1996 Volume 12 Issue 1
In absence of catalysts, Oscillations in the oxidation of KSCN、Na2S2O3 and SC(NH2)2 by H2O2 are observed in CSTR experiments, single-peak and other phenomena are observed in batch experiments. Oscillations in pH and Pt potential are antiphase in H2O2-Na2S2O3-H+ system and H2O2-KSCN-OH- system, but oscillations in pH and Pt potential are synchronous in H2O2-SC(NH2)2-H+ system.
The solubilities of C60 and C70 in toluene, o-xylene and CS2 between melting point and boiling point have been measured. The temperature-dependent solubillty of C60 displays the anomalous behavior. A solubility maximum of C60 around O℃ for toluene and CS2, and around 30℃ for o-xylene was observed. The temperature-dependent solubility of C70 displays the normal behavior in the same solvents.
Relativistic density-functional calculations on free Hg2, Hg4, Hg8, Pb2 and Pb4 clusters, and those clusters embedded in an alkali (A) atom surrounding are reported. Heavy metal-metal (M-M) distances, binding energies and effective charges have been calculated. The Hg-Hg distance in the weakly bound free clusters is over 330 pm. Upon embedding in an alkali surrounding, the bonding is strengthened; the bond lengths are reduced for square planar Hg4 to below 300 pm. The bonding in the hypothetical tetrahedral alkali-mercury cluster appear to be quite different, where Hg4 will under a transition to four Hg1. This explains the strict preference of square over the tetrahedral geometry of Hg4 clusters in amalgams. Pb4 is predicted to be stable in a pure cluster and does not show significantly different bonding feature in the lead-alkali crystal. The effective charges on Hg and Pb are calculated to be -0.4 and -0.6, respectively. The bonding characteristics are also examined by calculation of the M4-An interaction energies. The amalgamation energies lie in the range of 50 to 70 kJ/molHg. The formation energy of alkali-Pb is up to 150 kJ/molPb, much stronger than that of alkali-Hg.
TiO2-Al2O3 composites (TiO2 content is 0.08gTiO2/gAl2O3) were prepared by two methods: mixing gel and coprecipitation, and characterized by XRD, XPS, and LRS. The results show that γ-Al2O3 is the only species of crystal to be identified by XRD for both samples treated at 550℃ for 5 hours, but the forms of TiO2 are different. TiO2 is dispersed on the surface for the sample by mixing gel. As to the composite by coprecipitation, TiO2 is dispersed so well in the bulk that it is difficult to be detected by XRD or LRS.
The intramolecular electron transfer of TTP-(CH2)n-Pc was studied by means of time correlated single-photon counting method. When the Pc subunit of the compound is excited, the fluorescence of the compound is quenched by intramolecular electron transfer and the electron transfer is most favorable in the compound with n=4. When the TTP subunit of the compound is excited, the fluorescence decay of the compound will be biexponential, which shows the existence of an electron transfer process. Some kinetic parameters were derived from the experimental data. With n increasing, the activation energy and the reorganization energy increases whereas the electron transfer rate decreases. Moreover, the free enthalpy change of electron transfer reaction △G CS and the charge-separated rate kCS are in the order of:
△G CS (5) >△G CS (3) >△G CS (4) >△G CS (2)
kCS (2) >kCS (3) >kCS (4) >kCS (5)
The difference between the order of △G CS and of electron transfer rate can be interpreted according to Marcus theory.
The CIDEP of photolized р-benzosemiquinone and 2-hydroxy-2-propyl radicals was measured with time-resolved ESR spectrometer. The CIDEP of р-benzosemiquinone radical is belong to TM mechanism. The influence of microwave power and solution concentration on evoluation was investigated. The condition of spin polarization of 2 hydroxy-2-propyl radical, which is belong to RPM mechanism, was investigated.
The electrochemical behaviours of the hydrogen evolution reaction (HER) on electrodes prepared by composite coating of nanocrystalline Ni-Mo alloy particles which was formed by ball miling on nickel base has been studied by steady-state polarization and ac impedance techniques. The microstructure and the particle size of Ni-Mo alloy nanocrystals and the morphology of the composite-coated surface of the electrodes were examined by XRD, TEM and SEM. The mechanism of HER on the composite electrodes has been investigated as well. Results showed that for HER the nanocrystalline Ni-Mo alloys prepared by high-energy ball milling revealed high electrocatalytic activity which was enhanced with increasing milling time. The reaction rate of HER on the electrodes was proved to be controlled by electrodesorption. The direct composite coating of highly electroactive particles onto the surface may serve as a new approach to the preparation of electrode materials.
Abstraction of terminal hydrogens on a diamond (100) surface by atomic hydrogen has been considered as a possible rate-determining elementary step in the mechanism of low-pressure diamond growth by chemical vapor deposition. The author used MNDO(UHF) methods to estimate the potential barrier for this abstraction reaction. It is predicted that the theoretical values of the potential barrier for H abstraction from full dihydride (100)-(1×1):2H and monohydride (100)-(2×1):H diamond surface are 71 and 59kJ•mol respectively. The potential barrier for H abstraction from diamond (111) surface is smaller than those of diamond (100) surfaces. This results indicated that the creation of radical sites on diamond (111) surface via H abstraction is easier than that on (100) surface under the same growing condition. This conclution therefore supports the experimental result that the relative growth rate of (111) surface is greater than that of (100) surface.
The cathodic adsorption beheaviors of thiourea and 4 of its derivatives on iron in hydrochloric acid and sulphuric acid were investigated by polarization curves. The accordance of the adsorption beheavior of thiourea on iron in sulphuric acid with Temkin isotherm was deduced from hynamics, and the thiourea took part in the reaction of HER, this phenomena is a negative catalytic effect. The adsorption beheavoris of thiourea and its 4 derivatives on iron in hydrochloric acid was found to be in accord with Langmuir isotherm and this conclusion was deduced from thermodynamics, this phenomena is a blocking effect.
The two dimensional Wide Angle X-ray Scattering (WAXS) coherent intensity of oriented non-crystalline polyethylene tetrephthalate (PET) is determined by Symmetrical Transmission method; Besides, self-compiled WAXS Multi-peak Separation program 90 (MPS90) is used as well to separate the overlapped peaks at WAXS coherent intensity curves obtained at different azimuthal angles, thereof resulting in the two peaks caused by intermolecular atomic scattering, A(K=0.126) and B(K=0.169), and the other fives by intermolecular atomic scattering such as: C(K=0.304), D(K=0.553), E(K=0.374), F(K=0.465) and G(K=0.606)(K unit: nm-1), of which the origin of structure and the curves of primary peak parameters as a function of azimuthal angles are analysed in detail, thus obtaining the fine structural imformation from oriented non-crystalline PET.
The supramolecular assemblies consisting of metal-free tetra(N-trimethylaminobenoxy) phthalocyanate (H2TAPc) and its zinc complex (ZnTAPc) as well as metal-free tetra (4-sulfonatophyenyl) porphyrin (H2TSPP) and its zinc complex (ZnTSPP) in solution were studied by absorption spectroscopy. The stoichiometries of the hetero-aggregates were ascertained by Job’s photometric titration plots, indicating that the aggregates were either face to face heterodimers or sandwich structure heterotrimers. The composition of the hetero-aggregates are controlled by the affinity of the central metal ion of each chromophore for axially bound coordinating solvent molecules. The fluorescence of porphyrin and phthalocyanine in the supramolecular system are quenched by each other. The transient absorption spetra of cationic porphyrin radical (around 600-650nm region) and anionic phthalocyanine radical(around 550-600nm) were observed by nanosecond laser photolysis. The results indicated that intermolecular photoinduced electron transfer process from excited triplet state between the porphyrin and the phthalocyanine occured in the supramolecular system.
The limiting solubilization amount of aqueous solution of electrolytes, including NaCl, KCl, NaBr, NaI, CaCl2 and Na2SO4 in carbon tetrachloride solution of dodecylammonium propoinate was determined as the added amount of aqueous solution at which turbidity began to be visible. All of the results showed that with increasing concentration of electrolytes, the limiting solubilization amount of aqueous electrolyte solution increased first followed by decreased. This phenomenon could be explained as follows. When electrolyte was present in water pool of reverse micelle, it makes easier for surfactant molecules that surrounding the water pool to migrate to organic phase because of salting-out effect, thus the reverse micelle was expanded. This effect increased with increase of electrolyte concentration. On the other hand, surfactant molecules migrating easier to organic phase implies that the force making surfactant molecules to stick on the surface of water pool became weaker. When electrolyte concentration increased to a certain extent, this force became too weak to keep the reverse micelle, thus the limiting solubilization amount of aqueous solution decreased. According to simplified spherical reverse micelle model, the aggregation number as well as the radii of water pool of reverse micelle have been calculated for aqueous sodium chloride solution of different concentrations. The results support the above explanation.
The photochemical and photophysical behaviors of tri(4-tert-butoxycarbonyl oxyphenyl) sulphonium salts have been investigated. In ar n-satureted acetonitrile, the quantum yields of Bronsted acid formed during photolysis of these compounds was abount 0.5. In the transient absorption spectrum excited by 266nm in mathanol and dioxane an evident absorption peak at 360 nm decayed in accordance with pseudo-first-order reaction was observed. In the presence of poly-p-hydroxystyrene or diphenyl sulphide, the apparent second-order reaction decay rate constsnts were 107 and 108 L﹒mo-1﹒s-1, respectively. Results indicated that the transient absorption peak at 360nm was attributed to the diphenyl sulphide radical cations formed in photolysis of sulphonium salts, which were proposed by abstraction of hydrogen from solvent or polymer to yield the photonic acid and diphenyl sulphide as listed in eqns. (1) and (2). The influence of non-nuncleophilic anions of title compounds on their photochemical behavior was just less important.
Highly oriented Bi4Ti3O12 thin films were prepared by Sol-Gel technique on SrTiO3(100) single crystal, using Bi(NO3)3.5H2O, Ti(OC4H9)4 and CH3COOH as raw materials. The c-axis orientation was about 96%. The effect of pH value of solution on quality of the thin films was studied.
Rules of molten salt phase diagrams of binary system MeX-Me’X4 (Me is monovalent metal, Me’ quadrivalent metal, X halides) were investigated using chemical bond parameter and pattern recognition-artificial neural networks method. Formability of intermediate compounds, chemical stiochiometry, melting type (congruent or incongruent) of intermediate compounds Me2Me’X6 and MeMe’X5 were summarized and predicted, the results were of od reliability.
The rhodium-phosphine complex catalyst Rh(CO)(acac)(PPh3)(Ⅰ) for 1-hexene hydroformylation was studied under the following reaction conditions: CO/H2=1(mole rate), pressure 1.0 MPa, temperature 25-120℃, by using the pressurized in-situ 1H NMR technique. Experimental results indicated that the formation of a rhodium hydride complex from (Ⅰ) began at room temperature and its amount increased with increasing of reaction temperature. This intermediate complex began to decompose at 100℃ and disapeared completely at 120℃. The intensity change of the proton signal was parallel to catalytical activity in hydroformylation of olefins. Under pure CO pressure the proton signal of Ph-H bond was not observed. There was a 0.2 ppm difference in proton chemical shifts of Rh-H bond under pure H2 pressure and under H2+CO pressure. The results showed that the rhodium-hydride carbonyl complex is the active intermediate in the industrial hydroformylation process.
Molar conductances of NaCl and KCl in 0~100%(ω/ω) CH3OH-H2O have been measured by using the alternating conductance bridge method resembling that of Shedlovsky. The results show that the limiting molar conductances (Λ0) of both NaCl and KCl have the lowest curve points around 55%(ω/ω) CH3OH and the limiting molar conductances (Λ0) of KCl are larger than that of NaCl in 0~100%(ω/ω) CH3OH-H2O mixtures, which can be accounted for in terms of the micro-structure and ionic solvated situation of NaCl and KCl aqueous methanol solution. Furthermore, experimental limiting molar conductances (Λ0) for KCl-CH3OH-H2O system in this work are critically compared with that of Amis, which shows that measured results in this work are more reliable.
A new permeability coefficient equation was theoretically derived. It contains both the acid concentration of feed solution and the carrier concentration as well as the acid concentration of stripping solution. The relationship of permeability coefficient and acid concentration of stripping solution was further confirmed by the experimental results of Co2+、Ni2+、 Er3+ ions transporting through the supported liquid membranes.
γ-alumine membranes supported by porous titanium plate were prepared by sol-gel techniqe with alumina isopropoxide. The factors, which influenced membrane per formance, in the membrane preparing process were investigated. A dynamic flow-weighted active pore size distribution apparatus for inorganic membrane were set-up on the basis of Kelvine equation. The results showed that for composite porous membrane the active pore size distribution is about 6-8nm, the most probable pore size is about 7nm and nitrogen permeability is 7.1×10-6mol﹒m-2﹒Pa-1﹒s-2.
We used CD spectroscopy to study the conformations of three cyclic peptides (CP10E: cyclo[Glu(OBz1)-Pro-Gly-Glu(OBzl)-Gly]2, CP10K: cyclo[Lys(Z)-Pro-Gly-Lys(Z)-Gly]2, CP12K: cyclo[Phe-Lys(Z)-Pro-Gly-Lys(Z)-Gly]2 and their correspondent linear peptides (LP10E: Boc-[Glu(OBzl)-Pro-Gly-Glu(OBzl)-Gly]2-OPac, LP10K: Boc-[Lys(Z)-Pro-Lys(Z)-Pro]2-OMe, LP 12K: Bao- [-Lys(Z)-Pro-Gly-Lys(Z)-Gly]2- OMe) in three solvents of different polarity (chloroform, acetonitrile, 2,2,2-triliuroethanol), and it was found that all of linear and cyclicpeptides exists asγ-turn conformation in chloroform, however, in TFE& CH3CN solutions, the three linear peptides are inβ Ⅱ-turn conformations. CP10E isβI-turn conformation, CP10K &CP12K exists in more than one types of turn conformations. On the basis of our experiments, it was concluded: 1) In the presence of conformational constrained amino acids short linear peptides form obvious secondary structure; 2)The solvent polarity has influence on the peptide conformation and this influence on linear peptides is greater than that on cyclic peptides; 3)The backbone of cyclic peptide has constraint effect on its conformation and makes the secondary structure of cyclic peptide different from that of its relative linear peptide. This information might give some cules in the design of bioactive peptides with different receptor selectivity.