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2001 Volume 17 Issue 2
2001, 17(02): 97-100
doi: 10.3866/PKU.WHXB20010201
Abstract:
Ultrathin film of perfluorodecanoic acid expected to be excellent lubricant for micromachines was prepared successfully on single crystal silicon substrate.The film was characterized by means of Xray photoelectron spectroscopy (XPS) and contactangle meter.The chemical reaction involved in the preparation of the ultrathin film was discussed as well.After being immersed in a dilute aqueous solution of polyethyleneimine (PEI) for 15 minutes and rinsed with distilled water,the silicon substrate was coated with a thin film of PEI,which was then put into a dilute solution (1×10－3 mol•L－1) of perfluorodecanoic acid in hexadecane.Subsequently the steady perfluorodecanoic acid ultrathin film was developed on PEI coating in the presence of a covalent amide bond between carboxylic group and the primary or secondary amine groups of PEI.This process was accompanied by the contact angle changes of water droplet on the Si surface (see Table 1).Moreover,the reaction between perfluorodecanoic acid and PEI was significantly influenced by N,N′dicyclohexylcarbodiimide (DCCD).The contact angle on the ultrathin film of perfluorodecanoic acid is only 66.3° in the absence of DCCD in the reacting solution; it rises to 89.4° in the presence of DCCD.This indicates that the reaction between perfluorodecanoic acid and PEI was accelerated by DCCD,and the quality of perfluorodecanoic acid ultrathin film thus improved.XPS analysis of the ultrathin film indicates that the derivatization of PEI with perfluorodecanoic acid was accompanied by several changes.First,a large and highly symmetrical F 1s peak appeared at 688.3 eV (C－F).Secondly,a new peak of N 1s appeared at 400.7 eV (chemical shift 1.4 eV),which was attributed to the N atom attached to the carbonyl group (O=C－N).Thirdly,three new peaks of C 1s appeared at 286.1 eV (chemical shift 1.5 eV),288.1 eV (chemical shift 3.5 eV),and 291.0 eV (chemical shift 5.4 eV),respectively.These C 1s peaks were attributed to the C atom attached to the O=C－N group (O=C－N－C),the carboxyl C atom (O=C－N),and the C atom in －CF3 group (C－F),respectively.Therefore it can be concluded that perfluorodecanoic acid has been chemically adsorbed onto the surface of PEI and perfluorodecanoic acid ultrathin film prepared successfully.
Ultrathin film of perfluorodecanoic acid expected to be excellent lubricant for micromachines was prepared successfully on single crystal silicon substrate.The film was characterized by means of Xray photoelectron spectroscopy (XPS) and contactangle meter.The chemical reaction involved in the preparation of the ultrathin film was discussed as well.After being immersed in a dilute aqueous solution of polyethyleneimine (PEI) for 15 minutes and rinsed with distilled water,the silicon substrate was coated with a thin film of PEI,which was then put into a dilute solution (1×10－3 mol•L－1) of perfluorodecanoic acid in hexadecane.Subsequently the steady perfluorodecanoic acid ultrathin film was developed on PEI coating in the presence of a covalent amide bond between carboxylic group and the primary or secondary amine groups of PEI.This process was accompanied by the contact angle changes of water droplet on the Si surface (see Table 1).Moreover,the reaction between perfluorodecanoic acid and PEI was significantly influenced by N,N′dicyclohexylcarbodiimide (DCCD).The contact angle on the ultrathin film of perfluorodecanoic acid is only 66.3° in the absence of DCCD in the reacting solution; it rises to 89.4° in the presence of DCCD.This indicates that the reaction between perfluorodecanoic acid and PEI was accelerated by DCCD,and the quality of perfluorodecanoic acid ultrathin film thus improved.XPS analysis of the ultrathin film indicates that the derivatization of PEI with perfluorodecanoic acid was accompanied by several changes.First,a large and highly symmetrical F 1s peak appeared at 688.3 eV (C－F).Secondly,a new peak of N 1s appeared at 400.7 eV (chemical shift 1.4 eV),which was attributed to the N atom attached to the carbonyl group (O=C－N).Thirdly,three new peaks of C 1s appeared at 286.1 eV (chemical shift 1.5 eV),288.1 eV (chemical shift 3.5 eV),and 291.0 eV (chemical shift 5.4 eV),respectively.These C 1s peaks were attributed to the C atom attached to the O=C－N group (O=C－N－C),the carboxyl C atom (O=C－N),and the C atom in －CF3 group (C－F),respectively.Therefore it can be concluded that perfluorodecanoic acid has been chemically adsorbed onto the surface of PEI and perfluorodecanoic acid ultrathin film prepared successfully.
Rapid-Mixing Stopped-Flow Spectra Studies on Water-soluble Manganese Porphyrin Enzyme-Mimic Systems
2001, 17(02): 101-106
doi: 10.3866/PKU.WHXB20010202
Abstract:
The reaction of watersoluble Manganese porphyrin complex,MnⅢ(TMPyP) with a variety of oxidants(mCPBA,KHSO5,NaOCl and H2O2) under ambient conditions at different pH was investigated by stoppedflow techniques.Oxomanganese(IV) porphyrin complex intermediate (2) was the main product at lower pH.Highvalent oxomanganese(V) porphyrin (1) was fully formed and subsequently decayed to oxoMn(Ⅳ) at higher pH.It was shown that oxomanganese(V) porphyrin was the reactive complex with reducing substrates.
The reaction of watersoluble Manganese porphyrin complex,MnⅢ(TMPyP) with a variety of oxidants(mCPBA,KHSO5,NaOCl and H2O2) under ambient conditions at different pH was investigated by stoppedflow techniques.Oxomanganese(IV) porphyrin complex intermediate (2) was the main product at lower pH.Highvalent oxomanganese(V) porphyrin (1) was fully formed and subsequently decayed to oxoMn(Ⅳ) at higher pH.It was shown that oxomanganese(V) porphyrin was the reactive complex with reducing substrates.
2001, 17(02): 107-110
doi: 10.3866/PKU.WHXB20010203
Abstract:
The reaction F＋Cl2ClF＋Cl was investigated by density functional theory (DFT) at the B3LYP/6311G level. The reaction can occur via a linear transition states with a reaction barrier of 1.24 kJ•mol－1,and can also via two triangle transition states with reaction barriers of 46.37 and 105.09 kJ•mol1,respectively.In addition,we also found that there is no energy barrier when F attacks Cl2 with an angle ∠FClCl of 10－20°(or 160－120°).The energy barrier of the symmetrical reaction Cl′F＋ClCl′＋ClF was calculated to be 40.57 kJ•mol1.All transition states were confirmed by vibrational analyses and the possible reaction paths were obtained by IRC calculations.
The reaction F＋Cl2ClF＋Cl was investigated by density functional theory (DFT) at the B3LYP/6311G level. The reaction can occur via a linear transition states with a reaction barrier of 1.24 kJ•mol－1,and can also via two triangle transition states with reaction barriers of 46.37 and 105.09 kJ•mol1,respectively.In addition,we also found that there is no energy barrier when F attacks Cl2 with an angle ∠FClCl of 10－20°(or 160－120°).The energy barrier of the symmetrical reaction Cl′F＋ClCl′＋ClF was calculated to be 40.57 kJ•mol1.All transition states were confirmed by vibrational analyses and the possible reaction paths were obtained by IRC calculations.
2001, 17(02): 111-115
doi: 10.3866/PKU.WHXB20010204
Abstract:
MnNa2WO4/SiO2 is one of the best catalysts for oxidative coupling of methane.To investigate the nature of active centers and the reaction mechanism,the structure of possible metal sites formed by tungsten and manganese over the silica surface were studied using molecular simulation method and ab initio DFT calculations.Silica support exists in the catalyst as 岐瞔ristobalite and its (111) face exposes preferentially to the surface.The calculated results show that tungsten interacts with the silica surface by three or one bridge oxygen atoms to form tetrahedral [WO4],and manganese interacts with single bridge oxygen to form dispersed [MnO4] or exists as oxide clusters.The nature of the molecular orbitals and the electronic structure suggest that the tetrahedral [WO4] site with single bridge oxygen is the most probable active center responsible for methane activation.
MnNa2WO4/SiO2 is one of the best catalysts for oxidative coupling of methane.To investigate the nature of active centers and the reaction mechanism,the structure of possible metal sites formed by tungsten and manganese over the silica surface were studied using molecular simulation method and ab initio DFT calculations.Silica support exists in the catalyst as 岐瞔ristobalite and its (111) face exposes preferentially to the surface.The calculated results show that tungsten interacts with the silica surface by three or one bridge oxygen atoms to form tetrahedral [WO4],and manganese interacts with single bridge oxygen to form dispersed [MnO4] or exists as oxide clusters.The nature of the molecular orbitals and the electronic structure suggest that the tetrahedral [WO4] site with single bridge oxygen is the most probable active center responsible for methane activation.
2001, 17(02): 116-118
doi: 10.3866/PKU.WHXB20010205
Abstract:
NanoAg/Al2O3 assemblies were prepared by alternating current(AC) electrochemical deposition of Ag in the ordered pores of alumina membranes.TEM spectra show that Ag nanoparticles were deposited in porous alumina.The reason that metal was deposited in porous alumina by AC was attributed to rectifying properties of Al/Al2O3 interface.I－U curve of Al/Al2O3 interface was measured.
NanoAg/Al2O3 assemblies were prepared by alternating current(AC) electrochemical deposition of Ag in the ordered pores of alumina membranes.TEM spectra show that Ag nanoparticles were deposited in porous alumina.The reason that metal was deposited in porous alumina by AC was attributed to rectifying properties of Al/Al2O3 interface.I－U curve of Al/Al2O3 interface was measured.
Quasiclassical Trajectory Study of Reaction of Chlorine Substituting the Primary Hydrogen of Propane
2001, 17(02): 119-122
doi: 10.3866/PKU.WHXB20010206
Abstract:
The reaction of Cl substituting the primary hydrogen of C3H8 was investigated by quasiclassical trajectory method. The threebody LEPS potential function was used to build the potential surface of the reaction system. It shows that for the reaction of Cl substituting the primary hydrogen of C3H8,there are two reaction channels, the first one is a direct reaction process; while the other es through a collisional complex.
The reaction of Cl substituting the primary hydrogen of C3H8 was investigated by quasiclassical trajectory method. The threebody LEPS potential function was used to build the potential surface of the reaction system. It shows that for the reaction of Cl substituting the primary hydrogen of C3H8,there are two reaction channels, the first one is a direct reaction process; while the other es through a collisional complex.
2001, 17(02): 123-127
doi: 10.3866/PKU.WHXB20010207
Abstract:
According to the theoretical basis of thermokinetics,the thermokinetic equations of parallel first order reactions and parallel first and second order reactions have been derived,and the mathematical models for determining the kinetic parameters for parallel reactions from the thermoanalytical curve have been established in this paper.In order to test the validity of this method,two simulated parallel reaction systems (saponification of mixed esters in aqueous ethanol solvent) have been studied.The rate constants calculated by this method are in agreement with those published in literature,and therefore,the thermokinetic equations derived in this paper for parallel reactions is believed to be correct.
According to the theoretical basis of thermokinetics,the thermokinetic equations of parallel first order reactions and parallel first and second order reactions have been derived,and the mathematical models for determining the kinetic parameters for parallel reactions from the thermoanalytical curve have been established in this paper.In order to test the validity of this method,two simulated parallel reaction systems (saponification of mixed esters in aqueous ethanol solvent) have been studied.The rate constants calculated by this method are in agreement with those published in literature,and therefore,the thermokinetic equations derived in this paper for parallel reactions is believed to be correct.
2001, 17(02): 128-133
doi: 10.3866/PKU.WHXB20010208
Abstract:
Spectral behavior of mesotetrakis(4Nbenzylpyridyl)porphyrinmetaloxo cluster (SiW12O4－40) supramolecular systems in aqueous solution was studied by UVvisible spectrometry.The spectral evolution and Job's plots reveal that the stable aggregates contain equal numbers of the cationic porphyrins and the anionic SiW12O4－40.The electrocatalytic behavior of reducing O2 for the 1∶1 supramolecular complex [CoTMPyP][SiW12O40],was also investigated,the supramolecular complex might be hopeful for being used as a new material of modified electrodes for electrocatalytic reduction of O2.
Spectral behavior of mesotetrakis(4Nbenzylpyridyl)porphyrinmetaloxo cluster (SiW12O4－40) supramolecular systems in aqueous solution was studied by UVvisible spectrometry.The spectral evolution and Job's plots reveal that the stable aggregates contain equal numbers of the cationic porphyrins and the anionic SiW12O4－40.The electrocatalytic behavior of reducing O2 for the 1∶1 supramolecular complex [CoTMPyP][SiW12O40],was also investigated,the supramolecular complex might be hopeful for being used as a new material of modified electrodes for electrocatalytic reduction of O2.
2001, 17(02): 134-139
doi: 10.3866/PKU.WHXB20010209
Abstract:
The electrocatalysts of platinum based PbSb surface alloy were prepared by electrochemical codeposition under cyclic voltammetric conditions. The structure and properties of these electrocatalysts were studied by techniques of cyclic voltammetry, electrochemical quartz crystal microbalance(EQCM), scanning tunneling microscopy(STM) and Xray photoelectron spectroscopy(XPS). The results demonstrated that the hydrogen evolution on the prepared electrocatalyst was postponed to －0.45 V. i.e., 200 mV has been shifted negatively in comparison with hydrogen evolution at a platinum electrode. In addition,the oxidization of Pb and Sb components in surface alloy was positively shifted to above 0.15 V, which is much higher than the oxidization potential of Pb and Sb metal electrodes. The stability of surface alloy electrode is confirmed to be higher than Pb and Sb metal electrodes that were employed often in organic electrosynthesis. The process of formation of surface alloy was studied in situ by using an EQCM and ex situ by using a STM. The results have converged to illustrate that the surface alloy is constructed of nanoparticles with regular size of about 10 nanometers.The EQCM analysis and XPS depth profiling indicated that the surface alloy is formed on the top layer of a few nanometers in thickness of the SbPbPt/GC electrode.
The electrocatalysts of platinum based PbSb surface alloy were prepared by electrochemical codeposition under cyclic voltammetric conditions. The structure and properties of these electrocatalysts were studied by techniques of cyclic voltammetry, electrochemical quartz crystal microbalance(EQCM), scanning tunneling microscopy(STM) and Xray photoelectron spectroscopy(XPS). The results demonstrated that the hydrogen evolution on the prepared electrocatalyst was postponed to －0.45 V. i.e., 200 mV has been shifted negatively in comparison with hydrogen evolution at a platinum electrode. In addition,the oxidization of Pb and Sb components in surface alloy was positively shifted to above 0.15 V, which is much higher than the oxidization potential of Pb and Sb metal electrodes. The stability of surface alloy electrode is confirmed to be higher than Pb and Sb metal electrodes that were employed often in organic electrosynthesis. The process of formation of surface alloy was studied in situ by using an EQCM and ex situ by using a STM. The results have converged to illustrate that the surface alloy is constructed of nanoparticles with regular size of about 10 nanometers.The EQCM analysis and XPS depth profiling indicated that the surface alloy is formed on the top layer of a few nanometers in thickness of the SbPbPt/GC electrode.
2001, 17(02): 140-143
doi: 10.3866/PKU.WHXB20010210
Abstract:
The platinum based PbSb surface alloy supported on glassy carbon prepared by electrochemical codeposition has been applied to the reduction of oxalic acid. The results demonstrated that the surface alloy electrode exhibited a high activity, and reduced significantly the overpotential. In comparison with a lead cathode that was used usually in industry for the reduction of oxalic acid, the onset potential of oxalic acid reduction was shifted positively from 1.0 V on Pb to －0.4 V on the surface alloy electrode. The main product species were determined as glyoxylic acid by using in situ FTIR spectroscopy, illustrating that the surface alloy electrode exhibited also a high selectivity towards oxalic acid reduction.
The platinum based PbSb surface alloy supported on glassy carbon prepared by electrochemical codeposition has been applied to the reduction of oxalic acid. The results demonstrated that the surface alloy electrode exhibited a high activity, and reduced significantly the overpotential. In comparison with a lead cathode that was used usually in industry for the reduction of oxalic acid, the onset potential of oxalic acid reduction was shifted positively from 1.0 V on Pb to －0.4 V on the surface alloy electrode. The main product species were determined as glyoxylic acid by using in situ FTIR spectroscopy, illustrating that the surface alloy electrode exhibited also a high selectivity towards oxalic acid reduction.
2001, 17(02): 144-149
doi: 10.3866/PKU.WHXB20010211
Abstract:
Methods for study the microscopic properties of droplets in microemulsions by precise measurements of density, refractive index and turbidity have been established. The structural and interaction parameters of droplets in AOT/H2O/toluene microemulsions with molar ratio r of water to surfactant being 10.5 and 12 have been investigated and the molecular length L of AOT has been found to be 1.07 nm. The dependence of phaseseparation temperature on r has been discussed in terms of the interaction between droplets. With L=1.07 nm, microscopic structures of droplets of the two microemulsion systems of AOT/H2O/toluene and AOT/H2O/cyclohexane at various values of r have been investigated by measurements of density only. The results are excellently consistent with reported values. It has also been found that the density of water in droplets was significantly larger than that of free water, and was varied with the solvents, while the configuration of AOT molecule kept unvaried.
Methods for study the microscopic properties of droplets in microemulsions by precise measurements of density, refractive index and turbidity have been established. The structural and interaction parameters of droplets in AOT/H2O/toluene microemulsions with molar ratio r of water to surfactant being 10.5 and 12 have been investigated and the molecular length L of AOT has been found to be 1.07 nm. The dependence of phaseseparation temperature on r has been discussed in terms of the interaction between droplets. With L=1.07 nm, microscopic structures of droplets of the two microemulsion systems of AOT/H2O/toluene and AOT/H2O/cyclohexane at various values of r have been investigated by measurements of density only. The results are excellently consistent with reported values. It has also been found that the density of water in droplets was significantly larger than that of free water, and was varied with the solvents, while the configuration of AOT molecule kept unvaried.
2001, 17(02): 150-154
doi: 10.3866/PKU.WHXB20010212
Abstract:
The structure and microhardness of NiWB alloy were studied by means of electrochemical techniques, XPS, DSC and XRD before and after heat treatment. The results showed that the process of NiWB alloy electrodeposition was accompanied by the chemical deposition of Ni and adulteration of Na2B4O7 in the deposit. NiW alloy presented in nanocrystalline structure and NiWB in amorphous structure were both coarsened in grain size and led to the evolution of Ni4W, and precipitation of Ni－B compound such as Ni2B, Ni3B in NiWB alloy after heat treatment. The maximum microhardness could be observed for NiW alloy at the value of 919.8 kg•mm－2 after heat treatment for 2 hours at temperature of 400 ℃ and NiWB alloy at 1132.2 kg•mm－2 (500 ℃, 2 hrs).
The structure and microhardness of NiWB alloy were studied by means of electrochemical techniques, XPS, DSC and XRD before and after heat treatment. The results showed that the process of NiWB alloy electrodeposition was accompanied by the chemical deposition of Ni and adulteration of Na2B4O7 in the deposit. NiW alloy presented in nanocrystalline structure and NiWB in amorphous structure were both coarsened in grain size and led to the evolution of Ni4W, and precipitation of Ni－B compound such as Ni2B, Ni3B in NiWB alloy after heat treatment. The maximum microhardness could be observed for NiW alloy at the value of 919.8 kg•mm－2 after heat treatment for 2 hours at temperature of 400 ℃ and NiWB alloy at 1132.2 kg•mm－2 (500 ℃, 2 hrs).
2001, 17(02): 155-160
doi: 10.3866/PKU.WHXB20010213
Abstract:
The vaporliquid phase equilibria of the binary system of CO2C2H5OH were measured for four isotherms between 60 ℃ and 180 ℃ under the pressure range of 5.0 MPa to 14.5 MPa.The measurements were carried out in a cylindrical autoclave with a moveable piston and a window allowing observation. The compositions,densities and molar volumes of the two coexisting phases are presented. The critical values Tc.pc,xc were predicted.We have correlated phase equilibrium data with the PengRobinson equation of state and the WongSandle mixture combination rule for this system.The calculated results agree fairly with the experimental data.
The vaporliquid phase equilibria of the binary system of CO2C2H5OH were measured for four isotherms between 60 ℃ and 180 ℃ under the pressure range of 5.0 MPa to 14.5 MPa.The measurements were carried out in a cylindrical autoclave with a moveable piston and a window allowing observation. The compositions,densities and molar volumes of the two coexisting phases are presented. The critical values Tc.pc,xc were predicted.We have correlated phase equilibrium data with the PengRobinson equation of state and the WongSandle mixture combination rule for this system.The calculated results agree fairly with the experimental data.
2001, 17(02): 161-164
doi: 10.3866/PKU.WHXB20010214
Abstract:
Both Co/SiO2 and Co/ZrO2/SiO2 catalysts for FT synthesis were characterized by temperature programmed desorption (TPD) and FTIR spectra.H2TPD evidenced that there were two H2 desorption peaks over Co/SiO2 catalyst and that the amount of H2 adsorption decreased upon introduction of ZrO2.COTPD and COIR showed that addition of ZrO2 weakened the intensity of CO adsorption but increased the amount of adsorbed CO.In FT synthesis,ZrO2 promoter enhanced the formation of heavy hydrocarbons in addition to keeping high activity.Such a shift of product array to heavier hydrocarbon was related to the increase of surface H2/CO ratio.
Both Co/SiO2 and Co/ZrO2/SiO2 catalysts for FT synthesis were characterized by temperature programmed desorption (TPD) and FTIR spectra.H2TPD evidenced that there were two H2 desorption peaks over Co/SiO2 catalyst and that the amount of H2 adsorption decreased upon introduction of ZrO2.COTPD and COIR showed that addition of ZrO2 weakened the intensity of CO adsorption but increased the amount of adsorbed CO.In FT synthesis,ZrO2 promoter enhanced the formation of heavy hydrocarbons in addition to keeping high activity.Such a shift of product array to heavier hydrocarbon was related to the increase of surface H2/CO ratio.
2001, 17(02): 165-168
doi: 10.3866/PKU.WHXB20010215
Abstract:
ZrNp4 could react at room temperature with surface hydroxy groups of MCM41 molecular sieve, with formation of an organozirconium complex (≡Si－O)2Np2 on the surface. The method of preparation of the surface complex is presented. The effects of the reaction temperature, of the sublimation temperature of ZrNp4 and of the dehydration temperature of MCM41 on the preparation were investigated. The composition and structure of the surface complex were characterized by FTIR, solid state MAS NMR and chemical probe reaction.
ZrNp4 could react at room temperature with surface hydroxy groups of MCM41 molecular sieve, with formation of an organozirconium complex (≡Si－O)2Np2 on the surface. The method of preparation of the surface complex is presented. The effects of the reaction temperature, of the sublimation temperature of ZrNp4 and of the dehydration temperature of MCM41 on the preparation were investigated. The composition and structure of the surface complex were characterized by FTIR, solid state MAS NMR and chemical probe reaction.
2001, 17(02): 169-172
doi: 10.3866/PKU.WHXB20010216
Abstract:
The surface organic modification of TiO2 particles with titanate coupling reagent,which was precoated with double layers of SiO2 and Al2O3,was studied.Experiments showed that the modified particles exhibited hydrophobic characteristics.The modification state of the particle surface was characterized by IR spectroscopic measurement,pyrolytic gas chromatography,thermogravimetric analysis and Xray photoelectron spectra.The titanate coupling reagent binding with the hydroxyl on the particle surface was analyzed.The surface characteristics of premodification and postmodification particles were compared.
The surface organic modification of TiO2 particles with titanate coupling reagent,which was precoated with double layers of SiO2 and Al2O3,was studied.Experiments showed that the modified particles exhibited hydrophobic characteristics.The modification state of the particle surface was characterized by IR spectroscopic measurement,pyrolytic gas chromatography,thermogravimetric analysis and Xray photoelectron spectra.The titanate coupling reagent binding with the hydroxyl on the particle surface was analyzed.The surface characteristics of premodification and postmodification particles were compared.
2001, 17(02): 173-176
doi: 10.3866/PKU.WHXB20010217
Abstract:
The problem of polymer chains near an impenetrable plane is investigated by means of the probability method. It is shown that the 2kth moment of the reduced normal component of the endtoend distance A2k only depends on the reduced distance to the plane of the first segment AZ0, here, A=l－1•, n is the chain length, l is the bond length and fixed to be unity, which can be expressed as A2k=f(AZ0). When AZ0≈0, A2k is the maximum(A2k=k!), then it decreases rapidly and soon reaches the minimum with the increase of AZ0, afterwards A2k es up gradually and reaches the limit value [(2k－1)×(2k－3)×…×1]/2k when AZ0 is large enough. Suggesting that the polymer chain can be significantly elongated for small Z0 and contracted for an intermediate range of Z0 due to the barrier. The distribution of the endtoend distance also depends on the distance Z0 to the plane of the first segment.
The problem of polymer chains near an impenetrable plane is investigated by means of the probability method. It is shown that the 2kth moment of the reduced normal component of the endtoend distance A2k only depends on the reduced distance to the plane of the first segment AZ0, here, A=l－1•, n is the chain length, l is the bond length and fixed to be unity, which can be expressed as A2k=f(AZ0). When AZ0≈0, A2k is the maximum(A2k=k!), then it decreases rapidly and soon reaches the minimum with the increase of AZ0, afterwards A2k es up gradually and reaches the limit value [(2k－1)×(2k－3)×…×1]/2k when AZ0 is large enough. Suggesting that the polymer chain can be significantly elongated for small Z0 and contracted for an intermediate range of Z0 due to the barrier. The distribution of the endtoend distance also depends on the distance Z0 to the plane of the first segment.
2001, 17(02): 177-180
doi: 10.3866/PKU.WHXB20010218
Abstract:
By varying the hydrolysis and hydrothermal processing parameters in preparing TiO2 nanoparticles different sizes of TiO2 nanoparticles are obtained.(1) At higher autoclaving temperature,lower pH and longer autoclaving period,larger sizes of TiO2 nanoparticles are prepared.(2) The nanoporous electrodes made from sintering smaller TiO2 nanoparticles show relatively poor IPCE and low absorption in UVVis spectrum,(3) Higher IPCE can be achieved with TiO2 nanoporous electrodes made from sintering larger TiO2 nanoparticles.These electrodes are suitable for studying behavior of the photoelectrochemistry of dye sensitized nanoporous electrodes.
By varying the hydrolysis and hydrothermal processing parameters in preparing TiO2 nanoparticles different sizes of TiO2 nanoparticles are obtained.(1) At higher autoclaving temperature,lower pH and longer autoclaving period,larger sizes of TiO2 nanoparticles are prepared.(2) The nanoporous electrodes made from sintering smaller TiO2 nanoparticles show relatively poor IPCE and low absorption in UVVis spectrum,(3) Higher IPCE can be achieved with TiO2 nanoporous electrodes made from sintering larger TiO2 nanoparticles.These electrodes are suitable for studying behavior of the photoelectrochemistry of dye sensitized nanoporous electrodes.
2001, 17(02): 181-184
doi: 10.3866/PKU.WHXB20010219
Abstract:
A new Schiff base derived from tyrosine and salicylidene and its copper(Ⅱ) complex have been synthesized and characterized by elemental analyses,molar conductances,thermal analyses,infrared spectra,electronic spectra and EPR spectra.The composition of the complex is K[CuL(Ac)]•H2O, where L=H13C16NO4. EPR spectra of the copper(Ⅱ) complex were investigated in various solvents at different temperatures.It is found that the linewidth of four hyperfine lines on solution spectra at room temperature is unequal and changes with mⅠ ,this could be satisfactorily explained by the relaxation effect.The relaxation time and the relaxation rate were calculated.By using spectral parameters from solution spectra at low temperature,the bonding parameters of Cu(Ⅱ) complex were calculated.The bonding characterization and stability of the complex were disscussed.The results show that the inplane 螵瞓ond and the inplane 皙瞓ond in the complex all play an important role.
A new Schiff base derived from tyrosine and salicylidene and its copper(Ⅱ) complex have been synthesized and characterized by elemental analyses,molar conductances,thermal analyses,infrared spectra,electronic spectra and EPR spectra.The composition of the complex is K[CuL(Ac)]•H2O, where L=H13C16NO4. EPR spectra of the copper(Ⅱ) complex were investigated in various solvents at different temperatures.It is found that the linewidth of four hyperfine lines on solution spectra at room temperature is unequal and changes with mⅠ ,this could be satisfactorily explained by the relaxation effect.The relaxation time and the relaxation rate were calculated.By using spectral parameters from solution spectra at low temperature,the bonding parameters of Cu(Ⅱ) complex were calculated.The bonding characterization and stability of the complex were disscussed.The results show that the inplane 螵瞓ond and the inplane 皙瞓ond in the complex all play an important role.
2001, 17(02): 185-188
doi: 10.3866/PKU.WHXB20010220
Abstract:
The interaction of methylene blue(MB) and bovine serum albumin(BSA) is investigated in the SDS micelle system which is simulated as one kind of coexisted albumin. The interaction parameters of MB and BSA and simulated albumin such as partition coefficient 辍ormal binding free energy 腉、average binding number n are calculated. The results show that most of MB is in the form of monomer in SDS micelle systems；the main interaction of MB and BSA is of static electric and Hbind force,and that of MB and simulated albumin is only of static electric force.
The interaction of methylene blue(MB) and bovine serum albumin(BSA) is investigated in the SDS micelle system which is simulated as one kind of coexisted albumin. The interaction parameters of MB and BSA and simulated albumin such as partition coefficient 辍ormal binding free energy 腉、average binding number n are calculated. The results show that most of MB is in the form of monomer in SDS micelle systems；the main interaction of MB and BSA is of static electric and Hbind force,and that of MB and simulated albumin is only of static electric force.
2001, 17(02): 189-192
doi: 10.3866/PKU.WHXB20010221
Abstract:
The extraction of zinc by di(2ethylhexyl)dithiophosphoric acid(D2EHDTPA)trioctylamine(TOA) was investigated.Conductance titration and interfacial pressure measurement showed that when D2EHDTPA and TOA were mixed they reacted and formed an electrolyte of ionic pairs.The extraction of zinc by the electrolyte was of antisynergistic nature,and the reaction was Zn2＋＋2BHA(O) → ZnA2(O)＋2B(O)＋2H＋ (subscript (o) stand for “oil phase”).The zinc extraction was an endothermic reaction ,the heat of reaction was 130.1 kJ•mol－1.Some phenomena of interface concerned were also discussed.
The extraction of zinc by di(2ethylhexyl)dithiophosphoric acid(D2EHDTPA)trioctylamine(TOA) was investigated.Conductance titration and interfacial pressure measurement showed that when D2EHDTPA and TOA were mixed they reacted and formed an electrolyte of ionic pairs.The extraction of zinc by the electrolyte was of antisynergistic nature,and the reaction was Zn2＋＋2BHA(O) → ZnA2(O)＋2B(O)＋2H＋ (subscript (o) stand for “oil phase”).The zinc extraction was an endothermic reaction ,the heat of reaction was 130.1 kJ•mol－1.Some phenomena of interface concerned were also discussed.
