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2001 Volume 17 Issue 7
2001, 17(07): 577-581
doi: 10.3866/PKU.WHXB20010701
Abstract:
Comparison of the influences of the preparation methods and reaction conditions to the properties of SnO2 powder,especially the specific surface area and the stability under high temperature calcination were performed.SnO2 prepared by precipitation method using NaOH solutions as the precipitating agent in the pH region of 10 and aged at100℃ for 48h had the highest BET surface area of 93.5m2 g-1 after calcination at 500℃ for 4h.The materials maintained a surface area of75.2m2 g-1 after 800℃ and 53.2m2 g-1 after 1000℃ alcination. The sample using NH3 H2O as precipitation agent had the lowest BET surface area calcinied under the above three temperatures.It was shown that using NaOH as precipitation agedt and digestion at high temperature was beneficial to maintain high surface area and od stability under high temperature.One of the reas ons is that the digestion under high temperature reduced the water content in th e hydrous tin oxide gel,so the initial structure of the particle was enhanced du ring the drying and calcining process.The other reason is that the crystallizati on of the initial particles was enhanced during the digestion and the defect on the surface was reduced also,so the sintering due to the surface diffusion was restrained.Further more,washing with ethanol reduced the formation of hardcore agglomeration between the particles,thus improved the stability of the particles under high temperature calcining process.
Comparison of the influences of the preparation methods and reaction conditions to the properties of SnO2 powder,especially the specific surface area and the stability under high temperature calcination were performed.SnO2 prepared by precipitation method using NaOH solutions as the precipitating agent in the pH region of 10 and aged at100℃ for 48h had the highest BET surface area of 93.5m2 g-1 after calcination at 500℃ for 4h.The materials maintained a surface area of75.2m2 g-1 after 800℃ and 53.2m2 g-1 after 1000℃ alcination. The sample using NH3 H2O as precipitation agent had the lowest BET surface area calcinied under the above three temperatures.It was shown that using NaOH as precipitation agedt and digestion at high temperature was beneficial to maintain high surface area and od stability under high temperature.One of the reas ons is that the digestion under high temperature reduced the water content in th e hydrous tin oxide gel,so the initial structure of the particle was enhanced du ring the drying and calcining process.The other reason is that the crystallizati on of the initial particles was enhanced during the digestion and the defect on the surface was reduced also,so the sintering due to the surface diffusion was restrained.Further more,washing with ethanol reduced the formation of hardcore agglomeration between the particles,thus improved the stability of the particles under high temperature calcining process.
2001, 17(07): 582-585
doi: 10.3866/PKU.WHXB20010702
Abstract:
A molecularly imprinted polymer (MIP) was prepared using quercetin as the template and acrylamide as the hydrogen-bonding functional monomer in a pol ar solvent. The polymer exhibited high affinity for quercetin and od selectivi ty among the tested compounds. And when it was used as an extraction cartridge f or the hydrolyzate of gingko leaves,it can purify the flavonoid component in the hydrolyzate,catching mainly quercetin and kaempferol. Thus it demonstrated th e feasibility of using MIP in extracting specific pharmacophoric compounds direc tly from herbs.
A molecularly imprinted polymer (MIP) was prepared using quercetin as the template and acrylamide as the hydrogen-bonding functional monomer in a pol ar solvent. The polymer exhibited high affinity for quercetin and od selectivi ty among the tested compounds. And when it was used as an extraction cartridge f or the hydrolyzate of gingko leaves,it can purify the flavonoid component in the hydrolyzate,catching mainly quercetin and kaempferol. Thus it demonstrated th e feasibility of using MIP in extracting specific pharmacophoric compounds direc tly from herbs.
2001, 17(07): 586-593
doi: 10.3866/PKU.WHXB20010703
Abstract:
DFT-B3LYP was used to calculate the geometries of intermediates,trans ition states reactants products for 1CH2＋N2O reaction using the 6-31G(d,p) b asis set. Single point energies were calculated on the QCISD(T)/6-311G(d,p) lev el. The potential energy surfaces on the title reaction were characterized. The final product channels including N2＋H2CO and NO＋HCN＋H were found. The product channel of NO＋HCN＋H is more competitive than that of N2＋H2CO. The products N 2, H2CO, NO, and HCN should be observed in the experiment. We think that the tit le reaction proceeds by an addition-elimination mechanism at room temperature. At higher temperature, directive abstraction channel with N2＋H2CO products beco mes a possible pathway. The present work assists the experimental worker to dete rmine reaction products.
DFT-B3LYP was used to calculate the geometries of intermediates,trans ition states reactants products for 1CH2＋N2O reaction using the 6-31G(d,p) b asis set. Single point energies were calculated on the QCISD(T)/6-311G(d,p) lev el. The potential energy surfaces on the title reaction were characterized. The final product channels including N2＋H2CO and NO＋HCN＋H were found. The product channel of NO＋HCN＋H is more competitive than that of N2＋H2CO. The products N 2, H2CO, NO, and HCN should be observed in the experiment. We think that the tit le reaction proceeds by an addition-elimination mechanism at room temperature. At higher temperature, directive abstraction channel with N2＋H2CO products beco mes a possible pathway. The present work assists the experimental worker to dete rmine reaction products.
2001, 17(07): 594-599
doi: 10.3866/PKU.WHXB20010704
Abstract:
Polyacrylonitrile(PAN)-based activated carbon fibers (ACFs) prep ared by different activation methods were characterized using low-temperature nitrogen adsorption over a wid e relative pressure from 10-6 to 1. With the aid of nitrogen adsorption, the po re structure parameters and pore size distribution were calculated using differe nt models. By these analyses,the pore development and the dominant pores of samp les prepared by various activation methods could be clearly observed. For steam -activated series of samples, with increasing activation the values of specific surface area increase and the pores are gradually widened. The dominant pores c hange from micropores to mesopores and some macropores are developed when the de gree of activation is very high. For air-activated series of samples, only the ultramicropores are developed seriously. The dominant pores can be thought to be ultramicropore. For KOH-activated series of samples, the dominant pores can be thought to be supermicropores. Moreover, the adsorption measurement could provi de profound insight into the structural heterogeneity of the ACFs.
Polyacrylonitrile(PAN)-based activated carbon fibers (ACFs) prep ared by different activation methods were characterized using low-temperature nitrogen adsorption over a wid e relative pressure from 10-6 to 1. With the aid of nitrogen adsorption, the po re structure parameters and pore size distribution were calculated using differe nt models. By these analyses,the pore development and the dominant pores of samp les prepared by various activation methods could be clearly observed. For steam -activated series of samples, with increasing activation the values of specific surface area increase and the pores are gradually widened. The dominant pores c hange from micropores to mesopores and some macropores are developed when the de gree of activation is very high. For air-activated series of samples, only the ultramicropores are developed seriously. The dominant pores can be thought to be ultramicropore. For KOH-activated series of samples, the dominant pores can be thought to be supermicropores. Moreover, the adsorption measurement could provi de profound insight into the structural heterogeneity of the ACFs.
2001, 17(07): 600-603
doi: 10.3866/PKU.WHXB20010705
Abstract:
The acetylene (C2H2) adsorbed on Ru() surface has been studied by usin g angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). The dependence of the σCC peak intensity on incidence angle and emission angle shows that C- C axis of acetylene（C2H2）is not parallel to the Ru() surface(see Fig.2). The C -C axis of acetylene is tilted in <0001> azimuth according to its symmetry(see Fig.3). Not as the acetylene in gas phase,the C-H bond of the acetylene adsorbe d on Ru () surface is not along the direction of the C-C bond.
The acetylene (C2H2) adsorbed on Ru() surface has been studied by usin g angle-resolved ultraviolet photoelectron spectroscopy (ARUPS). The dependence of the σCC peak intensity on incidence angle and emission angle shows that C- C axis of acetylene（C2H2）is not parallel to the Ru() surface(see Fig.2). The C -C axis of acetylene is tilted in <0001> azimuth according to its symmetry(see Fig.3). Not as the acetylene in gas phase,the C-H bond of the acetylene adsorbe d on Ru () surface is not along the direction of the C-C bond.
2001, 17(07): 604-608
doi: 10.3866/PKU.WHXB20010706
Abstract:
2-amino-5-mercapto-1,3,4-thiadiazole is a new inhibitor to resist the corrosion of copper and its alloys.The corrosion behavior of bronze in the presence of AMT has been investigated in 5％ citric acid.Electrochemical potenti ostatic polarization method and electrochemical impedance spectroscopy (EIS) wer e applied to analysis the effect of the organic compound on the corrosion inhibi tion of bronze.The results showed that AMT could greatly retard the corrosion of bronze in citric acid,which was attributed mainly to the protective film formed by AMT.Fourier transform infrared (FTIR) was used to characterize the surface f ilm.A polymeric Cu(Ⅰ)-inhibitor complex exhibiting strong corrosion inhibition that totally covered the bronze surface was identified.AMT behaves as bidentate ligand through the aminic nitrogen atom and the closed ring nitrogen in these c omplexes.
2-amino-5-mercapto-1,3,4-thiadiazole is a new inhibitor to resist the corrosion of copper and its alloys.The corrosion behavior of bronze in the presence of AMT has been investigated in 5％ citric acid.Electrochemical potenti ostatic polarization method and electrochemical impedance spectroscopy (EIS) wer e applied to analysis the effect of the organic compound on the corrosion inhibi tion of bronze.The results showed that AMT could greatly retard the corrosion of bronze in citric acid,which was attributed mainly to the protective film formed by AMT.Fourier transform infrared (FTIR) was used to characterize the surface f ilm.A polymeric Cu(Ⅰ)-inhibitor complex exhibiting strong corrosion inhibition that totally covered the bronze surface was identified.AMT behaves as bidentate ligand through the aminic nitrogen atom and the closed ring nitrogen in these c omplexes.
2001, 17(07): 609-613
doi: 10.3866/PKU.WHXB20010707
Abstract:
The characteristic of electrochemical degradation of aniline on SnO2/T i anode have been studied.The results indicate that SnO2/Ti anode doped with F plays an obvious role of electrocatalysis on the degradation of aniline differen t from that on Pt anode.The kinetics factors that influent the oxidation rates o f aniline on SnO2/Ti anode are determined by the dissolving of intermediate prod ucts on anodes.The dissolving of the organic film with intermediate products on the anode is the rate determining step.The effects of aniline concentration,pH o f aniline solution and the current density on the rate of aniline degradation ha s been studied.Under the best condition,the most efficient rate of elimination o f aniline(99.1％) and current efficiency (99.8％) could be achieved.The complexi ty of the intermediate products,the basic cate ry of the intermediate products consiste of the black film have been analyzed.
The characteristic of electrochemical degradation of aniline on SnO2/T i anode have been studied.The results indicate that SnO2/Ti anode doped with F plays an obvious role of electrocatalysis on the degradation of aniline differen t from that on Pt anode.The kinetics factors that influent the oxidation rates o f aniline on SnO2/Ti anode are determined by the dissolving of intermediate prod ucts on anodes.The dissolving of the organic film with intermediate products on the anode is the rate determining step.The effects of aniline concentration,pH o f aniline solution and the current density on the rate of aniline degradation ha s been studied.Under the best condition,the most efficient rate of elimination o f aniline(99.1％) and current efficiency (99.8％) could be achieved.The complexi ty of the intermediate products,the basic cate ry of the intermediate products consiste of the black film have been analyzed.
2001, 17(07): 614-618
doi: 10.3866/PKU.WHXB20010708
Abstract:
The electrochemical behavior of 10％Ni-90％Cu, 30％Ni-70％Cu, 50％Ni -50％Cu,5.1％Co-94.9％Cu, 9.7％Co-90.3％Cu, 15％Co-85％Cu, 25％Co-75％Cu an d 40％Co-60％Cu alloys electrodes in a borax buffer solution(pH 8.5) was studie d by cyclic voltammetry, AC impedance spectroscopy and photocurrent response met hod. The copper-nickel and copper-cobalt electrodes all show p-type photoresp onses. The photoresponses of the copper-nickel electrodes come from Cu2O while those of the copper-cobalt electrodes are caused by Cu2O and cobalt oxides. iph ,max of 10 ％Ni-90 ％Cu, 30 ％Ni-70 ％Cu and 5.1 ％Co-94.9 ％Cu alloy electro des is larger than that of pure copper electrode. However, iph,max of 50％Ni-50 ％Cu, 15％Co-85％Cu,25％Co-75％Cu and 40％Co-60％Cu alloy electrodes is small er than that of pure copper electrode because there are nickel and cobalt oxides on the greater part of the surface of those electrodes. φv of the copper-nick el electrodes is more negative than that of pure copper electrode while φv of t he copper-cobalt electrodes is almost equal to that of pure copper electrode. N iO results in a more stability of Cu2O layer on the copper-nickel electrodes su rface. The results from photoelectrochemical measurements favourably agree with those by AC impedance technique.
The electrochemical behavior of 10％Ni-90％Cu, 30％Ni-70％Cu, 50％Ni -50％Cu,5.1％Co-94.9％Cu, 9.7％Co-90.3％Cu, 15％Co-85％Cu, 25％Co-75％Cu an d 40％Co-60％Cu alloys electrodes in a borax buffer solution(pH 8.5) was studie d by cyclic voltammetry, AC impedance spectroscopy and photocurrent response met hod. The copper-nickel and copper-cobalt electrodes all show p-type photoresp onses. The photoresponses of the copper-nickel electrodes come from Cu2O while those of the copper-cobalt electrodes are caused by Cu2O and cobalt oxides. iph ,max of 10 ％Ni-90 ％Cu, 30 ％Ni-70 ％Cu and 5.1 ％Co-94.9 ％Cu alloy electro des is larger than that of pure copper electrode. However, iph,max of 50％Ni-50 ％Cu, 15％Co-85％Cu,25％Co-75％Cu and 40％Co-60％Cu alloy electrodes is small er than that of pure copper electrode because there are nickel and cobalt oxides on the greater part of the surface of those electrodes. φv of the copper-nick el electrodes is more negative than that of pure copper electrode while φv of t he copper-cobalt electrodes is almost equal to that of pure copper electrode. N iO results in a more stability of Cu2O layer on the copper-nickel electrodes su rface. The results from photoelectrochemical measurements favourably agree with those by AC impedance technique.
2001, 17(07): 619-621
doi: 10.3866/PKU.WHXB20010709
Abstract:
The model six-residue linear peptide AAGDYY-NH2 from TEM-1 β-lact amase inhibitor protein and BLIP was predicted to adopt a β-turn conformation and synthesized in order to elucidate the mechanism of β-turn formation and s tability.Its structural preferences in solution were comprehensively characteriz ed using CD (circular dichroism),FT-IR and 1H-NMR spectroscopy.The set of obse rved short- and medium-range NOEs,the restrained molecular dynamics simulation ,CD and FT-IR spectroscopy were consistent with the formation of β-turn in so lution by the model peptide.The results implicate β-turn playing an important role in the process of protein folding.
The model six-residue linear peptide AAGDYY-NH2 from TEM-1 β-lact amase inhibitor protein and BLIP was predicted to adopt a β-turn conformation and synthesized in order to elucidate the mechanism of β-turn formation and s tability.Its structural preferences in solution were comprehensively characteriz ed using CD (circular dichroism),FT-IR and 1H-NMR spectroscopy.The set of obse rved short- and medium-range NOEs,the restrained molecular dynamics simulation ,CD and FT-IR spectroscopy were consistent with the formation of β-turn in so lution by the model peptide.The results implicate β-turn playing an important role in the process of protein folding.
2001, 17(07): 622-625
doi: 10.3866/PKU.WHXB20010710
Abstract:
The theoretical study on PuX＋(X=O,H,N,C) using density functional met hod(B3LYP) shows that PuO＋、PuH＋、PuN＋ and PuC＋ can be stable. Ground electr onic states are X 6Σ-(PuO＋)、X 7Σ-(PuH＋)、 X 5Σ＋(PuN＋) and X 8Σ-(PuC＋) respectively,and their potential energy functi ons are in well agreement with the Murrell-Sorbie function,their force constant s and spectroscopic data have been obtained.
The theoretical study on PuX＋(X=O,H,N,C) using density functional met hod(B3LYP) shows that PuO＋、PuH＋、PuN＋ and PuC＋ can be stable. Ground electr onic states are X 6Σ-(PuO＋)、X 7Σ-(PuH＋)、 X 5Σ＋(PuN＋) and X 8Σ-(PuC＋) respectively,and their potential energy functi ons are in well agreement with the Murrell-Sorbie function,their force constant s and spectroscopic data have been obtained.
2001, 17(07): 626-630
doi: 10.3866/PKU.WHXB20010711
Abstract:
Density functional (B3LYP/SDD) method with relativistic effective core potential (RECP) have been used to optimize the structure of ZrH,and to calcula te energy E,entropy S and enthalpy H of ZrH,ZrD and ZrT.Considering the characte ristics of different types of motion,the vibration energy or electronic and vibr ation entropy of the molecules are assumed to be the corresponding values of the ir solid states.ΔH,ΔG,ΔS and hydrogen isotope equilibrium pressures of the hydrogenating reaction have been calculated based on this approximation.The enthalpy of formation of ZrH(s) calculated at 298 K is 161.34 kJ mol-1 which i s close to the experimental value 173.5 kJ mol-1.The results show that the pre sent method is reasonable to the theoretical study of hydrogen storage materials .
Density functional (B3LYP/SDD) method with relativistic effective core potential (RECP) have been used to optimize the structure of ZrH,and to calcula te energy E,entropy S and enthalpy H of ZrH,ZrD and ZrT.Considering the characte ristics of different types of motion,the vibration energy or electronic and vibr ation entropy of the molecules are assumed to be the corresponding values of the ir solid states.ΔH,ΔG,ΔS and hydrogen isotope equilibrium pressures of the hydrogenating reaction have been calculated based on this approximation.The enthalpy of formation of ZrH(s) calculated at 298 K is 161.34 kJ mol-1 which i s close to the experimental value 173.5 kJ mol-1.The results show that the pre sent method is reasonable to the theoretical study of hydrogen storage materials .
2001, 17(07): 631-635
doi: 10.3866/PKU.WHXB20010712
Abstract:
Zeolites supported Mo nitrides were prepared via MoO3＋NH3 reaction in temperature programmed mannar.The XRD data show that the frame structure of NaY and Na-ZSM-5 zeolites can still be maintained after nitridation at 973K.By an alysis of the extended X-ray absorption fine structure(EXAFS) of the Mo K-abso rption edge,the structural informations of both oxidic and nitrided Mo catalysts were obtained.The supported MoO3 samples show three peaks in the radial structu re function(RSF).The first two peaks correspond to the nearest Mo-O coordinatio n shell,but the ratio of the first peak to the second one is much larger than th at of the MoO3.This suggests that the MoO3 supported on zeolites has more compac t structure than the unsupported one.There are three peaks in the RSF of Mo2N,re presenting one Mo-N and two Mo-Mo shells,which is in od agreement with the f ace-centered cubic model.Calculation from X-ray diffraction data and EXAFS spe ctra reveals that the N atoms in Mo2N lengthen the distance between Mo atoms and weaken the Mo-Mo bond.Supported Mo2N samples give out nearly the same RSFs as the Mo2N,only the peak corresponding to Mo-N shell is weak,suggesting that the supported Mo2N has more structural disorder than the unsupported one.Mo2N suppor ted on Na-ZSM-5 gives out shorter coordination distance than supported on NaY, suggesting stronger interaction between Mo2N and Na-ZSM-5.
Zeolites supported Mo nitrides were prepared via MoO3＋NH3 reaction in temperature programmed mannar.The XRD data show that the frame structure of NaY and Na-ZSM-5 zeolites can still be maintained after nitridation at 973K.By an alysis of the extended X-ray absorption fine structure(EXAFS) of the Mo K-abso rption edge,the structural informations of both oxidic and nitrided Mo catalysts were obtained.The supported MoO3 samples show three peaks in the radial structu re function(RSF).The first two peaks correspond to the nearest Mo-O coordinatio n shell,but the ratio of the first peak to the second one is much larger than th at of the MoO3.This suggests that the MoO3 supported on zeolites has more compac t structure than the unsupported one.There are three peaks in the RSF of Mo2N,re presenting one Mo-N and two Mo-Mo shells,which is in od agreement with the f ace-centered cubic model.Calculation from X-ray diffraction data and EXAFS spe ctra reveals that the N atoms in Mo2N lengthen the distance between Mo atoms and weaken the Mo-Mo bond.Supported Mo2N samples give out nearly the same RSFs as the Mo2N,only the peak corresponding to Mo-N shell is weak,suggesting that the supported Mo2N has more structural disorder than the unsupported one.Mo2N suppor ted on Na-ZSM-5 gives out shorter coordination distance than supported on NaY, suggesting stronger interaction between Mo2N and Na-ZSM-5.
2001, 17(07): 636-640
doi: 10.3866/PKU.WHXB20010713
Abstract:
One of the main achievments of Marcus electron-transfer theory is the predictions of the existence of normal and inverted regions.Conformation of the existence of inverted regions has been a hot point by experiments.The direct el ectron-transfer rate constants were worked out between conduction band and the γ-MnO2/K3[Fe(CN)6] soluton interface by measuring the flat band potentials and the Tafel plots and Marcus type inverted regions were observed from logket～V(a pplied bias potential) curve.Furthermore,the existence of inverted regions was d emonstrated theoretically in direct electron transfers between the semiconductor /electrolyte interface.
One of the main achievments of Marcus electron-transfer theory is the predictions of the existence of normal and inverted regions.Conformation of the existence of inverted regions has been a hot point by experiments.The direct el ectron-transfer rate constants were worked out between conduction band and the γ-MnO2/K3[Fe(CN)6] soluton interface by measuring the flat band potentials and the Tafel plots and Marcus type inverted regions were observed from logket～V(a pplied bias potential) curve.Furthermore,the existence of inverted regions was d emonstrated theoretically in direct electron transfers between the semiconductor /electrolyte interface.
2001, 17(07): 641-644
doi: 10.3866/PKU.WHXB20010714
Abstract:
The USY/ZnO/Al2O3 catalyst,prepared with impregnation and co-depositi on method,for gasoline desulfurization via catalytic cracking was evaluated in a fixed-bed reaction apparatus.The results show that the catalyst has excellent sulfur removal activity and selectivity (Table 1).Most of the sulfur removed fro m gasoline is transformed as H2S into the cracking gas and only a little deposit s on the catalyst (Fig.3),which is very favorable for sulfur recovery and protec ting the environment.Cracking desulfurization of sulfide is the result of synerg ism between cracking and hydrogen transfer.The two reactions require different a ppropriate temperatures.There is then an optimal temperature at around 420℃ for gasoline desulfurization.
The USY/ZnO/Al2O3 catalyst,prepared with impregnation and co-depositi on method,for gasoline desulfurization via catalytic cracking was evaluated in a fixed-bed reaction apparatus.The results show that the catalyst has excellent sulfur removal activity and selectivity (Table 1).Most of the sulfur removed fro m gasoline is transformed as H2S into the cracking gas and only a little deposit s on the catalyst (Fig.3),which is very favorable for sulfur recovery and protec ting the environment.Cracking desulfurization of sulfide is the result of synerg ism between cracking and hydrogen transfer.The two reactions require different a ppropriate temperatures.There is then an optimal temperature at around 420℃ for gasoline desulfurization.
2001, 17(07): 645-650
doi: 10.3866/PKU.WHXB20010715
Abstract:
The enthalpies of mixing of monomethylurea（MMU）with six kinds of ami no acids (glycine,L-alanine,L-serine,L-proline,L-threonine,L-valine) in aqu eous solutions have been determined by the LKB-2277 flow microcalorimetric syst em at 298.15 K.These results along with enthalpies of dilution of these solutes for the initial solutions were used to determine the enthalpic interaction coeff icients (hxy,hxxy,etc.) in terms of the McMillan-Mayer theory.The pairwise cros s interaction coefficients (hxy) of amino acids and MMU have been discussed.The results show that different side-groups of amino acids have different contribut ions to hxy.The hydrophobic-hydrophobic interactions of glycine,L-alanine and L-valine with MMU increase with the number of -CH2- groups on α-carbon.The hydroxyl group gives a negative contribution to hxy.The five-membered pyrolidin e ring in proline exhibits some hydrophobicity.The introduction of CH3 makes the hydrophobicity of MMU stronger than that of urea.
The enthalpies of mixing of monomethylurea（MMU）with six kinds of ami no acids (glycine,L-alanine,L-serine,L-proline,L-threonine,L-valine) in aqu eous solutions have been determined by the LKB-2277 flow microcalorimetric syst em at 298.15 K.These results along with enthalpies of dilution of these solutes for the initial solutions were used to determine the enthalpic interaction coeff icients (hxy,hxxy,etc.) in terms of the McMillan-Mayer theory.The pairwise cros s interaction coefficients (hxy) of amino acids and MMU have been discussed.The results show that different side-groups of amino acids have different contribut ions to hxy.The hydrophobic-hydrophobic interactions of glycine,L-alanine and L-valine with MMU increase with the number of -CH2- groups on α-carbon.The hydroxyl group gives a negative contribution to hxy.The five-membered pyrolidin e ring in proline exhibits some hydrophobicity.The introduction of CH3 makes the hydrophobicity of MMU stronger than that of urea.
2001, 17(07): 651-654
doi: 10.3866/PKU.WHXB20010716
Abstract:
Pitting corrosion of aluminum alloy 2024-T3 in NaCl solution was stud ied using electrochemical noise technique. The spectral analysis results showed that the more positive the values of cut-off frequency(fc), the slope of high- frequency linear part of SPD(k) and white noise level(W) are, the more easily th e pit initiates, but none of them can be used to depict the corrosion process in dividually. Two new parameters(SE and SG) were derived by using dimensional anal ysis method, and the value of SE characterize the severity of pitting of corrodi ng material. While the meaning of the other parameter(SG) remains for further in vestigation.
Pitting corrosion of aluminum alloy 2024-T3 in NaCl solution was stud ied using electrochemical noise technique. The spectral analysis results showed that the more positive the values of cut-off frequency(fc), the slope of high- frequency linear part of SPD(k) and white noise level(W) are, the more easily th e pit initiates, but none of them can be used to depict the corrosion process in dividually. Two new parameters(SE and SG) were derived by using dimensional anal ysis method, and the value of SE characterize the severity of pitting of corrodi ng material. While the meaning of the other parameter(SG) remains for further in vestigation.
2001, 17(07): 655-658
doi: 10.3866/PKU.WHXB20010717
Abstract:
Catalytic generation of hydrogen by the coupling of decomposition and partial oxidation of methanol over Cu/Zn and Cu/Zn/Ni catalysts have been studie d. These Cu-Zn based catalysts show high activity and stability for the partial oxidation of methanol. The catalytic activity and selectivity are affected by t he ratio of O2/CH3OH. The optimum reaction conditions for Cu-Zn catalyst are O2 /CH3OH=0.2, T=523 K. The formation of CuZn alloy was observed in the deactivated Cu/Zn catalysts after methanol decomposition at 523 K for 20 h. On the contrary , no CuZn alloy was found in the used Cu/Zn catalyst after partial oxidation of methanol for 150 h at 523 K. The presented results seem to indicate that the for mation of CuZn alloy is one of the main reasons for the deactivation of Cu-Zn b ased catalysts in methanol decomposition.
Catalytic generation of hydrogen by the coupling of decomposition and partial oxidation of methanol over Cu/Zn and Cu/Zn/Ni catalysts have been studie d. These Cu-Zn based catalysts show high activity and stability for the partial oxidation of methanol. The catalytic activity and selectivity are affected by t he ratio of O2/CH3OH. The optimum reaction conditions for Cu-Zn catalyst are O2 /CH3OH=0.2, T=523 K. The formation of CuZn alloy was observed in the deactivated Cu/Zn catalysts after methanol decomposition at 523 K for 20 h. On the contrary , no CuZn alloy was found in the used Cu/Zn catalyst after partial oxidation of methanol for 150 h at 523 K. The presented results seem to indicate that the for mation of CuZn alloy is one of the main reasons for the deactivation of Cu-Zn b ased catalysts in methanol decomposition.
2001, 17(07): 659-661
doi: 10.3866/PKU.WHXB20010718
Abstract:
MCM-48 was synthesized with tetraethylorthosilicate (TEOS) as silica source and cetyltrimethylammonium bromide (CTAB) as template at high pressure (c a.7 MPa) and 373 K. The synthesized compounds were characterized using different analytical techniques such as X-ray diffraction,N2 adsorption and desorption m easurement,and 29Si MAS NMR.MCM-48 synthesized at high pressure appeared higher thermal and hydrothermal stability than that synthesized at autogenous pressure .The 29Si MAS NMR results demonstrated that high pressure promoted the wall poly merization and leaded to a high quality MCM-48.MCM-48 was also synthesized wit h such a low ratio of CTAB/Si as 0.16,but that synthesized with high ratio of CT AB/Si was more stable.
MCM-48 was synthesized with tetraethylorthosilicate (TEOS) as silica source and cetyltrimethylammonium bromide (CTAB) as template at high pressure (c a.7 MPa) and 373 K. The synthesized compounds were characterized using different analytical techniques such as X-ray diffraction,N2 adsorption and desorption m easurement,and 29Si MAS NMR.MCM-48 synthesized at high pressure appeared higher thermal and hydrothermal stability than that synthesized at autogenous pressure .The 29Si MAS NMR results demonstrated that high pressure promoted the wall poly merization and leaded to a high quality MCM-48.MCM-48 was also synthesized wit h such a low ratio of CTAB/Si as 0.16,but that synthesized with high ratio of CT AB/Si was more stable.
2001, 17(07): 662-671
doi: 10.3866/PKU.WHXB20010719
Abstract:
Photodynamic therapy (PDT) is a new and developing method for cancer t reatment involving the preferential uptake of a photosensitizer by tumor and its subsequent activation by light with appropriate wavelength. Phthalocyanines hav e received increasing attention as photosensitizers for PDT since 1985, so that several works have been focused on this area. This paper gives some relationship s between structures and photodynamic anti-cancer activities of phthalocyanines based on 51 related references. The emphasis is directed to the effects of cent ral ions and ring substitutents and axial ligands on the PDT activities and rela tive physical and chemical properties. The main conclusion is that the amphiphil ic character is the promising factor of phthalocyanines for PDT.
Photodynamic therapy (PDT) is a new and developing method for cancer t reatment involving the preferential uptake of a photosensitizer by tumor and its subsequent activation by light with appropriate wavelength. Phthalocyanines hav e received increasing attention as photosensitizers for PDT since 1985, so that several works have been focused on this area. This paper gives some relationship s between structures and photodynamic anti-cancer activities of phthalocyanines based on 51 related references. The emphasis is directed to the effects of cent ral ions and ring substitutents and axial ligands on the PDT activities and rela tive physical and chemical properties. The main conclusion is that the amphiphil ic character is the promising factor of phthalocyanines for PDT.
