Catalyst-free preparation of 1,2,4,5-tetrasubstituted imidazoles from a novel unexpected domino reaction of 2-azido acrylates and nitrones

A highly efficient and convenient method for the synthesis of 1,2,4,5-tetrasubstituted imidazoles from readily accessible 2-azido acrylates and nitrones has been developed. This reaction proceeded under mild conditions without the assistance of any metal, acid, or base.     

5-methoxyaristololactam I, the first natural 5-substituted aristololactam from Asarum ichangense

A new aristololactam, 5-methoxyaristololactam I (1), was isolated from an ethanol extract of the whole plant of Asarum ichangense C. Y. Cheng et C. S. Yang, together with twenty known compounds (2-21). The structure of 1 was elucidated by spectroscopic methods. Compounds 11, 13, 17, and 19 were isolated from Aristolochiaceae for the first time. Compounds 2, 14, and 15 are considered as common constituents of the genus Asarum.     

A recursive approach to mortality-linked derivative pricing

In this paper, we develop a recursive method to derive an exact numerical and nearly analytical representation of the Laplace transform of the transition density function with respect to the time variable for time-homogeneous diffusion processes. We further apply this recursion algorithm to the pricing of mortality-linked derivatives. Given an arbitrary stochastic future lifetime T, the probability distribution function of the present value of a cash flow depending on T can be approximated by a mixture of exponentials, based on Jacobi polynomial expansions. In case of mortality-linked derivative pricing, the required Laplace inversion can be avoided by introducing this mixture of exponentials as an approximation of the distribution of the survival time T in the recursion scheme. This approximation significantly improves the efficiency of the algorithm.     

复杂网络局部结构的涌现:共同邻居驱动网络演化

在对真实网络的小世界和无标度特性进行了大量深入考量之后,最近的研究热点开始转移到更加细致的局部结构.实证数据显示,大量真实网络具有幂律的低阶集团度分布.这一普适的规律,无法由富者愈富以及熟人推荐的网络生长机理再现.本文提出一种由共同邻居驱动的网络演化模型,该模型能够重现实证研究所观察到的幂律集团度分布,暗示共同邻居驱动是复杂网络局部结构涌现形成的内在机理. 关键词： 复杂网络 演化模型 集团度分布 共同邻居     

共振散射比率法研究表面活性剂十二烷基磺酸钠与奎尼丁的相互作用

在pH 1.81的B-R缓冲介质中,由十二烷基磺酸钠(SDBS)与奎尼丁的相互反应导致其分别在278.0,377.0 nm两波长处所测得的共振散射信号(I)大大增强。当SDBS的浓度为3.0×10~(-4)mol·L~(-1)时,分别在上述两波长处测得的共振散射强度值(I_(278.0)及I_(377.0))与相应的奎尼丁浓度依次在0.067～40,0.062～40μmol·L~(-1)范围内呈线性关系,其检出限(3σ)分别为6.71,6.15nmol·L~(-1)。据此可作奎尼丁的单波长法共振散射光谱测定。进一步研究发现:如采用分别在240.0nm(波谷)及275.0nm(波峰)测得的共振散射强度的比率(即I_(240.0)/I_(375.0))作为参数,则其与奎尼丁浓度在0.007～75μmol·L~(-1)范围内呈线性关系,且奎尼丁检出限(3σ)为0.691nmol·L~(-1)。由此可见,采用双波长测量技术的共振散射比率法测定奎尼丁的效果优于前者。     

Adsorption of cyclohexene and its dehydrogenation intermediates on nAu/Pt(100)(n＝0,1,2) surfaces:A DFT study

Adsorption of cyclohexene and its dehydrogenation intermediates on the nAu/Pt(100) (n = 0, 1, 2 means clean Pt, one monolayer and two layers of Au covered Pt surfaces, respectively.) has been investigated by self-consistent (GGA-PW91) density functional theory combined with periodic slab model. It is found that on the clean platinum, there are two kinds of favorable adsorption sites, i.e., hollow sites and bridge sites, and the adsorption energy at the hollow site is larger than that at the bridge site. However, on the Au/Pt and 2Au/Pt surfaces, there are three kinds of adsorption sites, and the adsorption energies are alike at both the bridge site and the top site. The magnitude order of the adsorption energies is as follows: clean Pt > Au/Pt > 2Au/Pt. The configurations of cyclohexene molecule have been distorted a little during the geometry optimizations. The lengths of C–M (M = Pt or Au, on the top layer of the slab) bonds are closely related to the corresponding adsorption energies.     

Differentiation of α- or β-Aspartic Isomers in the Heptapeptides by the Fragments of [M + Na]<Superscript>+</Superscript> Using Ion Trap Tandem Mass Spectrometry

Electrospray ionization coupled with low energy collision induced dissociation (CID) in an ion trap mass spectrometer was used to examine the fragmentation patterns of the [M + Na]⁺ of eight pairs of heptapeptides containing α- or β-Asp residues in second and sixth amino acid positions, respectively. Selective cleavages at the peptide backbone C-terminal to two Asp residues were observed, which generated a series of C-terminal y₅ ions and N-terminal b₆ ions. Two typical ions: [ \texty₅ + \textNa-\textH ] ⁺ {\left[ {{{\text{y}}_{{5}}} + {\text{Na}}-{\text{H}}} \right]^{ + }} and [ \textb₆ + \textNa + \textOH ] ⁺ {\left[ {{{\text{b}}_{{6}}} + {\text{Na}} + {\text{OH}}} \right]^{ + }} , produced by α-Asp containing peptides were noted to be much more abundant than those of the peptides with β-Asp, which could be used for distinction of the isomers in Asp2 and Asp6, respectively. In addition, a series of internal ions generated by simultaneous cleavages at Asp residues were detected. Competitive reactions of carboxylic groups occurred between Asp6 side chain and C-terminus. Formation mechanisms of most product ions are proposed. The results obtained in this work are significant since low energy CID has been demonstrated to be effective for the distinction of Asp isomers.     

Theoretical studies on the transport property of oligosilane with p‐n junction

The electron transport properties of a novel p‐n junction nanowire caused by boron‐doping and phosphorus‐doping are investigated using density functional theory combined with the nonequilibrium Green's functions formalism. A satisfying rectification is observed. This is a reasonable result after the analysis of the molecular‐projected self‐consistent Hamitonian (MPSH) states, transmission spectra, the frontier orbitals, and the dipole moments. In contrast, the undoped chain has no rectification character. In addition, a negative differential resistance behavior is also observed at V = 1.8 ～ 2.2 V in the doped nanowire and it could be illustrated from the MPSH states and the transmission spectra. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Complexation thermodynamics between butyl rhodamine B and calix[n]arenesulfonates (n = 4, 6, 8)

The characteristics of host–guest complexation between water-soluble calix[n]arenesulfonates (CnS, n = 4, 6, 8) and butyl rhodamine B (BRB) were investigated by fluorescence spectrometry. Fluorescence spectroscopy experiments were performed in pH 8.0 Tris(3-aminomethane)–HCl buffer solution at different temperature to calculate the stability constants (K_S) for the stoichiometric 1:1 inclusion complexes of C4S, C6S, and C8S with BRB. The complex stability constant monotonically increased with the number of phenolic units in the calixarene ring. The thermodynamic parameters at T = 298 K for the inclusion complexes were calculated through Van’t Hoff analysis. The inclusion complexes of CnS with BRB were driven by the favorable enthalpic changes, accompanying negative entropy changes. The stability constants were affected by the acidity of the solution. When pH was 8.0, the stability constants reached the maximum. The complex interaction was mainly attributed to the weak forces including electrostatic interaction and hydrogen bonding.     

Fluorosurfactant-prepared triangular gold nanoparticles as postcolumn chemiluminescence reagents for high-performance liquid chromatography assay of low molecular weight aminothiols in biological fluids

Our recent study demonstrates the synthesized triangular gold nanoparticles (AuNPs) by trisodium citrate reduction of HAuCl(4) in the presence of nonionic fluorosurfactant (FSN) could display stronger catalytic activity towards luminol-chemiluminescence (CL) than spherical AuNPs. Ultratrace aminothiols may cause a great decrease in CL intensity of the triangular AuNPs-luminol CL system. In this article, we utilize the as-prepared triangular AuNPs as novel postcolumn CL reagents to explore a simple high-performance liquid chromatography (HPLC)-CL method for the determination of low molecular weight aminothiols (i.e., cysteine, homocysteine, glutathione, cysteinylglycine and glutamylcysteine). The as-prepared triangular AuNPs were easier to synthesize, stable at a wider pH range and high ionic strength, and highly selective and sensitive towards reduced aminothiols. The detection limits at a signal-to-noise ratio of 3 for cysteine, homocysteine, glutathione, cysteinylglycine and glutamylcysteine were 0.016, 0.08, 0.1, 0.04 and 0.1pmol, respectively. Recoveries from spiked urine and plasma samples were 95.7-104.3%. The applicability of the proposed method has been validated by determining these low molecular weight aminothiols in human urine and plasma samples with satisfactory results, and thus it will have great potential application in clinical diagnosis.