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1993 Volume 9 Issue 5
1993, 9(05): 577-580
doi: 10.3866/PKU.WHXB19930501
Abstract:
1993, 9(05): 581-583
doi: 10.3866/PKU.WHXB19930502
Abstract:
A simplified systematic search method for peptide conformational analysis was established, which changes subsequent main chain dihedral angles two by two by an increment of 10 degrees and selects low energy conformations according to energy contour maps. The characteristics of the method is the computational speed. It was applied to the conformational analysis of two linear pentapeptides which can cyclize to give a same product. The lowest energy conformations of both peptides show a turn-like structure. The distance between N_1 atom and C_5 atom correlates well with the cyclization reaction yield.
A simplified systematic search method for peptide conformational analysis was established, which changes subsequent main chain dihedral angles two by two by an increment of 10 degrees and selects low energy conformations according to energy contour maps. The characteristics of the method is the computational speed. It was applied to the conformational analysis of two linear pentapeptides which can cyclize to give a same product. The lowest energy conformations of both peptides show a turn-like structure. The distance between N_1 atom and C_5 atom correlates well with the cyclization reaction yield.
1993, 9(05): 584-588
doi: 10.3866/PKU.WHXB19930503
Abstract:
1993, 9(05): 589-593
doi: 10.3866/PKU.WHXB19930504
Abstract:
1993, 9(05): 594-596
doi: 10.3866/PKU.WHXB19930505
Abstract:
1993, 9(05): 597-603
doi: 10.3866/PKU.WHXB19930506
Abstract:
Azobenzene derivative (AD) was organized to form Z type polar films by Langmuir-Blodgett technique. The UV-VIS spectra show that the spectra of chloro-form solution exhibited a broad band with λ_(max) at 480 nm, corresponding to the mon-omer, while the spectra observed on AD film exhibited a sharp peak at 380 nm, corresponding to the absorption of the H-like aggregates. The 100 nm blue-shift of the absorption band from the monomer to the aggregates displays the existence of a high aggregate in the AD film. the linear dichroic FTIR spectra of AD film give informations on the molecular orientation of several main transition moments. The results show that the tilt angle of the axis of the hydrocarbon chain is 50° from the surface normal, and the tile angle of the azobenzene chromophore is 35°. The X-ray diffraction spectra display there are double long spacings of 3.5 nm and 3.1 nm respectively in the AD film. The further work of this system has been studied by temperature-changed UV-VIS spectra and infrared spectra.
According to the results mentioned above, the structure may play an important role in the high pyroelectric property owing to a contribution of the intermolecular additional dipole moments added to the spontaneous dipole moments.
Azobenzene derivative (AD) was organized to form Z type polar films by Langmuir-Blodgett technique. The UV-VIS spectra show that the spectra of chloro-form solution exhibited a broad band with λ_(max) at 480 nm, corresponding to the mon-omer, while the spectra observed on AD film exhibited a sharp peak at 380 nm, corresponding to the absorption of the H-like aggregates. The 100 nm blue-shift of the absorption band from the monomer to the aggregates displays the existence of a high aggregate in the AD film. the linear dichroic FTIR spectra of AD film give informations on the molecular orientation of several main transition moments. The results show that the tilt angle of the axis of the hydrocarbon chain is 50° from the surface normal, and the tile angle of the azobenzene chromophore is 35°. The X-ray diffraction spectra display there are double long spacings of 3.5 nm and 3.1 nm respectively in the AD film. The further work of this system has been studied by temperature-changed UV-VIS spectra and infrared spectra.
According to the results mentioned above, the structure may play an important role in the high pyroelectric property owing to a contribution of the intermolecular additional dipole moments added to the spontaneous dipole moments.
1993, 9(05): 604-609
doi: 10.3866/PKU.WHXB19930507
Abstract:
The radiation-induced chain-scission and racemization of isotactic poly(methylmethacrylate)(iso-PMMA) in amorphous and semi-crystalline state as well as in solution have been studied with nuclear magnetic resonance and molar mass deter-mination. It is shown that the chain-scission is dominant for iso-PMMA in dilute solution while the racemization reaction is not favorable in this case. On the contrary, the racemization is favorable when iso-PMMA was irradiated in its crystalline state while chain-scission is not. Such experimental results could be well explained by the mobility of molecules and "cage effect". The hypothesis, we proposed previously that the chain-scission, racemization and recombination are in competition and the final result depends on the state of molecular motion at which iso-PMMA was irradiated, has been verified verified once again.
The radiation-induced chain-scission and racemization of isotactic poly(methylmethacrylate)(iso-PMMA) in amorphous and semi-crystalline state as well as in solution have been studied with nuclear magnetic resonance and molar mass deter-mination. It is shown that the chain-scission is dominant for iso-PMMA in dilute solution while the racemization reaction is not favorable in this case. On the contrary, the racemization is favorable when iso-PMMA was irradiated in its crystalline state while chain-scission is not. Such experimental results could be well explained by the mobility of molecules and "cage effect". The hypothesis, we proposed previously that the chain-scission, racemization and recombination are in competition and the final result depends on the state of molecular motion at which iso-PMMA was irradiated, has been verified verified once again.
1993, 9(05): 610-616
doi: 10.3866/PKU.WHXB19930508
Abstract:
The relaxation-matrix theory of line width analysis in electron spin resonance spectra has been used to analyze the alternating line width effects arising from the motion of β protons of propagating radical, this motion was treated by using a Brow-nian motion model assuming a torsional oscillations about the C_α—C_β bond. The formula of line-width for β-protons obtained were applied to the analysis of the ESR spectra for styrene radicals in the whole process of bulk polymerization to explain the time dependence on polymerization. The results also support the assignment of the β protons hfs-constants.
The relaxation-matrix theory of line width analysis in electron spin resonance spectra has been used to analyze the alternating line width effects arising from the motion of β protons of propagating radical, this motion was treated by using a Brow-nian motion model assuming a torsional oscillations about the C_α—C_β bond. The formula of line-width for β-protons obtained were applied to the analysis of the ESR spectra for styrene radicals in the whole process of bulk polymerization to explain the time dependence on polymerization. The results also support the assignment of the β protons hfs-constants.
1993, 9(05): 617-621
doi: 10.3866/PKU.WHXB19930509
Abstract:
The process of spinodal decomposition in polymer blends has been investigated by elastic light scattering, image analysis, computer simulation, scaling and fractal concepts. The results show that there exists the scaling behaviour for structure function. The morphology of phase separation in polymer blends is a fractal structure. The fractal dimension nearly does not change with time. Fractal aggregation takes place in the process of phase separation, The fractal structure of the morphology of phase separation results in dynamical scaling of structure function.
The process of spinodal decomposition in polymer blends has been investigated by elastic light scattering, image analysis, computer simulation, scaling and fractal concepts. The results show that there exists the scaling behaviour for structure function. The morphology of phase separation in polymer blends is a fractal structure. The fractal dimension nearly does not change with time. Fractal aggregation takes place in the process of phase separation, The fractal structure of the morphology of phase separation results in dynamical scaling of structure function.
1993, 9(05): 622-626
doi: 10.3866/PKU.WHXB19930510
Abstract:
The activity coefficients of solvent for some phenols, i.e.p-cresol, m-cresol, o-cresol, 2,4-dimethyiphenol, 2,6-dimethylphenol and phenol mixtures p-cresol+m-cresol, p-cresol+o-cresol, m-cresol+o-cresol, 2,4-dimethylphenol+2,6-dimethylph-enol (1:1 mole ratio) in benzene and in p-xylene have been measured by freezing point depression. The data was treated with Wiehe-Bagley association model combining with a Hildebrand-Scatchard term to evaluate the association constants K_A of phenols. It is found that the K_A of phenols in each solvent follows the order: p-cresol>m-cresol>0-cresol; 2,4-dimethylphenol>2,6-dimethylphenol. The association constants of binary solute mixtures are all situated between the respective two pure components.
The activity coefficients of solvent for some phenols, i.e.p-cresol, m-cresol, o-cresol, 2,4-dimethyiphenol, 2,6-dimethylphenol and phenol mixtures p-cresol+m-cresol, p-cresol+o-cresol, m-cresol+o-cresol, 2,4-dimethylphenol+2,6-dimethylph-enol (1:1 mole ratio) in benzene and in p-xylene have been measured by freezing point depression. The data was treated with Wiehe-Bagley association model combining with a Hildebrand-Scatchard term to evaluate the association constants K_A of phenols. It is found that the K_A of phenols in each solvent follows the order: p-cresol>m-cresol>0-cresol; 2,4-dimethylphenol>2,6-dimethylphenol. The association constants of binary solute mixtures are all situated between the respective two pure components.
1993, 9(05): 627-629
doi: 10.3866/PKU.WHXB19930511
Abstract:
The structure of NaAlO_2 melt has been studied by computer simulation using Monte Carlo method. The RDF and local structure are obtained by calculation. It has been found that the NaAlO_2 melt consists of ionic clusters formed by sharing the corners of AlO_4 tetrahedra, sodium ions and xNa~+·yO~(2-) clusters.
The structure of NaAlO_2 melt has been studied by computer simulation using Monte Carlo method. The RDF and local structure are obtained by calculation. It has been found that the NaAlO_2 melt consists of ionic clusters formed by sharing the corners of AlO_4 tetrahedra, sodium ions and xNa~+·yO~(2-) clusters.
1993, 9(05): 630-634
doi: 10.3866/PKU.WHXB19930512
Abstract:
The decarboxylation reaction of acrylic acid in ground state has been investigated by using self-consistent-field molecular orbital method (Semi-empirical AMI and HF/3-21G ab initio methods). Our calculation showed that in addition to one-step process from reactant to product which has been reported by Ruelle, there is another reaction path which is a two-step reaction and the latter will be least competitive with the one step process. The rate constants of both the two reaction paths are very small, which is consistent with the experimental fact (at ca. 500 ℃ acrylic acid breaks down to the extent of ca. 25%). Furthermore, our investigation indicated that the intermediate is rather stable, therefore it can be expected that this substance might be observed. This needs to be confirmed by experiment.
The decarboxylation reaction of acrylic acid in ground state has been investigated by using self-consistent-field molecular orbital method (Semi-empirical AMI and HF/3-21G ab initio methods). Our calculation showed that in addition to one-step process from reactant to product which has been reported by Ruelle, there is another reaction path which is a two-step reaction and the latter will be least competitive with the one step process. The rate constants of both the two reaction paths are very small, which is consistent with the experimental fact (at ca. 500 ℃ acrylic acid breaks down to the extent of ca. 25%). Furthermore, our investigation indicated that the intermediate is rather stable, therefore it can be expected that this substance might be observed. This needs to be confirmed by experiment.
1993, 9(05): 635-641
doi: 10.3866/PKU.WHXB19930513
Abstract:
Kinetics of the electrophilic substitution reaction (1) of
CuCl_2+Cd(Ⅱ)P→Cu(Ⅱ)P+CdCl_2 (1)
cupric chloride with meso-tetrakis(meta-methylphenyl) porphyrin cadmium(Ⅱ) was studied by means of Shimadzu UV-240 spectrophotometer. The proposed mechanism is as follows:
Cd(Ⅱ)P+Cl~-<=>[Cd(Ⅱ)PCl]~- (2)
Cu(Ⅱ)+[Cd(Ⅱ)PCl]~-<=>[Cu(Ⅱ)PCl]~-+Cd(Ⅱ) (3)
[Cu(Ⅱ)PCl]~-→Cu(Ⅱ)P+Cl~- (4)
The experimental data were treated with AST-286 microcomputer. The equilibrim constant(K) of preequilibrium step(1) and the rate constants(k_1, k_(-1), k_2) of step (2) and step (3) were obtained. The standard molar enthalpy change △_rH_m~-θ-, and standard entropy change △_rS_m~-θ-, of step (1) and the activation parameters Δ~≠H_(m,1), Δ~≠H_(m,-1), Δ~≠H_(m,2) and Δ~≠S_(m,1), Δ~≠S_(m,-1), Δ~≠S_(m,2) were calculated.
Kinetics of the electrophilic substitution reaction (1) of
CuCl_2+Cd(Ⅱ)P→Cu(Ⅱ)P+CdCl_2 (1)
cupric chloride with meso-tetrakis(meta-methylphenyl) porphyrin cadmium(Ⅱ) was studied by means of Shimadzu UV-240 spectrophotometer. The proposed mechanism is as follows:
Cd(Ⅱ)P+Cl~-<=>[Cd(Ⅱ)PCl]~- (2)
Cu(Ⅱ)+[Cd(Ⅱ)PCl]~-<=>[Cu(Ⅱ)PCl]~-+Cd(Ⅱ) (3)
[Cu(Ⅱ)PCl]~-→Cu(Ⅱ)P+Cl~- (4)
The experimental data were treated with AST-286 microcomputer. The equilibrim constant(K) of preequilibrium step(1) and the rate constants(k_1, k_(-1), k_2) of step (2) and step (3) were obtained. The standard molar enthalpy change △_rH_m~-θ-, and standard entropy change △_rS_m~-θ-, of step (1) and the activation parameters Δ~≠H_(m,1), Δ~≠H_(m,-1), Δ~≠H_(m,2) and Δ~≠S_(m,1), Δ~≠S_(m,-1), Δ~≠S_(m,2) were calculated.
1993, 9(05): 642-649
doi: 10.3866/PKU.WHXB19930514
Abstract:
A many-body expansion interatomic potential obtained from bulk tin was used to predict the structures and energies of small and medium size tin clusters (Sn_2-Sn_(300)). The optimized results show that small tin clusters (Sn_2-Sn_(15)) prefer to take compact structures as their most stable configuration, all unrelated with the bulk lattice; while medium tin clusters, like, Sn_(47), Sn_(71), Sn_(87), and Sn_(147), are still kept in shell structures which are distortions of the microcrystalline fragments of solid tin, with all the shells compressed and some shells split. The energy per-atom of these clusters increases steadily with the increasing of the cluster size, approaching the cohesive energy of α-tin at about Sn_(740) (extrapolated), where the most stable structure should match the bulk lattice except for a few percents of surface atoms.
A many-body expansion interatomic potential obtained from bulk tin was used to predict the structures and energies of small and medium size tin clusters (Sn_2-Sn_(300)). The optimized results show that small tin clusters (Sn_2-Sn_(15)) prefer to take compact structures as their most stable configuration, all unrelated with the bulk lattice; while medium tin clusters, like, Sn_(47), Sn_(71), Sn_(87), and Sn_(147), are still kept in shell structures which are distortions of the microcrystalline fragments of solid tin, with all the shells compressed and some shells split. The energy per-atom of these clusters increases steadily with the increasing of the cluster size, approaching the cohesive energy of α-tin at about Sn_(740) (extrapolated), where the most stable structure should match the bulk lattice except for a few percents of surface atoms.
1993, 9(05): 650-656
doi: 10.3866/PKU.WHXB19930515
Abstract:
The chemical states and composition of the surface species of sulfided MoO_3/γ-Al_2O_3 catalysts with the promotion of variable KCI contents have been investigated and correlated to the sulfidation and reduction properties of the catalysts by means of XPS, XRD, ESR and TPR techniques. An interaction between the potassium cations and the molybdenum component occurred and was stoichiometrically saturated at a KCI loading with the K/Mo atomic ratio of 0.8. At the K/Mo ratios below 0.8 the potassium cations interacted with molybdenum component to form the interacting species and were enriched on the catalyst surface, while chloride anions were free and lost during preparation. At the K/Mo ratios above 0.8 the surplus potassium cations directly combined with the chloride anions to form bulk KCl crystallites. Due to the existence of the potassium promoter, the interaction between the supported Mo(VI) and the γ-Al_2O_3 became weaker and the sulfidation and reduction for catalysts were partly retarded. The active sites or phases, which were responsible for the alcohol formation activity, could be produced by sulfiding the interacting species composed of the potassium and molybdenum components.
The chemical states and composition of the surface species of sulfided MoO_3/γ-Al_2O_3 catalysts with the promotion of variable KCI contents have been investigated and correlated to the sulfidation and reduction properties of the catalysts by means of XPS, XRD, ESR and TPR techniques. An interaction between the potassium cations and the molybdenum component occurred and was stoichiometrically saturated at a KCI loading with the K/Mo atomic ratio of 0.8. At the K/Mo ratios below 0.8 the potassium cations interacted with molybdenum component to form the interacting species and were enriched on the catalyst surface, while chloride anions were free and lost during preparation. At the K/Mo ratios above 0.8 the surplus potassium cations directly combined with the chloride anions to form bulk KCl crystallites. Due to the existence of the potassium promoter, the interaction between the supported Mo(VI) and the γ-Al_2O_3 became weaker and the sulfidation and reduction for catalysts were partly retarded. The active sites or phases, which were responsible for the alcohol formation activity, could be produced by sulfiding the interacting species composed of the potassium and molybdenum components.
1993, 9(05): 657-662
doi: 10.3866/PKU.WHXB19930516
Abstract:
The compatibility and crystallization behaviour of the mixtures of poly(tetrahy-drofuran-methyl methacrylate)diblock copolymer(PTHF-b-PMMA) with polyvinyl chloride has been studied. We found that the compatibility of these blends, in which there is special interaction between the homopolymer and the PMMA block of the copolymer, is much better than that of the AB/A type blends; and that the crystalli-zation rate and crystallinity of PTHF microdomain changed greatly due to the swollen by PVC homopolymer. In this paper, these changes in cryatallization are well explained according to the theories of block copolymer blends and the density gradient moldel presented by JIANG Ming.
The compatibility and crystallization behaviour of the mixtures of poly(tetrahy-drofuran-methyl methacrylate)diblock copolymer(PTHF-b-PMMA) with polyvinyl chloride has been studied. We found that the compatibility of these blends, in which there is special interaction between the homopolymer and the PMMA block of the copolymer, is much better than that of the AB/A type blends; and that the crystalli-zation rate and crystallinity of PTHF microdomain changed greatly due to the swollen by PVC homopolymer. In this paper, these changes in cryatallization are well explained according to the theories of block copolymer blends and the density gradient moldel presented by JIANG Ming.
1993, 9(05): 663-667
doi: 10.3866/PKU.WHXB19930517
Abstract:
It has been proposed that in LCAO-MO theory the contribution of the interaction between atom A and B to the total molecular energy, E_(AB), may be considered as a measure of the bonding situation. E_(AB) is known as atom-pair interaction energy. In this paper, the proposition is examined by MNDO calculation. The E_(AB) value of bonding atoms is negative (E_(AB)<-0.10 eV) and of non-bonding atoms is positive or small negative (about E_(AB)>-0.10 eV). When there is single, double, or triple bond between atoms of the second period, the value of E_(AB) is about -15, -25, -35 eV respectively. For the bond between hydrogen and second period atom E_(AB) is about -13 eV. The bond strength in organic molecules, the acid catalyzed dehydration of alcohol, the conjugation system and the freqency displacement of carbonyl group can be explained by the value of E_(AB). Correlations are obtained by comparing E_(CH) for C—H bond in many simple organic molecules with their isolated streching vibrational freqencies, ν_(CH), dissociation energies D°_(298), and in situ bond energes, E_b.
It has been proposed that in LCAO-MO theory the contribution of the interaction between atom A and B to the total molecular energy, E_(AB), may be considered as a measure of the bonding situation. E_(AB) is known as atom-pair interaction energy. In this paper, the proposition is examined by MNDO calculation. The E_(AB) value of bonding atoms is negative (E_(AB)<-0.10 eV) and of non-bonding atoms is positive or small negative (about E_(AB)>-0.10 eV). When there is single, double, or triple bond between atoms of the second period, the value of E_(AB) is about -15, -25, -35 eV respectively. For the bond between hydrogen and second period atom E_(AB) is about -13 eV. The bond strength in organic molecules, the acid catalyzed dehydration of alcohol, the conjugation system and the freqency displacement of carbonyl group can be explained by the value of E_(AB). Correlations are obtained by comparing E_(CH) for C—H bond in many simple organic molecules with their isolated streching vibrational freqencies, ν_(CH), dissociation energies D°_(298), and in situ bond energes, E_b.
1993, 9(05): 668-674
doi: 10.3866/PKU.WHXB19930518
Abstract:
The dissociation degrees of bromophenol blue at various total ionic strengths in pure water and in 15%, 25 mass% ethanol-water mixed solvents were measured by U-3200 spectrophotometer, and the pH values of corresponding solution were also measured by Orion EA 940 ionometer. The thermodynamic dissociation constants of bromophenol blue in pure water and in the mixed solvents were determined by two methods: extrapolation and polynomial approximation. The effect of medium on absorption spectra of bromophenol blue was discussed.
1993, 9(05): 675-678
doi: 10.3866/PKU.WHXB19930519
Abstract:
The kinetic parameters and mechanism of dehydration of CaC_2O_4·H_2O have been studied by correlative judging method on the basis of thermogravimetry experiments. Results show that thermal dehydration of CaC_2O_4·H_2O is regulated by an A_3 mech-anism, i.e. random nucleation followed by subsequent growth. The kinetic parame-ters obtained are as follows: activation energy E=85.15 kJ·mol~(-1), frequency factor A=5.58×10~8 min~(-1), the compensation equation is log A=0.1119E-0.7832.
The kinetic parameters and mechanism of dehydration of CaC_2O_4·H_2O have been studied by correlative judging method on the basis of thermogravimetry experiments. Results show that thermal dehydration of CaC_2O_4·H_2O is regulated by an A_3 mech-anism, i.e. random nucleation followed by subsequent growth. The kinetic parame-ters obtained are as follows: activation energy E=85.15 kJ·mol~(-1), frequency factor A=5.58×10~8 min~(-1), the compensation equation is log A=0.1119E-0.7832.
1993, 9(05): 679-683
doi: 10.3866/PKU.WHXB19930520
Abstract:
A new kind of cationic polyacrylamide, PAm·MG, has been prepared by the modification of polyacrylamide (—CONH_z) with HCHO and dieyanodiamide. Three PAm·MG species with various degree of substitution (S) have been obtained by varying the ratio HCHO/-CONH_2. They are water-soluble and show effective floccu-lation for the active dyes. PAm·MG is a hydrochloride salt of weak polybase, whose dissociation depends on S, pH, and the concentration of added salt. η_(ap)/C of PAm·MG solution depends also on S and dissociation of the polymer, and on pH of solution as well. All these results are of significance in determining the optimum conditions for the synthesis and use of PAm·MG.
A new kind of cationic polyacrylamide, PAm·MG, has been prepared by the modification of polyacrylamide (—CONH_z) with HCHO and dieyanodiamide. Three PAm·MG species with various degree of substitution (S) have been obtained by varying the ratio HCHO/-CONH_2. They are water-soluble and show effective floccu-lation for the active dyes. PAm·MG is a hydrochloride salt of weak polybase, whose dissociation depends on S, pH, and the concentration of added salt. η_(ap)/C of PAm·MG solution depends also on S and dissociation of the polymer, and on pH of solution as well. All these results are of significance in determining the optimum conditions for the synthesis and use of PAm·MG.
1993, 9(05): 684-686
doi: 10.3866/PKU.WHXB19930521
Abstract:
The crystallization behavior of the uhrafine amorphous Ni-P alloy particles prepared by chemical reduction has been studied by TEM, XRD, XPS and surface area measurments. It is found that neither sintering nor redispersion of the ultrafine par-ticles occurred during thermal treatment, but the surface and bulk structure of the amorphous alloy (sample a)were changed. For the case of the sample treated at 573 K, the alloy was partially segregated to Ni microcrystallites dispersed on the amorphous martrix (sample b). The increase in the surface area of the sample indicates the higher surface beterogeneity of the partially crystallized alloy. Increasing the temperature of thermal treatment to 773 K, the amorphous alloy was completely crystallized and segregated to Ni and Ni_3P alloy (sample c), and the surface area of the particles was decreased due to the aggregation of Ni crystallites at higher temperature.
The crystallization behavior of the uhrafine amorphous Ni-P alloy particles prepared by chemical reduction has been studied by TEM, XRD, XPS and surface area measurments. It is found that neither sintering nor redispersion of the ultrafine par-ticles occurred during thermal treatment, but the surface and bulk structure of the amorphous alloy (sample a)were changed. For the case of the sample treated at 573 K, the alloy was partially segregated to Ni microcrystallites dispersed on the amorphous martrix (sample b). The increase in the surface area of the sample indicates the higher surface beterogeneity of the partially crystallized alloy. Increasing the temperature of thermal treatment to 773 K, the amorphous alloy was completely crystallized and segregated to Ni and Ni_3P alloy (sample c), and the surface area of the particles was decreased due to the aggregation of Ni crystallites at higher temperature.
1993, 9(05): 687-691
doi: 10.3866/PKU.WHXB19930522
Abstract:
The ternary iodides CsSm_2I_5 and CsSmI_3 which contain a divalentt rare earth cation have been synthesized by direct reaction of SmI_2 with CsI and by reaction between Sm, HgI_2 and CsI. Their crystal structures are determined by X-ray powder diffraction technique. CsSm_2I_5 is isostruetural with NH_4Pb_2Cl_5 (monoclinic, p2_1/c) a=1.0219(3) nm, b=9.093(2) nm, c=1.4300(6) nm, β=90.35(4)°, z=4, D_0=5.26 g·cm~(-3) at 25 ℃, D_x=5.34 g·cm~(-3) and MV_x=200.0 cm·mol~(-1). CsSmI_3 is Iso-structural with SrCeO_3 (orthorhombic, Pmmm), a=0.8631(3) nm, b=1.7999(6) nm, c=1.2564(5) nm, z=8, D_0=4.76 g·cm~(-3) at 25 ℃, D_x=4.52 g·cm~(-3), and MV_x=146.9 cm·mol~(-1). The valency of samarium in both compounds were determined and confirmed to be +2 by polarographic analyzer and fluorescence spectra.
The ternary iodides CsSm_2I_5 and CsSmI_3 which contain a divalentt rare earth cation have been synthesized by direct reaction of SmI_2 with CsI and by reaction between Sm, HgI_2 and CsI. Their crystal structures are determined by X-ray powder diffraction technique. CsSm_2I_5 is isostruetural with NH_4Pb_2Cl_5 (monoclinic, p2_1/c) a=1.0219(3) nm, b=9.093(2) nm, c=1.4300(6) nm, β=90.35(4)°, z=4, D_0=5.26 g·cm~(-3) at 25 ℃, D_x=5.34 g·cm~(-3) and MV_x=200.0 cm·mol~(-1). CsSmI_3 is Iso-structural with SrCeO_3 (orthorhombic, Pmmm), a=0.8631(3) nm, b=1.7999(6) nm, c=1.2564(5) nm, z=8, D_0=4.76 g·cm~(-3) at 25 ℃, D_x=4.52 g·cm~(-3), and MV_x=146.9 cm·mol~(-1). The valency of samarium in both compounds were determined and confirmed to be +2 by polarographic analyzer and fluorescence spectra.
1993, 9(05): 692-697
doi: 10.3866/PKU.WHXB19930523
Abstract:
The kinetics of the fast reaction between MnO_4~- and diacetone (Hacac) in acidic medium has been studied by the continuous flow-spectrophotometric method. This reaction is second-order overall, and the order with respect to both MnO_4~- and Hacac is one. Activation energy E_α and preexponential factor A has been determined. E_α=4.91×10~4 J·mol~(-1), A=9.75×10~9 mol~(-1)·dm~3·s~(-1). and the relation between k and T is In(k/mol~(-1)·dm~3·s~(-1))=23.0-5.91×10~3/(T/K). A possible mechanism of this fast reaction has been proposed.
The kinetics of the fast reaction between MnO_4~- and diacetone (Hacac) in acidic medium has been studied by the continuous flow-spectrophotometric method. This reaction is second-order overall, and the order with respect to both MnO_4~- and Hacac is one. Activation energy E_α and preexponential factor A has been determined. E_α=4.91×10~4 J·mol~(-1), A=9.75×10~9 mol~(-1)·dm~3·s~(-1). and the relation between k and T is In(k/mol~(-1)·dm~3·s~(-1))=23.0-5.91×10~3/(T/K). A possible mechanism of this fast reaction has been proposed.
1993, 9(05): 698-701
doi: 10.3866/PKU.WHXB19930524
Abstract:
Thermokinetics for a 2-2 reversible reaction system, 2-nitropropane with mor-pholion, have been studied at 25 and 30 ℃ in 40% (v/v) ethyl alcohol aqueous solution by the reduced extent method.
The rate constants、equilibrium constants、activation energies、activation free-energies、activation ethalpies and activation entropies of the reversible reaction have been calculated.
The concept of the reduced extent of thermokinetics and the experimetal results have been discussed in this paper.
Thermokinetics for a 2-2 reversible reaction system, 2-nitropropane with mor-pholion, have been studied at 25 and 30 ℃ in 40% (v/v) ethyl alcohol aqueous solution by the reduced extent method.
The rate constants、equilibrium constants、activation energies、activation free-energies、activation ethalpies and activation entropies of the reversible reaction have been calculated.
The concept of the reduced extent of thermokinetics and the experimetal results have been discussed in this paper.
1993, 9(05): 702-705
doi: 10.3866/PKU.WHXB19930525
Abstract:
Metallothioneins(MTs) are widely occuring proteins characterizied by a low molecular weight (6500—6800) and an extremely high metal and sulfur content. The mechanizm of pulse radiolysis of rabbit liver MT-I in aqueous solution was studied. After pulse radiolysis, two peaks occured with maximum absorption at 450 nm and 280 nm. It was supposed that the first peak was due to RSSR~- radical formed by the combination of RS·radical and RS~- anion. The observed kinetic constants of growth and decay of RSSR~- radical were estimated from the absorption spectra.
Metallothioneins(MTs) are widely occuring proteins characterizied by a low molecular weight (6500—6800) and an extremely high metal and sulfur content. The mechanizm of pulse radiolysis of rabbit liver MT-I in aqueous solution was studied. After pulse radiolysis, two peaks occured with maximum absorption at 450 nm and 280 nm. It was supposed that the first peak was due to RSSR~- radical formed by the combination of RS·radical and RS~- anion. The observed kinetic constants of growth and decay of RSSR~- radical were estimated from the absorption spectra.
1993, 9(05): 706-708
doi: 10.3866/PKU.WHXB19930526
Abstract:
SAPO-5 molecular sieves have been synthesized in the presence of HF and tripro-pylamine as template. The substitute routes was investigated by ~(31)P and ~(29)Si MAS NMR, electron probe microanalysis and XPS technique, which suggested that there is no P—O—Si linkage in the framework. The substitution can occur via (1) silicon substitution for phoshorus and (2) simultaneous substitution of two silicon for one aluminium and one phosphorus. The framework of SAPO-5 consists of phospho-aluminosilicate and aluminosilicate.
SAPO-5 molecular sieves have been synthesized in the presence of HF and tripro-pylamine as template. The substitute routes was investigated by ~(31)P and ~(29)Si MAS NMR, electron probe microanalysis and XPS technique, which suggested that there is no P—O—Si linkage in the framework. The substitution can occur via (1) silicon substitution for phoshorus and (2) simultaneous substitution of two silicon for one aluminium and one phosphorus. The framework of SAPO-5 consists of phospho-aluminosilicate and aluminosilicate.
1993, 9(05): 709-712
doi: 10.3866/PKU.WHXB19930527
Abstract:
The impedance of the electrochemical oxidation of adrenaline on a glassy carbon electrode was measured in sulfuric acid solution from 9 Hz to 15 kHz. These plots of impedance and admittance shown that the electrochemical oxidation of adrenaline is faradaie adsorption reaction. Some kinetic parameters were also determined.
The impedance of the electrochemical oxidation of adrenaline on a glassy carbon electrode was measured in sulfuric acid solution from 9 Hz to 15 kHz. These plots of impedance and admittance shown that the electrochemical oxidation of adrenaline is faradaie adsorption reaction. Some kinetic parameters were also determined.
1993, 9(05): 713-718
doi: 10.3866/PKU.WHXB19930528
Abstract:
Association constants of the complexes CaATP~(2-) and Ca_2ATP, K_1, K_2 and the product of solubility of CaCO_3, K_(sp), in the lecithin-water order system (PC-H_2O) have been measured by potentionmeter using a calcium ion selection membrance electrode. We have observed that formation constant of the complex CaATP~(2-), K_1, in the PC-H_2O order system is larger about an order of magnilude than K_1 in the H_2O, and K_1 (PC-H_2O) increases with the concentration of phospholipid in the PC-H_2O system. But the rate of increase of the K_1(PC-H_2O) is reduced with the increase of the concentration of the lecithin beyend(cmc). However, the formation constant of Ca_2ATP, K_2, does not change obviously in the process of increasing [PC]. When [PC]>[cmc], the K_(sp)(PC-H_2O) of CaCO_3 in the PC-H_2O system is larger than K_(sp)(H_2O) of CaCO_3 in the water. It illustrates that the solubility of CaCO_3 is increased in the liguid crystal order system.
It is expected that the liquid crystal state in biological body is favorable for the absorbtion of calcium.
Association constants of the complexes CaATP~(2-) and Ca_2ATP, K_1, K_2 and the product of solubility of CaCO_3, K_(sp), in the lecithin-water order system (PC-H_2O) have been measured by potentionmeter using a calcium ion selection membrance electrode. We have observed that formation constant of the complex CaATP~(2-), K_1, in the PC-H_2O order system is larger about an order of magnilude than K_1 in the H_2O, and K_1 (PC-H_2O) increases with the concentration of phospholipid in the PC-H_2O system. But the rate of increase of the K_1(PC-H_2O) is reduced with the increase of the concentration of the lecithin beyend(cmc). However, the formation constant of Ca_2ATP, K_2, does not change obviously in the process of increasing [PC]. When [PC]>[cmc], the K_(sp)(PC-H_2O) of CaCO_3 in the PC-H_2O system is larger than K_(sp)(H_2O) of CaCO_3 in the water. It illustrates that the solubility of CaCO_3 is increased in the liguid crystal order system.
It is expected that the liquid crystal state in biological body is favorable for the absorbtion of calcium.
