intensity 0.25 mA·cm-2, a color removal of 91.6% within 30 min could be obtained. The main cause of the discoloration could be attributed to a synergetic effect between electrochemical process and photochemical process, that is, to a synergetic effect between the active chlorine formed during the electrochemical treatment as well as the derived HO∙, O-, Cl∙ species under photo radiation and the photoelectrochemical degradation. The electrode performed well over a wide range of temperatures and initial concentrations of dye. This showed promise for the application of RuOx-PdO/Ti electrode in the treatment of dye-polluted water.
2007, 23(02): 274-284
doi: 10.3866/PKU.WHXB20070226
Abstract:
Recent progress in the studies of fluorescent film sensors was reviewed according to the preparation methods of the film sensors, which have been classified into physical method, chemical method, and method based on self-assembled monolayers (SAM) technique. Furthermore, the future of the research in this field is envisaged.
Recent progress in the studies of fluorescent film sensors was reviewed according to the preparation methods of the film sensors, which have been classified into physical method, chemical method, and method based on self-assembled monolayers (SAM) technique. Furthermore, the future of the research in this field is envisaged.
