2004 Vol. 17, No. 6

Letter
Article
The gas phase reaction of Cu plasma and acetonitrile clusters is studied by the laser ablation-molecular beam(LAMB) method. Four series of clustered complex ions Cu+(CH3CN)n, CH2CN+(CH3CN)n,H+(CH3CN)n and CH3CHCN+(CH3CN)n are observed. Interestingly,the species and sizes of the product clusters vary observably when the plasma acts on the different parts of the pulsed acetonitrile molecular beam. When the laser ablated Cu plasma acts on the head of the beam,the metal acetonitrile complex clusters Cu+(CH3CN)n together with protonated acetonitrile clusters H+(CH3CN)n and deprotonated acetonitrile clusters CH2CN+ (CH3CN)n are domain,while the plasma acts on the middle of the beam. However,CH2CN+(CH3CN)n and H+(CH3CN)n along with the clusters CH3CHCN+(CH3CN)n turn out to be the main resulting clusters. By comparing the intensities and the cluster sizes of CH3CHCN+(CH3CN)n with H+(CH3CN)n and CH2CN+(CH3CN)n,the formation of CH3CHCN +(CH3CN)n is contributed to the intracluster ion-molecule reaction of acetonitrile clusters.
The stochastic resonance in chemical reaction systems has recently attracted growing attentions. Using chemical Langevin equation,the effect of internal noise has been studied on the dynamical behavior of a single and a one-way coupled cubic autocatalator. For the single system,it is found that the internal noise can induce sustained oscillations,and the signal-to-noise ratio(SNR)undergoes a maximum with the variation of the system size. For the coupled system,the SNR passes through a maximum with changing coupling strengths as well as with changing system sizes,which demonstrates the occurrence of the internal noise stochastic resonance(INSR)and optimal size effect. In the presence or absence of influx into the system,the coupling enhanced or suppressed INSR is found in the coupled system. All cells of the coupled system appear to exhibit INSR at an approximately equal size at a suitable coupling strength,implying that the optimal system size and coupling strength can make the system reach an optimal chemical reaction state.
The reaction mechanism of CH2Cl radical with OH radical to produce HCCl+H2O,HCOCl+H2 and H2CO+HCl has been studied by using quantum chemistry ab initio calculations. The optimized geometrical parameters,and vibrational frequencies of all species were obtained at the UMP2(FC)level of theory in conjunction with 6-311++G* basis set. Besides,the zero-point energies(ZPE),relative energies and total energies of all species were calculated using Gaussian-3(G3)model. The results of theoretical study indicate that the activated intermediate CH2ClOH is first formed through a barrierless process,followed by atoms migration,radical groups rotation and bonds fission to produce HCCl+H2O,HCOCl+H2 and H2CO+HCl,respectively. And all channels are exothermic by 72.81,338.54 and 354.08 kJ/mol. The reaction heat of reactants to H2CO+HCl is 281.27 kJ/mol more than that of reactants to HCCl+H2O. This result accords with that of experiments.
The one-carbon unit transfer reaction catalysed by glycinamide ribonucleotide transformylase(GARTfase)is a key step in the de novo purine biosynthetic pathway. In order to give a theoretical research of the assumption from the experiments,the water-assisted mechanism in GAR Tfase catalysed one-carbon unit transfer reaction has been investigated by a Density Functional Theory method,B3LYP,at 6-31G* basis level. There are two possible reaction channels for the whole reaction,one is concerted(path a)and the other is stepwise(path b). The water molecule serve as a bridge to connect the proton donor to the proton acceptor. All the transition states in both paths have a six-membered ring in their structures due to the joint of the water molecule. The calculations show that the latter is preferable to the former due to the lower energy barriers. The results have verified the presumption from experiments,and proved that the joint of a water molecule can relax the strong strain in the unstable system,so it is propitious to the whole reaction.
The potential energy surface for the decomposition and isomerization of Chlorine Nitrate(ClONO2)is calculated using the G3 theory. Geometries of related species are optimized at the MP2( full)/6-31+G(d)and B3LYP/6-31+G(d)level. Vibrational frequencies and IR intensities of ClONO2 have been calculated at the same level. Obtained geometries and vibrational frequencies as well as IR intensities for ClONO2 are in good agreement with experimental values. A new stable stereoisomer is verified by CCSD(T)and QCISD(T)methods at 6-311G (d)basis set. Calculated geometries using above methods for this stereoisomer are in accord with each other. The calculated reaction heat of ClONO2 are also in good agreement with the available data in the literature. Among these reactions of ClONO2,the stereoisomer reaction is the hardest one. The barrier height for this reaction is 481.52 kJ/mol relative to ClONO2 and the reaction is endothermic by 299.85 kJ/mol. On the other hand,among these unimolecular reactions of ClONO2,the decomposition reaction of NO2+ClO is the easiest one. These results indicate that ClONO2 is very stable.
In order to study the electron property and the microlocal structure of Co-P amorphous alloy,a series of single-P(ConP)and two-P(ConP2)cluster models were chosen according to the experiment fact of the possible presence of direct P-P contact and short-range-ordering in the amorphous alloy. ConP and ConP2 cluster models were calculated with the DFT method and calculations showed that P(phosphor)accepted electron from Co(cobalt)in single-P(Co2P(2),Co3P(1)and Co4P(2))cluster models,which agrees well with the Pauli electronegative rule,and a very strong interaction between Co and P resulted in formation stable clusters Co2P(2),Co3P(1)and Co4P(2). However,two-P(ConP2)cluster models and single-P cluster Co5P(1)were unstable,and it was impossible to present direct P-P contact in two-P(ConP2)cluster models. It could be concluded that the clusters Co2P(2),Co3P(1)and Co4P(2) is more reasonable to represent the local structure of Co-P amorphous alloy.
Taking hypomycin B(HMB)as the model compound,HF / 6-31G and TD-B3LYP / 6-31G methods have been employed to explore the effect of chlorine,bromine and iodine substitutions on molecular properties and photosensitization of perylenequinonoid photosensitizer(PQP). It was found firstly that,the halogen substitutions lowered the EHOMO and ELUMO,and the ΔE. From chlorine,bromine to iodine substitutes,the EHOMO and ELUMO increased,while the corresponding ΔE decreased. Secondly,the halogen substitutions increased the molecular triplet-generating quantum yields and lowered the molecular lowest lying triplet energies,which resulted in the substitutes’similar 1O2 yields with their parent compounds. After halogen substitutions,the molecular adiabatic electron affinities increased,which made the substitutes possess lower O2· - -generating abilities than their parent compounds. Finally,the halogen substitutions lowered the intramolecular hydrogen bond energies,while enhancing the intramolecular proton transfer(IPT)barriers of cis isomers and lowering those of trans isomers on the ground state.
Based on the first principle,electrical properties of a molecular junction consisting of pyrene-1,8-dithiol molecule and gold surface have been investigated. The cluster of three gold atoms is used to simulate the gold surface. Density functional theory is employed to obtain the electronic structures of the molecule and the extended molecule. Then the frontier orbital theory and the perturbation theory are used to determine the interaction energy between the molecule and the gold surface quantitatively. The elastic Green function method is applied to study the current-voltage properties of the molecular junction. Numerical results show that the sulfur atoms can be chemically absorbed on the gold surface and the bonding between the molecule and gold is mainly covalent-typed. The fermienergy of the extended molecular system lies between the HOMO and the LUMO and closer to the HOMO of the system. When the external applied bias is lower than 1 V,there is a current gap for the molecular junction. With the increasing of the bias,the conductance of the junction exhibits plateaus. These electrical properties are closely related with the electronic structures of the molecular junction. The extended molecular orbits have great contribution to the charge transport. Localized molecular orbits give little contribution to the current while charge transport is taken place by tunneling.
Based on the conjugated polarization theory,it is expressed as the conjugated polarizability potential (CPP)that the discrepancy between the average electrostatic energy of dipolar state and the electrostatic energy of non-polar state in the conjugated polarizability procedure for the conjugated alkenes. The correlation between CPP and the energy of ultraviolet absorption maximum,and the correlation between the energy of frontier molecular orbital obtained by ab initio calculation of quantum chemistry and the energy of ultraviolet absorption maximum have been carried out for the conjugated alkenes. Both correlation equations show a similar estimated precision. Further, the contribution of alkyl polarizability effect to the stability of dipolar state for the alkyl substituted alkenes with the effective polarizability effect index(PEI(ef))was quantified. Relating the above two parameters CPP and PEI(ef)to the energy of ultraviolet absorption maximum of the substituted alkenes in a two-parameter expression with a good prediction ability was obtained:v=1.1746+5.0187CPP-0.43204PEI (ef),R=0.9995,s=0.0403,F=10853.28,n=23. The investigated results also indicate that it is less effective to reduce the energy of ultraviolet absorption maximum by means of increasing the alkyl substituent groups than lengthening the conjugated backbone chain in the conjugated alkenes.
Two systems of 1: 1 inclusion of host β-cyclodextrin and guest p-cresol in nano-drip including 427 H2O molecules and in vacuum have been studied by the constrain molecular dynamics simulation technique with pcff force field and Rattle bond algorithm. The analysis on the dynamic structure of inclusion and radial distribution function of several kinds of oxygen atoms shows that the CD inclusion was stable during the simulation time period in two systems and none of water molecule was found to move into the CD cavity in the drip within 200 ps which conformed the hydrophobic property of CD cavity. In the drip,an obvious hydration caused by H-bonding existing in the CD hydrophilic outsides was observed,and it agreed well with the CD properties. The obvious H-bonding interactions existing between phenyl hydroxyl and water molecules in the drip and between phenyl hydroxyl and CD cavity in vacuum made the guest molecule insert into the CD cavity shallower in drip case than in vacuum case. It was concluded that the constrain molecular dynamics simulation technique can be used to investigate the dynamic behavior of CD aqueous solution.
The geometry,electronic structure and electronic transmission of Au electrode-compressed C20 fullerene Au electrode systems are investigated systemically,and some interesting results are obtained by use of molecular dynamics,Extend Hückel method of the first principle,and Green's function based method. The analytical results show that,due to intervention of Au electrodes,the electronic structure of compressed C20 fullerene is changed significantly,the coalescent between C20 fullerene and Au electrodes is intervenient of covalent bond and electrovalent bond,and the compressed C20 fullerenes are better conductors of electricity than those uncompressed or slightly compressed ones. The methods and the relative conclusions are beneficial to go further deep into electronic transmission of carbon fullerenes.
A simulation study on the formation characteristics of clusters in a large-scale liquid Al system consisting of 105 atoms has been performed by the molecular dynamics method. And a cluster-type index method(CTIM)has been used to describe the structural configurations of various clusters. The results demonstrate that the icosahedron clusters(12 0 12 0)and their combinations play the most important role in the microstructure transition. The nanoclusters(containing up to 104 atoms)have been formed by combining some middle clusters which have been formed by combining smaller basic clusters. The structures of these nano-clusters are very different from those of nano-clusters obtained by evaporation,ionic spray methods,and so on. The latter is formed by the multi-shell crystals accumulated with an atom as the center and the surrounding atoms arranged according to octahedron configuration. The center atoms of these basic clusters are bond-connected each other with the linear or twisting mode. The corners of the nano-cluster just could become the starting points of the dendrite growth in the solidification processes of liquid metals.
The microstructural properties of gelatin samples derived from the bovine bone as well as skin of fish which inhabit in the cold sea were examined at molecular scale by using the positron annihilation lifetime spectroscopy(PALS). The longest-lived component of PALS provides information about the free-volume holes in gelatin macromolecules. The results show that both average size and number of free-volume holes in the fish gelatin macromolecules are lower than those in the bovine gelatin macromolecules. Silver halide emulsions were also precipitated by using the balanced double-jet technique,for which two types of media containing fish gelatin and bone gelatin were used in the stage of nucleus formation,respectively. The monodispersibility of silver halide crystallites can be improved and the growth and coalescence of nucleus grains can be restricted when the fish gelatino-peptizer was used as dispersion medium at the nucleus formation. It thus suggested that the function of gelatino-peptizers as protective colloid is correlated with the microstructure character of gelatin macromolecules established by PALS. The gelatino-peptizer derived from the fish skin possesses stronger power governing nucleation and growth of silver halide grains compared with that made from the bovine bone.
Both negatively and positively charged silver colloids were prepared in aqueous solution for surface-enhanced Raman scattering (SERS) by the reduction of silver nitrate with sodium citrate and hydrogen peroxide under basic condition, respectively. By means of transmission electron microscopy (TEM), the observation of morphologies of negatively charged silver colloid (NSC) and positively charged silver colloid (PSC) has been presented, and the aggregation behaviors of NSC and PSC as well as the mixture of NSC and PSC induced by the addition of fuchsine basic molecules examined. SERS from fuchsine basic molecules in above mentioned colloidal systems were recorded respectively and compared with each other. The results show that the mixture of NSC and PSC could form the aggregation morphology different from that of single NSC and PSC and bring about the favorable effect on SERS behavior for the adsorbed fuchsine basic.
Fulerene complexe C60 Pd( Ph2PCH2PPh2)was perpared by the method of ligand substitution via the reaction of C60 with Pd(Ph2PCH2PPh2)2 under condition of a nitrogen atmosphere and refluxing,and the title compound was appraised and characterized by methods of elemental analysis,FT-IR,UV-vis,XPS and XRD. The results showed that the structure of purposeful product was that the Ph2PCH2PPh2 took up two coordination sites of the central metal,and C60 took up another two sites in σ-π feeback pattern. The porperties on photoelectricity,redox and thermostability of the title complexe were studied. The results of studying on photoelectricity showed that the photovoltaic effect of(n+n)heterojunction electrode formed by C60Pd(Ph2PCH2PPh2)/ GaAs was supper,especially in the BQ/ H2Q redox couple,and the greatest value of photovoltaic potential was up to 174 mV. The photovoltaic performance of C60Pd(Ph2PCH2PPh2)/GaAs electrode at 1 μm for thickness of C60Pd(Ph2PCH2PPh2)film was the best.
Using close-packed colloidal crystals-silica as the template,a novel 3D well-ordered and long-ranged periodic macroporous material MnO2 has been prepared by colloidal crystals template methods. The prepared product has been characterized by means of X-ray diffraction(XRD)and scanning electron micrography(SEM). The X-ray diffraction displays that the phase of MnO2 is tetragonal,and the scanning electron micrography shows that MnO2 replicates the structure of the started template and exhibits 3D long-range ordered honeycomb framework. The process of preparing the 3D order macroporous MnO2 was discussed. The effect of the infiltration times to the final morphology of MnO2 was studied and an abnormity existed in the shrinkage of the final outcome.
The Giant Magnetic Impedance(GMI)effect of complex wires which were produced by pulse electrodeposing Fe-Ni alloy over cylindrical Cu substrates has been studied. It is found that the soft magnetic property is better,and the GMI effect of the sample is stronger. The maximum GMI ratio is 27.19% among these samples. The dependance of the impedance and GMI ratio on DC magnetic field is influenced by magnetic anisotropy in magnetic microtubes of complex wire. The variation of GMI effect with AC current frequency is investigated. The experimental results show that the GMI effect of the complex-structure sample Fe17 Ni83 has a very low critial frequency of 30 kHz(GMI=9.95%)and charicteristic frequency 300 kHz(GMI=27.19%)and its cutoff frequency is 10 MHz(GMI=10.36%). Not only such low critial and charicteristic frequency but also wider work frenquency range are of importance for technological applications.
The plot of viscosity versus particle volume fraction for the water carrier of self-formed CoFe2O4 magnetic fluid is abnormal in zero magnetic field. However,the viscosity theory of the suspension with the global rigid particle filling cannot explain the experiment well. That is because the nanoparticles have aggregated before preparation of magnetic fluid. The fact is found that the sedimentation without magnetic field and the becoming chains in magnetic field of this type of magnetic fluid need the big particles which core are pre-aggregates by researching the interaction of particles of magnetic fluid. Around the big particles,nanoparticles are absorbed with the type of dynamic state. It is on that idea that the model of fluctuant aggregation is made. So,the average diameter,Einstein ratio and particles size distributive deviation of free suspended bodies in zero magnetic fluid are the functions of the particles volume fraction. And then,Popplewell’s formula of the viscosity is modified with this model. As a result,a well-fitted curve is obtained.
A kind of cellulose magnetic nanoparticle with a core / shell structure has been prepared by ultrasonic irradiation. Cellulose acts as the shell while Fe3O4 magnetic nanoparticles take the role as the core. Magnetic force microscopy(MFM)with atomic force microscopy(AFM)measurement showed that the size of the magnetic nanoparticles is about 30-50 nm in diameter,while the Fe3O4 core is about 20-30 nm. FT-IR,XRD and MFM was used to provide the chemical and magnetic information of the nanoparticles. The MFM image showed that the nanoparticles separate very well with each other,indicating the cellulose shell produces a good prevention from the aggregation of the Fe3O4 particles. MFM studies also showed two magnetic nanoparticles can form particle-pairs,indicating a weak magneto-dipole interaction between magnetic nanoparticles. It is also found that the average sizes of magnetic nanoparticles have relation to the power of ultrasonic irradiation,and the possible mechanism is discussed.
In order to investigate the catalytic activity of high temperature treated CoPc toward oxygen reduction, and find the active site of the catalyst, using cobalt (Ⅱ) phthalocyanine (CoPc) as raw material, through thermal chemical vapor deposition method at 850℃ under a current of Ar/H2, two layer well-aligned multiwalled carbon nanotubes (CNTs) were made. The diameters of the well-aligned carbon nanotubes were distributed in the range of 60~120 nm and the length was about 40 μm. The Co particle with 10 nm in diameter was encapsulated in the CNTs compartment. The products were observed by field emission scanning electron microscope (SEM), and transmission electron microscope (TEM). The well-aligned carbon nanotubes were characteriszed by Raman scattering spectrum and X-ray diffraction (XRD). The cyclic voltammetric measurement demonstrates that the CNTs have some effect to prevent the metal nanoparticle encapsulated from eroding rapidly. It is assumed that the small amount of the N element in the CNTs is very necessary for the bamboo-like morphology and the protected action for metal particles against dissolution in the acid medium. The radian of the winding wall should be affected by the amount of the N and the interaction between the N in the carbon network and the metal cluster. In addition, the CNTs greater electrochemically active surface area is a great advantage for any electrocatalytic application.
The effects of concentration of NaCl and pH values on the adsorption isotherms of poly(diallyldimethylammonium chloride)( PDADMAC)on SiO2 microspheres and Zeta-potential of adsorbed-silica in different pH buffer have been investigated. The results show that the adsorption of the polyelectrolyte increases with increasing salt concentration and pH values,respectively. It follows the Langmiur isotherm. The isoelectric point of SiO2 microspheres gradually migrates toward the high pH values with increasing the adsorption of PDADMAC. Under alkaline conditions the PDADMAC adsorption on SiO2 microspheres shows good stability of disperse. The X-ray photoelectron spectroscopy(XPS)analysis of the PDADMAC adsorpted SiO2 microspheres sample exhibits the presence of nitrogen-containing intermediates with N1s XPS peaks at the binding energy of 401.7 eV. The O1s spectra show two distinct peaks which are oxygen-containing silica corresponding lower binding energy and adsorping oxygen corresponding higher binding energy,respectively. With the PDADMAC adsorption on SiO2 microspheres the peak of O1s contributed from the part of adsorping oxygen increases.
PMMA/ SiO2 organic-inorganic hybrid sol was synthesized by monomer methyl methacrylate,3-(triethoxysilyl)propylmethacrylate(mol ration is 1: 1),0.2%(total weight of monomers)initiator azodiisobutyronitrile,solvent tetrahydrofuran and 20%(total weight of the system)tetraethylorthosilicate. PDMS stamp with micropatterns was placed on the hybrid sol film prepared by spin-coating on the clean glass slides. Heat treatment under 120℃ for 2 h with a weak pressure of 1 N makes the sol convert to gel. PMMA/SiO2 hybrid material micropatterns remain on the substrate after being peeled off the stamp. Optical microscope images show stringent pattern fidelity using the micromolding method which also indicates the further application in the micropatterns fabrication.
The kinetic parameters of the exothermic decomposition reaction of the title compound in a temperature-programmed mode have been studied by means of DSC. The DSC data obtained are fitted to the integral, differential and exothermic rate equations by linear least-squares, iterative, combined dichotomous and least-squares methods, respectively. After establishing the most probable general expression of differential and integral mechanism functions by the logical choice method, the corresponding values of the apparent activation energy (Ea), pre-exponential factor (A) and reaction order (n) will be obtained by the exothermic rate equation. The results show that the empirical kinetic model function in differential form and the values of Ea and A of this reaction are (1-α)0.44, 230.4 kJ/mol and 1018.16 s-1, respectively. With the help of the heating rate and obtained kinelic parameters, the kinetic equation of the exothermic decomposition reaction process of the title compound is proposed. The critical temperature of thermal explosion of the compound is 302.6℃. The above-mentioned kinetic parameters are quite useful for analyzing and evaluating the stability and thermal change rule of the title compound.