Photofragment translational spectroscopy of iodobenzene at 266 nm

The photofragmentation of C_6 H_5I at 266 nm is investigated on the nuiversal crossed molecular beam machine, and the translational spectroseopy as well as the angular distribution of I atom is measured. The results reveal that under the laser intensity of 10~8 W/cm~2 the single-phuton dissociation competes with multi-photon processes. In singlephoton dissociation the anisotropy parameter β is 0.4 and the average translational energy is only 1.04 keal/mol, which indicates that this process is a slow predissociation. In two-photon phutofragmentation the average translational energy is 51.64 kcal/mol, which accounts for about 35% of the available energy. Another photofragmentation channel is even more faster, whose peak in time-of-flight spectra corresponds to four or five photon absorptions. The branching ratio of these three channels is determined to be about 3: 3: 4.     

Study on the oscillating phenomena of electrical potential across a liquid membrane

The electrical oscillations across a liquid membrane in water/oil/water system was studied with octanol as oil phase by introducing two opposite charged surfactants in oil and aqueous phase, respectively. The sustained and rhythmic oscillation was observed. To a certain extent, the features of the oscillation (e.g. induction time, frequency, life time and orientation of the pulse pikes) strongly depend on the property of surfactant, dissolved in octanol. The mechanism may be explained by the formation and destruction of dual-ion surfactant membrane accompanying with emulsification at the interface and considering the coupling effect of diffusion and associated reaction in the vicinity of the interface.     

Two-dimensional correlation analysis of continuous online in situ ATR-FTIR on the adsorption of butyl xanthate at the surface of α-PbO

The adsorption behavior of butyl xanthate on the surface of lead oxide was investigated using continuous online in situ attenuated total reflectance Fourier transform infrared(ATR-FTIR) spectroscopy technique and two dimensional(2D) correlation analysis.The adsorbed layer studied was prepared by coating α-PbO particles onto the surfaces of the ZnSe crystal.The appearance of spectral peaks at 1203 cm~(-1),1033 cm~(-1) and their red shift indicated the formation and aggregation of xanthate at the surface of α-PbO.According to 1R intensity changes after rinsing with deionized water and a NaOH solution,the adsorption was proved to be a chemisorption type.The competition between xanthate and OH for the surfaces leads to desorption of xanthate at higher pH.The technique of 2D correlation ATR-FTIR spectroscopy was used to evaluate the changing order of spectral intensities in the adsorption process,and the results indicated that xanthate micelles were formed at the surfaces.The adsorption kinetics of butyl xanthate was found to be a pseudo-second-order reaction model and the adsorption capacity of butyl xanthate at α-PbO was as high as 281 mg g~(-1) after 150 min.     

Cloud point phenomenon in aqueous mixtures of cationic-anionic surfactants

It used to be held that the cloud point phenomenon was only a characteris-tic of nonionic surfactants alone. Such phenomenon is rarely observed in ionicsurfactants. The present study shows that the mixture of cationic-anionic surfac-tants not only has a krafft point which is the characteristic of an ionic surfactant,but also exhibits the cloud point phenomenon obviously at certain concentrations.     

Characters of the Plateau of Methanol Increment in Frontal Analysis in Reversed Phase Liquid Chromatography

With insulin methanol-water,and the ion-pairing agent,hydrochloric acid and trifluroacetic acid(TEA),the character of the first plateau(FP)on the elution curve of frontal analysis in reversed phase liquid chromatography(RPLC)was investigated by on-line UV-spectrometry and identified with nuclear magnetic resonance(NMR) spectrometry and mass spectrometry.The profile of the FP is the same as that of a usual elution curve of methanol in frontal analysis(FA).When the insulin concentration was limited to a certain range,the height of the FP was found to be proportional to the insulin concentration in mobile phase and its length companying to shorten,The FP profile on the intersection of two tangents reflects the components of the microstructure in the depth direction of the bonded stationary phase layer and the desorption dynamics of the displaced components.The displaced methanol was quantitatively determined by NMR and on-line UV spectrometries.TFA with high UV absorbance can not be used as an ionpairing agent for the investigation of the FP in RPLC,but if can be used as a good marker to investigate the complicated transfer process of components in the stationary phase in RPLC.A stoichiometric displacement process between solute and solvent was proved to be valid in both usual and FA in RPLC.From the point of view of dynamics of mass transfer, the solutes can only contact to the surface of stationary phase in usual RPLC,while solute can penetrate into it in FA of RPLC.The solvation of insulin in methanol and water solution as an example indicating the usage of the FP in the FA was also investigated in this paper.     

A New Expert System for Structural Interpretation of IR Spectra

A new expert system has been developed which can be used to aid chemists in structural interpretation of infrared spectra. The system consists of five essential portions: knowledge-base , inference engine, database, knowledge-acquisition module and explanatory interface. The system is implemented in Turbo PROLOG artificial intelligence language. Compared with other spectral interpretation systems this system is of the following advantages, i. e. the system has a friendly user interface, two kinds of methods for managing toowledge-base, several useful explanatory facilities such as why and how should explanation be made, etc. ; in addition, it can be run on the IBM PC/XT and its compatible microcomputers. Another important feature of the system is that it can simulate the reasoning procedure by which experienced chemists may interpret spectra as well as deduce complete molecular structures. So the system can also be used as a helpful learning tool for training chemistry students in IR spectrum interpreta     

A STUDY ON NUMERICAL SIMULATION OF CLOUD MERGERS AND INTERACTIONS

A two-dimensional, time-dependent and warm cumulus cloud model has been used to investigate problems concerning cloud merger and interaction. The results of numerical experiment show: (ⅰ) Two clouds formed at the same time have influence on each other at a shorter distance;on one hand, it is possible that they merge with equal intensity, and on the other, it is impossible that they merge with unequal intensity;in case of quite different intensities the weak cloud is depressed and the strong cloud accretes. (ⅱ) Two clouds, developing with timing difference at a shorter distance and in the same growth stages, may merge. (ⅲ) The merged cloud develops more violently than the unmerged and produces more rainfall. (ⅳ) Cloud merger results from the action of a horizontal pressure gradient accompanied with a circulation field in the lower layer of clouds.     

Application of Single—labelled Probe—primer in PCR Amplification to the Detection of Hepatitis B Virus DNA

A new method based on the incorporation of a single-lablled probe-primer into polymerase chain reaction(PCR) for the detection of PCR-amplified DNA in a closed system is reported.The probeprimerc consists of a specific probe sequence on the 5‘‘‘‘‘‘‘‘-end and a primer sequence on the 3‘‘‘‘‘‘‘‘-end.A flurophore is located at the 5‘‘‘‘‘‘‘‘end.The primeR-quencher is an oligonucleotide,which is complementary to the probe sequence of probe-primer and labelled with a quencher at the 3‘‘‘‘‘‘‘‘-end.In the duplex formed by probe-primer and primer-quencher.the fluorophore and quencher are kept in close proximity to each other.Therefore the fluorescence is quenched.During PCR amplificatio,the specific probe sequence of probeprimer binds to its complement within the same strand of DNA,and is cleaved by Taq DNA polymerase,resulting in the restoration of fluorescence.This system has the same energy transfer mechanism as molecular beacons,and a good quenching effciency can be ensured.Following optimization of PCR conditions,this method was used to detect hepatitis b virus(HBV) dna in patient sera.This technology eliminates the risk of carry-over contamination,simplifies the amplification assay and opens up new possibilities for the real-time detection of the amplified DNA.     

Investigation of the Crystallization Kinetics of Zn(Met)(AcO)_2·H_2O in Mixed Solution of Water and Acetone by Microcalorimetry

Introduction The complexes of zinc salts with -amino acid as additive have a wide application in medicine, foodstuff and cosmetics.1-3 The synthesis methods of the com-plexes of zinc salts with -amino acid have been re-viewed.4 The solubility of Zn(AcO)2-Met-H2O system at 298.15 K has ever been investigated by the semi-micro-phase equilibrium method.5 The phase diagram is a simple one, in which the solid complex of Zn(AcO)2 and Met can not be obtained at 298.15 K. Zn(Met)2+ in solution w…     

Development and Validation of Spectrophotometric Methods for the Determination of Cefetamet in Pharmaceutical Dosage Forms

Two simple and sensitive spectrophotometric methods for the determination of cefetamet in either pure form or in its pharmaceutical formulations were described. The method Ⅰ is based on the interaction of 3-methylbenzo[d]- thiazolin-2-one hydrazone （MBTH） with cefetamet in the presence of freshly prepared ferric chloride in a neutral medium. The resulting blue colored product has λmax at 628 nm. The method Ⅱ describes the reduction of ferric ion by the drug to ferrous ion followed by a complex formation reaction with 1,10-phenanthroline （1,10-phen） to form an orange red colored chromogen exhibiting 2max at 510 nm. The products are stable for more than 5 and 8 h respectively. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed methods. Both methods are highly reproducible and have been applied to a wide variety of pharmaceutical preparations and the results are comparable with those of official methods.     

Staircase pulse voltammetry

The faradaic current of interest can often be obscured by some extraneous current. A new method called staircase pulse voltammetry (SPV), with which involving a potential pulse is superimposed on a staircase, is used for removing the double-layer charging current. This paper presents the theoretical consideration and the experimental evidence of this method for a simple reversible system and a catalytic process. The parameters affecting currents are also discussed. Experimental verifications are in agreement with the theories.     

Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

Chemo-and regioselective hydroboration of △^14,15 in certain cephalostatin analogue

The symmetrical diketone Ⅱ, which can be synthesized in gram scale using a well established method, was used as a starting material to prepare the 11α-methoxy ketomethylene Ⅵ. This is in continuation of our study aiming at the synthesis of multihydroxylated cephalostatin analogues, as for example cephalostatin 1Ⅰ, a potent anti-tumor natural product. Compound Ⅵ underwent chemo- and regioselective hydroboration reaction at only one of △14.15 double bonds furnishing compound Ⅸ as a major product in a fair yield.     

Synthesis of Acetic Acid on Pd-H_4SiW_(12)O_(40)-Based Catalysts by Direct Oxidation of Ethylene

Synthesis of acetic acid by direct oxidation of ethylene on Pd-H4SiW12O40-based catalysts was studied in a fixed-bed integral reactor and a pulse differential reactor. From the performance of the catalysts with different compositions and configurations, it is proposed that acetic acid is predominantly produced via an intermediate of acetaldehyde. This can be easily confirmed by comparing the product distributions in the integral and the differential reactors. The active sites for acetic acid formation are considered to exist mainly at the boundaries between the H4SiW12O40 and the Pd particles. The Pd-based catalysts reduced by H2/N2 have higher activities than those reduced by hydrazine, as explained by the degree of Pd dispersion obtained from the characteristics of hydrogen chemical adsorption. It was found that the Pd-Se-SiW12/SiO2 catalyst with selenium tetrachloride as a precursor was more active than that with potassium selenite, and that the acetic acid yield can be greatly increased by adding a s     

Molecular dynamics study of the nucleation behavior and lamellar mergence in polyethylene globule crystallization

The site order parameter (SOP) has been adopted to analyze various orders of structure formation and distribution during the crystallization of a polyethylene globule simulated by molecular dynamics. The SOP not only identifies different orders among the structures but also different phases. The results showed that intermediate structures with medium order exist unevenly in the early stage of nucleation, which differs from traditional models. We found that the nucleation relies on crystallinity fluctuations with increasing amplitude, and a baby nucleus with different shape and increasing size suddenly appears in the fluctuations. Once its size is large enough, the baby nucleus becomes the nucleus. In the growth stage, a number of lamellar mergences were observed and their selective behaviors were related to the orientation differences between the lamellae to be merged. The SOP distribution of all atoms in the system during crystallization had two peaks: one for the amorphous phase and the other for the crystalline phase. The intermediate structures with medium orders are located between the two peaks as an order promotion pathway. The data show that the medium order structure fluctuates at the growth front and is not always available, and that the medium order structure existing at the front is not always good for development. It is possibly caused by chain entanglement. Structure fluctuation at the growth front enables the system showing thousands of the most probable configurations to approach the precursor. The growth front is thus active for a while and inactive at other times.     

TRANSPORTATION THEORY OF MULTIPLE SCATTERING AND ITS APPLICATION TO SEISMIC CODA WAVES OF IMPULSE SOURCE

The energy distribution of elastic waves in an infinite elastic medium with uniformly and randomly distributed scatterers has been researched. The scattering process is assumed to be isotropic and without conversions between wave types. We get the equation on the distribution of energe density in time and space covering single as well as multiple scattering. Taking physical symmetry of the field into account, it can be simplified. In the case of small earthquakes, the energy source of elastic waves can be assumed as a short pulse emitted isotropically at t=0. The first-order approximate solution in the 3-dimensional space can be obtained, and it is equivalent to Sato's solution for single scattering. In the 2-dimensional space the complete analytical solution has been derived by the mathematical inductance which leads to a conclusion that the codas of surface waves can give the Q-factor related to intrinsic absorption. The equation obtained in this paper is more general.     

Design and Synthesis of Chiral Molecular Tweezers Based on Deoxycholic Acid

Molecular tweezers is a novel type of artificial receptors, which not only offer the advantage of efficient construction but also their surfaces can be tailored for specific applications. The clefts of molecular tweezers are particularly effective in regard to complementarity with substrates since functional groups attached to the interior of the cleft converge on substrates held inside1. So, in recent years, the molecular tweezers receptors have attracted more and more attention in molecular …     

Selective Oxidation of Propane by Lattice Oxygen of Vanadium-Phosphorous Oxide in a Pulse Reactor

Selective oxidation of propane by lattice oxygen of vanadium-phosphorus oxide (VPO) catalysts was investigated with a pulse reactor in which the oxidation of propane and the re-oxidation of catalyst were implemented alternately in the presence of water vapor. The principal products are acrylic acid (AA),acetic acid (HAc), and carbon oxides. In addition, small amounts of C1 and C2 hydrocarbons were also found, molar ratio of AA to HAc is 1.4-2.2. The active oxygen species are those adsorbed on catalyst surface firmly and/or bound to catalyst lattice, i.e. lattice oxygen; the selective oxidation of propane on VPO catalysts can be carried out in a circulating fluidized bed (CFB) riser reactor. For propane oxidation over VPO catalysts, the effects of reaction temperature in a pulse reactor were found almost the same as in a steady-state flow reactor. That is, as the reaction temperature increases, propane conversion and the amount of C1 C2 hydrocarbons in the product increase steadily, while selectivity to acrylic acid and to acetic acid increase prior to 350℃ then begin to drop at temperatures higher than 350℃, and yields of acrylic acid and of acetic acid attained maximum at about 400℃. The maximum yields of acrylic acid and of acetic acid for a single-pass are 7.50% and 4.59% respectively, with 38.2% propane conversion. When theamount of propane pulsed decreases or the amount of catalyst loaded increases, the conversion increases but the selectivity decreases. Increasing the flow rate of carrier gases causes the conversion pass through a minimum but selectivity and yields pass through a maximum. In a fixed bed reactor, it is hard to obtainhigh selectivity at a high reaction conversion due to the further degradation of acrylic acid and acetic acid even though propane was oxidized by the lattice oxygen. The catalytic performance can be improved inthe presence of excess propane. Propylene can be oxidized by lattice oxygen of VPO catalyst at 250℃, nevertheless, selectivity to AA and to HAc are even lower, much more acetic acid was produced (molar ratio of AA to HAc is 0.19:1-0.83:1) though the oxidation products are the same as from propane.     

Kinetics and Mechanism of Oxidation of Lactic Acid by Dihydroxyditelluratoargentate（Ⅲ）in Alkaline Medium

The kinetics of the oxidation of lactic acid(Lac) by dihydroxyditelluratoargentate(Ⅲ）[abbreviated as DDA of Ag(Ⅲ）]anions was studied in an aqueous alkaline medium by conventional spectrophotometry in a temperature range of 25-40℃.The order of the redox reaction of lactic acid and DDA was found to be first-order.The rates increased with the increase in [OH^-]and decreased with the increase in [tellurate].No free radical was detected.In the view of this the dihydroxymonotelluratoargentate(Ⅲ）species(DMA) is assumed to be the active species.A plausible mechanism involving a two-electron transfer is proposed,and the rate equation derived from the mechanism can be used to explain all the experimenttal results.The activation parameters(25℃）and the rate constants of the rate-determining step along with the preequilibrium constants at different temperatures were evaluated.     

Self-supported Ni2P nanosheets on low-cost three-dimensional Fe foam as a novel electrocatalyst for efficient water oxidation

Electrochemical water splitting into hydrogen and oxygen is a promising strategy for future renewable energy conversion devices.The oxygen evolution reaction(OER)is considered as the bottleneck reaction in an overall water splitting system because it involves 4e~- and 4H~+ transfer processes.Currently,it is highly desirable to explore low-cost alternative catalysts for OER at ambient conditions.Herein,we report for the first time that nickel phosphide(Ni_2P)nanosheets can be facilely grown on Fe foam(FF)as an efficient electrocatalyst for OER with excellent durability and catalytic activity under alkaline conditions.To reach a current density of 10 m A/cm~2,the Ni_2P-FF catalyst required a low overpotential of only 198 mV for OER.The catalyst’s high OER activity and durability were well maintained at a high current density.The required overpotentials were only 267 and 313 mV to achieve the current densities of 100 and 300 m A/cm~2,respectively.The combination of low-cost Fe foam with Ni_2P provides a promising low-cost catalyst for large-scale application of electrocatalytic water splitting.