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2006 Volume 22 Issue 11
2006, 22(11): 1305-1309
doi: 10.3866/PKU.WHXB20061101
Abstract:
An improved preparation method for carbon supported PtRu catalysts has been developed, by reduction of Pt(IV) and Ru(III), using SDS as stabilizer in ethylene glycol (EG) solution. The results indicate that high loading and high dispersion of PtRu/C catalysts, with the average particle size 2.7 nm, can be obtained by this technique. The morphology, structure, and electrochemical activity of the prepared electrodes have been analyzed by TEM, XRD, and cyclic voltammeter (CV). Compared with the PtRu/C catalysts prepared in traditional EGl solution, the as prepared nano PtRu/C catalysts possess a higher catalytic activity and a better tolerance capacity to CO in direct methanol fuel cell (DMFC).
An improved preparation method for carbon supported PtRu catalysts has been developed, by reduction of Pt(IV) and Ru(III), using SDS as stabilizer in ethylene glycol (EG) solution. The results indicate that high loading and high dispersion of PtRu/C catalysts, with the average particle size 2.7 nm, can be obtained by this technique. The morphology, structure, and electrochemical activity of the prepared electrodes have been analyzed by TEM, XRD, and cyclic voltammeter (CV). Compared with the PtRu/C catalysts prepared in traditional EGl solution, the as prepared nano PtRu/C catalysts possess a higher catalytic activity and a better tolerance capacity to CO in direct methanol fuel cell (DMFC).
2006, 22(11): 1310-1316
doi: 10.1016/S1872-1508(06)60064-8
Abstract:
The effects of copper and potassium on the activity and selectivity of coprecipitated Fe-Mn/SiO2 catalysts for Fischer-Tropsch (F-T) synthesis were studied in a slurry phase continuous stirred tank reactor. The reduction and adsorption behaviors of the catalysts were investigated using temperature programmed reduction/temperature programmed desorption (TPR/TPD) methods. It was found that copper improves the reduction of the catalyst in H2 or CO. Potassium improves the reduction of the catalyst in CO, whereas it suppresses the reduction of the catalyst in H2. Copper enhances the H2 adsorption, whereas potassium has no influence on the H2 adsorption. In the F-T synthesis reaction, copper shortens the induction period required for reaching the steady state activity, whereas potassium prolongs the induction period. The potassium promoter increases the activity and decreases the selectivity of methane. The promotion effects of Cu and K on the activity and selectivity is more obvious than that of Cu, that is, the activity is higher and the methane selectivity is lower on the doubly promoted catalyst.
The effects of copper and potassium on the activity and selectivity of coprecipitated Fe-Mn/SiO2 catalysts for Fischer-Tropsch (F-T) synthesis were studied in a slurry phase continuous stirred tank reactor. The reduction and adsorption behaviors of the catalysts were investigated using temperature programmed reduction/temperature programmed desorption (TPR/TPD) methods. It was found that copper improves the reduction of the catalyst in H2 or CO. Potassium improves the reduction of the catalyst in CO, whereas it suppresses the reduction of the catalyst in H2. Copper enhances the H2 adsorption, whereas potassium has no influence on the H2 adsorption. In the F-T synthesis reaction, copper shortens the induction period required for reaching the steady state activity, whereas potassium prolongs the induction period. The potassium promoter increases the activity and decreases the selectivity of methane. The promotion effects of Cu and K on the activity and selectivity is more obvious than that of Cu, that is, the activity is higher and the methane selectivity is lower on the doubly promoted catalyst.
2006, 22(11): 1317-1320
doi: 10.1016/S1872-1508(06)60065-X
Abstract:
The process of electroless copper plating, using sodium hypophosphite as the reductant and sodium citrate as the chelating agent, was studied using linear sweep voltametry. The effects of temperature, pH, and concentration of nickel ion on the anodic oxidation of hypophosphite and the cathodic reduction of copper ion were tested. The results indicated that the higher ultrasonic bath temperature accelerated both the anodic and the cathodic processes. The increasing pH value promoted hypophosphite oxidation, whereas it blocked the reduction of the copper ion. The nickel ion not only intensively catalyzed the hypophosphite oxidation, but also codeposited with the copper ion to form the Cu-Ni alloy. With regard to its catalytic activity, this alloy enabled the continuation of the electroless copper plating reaction.
The process of electroless copper plating, using sodium hypophosphite as the reductant and sodium citrate as the chelating agent, was studied using linear sweep voltametry. The effects of temperature, pH, and concentration of nickel ion on the anodic oxidation of hypophosphite and the cathodic reduction of copper ion were tested. The results indicated that the higher ultrasonic bath temperature accelerated both the anodic and the cathodic processes. The increasing pH value promoted hypophosphite oxidation, whereas it blocked the reduction of the copper ion. The nickel ion not only intensively catalyzed the hypophosphite oxidation, but also codeposited with the copper ion to form the Cu-Ni alloy. With regard to its catalytic activity, this alloy enabled the continuation of the electroless copper plating reaction.
2006, 22(11): 1321-1324
doi: 10.3866/PKU.WHXB20061104
Abstract:
An interaction model between the host and the guest of layered double hydroxides (LDHs) is proposed. The structure parameters and vibration frequencies of LDHs are calculated using density functional theory B3LYP method at the 6-31G(d) level, and the interaction energies are evaluated with the B3LYP/6-31G(d) and B3LYP/6-311++G(d, p) methods, respectively. The supra-molecular interaction between a host layer and a guest anion has been investigated by analyzing the geometric parameters, charge population, frontier orbital, interaction energy, and thermodynamic parameters. The results show that the binding process of the host layer and halide anion is spontaneous. There is a strong supra-molecular interaction between the host layer and a guest anion F- or Cl-. The host-guest interaction energies of Mg6Al(OH)14+:F- and Mg6Al(OH)14+:Cl- are -592.45 and -444.01 kJ·mol-1, respectively. Supra-molecular interactions are resulted mainly from the electrostatic interaction and the hydrogen-bond. The frontier orbital of the host layer interacts with that of the guest anion, and the electron is transferred from HOMO of halide anion to LUMO of the host layer. Moreover, Mg6Al(OH)14+:F-is more stable than the Mg6Al(OH)14+:Cl-.
An interaction model between the host and the guest of layered double hydroxides (LDHs) is proposed. The structure parameters and vibration frequencies of LDHs are calculated using density functional theory B3LYP method at the 6-31G(d) level, and the interaction energies are evaluated with the B3LYP/6-31G(d) and B3LYP/6-311++G(d, p) methods, respectively. The supra-molecular interaction between a host layer and a guest anion has been investigated by analyzing the geometric parameters, charge population, frontier orbital, interaction energy, and thermodynamic parameters. The results show that the binding process of the host layer and halide anion is spontaneous. There is a strong supra-molecular interaction between the host layer and a guest anion F- or Cl-. The host-guest interaction energies of Mg6Al(OH)14+:F- and Mg6Al(OH)14+:Cl- are -592.45 and -444.01 kJ·mol-1, respectively. Supra-molecular interactions are resulted mainly from the electrostatic interaction and the hydrogen-bond. The frontier orbital of the host layer interacts with that of the guest anion, and the electron is transferred from HOMO of halide anion to LUMO of the host layer. Moreover, Mg6Al(OH)14+:F-is more stable than the Mg6Al(OH)14+:Cl-.
2006, 22(11): 1325-1330
doi: 10.3866/PKU.WHXB20061105
Abstract:
1-naphthylamine is a probe with intra-molecular charge transfer in nature. Its characteristic band ( ) is sensitive to the polarity of environment. It was found that the semilogarithmic plot of versus surfactant concentration C appeared the two inflection points. The first inflection point corresponded to the critical micelle concentration (cmc), and the second inflection point (Ccm) addressed the critical point reaching dense structure in the micellar core. The results showed that gemini surfactant only form small aggregates at the cmc. Over the range of cmc to Ccm, the aggregation number of the micelle rapidly increases with increasing C.
1-naphthylamine is a probe with intra-molecular charge transfer in nature. Its characteristic band ( ) is sensitive to the polarity of environment. It was found that the semilogarithmic plot of versus surfactant concentration C appeared the two inflection points. The first inflection point corresponded to the critical micelle concentration (cmc), and the second inflection point (Ccm) addressed the critical point reaching dense structure in the micellar core. The results showed that gemini surfactant only form small aggregates at the cmc. Over the range of cmc to Ccm, the aggregation number of the micelle rapidly increases with increasing C.
2006, 22(11): 1331-1336
doi: 10.1016/S1872-1508(06)60066-1
Abstract:
Electronic structures of LaNi5−xCox (x=0, 0.5, 1) hydrogen-storage alloy have been studied theoretically using the method of total energy based on the density functional theory (DFT). The plane wave function was selected as the basis set in combination with the ultrasoft pseudopotential technology. Crystal structure, energy band structure, electronic density of states, and Mulliken density of LaNi5−xCox were calculated. The results indicated that valence electrons were mainly fastened around fermi energy (EF) and EF moved toward the direction of lower energy with the increase of the Co content. According to the analysis of Mulliken overlap populations, the numerical values of the bonds between Ni3g—Ni3g and Ni2c—Ni2c decreased. It showed that Co doping let to the decrease in the bond energy between Ni—Ni. However, the values on the bond between La—Ni increased and the relevant bond energy increased.
Electronic structures of LaNi5−xCox (x=0, 0.5, 1) hydrogen-storage alloy have been studied theoretically using the method of total energy based on the density functional theory (DFT). The plane wave function was selected as the basis set in combination with the ultrasoft pseudopotential technology. Crystal structure, energy band structure, electronic density of states, and Mulliken density of LaNi5−xCox were calculated. The results indicated that valence electrons were mainly fastened around fermi energy (EF) and EF moved toward the direction of lower energy with the increase of the Co content. According to the analysis of Mulliken overlap populations, the numerical values of the bonds between Ni3g—Ni3g and Ni2c—Ni2c decreased. It showed that Co doping let to the decrease in the bond energy between Ni—Ni. However, the values on the bond between La—Ni increased and the relevant bond energy increased.
2006, 22(11): 1336-1341
doi: 10.3866/PKU.WHXB20061107
Abstract:
Li4Ti5O12 was modified by doped Sb2O3. The samples were characterized by galvanostatic charge-discharge，cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). The results indicated that the initial capacity was as high as 595.84mAhog-1 and the colombic efficiency was 45.7％when Ti：Sb＝4：1. The capacity was still 249.57mAhog-1 after 20 charge-discharge cycles. The possible reaction mechanism was proposed and used to explained the losses of capacity. EIS results showed that Sb-doping could suppressed the electrochemical reaction resistant.
Li4Ti5O12 was modified by doped Sb2O3. The samples were characterized by galvanostatic charge-discharge，cyclic voltammetry(CV) and electrochemical impedance spectroscopy(EIS). The results indicated that the initial capacity was as high as 595.84mAhog-1 and the colombic efficiency was 45.7％when Ti：Sb＝4：1. The capacity was still 249.57mAhog-1 after 20 charge-discharge cycles. The possible reaction mechanism was proposed and used to explained the losses of capacity. EIS results showed that Sb-doping could suppressed the electrochemical reaction resistant.
2006, 22(11): 1342-1346
doi: 10.1016/S1872-1508(06)60067-3
Abstract:
A novel magnetic nanoadsorbent was prepared by the covalent binding of carboxymethyl chitosan (CMC) onto the surface of Fe3O4 magnetic nanoparticles, which was developed using a coprecipitation method. This nanoadsorbent was characterized by transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD), etc. Moreover, the adsorption performance of the nanoadsorbent towards Zn2+ ions was investigated. The results showed that the mean diameter of the magnetic nanoadsorbent was 18 nm and the amount of CMC was about 5%. The nanoadsorbent showed high efficiency for the removal of Zn2+ ions. The adsorption rate was so rapid that the equilibrium was achieved within 2 min. The isotherm adsorption data obeyed the Langmuir model, with a maximum adsorption capacity of 20.4 mg•g−1 and an adsorption equilibrium constant of 0.0314 L•mg−1. The thermodynamic calculation indicated that the adsorption process was exothermic and the enthalpy change was -5.68 kJ•mol−1.
A novel magnetic nanoadsorbent was prepared by the covalent binding of carboxymethyl chitosan (CMC) onto the surface of Fe3O4 magnetic nanoparticles, which was developed using a coprecipitation method. This nanoadsorbent was characterized by transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD), etc. Moreover, the adsorption performance of the nanoadsorbent towards Zn2+ ions was investigated. The results showed that the mean diameter of the magnetic nanoadsorbent was 18 nm and the amount of CMC was about 5%. The nanoadsorbent showed high efficiency for the removal of Zn2+ ions. The adsorption rate was so rapid that the equilibrium was achieved within 2 min. The isotherm adsorption data obeyed the Langmuir model, with a maximum adsorption capacity of 20.4 mg•g−1 and an adsorption equilibrium constant of 0.0314 L•mg−1. The thermodynamic calculation indicated that the adsorption process was exothermic and the enthalpy change was -5.68 kJ•mol−1.
2006, 22(11): 1347-1352
doi: 10.3866/PKU.WHXB20061109
Abstract:
The new concept of the glass-transition temperature of the partially freeze-concentrated solution (Tgf) is brought forward and a new method is given for measuring Tgf of 20% and 45% glucose solution using differential scanning calorimetry (DSC), which is based on annealing samples for long periods of time at different temperatures. The influence of annealing temperature on Tgf is studied. It is found that the Tgf increases initially with annealing temperature up to −50 ℃, and decreases as the temperature continues to increase, and exhibiting a od linear relation in both cases. The same phenomenon was observed for glucose solutions of different concentrations. It is concluded that the Tg′ (glass transition temperature of the maximally freeze-concentrated solution) can be determined from the intersection of the two curves reflecting the Tgf change with annealing temperature. The optimal annealing temperature(−50 ℃) and accurate glass transition temperature(Tg′, −55 ℃） of glucose solution are obtained.
The new concept of the glass-transition temperature of the partially freeze-concentrated solution (Tgf) is brought forward and a new method is given for measuring Tgf of 20% and 45% glucose solution using differential scanning calorimetry (DSC), which is based on annealing samples for long periods of time at different temperatures. The influence of annealing temperature on Tgf is studied. It is found that the Tgf increases initially with annealing temperature up to −50 ℃, and decreases as the temperature continues to increase, and exhibiting a od linear relation in both cases. The same phenomenon was observed for glucose solutions of different concentrations. It is concluded that the Tg′ (glass transition temperature of the maximally freeze-concentrated solution) can be determined from the intersection of the two curves reflecting the Tgf change with annealing temperature. The optimal annealing temperature(−50 ℃) and accurate glass transition temperature(Tg′, −55 ℃） of glucose solution are obtained.
2006, 22(11): 1353-1360
doi: 10.3866/PKU.WHXB20061110
Abstract:
Based on the study of the adsorption and thermal reactions of 2-iodoethanol on clean Ni(100) surface, further research and discussion were conducted on the results of experimental data, and the mechanism of chemical reaction was analyzed in detail. Two potential intermediates (2-hydroxyethyl and oxametallacycle surface species) in catalytic oxidation hydrocarbons were studied. 2-iodoethanol adsorbed molecularly on Ni(100) at 100 K starts chemical reaction around 140 K and produces small amounts of ethylene and water, due to the concerted decomposition or disproportionation of the adsorbed molecular species. Around 150 K with an initial C—I bond scission, 80% of 2-iodoethanol decompose to form —O(H)CH2CH2—, while 20% of 2-iodoethanol transform to 2-hydroxyethyl intermediates. The subsequent reaction of the 2-hydroxyethyl species around 160 K concerns two competing reactions: a reductive elimination with surface hydrogen to yield ethanol, and a β-H elimination to from surface vinyl alcohol. At the same temperature, the —O(H)CH2CH2— intermediate dehydrogenates to a —OCH2CH2— oxametallacycle species. Both 2-hydroxyethyl and oxametallacycle species tautomerize to acetaldehyde, around 210 K and above 250 K, respectively. Some of that acetaldehyde desorbs while the rest decomposes to hydrogen and carbon monoxide. The implications of this chemical process to catalysis are discussed.
Based on the study of the adsorption and thermal reactions of 2-iodoethanol on clean Ni(100) surface, further research and discussion were conducted on the results of experimental data, and the mechanism of chemical reaction was analyzed in detail. Two potential intermediates (2-hydroxyethyl and oxametallacycle surface species) in catalytic oxidation hydrocarbons were studied. 2-iodoethanol adsorbed molecularly on Ni(100) at 100 K starts chemical reaction around 140 K and produces small amounts of ethylene and water, due to the concerted decomposition or disproportionation of the adsorbed molecular species. Around 150 K with an initial C—I bond scission, 80% of 2-iodoethanol decompose to form —O(H)CH2CH2—, while 20% of 2-iodoethanol transform to 2-hydroxyethyl intermediates. The subsequent reaction of the 2-hydroxyethyl species around 160 K concerns two competing reactions: a reductive elimination with surface hydrogen to yield ethanol, and a β-H elimination to from surface vinyl alcohol. At the same temperature, the —O(H)CH2CH2— intermediate dehydrogenates to a —OCH2CH2— oxametallacycle species. Both 2-hydroxyethyl and oxametallacycle species tautomerize to acetaldehyde, around 210 K and above 250 K, respectively. Some of that acetaldehyde desorbs while the rest decomposes to hydrogen and carbon monoxide. The implications of this chemical process to catalysis are discussed.
2006, 22(11): 1361-1366
doi: 10.1016/S1872-1508(06)60068-5
Abstract:
The electrochemical quartz crystal microbalance (EQCM) method was used to quantitatively examine the precipitation of LiOH (or NaOH) onto a ld electrode at potentials negative to ca −0.8 V (vs SCE) during the cathodic sweep reduction of dissolved oxygen and coexisting water in acetone, DMF, DMSO, C2H5OH, or CH3OH containing hydrated perchlorate, as a result of the poor solubility of electrogenerated hydroxide in the nonaqueous medium. In contrast, the EQCM response indicative of precipitate adherence was negligibly small, when tetrabutyl ammonium bromide was used as supporting electrolyte. Effects of electrolyte and its concentration, solvent, and water content on the electrodeposition of hydroxide were discussed, and the electrode-collection efficiency for the precipitate was evaluated.
The electrochemical quartz crystal microbalance (EQCM) method was used to quantitatively examine the precipitation of LiOH (or NaOH) onto a ld electrode at potentials negative to ca −0.8 V (vs SCE) during the cathodic sweep reduction of dissolved oxygen and coexisting water in acetone, DMF, DMSO, C2H5OH, or CH3OH containing hydrated perchlorate, as a result of the poor solubility of electrogenerated hydroxide in the nonaqueous medium. In contrast, the EQCM response indicative of precipitate adherence was negligibly small, when tetrabutyl ammonium bromide was used as supporting electrolyte. Effects of electrolyte and its concentration, solvent, and water content on the electrodeposition of hydroxide were discussed, and the electrode-collection efficiency for the precipitate was evaluated.
2006, 22(11): 1367-1371
doi: 10.3866/PKU.WHXB20061112
Abstract:
Molecular dynamics simulations of low index direction surfaces in melting processes at different temperatures were performed for metal Cu. The variation of the structure in the system and the movement of the interface position between solid and liquid during surface melting process were observed. The interaction between atoms in the system was calculated by adopting the embedded atom potential proposed by Mishin. The order in the stability follows the same order as in the packing density: (110), (100) and (111). The solid-liquid interface remains unchanged during the surface melting process around temperature 1360～1380 K which coincides well with the experiment datum 1358 K. The kinetic coefficient is defined as the ratio of the interface velocity to undercooling. The values of kinetic coefficient for low interface (100), (110), (111) are anisotropic: k100=39 cm•s−1•K−1, k110=29 cm•s−1•K−1, k111=20 cm•s−1•K−1. The relationship between the kinetic coeficients in directions (100) and (110) agrees well with the collision-limited theory, however the kinetic coefficient of direction (111) is 4 times less than the theoretical limit.
Molecular dynamics simulations of low index direction surfaces in melting processes at different temperatures were performed for metal Cu. The variation of the structure in the system and the movement of the interface position between solid and liquid during surface melting process were observed. The interaction between atoms in the system was calculated by adopting the embedded atom potential proposed by Mishin. The order in the stability follows the same order as in the packing density: (110), (100) and (111). The solid-liquid interface remains unchanged during the surface melting process around temperature 1360～1380 K which coincides well with the experiment datum 1358 K. The kinetic coefficient is defined as the ratio of the interface velocity to undercooling. The values of kinetic coefficient for low interface (100), (110), (111) are anisotropic: k100=39 cm•s−1•K−1, k110=29 cm•s−1•K−1, k111=20 cm•s−1•K−1. The relationship between the kinetic coeficients in directions (100) and (110) agrees well with the collision-limited theory, however the kinetic coefficient of direction (111) is 4 times less than the theoretical limit.
2006, 22(11): 1372-1376
doi: 10.1016/S1872-1508(06)60069-7
Abstract:
Indolo[1,2-b]quinazoline derivatives have recently been reported as a type of compound with potential anticancer activity. On the basis of our the published two-dimensional quantitative structure-activity relationship (2D-QSAR) of these compounds, a further study on the three-dimensional quantitative structure-activity relationship (3D-QSAR) was carried out using the method of comparative molecular field analysis (CoMFA). A reasonable, receivable, and an effective 3D-QSAR model has been established, in which the correlation coefficient (r2) and cross-validation coefficient (q2) values are 0.986 and 0.695, respectively, the statistical squared deviation ratio (F) is 114.6, and the standard deviation (SD) is 0.084. The results suggest that the electrostatic effect of substituent R1 and steric effect of substituent R2 play a very important roles in the improvement of the anticancer activity of these compounds. In this article, some significant conclusions were drawn, which are in od agreement with the conclusions obtained using 2D-QSAR, which are as follows: A electrostatic effect in the substituent R1 part plays a major role，and it is very important to make the first atom of R1 carrying more positive charges in order to improve the anticancer activity of the compounds. B the steric effect plays a major role in the substituent R2 part，and the volume of R2 should be moderate. Based on the above conclusions, three new molecules of Indolo[1,2-b]quinazoline derivatives with higher anticancer activity have been theoretically designed and are waiting for support from experiment. The QSAR results can offer a theoretical reference for the pharmaceutical synthesis.
Indolo[1,2-b]quinazoline derivatives have recently been reported as a type of compound with potential anticancer activity. On the basis of our the published two-dimensional quantitative structure-activity relationship (2D-QSAR) of these compounds, a further study on the three-dimensional quantitative structure-activity relationship (3D-QSAR) was carried out using the method of comparative molecular field analysis (CoMFA). A reasonable, receivable, and an effective 3D-QSAR model has been established, in which the correlation coefficient (r2) and cross-validation coefficient (q2) values are 0.986 and 0.695, respectively, the statistical squared deviation ratio (F) is 114.6, and the standard deviation (SD) is 0.084. The results suggest that the electrostatic effect of substituent R1 and steric effect of substituent R2 play a very important roles in the improvement of the anticancer activity of these compounds. In this article, some significant conclusions were drawn, which are in od agreement with the conclusions obtained using 2D-QSAR, which are as follows: A electrostatic effect in the substituent R1 part plays a major role，and it is very important to make the first atom of R1 carrying more positive charges in order to improve the anticancer activity of the compounds. B the steric effect plays a major role in the substituent R2 part，and the volume of R2 should be moderate. Based on the above conclusions, three new molecules of Indolo[1,2-b]quinazoline derivatives with higher anticancer activity have been theoretically designed and are waiting for support from experiment. The QSAR results can offer a theoretical reference for the pharmaceutical synthesis.
2006, 22(11): 1377-1382
doi: 10.1016/S1872-1508(06)60070-3
Abstract:
Two long-chain multidentate ligands, 2,9-di(n-2′,5′,8′-triazanonyl)-1,10-phenanthroline (L1) and 2,9-di(n-4′,7′,10′-triazaundecyl)-1,10-phenanthroline (L2), were synthesized and characterized using 1H NMR and elemental analysis. The thermodynamic properties of the ligands and their complexes with transition metal ions and rare earth metal ions were investigated using potentiometric titrations. The coordination capabilities of the ligands with the transition metal ions followed the Irving-William sequence: Co(II)Zn(II). The stability constants of the ligands with the rare earth metal ions increase from La(III) to Gd(III). The coordination ratio of the ligands and the metal ions is 1?1. The similarities and the differences between the two series of complexes were studied. In addition, the factors influencing the results were researched. The results of this study indicate that all rare earth complexes in this study have the species 11-1, which can catalyze the hydrolysis of biological macromolecules. This property means that they are potentially useful as a od model of hydrolysis enzyme that has the capacity to cleave DNA and diester phosphate.
Two long-chain multidentate ligands, 2,9-di(n-2′,5′,8′-triazanonyl)-1,10-phenanthroline (L1) and 2,9-di(n-4′,7′,10′-triazaundecyl)-1,10-phenanthroline (L2), were synthesized and characterized using 1H NMR and elemental analysis. The thermodynamic properties of the ligands and their complexes with transition metal ions and rare earth metal ions were investigated using potentiometric titrations. The coordination capabilities of the ligands with the transition metal ions followed the Irving-William sequence: Co(II)Zn(II). The stability constants of the ligands with the rare earth metal ions increase from La(III) to Gd(III). The coordination ratio of the ligands and the metal ions is 1?1. The similarities and the differences between the two series of complexes were studied. In addition, the factors influencing the results were researched. The results of this study indicate that all rare earth complexes in this study have the species 11-1, which can catalyze the hydrolysis of biological macromolecules. This property means that they are potentially useful as a od model of hydrolysis enzyme that has the capacity to cleave DNA and diester phosphate.
2006, 22(11): 1383-1387
doi: 10.1016/S1872-1508(06)60071-5
Abstract:
ZnO phosphor was synthesized by annealing ZnO powder at low O2 partial pressure and in vacuum. ZnO has two emissions, which are located at about 380 nm (UV emission) and 510 nm (green emission). The UV emission can be attributed to the exciton emission, which is a single-center process, whereas the green emission is related to native defects, such as VO• and VZn′, which is a two-center (donor-acceptor) recombination process. The high-density excitation favors the UV emission, whereas the green emission likely appears in the samples annealed at low O2 partial pressure. It was shown that the energy transfer may occur from the UV emission center to the green emission center, and the exciton diffusion mechanism for the transfer was proposed.
ZnO phosphor was synthesized by annealing ZnO powder at low O2 partial pressure and in vacuum. ZnO has two emissions, which are located at about 380 nm (UV emission) and 510 nm (green emission). The UV emission can be attributed to the exciton emission, which is a single-center process, whereas the green emission is related to native defects, such as VO• and VZn′, which is a two-center (donor-acceptor) recombination process. The high-density excitation favors the UV emission, whereas the green emission likely appears in the samples annealed at low O2 partial pressure. It was shown that the energy transfer may occur from the UV emission center to the green emission center, and the exciton diffusion mechanism for the transfer was proposed.
2006, 22(11): 1388-1392
doi: 10.1016/S1872-1508(06)60072-7
Abstract:
The growth mechanism of armchair single-walled carbon nanotube has been studied theoretically by AM1 method as implemented in Gaussian03 program. The following results were obtained. (1) Let C2 radicals be the carbon source for the growth of the carbon nanotube, then the most likely growth mechanism would be as follows. An intermediate is formed firstly by the direct addition of C2 radical to the open end of the carbon nanotube without an energy barrier, then via a transition state the reaction produces the product, i.e., C2 becomes the component of the hexa n of the nanotube. (2) From (3,3) to (6,6), the activation energy decreases (from 66.8 to 46.1 kJ•mol−1), whereas the conjugation of the nanotube increases. (3) The distribution of the frontier molecular orbitals indicates that the two edges of the newly formed hexa n maybe grow easily.
The growth mechanism of armchair single-walled carbon nanotube has been studied theoretically by AM1 method as implemented in Gaussian03 program. The following results were obtained. (1) Let C2 radicals be the carbon source for the growth of the carbon nanotube, then the most likely growth mechanism would be as follows. An intermediate is formed firstly by the direct addition of C2 radical to the open end of the carbon nanotube without an energy barrier, then via a transition state the reaction produces the product, i.e., C2 becomes the component of the hexa n of the nanotube. (2) From (3,3) to (6,6), the activation energy decreases (from 66.8 to 46.1 kJ•mol−1), whereas the conjugation of the nanotube increases. (3) The distribution of the frontier molecular orbitals indicates that the two edges of the newly formed hexa n maybe grow easily.
2006, 22(11): 1393-1398
doi: 10.3866/PKU.WHXB20061117
Abstract:
Both the C2h and C2v configurations of trimethylaluminum dimer (d-TMA) and the C3h structure of monomer were obtained by full optimization at B3LYP/6-311++G(3df, 2pd) level. With Complete Basis Set method CBS-4M as emphasis, the thermodynamic function values of each species of TMA in gas-phase equilibrium at 1.01×105 Pa and in the range of 300～550 K were calculated by simulation. Through the consideration of the triplet-state configuration of d-TMA and the effect of heterolytic reaction on system entropy value, ΔrHm and ΔrSm of the dissociation reaction of d-TMA were accurately calculated at the same time. The plot of lnKd vs 1/T had a perfectly linear relation: lnKd=−9624.4363/T+20.2303, and the correlation coefficient R2=1.0000, which agreed quite well with the predecessors′ experimental results. Based upon these findings, a new dissociation-association reaction mechanism of d-TMA in gas phase was proposed.
Both the C2h and C2v configurations of trimethylaluminum dimer (d-TMA) and the C3h structure of monomer were obtained by full optimization at B3LYP/6-311++G(3df, 2pd) level. With Complete Basis Set method CBS-4M as emphasis, the thermodynamic function values of each species of TMA in gas-phase equilibrium at 1.01×105 Pa and in the range of 300～550 K were calculated by simulation. Through the consideration of the triplet-state configuration of d-TMA and the effect of heterolytic reaction on system entropy value, ΔrHm and ΔrSm of the dissociation reaction of d-TMA were accurately calculated at the same time. The plot of lnKd vs 1/T had a perfectly linear relation: lnKd=−9624.4363/T+20.2303, and the correlation coefficient R2=1.0000, which agreed quite well with the predecessors′ experimental results. Based upon these findings, a new dissociation-association reaction mechanism of d-TMA in gas phase was proposed.
2006, 22(11): 1399-1403
doi: 10.3866/PKU.WHXB20061118
Abstract:
The critical overlap concentration c* of poly (4-vinylpyridine) (P4VP) in a mixed solvent of ethanol and water (V/V=1/1) was determined with viscometry. Afterward, the coordination process and complex structure between P4VP and Cu2+ ions were studied in dilute solution range and semi-dilute solution range with visible spectral method and coordination-conductometric titration method, respectively. The chemical structure of the complex was characterized by FTIR spectra, and the thermal property was measured with differential scanning calorimetry (DSC). The experiment results show that the critical overlap concentration c* for P4VP with Mr=1.06×105 is 15 mmol•L−1. In dilute solution, the intramolecular coordination of the macromolecular chains of P4VP with Cu2+ performs, and a blue soluble complex forms. It was found that the intramolecular complex needed at least nine or ten ligand units per cupric ion owing to the rigidity of polymer chains and the steric hindrance of bulky pyridine rings. Over the critical overlap concentration c*, namely in semi-dilute solution, the intermolecular coordination of the macromolecular chains of P4VP with Cu2+ takes place, an insoluble complex P4VP-Cu(II) forms due to coordination crosslinking, and the coordination number of the complex is three. The glass transition temperature (Tg) of the complex P4VP-Cu(II) is higher than that of P4VP.
The critical overlap concentration c* of poly (4-vinylpyridine) (P4VP) in a mixed solvent of ethanol and water (V/V=1/1) was determined with viscometry. Afterward, the coordination process and complex structure between P4VP and Cu2+ ions were studied in dilute solution range and semi-dilute solution range with visible spectral method and coordination-conductometric titration method, respectively. The chemical structure of the complex was characterized by FTIR spectra, and the thermal property was measured with differential scanning calorimetry (DSC). The experiment results show that the critical overlap concentration c* for P4VP with Mr=1.06×105 is 15 mmol•L−1. In dilute solution, the intramolecular coordination of the macromolecular chains of P4VP with Cu2+ performs, and a blue soluble complex forms. It was found that the intramolecular complex needed at least nine or ten ligand units per cupric ion owing to the rigidity of polymer chains and the steric hindrance of bulky pyridine rings. Over the critical overlap concentration c*, namely in semi-dilute solution, the intermolecular coordination of the macromolecular chains of P4VP with Cu2+ takes place, an insoluble complex P4VP-Cu(II) forms due to coordination crosslinking, and the coordination number of the complex is three. The glass transition temperature (Tg) of the complex P4VP-Cu(II) is higher than that of P4VP.
2006, 22(11): 1404-1408
doi: 10.3866/PKU.WHXB20061119
Abstract:
Co-ZrO2 co-precipitation catalysts were used to investigate the effect of the pretreatment atmosphere on the texture, crystal phase, and morphology of catalysts. The result indicated that the catalysts were sintered evidently above 500 ℃ in Ar and H2 atmospheres. After the pretreated catalysts were exposed to air, all the cobalt species were in existence as Co3O4 phase and the particle shape of the catalysts changed little. The pretreatment in CO atmosphere led to serious cracking and obvious coke deposition, and the catalyst mainly contained the cubic cobalt species. The pretreatment of the catalyst with syngas gave rise to serious sintering and trace of fragmentation, and it was found that the cubic and hexa nal cobalt co-existed in the catalyst.
Co-ZrO2 co-precipitation catalysts were used to investigate the effect of the pretreatment atmosphere on the texture, crystal phase, and morphology of catalysts. The result indicated that the catalysts were sintered evidently above 500 ℃ in Ar and H2 atmospheres. After the pretreated catalysts were exposed to air, all the cobalt species were in existence as Co3O4 phase and the particle shape of the catalysts changed little. The pretreatment in CO atmosphere led to serious cracking and obvious coke deposition, and the catalyst mainly contained the cubic cobalt species. The pretreatment of the catalyst with syngas gave rise to serious sintering and trace of fragmentation, and it was found that the cubic and hexa nal cobalt co-existed in the catalyst.
2006, 22(11): 1409-1412
doi: 10.3866/PKU.WHXB20061120
Abstract:
Three nanosized Co-Sn intermetallic compounds, namely, CoSn2, CoSn, and Co3Sn2, were prepared by solvothermal route and studied as new candidate anode materials for secondary lithium-ion batteries. The as-prepared powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). It was found that these three intermetallic compounds showed a high charge-discharge stability. However, they exhibit low electrochemical activity, especially for Co3Sn2, whose first charge capacity is only 93 mAh•g−1, because Li-ions cannot reach the interior of the crystal due to the low Li-ions diffusion rate.
Three nanosized Co-Sn intermetallic compounds, namely, CoSn2, CoSn, and Co3Sn2, were prepared by solvothermal route and studied as new candidate anode materials for secondary lithium-ion batteries. The as-prepared powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). It was found that these three intermetallic compounds showed a high charge-discharge stability. However, they exhibit low electrochemical activity, especially for Co3Sn2, whose first charge capacity is only 93 mAh•g−1, because Li-ions cannot reach the interior of the crystal due to the low Li-ions diffusion rate.
2006, 22(11): 1413-1418
doi: 10.3866/PKU.WHXB20061121
Abstract:
Lithium phosphorus oxynitride (LiPON) thin films were prepared by radio frequency (RF) magnetron sputtering. The morphology, composition and electrochemical performance of LiPON electrolyte thin films placed in humid ambient were investigated using SEM, XRD and XPS, and electrochemical measurements of AC (alternating current) impedance and potential linear scanning, respectively. Obvious changes in surface morphology, composition and electrochemical properties were found for the as-deposited LiPON film placed in humid ambient with a relative humidity of 40% for 24 h. Results showed that the uniformity of the film surface became poor, the contents of phosphorous and nitrogen in LiPON film decreased due to its reaction with H2O, releasing gaseous PH3 and NH3. In addition, the formation of Li2CO3 obviously increased the contents of carbon and oxygen in LiPON film. Therefore, LiPON thin films placed in humid ambient resulted in a bad effect on its electrochemical performance such as the ionic conductivity and the electrochemical stability window.
Lithium phosphorus oxynitride (LiPON) thin films were prepared by radio frequency (RF) magnetron sputtering. The morphology, composition and electrochemical performance of LiPON electrolyte thin films placed in humid ambient were investigated using SEM, XRD and XPS, and electrochemical measurements of AC (alternating current) impedance and potential linear scanning, respectively. Obvious changes in surface morphology, composition and electrochemical properties were found for the as-deposited LiPON film placed in humid ambient with a relative humidity of 40% for 24 h. Results showed that the uniformity of the film surface became poor, the contents of phosphorous and nitrogen in LiPON film decreased due to its reaction with H2O, releasing gaseous PH3 and NH3. In addition, the formation of Li2CO3 obviously increased the contents of carbon and oxygen in LiPON film. Therefore, LiPON thin films placed in humid ambient resulted in a bad effect on its electrochemical performance such as the ionic conductivity and the electrochemical stability window.
2006, 22(11): 1419-1422
doi: 10.3866/PKU.WHXB20061122
Abstract:
The excess enthalpies of α-pinene+p-cymene and β-pinene+p-cymene binary systems were determined at 298.15 K, 308.15 K and 318.15 K and at atmospheric pressure by using a Calvet microcalorimeter (BT2.15). The experimental excess enthalpy data were correlated with Redlich-Kister equation and the standard deviations were all very small. It was found that all the excess enthalpies of these two binary systems were positive in the range of the experimental concentrations and reach their maxima when the mole concentration x1 was about 0.5. The excess enthalpies were larger at the higher mixing temperatures. At the same temperatures, the excess enthalpies of α-pinene+p-cymene system were larger than that of β-pinene+p-cymene.
The excess enthalpies of α-pinene+p-cymene and β-pinene+p-cymene binary systems were determined at 298.15 K, 308.15 K and 318.15 K and at atmospheric pressure by using a Calvet microcalorimeter (BT2.15). The experimental excess enthalpy data were correlated with Redlich-Kister equation and the standard deviations were all very small. It was found that all the excess enthalpies of these two binary systems were positive in the range of the experimental concentrations and reach their maxima when the mole concentration x1 was about 0.5. The excess enthalpies were larger at the higher mixing temperatures. At the same temperatures, the excess enthalpies of α-pinene+p-cymene system were larger than that of β-pinene+p-cymene.
2006, 22(11): 1423-1426
doi: 10.3866/PKU.WHXB20061123
Abstract:
The nonlinear optical properties (μ, α, β) of van der Waals complexes X•••H2O(X=Li, Na, K) was calculated with 6-311G basis set series at MP2 level of theory, and the contribution of the effects of basis set and electronic correlation was analysed. The results show that these three complexes all have huge first hyperpolarizability, and the dispersion characteristic of their outer-shell electrons has a great influence on the first hyperpolerizability.
The nonlinear optical properties (μ, α, β) of van der Waals complexes X•••H2O(X=Li, Na, K) was calculated with 6-311G basis set series at MP2 level of theory, and the contribution of the effects of basis set and electronic correlation was analysed. The results show that these three complexes all have huge first hyperpolarizability, and the dispersion characteristic of their outer-shell electrons has a great influence on the first hyperpolerizability.
2006, 22(11): 1427-1430
doi: 10.3866/PKU.WHXB20061124
Abstract:
The size of nano Fe powders was determined to be 25 nm in diameter by SEM. The isobaric molar heat capacity Cp of the nano Fe was measured with the high precision adiabatic low-temperature calorimeter in the temperature range from 84 K to 350 K. The relationship of Cp with temperature T was established as: Cp=36.831+14.772 x−5.4968x2−0.7099x3−1.3188x4, where x=(T−234)/156. The thermodynamic functions of the nano Fe, relative to the standard temperature of 298.15 K, were derived based on the heat capacity data through thermodynamic relationship. The measured Cp values were compared with those of coarse crystal powders and 87 nm Fe powders cited from literature and the difference between the Cp curves was analyzed
The size of nano Fe powders was determined to be 25 nm in diameter by SEM. The isobaric molar heat capacity Cp of the nano Fe was measured with the high precision adiabatic low-temperature calorimeter in the temperature range from 84 K to 350 K. The relationship of Cp with temperature T was established as: Cp=36.831+14.772 x−5.4968x2−0.7099x3−1.3188x4, where x=(T−234)/156. The thermodynamic functions of the nano Fe, relative to the standard temperature of 298.15 K, were derived based on the heat capacity data through thermodynamic relationship. The measured Cp values were compared with those of coarse crystal powders and 87 nm Fe powders cited from literature and the difference between the Cp curves was analyzed
2006, 22(11): 1431-1434
doi: 10.3866/PKU.WHXB20061125
Abstract:
The As-doping ZnO nanowires were synthesized via a chemical vapor deposition method. SEM, EDX, and HRTEM measurements demonstrated that ZnO nanowires possessed od crystal structures. The luminescence spectra had two emission peaks at about 385 nm and 505 nm. As-doping had effect on the luminescence property of ZnO nanowires, the emission peak at 385 nm shifted to 393 nm, and the intensity of the emission peak at 505 nm increased distinctly.
The As-doping ZnO nanowires were synthesized via a chemical vapor deposition method. SEM, EDX, and HRTEM measurements demonstrated that ZnO nanowires possessed od crystal structures. The luminescence spectra had two emission peaks at about 385 nm and 505 nm. As-doping had effect on the luminescence property of ZnO nanowires, the emission peak at 385 nm shifted to 393 nm, and the intensity of the emission peak at 505 nm increased distinctly.
