2005 Vol. 18, No. 3

Review
NMR technologies such as relaxation, self-diffusion coefficient and other NMR methods were reviewed. The results of NMR measurements, especially, on 1H, 13C, 19F-NMR spectra and quadrupolar echo of 2H-NMR spectra on self-assembled properties and structures have been obtained. The investigations on the self-assembly of amphiphiles and the transition of selfassembled structures were introduced and the determination of NMR measurements on micelles, vesicles and microemulsions was summed.
Letter
The frontier molecular orbitals (HOMO and NHOMO) of CF2BrCl molecule have been firstly investigated by (e,2e) electron momentum spectroscopy. The experimental momentum profiles are compared with the theoretical profiles employing Hartree-Fock and density functional theory with 6-31G and 6-311+G(d) basis sets. Both HF and DFT calculations using 6-311+G(d) basis set can well describe the experiment, whereas those calculated using 6-31G basis set largely underestimate the experiment at the low momentum region. Furthermore, orbital electron density images show that HOMO and NHOMO have a mixed character of the bromine and chlorine lone pairs.
Article
Tunable intense Vacuum Ultraviolet (VUV) laser was generated by two-photon resonant four wave difference frequency mixing (ω-=2ωUV-ωT) in Xenon. In the experiment some resonance attenuations of the VUV were observed at certain difference frequencies. These attenuations occur when the sum frequencies ω+=2ωUV+ωT coincide with excited ns (n=10,11) and nd (n=8~13) states. The third order linear susceptibility χ(3)(2ωUV+ωT;ωUV,ωUV+ωT) is reasonably increased by the double resonance enhancement, so the conversion efficiency of sum frequency mixing can be very high and the power of the pump laser is decreased and thus the difference frequency output is attenuated.
The 4f electronic transition accompanied by electron-phonon interaction was studied through the Brownian oscillator model in Nd∶YAG. The expression of electron-phonon coupling was derived, the excitation spectroscopies of different electron-phonon coupling constants were calculated and the results indicated the absorption peak of phonon in two sides of electronic peak is produced by electronphonon coupling. The stronger electron-phonon coupling, the more phonon peaks. Through excitation spectroscopy simulation, the electron-phonon coupling constant and phonon frequency were obtained. From these data, the theoretical time resolved coherent spectroscopy was calculated and is good agreement with experiment result. It also indicated that the electron-phonon coupling in rare earth ion’s 4f electronic transition is weak because of the smaller constant of electronphonon coupling compared with that of semiconductor.
An orthogonal injection (OI) home-made reflectror type time-of-flight (TOF) mass spectrometer has been constructed with a matrix-assisted laser desorption/ionization (MALDI) source. Ions generated by MALDI are measured using a pulsed voltage delayed extraction method. The laser used is a frequency quadrupled Nd:YAG laser with output at wavelength of 266 nm, the matrix used here is 2,5-dihydroxybenzonic acid (DHB), and the analytes are Malachite green and peptides. Measurements of resolving power and statistical evaluation of the mass accuracy are reported here. The results indicate that resolving power in the range of 3400 to 4000 (full width at half maximum), the average error of the mass accuracy is below 0.0075%, A perfectly linear (m/z)1/2 versus t plot is found. Finally, the initial velocity distribution of analyte and matrix ions in the range of 400~1000 m/s is measured.
Based on Fourier-transform intra-cavity laser absorption spectroscopy (FT-ICLAS) setup reported, a signal differential module is introduced to reduce the noise rising from the fluctuation of the laser power and to improve the quality of the interferogram obtained in the experiment. The capability to do quantitative measurement was demonstrated by recording the atmospheric oxygen absorption near 760 nm. The v=6 local mode stretching overtone spectra of phosphine were recorded with different sample pressure. The pressure caused self-broadening and line shift parameters of this band were achieved.
The internal energy distributions of product CaBr in the collision reactions Ca+C2H5Br and Ca+nC3H7Br are studied by using the quasiclassical trajectory method. The average vibrational, rotational and translational energies and total available energies of the product CaBr molecules are calculated. The results indicate that when the collision energy is equal to 7.54 kJ/mol the energy of product CaBr is mainly the vibrational energy. As the reactant collision energy increases, the average translational and rotational energies of the product CaBr increase, the average vibrational energy decreases slightly, and the most probable vibrational state shifts to lower vibrational energy levels. The internal states of reagents have little influence on the internal energy distribution of the product. The bigger the radical group is, the higher ratio of the vibrational energy to the available energy of the product is. There exist two competitive reaction paths for the collision reactions Ca+C2H5Br and Ca+nC3H7Br, the migratory encounter and direct reaction paths. The former produces high vibrational excited state product CaBr and the latter causes C-Br bond to break. When the collision energy increases, the reactions tend to the latter path.
By comparing the ready experimental results with the calculated results obtained at 7 basis sets and 3 theoretical levels, respectively, for the tautomeric form Cyt1 of cytosine, the relatively accurate B3LYP/6-311+G** theoretical method to study the tautomerism of cytosine was chosen. The ground-state structures of 8 tautomers of cytosine were fully optimized at B3LYP/6-311+G** level, and the tautomerism of 6 relatively stable tautomers of cytosine was studied. The frequency analysis was performed on all the optimized structures. For the groundstate geometries, all the calculated frequencies are real; for the transition-state geometries, there is only one imaginary frequency for each structure. Detailed Intrinsic Reaction Coordination calculations were carried out to guarantee the optimized transition-state structures being connected to the related tautomers. All the energies given include the zero-point energy corrections. The theoretical results can give a reasonable interpretation for the experimental results.
The results of the quantum chemistry study of the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]+[BF4]-) were reported. The ab initio method and density functional theory (B3LYP method) was used to optimize the stable structure of the gas phase ion pair at the level of 6-311++G** basis set, respectively. An IR spectra for [EMIM]+[BF4]- were obtained through the vibrational analysis. The changes of atomic charge assignments have been investigated using the Natural Bond Orbital method. The computational results show that there exist hydrogen bonds and other weak interactions between the cation and the anion. Using counterpoise correction method to estimate the basis set superposition error, the interaction energy between the cation and anion is 346.78 kJ/mol.
The chemical adsorption of Benzene on Pt under the effect of water has been fulloptimally computed with density functional B3LYP/LanL2DZ from Gaussian 98(A.9 version). The result showed the adsorption of benzene on Pt is a spontaneous process. The adsorption energies are -149.6535 and -202.1635 kJ/mol respectively in two cases, without water and in water. The adsorption energy is decreased in water solvent and the effect of water solvent is shown. The transition state of the transfer Pt on benzene was found by QST2 computation, and corresponding transfer active energies are 61.2537 and 70.8356 kJ/mol without water and in water respectively.
Based on atomic and molecular reaction statics and group theory, the density functional method (B3P86) with basis sets SDD** for Pd and 6-311G** for H(D and T) have been used, and the ground states of H2(D2,T2) and PdH(PdD,PdT) are derived to be 1Σ+g(D∞v) and 2Σ+(C∞v), respectively, the dissociation energy of H2(D2,T2) and PdH(PdD,PdT) are 4.5918 and 2.6268 eV, respectively. The △Hf°,△Sf°and △Gf° from those reactions and the relationship of the equilibrium pressure with the temperature are obtained. It indicates that these results have good accordance with experimental data.
The stability and diffusion behaviors of 1.3 MPa Pt, Pd, Ni and Cu clusters supported on Pd(001) surface were studied by the Monte Carlo method. The support surface can strongly influence the stability and diffusion behaviors of the supported clusters. The structure transition temperatures of the supported clusters are much lower than the melting temperatures of their corresponding free clusters due to the vibration coupling between the support and the clusters. The stability of the supported clusters depends on not only the strength of metalsupport interaction but also the strength of the metalmetal interaction. The diffusion constants of supported 1.3 MPa clusters are similar to those of corresponding metal atoms. Combining the diffusion parameters with the critical temperature of the supported clusters, the thermal stability is closely related to the diffusion behaviors of the metal clusters.
By the molecular mechanics/quantum mechanics method, the geometry distortion and configuration invalidity of dimmer C60fullerene (2C60) molecule in external electric field are simulated. The effect of the electric field, with three different directions, on geometry distortion, configuration invalidity, polarization charge distribution and dipole moment for 2C60 molecule is discussed systemtically. Further the geometry distortion and invalidity of 2C60 molecule are respectively compared with those of C60 fullerene molecule in electric field. By comparison, it is shown that geometry distortion and configuration invalidity behavior of 2C60 molecule are sensitive to the direction of electric field, when the directions of the applied electric field are parallel to the bridged C-C bonds. For 2C60molecule it is very easy for the configuration of 2C60 molecule to be invalidated and the invalidity mode is very particular as well.
The transport of monovalent ions through a charged membrane was investigated by percolation approach. Based on percolation concept and theory, the theoretical simulation was conducted for two-dimension (2D) and three-dimension (3D). The results showed that for 2D lattices there has a obviously skip or percolation threshold with charged components from 0.4 to 0.6, and for 3D lattices, such value is between 0.1-0.2. The simulative results were well conformed to those by Monto Carlo simulation for a random system. A practical charged membrane which prepared from the blends of sulphonated polyphenylene sulfide (SPPS)/poly(ether sulfone) (PES) can be considered as a 3D lattices. The experimental conductivity was related with a 3D simulation and the result showed the membrane has a transition from insulator to conductor at the ratio of charged components SPPS about 0.144. Obviously, this value falls in the range of a theoretical simulation for a 3D lattices.
The geometries of phenol, hydroquinone, resorcinol, catechol, o-aminophenol, p-nitrophenol and 2,4,6-trinitrophenol were optimized using ab initio Hartree-Fock and density functional theory B3LYP method at 6-31G(d) level. The molecular radius and molar volume in gas, the dipole moment in gas, water and methanol, the sum of negative Mülliken charges and the frontier molecular orbital (LUMO and HOMO) were also calculated at the same level. Seven phenol compounds were separated by inversed-phase high performance liquid chromatography (HPLC). The correlation coefficient of retention time the molecular radius or molar volume, the dipole moment, the sum of negative Mülliken charges and LUMO are more than 0.9957 using multiple linear regression (MLR). The results show that the retention time of solute in HPLC is controlled by the molecular radius or molar volume, the dipole moment, the sum of negative Mülliken charges LUMO and the interaction between solution and solute.
A dynamical model of electrode BZ reaction system was establisheed on the basis of three variables Oregonator model and kinetics of electrode process. Under weak periodical constraint approximation, dynamical stability of quasisteady state on the slowmanifold of the system is analyzed by means of linearized stability analysis of threevariable system. Meanwhile, the corresponding regime favorable for the appearance of limit cycle oscillation is calculated. Computer simulation shows that limit cycle oscillatory regime has degenerated because of the external periodical potential constraint in the electrode phase. In this regime the system behaves as a temporary self-organization. Whereas, outside this regime a kind of response oscillation appear, with same period as the constraint.
It was found that the ionization potentials (Ip) is related with the polarizability effect index (PEI) for the fragments CH, CH2, and CH3 of polycyclic aromatic hydrocarbon. Therefore a kind of adjacent matrix of molecular graph was constructed, in which the characteristics of the diagonal elements were expressed with the PEI of the fragments C, CH, CH2, and CH3 in molecular graph. The research result shows that there is a good correlation between the eigenvalue of the matrix and the ionization potential for the title compounds: Ipi=4.756+2.870OMOi, R=0.9853, s=0.1765, n=446. This new calculation method has only one parameter for calculating ionization potentials of polycyclic aromatic hydrocarbon. The obtained result shows that the topologic molecular method is convenient and reliable.
First a short review on the crystal growth theories and the experimental data was presented. Then a set of quantitative expressions for the size growth-rate of crystals produced by four different micro-growth mechanisms (folding, extending and two types of combination for folding and extending) was derived by a general evaluating method. A set of quantitative expressions for the correlations between the crystal size growth-rate and the product of crystalline temperature and super-cooling temperature at four different micro-growth mechanisms was obtained. Three growth-rate regimes were divided, the variations of the morphology for the crystals in the three types of regimes with the crystalline and super-cooling temperatures were discussed. They showed that these theoretical correlations between the morphology of crystals and the crystalline and super-cooling temperatures are in agreement with the later important observation on the lateral shape of crystals.
Solid material of supported coupled semiconductors MoO3-TiO2/SiO2 was prepared by the chemical modification method. BET, XRD, TEM,IR, Raman and UV-Vis DRS experiments were used to characterize the surface structure, photon absorbing and chemisorbing ability of the material. It was shown that there are some extremely small particles of anatase and MoO3 crystallites dispersed well on the surface of SiO2, which also can be coupled each other by the bonds of Ti-O-Mo. The active adsorption sites of the material exist on its surface, according to IR results, and C3H8 can be chemisorbed at the Lewis base sites of the Mo=O bonds to form molecular states. Compared with MoO3 and TiO2, the edge energy of MoO3-TiO2/SiO2 was improved and a significant rise of the photon absorbing intensity is observed, which proves the coupled structure has stronger photon ability to take in the UV light, hold back the recombination of photoexcited electronhole pairs and exhibit the quantum size effects.
ZnO-MgO nanocomposite was prepared by glycinenitrate combustion method.Its photoluminescence property, the structure and annealing temperature dependence was studied by XRD, FTIR and SEM. The results show that the photoluminescence property of ZnO-MgO nanocomposite is greatly improved compared with that of pure ZnO. Under 325 nm laser excitation, the emission spectra of the 900 ℃ treated composite sample had an obviously enhanced ultraviolet (UV) band centered at 385 nm at room temperature. The luminescence intensity of the UV band became stronger with the increase of annealing temperatures and reached a maximum at 900 ℃ but decreased at 1000 ℃. The photoluminescence intensity was mainly affected by the grain size, the crystallization and the action between ZnO and MgO nanoparticles. In addition, an appropriate G/N value was favorable for improving the UV-PL properties of the nanocomposite samples.
Layer-structured crystals of β-MNCl (M=Zr,Hf) could be electron-doped by reactions with different alkali metal azides RN3 (R=Li,Na,K,Rb), and controlling the amounts with the molar ratios of azides to β-MNCl. All the prepared compounds show superconductivity with the same transition temperatures at 13.5 K for β-ZrNCl and 23.5 K for β-HfNCl. However the different alkali metal azides RN3 show different reactivity with β-MNCl, and the properties of the products such as superconducting fractions, the lattice constant, and stability against thermal or air, are very dependent on the kinds of alkali metals used. Based on the the results of SQUID measurements, it can be concluded that NaN3 and KN3 are the best react agents for β-ZrNCl and β-HfNCl respectively.
The absorption and chemical reactions of 1,1-dimethyl-hydrazine(C2H8N2) on the surface of magnesium fluoride(MgF2) coating was studied. The coating surface is firstly contaminated by liquid or gaseous C2H8N2 , and then it is placed into a vacuum environment for a long period. Contrasting the infrared absorption spectra, X-ray photoelectron energy spectra and diffusive reflectivity of MgF2 coating surfaces before and after experiment, it may be learned that the absorption and chemical reactions occur at the surface. The experimental results show that the molecules of a liquid film of C2H8N2 over MgF2 coating surface take about two hours to desorb adequately in a vacuum environment, after the adequate desorption, there only exists a single chemical absorption layer over the coating surface, with a mass density of about 27 ng/cm2. The diffusive reflectivity of MgF2 coating surface decreases about 10%-15% after the contamination of liquid C2H8N2. For MgF2 coating surfaces immersed in C2H8N2 vapor at the pressure of 3 kPa for ten minutes, there are neither changes in their atomic constitution and diffusive reflectivity, nor characteristic peaks of C2H8N2 appear in their infrared absorption spectrum.
High quality SWNTs are synthesized by catalytic decomposition of CH4/N2 at 1000 ℃ on the Fe-Mo/MgO catalyst prepared by a combustion method. The best combustion temperature is 550 ℃ for the catalyst. The fitting acidity-basicity can explain the high catalytic performance. The as-prepared SWNTs have been characterized by SEM, TEM, HRTEM, TGA and Raman spectroscopy. The results show that the synthesized SWNTs are usually bundles and they have a narrow diameter distribution with 0.85~1.22 nm. The best reaction atmosphere is 50/300 for the catalyst. Under this ratio of CH4/N2, the content of the prepared raw SWNTs is close to 40% weighting over the catalyst. After the raw SWNTs are treated by diluted HCl at room temperature, the sample can contain yield of SWNTs to over 75%.
After purification pretreatment by heating in air and dilute HNO3, multi-walled carbon nanotubes (MWNTs) were treated with Fenton’s reagents under different experimental conditions. The results of FTIR spectra confirmed that hydroxyl groups and carbonyl groups could be brought into the MWNTs after Fenton chemical treatment. Moreover, the absorption intensity of carbonyl groups become increasingly stronger along with prolonged time. When MWNTs were treated with Fenton’s reagents, the following factors, molar ratio of H2O2 and Fe2+, pH value and reaction time, could affect the modification outcome of MWNTs. Experimental results indicated that when molar ratio of H2O2 and Fe2+ was maintained at 10 and pH value at 3 under acidic condition, more carbonyl groups could be produced on the MWNTs after the treatment was carried out for 10 h. In addition, according to formation mechanism of hydroxyl radical and FTIR spectral changes before and after treatment, the possible mechanism of reaction between Fenton’s reagents and MWNTs was discussed. The possible mechanism showed that existence of hydroxyl groups and carbonyl groups could be viewed as the outcome of addition and oxidation reaction of electrophilic hydroxyl radical on unsaturated bonds on the sidewalls of MWNTs.
A novel type of composite electrode based on multiwalled carbon nanotubes coated with nano nickel oxide particles has been used in supercapacitors. Nickel oxide cathodically deposited from Ni(NO3)2 solution with carbon nanotubes as the matrix exhibited large pseudocapacitance of 25F/g in 6 mol/L KOH. The morphology of composites was examined by scanning electron microscope (SEM). To characterize the CNTs/nickel oxide composite electrode, a chargedischarge cycling test for measuring specific capacitance, cyclic voltammetry, and ac impedance test is executed. The nickel oxide composite exhibiting excellent pseudocapacitive behavior(i.e.high reversibility, high specific capacitance, and low selfdischarge rate) has been demonstrated to be a potential candidate for the application of electrochemical supercapacitors.
A novel gas diffusion electrode using binary carbon supports (carbon nanotubes and active carbon) as the catalyst layer was prepared. The electrochemical properties for oxygen reduction reaction (ORR) in alkaline electrolyte were investigated by polarization curves and electrochemical impedance spectroscopy. The results show that the binary-support electrode exhibits higher electrocatalytic activity than the single-support electrode, and the best performance is obtained when the mass ratio of carbon nanotubes and activated carbon is 50 ∶50. The results from their electrode kinetic parameters indicate that the introduction of carbon nanotubes as a secondary support provides high accessible surface area, good electronic conductivity and fast ORR kinetics. The electrocatalytic activity of binary-support electrodes is obviously improved by the deposition of Pt nanoparticles on carbon nanotubes, even at very low Pt loading (45.7 μg/cm2). In addition, the EIS analysis results show that the process of ORR may be controlled by diffusion of oxygen in the thin film for binary-support electrodes with or without Pt catalyst.
CNx nanotubes was synthesized by thermal decomposition ethylenediamine catalyzed by pure iron, cobalt, nickel, and ferrocene. The effect of the catalyst on the CNx nanotubes’ morphology and yield was studied. The catalysis growth mechanism was also discussed. The CNx nanotubes with the “bamboo-like” structure and lower yield are produced when iron or ferrocene is used as the catalyst, whereas the curved CNx nanotubes with many pleats through the nanotube walls and higher yield are generated when cobalt is used. The CNx nanotubes catalyzed by nickel are only helix tubes with the diameter of about 500 nm. Raman spectroscopy studies show that the CNx nanotubes catalyzed by ferrocene have a worse crystallinity due to a higher nitrogen incorporation.
Microstructures of various polymers, such as polystyrene and polymethyl methacrylate, were fabricated with microcontact printing, directly using the corresponding dilute polymeric solutions as “inks”, whose concentrations were about 10 g/L. By repeatedly cross-stamping with the inks, multilayer quasi-three-dimensional polymeric microstructures could be obtained. Both optical photographs and SEM photos showed clear microstructures, which were nearly accurate replication of the original patterns in the PDMS stamps. Microlines of poly-[bis-(p-toluene sulfonate)-2,4-hexadiyne-1,6-diol)] (PTS) were also fabricated by first processed microcontact printing with solution of the corresponding monomer TS/acetone as ink, then followed with UVpolymerization of the monomer micropatterns at solid state. Unlike small molecule processes, the molecules of polymeric inks did not selfassembly on the surface of substrates. The formation of polymeric microstructures could be ascribed to the fact that, after volatilization of solvents, polymers tend to stick to the surface of glass substrate which has higher surface free energy (about 72 mN/m), but not to the surface of PDMS stamp which has lower surface free energy (about 20 mN/m). Also the microcontact printing process was studied with optical microscopy, and the main factor--volatilization time of solvent was discussed. The results showed that the volatilization time of solvent is very crucial to the process of polymeric microcontact printing, and with too longer or too shorter volatilization time, the obtained microstructures would become discontinuous or distorted, respectively. For example, with a polystyrene/chloroform solution as ink, the optimal volatilization time was about 15~20 s.
Based on the synthesis and characterization of side-chain liquid crystal polysiloxanes containing p-methoxyl phenyl benzolate, the homogeneous electrorheological (ER) liquid and its smart damper were fabricated. The properties of the homogeneous ER liquid and its smart damper were tested. The results indicated that the homogeneous ER liquid with significant ER effect at room temperature is obtained by mixing the side-chain liquid crystal polysiloxanes containing p-methoxyl phenyl benzolate and silicone oil. Its shear stress reached 1550Pa at electrical field strength (E) of 2.2 kV/mm and shear rate of 300 s-1. The damping forces of the smart damper based on the homogeneous ER liquid enhanced if E and oscillation frequency increased. Consequently, an effective way for semi-active control using the smart damper based on the homogeneous ER liquid was put forward to reduce the seismic responses of the structures.
A series of novel aqueous emulsion of siloxanemodified polyurethane (PU(PE-PSI)) were synthesized based on poly(propylene glycol) (PPG), polyether-grafted polysiloxane (PEPSI), 2,4-tolylene diisocyanate (TDI), dimethylol propionic acid (DMPA) and 1,4butanediol (BDO) through a direct water emulsification of triethylamine (TEA). The aqueous emulsion was transparent and had a good stability. Fourier transform infrared spectroscopy (FTIR) was used to identify the structure of PU(PEPSI), indicating that the polysiloxane segment had been incorporated with polyurethane chain. Investigation of Electron Spectroscopy for Chemical Analysis (ESCA) and the water contact angle demonstrated that the siloxane migrated to the surface of film. The results also showed that PU(PE-PSI) was still a very good elastomer. With increasing the content of PEPSI, the resistance to water improved and tensile strength increased, while the ultimate elongation decreased slightly for the PU(PE-PSI) film.
Isopiestic measurements have been carried out at 298.15 K for the quaternary aqueous solution H2O+KCl(sat)+NaCl+NH4Cl saturated with potassium chloride and its ternary subsystems H2O+KCl (sat)+NaCl and H2O+KCl(sat)+NH4Cl. Taking sodium chloride (aq) or calcium chloride (aq) as reference solutions, osm otic coefficients and water activities of the aqueous solution were determined. The experiment results show that the isopiestic actions of the quaternary system related to its ternary sub-systems are in excellent agreement with the ideallike solution model.
In order to examine the effects of water contents and heating/cooling rates on the glass transition and the structure relaxation parameters of glycerol/water mixtures, five aqueous solutions (60%, 70%, 80%, 90% and 100%) were investigated using the differential scanning calorimetry. Four scanning rates (10, 15, 20, 25 K/min) were used to obtain the glass transition parameters. The fitting results of plasticization constants indicated that Gordon-Taylor relationship could not be used effectively without considering scanning rates and that point on calorimetric step was chosen as the glass transition temperature. The specific heat changes during glass transition processes were relative not only to water content but also to heating rates. With the increasing of water contents in glycerol aqueous solutions, the structure relaxation activation energies and dynamic fragilities were decreased. Since the thermodynamic fragilities were increased with the increasing of water content, so the dynamic fragility and thermodynamic fragility were changed inversely if the water contents were changed in glycerol/water mixtures.