N-亚苯基氨基酰胺气相高温分解反应机理的密度泛函研究

利用密度泛函理论研究了N-亚苯基氨基酰胺气相高温分解生成苯腈和苯甲酰胺的反应机理。首先用B3LYP／6-31G(d,p)方法优化反应中反应物、过渡态、中间体及产物的几何构型,通过振动分析确认了过渡态的结构,并通过内稟反应坐标方法(IRC)确认能量最低的反应途径。本文报道了三条可能的反应通道,包括一条直接协同高温分解反应和两条先成环后协同高温分解反应途径,其中直接协同高温分解反应由于能垒低,因此发生的几率较大     

Partington: The Missing Part

Abstract

J. R. Partington (1886–1965) was a prolific author, making major contributions in physical chemistry and history of chemistry. He spent most of his career teaching chemistry at Queen Mary College, University of London. Retiring to Cambridge in 1951, much of his time was devoted to writing the biographically and bibliographically rich A History of Chemistry. Three volumes were published by Macmillans from 1961 to 1964, with the first part of volume four appearing posthumously in 1970. This paper considers the reasons why its second part, though planned and partly written, was never published. The evidence is contained in an archive of papers in the Science Museum Library, and amongst the correspondence of Joseph Needham, who struck up a close relationship with Partington. Prominent historians who were involved in Macmillans’ eventual decision not to complete the series, either directly or indirectly, included William Brock, Allen Debus, June Fullmer, Frank Greenaway, Geoffrey Lewis, Robert Multhauf, Walter Pagel, Harry Sheppard, Nathan Sivin, William Smeaton, and Needham himself.     

Glucosinolates: The synthetic approach

Acting generally as bio-precursors of isothiocyanates, glucosinolates (GLs) are important thiosaccharidic metabolites which occur in all plant families of the order Brassicales – namely in our daily vegetables. All known GLs (ca 120 characterized molecules) display a remarkable structural homogeneity invariably based on a β-D-glucopyrano unit and an O-sulfated anomeric (Z)-thiohydroximate function connected to a side chain which constitution, depending on plant species, is the sole structural variant. Dedicated extractive methods allow one to isolate a number of GLs from adequate plant material, but in many cases, organic synthesis brings crucial help for the production of natural GLs. In other respects, synthesis is the only way to elaborate a diversified range of artificial GL analogues. This account summarizes the varied synthetic approaches developed by us and by others since the early 1960s.     

The system: Water-p-xylene-l-aminooctane-octanoic acid

Summary The influence of the presence of a neat soap mesomorphic phase on the stability of emulsions is shown by investigations on a model system of water, p-xylene, octanoic acid and l-amino-octane. The mesomorphic phase could be formed in the system by increasing the emulsifier to oil ratio or by making the amine: acid ratio greater than above. In both cases, the stability of the emulsion increased suddenly when the system was changed in such a manner so that the mesomorphic phase was formed.The investigations have also shown the presence of optically anisotropic layers in the region of the oil phase adjacent to the interfaces for stable emulsions, where no mesomorphic phase can be formed at equilibrium. This is cnsidered to be due to the ordering influence of the interface, adding the small energy necessary to orientate the molecules.Maximum stabilizing power of the mesomorphic phase is also found to be at a maximum when the amino: acid ratio is about 11.With 6 figures     

The thermolysis of dicarbonylcyclopentadienyliron dimer: The formation of biferrocene

The thermolysis of dicarbonylcyclopentadienyliron dimer in a sealed tube at 300°C has been reported to produce ferrocene, carbon monoxide, carbon dioxide, cyclopentadiene and elemental iron. We observe in addition to these products the production of biferrocene and elemental carbon. Thermolysis of carbonylcyclopentadienyliron tetramer (produced from the dimer by thermolysis in refluxing xylene) produces ferrocene, iron and carbon monoxidre; no biferrocene, carbon dioxide or elemental carbon are produced. A scheme is proposed to account for these products.     

The Potential Effects of Phytoestrogens: The Role in Neuroprotection

Phytoestrogens are naturally occurring non-steroidal phenolic plant compounds. Their structure is similar to 17-β-estradiol, the main female sex hormone. This review offers a concise summary of the current literature on several potential health benefits of phytoestrogens, mainly their neuroprotective effect. Phytoestrogens lower the risk of menopausal symptoms and osteoporosis, as well as cardiovascular disease. They also reduce the risk of brain disease. The effects of phytoestrogens and their derivatives on cancer are mainly due to the inhibition of estrogen synthesis and metabolism, leading to antiangiogenic, antimetastatic, and epigenetic effects. The brain controls the secretion of estrogen (hypothalamus-pituitary-gonads axis). However, it has not been unequivocally established whether estrogen therapy has a neuroprotective effect on brain function. The neuroprotective effects of phytoestrogens seem to be related to both their antioxidant properties and interaction with the estrogen receptor. The possible effects of phytoestrogens on the thyroid cause some concern; nevertheless, generally, no serious side effects have been reported, and these compounds can be recommended as health-promoting food components or supplements.     

考虑极性基团相互作用影响的疏水常数计算方法

通过对点价的修正,将分子连接性指数转变成为一种量子拓扑指数。由于改进后的量子拓扑指数能够很好地表达分子的体积和电性等结构信息,因此该指数与疏水常数计算中的极性基团相互作用有很好的相关性。实际计算表明,对于含有极性基团的分子,用该指数计算的结果更加精确。     

Pinensins: The First Antifungal Lantibiotics

Lantibiotics (lanthionine‐containing antibiotics) from Gram‐positive bacteria typically exhibit activity against Gram‐positive bacteria. The activity and structure of pinensin A ( 1 ) and B ( 2 ), lantibiotics isolated from a native Gram‐negative producer Chitinophaga pinensis are described. Surprisingly, the pinensins were found to be highly active against many filamentous fungi and yeasts but show only weak antibacterial activity. To the best of our knowledge, lantibiotic fungicides have not been described before. An in‐depth bioinformatic analysis of the biosynthetic gene cluster established the ribosomal origin of these compounds and identified candidate genes encoding all of the enzymes required for post‐translational modification. Additional encoded functions enabled us to build up a hypothesis for the biosynthesis, export, sensing, and import of this intriguing lantibiotic.     

化学亲情篇——烯烃

Through three stories about carbon-carbon double bonds, the series of dialogues between the protagonist Xiaoxi and her family members discuss the three structures and real life applications of alkenes containing the planar carbon-carbon double bond, namely the most basic ethene as a plant hormone, the health effect of cis or trans-unsaturated fatty acids, and the light sensing via the fast conversion of 11-cis-retinal cis-trans in rhodopsin.     

MOLCAS 7: The Next Generation

Some of the new unique features of the MOLCAS quantum chemistry package version 7 are presented in this report. In particular, the Cholesky decomposition method applied to some quantum chemical methods is described. This approach is used both in the context of a straight forward approximation of the two‐electron integrals and in the generation of so‐called auxiliary basis sets. The article describes how the method is implemented for most known wave functions models: self‐consistent field, density functional theory, 2nd order perturbation theory, complete‐active space self‐consistent field multiconfigurational reference 2nd order perturbation theory, and coupled‐cluster methods. The report further elaborates on the implementation of a restricted‐active space self‐consistent field reference function in conjunction with 2nd order perturbation theory. The average atomic natural orbital basis for relativistic calculations, covering the whole periodic table, are described and associated unique properties are demonstrated. Furthermore, the use of the arbitrary order Douglas‐Kroll‐Hess transformation for one‐component relativistic calculations and its implementation are discussed. This section especially focuses on the implementation of the so‐called picture‐change‐free atomic orbital property integrals. Moreover, the ElectroStatic Potential Fitted scheme, a version of a quantum mechanics/molecular mechanics hybrid method implemented in MOLCAS, is described and discussed. Finally, the report discusses the use of the MOLCAS package for advanced studies of photo chemical phenomena and the usefulness of the algorithms for constrained geometry optimization in MOLCAS in association with such studies. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

The Pocket Laboratory: The Blowpipe in Eighteenth-Century Swedish Chemistry

This article examines the role of the blowpipe in the discovery process of the disproportionately large number of new elements found by Swedish chemists during the eighteenth century and into the nineteenth. While individual chemists abroad used versions of the tool, in Sweden alone its use was ubiquitous across the chemical and mineralogical research community, and its consistently simple handheld design made basic dry chemical analysis quick, cheap, and portable. This shared use of the tool was crucial to the development of the mineral analysis projects that uncovered new substances, first by enabling the adoption of a system defining minerals by their chemical components and mineralogy by chemical analysis, and second by providing a simple and practical method for that analysis that facilitated collaboration across institutions, physical distance, and time.     

The conjugated-circuit model: The optimum parameters for benzenoid hydrocarbons

A search for the optimum set of parameters for the conjugated-circuit computations on benzenoid hydrocarbons in reported. The SCFπ-MO resonance energies (REs) of Dewar and de Llano were used as standards for the determination ofR _n (n= l,2,3) parameters, which correspond to 4n + 2 conjugated circuits. The following set of parameters:R ₁ = 0.827 eV.R ₂ = 0.317 andR ₃ = 0.111 eV produced the best agreement between the REs calculated by the conjugated-circuit model and the REs calculated using the SCF π-MO model.     

The electrochemical reduction of maleimide: The synthesis of succinimide

The electrochemical reduction of maleimide has been investigated in the pH range 0–14 at a variety of electrode materials. The reaction scheme was found to fall into three distinct sections, depending upon the pH at which the reduction was performed. At low pH the reduction product was found to be succinimide, and the mechanism of its formation is described. At higher pH values, the hydrolysis of starting materials complicates the interpretation of the electrochemical measurements, but nevertheless the overalls reduction mechanism could be deduced. Polarographic data complement information obtained from rotating disc experiments, and comparison is made with the electrochemical reduction of phthalimide.