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2003 Volume 19 Issue 8
2003, 19(08): 681-685
doi: 10.3866/PKU.WHXB20030801
Abstract:
Molecular dynamics simulations are employed to study heating rate induced superheating and melting behaviors of bulk Pb. Quantum Sutton-Chen many body potential is used for these simulations. The superheating and melting behavior are found to be strongly affected by the heating rate, the rapid the heating rate,the higher the melting temperature and there is an upper limit for the heating rate induce superheating. Stability study shows that heating rate induced randomization is the main reason to eliminate the energy barrier for phase transformation to occur. Not only Pb crystals but also Pb crystals with defects are studied. And the upper limit of heating rate induced superheating is determined to be around 780 K.
Molecular dynamics simulations are employed to study heating rate induced superheating and melting behaviors of bulk Pb. Quantum Sutton-Chen many body potential is used for these simulations. The superheating and melting behavior are found to be strongly affected by the heating rate, the rapid the heating rate,the higher the melting temperature and there is an upper limit for the heating rate induce superheating. Stability study shows that heating rate induced randomization is the main reason to eliminate the energy barrier for phase transformation to occur. Not only Pb crystals but also Pb crystals with defects are studied. And the upper limit of heating rate induced superheating is determined to be around 780 K.
2003, 19(08): 686-688
doi: 10.3866/PKU.WHXB20030802
Abstract:
The threshold energies of electron-stimulated desorption of N2 and O2 from polycrystalline W in vacuum (1×10－3 Pa) at T=300 K are measured. For O2-W couple, the threshold energy is about 15.5 eV; For N2-W couple, the threshold energy is about 13.8 eV. The displacement adsorption of N2 by O2 from the surface of polycrystalline W is studied using the measured threshold energy. The result shows that within a given time interval, N2 could be displaced by O2 on the surface of W, but the opposite process could not occur.
The threshold energies of electron-stimulated desorption of N2 and O2 from polycrystalline W in vacuum (1×10－3 Pa) at T=300 K are measured. For O2-W couple, the threshold energy is about 15.5 eV; For N2-W couple, the threshold energy is about 13.8 eV. The displacement adsorption of N2 by O2 from the surface of polycrystalline W is studied using the measured threshold energy. The result shows that within a given time interval, N2 could be displaced by O2 on the surface of W, but the opposite process could not occur.
2003, 19(08): 689-694
doi: 10.3866/PKU.WHXB20030803
Abstract:
The phenolformaldehyde resin activated carbon without ‘ink bottle’ porous structure was first introduced to study the influence of porous structure on capacitance of electrode material. The relation between the porous structure of the activated carbon and its electric double-layer capacitance, and the effect of its pore size distribution on discharge rates were discussed by means of nitrogen gas adsorption, AC impedance spectroscopy and constant current discharge techniques. The capacitance of activated carbons is attributed to both external surface (pore diameter > 2.0 nm) and micropore surface (pore diameter < 2.0 nm), but mainly to the latter. The capacitance on the microporous surface is 21.4 μF•cm－2, on the external surface < 10 μF•cm－2. Possibly the space charge layer exists on the interface in series with electric double layer, which makes the capacitance on the external surface much smaller than the usual capacitance. The activated carbon with larger micropore has larger specific capacitance and higher discharge rate.
The phenolformaldehyde resin activated carbon without ‘ink bottle’ porous structure was first introduced to study the influence of porous structure on capacitance of electrode material. The relation between the porous structure of the activated carbon and its electric double-layer capacitance, and the effect of its pore size distribution on discharge rates were discussed by means of nitrogen gas adsorption, AC impedance spectroscopy and constant current discharge techniques. The capacitance of activated carbons is attributed to both external surface (pore diameter > 2.0 nm) and micropore surface (pore diameter < 2.0 nm), but mainly to the latter. The capacitance on the microporous surface is 21.4 μF•cm－2, on the external surface < 10 μF•cm－2. Possibly the space charge layer exists on the interface in series with electric double layer, which makes the capacitance on the external surface much smaller than the usual capacitance. The activated carbon with larger micropore has larger specific capacitance and higher discharge rate.
2003, 19(08): 695-700
doi: 10.3866/PKU.WHXB20030804
Abstract:
Quantitative structure-activity relationships (QSARs) for 43 benzofuran and benzothiophene biphenyls were studied. By using a genetic al rithm (GA), a group of multiple regression models with high fitness scores (r2 was up to 0.70) were generated. From the statistical analyses of the descriptors used in the evolution procedure, four of them, including the partition coefficient (lgP), the molecular surface area (Area), the molecular weight (MW), and the dipole vector (Dip) were found to be the principal features affecting the biological activity. For example, the molecular surface area appeared in 94％ of the models in the elite populations. That is to say, the hydrophobic interactions between the inhibitors and the receptors are very important to the biological activity, which supplies a guide for the design and reconstruction of new PTP1B inhibitors.
Quantitative structure-activity relationships (QSARs) for 43 benzofuran and benzothiophene biphenyls were studied. By using a genetic al rithm (GA), a group of multiple regression models with high fitness scores (r2 was up to 0.70) were generated. From the statistical analyses of the descriptors used in the evolution procedure, four of them, including the partition coefficient (lgP), the molecular surface area (Area), the molecular weight (MW), and the dipole vector (Dip) were found to be the principal features affecting the biological activity. For example, the molecular surface area appeared in 94％ of the models in the elite populations. That is to say, the hydrophobic interactions between the inhibitors and the receptors are very important to the biological activity, which supplies a guide for the design and reconstruction of new PTP1B inhibitors.
2003, 19(08): 701-704
doi: 10.3866/PKU.WHXB20030805
Abstract:
It was demonstrated by electron diffraction patterns that lead sulfide (PbS) semiconductor particles films were obtained under arachidic acid monolayer, floating on lead nitrate solution, by injection of S2－ aqueous beneath the monolayer. Different shapes of the PbS semiconductor nanocrystallites, such as triangle, quadrangle and wooden club, were formed under different surface pressure of monolayer. The influence of surface pressure of monolayer preparation of arachdic acid on the structure of PbS nanocrystallites was studied by TEM images and electron diffraction patterns. Controlling surface pressure at 25 mN•m－1, the epitaxial growth of PbS nanocrystallites with their (111) planes parallelling to the (110) planes of monolayer, was proved by TEM images and electron diffraction patterns. A mechanism for the PbS nanocrystallites epitaxial growth was rationalized in terms of lattic matching between the arachidic acid headgroups in the monolayer and the semiconductor nanocrystallites, which were fabricated under monolayer.
It was demonstrated by electron diffraction patterns that lead sulfide (PbS) semiconductor particles films were obtained under arachidic acid monolayer, floating on lead nitrate solution, by injection of S2－ aqueous beneath the monolayer. Different shapes of the PbS semiconductor nanocrystallites, such as triangle, quadrangle and wooden club, were formed under different surface pressure of monolayer. The influence of surface pressure of monolayer preparation of arachdic acid on the structure of PbS nanocrystallites was studied by TEM images and electron diffraction patterns. Controlling surface pressure at 25 mN•m－1, the epitaxial growth of PbS nanocrystallites with their (111) planes parallelling to the (110) planes of monolayer, was proved by TEM images and electron diffraction patterns. A mechanism for the PbS nanocrystallites epitaxial growth was rationalized in terms of lattic matching between the arachidic acid headgroups in the monolayer and the semiconductor nanocrystallites, which were fabricated under monolayer.
2003, 19(08): 705-708
doi: 10.3866/PKU.WHXB20030806
Abstract:
Crystallization behaviors of electroless Ni-P deposits with 12％(w) P were studied by differential thermal analysis (DTA), thermogravimetry (TG) and in situ X-ray diffraction (XRD). The Ni-P alloys were prepared from a bath containing NiSO4 28 g•L－1, NaH2PO2•3H2O 32 g•L－1, C6H8O7•H2O 16 g•L－1,EDTA[CH2N(CH2COOH)2]2 7 g•L－1, C4H4O6 6 g•L－1, NaAc 18 g•L－1, C3H6O3 6 g•L－1, KIO3 0.001 g•L－1, with pH 4.5～5.0， at 90 ℃. The DTA curves of the alloys indicate that there were two exothermic processes at 350 and 420 ℃, respectively, which could be related to the processes of phases change of the alloys as the mass change is less than ±1％ as revealed by the TG curves. The results of in situ XRD show that the structure of the alloy is amorphous when the temperature bellows 300 ℃. The XRD pattern of metastable Ni5P2 and Ni12P phases initially appeared at the temperature over 320 ℃, and disappeared completely at 400 ℃. The XRD peaks belonging to Ni3P and Ni stable phases emerged at 360 ℃. The metastable Ni5P2 and Ni12P5 remained during the testing period of 2 h at 325 ℃, and lasted just for 40 min at 350 ℃ before transferring into the stable phases of Ni3P and Ni. According to the results, the exothermic peak of the DTA curves for the deposits at 350 ℃ should result from the two processes, i.e., the amorphous Ni-P alloys crystallized into metastable Ni5P2 and Ni12P5 phases, and then the metastable phases partially turned into the stable phases of Ni3P and Ni.
Crystallization behaviors of electroless Ni-P deposits with 12％(w) P were studied by differential thermal analysis (DTA), thermogravimetry (TG) and in situ X-ray diffraction (XRD). The Ni-P alloys were prepared from a bath containing NiSO4 28 g•L－1, NaH2PO2•3H2O 32 g•L－1, C6H8O7•H2O 16 g•L－1,EDTA[CH2N(CH2COOH)2]2 7 g•L－1, C4H4O6 6 g•L－1, NaAc 18 g•L－1, C3H6O3 6 g•L－1, KIO3 0.001 g•L－1, with pH 4.5～5.0， at 90 ℃. The DTA curves of the alloys indicate that there were two exothermic processes at 350 and 420 ℃, respectively, which could be related to the processes of phases change of the alloys as the mass change is less than ±1％ as revealed by the TG curves. The results of in situ XRD show that the structure of the alloy is amorphous when the temperature bellows 300 ℃. The XRD pattern of metastable Ni5P2 and Ni12P phases initially appeared at the temperature over 320 ℃, and disappeared completely at 400 ℃. The XRD peaks belonging to Ni3P and Ni stable phases emerged at 360 ℃. The metastable Ni5P2 and Ni12P5 remained during the testing period of 2 h at 325 ℃, and lasted just for 40 min at 350 ℃ before transferring into the stable phases of Ni3P and Ni. According to the results, the exothermic peak of the DTA curves for the deposits at 350 ℃ should result from the two processes, i.e., the amorphous Ni-P alloys crystallized into metastable Ni5P2 and Ni12P5 phases, and then the metastable phases partially turned into the stable phases of Ni3P and Ni.
2003, 19(08): 709-713
doi: 10.3866/PKU.WHXB20030807
Abstract:
A Series of simulations of the heating and melting processes of metal Cu have been carried out by means of the constant-temperature, constant-pressure molecular dynamics simulation technique. The Finnis-Sinclair (FS) potential was used to describe the inter-atomic interactions in the simulation. To reveal the structural evolution of Cu during the melting process, the pair correlation function, mean square displacement, etc. were calculated. It is shown that metal Cu melts at 1 444 K during the heating process, and its diffusion constant is about 4.31×10－9 m2•s－1 at this melting point. These results are in better line with experiment than those of simulations using the embedded-atom method, which indicates that the FS potential is suitable for disordered systems such as liquid Cu. The heating rate turns out to be very important during the heating processes.
A Series of simulations of the heating and melting processes of metal Cu have been carried out by means of the constant-temperature, constant-pressure molecular dynamics simulation technique. The Finnis-Sinclair (FS) potential was used to describe the inter-atomic interactions in the simulation. To reveal the structural evolution of Cu during the melting process, the pair correlation function, mean square displacement, etc. were calculated. It is shown that metal Cu melts at 1 444 K during the heating process, and its diffusion constant is about 4.31×10－9 m2•s－1 at this melting point. These results are in better line with experiment than those of simulations using the embedded-atom method, which indicates that the FS potential is suitable for disordered systems such as liquid Cu. The heating rate turns out to be very important during the heating processes.
2003, 19(08): 714-717
doi: 10.3866/PKU.WHXB20030808
Abstract:
Co-precipitated CuO-ZrO2 mixed oxides were characterized by XRD,EXAFS, XPS methods. For the samples calcined at 500 ℃, amorphous solid solution forms between CuO and ZrO2 in the co-precipitated samples. The extra CuO crystal exists if CuO is more than its solubility in ZrO2, and extra tetra nal ZrO2 crystal exists if ZrO2 content is more than its solubility in CuO. After calcined at 800 ℃, the samples compose of monoclinic ZrO2 and CuO crystals.
Co-precipitated CuO-ZrO2 mixed oxides were characterized by XRD,EXAFS, XPS methods. For the samples calcined at 500 ℃, amorphous solid solution forms between CuO and ZrO2 in the co-precipitated samples. The extra CuO crystal exists if CuO is more than its solubility in ZrO2, and extra tetra nal ZrO2 crystal exists if ZrO2 content is more than its solubility in CuO. After calcined at 800 ℃, the samples compose of monoclinic ZrO2 and CuO crystals.
2003, 19(08): 718-722
doi: 10.3866/PKU.WHXB20030809
Abstract:
Kinetics and mechanism of hypophosphite oxidation on a nickel electrode were studied by means of the electrochemical mass spectroscopy (EMS) and kinetic model analysis. In the kinetic model, the electrooxidation of hypophosphite under es an H abstraction of hypophosphite from the P－H bond to form the phosphorus-centered radical, PHO2－•,which subsequently is electrochemically reacted with water to form the final product, phosphite. The kinetic equations were derived, and the kinetic parameters were obtained from a comparison of experimental results and the kinetic equations. The process of hypophosphite electrooxidation on a nickel electrode could be well simulated by this model.
Kinetics and mechanism of hypophosphite oxidation on a nickel electrode were studied by means of the electrochemical mass spectroscopy (EMS) and kinetic model analysis. In the kinetic model, the electrooxidation of hypophosphite under es an H abstraction of hypophosphite from the P－H bond to form the phosphorus-centered radical, PHO2－•,which subsequently is electrochemically reacted with water to form the final product, phosphite. The kinetic equations were derived, and the kinetic parameters were obtained from a comparison of experimental results and the kinetic equations. The process of hypophosphite electrooxidation on a nickel electrode could be well simulated by this model.
2003, 19(08): 723-726
doi: 10.3866/PKU.WHXB20030810
Abstract:
A simplified aqueous solvation model (SAWSA 2) for protein was developed. The model classified the atoms in protein into 20 basic types; and the aqueous free energies of solvation was calculated by solvent-accessible surface areas of each atom type and corresponding solvation parameters. The solvation parameter for each atom type was obtained by fitted the calculated aqueous free energies of solvation from PB/SA of 110 proteins. The solvation model developed in this work was applied to predict the solvation free energies of 20 proteins. The predicted values from SAWSA 2 model were in od agreement with those from PB/SA model, and were much better than those given by the two models previously reported.
A simplified aqueous solvation model (SAWSA 2) for protein was developed. The model classified the atoms in protein into 20 basic types; and the aqueous free energies of solvation was calculated by solvent-accessible surface areas of each atom type and corresponding solvation parameters. The solvation parameter for each atom type was obtained by fitted the calculated aqueous free energies of solvation from PB/SA of 110 proteins. The solvation model developed in this work was applied to predict the solvation free energies of 20 proteins. The predicted values from SAWSA 2 model were in od agreement with those from PB/SA model, and were much better than those given by the two models previously reported.
Surface Complex Adsorption Wave of Cadmium Ion at Ultra-micro Disc-electrode Modified by Polyaniline
2003, 19(08): 727-732
doi: 10.3866/PKU.WHXB20030811
Abstract:
The ultra-micro disc-electrode is combined by adhering with 12-carbon fibers of 7 μm in diameter ,after that this electrode is modified by polyaniline in electrolytic polymerization. The absorption characteristics and the electrode process of cadmium ion on this electrode are studied by cyclic voltammetry, step-scan voltammetry, two-step chronocoulometry and AC impedance method. There are two reduction peaks in cyclic voltammetric curve at －0.90 V and －1.06 V, respectively(Fig.1).Experiments and theory show that the electro-active adsorptive surface complex of Cd2＋ is formed from chemical adsorption of Cd2＋ by polyaniline at the electrode surface. So ,this kind of surface complex rather than Cd2＋is reduced firstly .The potential of the reduction peak is at －0.90 V, which is more positive than the directly reduced potential (－0.98 V) of Cd2＋.There is no corresponding oxide peak appearing in cyclic scanning. The reaction mechanism of electrode process is inferred according to experimental data, which proves that the characteristics of reduction peak are simultaneously controlled by diffusing and surface complex reactions. The theoretic curve calculated by this mechanism is agreement with the experimental curve determined by step-scan voltammetry (Fig.2).The formation constant (K=924) of surface adsorptive complex, the maximum adsorptive capacity(Γo=2.08×10－9 mol•cm－2), the kinetic parameters（kf =4.04×10－3 mol－1•cm3•s－1, kb =4.37×10－6 s－1） of surface complex reaction, the diffusion coefficient（D=8.7×10－6 cm2•s－1）of Cd2＋ ,the thickness of diffusion layer （δd=2.75×10－4 cm）and reaction layer（δk=5.14×10－5 cm） are calculated. Experiment also proves that the reduction peak at －1.06 V is a catalytic reduction peak of hydrogen ion, formed by inductive effect of reduced surface complex of Cd2＋.
The ultra-micro disc-electrode is combined by adhering with 12-carbon fibers of 7 μm in diameter ,after that this electrode is modified by polyaniline in electrolytic polymerization. The absorption characteristics and the electrode process of cadmium ion on this electrode are studied by cyclic voltammetry, step-scan voltammetry, two-step chronocoulometry and AC impedance method. There are two reduction peaks in cyclic voltammetric curve at －0.90 V and －1.06 V, respectively(Fig.1).Experiments and theory show that the electro-active adsorptive surface complex of Cd2＋ is formed from chemical adsorption of Cd2＋ by polyaniline at the electrode surface. So ,this kind of surface complex rather than Cd2＋is reduced firstly .The potential of the reduction peak is at －0.90 V, which is more positive than the directly reduced potential (－0.98 V) of Cd2＋.There is no corresponding oxide peak appearing in cyclic scanning. The reaction mechanism of electrode process is inferred according to experimental data, which proves that the characteristics of reduction peak are simultaneously controlled by diffusing and surface complex reactions. The theoretic curve calculated by this mechanism is agreement with the experimental curve determined by step-scan voltammetry (Fig.2).The formation constant (K=924) of surface adsorptive complex, the maximum adsorptive capacity(Γo=2.08×10－9 mol•cm－2), the kinetic parameters（kf =4.04×10－3 mol－1•cm3•s－1, kb =4.37×10－6 s－1） of surface complex reaction, the diffusion coefficient（D=8.7×10－6 cm2•s－1）of Cd2＋ ,the thickness of diffusion layer （δd=2.75×10－4 cm）and reaction layer（δk=5.14×10－5 cm） are calculated. Experiment also proves that the reduction peak at －1.06 V is a catalytic reduction peak of hydrogen ion, formed by inductive effect of reduced surface complex of Cd2＋.
2003, 19(08): 733-736
doi: 10.3866/PKU.WHXB20030812
Abstract:
(NH4)3PMo6W6O40 nanoparticles were synthesized by the solid state reaction of H3PMo6W6O40•23H2O with (NH4)2C2O4•H2O at room temperature. Its structure, particle size and appearance were characterized with elemental analysis, IR, UV-Vis, XRD, TEM, TG-DTA and BET techniques. The results show that (NH4)3PMo6W6O40 nanoparticles are found to exhibit Keggin structure, have a surface area of 167.6 m2•g－1, below 465 ℃, the nanoparticles have a higher thermal stability, the mean grain size is of the value of 10 nm. In this solid state reaction, grinding and reaction thermal energy can accelerate the speed of reactant diffusion and product nucleation and decrease the particle′s size, water of crystallization of reactants and product H2C2O4•2H2O play a key role of forming the small size (NH4)3PMo6W6O40 nanoparticles.
(NH4)3PMo6W6O40 nanoparticles were synthesized by the solid state reaction of H3PMo6W6O40•23H2O with (NH4)2C2O4•H2O at room temperature. Its structure, particle size and appearance were characterized with elemental analysis, IR, UV-Vis, XRD, TEM, TG-DTA and BET techniques. The results show that (NH4)3PMo6W6O40 nanoparticles are found to exhibit Keggin structure, have a surface area of 167.6 m2•g－1, below 465 ℃, the nanoparticles have a higher thermal stability, the mean grain size is of the value of 10 nm. In this solid state reaction, grinding and reaction thermal energy can accelerate the speed of reactant diffusion and product nucleation and decrease the particle′s size, water of crystallization of reactants and product H2C2O4•2H2O play a key role of forming the small size (NH4)3PMo6W6O40 nanoparticles.
2003, 19(08): 737-741
doi: 10.3866/PKU.WHXB20030813
Abstract:
Using low-cost Al(NO3)3•9H2O as raw material and citric acid as chelator, highly ordered three-dimensional macroporous (3DOM) Al2O3 with pore size of 250～350 nm has been successfully fabricated by a template method in which polystyrene colloidal crystal with diameter of about 600 nm were used as template. The TGA, TG-IR and SEM observations show that adding citric acid is in favor of forming the three-dimensional ordered structure since it can avoid forming agglomerated particles during heat treatment. Within the range of 0.5～0.8 mol•L－1 of the precursor concentration, the Al2O3 samples obtained are highly ordered three-dimensional macroporous materials, and such macroporou structure is maintained up to 1 100 ℃,showing a high thermostability.
Using low-cost Al(NO3)3•9H2O as raw material and citric acid as chelator, highly ordered three-dimensional macroporous (3DOM) Al2O3 with pore size of 250～350 nm has been successfully fabricated by a template method in which polystyrene colloidal crystal with diameter of about 600 nm were used as template. The TGA, TG-IR and SEM observations show that adding citric acid is in favor of forming the three-dimensional ordered structure since it can avoid forming agglomerated particles during heat treatment. Within the range of 0.5～0.8 mol•L－1 of the precursor concentration, the Al2O3 samples obtained are highly ordered three-dimensional macroporous materials, and such macroporou structure is maintained up to 1 100 ℃,showing a high thermostability.
2003, 19(08): 742-746
doi: 10.3866/PKU.WHXB20030814
Abstract:
This paper proposes a novel surplus function quantum Monte Carlo al rithm, which is a self-optimizing and self-improving procedure. In contrast to previous procedure, the trial function is optimized synchronistically in the surplus function method, but not before the variational Monte Carlo computation. In order to optimize the trial function, an improved steepest descent technique is used, with the step size automatically adjusted to obtain a procedure, which converges superlinearly. The author also uses a novel correlation function, which has both the correct electron-electron and electron-nucleus cusp conditions. The method is employed to calculate the ground state energies of H2、LiH、Li2、H2O and the energy values of X 3B1 state, 1 1A1 state, and 2 1A1 state of CH2.
This paper proposes a novel surplus function quantum Monte Carlo al rithm, which is a self-optimizing and self-improving procedure. In contrast to previous procedure, the trial function is optimized synchronistically in the surplus function method, but not before the variational Monte Carlo computation. In order to optimize the trial function, an improved steepest descent technique is used, with the step size automatically adjusted to obtain a procedure, which converges superlinearly. The author also uses a novel correlation function, which has both the correct electron-electron and electron-nucleus cusp conditions. The method is employed to calculate the ground state energies of H2、LiH、Li2、H2O and the energy values of X 3B1 state, 1 1A1 state, and 2 1A1 state of CH2.
2003, 19(08): 747-750
doi: 10.3866/PKU.WHXB20030815
Abstract:
It is well known that phosphatidylcholine (PC) vesicles are predominant carriers of cholesterol in human bile. Although the interaction of bile salts with PC has been extensively studied, relatively little attention has been given to effects of divalent metal ions on the aggregation properties of PC. We used both light scattering and UV spectroscopies to follow the effects of divalent metal ions on EYPC (egg yellow PC) vesicles. We conclude that when divalent metal ions existed, the mixed vesicles formed by PC and TC (sodium taurocholate) with the ratio of 1:3 were more stable. Free divalent metal ions act to precipitate unilamellar PC vesicles whereas, in combination with sodium taurocholate, these ions act to decrease the size of PC vesicles and induce a phase transition from PC vesicles to mixed micelles. It is a possible reason for gallstones formation when extra free divalent metal ions exist in human bile.
It is well known that phosphatidylcholine (PC) vesicles are predominant carriers of cholesterol in human bile. Although the interaction of bile salts with PC has been extensively studied, relatively little attention has been given to effects of divalent metal ions on the aggregation properties of PC. We used both light scattering and UV spectroscopies to follow the effects of divalent metal ions on EYPC (egg yellow PC) vesicles. We conclude that when divalent metal ions existed, the mixed vesicles formed by PC and TC (sodium taurocholate) with the ratio of 1:3 were more stable. Free divalent metal ions act to precipitate unilamellar PC vesicles whereas, in combination with sodium taurocholate, these ions act to decrease the size of PC vesicles and induce a phase transition from PC vesicles to mixed micelles. It is a possible reason for gallstones formation when extra free divalent metal ions exist in human bile.
2003, 19(08): 751-756
doi: 10.3866/PKU.WHXB20030816
Abstract:
By scanning some special configurations on the ground state potential energy surface of [He3H]＋ molecule with the CCSD(T)/aug-cc-pVTZ method, the influence of three-body interaction in the traditional many-body expansion is discussed. It is found that to describe the potential even in such a simple system the inclusion of three-body interaction is necessary. On the other hand, around the stable structures the potential expansion up to three-body interaction is fairly accurate, even though the error grows up in the repulsive region. The equilibrium geometries of [He4H]＋ are also investigated. It is shown that there exists a core of [He2H]＋ in the [HenH]＋ clusters. Fig.5 Tab.3 Ref.27
By scanning some special configurations on the ground state potential energy surface of [He3H]＋ molecule with the CCSD(T)/aug-cc-pVTZ method, the influence of three-body interaction in the traditional many-body expansion is discussed. It is found that to describe the potential even in such a simple system the inclusion of three-body interaction is necessary. On the other hand, around the stable structures the potential expansion up to three-body interaction is fairly accurate, even though the error grows up in the repulsive region. The equilibrium geometries of [He4H]＋ are also investigated. It is shown that there exists a core of [He2H]＋ in the [HenH]＋ clusters. Fig.5 Tab.3 Ref.27
2003, 19(08): 757-761
doi: 10.3866/PKU.WHXB20030817
Abstract:
A scoring function that contains the electrostatic, desolvation and van der Waals energy was used to discriminate the near-native conformations in protein-protein docking. The analysis results of the docked structures for seventeen protein complexes showed that the scoring function including van der Waals energy（ΔEele＋ΔGACE＋ΔEvdw） had much more potentiality in distinguishing the near-native conformations from the incorrect ones compared with other scoring functions, such as ΔEele, ΔGACE, ΔEele＋ΔGACE, ΔEele＋ΔEvdw andΔGACE＋ΔEvdw. It was found that energy minimization could improve the discrimination results for all the scoring functions mentioned above to some extent, especially forΔEele＋ΔGACE＋ΔEvdw. Finally, to further determinate the near-native structure, we performed the molecular dynamics (MD) simulations for the candidate structures of 4INSXX. According to the variations of the mean square deviation (MSD) of the structures in MD trajectories relative to the initial structures, the false structures could be excluded.
A scoring function that contains the electrostatic, desolvation and van der Waals energy was used to discriminate the near-native conformations in protein-protein docking. The analysis results of the docked structures for seventeen protein complexes showed that the scoring function including van der Waals energy（ΔEele＋ΔGACE＋ΔEvdw） had much more potentiality in distinguishing the near-native conformations from the incorrect ones compared with other scoring functions, such as ΔEele, ΔGACE, ΔEele＋ΔGACE, ΔEele＋ΔEvdw andΔGACE＋ΔEvdw. It was found that energy minimization could improve the discrimination results for all the scoring functions mentioned above to some extent, especially forΔEele＋ΔGACE＋ΔEvdw. Finally, to further determinate the near-native structure, we performed the molecular dynamics (MD) simulations for the candidate structures of 4INSXX. According to the variations of the mean square deviation (MSD) of the structures in MD trajectories relative to the initial structures, the false structures could be excluded.
2003, 19(08): 762-765
doi: 10.3866/PKU.WHXB20030818
Abstract:
The complex kinetics of ClO2―-S2O32－ nonlinear reaction system in an unbuffered solution has been investigated in a CSTR. Both quasiperiodic and mixed-mode oscillations of pH and Pt potential were observed. At relatively low [NaClO2]0/[Na2S2O3]0 ratio, the system changed from small-amplitude oscillations and quasiperiodic oscillations to chaos and pure large-amplitude oscillations with increasing the flow rate. At higher initial concentration ratio, however, quasiperiodicity was given way to mixed-mode oscillations in which each period consists of one large and n small peaks (LSn). LS, LS2,LS3,…, LSn were obtained when the flow rate was decreased. For a narrow range of flow rate between each pair of periodic regions(LSn, LSn＋1), a region of aperiodic behavior, an apparently stochastic mixture of LSn and LSn＋1, was also observed. A general model based upon changes in the oxidation state of sulfur in the presence of a generic oxidant simulated the mixed-mode oscillations and aperiodic behavior.
The complex kinetics of ClO2―-S2O32－ nonlinear reaction system in an unbuffered solution has been investigated in a CSTR. Both quasiperiodic and mixed-mode oscillations of pH and Pt potential were observed. At relatively low [NaClO2]0/[Na2S2O3]0 ratio, the system changed from small-amplitude oscillations and quasiperiodic oscillations to chaos and pure large-amplitude oscillations with increasing the flow rate. At higher initial concentration ratio, however, quasiperiodicity was given way to mixed-mode oscillations in which each period consists of one large and n small peaks (LSn). LS, LS2,LS3,…, LSn were obtained when the flow rate was decreased. For a narrow range of flow rate between each pair of periodic regions(LSn, LSn＋1), a region of aperiodic behavior, an apparently stochastic mixture of LSn and LSn＋1, was also observed. A general model based upon changes in the oxidation state of sulfur in the presence of a generic oxidant simulated the mixed-mode oscillations and aperiodic behavior.
2003, 19(08): 766-769
doi: 10.3866/PKU.WHXB20030819
Abstract:
Different flow behaviors influenced by shear rate were observed in two concentration regions (3～9 mmol•kg－1 and 10～40 mmol•kg－1) of quaternary ammonium Gemini surfactant C12-s-C12•2Br(s=2) in aqueous solution. The solution in the former concentration region kept Newtonian flow through out the range of shear rate γ examined from 0 to 1 875 s－1.But in the latter concentration region, the flow transformed from Newtonian to dilatant flow after γ reached a value of critical shear rate γ* which depended on temperature and concentration. And a sharp increase of the zero-shear viscosity η0 along with the raise of c appeared in this region. It was suggested that the tangle of thread-like micelles of C12-s-C12•2Br(s=2) existed in the solution led to the phenomenon mentioned above. The surfactants C12-s-C12•2Br(s=2) turns to C12-s-En-C12•2Br(s=2, n=1,2,3) by insertion of one, two or three oxyethyl groups into the spacer of it. By the reason of the evident variation in geometric shape of unit molecule, this kind of Gemini surfactant in aqueous solution only aggregated into sphere micelles so that it retained Newtonian behavior over the range of c=0～120 mmol•kg－1 and γ=0～1 875 s－1 with slight increase of η0.In addition, reducing temperature favors shear induced structure transform but gives small effect on those systems keeping Newtonian behaviors over the temperatures range studied.
Different flow behaviors influenced by shear rate were observed in two concentration regions (3～9 mmol•kg－1 and 10～40 mmol•kg－1) of quaternary ammonium Gemini surfactant C12-s-C12•2Br(s=2) in aqueous solution. The solution in the former concentration region kept Newtonian flow through out the range of shear rate γ examined from 0 to 1 875 s－1.But in the latter concentration region, the flow transformed from Newtonian to dilatant flow after γ reached a value of critical shear rate γ* which depended on temperature and concentration. And a sharp increase of the zero-shear viscosity η0 along with the raise of c appeared in this region. It was suggested that the tangle of thread-like micelles of C12-s-C12•2Br(s=2) existed in the solution led to the phenomenon mentioned above. The surfactants C12-s-C12•2Br(s=2) turns to C12-s-En-C12•2Br(s=2, n=1,2,3) by insertion of one, two or three oxyethyl groups into the spacer of it. By the reason of the evident variation in geometric shape of unit molecule, this kind of Gemini surfactant in aqueous solution only aggregated into sphere micelles so that it retained Newtonian behavior over the range of c=0～120 mmol•kg－1 and γ=0～1 875 s－1 with slight increase of η0.In addition, reducing temperature favors shear induced structure transform but gives small effect on those systems keeping Newtonian behaviors over the temperatures range studied.
2003, 19(08): 770-773
doi: 10.3866/PKU.WHXB20030820
Abstract:
The interaction between LiF and Al has been studied by X-ray photoemission spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS).The reaction between LiF and Al occurs in the presence of Alq3 at room temperature. In the Al/LiF/Alq3 system, the Li 1s peak shifts 0.25 eV relative to the F 1s peak during the reaction. On warming the Al substrate covered LiF to 350 K, interaction between LiF and Al is revealed by a shoulder peak, which is about 0.85 eV below the original Li 1s peak. XPS measurement revealed that the shoulder peak corresponds to metal Li 1s, this result is confirmed by HREELS measurements.
The interaction between LiF and Al has been studied by X-ray photoemission spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS).The reaction between LiF and Al occurs in the presence of Alq3 at room temperature. In the Al/LiF/Alq3 system, the Li 1s peak shifts 0.25 eV relative to the F 1s peak during the reaction. On warming the Al substrate covered LiF to 350 K, interaction between LiF and Al is revealed by a shoulder peak, which is about 0.85 eV below the original Li 1s peak. XPS measurement revealed that the shoulder peak corresponds to metal Li 1s, this result is confirmed by HREELS measurements.
2003, 19(08): 774-778
doi: 10.3866/PKU.WHXB20030821
Abstract:
The soapless polystyrene (PSt) latex particles were prepared by using microwave irradiation in a closed reactor under controlled pressure, microwave irradiation and water bathing under normal pressure, respectively. The apparent molecular weight of the particles and their sizes and distribution were characterized by using static laser light scattering (SLLS) and dynamic laser light scattering (DLLS). It was found that microwave irradiation has important effect on the formation of the small size and monodisperse particles. The average numbers of the polymer chain in the PSt particles were calculated by the combination of gel permeation chromatography (GPC) and Zimm plot. The molecular weight of the PSt particles prepared by microwave irradiation under controlled pressure was bigger than that prepared by other ways. The results showed that the dispersity of the particles was not determined by the dispersity of the polymer chain directly. In the soapless emulsion polymerization under microwave irradiation, the latex particles composed of the intertwined polymer chain showed a od monodispersivity, although the polymer chains were not distributed uniformly .In studies of the aging of the homopolymerization and the copolymerization of emulsion, it was also found that the stability of the soapless polymer particles has an intimate relationship with the method of preparation, the structure and quality of the comonomer.
The soapless polystyrene (PSt) latex particles were prepared by using microwave irradiation in a closed reactor under controlled pressure, microwave irradiation and water bathing under normal pressure, respectively. The apparent molecular weight of the particles and their sizes and distribution were characterized by using static laser light scattering (SLLS) and dynamic laser light scattering (DLLS). It was found that microwave irradiation has important effect on the formation of the small size and monodisperse particles. The average numbers of the polymer chain in the PSt particles were calculated by the combination of gel permeation chromatography (GPC) and Zimm plot. The molecular weight of the PSt particles prepared by microwave irradiation under controlled pressure was bigger than that prepared by other ways. The results showed that the dispersity of the particles was not determined by the dispersity of the polymer chain directly. In the soapless emulsion polymerization under microwave irradiation, the latex particles composed of the intertwined polymer chain showed a od monodispersivity, although the polymer chains were not distributed uniformly .In studies of the aging of the homopolymerization and the copolymerization of emulsion, it was also found that the stability of the soapless polymer particles has an intimate relationship with the method of preparation, the structure and quality of the comonomer.
2003, 19(08): 779-784
doi: 10.3866/PKU.WHXB20030822
Abstract:
Formation of vesicles, micelles and other self-organized molecular assemblies in nonaqueous and mixed solvents was reviewed. Especially, the influences of dielectric constant variation on aggregation behavior of cataionic surfactant mixtures in nonaqueous solvents were fully discussed. The situation about the formation of reverse micelles and other self-organized molecular assemblies in nonaqueous solvents was also summarized.
Formation of vesicles, micelles and other self-organized molecular assemblies in nonaqueous and mixed solvents was reviewed. Especially, the influences of dielectric constant variation on aggregation behavior of cataionic surfactant mixtures in nonaqueous solvents were fully discussed. The situation about the formation of reverse micelles and other self-organized molecular assemblies in nonaqueous solvents was also summarized.
