2-Amino-4-bromobutanoic Acid

(2S)- and (2R)-2-Amino-4-bromobutanoic acid were prepared starting from N-Boc-glutamic acid α tert-butyl ester. The double tert-butyl protection was necessary to prevent a partial racemisation during Barton’s radical decarboxylation used to transform the γ-carboxylic group into a bromide. This bromide reacted with different nitrogen, oxygen and sulphur nucleophiles to give nonnatural amino acids characterised by basic or heterocyclic side chains. The title compound was also used to prepare a conformationally constrained peptidomimetic.     

The outer valance orbital electron densities of cyclopentane by binary (e,2e) spectroscopy

The binding energy spectra and electron distributions in momentum space of the valence orbitals of cyclopentane (C(5)H(10)) are studied by Electron Momentum Spectroscopy (EMS) in a noncoplanar symmetric geometry. The impact energy was 1200 eV plus binding energy and energy resolution of the EMS spectrometer was 1.2 eV. The experimental momentum profiles of the outer valence orbitals are compared with the theoretical momentum distributions calculated using Hartree-Fock and density functional theory (DFT) methods. The shapes of the experimental momentum distributions are generally quite well described by both the Hartree-Fock and DFT calculations when the large and diffuse basis sets are used.     

Electron momentum spectroscopy of CF2Cl2: experimental and theoretical momentum profiles for outer valence orbitals

Electron momentum distributions for outer valence orbitals of CF2Cl2 have been obtained by (e,2e) electron momentum spectroscopy at an incident energy of 1200 eV + binding energy. The experimental electron momentum profiles are compared with Hartree-Fock and density functional theory (DFT) calculations using B3LYP hybrid functional with the 6-31G and 6-311+G* basis sets. Generally, the shapes of the experimental momentum profiles are well reproduced by DFT calculations using larger basis sets 6-311 + G*. An attempt has been made to clarify the ordering of the outer valence orbitals, which have been in controversy, by comparing experimental results with B3LYP/6-311 + G* calculations.     

A New Activation Method for Electroless Metal Plating：Palladium Laden via Bonding with Self—Assembly Monolayers

A new activation method has been developed for electroless copper plating on silicon wafer based on palladium chemisorption on SAMs of APTS without SnCl2 sensitization and roughening condition.A closely packed electroless copper film with strong adhesion is successfully formed by AFM observation.XPS study indicates that palladium chemisorption occurred via palladium chloride bonding to the pendant amino group of the SAMs.     

Total syntheses of epothilones B and d

A convergent, total synthesis of epothilones B (2) and D (4) is described. The key steps are Normant coupling to establish the desired (Z)-stereochemistry at C12-C13, Wadsworth-Emmons olefination of methyl ketone 28 with the phosphonate ester 8, diastereoselective aldol condensation of aldehyde 5 with the enolate of keto acid derivatives to form the C6-C7 bond, selective deprotection of acid 52, and macrolactonization.     

Determination of the Dissociation Constants of Urocanic Acid Isomers in Aqueous Solutions

Summary. (E)- and (Z)-Urocanic acids are endogenous chemicals in the normal mammalian skin. The first and the second thermodynamic dissociation constants (pK _a1 and pK _a2) of urocanic acid isomers were determined using UV spectrophotometry in aqueous solutions. The values with standard deviation (pK _a1 = 3.43 ± 0.12 and pK _a2 = 5.80 ± 0.04) and (pK _a1 = 2.7 ± 0.3 and pK _a2 = 6.65 ± 0.04) were obtained to (E)- and (Z)-urocanic acids, respectively. The second dissociations were studied also by potentiometric titration in aqueous sodium chloride solutions up to the isotonic salt concentration (0.154 mol dm⁻³), and the second thermodynamic dissociation constants as well as activity parameters for both isomers were determined at temperature 25°C and for (E)-urocanic acid also at 37°C. The obtained pK _a2 values were close to those found by UV spectrophotometry. The equations for the calculation of the second stoichiometric dissociation constants of urocanic acid isomers on molality and molarity scale in aqueous sodium chloride solutions were derived. The obtained pK _a1 and pK _a2 values for (Z)-urocanic acid appear to be essentially lower than some previously reported values in literature. An erratum to this article is available at .     

Conductivity Studies of <Emphasis Type="Italic">n</Emphasis>-Tetrabutylammonium Tetraphenylborate in 3-Pentanone in the Temperature Range from 283.15 to 329.15 K

The molar conductivities (Λ) of solutions of n-tetrabutylammonium tetraphenylborate (NBu₄BPh₄) in 3-pentanone have been measured in the temperature range from 283.15 to 329.15 K. The conductance data have been analyzed using the Lee-Wheaton conductivity equation with the distance parameter (a) set at Bjerrum’s pairing distance, and the limiting molar conductivities (Λ_o) and the association equilibrium constants (K _A) have been derived. The limiting ion conductivities (λ_±^o) have been evaluated according to the method of Krumgalz. The λ₊ ^o values have been compared with λ₊ ^o values calculated from the empirical equation of Gill. The thermodynamic functions, Gibbs energy (Δ G _A ^o), enthalpy (Δ H _A ^o) and entropy (Δ S _A ^o) for the process of ion-pair formation as well as the activation energy of the ionic movement (ΔH ^∗) have been evaluated. The obtained results are discussed in terms of ion-ion and ion-solvent interactions.     

GaAs光导开关飞秒激光点触发实验及分析

针对光导开关阵列和光纤分束耦合的实际应用环境,提出一种新的实验方案,用于测试当触发光源相对于开关光敏面为点光源时入射位置对输出脉冲的影响.实验证明,不同的入射位置对开关输出脉冲有很大的影响.在入射光从负极向正极扫描过程中输出脉冲逐渐增强,在正极附近输出达到峰值,但在电极边缘处有所减弱.分析表明,这一现象和开关体内电场的分布有密切联系.     

Ceria supported Ru~0-Ru~(δ+) clusters as efficient catalyst for arenes hydrogenation

Selective hydrogenation of aromatic amines,especially chemicals such as aniline and bis(4-aminocyclohexyl)methane for non-yellowing polyurethane,is of particular interests due to the extensive applications.To conquer the existing difficulties,in selective hydrogenation,,the Ru~0-Ru~(δ+)/CeO_2 catalyst with solid frustrated Lewis pairs was developed for aromatic amines hydrogenation with excellent activity and selectivity under relative milder conditions.The morphology,electronic and chemical properties,especially the Ru~O-Ru~(δ+) clusters and reducible ceria were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),sca nning electronic microscopy(SEM),X-ray photoelectron sp ectroscopy(XPS),CO_2 tempe rature programmed deso rption(CO_2-TPD),H_2 tempe rature programmed reduction(H_2-TPR),H_2 diffuse reflectance Fourier transform infrared spectroscopy(H_2-DRIFT),Raman,etc.The 2% Ru/CeO_2 catalyst exhibited good conversion of 95% and selectivity greater than 99% toward cyclohexylamine.The volcano curve describing the activity and Ru state was found.Owning to the "acidic site isolation" by surrounding alkaline sites,condensation between the neighboring amine molecules could be effectively suppressed.The catalyst also showed good stability and applicability for other aromatic amines and heteroarenes containing different functional groups.     

经典弹性力学与应用力学方法

通过对经典弹性力学半反演法的特点与应用力学方法的特点的对比,阐明应用力学方法是在经典弹性力学半反演法的基础上发展出来的,指出应用力学方法源自经典弹性力学．讨论了在弹性力学的教学过程中,突出半反演法和应用力学方法之间的关联,会产生很好的教学效果．