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1989 Volume 5 Issue 4
1989, 5(04): 385-387
doi: 10.3866/PKU.WHXB19890401
Abstract:
Kirkwood theory was applied to investigate the influence of substituting surface charged groups in protein engineering on pK_a of active site residues in enzymes. An expression was obtained to calculate the change of pK_a quartitatively, which was successfully used in calculating the change of pK_a of histidine in the active site in subtilisin and trypsin. The results of subtilisin agrees with experimental data well When surface positive residues were changed to neutral or negative ones, the pK_a would be raised; and when surface negative residues were changed to neutral or positive ones, the pK_a would be lowered. There is an obvious relationship between the position of surface chares and the change of pK_a. For trypsin, when surface charges are within a cone with a base angle of 70°around His (57), the pK_a of His (57) will be changed remarkablly. Four mutants in rat-trypsin were selected as potential sites to raise the pK_a of His (57).
Kirkwood theory was applied to investigate the influence of substituting surface charged groups in protein engineering on pK_a of active site residues in enzymes. An expression was obtained to calculate the change of pK_a quartitatively, which was successfully used in calculating the change of pK_a of histidine in the active site in subtilisin and trypsin. The results of subtilisin agrees with experimental data well When surface positive residues were changed to neutral or negative ones, the pK_a would be raised; and when surface negative residues were changed to neutral or positive ones, the pK_a would be lowered. There is an obvious relationship between the position of surface chares and the change of pK_a. For trypsin, when surface charges are within a cone with a base angle of 70°around His (57), the pK_a of His (57) will be changed remarkablly. Four mutants in rat-trypsin were selected as potential sites to raise the pK_a of His (57).
1989, 5(04): 388-391
doi: 10.3866/PKU.WHXB19890402
Abstract:
The infrared multiphoton dissociation (IR MPD) of CF_2HCl by measuring the C_2F_4 product after laser irradiation is investigated, The dissociation fraction of CF_2HCl as a function of the CF_2HCl pressure, laser energy fluence and number of laser pulses is measured. Under the low pressure condition the bottleneck effect is observed. Under the collision condition the dissociation fraction of CF_2HCl is affected by the competition between rotaional hole filling (collisional repoputation of pumped rotational states) and collisional deactivation of excited CF_2HCl moleculae.
The infrared multiphoton dissociation (IR MPD) of CF_2HCl by measuring the C_2F_4 product after laser irradiation is investigated, The dissociation fraction of CF_2HCl as a function of the CF_2HCl pressure, laser energy fluence and number of laser pulses is measured. Under the low pressure condition the bottleneck effect is observed. Under the collision condition the dissociation fraction of CF_2HCl is affected by the competition between rotaional hole filling (collisional repoputation of pumped rotational states) and collisional deactivation of excited CF_2HCl moleculae.
1989, 5(04): 392-394
doi: 10.3866/PKU.WHXB19890403
Abstract:
Using the MMPI program and 3-D high resolution molecular modeling system, a preliminary structure-activity relationship (SAR) based upon molecular shape analysis has been developed for a set of 20 4-R-3, 3-dialkylphenyl-triazenes for which antitumor potency against L1712 Leukemia in mice is reported. The SAR suggests that for antitumor potency, here is a significant difference between the shapes of the active and inactive molecules.
Using the MMPI program and 3-D high resolution molecular modeling system, a preliminary structure-activity relationship (SAR) based upon molecular shape analysis has been developed for a set of 20 4-R-3, 3-dialkylphenyl-triazenes for which antitumor potency against L1712 Leukemia in mice is reported. The SAR suggests that for antitumor potency, here is a significant difference between the shapes of the active and inactive molecules.
PHOTOCHEMISTRY OF HETEROCYCLES——Ⅺ. STUDIES OF PHOTOREACTION OF 1,3-DIMETHYL6-AZATHYMINE WITH ACETONE
1989, 5(04): 395-397
doi: 10.3866/PKU.WHXB19890404
Abstract:
1989, 5(04): 398-402
doi: 10.3866/PKU.WHXB19890405
Abstract:
It is known that there are many examples of the thermal elimination of quaternary ammonium hydroxides which do not follow the Hofmann rule. Ye Xiulin et al. proposed the “conformation rule” for the elimination of quaternary ammonium hydroxides, and then, eight quaternary ammonium hydroxides were synthesised and subjected to the elimination. The results show that the conformational rule is superior and acceptable.DPCILO and CNDO/2 methods were used to calculate the conformational energy of some quaternary ammonium cations with different conformations andthe distribution of charge for studying the mechanism of Hofmann eliminaion reaction. The results show that the conformational rule, based on the conformational energy, can be used to explain the Hofmann elimination reaction well, but the elimination of straight chain alkyl groups other than the ethylic groups should follow cis-E_2 elimination mechanism instead of trans-E_2 one proposed by Ye Xiulin.
It is known that there are many examples of the thermal elimination of quaternary ammonium hydroxides which do not follow the Hofmann rule. Ye Xiulin et al. proposed the “conformation rule” for the elimination of quaternary ammonium hydroxides, and then, eight quaternary ammonium hydroxides were synthesised and subjected to the elimination. The results show that the conformational rule is superior and acceptable.DPCILO and CNDO/2 methods were used to calculate the conformational energy of some quaternary ammonium cations with different conformations andthe distribution of charge for studying the mechanism of Hofmann eliminaion reaction. The results show that the conformational rule, based on the conformational energy, can be used to explain the Hofmann elimination reaction well, but the elimination of straight chain alkyl groups other than the ethylic groups should follow cis-E_2 elimination mechanism instead of trans-E_2 one proposed by Ye Xiulin.
1989, 5(04): 403-408
doi: 10.3866/PKU.WHXB19890406
Abstract:
An anion negative adsorption equation in the clay colloid suspension of overlapping flat double layer has been derived according to the electric double layer theory of uy-Chapman. The electric potential at the Outer Helmhotz Plane(OHP), ψ_δ, and electric potential at the midplane, ψ_d, have been solved by FACOM M-34-OS computer using the anion negative adsorption equation on the basis of experiment. The results are concluded as following:(1) The values of ψ_δ and ψ_d increase with the decrease of distance λ (Fig.4 and Fig.5). (2) The change of ψ_d/ψ_δ with distance λ can explain the overlapping degree of flat double layer mor appropriate than that of ψ_d in previous work (Fig.6). (3) Due to compression of the flat double layers at increasing electrolyte concentrations, the values of ψ_δ and ψ_d are considerably reduced at a given distance λ.
An anion negative adsorption equation in the clay colloid suspension of overlapping flat double layer has been derived according to the electric double layer theory of uy-Chapman. The electric potential at the Outer Helmhotz Plane(OHP), ψ_δ, and electric potential at the midplane, ψ_d, have been solved by FACOM M-34-OS computer using the anion negative adsorption equation on the basis of experiment. The results are concluded as following:(1) The values of ψ_δ and ψ_d increase with the decrease of distance λ (Fig.4 and Fig.5). (2) The change of ψ_d/ψ_δ with distance λ can explain the overlapping degree of flat double layer mor appropriate than that of ψ_d in previous work (Fig.6). (3) Due to compression of the flat double layers at increasing electrolyte concentrations, the values of ψ_δ and ψ_d are considerably reduced at a given distance λ.
1989, 5(04): 409-414
doi: 10.3866/PKU.WHXB19890407
Abstract:
The behaviors of cyanide ions on platium electrode were studied using cyclic voltammetry and in-situ FTIR spectroelectrochemistry. The system was 0.5 moIL~(-1) NaCN +0.5 moIL~(-1) NaF/Pt. Four bands near 2076, 2087—2095, 2138 and 2170 cm~(-1) were found when potential changed staircasely from -0.80 to 1.00 V(vs.SCE). These bands were attributed to CN-(2076 cm~(-1)) in the solution, adsorbed CN~-(2087-2095 cm~(-1)), complex compound Pt(CN)_4~(2-) and/or Pt(CN)_2(2138 cm~(-1)) and solution species NCO~- (2170 cm~(-1), respectively. The band near 2087 cm~(-1) for adsorbed CN~- showed blue shift with increasing potential. The experiment results showed that the adsored CN~- existed over the whole potential range studied. Two electrochemical reactions were observed as potential was made more positive than about 0.20 V with the products being Pt(CN)~2_4 and/or Pt(CN)_2 and NCO~- and surface complexes took place, generating CO_2 and N_2.
The behaviors of cyanide ions on platium electrode were studied using cyclic voltammetry and in-situ FTIR spectroelectrochemistry. The system was 0.5 moIL~(-1) NaCN +0.5 moIL~(-1) NaF/Pt. Four bands near 2076, 2087—2095, 2138 and 2170 cm~(-1) were found when potential changed staircasely from -0.80 to 1.00 V(vs.SCE). These bands were attributed to CN-(2076 cm~(-1)) in the solution, adsorbed CN~-(2087-2095 cm~(-1)), complex compound Pt(CN)_4~(2-) and/or Pt(CN)_2(2138 cm~(-1)) and solution species NCO~- (2170 cm~(-1), respectively. The band near 2087 cm~(-1) for adsorbed CN~- showed blue shift with increasing potential. The experiment results showed that the adsored CN~- existed over the whole potential range studied. Two electrochemical reactions were observed as potential was made more positive than about 0.20 V with the products being Pt(CN)~2_4 and/or Pt(CN)_2 and NCO~- and surface complexes took place, generating CO_2 and N_2.
1989, 5(04): 415-419
doi: 10.3866/PKU.WHXB19890408
Abstract:
The fluorescence spectra of N-alkylindoles and 3-methyl-N-alkylindoles with various chain lengths in dimethyl sulfoxide-water(DMSO-H_2O) were studied under stationary and nonstationary condition. As the fraction of water in solvent mixture (Φ) increases, the indoles with short chain display red shifts in fluorescence λ_(max) and increases in fluorescence lifetime. On the contrary, the fluorescence λ_(max) of long chain indoles shift to blue side and their fluorescence lifetimes decrease with increasing in Φ. This observation supports intermolecular aggregation of long chain indoles in poor solvents, The microscopic polarity in aggregates is similar to that in cyclohexane. The distribution of indoles between bulk solution and aggregates was determined by time resolved fluorescence technique.
The fluorescence spectra of N-alkylindoles and 3-methyl-N-alkylindoles with various chain lengths in dimethyl sulfoxide-water(DMSO-H_2O) were studied under stationary and nonstationary condition. As the fraction of water in solvent mixture (Φ) increases, the indoles with short chain display red shifts in fluorescence λ_(max) and increases in fluorescence lifetime. On the contrary, the fluorescence λ_(max) of long chain indoles shift to blue side and their fluorescence lifetimes decrease with increasing in Φ. This observation supports intermolecular aggregation of long chain indoles in poor solvents, The microscopic polarity in aggregates is similar to that in cyclohexane. The distribution of indoles between bulk solution and aggregates was determined by time resolved fluorescence technique.
1989, 5(04): 420-426
doi: 10.3866/PKU.WHXB19890409
Abstract:
In this paper restricted open shell CNDO/2 (RHF) method was developed to calculate open shell molecular. Program has been performed on IBM-PC/XT microcomputer. Some small open shells molecular and transition metal compounds have been investigated. Obtained total energies, charges, bond orders and binding energies of small molecule are in od agreement with that obtained using CNDO/2 (UHF) method. The RHF energy level profile obtained is clearer than that, by UHF scheme, and former provides a better wavefunction for calculating density of electron dipole transition, magnetic hyperfine coupling constant and unitary group CI.
In this paper restricted open shell CNDO/2 (RHF) method was developed to calculate open shell molecular. Program has been performed on IBM-PC/XT microcomputer. Some small open shells molecular and transition metal compounds have been investigated. Obtained total energies, charges, bond orders and binding energies of small molecule are in od agreement with that obtained using CNDO/2 (UHF) method. The RHF energy level profile obtained is clearer than that, by UHF scheme, and former provides a better wavefunction for calculating density of electron dipole transition, magnetic hyperfine coupling constant and unitary group CI.
1989, 5(04): 427-431
doi: 10.3866/PKU.WHXB19890410
Abstract:
The anodic oxidation of annealed pure aluminium (99.99%) was carried out in 15% H_2SO_4 at different electrolytic conditions. The positron annihilation lifetime spectra of the anodized aluminium were measured and fitted into three lifetime components. The second component(τ_2, Ι_2) was assigned to the positron annihilation in the anodic film. It has been deduced that, from the Ι_2 curves, the film thirkness is propertional to the cell voltage and reaches a limit under constant cell voltage and temperature and that, form the τ_2 curves, the crystallinity of the anodic film increases with increasing cell voltage and anodizing time. The local crystallization in the anodic film would induce the void-like defects and hence result in the film less compact. An idea for improvement of mechanic properties of the anodic film on aluminium has been proposed.
The anodic oxidation of annealed pure aluminium (99.99%) was carried out in 15% H_2SO_4 at different electrolytic conditions. The positron annihilation lifetime spectra of the anodized aluminium were measured and fitted into three lifetime components. The second component(τ_2, Ι_2) was assigned to the positron annihilation in the anodic film. It has been deduced that, from the Ι_2 curves, the film thirkness is propertional to the cell voltage and reaches a limit under constant cell voltage and temperature and that, form the τ_2 curves, the crystallinity of the anodic film increases with increasing cell voltage and anodizing time. The local crystallization in the anodic film would induce the void-like defects and hence result in the film less compact. An idea for improvement of mechanic properties of the anodic film on aluminium has been proposed.
1989, 5(04): 432-437
doi: 10.3866/PKU.WHXB19890411
Abstract:
The CL reactions of Sr(~1S), Sr(~3P)+Cl_2 have been studied under single collision condition on a beam-gas apparatus in the pressure of range 10~(-5)—10~(-4) Torr.The temperature of the metal oven was about 1000 K. The CL spectra of SrCl (A,B) and SrCl_2~* produced in the reactions of Sr, Sr~* +Cl_2 have been observed and analyzed. The CL spectra are always dominated by the monochloride emission while the subcontinuous emission of dichloride SrCl_2~* becomes stronger with increasing Cl_2 pressure. The experimental results show that the intensity of SrCl~* emission depends linearly upon both Cl_2 pressure and Sr number density. This means that SrCl~* is the direct product of single collisions. Whereas the quadratic dependency of SrCl~*_2 intensity upon the Cl_2 pressure shows that it is produced in arreaction of SrCl+Cl_2, the same mechanism as BaCl~*_2 produced in reaction of Ba+Cl_2~([4,5]). The total cross section for the removal of metal atoms in ground state Sr(~1S) and excited states Sr(~3P) by Cl_2 molecules are 5.8 nm~2 and 9.7 nm~2 respectively. The relative photon yield of SrCl(nm) produced by Sr(~1S) and Sr(~3P) reacting with Cl_2 is about Φ~*/Φ~0=115.
The CL reactions of Sr(~1S), Sr(~3P)+Cl_2 have been studied under single collision condition on a beam-gas apparatus in the pressure of range 10~(-5)—10~(-4) Torr.The temperature of the metal oven was about 1000 K. The CL spectra of SrCl (A,B) and SrCl_2~* produced in the reactions of Sr, Sr~* +Cl_2 have been observed and analyzed. The CL spectra are always dominated by the monochloride emission while the subcontinuous emission of dichloride SrCl_2~* becomes stronger with increasing Cl_2 pressure. The experimental results show that the intensity of SrCl~* emission depends linearly upon both Cl_2 pressure and Sr number density. This means that SrCl~* is the direct product of single collisions. Whereas the quadratic dependency of SrCl~*_2 intensity upon the Cl_2 pressure shows that it is produced in arreaction of SrCl+Cl_2, the same mechanism as BaCl~*_2 produced in reaction of Ba+Cl_2~([4,5]). The total cross section for the removal of metal atoms in ground state Sr(~1S) and excited states Sr(~3P) by Cl_2 molecules are 5.8 nm~2 and 9.7 nm~2 respectively. The relative photon yield of SrCl(nm) produced by Sr(~1S) and Sr(~3P) reacting with Cl_2 is about Φ~*/Φ~0=115.
1989, 5(04): 438-445
doi: 10.3866/PKU.WHXB19890412
Abstract:
The four Hydrogen-Bonded systems of C≡N—H…OH_2, N≡C—H…OH_2 and H—N≡C…H—OH,H—C≡N…H—OH have been studied with ab initio LCAO-MO-SCF methods at 4-31G level. The complete structure optimization have been carride out. We have also performed the Morokuma's Energy Decomposition Analysis for these four systems.The results show that, the electrostatic interaction (ES) is the most important attractive component in the H-Bond and the charge transfer interaction (CT) is the next largest attractive one. In most cases the order of ES can determine the H-Bond strength order betreen similar systems such as C≡N…H—OH_2 N≡C_2. But in some particular cases, we must consider both ES and CT to predict the order of H-Bond strength, such as H—N≡C…H—OH and H—C≡N…H—OH. We have discussed that the energy components are strongly distance dependent. At relatively small separations, the ES, CT, PL can all be important attractive components. At longer distance for the same systems the relative importance of the CT interaction maybe increased.
The four Hydrogen-Bonded systems of C≡N—H…OH_2, N≡C—H…OH_2 and H—N≡C…H—OH,H—C≡N…H—OH have been studied with ab initio LCAO-MO-SCF methods at 4-31G level. The complete structure optimization have been carride out. We have also performed the Morokuma's Energy Decomposition Analysis for these four systems.The results show that, the electrostatic interaction (ES) is the most important attractive component in the H-Bond and the charge transfer interaction (CT) is the next largest attractive one. In most cases the order of ES can determine the H-Bond strength order betreen similar systems such as C≡N…H—OH_2 N≡C_2. But in some particular cases, we must consider both ES and CT to predict the order of H-Bond strength, such as H—N≡C…H—OH and H—C≡N…H—OH. We have discussed that the energy components are strongly distance dependent. At relatively small separations, the ES, CT, PL can all be important attractive components. At longer distance for the same systems the relative importance of the CT interaction maybe increased.
1989, 5(04): 446-451
doi: 10.3866/PKU.WHXB19890413
Abstract:
A.C. impedance plot often shows rotation of semicircle it, complex plane, i.e. the centre of semicircle locates below real axis. However, the physical causes of that phenomenon are not yet completely clear. One possible cause is the surface roughness of electrode. In regard to metal eleetrods covered with surface film,the film can be considered as dielectric inserted between metal and electrolyte just as the case of a capacitor. Owing to dielectric dispersion, the capacitance of that capacitor in alternating electric field is a complex parameter C=C′-jC″. Literature data indicated that in the frequency range of a.c. impedance measurement both real and imaginary components of complex capacitance C′ and C″ are independent of frequency. It is postulated that the dielelctric behaviour of that capacitance might be the cause of impedance semicircle rotation. Based on equivalent circuit shown in Figure 4, it could be deduced that the semicircle equation on polar cooordinate is ρ=(R_t/cosδ)cos(θ+δ), and parameters of eqnivalent circuit can be calculated from impedance semicircle according to C′=1/ωR_t·1/(ctgθ-thδ) and C″=C′tanδ, Besides, the apex frequency on semicircle is f~*=fcosδ(ctanθ-tanδ). Above formulate can be reduced to normal semicircle in case δ=0.
A.C. impedance plot often shows rotation of semicircle it, complex plane, i.e. the centre of semicircle locates below real axis. However, the physical causes of that phenomenon are not yet completely clear. One possible cause is the surface roughness of electrode. In regard to metal eleetrods covered with surface film,the film can be considered as dielectric inserted between metal and electrolyte just as the case of a capacitor. Owing to dielectric dispersion, the capacitance of that capacitor in alternating electric field is a complex parameter C=C′-jC″. Literature data indicated that in the frequency range of a.c. impedance measurement both real and imaginary components of complex capacitance C′ and C″ are independent of frequency. It is postulated that the dielelctric behaviour of that capacitance might be the cause of impedance semicircle rotation. Based on equivalent circuit shown in Figure 4, it could be deduced that the semicircle equation on polar cooordinate is ρ=(R_t/cosδ)cos(θ+δ), and parameters of eqnivalent circuit can be calculated from impedance semicircle according to C′=1/ωR_t·1/(ctgθ-thδ) and C″=C′tanδ, Besides, the apex frequency on semicircle is f~*=fcosδ(ctanθ-tanδ). Above formulate can be reduced to normal semicircle in case δ=0.
1989, 5(04): 452-456
doi: 10.3866/PKU.WHXB19890414
Abstract:
The conducting polymer, polyparaphenylene (PPP), can be electrochemically polymerized in concentrated sulphric acid. The iu-situ ESR experiment shows that the PPP film possesses high conductivity and low spin susceptibility. Polarons and bipolarons are the main conducting species and interchange each other according to the electrode potential.The unpaired spins are highly delocallized.There may be some interchain O-bridges existing in the PPP film. The bridged structure may produce a space effect, which make the film easily doped and increase the conductivity through interchain charge hopping. In conc. H_2SO_4, the electrochemical intercalation of HSO~-_4 ions is reversible. The doping capacity can be as high as 22%, implying one positive charge in every 5 benzene units. It is possible to use this polymer as stable electrode material for secondary battery.
The conducting polymer, polyparaphenylene (PPP), can be electrochemically polymerized in concentrated sulphric acid. The iu-situ ESR experiment shows that the PPP film possesses high conductivity and low spin susceptibility. Polarons and bipolarons are the main conducting species and interchange each other according to the electrode potential.The unpaired spins are highly delocallized.There may be some interchain O-bridges existing in the PPP film. The bridged structure may produce a space effect, which make the film easily doped and increase the conductivity through interchain charge hopping. In conc. H_2SO_4, the electrochemical intercalation of HSO~-_4 ions is reversible. The doping capacity can be as high as 22%, implying one positive charge in every 5 benzene units. It is possible to use this polymer as stable electrode material for secondary battery.
1989, 5(04): 457-462
doi: 10.3866/PKU.WHXB19890415
Abstract:
The activity coefficients f of naphthalene in the aqueous salt solution were determined at 25 ℃ by spectrophotometer. The salts used are LiBr, NaBr, KBr, NH_4Cl, NaF and KF.When lgf is ploted vs. c_s for these salts, the results obtained are all straight lines The salting-out constants κ were calculated.We have calculated the salting-out constants of naphthalene in six aqueous salt solutions by the formulas of (1) Debye-McAulay, (2) Conway-Desnoyers-Smith, (3) McDevit-Long, (4) scaled partical theory, (5) modified Bockris′ dispersion energy theory and (6) modified internal pressure theory. In the systems having ions and nonelectrolyte molecules both of large size, the effect of dispersion forces can not be neglected. Modified Bockris′ theory indicates signs of salting-out effect correctly. For large nonelectrolyte molecules, the equation of modified internal pressure theory gives results in better agreement with the experiment than others.
The activity coefficients f of naphthalene in the aqueous salt solution were determined at 25 ℃ by spectrophotometer. The salts used are LiBr, NaBr, KBr, NH_4Cl, NaF and KF.When lgf is ploted vs. c_s for these salts, the results obtained are all straight lines The salting-out constants κ were calculated.We have calculated the salting-out constants of naphthalene in six aqueous salt solutions by the formulas of (1) Debye-McAulay, (2) Conway-Desnoyers-Smith, (3) McDevit-Long, (4) scaled partical theory, (5) modified Bockris′ dispersion energy theory and (6) modified internal pressure theory. In the systems having ions and nonelectrolyte molecules both of large size, the effect of dispersion forces can not be neglected. Modified Bockris′ theory indicates signs of salting-out effect correctly. For large nonelectrolyte molecules, the equation of modified internal pressure theory gives results in better agreement with the experiment than others.
1989, 5(04): 463-468
doi: 10.3866/PKU.WHXB19890416
Abstract:
A high sensitive pulsed laser photoacoustic calorimeter for liquid sample has been set up in our laboratory. Using this equipment, the radiationless quantum yields of three coumarins in absolute ethanol were measured to be 0.50±0.02, 0.47±0.02, and 0.38±0.02 for C428, C47 and C120, respectively.
A high sensitive pulsed laser photoacoustic calorimeter for liquid sample has been set up in our laboratory. Using this equipment, the radiationless quantum yields of three coumarins in absolute ethanol were measured to be 0.50±0.02, 0.47±0.02, and 0.38±0.02 for C428, C47 and C120, respectively.
1989, 5(04): 469-473
doi: 10.3866/PKU.WHXB19890417
Abstract:
The bonding and configuration of the chemisorption of NH_3 at the on-top and hollow sites of Ni(111) surfaces are calculated and discussd by use of MO theory and energy band theory. The results show that the density of state and crystal orbital overlap population of the adsorption state at the on-top site have superiority over those of hollow site.
The bonding and configuration of the chemisorption of NH_3 at the on-top and hollow sites of Ni(111) surfaces are calculated and discussd by use of MO theory and energy band theory. The results show that the density of state and crystal orbital overlap population of the adsorption state at the on-top site have superiority over those of hollow site.
1989, 5(04): 474-478
doi: 10.3866/PKU.WHXB19890418
Abstract:
(Me_4N)_6 (Ag_6(S_2C=C(CN)_2)_6) H_2O(Ⅰ), (Et_4N)_4 (Cu_8(S_2C=C(CN)_2)_6)(Ⅱ) and (Me_N)_4(Cu_5Ag_3(S_2C=(CN)_2)_6H_2O (Ⅲ) were synthesized. The crystal and molecular structures of the compounds (Ⅰ) and (Ⅱ) were determined with single crystal x-ray diffraction method, crystal data: complex (Ⅰ), tri nal, space group R3, hexa nal cell dimensions, a=b=2.38358, c=1.16716 nm, v=574.28 nm~3, Mr=1951.23, z=3, D_c=1.693 g cm~(-3), final R=0.044 for 3648 independent reflections with Ⅰ≥3σ(Ⅰ); Complex(Ⅱ), monclinic, space group P2_1/n, a=1.47243, b=1.72275, c=1.55944 nm, β=100.75°, v=388.63 nm~3, Mr=1870.46, z=2, D_c=1.598 gcm~(-3), final R=0.061 for 3890 independent reflections with I≥3δ(I). The molecular symmetry of complex (I) is 3, contaioning an Ag_6S_(12) core. six Ag atoms form two centrosymetrically related equilateral triangles antiprism, with the Ag-Ag distances of 0.3610(1) nm, Each Ag atom is bounded two nearest neighbour Ag atoms of other equilateral triangle to form a isosceles triangle with two Ag-Ag distances of 0.3127(1) nm. The molecular symmetry of complex (II) is Ci, containing a Cu_8S_(12) core, eight coper atoms form a distorted cubic, with the Cu-Cu distances of 0.2755(1)-0.2872 nm. The complex (III) have been characterized by ICP elemental analyses and IR spectra, the Cu_5Ag_3S_(12) core of complex (III) is probably similar to the Cu_8S_(12) core of complex (II).
1989, 5(04): 479-482
doi: 10.3866/PKU.WHXB19890419
Abstract:
As part of our study of the structure-properties of the active centre in the superoxide dismutase, the title compound was synthesized and its single crystal structure was determined by X-ray diffraction method. The title compound is orthorhombic, Pnma, a=1.4061(1), b=1.2347(2), c=0.9308(1) nm, V=1.6160 nmZ=4, D_c=1.782g cm~(-3) D_0=1.78g cm~(-3) μ(MoK_α)=17.3cm~(-1) F(000)=884. Structure was determined by direct method using MULTAN-82 and refined by fullmatrix least-squares to a R value of 0.055 using 1344 reflections. The molecule is mirror symmetric with the imidazole ring disordered and the Cu atom located in a tetra nally distorted octahedral enviroment of the coordination type 4+2 with four nitrogen atoms from diethylenetriamine and imidazole in square planar configuration and two oxyzen atoms from perchlorate ions in the axial positions. The reason we prefer to describe the structure in centrosymmetric space group is briefly discussed.
As part of our study of the structure-properties of the active centre in the superoxide dismutase, the title compound was synthesized and its single crystal structure was determined by X-ray diffraction method. The title compound is orthorhombic, Pnma, a=1.4061(1), b=1.2347(2), c=0.9308(1) nm, V=1.6160 nmZ=4, D_c=1.782g cm~(-3) D_0=1.78g cm~(-3) μ(MoK_α)=17.3cm~(-1) F(000)=884. Structure was determined by direct method using MULTAN-82 and refined by fullmatrix least-squares to a R value of 0.055 using 1344 reflections. The molecule is mirror symmetric with the imidazole ring disordered and the Cu atom located in a tetra nally distorted octahedral enviroment of the coordination type 4+2 with four nitrogen atoms from diethylenetriamine and imidazole in square planar configuration and two oxyzen atoms from perchlorate ions in the axial positions. The reason we prefer to describe the structure in centrosymmetric space group is briefly discussed.
1989, 5(04): 483-486
doi: 10.3866/PKU.WHXB19890420
Abstract:
In this paper impedance of n-InP in Fe~(3+)/Fe~(2+) solution is determined. The impedance at low frequencies in accord with Randles frequencies spectra figure and the electrode reaction are irreversible. Influences of electrode potential and light intensities are investigated. The results obtained can be explained with a theoretical model derived.
In this paper impedance of n-InP in Fe~(3+)/Fe~(2+) solution is determined. The impedance at low frequencies in accord with Randles frequencies spectra figure and the electrode reaction are irreversible. Influences of electrode potential and light intensities are investigated. The results obtained can be explained with a theoretical model derived.
1989, 5(04): 487-491
doi: 10.3866/PKU.WHXB19890421
Abstract:
By using an LKB 8721-3 vaporization calorimeter, enthalpies of vaporization of o-and m-dichlorobenzenes and enthalpy of sublimation of p-dichlorobenzene at 298.15K were determined as 48.53±0.12, 47.40±0.08 and 65.15±0.20 kJ mol~(-1) respectively. Data of ΔH_v~° and ΔH_s~° for chlorobenzenes reported here and in literature and their normal boiling points, t_b in ℃, can fit following two linear equations: ΔH_v~° (kJ mol~(-1))=17.51+0.17269 t_b; ΔH_s~° (kJ mol~(-1))=26.25+0.22349 t_b. From these equations other unknown values of ΔH_v~°and ΔH_s~°of chlorobenzenes have been estimated.
By using an LKB 8721-3 vaporization calorimeter, enthalpies of vaporization of o-and m-dichlorobenzenes and enthalpy of sublimation of p-dichlorobenzene at 298.15K were determined as 48.53±0.12, 47.40±0.08 and 65.15±0.20 kJ mol~(-1) respectively. Data of ΔH_v~° and ΔH_s~° for chlorobenzenes reported here and in literature and their normal boiling points, t_b in ℃, can fit following two linear equations: ΔH_v~° (kJ mol~(-1))=17.51+0.17269 t_b; ΔH_s~° (kJ mol~(-1))=26.25+0.22349 t_b. From these equations other unknown values of ΔH_v~°and ΔH_s~°of chlorobenzenes have been estimated.
1989, 5(04): 492-495
doi: 10.3866/PKU.WHXB19890422
Abstract:
We found that the photochemical reaction of dilute vitamin C solution is zero order at stirring. While nonstirring using a HP-8451 spectrophotometer have been able to record decay and regular periodic oscillations on certain concentration range and nearby 25 ℃. It is shown that these oscillations, however, will appear preperiod which is more than 1200 sec after the start of the irradiation. The main oscillating periodsare 117±6 sec and the largest amplitude is 0.035 Abs. In this paper the effects of concentration, temperature and stirring on the photochemical oscillation are investigated, and the possible mechanism of photochemical reaction in dilute vitamin C solution and of forming photochemical oscillation are proposed and discussed. Until now there are no reported on it.
We found that the photochemical reaction of dilute vitamin C solution is zero order at stirring. While nonstirring using a HP-8451 spectrophotometer have been able to record decay and regular periodic oscillations on certain concentration range and nearby 25 ℃. It is shown that these oscillations, however, will appear preperiod which is more than 1200 sec after the start of the irradiation. The main oscillating periodsare 117±6 sec and the largest amplitude is 0.035 Abs. In this paper the effects of concentration, temperature and stirring on the photochemical oscillation are investigated, and the possible mechanism of photochemical reaction in dilute vitamin C solution and of forming photochemical oscillation are proposed and discussed. Until now there are no reported on it.
1989, 5(04): 496-498
doi: 10.3866/PKU.WHXB19890423
Abstract:
This paper considers the extraction process to consist of two steps: (1) the creation of a cavity in the solvent of suitable size to accomodete the solute; and (2) the introduction into the cavity of a solute molecule which interacts with the solvent. Each step is a set of thermodynamic functions ΔG~°_s=G_c+G_i+RTln(RT/V) The partial molar Gibbs free energy G_c and C_i is expressed by applying the scaled particle theory in Eqs. (6) and (7). The theoretical calculation of the partition constants of inert gases by Eqs.(1), (4)—(7), as given in Table 1, are in od agreement with experimental values.
This paper considers the extraction process to consist of two steps: (1) the creation of a cavity in the solvent of suitable size to accomodete the solute; and (2) the introduction into the cavity of a solute molecule which interacts with the solvent. Each step is a set of thermodynamic functions ΔG~°_s=G_c+G_i+RTln(RT/V) The partial molar Gibbs free energy G_c and C_i is expressed by applying the scaled particle theory in Eqs. (6) and (7). The theoretical calculation of the partition constants of inert gases by Eqs.(1), (4)—(7), as given in Table 1, are in od agreement with experimental values.
1989, 5(04): 499-503
doi: 10.3866/PKU.WHXB19890424
Abstract:
In this paper, the mechnism of the electrochemical oxidation of vitamin E in acetonitrile and ethanol solvents was studied by cyclic voltammetry, controlled-potential electrolysis coulometry and double potential step chronoamperometry. The oxidation mechanism of vitamin E was suggested by cyclic voltammogram and compared with V. D. Parker′s work for the model compound of vitamin E. Controlledpotential electrolysis coulometry showed that for the oxidition of each molecule of vitamin E two electrons were transferred. The rate constants of the follow-up hydrolysis and ethanolysis reactions of the primary oxidation product were measured and the relative magnitude of this two kinds of follow-up reactions was compared.
In this paper, the mechnism of the electrochemical oxidation of vitamin E in acetonitrile and ethanol solvents was studied by cyclic voltammetry, controlled-potential electrolysis coulometry and double potential step chronoamperometry. The oxidation mechanism of vitamin E was suggested by cyclic voltammogram and compared with V. D. Parker′s work for the model compound of vitamin E. Controlledpotential electrolysis coulometry showed that for the oxidition of each molecule of vitamin E two electrons were transferred. The rate constants of the follow-up hydrolysis and ethanolysis reactions of the primary oxidation product were measured and the relative magnitude of this two kinds of follow-up reactions was compared.
1989, 5(04): 504-506
doi: 10.3866/PKU.WHXB19890425
Abstract:
It is reported in this paper that the acidity function H_0 of perfluorooctanesulfonic acid (POSA) is -12.11±0.03, which was measured first time by ~1H NMR method, in term of the α-H chemical shifts of the acid-ether systems, using 98% to 100% H_2SO_4 as reference standards. This method provides a new procedure for measuring the H_0 value of solid perfluoroalkanesulfonie acid C_nH_(2n+1)SO_3H(n>7).
It is reported in this paper that the acidity function H_0 of perfluorooctanesulfonic acid (POSA) is -12.11±0.03, which was measured first time by ~1H NMR method, in term of the α-H chemical shifts of the acid-ether systems, using 98% to 100% H_2SO_4 as reference standards. This method provides a new procedure for measuring the H_0 value of solid perfluoroalkanesulfonie acid C_nH_(2n+1)SO_3H(n>7).
1989, 5(04): 507-510
doi: 10.3866/PKU.WHXB19890426
Abstract:
The chemisorption of benzene on the Rh(111) surface is calculated using DVX_a method. The electronic structure, the ground states valence levels, Mulliken overlap populations, and the density of states (LDOS and TDOS) of the adsorption system C_6H_6/Rh_6(111) are obtained. The results of DV-X_a calculations indicate that the adsorbed benzene structure is unpertured from its stable gas-phase structure, is π-bonded to the Rh surface with ring plane parallel to the metal plane, and has a C_(3ν)(σ_d) bonding symmetry. We also discuss the charge transfer between adsorbate and substrate. The π electrons of benzene transfer to the empty d orbitals of Rh, so is resonance stability decreases and is easy to be hydrogenated. The results of TDOS are in agreement with UPS, supporting the LEED structural analysis. From figure 3, it can be found that the two peaks at 5—6 eV and 7—9 eV under Fermi level (E_F) move to left by about 0.5 eV in the process of adsorption, which are mainly contributed by the 2π and 1π orbiatls of benzene respectively and are widened, and the peaks at 2 eV and 4 eV over Fermi level also move to left, which are contributed by the empty d orbitals of Rh.
The chemisorption of benzene on the Rh(111) surface is calculated using DVX_a method. The electronic structure, the ground states valence levels, Mulliken overlap populations, and the density of states (LDOS and TDOS) of the adsorption system C_6H_6/Rh_6(111) are obtained. The results of DV-X_a calculations indicate that the adsorbed benzene structure is unpertured from its stable gas-phase structure, is π-bonded to the Rh surface with ring plane parallel to the metal plane, and has a C_(3ν)(σ_d) bonding symmetry. We also discuss the charge transfer between adsorbate and substrate. The π electrons of benzene transfer to the empty d orbitals of Rh, so is resonance stability decreases and is easy to be hydrogenated. The results of TDOS are in agreement with UPS, supporting the LEED structural analysis. From figure 3, it can be found that the two peaks at 5—6 eV and 7—9 eV under Fermi level (E_F) move to left by about 0.5 eV in the process of adsorption, which are mainly contributed by the 2π and 1π orbiatls of benzene respectively and are widened, and the peaks at 2 eV and 4 eV over Fermi level also move to left, which are contributed by the empty d orbitals of Rh.
