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1987 Volume 3 Issue 6
1987, 3(06): 561-564
doi: 10.3866/PKU.WHXB19870601
Abstract:
In this paper the energies of six X-ray crystallographic conformations of insulin B-chain helix have been analysed preliminarily and the conversion processes appeared between those conformations have been simulated on the VAX/VMS 780 computer, which showed that the conformational energies of molecule 1 B-chain helix were less than that of molecule 2 in those three crystals of insulin and the sharp changes of the energies in the conformational conversion processes were mainly the contributions of the interactions between a few atoms. Our studies indicated semi-quantitatively that the mode of sequential conformational changes one amino acid residue by one could not be present in the processes mentioned above. Our studies also indicated that the program ECEPP/2 was not suitable to the peptide model with more amino acid residues for the purposes of adding the hydrogen atoms to the model theoretically.
In this paper the energies of six X-ray crystallographic conformations of insulin B-chain helix have been analysed preliminarily and the conversion processes appeared between those conformations have been simulated on the VAX/VMS 780 computer, which showed that the conformational energies of molecule 1 B-chain helix were less than that of molecule 2 in those three crystals of insulin and the sharp changes of the energies in the conformational conversion processes were mainly the contributions of the interactions between a few atoms. Our studies indicated semi-quantitatively that the mode of sequential conformational changes one amino acid residue by one could not be present in the processes mentioned above. Our studies also indicated that the program ECEPP/2 was not suitable to the peptide model with more amino acid residues for the purposes of adding the hydrogen atoms to the model theoretically.
1987, 3(06): 565-569
doi: 10.3866/PKU.WHXB19870602
Abstract:
Similar to other serine proteinases, the pertinent active site amino acids are preserved in urokinase and the amino acids forming the specific pocket shows a considerable homology with other serine proteinases, especially with trypsin. But urokinase can not be inhibited by pancreatic trypsin inhibitor (PTI) which is the best inhibitor of trypsin. Using Chou-Fasman and ECEPP/2 programs the secondary structure and tertiary structure of urokinase fragments 177-189(UKf2)and 245-255 (UKf1) were predicted in order to investigate the reason of different activities between urokinase and trypsin.
The results showed that amino acids 246-252 in UKf1 formed a α-helix structure. The dihedral angles φ of these residues were around -57° and Ψ -47°. Amino acids 185-188 in UKf2 formd a β-sheet, 181-184 were in a β-turn structure. Comparing with the stereoscopric structure of the corresponding fragments in trypsin, it can be found that since the lack of two residues in trypsin in the fragment corresponding to UKf1, only a turn structure existed in this fragment. The existance of α-helix structure in UKf1 hindered the combining of PT1 with the active sites of UK and made urokinase not being inhibited by PTI.
Similar to other serine proteinases, the pertinent active site amino acids are preserved in urokinase and the amino acids forming the specific pocket shows a considerable homology with other serine proteinases, especially with trypsin. But urokinase can not be inhibited by pancreatic trypsin inhibitor (PTI) which is the best inhibitor of trypsin. Using Chou-Fasman and ECEPP/2 programs the secondary structure and tertiary structure of urokinase fragments 177-189(UKf2)and 245-255 (UKf1) were predicted in order to investigate the reason of different activities between urokinase and trypsin.
The results showed that amino acids 246-252 in UKf1 formed a α-helix structure. The dihedral angles φ of these residues were around -57° and Ψ -47°. Amino acids 185-188 in UKf2 formd a β-sheet, 181-184 were in a β-turn structure. Comparing with the stereoscopric structure of the corresponding fragments in trypsin, it can be found that since the lack of two residues in trypsin in the fragment corresponding to UKf1, only a turn structure existed in this fragment. The existance of α-helix structure in UKf1 hindered the combining of PT1 with the active sites of UK and made urokinase not being inhibited by PTI.
1987, 3(06): 570-572
doi: 10.3866/PKU.WHXB19870603
Abstract:
XPS has been used to study the thermal stability of the surface oxides on transition-metal foils including Ni, Fe, Cu, Ti, Zr, Nb and Ta formed by oxida- tion of the metals in dry air at different temperatures. The results show that the room-temperature surface oxides (NiO, Fe_2O_3, CuO or Cu_2O, TiO_2, ZrO_2, Nb_2O_5 and Ta_4O_5) are converted to the metals after heating the samples in vacuum at 300~400 ℃. The surface oxides (NiO, Fe_2O_3, Cu_2O, TiO_2, ZrO_2, Nb_2O_5 and Ta_2O_5) formed at 250~400 ℃, however, cn not be converted to the metals by heating the samples in vacuum at the same temperatures. The reduction of room-temperature surface NiO is caused by reaction with surface hydrocarbon contaminants. For room-temperature surface oxides TiO_2, ZrO_2, Nb_2O_5 and Ta_2O_5, the apparent deoxidation may be explained by diffusion of oxygen atoms from the surface into the metallic lattice, the reduction caused by reaction with carbon-containing contaminants, however, can not be completely ruled out because carbides are formed after heating these samples in vacuum. It has been suggested that the lower thermal stability for room-temperature surface oxides can be attributed to its “two-dimensional structure” feature. Since the surface energy is higher and there are more structural defects as well as chemical defects in two-dimensional film, the net results are a weakening of the metal-oxygen bond and a lowering of thermal stability. The higher thermal stability for the high-temperature surface oxides can be explained by surface sintering and the formation of bulk oxide. SEM observation revealed that the room-temperature surface oxide for vapor-deposited Ni film agglomerates into a great number of grains after heating the film at 250 ℃ for 2 hours. Along with surface sintering, reconstruction and phase change of the surface oxides may also occur and thus decrease the surface energy and increase the thermal stability.
XPS has been used to study the thermal stability of the surface oxides on transition-metal foils including Ni, Fe, Cu, Ti, Zr, Nb and Ta formed by oxida- tion of the metals in dry air at different temperatures. The results show that the room-temperature surface oxides (NiO, Fe_2O_3, CuO or Cu_2O, TiO_2, ZrO_2, Nb_2O_5 and Ta_4O_5) are converted to the metals after heating the samples in vacuum at 300~400 ℃. The surface oxides (NiO, Fe_2O_3, Cu_2O, TiO_2, ZrO_2, Nb_2O_5 and Ta_2O_5) formed at 250~400 ℃, however, cn not be converted to the metals by heating the samples in vacuum at the same temperatures. The reduction of room-temperature surface NiO is caused by reaction with surface hydrocarbon contaminants. For room-temperature surface oxides TiO_2, ZrO_2, Nb_2O_5 and Ta_2O_5, the apparent deoxidation may be explained by diffusion of oxygen atoms from the surface into the metallic lattice, the reduction caused by reaction with carbon-containing contaminants, however, can not be completely ruled out because carbides are formed after heating these samples in vacuum. It has been suggested that the lower thermal stability for room-temperature surface oxides can be attributed to its “two-dimensional structure” feature. Since the surface energy is higher and there are more structural defects as well as chemical defects in two-dimensional film, the net results are a weakening of the metal-oxygen bond and a lowering of thermal stability. The higher thermal stability for the high-temperature surface oxides can be explained by surface sintering and the formation of bulk oxide. SEM observation revealed that the room-temperature surface oxide for vapor-deposited Ni film agglomerates into a great number of grains after heating the film at 250 ℃ for 2 hours. Along with surface sintering, reconstruction and phase change of the surface oxides may also occur and thus decrease the surface energy and increase the thermal stability.
1987, 3(06): 573-580
doi: 10.3866/PKU.WHXB19870604
Abstract:
The title compound has been synthesized by the reaction of (NH_4)_2WS_4 and CuCl_2·2H_2O in pyridine solution, 4[CuCl(C_5H_5N)_4] ·[W_(10)O_(32)]·2(C_5H_5N)·3H_2O is triclinic, space group P1, a=1.3555(7), b=1.3666(5), c=1.7860(13) nm, α=69.08(4)°, β=87.39(5)°, γ=70.72(4)°. V=2.907(3) nm, z=1. D_m=2.56 gcm~(-3). The structure was solved by Patterson method and Fourier methods. The final R is 0.046. The result indicates that the crystal is composed of W_(10)O_(32)~(4-), [CuCl(C_5H_5N)_4]~+, C_5H_5N and H_2O. The structure of W_(10)O_(32)~(4-) is shown in Fig.1. The W atom is coordinated by six O atoms of octahedra, which united by edges and corner. The structure of [CuCl(C_5H_5N)_4]~+ isshown in Fig.2. The Cu atom is coordinated by one Cl and four N atoms that form slightly deformed pyramid. This kind of [CuCl(C_5H_5N)_4]~+ cation has not been reported before. C_5H_5N and H_2O molecules are distributed in the interstices of the packing of the ions.
The title compound has been synthesized by the reaction of (NH_4)_2WS_4 and CuCl_2·2H_2O in pyridine solution, 4[CuCl(C_5H_5N)_4] ·[W_(10)O_(32)]·2(C_5H_5N)·3H_2O is triclinic, space group P1, a=1.3555(7), b=1.3666(5), c=1.7860(13) nm, α=69.08(4)°, β=87.39(5)°, γ=70.72(4)°. V=2.907(3) nm, z=1. D_m=2.56 gcm~(-3). The structure was solved by Patterson method and Fourier methods. The final R is 0.046. The result indicates that the crystal is composed of W_(10)O_(32)~(4-), [CuCl(C_5H_5N)_4]~+, C_5H_5N and H_2O. The structure of W_(10)O_(32)~(4-) is shown in Fig.1. The W atom is coordinated by six O atoms of octahedra, which united by edges and corner. The structure of [CuCl(C_5H_5N)_4]~+ isshown in Fig.2. The Cu atom is coordinated by one Cl and four N atoms that form slightly deformed pyramid. This kind of [CuCl(C_5H_5N)_4]~+ cation has not been reported before. C_5H_5N and H_2O molecules are distributed in the interstices of the packing of the ions.
1987, 3(06): 581-586
doi: 10.3866/PKU.WHXB19870605
Abstract:
Tightly binding calculations have been performed on the linear screw chain as well as the three dimensional lattice of tri nal selenium. Energy bands can be classified into three sets, namely bonding, nonbonding (lone pair bands) and anti- bonding which have been analyzed in terms of space symmetry. In order to eluci- date the bonding analogy inherent in both the lattice and its finite fragment, a hy- pothetical ring cluster with formula Se_6 is elected and investigated by means of EH program in addition. Parallel to COOP introduced by Hughbanks and Hoffmann, a similar quantity-clusterorbital orverlap population is defined which qualitatively estimates the bonding extent between a pair of atoms distributed in the neighborhood of a fixed energy value. Much like results as drawing in curves of energy bands, density of states and COOP have been shown between the lattice and the hypothetical cluster. This reveals to believe that quite similar electron behaviors exist in this kind of solid and the appropriate finite molecule.
Tightly binding calculations have been performed on the linear screw chain as well as the three dimensional lattice of tri nal selenium. Energy bands can be classified into three sets, namely bonding, nonbonding (lone pair bands) and anti- bonding which have been analyzed in terms of space symmetry. In order to eluci- date the bonding analogy inherent in both the lattice and its finite fragment, a hy- pothetical ring cluster with formula Se_6 is elected and investigated by means of EH program in addition. Parallel to COOP introduced by Hughbanks and Hoffmann, a similar quantity-clusterorbital orverlap population is defined which qualitatively estimates the bonding extent between a pair of atoms distributed in the neighborhood of a fixed energy value. Much like results as drawing in curves of energy bands, density of states and COOP have been shown between the lattice and the hypothetical cluster. This reveals to believe that quite similar electron behaviors exist in this kind of solid and the appropriate finite molecule.
MEASUREMENTS OF THE POTENTIAL DIFFERENCE ACROSS THE Na-BETA ALUMINA/NaOH AQUEOUS SOLUTION INTERFACES
1987, 3(06): 587-591
doi: 10.3866/PKU.WHXB19870606
Abstract:
EMF of the concentration cells of sodium beta alumina tubes in four aqueous solutions: NaOH, NaOH-KOH, NaOH-(CH_3)_4NOH and NaOH-NaCl were measured. The potential differences across the Na-beta alumina/NaOH aqueous solution interfaces Δφ, were obtained. The results showed that the relations between Δφ and loga_2 (Na)~+/a_1(Na~+) obeyed the Nernst equation in NaOH, NaOH-NaCl aqueous solutions. The presence of K~+ ions influenced Δφ, but OH~-, (CH_3)_4N~+ did not. The possi- bility of using the beta alumina as a Na~+-ion selective electrode in alkaline Na~+-ion aqueous solutions (if Na~+ concentration≥0.01 mol L~(-1).) was discussed.
EMF of the concentration cells of sodium beta alumina tubes in four aqueous solutions: NaOH, NaOH-KOH, NaOH-(CH_3)_4NOH and NaOH-NaCl were measured. The potential differences across the Na-beta alumina/NaOH aqueous solution interfaces Δφ, were obtained. The results showed that the relations between Δφ and loga_2 (Na)~+/a_1(Na~+) obeyed the Nernst equation in NaOH, NaOH-NaCl aqueous solutions. The presence of K~+ ions influenced Δφ, but OH~-, (CH_3)_4N~+ did not. The possi- bility of using the beta alumina as a Na~+-ion selective electrode in alkaline Na~+-ion aqueous solutions (if Na~+ concentration≥0.01 mol L~(-1).) was discussed.
1987, 3(06): 592-598
doi: 10.3866/PKU.WHXB19870607
Abstract:
The chemiluminescent spectra of the reactions of Pb with discharged oxygen, O_2(1Δ), have deen measured in an atomic beam apparatus, and some new bands have been obtained, When the presure of the observed region was larger than 2.5× 10~(-2) Torr, the intensities of the(3,0) and (4,0) viberational bands of the B~3Π-X~1Σ~+ transition were enhanced remarkedly, this can be interpreted with the aid of the processes of the near-resonance collision transfer energy between PbO and O_2 (1Δ) as well as the collision induced in tramolecular energy transfer of PdO.
The chemiluminescent spectra of the reactions of Pb with discharged oxygen, O_2(1Δ), have deen measured in an atomic beam apparatus, and some new bands have been obtained, When the presure of the observed region was larger than 2.5× 10~(-2) Torr, the intensities of the(3,0) and (4,0) viberational bands of the B~3Π-X~1Σ~+ transition were enhanced remarkedly, this can be interpreted with the aid of the processes of the near-resonance collision transfer energy between PbO and O_2 (1Δ) as well as the collision induced in tramolecular energy transfer of PdO.
1987, 3(06): 599-603
doi: 10.3866/PKU.WHXB19870608
Abstract:
A procedure is described whereby Fe(CN)_6~(n-) (n=3 or 4)-incorporated polypyr- role (PP) film can be formed on electrodes by electrochemical polymerization in aqueous solutions. Stable electrochemistry of the electrode thus formed is observed. The redox potential is affected by changes of the concentration of H~+ in the elec- trolyte. By means of XPS, IR and ESR characterizations, the interactions between the incorporated species Fe(CN)_6~(n-) and PP~+ has been investigated. A possible model of the orbital interactions involved in the film has been discussed.
A procedure is described whereby Fe(CN)_6~(n-) (n=3 or 4)-incorporated polypyr- role (PP) film can be formed on electrodes by electrochemical polymerization in aqueous solutions. Stable electrochemistry of the electrode thus formed is observed. The redox potential is affected by changes of the concentration of H~+ in the elec- trolyte. By means of XPS, IR and ESR characterizations, the interactions between the incorporated species Fe(CN)_6~(n-) and PP~+ has been investigated. A possible model of the orbital interactions involved in the film has been discussed.
1987, 3(06): 604-608
doi: 10.3866/PKU.WHXB19870609
Abstract:
The influences of the different substituents R~1 and R~2 on the structures of (μ-R~1S)(μ-R~2S)Fe_2(CO)_6 cluster complexes were studied. The [-Fe(CO)_2Cp] is a novel substituent, and thus there are some characteristics in the complex. The title complex belongs to monoclinic system, space group P2_1/n. The unit cell parameters a=0.79099(7), b=1.0774(1), c=2.2531(4) nm, γ=92.91(1)°, z=4, and D_=1.856 gcm~(-3). Refinement converged at R=0.024 and R_w=0.030 for the 2110 reflections with I≥3σ(I). The Fe-S(2) bond length are longer than the Fe-S(1) bond lengty, and the S(2) atom is bonded with the larger substituent Fe(CO)_2Cp. The unequivalency of the Fe-S bonds in the S bridges relates to the diffrentia between R~1 and R~2. The average length of Fe-S bonds is increased, when the fe or S atom is bonded with a large substituent, like PPh_3 or Fe(CO)_2Cp. Besides, the torsion angle of the cluster skeleton is sensitive to the existence of the large substituent. The Fe-S bond distancs inside the cluster skeleton ae shorter than that outside the cluster skeleton. It is thus obvious that the Fe-Fe bond has the effect of stabilizing the skeleton. The conformation of the substituents is (a,e) type. This is favourable for decreasing the reelling effect between the substituents.
【DOI】 cnki:ISSN:1000-6818.0.1987-06-008
The influences of the different substituents R~1 and R~2 on the structures of (μ-R~1S)(μ-R~2S)Fe_2(CO)_6 cluster complexes were studied. The [-Fe(CO)_2Cp] is a novel substituent, and thus there are some characteristics in the complex. The title complex belongs to monoclinic system, space group P2_1/n. The unit cell parameters a=0.79099(7), b=1.0774(1), c=2.2531(4) nm, γ=92.91(1)°, z=4, and D_=1.856 gcm~(-3). Refinement converged at R=0.024 and R_w=0.030 for the 2110 reflections with I≥3σ(I). The Fe-S(2) bond length are longer than the Fe-S(1) bond lengty, and the S(2) atom is bonded with the larger substituent Fe(CO)_2Cp. The unequivalency of the Fe-S bonds in the S bridges relates to the diffrentia between R~1 and R~2. The average length of Fe-S bonds is increased, when the fe or S atom is bonded with a large substituent, like PPh_3 or Fe(CO)_2Cp. Besides, the torsion angle of the cluster skeleton is sensitive to the existence of the large substituent. The Fe-S bond distancs inside the cluster skeleton ae shorter than that outside the cluster skeleton. It is thus obvious that the Fe-Fe bond has the effect of stabilizing the skeleton. The conformation of the substituents is (a,e) type. This is favourable for decreasing the reelling effect between the substituents.
【DOI】 cnki:ISSN:1000-6818.0.1987-06-008
1987, 3(06): 609-614
doi: 10.3866/PKU.WHXB19870610
Abstract:
A new method called potentiometric stripping analysis (PSA)for determination of diffusion coefficients of metal in mercury is presented in this paper. The principle of the method is: amalgam in a hanging mercury drop electrode (HMDE) is carried out at first by electrolysis, then the potentiostatic circuit is disconnected and the amalgamated metals are oxidized consecutively by oxidizer added to the solution. The redox potential of HMDE is recorded on a high-impendence X-t recorder, the time (τ) between two consecutive equivalence is taked as signal of determination of diffusion coefficients of metal in mercury, which is based on the equation derived in this paper as follow:
τ=Kc_0°-r_0~2/15D_R
If graph of τ vs c_0° is made, intercept (τ_0) on coordinate of τ is derived by extending the curve of τ vs c_0° as for as c_0°→0, and D_R iscalculated according to:
D_R=-r_0~2/15τ_0
Diffusion coefficients D_R of some metals in single amalgam are determined by this method. The values of D_R are in agreement with those obtained by former researchaers. Diffusion coefficients of Zn and Cd in multi-amalgam are also determned. It is discorved that the values of diffusion coefficients of Zn and Cd in multi amalgamare almost the same as those in single amalgam.
A new method called potentiometric stripping analysis (PSA)for determination of diffusion coefficients of metal in mercury is presented in this paper. The principle of the method is: amalgam in a hanging mercury drop electrode (HMDE) is carried out at first by electrolysis, then the potentiostatic circuit is disconnected and the amalgamated metals are oxidized consecutively by oxidizer added to the solution. The redox potential of HMDE is recorded on a high-impendence X-t recorder, the time (τ) between two consecutive equivalence is taked as signal of determination of diffusion coefficients of metal in mercury, which is based on the equation derived in this paper as follow:
τ=Kc_0°-r_0~2/15D_R
If graph of τ vs c_0° is made, intercept (τ_0) on coordinate of τ is derived by extending the curve of τ vs c_0° as for as c_0°→0, and D_R iscalculated according to:
D_R=-r_0~2/15τ_0
Diffusion coefficients D_R of some metals in single amalgam are determined by this method. The values of D_R are in agreement with those obtained by former researchaers. Diffusion coefficients of Zn and Cd in multi-amalgam are also determned. It is discorved that the values of diffusion coefficients of Zn and Cd in multi amalgamare almost the same as those in single amalgam.
1987, 3(06): 615-620
doi: 10.3866/PKU.WHXB19870611
Abstract:
In this paper the reaction cross sections of H+O_2(n_0j_o)→HO+O and C+H_2(n_0j_0)→NCH+H systems with long-lived complex on their ab initio potential energy sur- faces were calculated using Marcus′ Microcanonical Transition State Theory. Ef- fects of the properties of potential energy surfaces on the reaction cross sections were discussed. We found that the reaction cross sections of the two systems first increase and then decrease as collision energy increases at given vibrational-rota-tional quantum number (n_0j_0), except n_0=0 and j_0=1; the reaction cross sections of the two reactions are all increased obviously with increase of n_0 at given collision energy and internal rotational state j_0; the variation of the reaction cross sections is complicated with increase of j_0 for H+O_2 system, and monotonous for the C+H_2 system except j_0=1. These calculated results of the reaction H+O_2(n_0j_0)→HO+O are in od argreement with that obtained by Quasiclassical Trajectory Theory and the experimental measurement.
In this paper the reaction cross sections of H+O_2(n_0j_o)→HO+O and C+H_2(n_0j_0)→NCH+H systems with long-lived complex on their ab initio potential energy sur- faces were calculated using Marcus′ Microcanonical Transition State Theory. Ef- fects of the properties of potential energy surfaces on the reaction cross sections were discussed. We found that the reaction cross sections of the two systems first increase and then decrease as collision energy increases at given vibrational-rota-tional quantum number (n_0j_0), except n_0=0 and j_0=1; the reaction cross sections of the two reactions are all increased obviously with increase of n_0 at given collision energy and internal rotational state j_0; the variation of the reaction cross sections is complicated with increase of j_0 for H+O_2 system, and monotonous for the C+H_2 system except j_0=1. These calculated results of the reaction H+O_2(n_0j_0)→HO+O are in od argreement with that obtained by Quasiclassical Trajectory Theory and the experimental measurement.
1987, 3(06): 621-625
doi: 10.3866/PKU.WHXB19870612
Abstract:
In the present paper ESR spectra of six acidic phosphates (phosphonates) co- pper (Ⅱ) complexes in solid state at room temperature have been examined, and their ESP spectral parameters in THE at low temperature have been determined. The bonding parameters and difference of reducible level of these complexes were calculated. The bonding characterization of these copper (Ⅱ) complexes were dis- cussed. The result shows that the in-plane σ-bond in these complexes plays an important role, but the action of in-plane π-bond on bonding of these complexes may not be also neglected.
In the present paper ESR spectra of six acidic phosphates (phosphonates) co- pper (Ⅱ) complexes in solid state at room temperature have been examined, and their ESP spectral parameters in THE at low temperature have been determined. The bonding parameters and difference of reducible level of these complexes were calculated. The bonding characterization of these copper (Ⅱ) complexes were dis- cussed. The result shows that the in-plane σ-bond in these complexes plays an important role, but the action of in-plane π-bond on bonding of these complexes may not be also neglected.
1987, 3(06): 626-631
doi: 10.3866/PKU.WHXB19870613
Abstract:
Hydrogen spillover and its effect on Pt/SnO, has been studied in comparison with carbon-monoxide. The catalyst used was prepared by impregnation. The experiments of H_2-O_2 cycle pulse titration and reaction of H-saturated Pt/SnO_2 with O_2 evidently illustrated that hydrogen adsorbed on Pt/SnO_2 can migrate from Pt to platinized SnO_2 freely even at room temperature. Studying the behaviour of unplatinized SnO_2 mixed with Pt/SnO_2, we have shown the occurence of second- ary hydrogen spillover, i.e. the spillover hydrogen can migrate from Pt/SnO2 particles to bare SnO_2 particles as well.
It is demonstrated that while the catalyst surface exerts actions on the adsorbed molecules activating them, the adsorbates make a re-action on the catalyst in turn. By the electrical conductance measurement and Mössbauer spectra, it is revealed that the hydrogen migrating to SnO_2 from Pt interacted with SnO_2. The electron of spillover hydrogen transfered to the conduction band of semiconductor SnO_2, Causing an increase in the electrical conductance of SnO_2, and resulting in partial reduction of Sn~(4+). At a little higher temperature, the concentration of low-valence tin was high enough to be detected by Mössbauer spectra.
Hydrogen spillover and its effect on Pt/SnO, has been studied in comparison with carbon-monoxide. The catalyst used was prepared by impregnation. The experiments of H_2-O_2 cycle pulse titration and reaction of H-saturated Pt/SnO_2 with O_2 evidently illustrated that hydrogen adsorbed on Pt/SnO_2 can migrate from Pt to platinized SnO_2 freely even at room temperature. Studying the behaviour of unplatinized SnO_2 mixed with Pt/SnO_2, we have shown the occurence of second- ary hydrogen spillover, i.e. the spillover hydrogen can migrate from Pt/SnO2 particles to bare SnO_2 particles as well.
It is demonstrated that while the catalyst surface exerts actions on the adsorbed molecules activating them, the adsorbates make a re-action on the catalyst in turn. By the electrical conductance measurement and Mössbauer spectra, it is revealed that the hydrogen migrating to SnO_2 from Pt interacted with SnO_2. The electron of spillover hydrogen transfered to the conduction band of semiconductor SnO_2, Causing an increase in the electrical conductance of SnO_2, and resulting in partial reduction of Sn~(4+). At a little higher temperature, the concentration of low-valence tin was high enough to be detected by Mössbauer spectra.
1987, 3(06): 632-637
doi: 10.3866/PKU.WHXB19870614
Abstract:
The acetyl, sulfonyl and phosphoryl are three amino protecting groups. The natural abundance ~(15)N-NMR of their derivatives of the phenylethylglycine and β- phenylethylamine has been studied.We found that there are great differences in the chemical shifts of the three protected compounds. δ~(15)N is shifted to upfield in turn.Among these three amino protecting groups, the diisopropoxyphosphinyl one produces the least deshielding effect, while the acetyl group gives the strongest deshielding effect, and the tosyl group is in the middle. The trend of deshielding effect of the three protecting groups occurred also in the ~1H NMR (Table 1). Furthermore, we have studied the relation of chemical shifts to the atomic charge and molecular structures by means of semiempirical molecular orbital CNDO/2 and X-ray diffraction of single crystal structure analysis.
Model moleculae has been calculated by semiempirical molecular orbital CNDO/2 method. The results were shown in Table 2. The trend of the nitrogen net charges of these moleculae is the same as the ~(15)N NMR chemical shifts. These data show that the phosphoryl group is the most effective nitrogen lone pair electron localizing group among the three kinds of protecting groups. And the acetyl one is the least one.
By using the data of the single crystal structure of N-diisopropoxyphosphinyl-N-2-(3,4-methylenedioxy) phenyl) ethylglycine. The bonding types of the P-N, S-N and C-N of the related compounds were analyzed. The localizing effect of the phosphoryl group on the lone pair electron of nitrogen has been discussed. The one bond coupling constants of the N-phosphoryl system (Table 1) showed that the nitrogen through sp~2 hybrides formed bonds with one phosphorus atom and two carbon atoms. Thus, the nitrogen is in a planar conformation. It is consistent with the results of X0ray diffraction.
The acetyl, sulfonyl and phosphoryl are three amino protecting groups. The natural abundance ~(15)N-NMR of their derivatives of the phenylethylglycine and β- phenylethylamine has been studied.We found that there are great differences in the chemical shifts of the three protected compounds. δ~(15)N is shifted to upfield in turn.Among these three amino protecting groups, the diisopropoxyphosphinyl one produces the least deshielding effect, while the acetyl group gives the strongest deshielding effect, and the tosyl group is in the middle. The trend of deshielding effect of the three protecting groups occurred also in the ~1H NMR (Table 1). Furthermore, we have studied the relation of chemical shifts to the atomic charge and molecular structures by means of semiempirical molecular orbital CNDO/2 and X-ray diffraction of single crystal structure analysis.
Model moleculae has been calculated by semiempirical molecular orbital CNDO/2 method. The results were shown in Table 2. The trend of the nitrogen net charges of these moleculae is the same as the ~(15)N NMR chemical shifts. These data show that the phosphoryl group is the most effective nitrogen lone pair electron localizing group among the three kinds of protecting groups. And the acetyl one is the least one.
By using the data of the single crystal structure of N-diisopropoxyphosphinyl-N-2-(3,4-methylenedioxy) phenyl) ethylglycine. The bonding types of the P-N, S-N and C-N of the related compounds were analyzed. The localizing effect of the phosphoryl group on the lone pair electron of nitrogen has been discussed. The one bond coupling constants of the N-phosphoryl system (Table 1) showed that the nitrogen through sp~2 hybrides formed bonds with one phosphorus atom and two carbon atoms. Thus, the nitrogen is in a planar conformation. It is consistent with the results of X0ray diffraction.
1987, 3(06): 638-641
doi: 10.3866/PKU.WHXB19870615
Abstract:
The kinetics of L-ascorbic acid (H_2A) oxidation catalysed by Cu(Ⅱ) -Tyrosine complex has been studied in phosphate buffer (pH=7.44) at room temperature. The rate of Cu(Ⅱ)-Tyr_2 catalysed reaction comformed to the Michalies-Menten equation with respect to ascorbate (K_m=4.29×10~(-4) mol L~(-1); v_(max)=1.66×10~(-4) mol min~(-1)). H_2O_2 and O_2~- were produced during this reaction. The rates were decreased due to add the CAT or SOD respectively, A mechanism has been proposed.
The kinetics of L-ascorbic acid (H_2A) oxidation catalysed by Cu(Ⅱ) -Tyrosine complex has been studied in phosphate buffer (pH=7.44) at room temperature. The rate of Cu(Ⅱ)-Tyr_2 catalysed reaction comformed to the Michalies-Menten equation with respect to ascorbate (K_m=4.29×10~(-4) mol L~(-1); v_(max)=1.66×10~(-4) mol min~(-1)). H_2O_2 and O_2~- were produced during this reaction. The rates were decreased due to add the CAT or SOD respectively, A mechanism has been proposed.
1987, 3(06): 642-647
doi: 10.3866/PKU.WHXB19870616
Abstract:
By taking the N_2 as the carrier gas, the water vapour varying with different relative humidities passed through a sealed sample cell with a thin Poly A film coated on the BaF_2 window to achieve dynamic equilibrium. According to the asending and desending order of relative humidity (from 0% to 100%, then down to 0% again), a series of FT-IR and subtraction spectra have been studied in the region of 4000 to 800 cm~(-1) at (25±1) ℃ (Fig.1, 2). The results are concluded as following:
(1) In comparision with the static process studied by the authors′ previous work~[3], the essential features of hydration effect resemble each other. The strongest hydrating sites are on the —NH_2 and PO_2~- group. But the dynamic hydration behaves faster and stronger than that of static case. During the dynamic process the hydration usually begins at low humidity and then gradually increase; but in the static case, it begins almost around RH=75% then rises steeply (Fig.3). Besides, some new peaks around 1500 cm~(-1) have been observed.
(2) The hydration and dehydration process are irreversible. Both absorbance and peak position can not be restored (Fig.3). It indicates that the hydrating water molecules in Poly A have strong chemical bonding and cannot desorb easily at low humidity. The strongest hysteresis sites are ribose ring —NH_2 and PO_2~- group. So they are not exactly in correspondence with the strongest hydrating sites. This shows, the water molecules may redistribute among the different sites and it takes a quite long time to each equilibrium.
(3) The absorption and desorption isotherm of Poly A film is the well known sigmoidal shape (Fig.5). The number of absorbed water molecules per nucleotide unit at RH=100% is about 8.8. It is roughly approximate to the calculation by Clementi~[4] for the first solvation shell of B-DNA.
By taking the N_2 as the carrier gas, the water vapour varying with different relative humidities passed through a sealed sample cell with a thin Poly A film coated on the BaF_2 window to achieve dynamic equilibrium. According to the asending and desending order of relative humidity (from 0% to 100%, then down to 0% again), a series of FT-IR and subtraction spectra have been studied in the region of 4000 to 800 cm~(-1) at (25±1) ℃ (Fig.1, 2). The results are concluded as following:
(1) In comparision with the static process studied by the authors′ previous work~[3], the essential features of hydration effect resemble each other. The strongest hydrating sites are on the —NH_2 and PO_2~- group. But the dynamic hydration behaves faster and stronger than that of static case. During the dynamic process the hydration usually begins at low humidity and then gradually increase; but in the static case, it begins almost around RH=75% then rises steeply (Fig.3). Besides, some new peaks around 1500 cm~(-1) have been observed.
(2) The hydration and dehydration process are irreversible. Both absorbance and peak position can not be restored (Fig.3). It indicates that the hydrating water molecules in Poly A have strong chemical bonding and cannot desorb easily at low humidity. The strongest hysteresis sites are ribose ring —NH_2 and PO_2~- group. So they are not exactly in correspondence with the strongest hydrating sites. This shows, the water molecules may redistribute among the different sites and it takes a quite long time to each equilibrium.
(3) The absorption and desorption isotherm of Poly A film is the well known sigmoidal shape (Fig.5). The number of absorbed water molecules per nucleotide unit at RH=100% is about 8.8. It is roughly approximate to the calculation by Clementi~[4] for the first solvation shell of B-DNA.
1987, 3(06): 648-652
doi: 10.3866/PKU.WHXB19870617
Abstract:
Polyacrylonitrile (PAN) film attached to n-GaAs, n-GaP photoelectrode surface by plasma polymerization has been studied. Both electrochemical behaviors and stability of the modified electrodes have been investigated. The results showed that the semiconductor electrodes with PAN film decreased photocorrosion in a certain degree, and their electrochemical characteristics and stability were improved remarkably after plasma doping.
Cyclic voltammetric analysis demonstrated that the redox reaction occurred in I-PAN films could be carried out rapidly on electrode surfaces, in favor of the capture and transfer of photoinduced holes by the films to redox couples in solution.
Polyacrylonitrile (PAN) film attached to n-GaAs, n-GaP photoelectrode surface by plasma polymerization has been studied. Both electrochemical behaviors and stability of the modified electrodes have been investigated. The results showed that the semiconductor electrodes with PAN film decreased photocorrosion in a certain degree, and their electrochemical characteristics and stability were improved remarkably after plasma doping.
Cyclic voltammetric analysis demonstrated that the redox reaction occurred in I-PAN films could be carried out rapidly on electrode surfaces, in favor of the capture and transfer of photoinduced holes by the films to redox couples in solution.
1987, 3(06): 653-657
doi: 10.3866/PKU.WHXB19870618
Abstract:
The effects of Pt particle size and vacuum grease on hydrogen spillover were studied by the exchange reaction of deuterium gas with the hydroxyl groups in the system of PtNaY/HY using infrared spectroscopy.
It was found that the smaller the Pt particle size the faster the exchange rate, also the exchange rate can be accelerated by vacuum grease.
The exchange rates at three different temperatures (50 ℃, 100 ℃, 150 ℃)were measured, and the exchange mechanism was discussed.
The effects of Pt particle size and vacuum grease on hydrogen spillover were studied by the exchange reaction of deuterium gas with the hydroxyl groups in the system of PtNaY/HY using infrared spectroscopy.
It was found that the smaller the Pt particle size the faster the exchange rate, also the exchange rate can be accelerated by vacuum grease.
The exchange rates at three different temperatures (50 ℃, 100 ℃, 150 ℃)were measured, and the exchange mechanism was discussed.
1987, 3(06): 658-662
doi: 10.3866/PKU.WHXB19870619
Abstract:
The heat treatment of iron tetraphenylporphyrin chemically modified glassy carbon electrode has been described. The modified electrode by heat treatment shows od catalytic activity and stability for dioxygen reduction. Its catalytic activity is still maintained through 1000 cireles of cyclic voltametrie scans (100 V s~(-1)) in air saturated 0.05 mol L~(-1) H_2SO_4 solution. The effects of heat treatment temperature from 300 to 800 ℃ on the praparation and catalytic activity of the modified electrode have been studied. Using X.P.S, UV-VIS spectroscopy and Mass-spectroscopy the possible microstructure on electrode surface has been analyzed. The electrocatalytic and dynamic behaviors for dioxygen reduction at the electrode have been studied by cyclic voltametry and rotating disk electrode respectively. The rate constants of dioxygen reduction at the electrode in a variety of pH solutions have been measured. The catalytic reduction of dioxygen at this modified electrode belongs to irreversible processes including 2-electron to H_2O_2 and 4-electron to water.
The heat treatment of iron tetraphenylporphyrin chemically modified glassy carbon electrode has been described. The modified electrode by heat treatment shows od catalytic activity and stability for dioxygen reduction. Its catalytic activity is still maintained through 1000 cireles of cyclic voltametrie scans (100 V s~(-1)) in air saturated 0.05 mol L~(-1) H_2SO_4 solution. The effects of heat treatment temperature from 300 to 800 ℃ on the praparation and catalytic activity of the modified electrode have been studied. Using X.P.S, UV-VIS spectroscopy and Mass-spectroscopy the possible microstructure on electrode surface has been analyzed. The electrocatalytic and dynamic behaviors for dioxygen reduction at the electrode have been studied by cyclic voltametry and rotating disk electrode respectively. The rate constants of dioxygen reduction at the electrode in a variety of pH solutions have been measured. The catalytic reduction of dioxygen at this modified electrode belongs to irreversible processes including 2-electron to H_2O_2 and 4-electron to water.
1987, 3(06): 663-667
doi: 10.3866/PKU.WHXB19870620
Abstract:
The molecular and crystal structure of the cbarge-transfer complex formed between 2,4,7-trinitrofluorenone (TNF) and 1,6-di-(N-carbazolyl-) 2,4-hexadiyne (DCH) has been determined from three dimensional intensity measured on a R3m/E four circle diffractometer. The complex crystallizes with one donor (DCH) and two acceptor (TNF) in a triclinic cell (P_1) of dimensions a=0.7190(1), b=1.0760(2), c=1.5438(3) nm and α=88.34(2), β=88.86(2), γ=87.92(2)°. The structure was solved by direct method using SHELXTL program. The H atoms coordinates were caculated geometrically. The 1609 statistically significant reflections were refined by “blocked cascade” least squares to a final value of R=0.073. The spearate schematic drawings of the donor and acceptor molecules with the bond lengths and angles are shown in Fig.1a and 1b. The acceptor (TNF) and donor (DCH) molecules lie in bc-planes with average distance of 0.34 nm between the molecules.
The molecular and crystal structure of the cbarge-transfer complex formed between 2,4,7-trinitrofluorenone (TNF) and 1,6-di-(N-carbazolyl-) 2,4-hexadiyne (DCH) has been determined from three dimensional intensity measured on a R3m/E four circle diffractometer. The complex crystallizes with one donor (DCH) and two acceptor (TNF) in a triclinic cell (P_1) of dimensions a=0.7190(1), b=1.0760(2), c=1.5438(3) nm and α=88.34(2), β=88.86(2), γ=87.92(2)°. The structure was solved by direct method using SHELXTL program. The H atoms coordinates were caculated geometrically. The 1609 statistically significant reflections were refined by “blocked cascade” least squares to a final value of R=0.073. The spearate schematic drawings of the donor and acceptor molecules with the bond lengths and angles are shown in Fig.1a and 1b. The acceptor (TNF) and donor (DCH) molecules lie in bc-planes with average distance of 0.34 nm between the molecules.
1987, 3(06): 668-671
doi: 10.3866/PKU.WHXB19870621
Abstract:
The enthalpies of vaporization of α-Pinene (99.7%) and β-Pinene (99.7%) have been determined at 25.0 ℃ by using a LKB-8721-3 Vaporization Calorimeter, ΔH_v~o are 44.57±0.06 and 45.80±0.08 kJ mol~(-1) respectively.
The enthalpies of vaporization of α-Pinene (99.7%) and β-Pinene (99.7%) have been determined at 25.0 ℃ by using a LKB-8721-3 Vaporization Calorimeter, ΔH_v~o are 44.57±0.06 and 45.80±0.08 kJ mol~(-1) respectively.
