Local group representations

As a generalization of the usual notion of a group representation, a local group representation of connected and locally connected groups G is introduced as a certain sheaf A with base G, such that all fibres A _x may be identified with a fixed linear subspace D of the representation space. The sheaf provides a means of expressing a group symmetry which is known to hold only locally (in a sense which will be made precise). The problem of extending a local representation to a global one may be considered as a noncommutative counterpart of the dilation theory of systems of doubly commuting contractions. If G is a Lie group, one may associate a derived representation of the enveloping algebra (g) of the Lie algebra g of G. In case of isometric local representations in a Hilbert space, these are *-representations and determine the appropriate local representation uniquely. As an application we obtain that the n-tuples of antisymmetric operators of partial derivatives on L ²(), where is a connected open subset of ⁿ, determine up to translation.     

Effect of substituents on the first ionization potentials of aromatic and heteroaromatic compounds. The {ie2532-1} resonance parameters of Si-, Ge-, Sn-, and Pb-containing fragmentsresonance parameters of Si-, Ge-, Sn-, and Pb-containing fragments

The first vertical ionization potentials (IP) of monosubstituted benzenes, hexafluorobenzenes, naphthalenes, anthracenes, furans, thiophenes, and selenophenes and the secondIP of monosubstituted tellurophenes are related to the inductive, resonance, and polarization parameters of substituents by dependences of the type {ie2532-2}. The contribution of polarizability effect, {ie2532-3}, to theIP value is determined by the degree of delocalization of the positive charge in radical cations formed upon photoionization of the compounds studied. The {ie2532-4} resonance parameters of nineteen Si-, Ge-, Sn-, and Pb-containing substitutents in naphthalene, furan, and thiophene series were calculated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2434–2438, December, 1998.     

An access to 3,4-(aminomethano)proline in racemic and enantiomerically pure form

Protected racemic and enantiomerically pure 3,4-(aminomethano)prolines rac-9 and (2S,2'R,3R,4R)-9 have been prepared applying a titanium-mediated reductive cyclopropanation as a key step. Thus, cyclopropanations of N,N-dibenzylformamide with titanacyclopropanes generated in situ from racemic or enantiomerically pure tert-butyl N-Boc-3,4-dehydroprolinates rac-8 or (S)-8 proceed diastereoselectively, and furnish the protected racemic and enantiomerically pure diamino acid 9. The latter was incorporated into three tripeptides containing glycyl, alanyl and phenylalanyl moieties.     

Syntheses and structures of highly hindered N-functionalised alkyl and amido group 12 complexes MR2 (M=Zn, Cd, and Hg), [MRCl]2 (M=Zn and Hg)

The reaction of MCl₂ (M=Zn, Cd and Hg) with Li(2-(C(SiMe₃)₂)(6-Me-C₅H₃N)), [Li(MeR)], affords mononuclear metal(II) alkyls. These, in the solid state, show intramolecular M-N interactions in their four-membered chelate rings, which progressively weaken down the series, the C-M-C angles becoming more open (〈M-N〉= 2.30(2), 2.52(2), 2.913(4) Å, C-M-C=160.7(2), 168.5(2), 180(-)°). Alkylmercury chloride complexes have been prepared by the reaction of HgCl₂ with [Li(MeR)], Li(2-(C(SiMe₃)₂)(C₅H₄N)), [Li(HR)], or Li(2-(NSiMe₃)(6-Me-C₅H₃N)), [Li(mpsa)], or from the redistribution reaction of the dialkyl (or amido) mercury complex with HgCl₂. The alkylmercury chloride complexes are dimeric or polymeric in nature with near-linear 2-coordination; (Hg-Cl=2.329(5), 2.318(4), 2.272(8) Å, Cl-Hg-C(N)=175.0(4), 174.7(4), 175.6(5)°). Cd(2-(CH(SiMe₃))(6-Me-C₅H₃N))₂(tmen), prepared from the reaction of Li(2-(CH(SiMe₃))(6-Me-C₅H₃N)) and CdCl₂ in the presence of tmen, has also been structurally authenticated as the rac isomer with the ipso protons directed towards the tmen.     

Quantitative surface analysis by X-ray photoelectron spectroscopy and X-ray excited auger electron spectroscopy

It is shown that X-ray excited KLL Auger electron spectra allow it to describe measured signal strengths similarly to X-ray photoelectron signals, thus offering valuable information on the quantitative surface composition of a solid sample. The principal equation and corresponding fundamental parameters are discussed. As a result Auger spectra of C, N, O, F, and Na can be easily used in a multiline approach for quantitative analysis. LMM and MNN spectra give rise to more problems, due to their more complicated structure, uncertainties with regard to the background and the influence of Coster-Kronig transitions. These problems are overcome by the use of empirical ratios of the strongest lines of 2p/LMM or 3d/MNN. Since these ratios are independent of sample composition, they allow it to transform the Auger signal into the corresponding photoelectron signal, provided that a standard sample has been measured. Thus a true additional information is obtained and moreover difficulties in cases of photoelectron spectra with overlapping lines from other chemical elements can be overcome.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Stand alone accreditation of RM producers: arguments against it

Accreditation has a special responsibility in the European conformity assessment system. Before starting a new activity like stand alone accreditation of reference material producers, the consequences for the market place should be considered.     

通用小型汽油机催化器应用研究

简要介绍了中国通用小型汽油机行业的现状及美国EPA对于通用小型汽油机的排放要求,并结合国内通用小型汽油机的排放统计现状,指出了催化器在通用小型汽油机行业应用的技术可能性,并针对通用小型汽油机的排放特点,指出了催化器应用于通用小型汽油机需注意的问题.     

Group 4 metallacarboranes of constrained geometries derived from B(cage)- and C(cage)-silylamido-substituted carborane ligands: a synthetic and structural investigation

The reactions of RNHSi(Me)₂Cl (1, R=t-Bu; 2, R=2,6-(Me₂CH)₂C₆H₃) with the carborane ligands, nido-1-Na(C₄H₈O)-2,3-(SiMe₃)₂-2,3-C₂B₄H₅ (3) and Li[closo-1-R′-1,2-C₂B₁₀H₁₀] (4), produced two kinds of neutral ligand precursors, nido-5-[Si(Me)₂N(H)R]-2,3-(SiMe₃)₂-2,3-C₂B₄H₅, (5, R=t-Bu) and closo-1-R′-2-[Si(Me)₂N(H)R]-1,2-C₂B₁₀H₁₀ (6, R=t-Bu, R′=Ph; 7, R=2,6-(Me₂CH)₂C₆H₃, R′=H), in 85, 92, and 95% yields, respectively. Treatment of closo-2-[Si(Me)₂NH(2,6-(Me₂CH)₂C₆H₃)]-1,2-C₂B₁₀H₁₁ (7) with three equivalents of freshly cut sodium metal in the presence of naphthalene produced the corresponding cage-opened sodium salt of the “carbons apart” carborane trianion, [nido-3-{Si(Me)₂N(2,6-(Me₂CH)₂C₆H₃)}-1,3-C₂B₁₀H₁₁]³⁻ (8) in almost quantitative yield. The reaction of the trianion, 8, with anhydrous MCl₄ (M=Ti and Zr) in 1:1 molar ratio in dry tetrahydrofuran (THF) at −78 °C, resulted in the formation of the corresponding half-sandwich neutral d⁰-metallacarborane, closo-1-M[(Cl)(THF)_n]-2-[1′-η¹σ-N(2,6-(Me₂CH)₂C₆H₃)(Me)₂Si]-2,4-η⁶-C₂B₁₀H₁₁ (M=Ti (9), n=0; M=Zr (10), n=1) in 47 and 36% yields, respectively. All compounds were characterized by elemental analysis, ¹H-, ¹¹B-, and ¹³C-NMR spectra and IR spectra. The carborane ligand, 7, was also characterized by single crystal X-ray diffraction. Compound 7 crystallizes in the monoclinic space group P2₁/c with a=8.2357(19) Å, b=28.686(7) Å, c=9.921(2) Å; β=93.482(4)°; V=2339.5(9) ų, and Z=4. The final refinements of 7 converged at R=0.0736; wR=0.1494; GOF=1.372 for observed reflections.     

Optimal group symmetric localized molecular orbitals

Summary The concept and generating method of optimum group symmetric localized molecular orbitals (OSLMOs) are proposed. The OSLMOs have strong points of orthogonality, equivalence and symmetry, and they are simultaneously as close to the classical VB structure as possible. By using the OSLMOs as one-electron orbitals the multiconfigurational correlation calculations are reduced. The scheme is also a valuable popularization and development to hybridization theory.     

芳香族化合物生物降解性的QSBR研究

分别采用线性基团贡献法和人工神经网络法对芳香族化合物的生物降解最大去除率QTOD进行QSBR研究。得到不同基团对生物降解性的贡献顺序为 :C6H5>COOH >OH >CO >CH3 >C1 >NH2>NO2 。线性基团贡献法对于训练组和测试组的预测正确率分别为 86%和 80 % ,总的预测正确率达85 % ;而人工神经网络法的预测正确率分别为 94%、80 %和 92 %。结果表明 ,线性基团贡献法和神经网络法的预测效果均很好 ,而神经网络法的预测更精确。