取代基对氮和氧自由基稳定性影响的理论研究

用MNDO方法，全构型优化，研究了15个氮自由基4-RC6H4NH，和15个氧自由基4-RC6H4O（R＝－H；－OCH3，－Cl，－F，－CN，－COCH3，－NO2，－CH3，－CF3，－SCH3，－C6H5，－Nh2，－BH2，－PH2，－SiH3）的稳定化能．结果表明：－NH2，－CH3，－OCH3，－F基团对自由基起稳定化作用，－CF3，－NO2；－CN，－COCH3，－BH2基团对自由基起去稳定化作用．苯基对氧自由基有较大的稳定化作用，而对氮自由基的稳定性影响较小．－SCH3，－PH2，－SiH3，－Cl基团表现弱的去稳定化作用．计算和实验结果基本相符．     

Laser two-photon ionization of organic molecules in dielectric liquids

The ionization threshold of fluoranthene and of TMPD in n-pentane was determined by laser two-photon ionization (TPI) and found to be 4.50 ± 0.05 and 3.88 ± 0.05 eV respectively. For both molecules the TPI spectra show distinct structure due to autoionization. For fluoranthene the TPI spectrum suggests that the molecule dissociates via the first excited singlet state.     

Surface free energies of styrene-acrylic acid copolymer plates prepared in various frames

Styrene (St)-acrylic acid (AA) copolymer plates were synthesized in the frames made of glass, aluminum (Al) and poly(difluoroethylene) (PDFE). Surface properties of the prepared copolymer plates were characterized with regard to critical surface tension ( _C ), chemical components by IR analysis and surface energies (total energy, _S ; dispersion force components, _S ^d ; polar component, _S ^p ; hydrogen bonding component, _S ^h ) and the following results were obtained.The _C values of the copolymer plates increased with AA content and also depended on the sort of the used frame. The increasing order of the _C values of the copolymer plates corresponded to those of the used frames, namely, PDFE frame < Al frame < Glass frame.The prepared copolymer plates with low AA contents (ca. 10 mol%) were enriched in the AA moiety in the surface layer regardless of the kind of the used frame.The total and the individual components of the surface free energies of the copolymer plates were largely affected by the property of the used frame. The glass frame gave the plate with higher _S ^h values suggesting preferential orientation of the polar site of AA component.     

The use of the isotropic orientation factor in fluorescence resonance energy transfer (FRET) studies of the actin filament

A Dale-Eisinger style analysis (R. E. Daleet al., Biophys. J. 26, 161, 1979) is used to produce three-dimensional plots that display the limits on the average orientation factor k ² that is required to calculate molecular distances in F-actin from fluorescence resonance energy transfer measurements. Maxima and minima plots are generated for the transfer of energy from a donor to a single acceptor and for transfer to multiple acceptors that are related by F-actin helical symmetry. The analysis is performed in terms of dipole cone half-angles rather than depolarization factors, in order to facilitate the modeling of the multiple acceptor problem. Calculations are carried out under the restrictive condition of a single electric dipole moment per fluorophore. In addition, both surface and volume averaging of the donor and acceptor dipoles are considered. Comparisons between the plots show that for the multiple acceptor cases with F-actin symmetry, there is a great reduction in the range for maxima and minima limits on k ². The calculations also suggest guidelines for the choice of fluorescence label that will result in an average orientation factor occurring within acceptable limits, i.e., inside the limits for which k ²=2/3 may be employed. Thus, without having detailed knowledge of the mean donor or acceptor dipole relative orientations, the use of k ²=2/3 in radial coordinate studies of F-actin is more than reasonable and is fairly assured of being correct.     

环形装置中三维MHD平衡与稳定性的计算机模拟

一、引 言 在聚变研究中,环形等离子体的磁约束起着重要作用。目前托卡马克研究的进展令人鼓舞,其理论与实验比较符合,定标关系清楚。但是无论从聚变的最终目标来看,还是从实验的安排考虑,完全轴对称的几何形状给各方面部带来许多不便。人们希望知道如果把环形几何中加进直线段,或者把圆环改成不具有对称性的环形,会对等离子体约束产生何种影响?     

Magnetic field effects on the crystal orientation and surface morphology of electrodeposited iron films

The effects of a magnetic field (5 T) on crystal orientation and surface morphology were investigated for iron films electrodeposited in ferrous aqueous solution. XRD measurements for the iron films showed that the preferred orientation parallel to the substrate was determined by the current density and not influenced by the magnetic field. By X-ray pole figure measurements, however, the crystal texture of the iron films electrodeposited at 10 mA cm^–2 and 30 mA cm^–2 was found to be controlled by the magnetic field. That is, the (110) planes were orientated in same direction of the magnetic field vector at angles of 30° and 35° to the direction normal to the substrate plane at 10 mA cm^–2 and 30 mA cm^–2, respectively. When the morphology was observed by SEM, iron grains at 30 mA cm^–2 changed from a triangular pyramid shape at 0 T to a complex star-like shape at 5 T.Presented at the 3rd International Symposium on Electrochemical Processing of Tailored Materials held at the 53rd Annual Meeting of the International Society of Electrochemistry, 15–20 September 2002, Düsseldorf, Germany     

Photochemistry of β, γ-unsaturated ketones-V: The direct irradiation of some γ-phenyl β, γ-enones

The photochemistry of some members of the two series of γ-phenyl substituted acyclic β, γ-unsaturated ketones 1 and 2 upon direct irradiation with γ 310nm has been investigated, viz 1c–1h and 2b+2c.The alkyl substituted (E)-5-phenyl-4-penten-2-ones 1c–1h yield the corresponding 1,3-acyl shift products and (Z)-isomers, and 1g and 1h in addition two decarbonylated products. 2b only yields the (Z)-isomer and some benzaldehyde, but 2c yields the 1,3-acyl shift product, the ODPM product, three hydrocarbons formed by disproportionation of the allyl radical, and some benzaldehyde. The β-phenyl β, γ-UK 3a proved to be photostable. The 1,3-acyl shift products of 1c–1h result mainly from the singlet excited state in a cage radical process. The exclusive formation of the (E)-configuration of the 1,3-acyl shift product is explained in terms of conformational preference of the intermediate allyl radical. It is proposed that the formation of the (Z)-isomer proceeds from ¹T(π -π^*) which is populated according to

. Evidence is presented which supports the proposed mechanism.The β,γ-UK 2b containing a benzoyl moiety leads to a higher degree of (E)-(Z) isomerization than the corresponding 1d which has an acetyl moiety.The triplet energies of (E)- and (Z)-1h are 56 and ca 70 kcal/mol respectively.     

Structural studies of DMβCD/dihalogenated norcarane inclusion complexes

Inclusion complexes of 7,7-dibromonorcarane (1) and 7,7-dichloronorcarane (2) with 2,6-dimethyl--cyclodextrin (DMCD) have been synthesized. Their structures have been studied by chemical analysis, thermal behavior, IR spectra, UV absorptions and¹³C NMR spectra in DMSO solutions. The studies show that the orientation of (1) is different from that of (2) in the DMCD cavity.Presented at the 6th International Symposium on Molecular Recognition and Inclusion, Berlin, Germany, 10–14 September 1990.     

Molecular structure of carbonyl bromide as studied by gas electron diffraction

The molecular structure of COBr₂ has been determined as follows by an analysis of electron diffraction intensity: r_g(CO) = 1.178 ± 0.009 Å, r_g(C-Br) = 1.923 ± 0.005 Å and θ°_α(Br-C-Br) = 112.3 ± 0.4°. The uncertainties represent estimated limits of error. The observed systematic trends in the bond lengths and bond angles in carbonyl and thiocarbonyl halides are discussed.     

Crystalline orientation of the InN films prepared by atmospheric pressure halide chemical vapor deposition

The structural analysis of the hexagonal InN film prepared on a Si(100) substrate by the AP-HCVD technique using InCl₃ and NH₃ as starting materials were carried out by the X-ray pole figure analysis. The deposited films consist of the hexagonal InN pillar crystals. It was found that the pillar crystals, which have random rotation around the 100 axis, were grown at an angle of 70–90° to the substrate.