Ruthenium‐catalyzed formal alkyl group transfer: Synthesis of quinolines from nitroarenes and alkylammonium halides

Nitroarenes are reductively cyclized with an array of tetraalkylammonium halides and trialkylarnmonium chlorides in the presence of a catalytic amount of a ruthenium catalyst along with tin(II) chloride dihydrate at 180° to afford the corresponding quinolines in moderate to good yields. The addition of tin(II) chloride dihydrate is necessary for the effective formation of quinolines and toluene is the solvent of choice. A reaction pathway involving initial reduction of nitroarenes to anilines and conversion of alkylammonium halides to alkylamines, alkyl group transfer from alkylamines to anilines to form an imine, dimerization of imine, and heteroannulation is proposed for this catalytic process.     

Molecular dynamics study of hydration in ethanol-water mixtures using a polarizable force field

The abnormal physicochemical characteristics of ethanol solvation in water are commonly attributed to the phenomenon of hydrophobic hydration. To investigate the structural organization of hydrophobic hydration in water-ethanol mixtures, we use molecular dynamics simulations based on detailed atomic models. Induced polarization is incorporated into the potential function on the basis of the classical Drude oscillator model. Water-ethanol mixtures are simulated at 11 ethanol molar fractions, from 0.05 to 0.9. Although the water and ethanol models are parametrized separately to reproduce the vaporization enthalpy, static dielectric constant, and self-diffusion constant of neat liquids at ambient conditions, they also reproduce the energetic and dynamical properties of the mixtures accurately. Furthermore, the calculated dielectric constant for the various water-alcohol mixtures is in excellent agreement with experimental data. The simulations provide a detailed structural characterization of the mixtures. A depletion of water-water hydrogen bonding in the first hydration shell of ethanol is compensated by an enhancement in the second hydration shell. The structuring effect from the second solvation shell gives rise to a net positive hydrogen-bonding excess for ethanol molar fractions up to approximately 0.5. For larger molar fractions, the second hydration shell is not sufficiently populated to overcome the net H-bond depletion from the first shell.     

β-内酰胺类抗生素酶促合成新进展

β-内酰胺类抗生素的合成在制药工业中占据重要的地位, 相关的酶促合成方法研究备受关注; 酶促合成显著提高合成效率, 减少三废的排放, 是实现绿色合成的有效方法. 综述了近年来β-内酰胺类抗生素酶促合成研究的新进展, 包括一锅合成法、原位产物排出法、介质技术和酶固定化方法.     

Thermal and electrochemical C-X activation (X = Cl,Br, I) by the strong Lewis acid Pd3(dppm)3(CO)2+ cluster and its catalytic applications

The stoichiometric and catalytic activations of alkyl halides and acid chlorides by the unsatured Pd(3)(dppm)(3)(CO)(2+) cluster (Pd(3)(2+)) are investigated in detail. A series of alkyl halides (R-X; R = t-Bu, Et, Pr, Bu, allyl; X = Cl, Br, I) react slowly with Pd(3)(2+) to form the corresponding Pd(3)(X)(+) adduct and "R(+)". This activation can proceed much faster if it is electrochemically induced via the formation of the paramagnetic species Pd(3)(+). The latter is the first confidently identified paramagnetic Pd cluster. The kinetic constants extracted from the evolution of the UV-vis spectra for the thermal activation, as well as the amount of electricity to bring the activation to completion for the electrochemically induced reactions, correlate the relative C-X bond strength and the steric factors. The highly reactive "R(+)" species has been trapped using phenol to afford the corresponding ether. On the other hand, the acid chlorides react rapidly with Pd(3)(2+) where no induction is necessary. The analysis of the cyclic voltammograms (CV) establishes that a dissociative mechanism operates (RCOCl --> RCO(+) + Cl(-); R = t-Bu, Ph) prior to Cl(-) scavenging by the Pd(3)(2+) species. For the other acid chlorides (R = n-C(6)H(13), Me(2)CH, Et, Me, Pr), a second associative process (Pd(3)(2+) + RCOCl --> Pd(3)(2+.....)Cl(CO)(R)) is seen. Addition of Cu(NCMe)(4)(+) or Ag(+) leads to the abstraction of Cl(-) from Pd(3)(Cl)(+) to form Pd(3)(2+) and the insoluble MCl materials (M = Cu, Ag) allowing to regenerate the starting unsaturated cluster, where the precipitation of MX drives the reaction. By using a copper anode, the quasi-quantitative catalytic generation of the acylium ion ("RCO(+)") operates cleanly and rapidly. The trapping of "RCO(+)" with PF(6)(-) or BF(4)(-) leads to the corresponding acid fluorides and, with an alcohol (R'OH), to the corresponding ester catalytically, under mild conditions. Attempts were made to trap the key intermediates "Pd(3)(Cl)(+)...M(+)" (M(+) = Cu(+), Ag(+)), which was successfully performed for Pd(3)(ClAg)(2+), as characterized by (31)P NMR, IR, and FAB mass spectrometry. During the course of this investigation, the rare case of PF(6)(-) hydrolysis has been observed, where the product PF(2)O(2)(-) anion is observed in the complex Pd(3)(PF(2)O(2))(+), where the substrate is well-located inside the cavity formed by the dppm-Ph groups above the unsatured face of the Pd(3)(2+) center. This work shows that Pd(3)(2+) is a stronger Lewis acid in CH(2)Cl(2) and THF than AlCl(3), Ag(+), Cu(+), and Tl(+).     

Optically active sum frequency generation from molecules with a chiral center: amino acids as model systems

With amino acids as model systems, optically active sum frequency generation (OA-SFG) was used to probe the chirality of molecules with a chiral center and an intrinsically achiral chromophore in isotropic solution for the first time. Like that of circular dichroism (CD), the OA-SFG's near electronic resonance originates from the extrachromophoric chiral perturbation on the carboxyl chromophore. The difference in the relative strengths of OA-SFG and CD among different amino acids can be explained by the difference in the details of perturbations.     

Adenanthusone,a New Ursane Type Nortriterpenoid from Isodon adenanthus

A new ursane‐type nortriterpenoid, adenanthusone (=(11α,12α)‐4‐demethyl‐11,12‐epoxy‐3,13‐dihydroxy‐2‐oxoursa‐3,20(30)‐diene‐28‐oic acid γ‐lactone; 1 ) was isolated from Isodon adenanthus. Its structure was determined by NMR spectra and X‐ray crystallographic diffraction analysis. The biogenetic implication of the nortriterpene is discussed.     

A theoretical investigation of titanium aluminium nitrides, (Ti,Al)N: Electronic structure and chemical bonding

Titanium aluminium nitrides, Ti_1-x Al _x N, can be prepared as films by various sputtering methods. They form metastable phases in which the titanium and aluminium atoms are randomlydistributed over the metal sublattice. In the present work two ordered model structures, Ti₃AlN₄ and TiAlN₂, have been chosen, for which LAPW band-structure calculations have been performed. The calculated densities of states (DOS) and the local partial DOS for both model structures are compared with the corresponding values for TiN. Characteristic changes in the DOS of the p band are observed which are caused by the nitrogenp orbitals that point towards the aluminium spheres. The bonding situation is investigated on the basis of electron density and difference electron density plots. The substitution of titanium atoms by aluminium atoms leads to stronger covalent Ti–Ti and N–Ti bonds and to additional ionic bonding contributions by the aluminium atoms whose ionicity increases from Ti_0.50Al_0.50N to Ti_0.75Al_0.25N.     

基于三维静电势参数研究C60溶解性的构效关系

在量子化学从头算基础上,对一系列溶剂化合物分子进行了结构优化和三维静电势参数计算,运用多元线性回归分析和神经网络方法对C60在121种不同溶剂的溶解性与计算的结构参数进行了构效关系研究.用建立起来的QSPR 关系式对15种不同结构类型溶剂进行了预测,并阐述了C60溶质与不同溶剂之间的相互作用,获得了满意的结果.     

Sorption of radionuclides on natural materials

Information about the sorption of radionuclides on natural materials used for cementation of liquid radioactive wastes (RAW) is important for predictions of migration rates of radionuclides in the products of fixation. Cementation process for conditioning liquid RAW uses, besides cement, materials which improve quality of products. In Czechoslovakia technology among these materials are clinoptilolite tuffit, mordenite tuff, tobermorite and fly ash. Liquid RAW issued from nuclear power plants contains the principal radionuclides⁶⁰Co,¹³⁴Cs and¹³⁷Cs, therefore, a sorption study of these radionuclides was carried out. pH of liquid RAW was 12.5–13.7 and salt content ca. 200 g·dm^–3. Results of sorption are given by distribution coefficients. The best results for cesium in those pH region and salt content had mordenite tuff D_Cs=100 dm³·kg^–1 and the worst results had fly ash D_Cs=4.1 dm³·kg^–1. The best results for cobalt in those solutions had tobermorite D_Co=38 dm³·kg^–1 and the worst results had fly ash D_Co=6.9 dm³·kg^–1.     

Miscibility of PVC/PMMA blends by vicat softening temperature, viscometry, DSC and FTIR analysis

 This paper deals with the miscibility of polyvinyl chloride (PVC) with polymethyl methacrylate (PMMA). Blends of variable compositions from 0 to 100 wt% were prepared in the presence (15, 30 and 50 wt%) and in the absence of di ethyl- 2 hexyl phtalate as plasticizer. Their miscibility was investigated by using various analytical methods: determination of the Vicat softening temperature, a viscometry method based on the criterion of polymer–polymer miscibility, differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The results show that the plot of Vicat temperature against composition is a continuous curve, indicating the miscibility of the blend. The viscometry method and DSC find that the two polymers are miscible up to about 60 wt% of PMMA. This miscibility is due to a specific interaction of hydrogen bonding type between carbonyl groups (C=O) of PMMA and hydrogen from (CHCl) groups of PVC, as evidenced by FTIR spectroscopy. The two-band deconvolution shows an increase in associated groups percentage in the domain of miscibility.