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2002 Volume 18 Issue 9
2002, 18(09): 769-775
doi: 10.3866/PKU.WHXB20020901
Abstract:
We report an investigation on the surface behaviors, including diffusion, desorption and fluorescence blinking, of rhodamine-labeled phospholipid molecules at single-molecule level by confocal fluorescence microscopy. It was found that besides an average force field on the hydrophilic glass surface there exist special sites that strongly adsorb rhodamine-labeled phospholipid molecules. The desorption rate of the strongly adsorbed molecules is determined to be (5.9±0.2) s－1. The diffusion coefficient of the molecules on the surface, (3.3±0.1)×10－8 cm2•s－1, is much smaller than that in aqueous solution, (2.3±0.1)×10－6 cm2•s－1, but is in the same order as that in a fluid phospholipid membrane. Fluorescence blinking was observed in some of the strongly adsorbed molecules, which may be attributed to reversible quantum jumps to dark states induced by the strong interaction between the molecule and adsorption sites.
We report an investigation on the surface behaviors, including diffusion, desorption and fluorescence blinking, of rhodamine-labeled phospholipid molecules at single-molecule level by confocal fluorescence microscopy. It was found that besides an average force field on the hydrophilic glass surface there exist special sites that strongly adsorb rhodamine-labeled phospholipid molecules. The desorption rate of the strongly adsorbed molecules is determined to be (5.9±0.2) s－1. The diffusion coefficient of the molecules on the surface, (3.3±0.1)×10－8 cm2•s－1, is much smaller than that in aqueous solution, (2.3±0.1)×10－6 cm2•s－1, but is in the same order as that in a fluid phospholipid membrane. Fluorescence blinking was observed in some of the strongly adsorbed molecules, which may be attributed to reversible quantum jumps to dark states induced by the strong interaction between the molecule and adsorption sites.
2002, 18(09): 776-780
doi: 10.3866/PKU.WHXB20020902
Abstract:
Linear Poly(N,N-diethylacrylamide)(PDEA) was synthesized by radical polymerization. The temperature dependence of the relative viscosity of PDEA-THF, PDEA-H2O and PDEA-THF-H2O solutions was investigated. Our results showed that the viscosity of PDEA in three different solvents was influenced differently by temperature. The relative viscosity of PDEA-THF solution increased with increasing temperature, while that of PDEA- H2O and PDEA-THF-H2O showed the inverse trend, namely, increasing of temperature led to the decreasing of viscosity, at the same time, the phenomenon of transparent-opaque transition could be observed as the volume fraction of THF (φTHF) was less than 0.7. For PDEA-THF-H2O solution, on the other hand, the transparent-opaque transition temperature increased with the increasing of φTHF. However, when φTHF was 0.7, the transparent-opaque transition phenomenon disappeared.
Linear Poly(N,N-diethylacrylamide)(PDEA) was synthesized by radical polymerization. The temperature dependence of the relative viscosity of PDEA-THF, PDEA-H2O and PDEA-THF-H2O solutions was investigated. Our results showed that the viscosity of PDEA in three different solvents was influenced differently by temperature. The relative viscosity of PDEA-THF solution increased with increasing temperature, while that of PDEA- H2O and PDEA-THF-H2O showed the inverse trend, namely, increasing of temperature led to the decreasing of viscosity, at the same time, the phenomenon of transparent-opaque transition could be observed as the volume fraction of THF (φTHF) was less than 0.7. For PDEA-THF-H2O solution, on the other hand, the transparent-opaque transition temperature increased with the increasing of φTHF. However, when φTHF was 0.7, the transparent-opaque transition phenomenon disappeared.
2002, 18(09): 781-785
doi: 10.3866/PKU.WHXB20020903
Abstract:
A basic sol containing amorphous SiO2 particles was prepared by sol-gel process with TEOS ( tetraethoxysilane ) as precursor in alcohol system. A solution containing polymer of MTES ( methyltriethoxysilane ) was also prepared under acidic condition. The mixed sol was tested by the small angle X-ray scattering (SAXS) at Station of Beijing Synchrotron Radiation Facility (BSRF). The average rotation radius, the average particle diameter, the percentage of scattering particles, the thickness of interface layer and the specific inner surface area between the two phases were calculated. With the assistant of photon correlation spectrum (PCS) and transmission electronic microscopy (TEM), the microstructure of TEOS-MTES mixed sol was obtained in which SiO2 particles were interlinked through the polymers of MTES. By SAXS experiment, we found negative deviation from the Porod law on all the samples, which showed clearly interface layer between the two phases in mixed sol.
A basic sol containing amorphous SiO2 particles was prepared by sol-gel process with TEOS ( tetraethoxysilane ) as precursor in alcohol system. A solution containing polymer of MTES ( methyltriethoxysilane ) was also prepared under acidic condition. The mixed sol was tested by the small angle X-ray scattering (SAXS) at Station of Beijing Synchrotron Radiation Facility (BSRF). The average rotation radius, the average particle diameter, the percentage of scattering particles, the thickness of interface layer and the specific inner surface area between the two phases were calculated. With the assistant of photon correlation spectrum (PCS) and transmission electronic microscopy (TEM), the microstructure of TEOS-MTES mixed sol was obtained in which SiO2 particles were interlinked through the polymers of MTES. By SAXS experiment, we found negative deviation from the Porod law on all the samples, which showed clearly interface layer between the two phases in mixed sol.
2002, 18(09): 786-790
doi: 10.3866/PKU.WHXB20020904
Abstract:
The coordination states of aluminum species in calcined HZSM-5 zeolites have been investigated using 29Si, 27Al MAS and 2D MQMAS NMR methods. A broad peak at δ 45 in presents in the 27Al MAS NMR spectra of calcined HZSM-5 zeolites. From the 27Al 3QMAS NMR spectrum, it is evident that the peak at δ 45 comes mainly from the distorted tetrahedral Al with a quadrupolar-coupling constant of 5.2 MHz. Simulation of the 27Al 1D MAS NMR spectra of samples calcined at 700 and 750 ℃ shows that a small peak at about δ 30 emerges, which is probably due to 5- coordinated non-framework Al. The existence of this Al species is also confirmed by 27Al 3QMAS NMR.HZSM-5 zeolite calcined at temperature higher than 700 ℃ suffers severe dealumination. Calcination causes part of the Al species “NMR invisible” in the corresponding 27Al MAS spectra.
The coordination states of aluminum species in calcined HZSM-5 zeolites have been investigated using 29Si, 27Al MAS and 2D MQMAS NMR methods. A broad peak at δ 45 in presents in the 27Al MAS NMR spectra of calcined HZSM-5 zeolites. From the 27Al 3QMAS NMR spectrum, it is evident that the peak at δ 45 comes mainly from the distorted tetrahedral Al with a quadrupolar-coupling constant of 5.2 MHz. Simulation of the 27Al 1D MAS NMR spectra of samples calcined at 700 and 750 ℃ shows that a small peak at about δ 30 emerges, which is probably due to 5- coordinated non-framework Al. The existence of this Al species is also confirmed by 27Al 3QMAS NMR.HZSM-5 zeolite calcined at temperature higher than 700 ℃ suffers severe dealumination. Calcination causes part of the Al species “NMR invisible” in the corresponding 27Al MAS spectra.
2002, 18(09): 791-795
doi: 10.3866/PKU.WHXB20020905
Abstract:
Many cerium compounds are promising corrosion inhibitors for aluminum alloy. However, the formation mechanism of Ce conversion films is not clear yet. Scanning microreference electrode technique (SMRE) was used to probe the potential imaging of 2024-T3 Al alloy in CeCl3 solution. The pitting corrosion of Al alloy in CeCl3 decreased with immersion time and disappeared finally. Additionally, the competition of inhibition and corrosion between Ce3＋ and Cl－ on Al alloy was in situ monitored in CeCl3 by SMRE. The results of X-ray photoelectron spectroscopy (XPS) showed that the Ce conversion films consisted of Al2O3, CeO2 and Ce2O3 (Ce(OH)3), and CeO2/Ce2O3 mass ratio decreased with immersion time. It is concluded that when the critical pH for Ce(OH)3 formation is reached, Ce(OH)3 will precipitate at micro cathodic area of the Al alloy surface. Consequently, H2O2, the product of the catholic reaction will oxidize part of Ce(OH)3 to CeO2.
Many cerium compounds are promising corrosion inhibitors for aluminum alloy. However, the formation mechanism of Ce conversion films is not clear yet. Scanning microreference electrode technique (SMRE) was used to probe the potential imaging of 2024-T3 Al alloy in CeCl3 solution. The pitting corrosion of Al alloy in CeCl3 decreased with immersion time and disappeared finally. Additionally, the competition of inhibition and corrosion between Ce3＋ and Cl－ on Al alloy was in situ monitored in CeCl3 by SMRE. The results of X-ray photoelectron spectroscopy (XPS) showed that the Ce conversion films consisted of Al2O3, CeO2 and Ce2O3 (Ce(OH)3), and CeO2/Ce2O3 mass ratio decreased with immersion time. It is concluded that when the critical pH for Ce(OH)3 formation is reached, Ce(OH)3 will precipitate at micro cathodic area of the Al alloy surface. Consequently, H2O2, the product of the catholic reaction will oxidize part of Ce(OH)3 to CeO2.
2002, 18(09): 796-801
doi: 10.3866/PKU.WHXB20020906
Abstract:
The chemical shifts induced by the ring current was calculated for H1′ and H2′ of ATP with different torsion angle χ (O4′－C1′－N9－C4) based on the method of Johnson and Bovey. The chemical shift of H1′ showed relatively strong dependence on the χ angle, which reflected fine conformation changes with pH. By comparing the calculated results with the experimental data, it is shown that in the pH range (1～10) studied in this paper and in the presence of Mg2＋,the torsion angle χ of ATP varies in the small range from 230° to 360°.As the pH of the solution is decreased, the conformation of the ATP molecule changes from trans to cis through -gauche form. At lower pH, the ATP molecule is more likely to take the cis conformation, while at higher pH, the trans conformation is more stable. This supports the conclusion that N1 binds the metal ion at lower pH while the binding site becomes N7 when pH is neutral. In the discussion, the change of the ring current strength induced by pH variation was also taken into account.
The chemical shifts induced by the ring current was calculated for H1′ and H2′ of ATP with different torsion angle χ (O4′－C1′－N9－C4) based on the method of Johnson and Bovey. The chemical shift of H1′ showed relatively strong dependence on the χ angle, which reflected fine conformation changes with pH. By comparing the calculated results with the experimental data, it is shown that in the pH range (1～10) studied in this paper and in the presence of Mg2＋,the torsion angle χ of ATP varies in the small range from 230° to 360°.As the pH of the solution is decreased, the conformation of the ATP molecule changes from trans to cis through -gauche form. At lower pH, the ATP molecule is more likely to take the cis conformation, while at higher pH, the trans conformation is more stable. This supports the conclusion that N1 binds the metal ion at lower pH while the binding site becomes N7 when pH is neutral. In the discussion, the change of the ring current strength induced by pH variation was also taken into account.
2002, 18(09): 802-807
doi: 10.3866/PKU.WHXB20020907
Abstract:
The processes of the proton transfer between 2-hydroxy pyridine (Hy) and 2(1H)-pyridone (Py) were investigated by using density functional theory of quantum chemistry method at B3LYP/6-31G(d) level. The four possible reaction pathways: (a) intramolecular proton transfer;(b) water-assisted intermolecular transfer; (c) isomerization by double-proton transfer in the dimer and (d) intermolecular proton transfer via the complex formed by Hy and Py were investigated in the present paper. The calculated results showed that the processes in (b),(c) and (d) has lower activation energies than that of the intramolecular tautomeric oxo-hydroxy reaction (a) because of the formation of hydrogen-bonded complexes in (b),(c) and (d).The activation energies corrected by scaled zero-point vibrational energies for the four reaction processes calculated at the B3LYP/6-31G(d) level are 137.2,38.7,2.6 and 17.3 kJ•mol－1,respectively.It is likely that the hydrogen bonds formed in the complexes play an important role in proton transfer processes in the later three reaction pathways.
The processes of the proton transfer between 2-hydroxy pyridine (Hy) and 2(1H)-pyridone (Py) were investigated by using density functional theory of quantum chemistry method at B3LYP/6-31G(d) level. The four possible reaction pathways: (a) intramolecular proton transfer;(b) water-assisted intermolecular transfer; (c) isomerization by double-proton transfer in the dimer and (d) intermolecular proton transfer via the complex formed by Hy and Py were investigated in the present paper. The calculated results showed that the processes in (b),(c) and (d) has lower activation energies than that of the intramolecular tautomeric oxo-hydroxy reaction (a) because of the formation of hydrogen-bonded complexes in (b),(c) and (d).The activation energies corrected by scaled zero-point vibrational energies for the four reaction processes calculated at the B3LYP/6-31G(d) level are 137.2,38.7,2.6 and 17.3 kJ•mol－1,respectively.It is likely that the hydrogen bonds formed in the complexes play an important role in proton transfer processes in the later three reaction pathways.
2002, 18(09): 808-811
doi: 10.3866/PKU.WHXB20020908
Abstract:
Quercetin and isorhamnetin are the main function integrants in Hippophae rhamnoidse Linn. curing and guarding against cardiovascular disease. A molecularly imprinted polymer(MIP)was prepared using quercetin as the template. The MIP was used to extract these two flavonoid compounds from the crude aqueous extract. The result is satisfied.
Quercetin and isorhamnetin are the main function integrants in Hippophae rhamnoidse Linn. curing and guarding against cardiovascular disease. A molecularly imprinted polymer(MIP)was prepared using quercetin as the template. The MIP was used to extract these two flavonoid compounds from the crude aqueous extract. The result is satisfied.
2002, 18(09): 812-816
doi: 10.3866/PKU.WHXB20020909
Abstract:
This work presents the study on the oxidation of TyrOH by SO4●－ in water/ACN mixed media. Investigations show that the reaction mechanism between TyrOH and SO4●－ does not change by the addition of ACN, whereas the kinetic behavior of the transient species produced is significantly affected. The decay of SO4●－ decelerates with increasing volume fraction of ACN in mixed media whereas the decay of TyrO● accelerates. We suggest that the contrary effects of the solvent on the decay of both SO4●－ and TyrO● are due to their different charges. The deceleration of the oxidation of TyrOH by SO4●－ with the increase of ACN fraction may demonstrate that in the presence of organic solvents the redox potential of TyrO●/TyrOH is altered, which provides support for the suggestion that the redox potential of TyrO●/ TyrOH might be altered with their inclusion into peptides and proteins.
This work presents the study on the oxidation of TyrOH by SO4●－ in water/ACN mixed media. Investigations show that the reaction mechanism between TyrOH and SO4●－ does not change by the addition of ACN, whereas the kinetic behavior of the transient species produced is significantly affected. The decay of SO4●－ decelerates with increasing volume fraction of ACN in mixed media whereas the decay of TyrO● accelerates. We suggest that the contrary effects of the solvent on the decay of both SO4●－ and TyrO● are due to their different charges. The deceleration of the oxidation of TyrOH by SO4●－ with the increase of ACN fraction may demonstrate that in the presence of organic solvents the redox potential of TyrO●/TyrOH is altered, which provides support for the suggestion that the redox potential of TyrO●/ TyrOH might be altered with their inclusion into peptides and proteins.
2002, 18(09): 817-820
doi: 10.3866/PKU.WHXB20020910
Abstract:
The complex kinetics of the reaction of periodate and sulfite has been investigated. This is a novel periodate-based oscillator. In excess of sulfite and in acidic medium（pH< 3）, batch single-peak phenomena and CSTR sustained oscillations of Pt 、I－ and pH potential, and the complex dynamics in a semibatch are obtained, while the alternative change of color from colorless to brown is also observed. The oscillation behavior is related to [KIO4]0/[Na2SO3]0 ratio and acidity. A possible reaction mechanism, which consists of an autocatalytic production of H＋(positive feedback) and a H＋-consuming pathway (negative feedback), along with the production and elimination of iodine, could fairly explain the complex dynamical behavior.
The complex kinetics of the reaction of periodate and sulfite has been investigated. This is a novel periodate-based oscillator. In excess of sulfite and in acidic medium（pH< 3）, batch single-peak phenomena and CSTR sustained oscillations of Pt 、I－ and pH potential, and the complex dynamics in a semibatch are obtained, while the alternative change of color from colorless to brown is also observed. The oscillation behavior is related to [KIO4]0/[Na2SO3]0 ratio and acidity. A possible reaction mechanism, which consists of an autocatalytic production of H＋(positive feedback) and a H＋-consuming pathway (negative feedback), along with the production and elimination of iodine, could fairly explain the complex dynamical behavior.
2002, 18(09): 821-824
doi: 10.3866/PKU.WHXB20020911
Abstract:
A pair of diastereoisomer of Pro-Obzl of keterolac amide, formed by the reaction of(±)-ketorolac and L-proline under the action of condensation agent, were resolved using column chromatography and characterized by 1H NMR, 13C NMR, IR, MS spectra and elemental analysis. The crystal structure of one diastereoisomer of the amides was determined by single crystal diffraction analysis, and the absolute configuration of which was deduced by internal reference. The crystal belongs to orthorhombic space group P212121. Crystallographic data are:a=0.896 45(1)nm, b=1.271 23(2)nm, c=2.076 21(4)nm, V=2.366 04(6)nm3, Z=4, R1=0.0464.
A pair of diastereoisomer of Pro-Obzl of keterolac amide, formed by the reaction of(±)-ketorolac and L-proline under the action of condensation agent, were resolved using column chromatography and characterized by 1H NMR, 13C NMR, IR, MS spectra and elemental analysis. The crystal structure of one diastereoisomer of the amides was determined by single crystal diffraction analysis, and the absolute configuration of which was deduced by internal reference. The crystal belongs to orthorhombic space group P212121. Crystallographic data are:a=0.896 45(1)nm, b=1.271 23(2)nm, c=2.076 21(4)nm, V=2.366 04(6)nm3, Z=4, R1=0.0464.
2002, 18(09): 825-829
doi: 10.3866/PKU.WHXB20020912
Abstract:
The dilution enthalpies of serine in aqueous sucrose solutions at 298.15 K were measured by LKB 2277 flow microcalorimetry. Using the McMillan-Mayer theory, the enthalpic pair interaction coefficients (h2) of serine over whole range of aqueous sucrose solutions have been calculated and compared with the enthalpic pair interaction coefficients of serine in aqueous glucose solutions. It is found that h2 of serine in aqueous sucrose and h2 in glucose solutions are negative and become less negative with increasing the concentration of sucrose and glucose. The results are discussed in terms of solute-solute and solute-solvent interactions.
The dilution enthalpies of serine in aqueous sucrose solutions at 298.15 K were measured by LKB 2277 flow microcalorimetry. Using the McMillan-Mayer theory, the enthalpic pair interaction coefficients (h2) of serine over whole range of aqueous sucrose solutions have been calculated and compared with the enthalpic pair interaction coefficients of serine in aqueous glucose solutions. It is found that h2 of serine in aqueous sucrose and h2 in glucose solutions are negative and become less negative with increasing the concentration of sucrose and glucose. The results are discussed in terms of solute-solute and solute-solvent interactions.
2002, 18(09): 830-834
doi: 10.3866/PKU.WHXB20020913
Abstract:
The interaction of molecules on the surface and in the micelle of the mixed system of cationic bolaamphiphile/sodium dodecyl sulfate(SDS) was studied by using regular solution theory. The interaction parameter indicates that strong interaction exists both in the surface adsorption layer and in the micelle. The strength of the interaction is similar to that of conventional alkyl quaternary ammonium salt/alkyl sodium sulfate mixed system. This means the synergism in the bolaamphiphile/SDS mixed system is mainly caused by the electrostatic interaction between the hydrophilic head group, but not apparently affected by the hydrophobic part of the bola molecules.
The interaction of molecules on the surface and in the micelle of the mixed system of cationic bolaamphiphile/sodium dodecyl sulfate(SDS) was studied by using regular solution theory. The interaction parameter indicates that strong interaction exists both in the surface adsorption layer and in the micelle. The strength of the interaction is similar to that of conventional alkyl quaternary ammonium salt/alkyl sodium sulfate mixed system. This means the synergism in the bolaamphiphile/SDS mixed system is mainly caused by the electrostatic interaction between the hydrophilic head group, but not apparently affected by the hydrophobic part of the bola molecules.
2002, 18(09): 835-837
doi: 10.3866/PKU.WHXB20020914
Abstract:
In this paper, the solubility of Li＋,Na＋∥,CO32－,B4O72－-H2O quaternary system at 288 K has been determined by isothermal equilibrium method. Based on the solubility data, the phase diagram of the system has also been plotted, in which there are two invariant point E and F(see Fig.1)， five univariant curves E1F, E2F, E3E, E4E and EF, and four crystallization fields: Na2CO3•10H2O，Li2B4O7•3H2O，Na2B4O7•10H2O, Li2CO3.
In this paper, the solubility of Li＋,Na＋∥,CO32－,B4O72－-H2O quaternary system at 288 K has been determined by isothermal equilibrium method. Based on the solubility data, the phase diagram of the system has also been plotted, in which there are two invariant point E and F(see Fig.1)， five univariant curves E1F, E2F, E3E, E4E and EF, and four crystallization fields: Na2CO3•10H2O，Li2B4O7•3H2O，Na2B4O7•10H2O, Li2CO3.
2002, 18(09): 838-840
doi: 10.3866/PKU.WHXB20020915
Abstract:
Ab initio UMP2(full) method has been used to study the mechanism of NH2＋O3 reaction. The geometry configurations of reactants,productions, intermediates and transition states were optimized at 6-31G* level, and the energy parameters were calculated using Ganssian-3(G3) model. The results show that there are two different pathways for the reaction of NH2 radicals with ozone. One of them has very low activation energy, so it happens easily. Therefore, the results of this theoretical study indicate that NH2 radicals in the atmosphere are able to deplete ozone remarkably.
Ab initio UMP2(full) method has been used to study the mechanism of NH2＋O3 reaction. The geometry configurations of reactants,productions, intermediates and transition states were optimized at 6-31G* level, and the energy parameters were calculated using Ganssian-3(G3) model. The results show that there are two different pathways for the reaction of NH2 radicals with ozone. One of them has very low activation energy, so it happens easily. Therefore, the results of this theoretical study indicate that NH2 radicals in the atmosphere are able to deplete ozone remarkably.
2002, 18(09): 841-845
doi: 10.3866/PKU.WHXB20020916
Abstract:
The method and conditions of preparing ferulic acid film at glassy carbon electrode by electropolymerization have been studied. The electrochemical characteristics and charge transmission process in films have been explored initially with cyclic voltammetry, staircase voltammetry and A.C. impedance. The apparent electron transfer coefficient and standard rate constant (ks) was o.49 and 6.56 s－1 for poly (ferulic acid) film (L=0.5 μm) respectively. The diffusion coefficients within the film is 7.9×108 cm2•s－1 for oxide and is 4.8 ×108 cm2•s－1 for reductive poly(ferulic acid).The ferulic acid modified electrode shows electrocatalytic activity for oxidation of NADH in 0.1 mol•dm－3 phosphate buffer solution. The peak currents were proportional to the concentrations of NADH in the range of 0.01～5.0 mmol•dm－3.
The method and conditions of preparing ferulic acid film at glassy carbon electrode by electropolymerization have been studied. The electrochemical characteristics and charge transmission process in films have been explored initially with cyclic voltammetry, staircase voltammetry and A.C. impedance. The apparent electron transfer coefficient and standard rate constant (ks) was o.49 and 6.56 s－1 for poly (ferulic acid) film (L=0.5 μm) respectively. The diffusion coefficients within the film is 7.9×108 cm2•s－1 for oxide and is 4.8 ×108 cm2•s－1 for reductive poly(ferulic acid).The ferulic acid modified electrode shows electrocatalytic activity for oxidation of NADH in 0.1 mol•dm－3 phosphate buffer solution. The peak currents were proportional to the concentrations of NADH in the range of 0.01～5.0 mmol•dm－3.
2002, 18(09): 846-849
doi: 10.3866/PKU.WHXB20020917
Abstract:
The ld electrode was modified with a derivative compound of Schiff base. Cyclic voltammetric technique was used to investigate the electrochemical behavior of the electrode. An electrochemical irreversible reduction/oxidation process of the schiff base molecule in 0.1 mol•L－1 KCl solution was found. Electrochemical study shows that the apparent electron-transfer rate constant (kapp) decreases with the increasing of assembled time. Considering the effecting factors on the apparent electron-transfer rate, we deduced that the main factor effecting Schiff bases electrochemical behavior is the interaction force between the Schiff bases molecules. This interaction affects the changing of structure during the electrochemical redox process.
The ld electrode was modified with a derivative compound of Schiff base. Cyclic voltammetric technique was used to investigate the electrochemical behavior of the electrode. An electrochemical irreversible reduction/oxidation process of the schiff base molecule in 0.1 mol•L－1 KCl solution was found. Electrochemical study shows that the apparent electron-transfer rate constant (kapp) decreases with the increasing of assembled time. Considering the effecting factors on the apparent electron-transfer rate, we deduced that the main factor effecting Schiff bases electrochemical behavior is the interaction force between the Schiff bases molecules. This interaction affects the changing of structure during the electrochemical redox process.
2002, 18(09): 850-854
doi: 10.3866/PKU.WHXB20020918
Abstract:
Conductance measurements have been made on four neodymium salts: Nd(CF3SO3)3, Nd(ClO4)3, Nd(NO3)3 and NdCl3 dissolved in dimethylformamide. The limiting molar conductivity of Nd(CF3SO3)3 and Nd(ClO4)3 at 25 ℃ calculated by liner fit are 278.8 and 280.7 S•cm2•mol－1 respectively, those of Nd(NO3)3 and NdCl3 obtained by indirect method are 297.2 and 287.3 S•cm2•mol－1 respectively. The electrical conductivity of Nd(CF3SO3)3 and Nd(ClO4)3 increase linearly in the temperature range(25～65)℃. Significant ionic association exists in Nd(NO3)3 and NdCl3 solution.
Conductance measurements have been made on four neodymium salts: Nd(CF3SO3)3, Nd(ClO4)3, Nd(NO3)3 and NdCl3 dissolved in dimethylformamide. The limiting molar conductivity of Nd(CF3SO3)3 and Nd(ClO4)3 at 25 ℃ calculated by liner fit are 278.8 and 280.7 S•cm2•mol－1 respectively, those of Nd(NO3)3 and NdCl3 obtained by indirect method are 297.2 and 287.3 S•cm2•mol－1 respectively. The electrical conductivity of Nd(CF3SO3)3 and Nd(ClO4)3 increase linearly in the temperature range(25～65)℃. Significant ionic association exists in Nd(NO3)3 and NdCl3 solution.
2002, 18(09): 855-864
doi: 10.3866/PKU.WHXB20020919
Abstract:
This account summarizes recent research in my laboratory on the integration of organic functionalities to silicon surfaces. We have discovered and developed novel, two-step strategies for the assembly of organic monolayers on silicon, silica, and related materials. These methods are simple and reproducible and lead to close packed monolayers with excellent physical/chemical properties. Exciting applications of these monolayers include (a) resists in soft-lithography, particularly micro-contact printing; (b) monolayer lubricant in silicon based micromachines, also called micro electromechanic systems (MEMS); and (c) molecular basis for the immobilization of DNA and protein molecules in microarrays.
This account summarizes recent research in my laboratory on the integration of organic functionalities to silicon surfaces. We have discovered and developed novel, two-step strategies for the assembly of organic monolayers on silicon, silica, and related materials. These methods are simple and reproducible and lead to close packed monolayers with excellent physical/chemical properties. Exciting applications of these monolayers include (a) resists in soft-lithography, particularly micro-contact printing; (b) monolayer lubricant in silicon based micromachines, also called micro electromechanic systems (MEMS); and (c) molecular basis for the immobilization of DNA and protein molecules in microarrays.
