Versuche mit Natrium. Leucht‐ und Lumineszenzerscheinungen

The yellow light of burning sodium is well known but some other reactions which are running by emitting light are not yet properly investigated. In the article reactions of sodium are demonstrated which show interesting luminescence phenomena. One reaction is emitting a blue light which is not described in scientific literature until now.     

Oligomeric polyaromatic ether-ketone-sulfones with acetylenic end groups. IX.

Two oligomeric polyaryl ether-ketone-sulfones with acetylenic end groups have been prepared. These materials which are low melting and readily soluble in organic solvents on heating undergo reactions which are presumably trimerizations of the terminal acetylenic groups to give cured polymers which do not soften until about 200°C and which are stable in circulating air at 300°C with less than 10% weight loss in 10 days.     

The effect of inhomogeneous stickiness on polymer aggregation

The aggregation of polymers is important in the formation of marine aggregates and the vertical transport of material in the ocean. A polymer may be inhomogeneous along its length, with associating groups at some points along its length where bonds are more likely to form. In this paper we investigate the effects of inhomogeneous 'stickiness' along the polymer length. We describe the results of three-dimensional off-lattice simulations of polymer-polymer aggregation for four different types of polymer: polymers which are sticky along their entire length, polymers which are sticky at the ends only and two types of polymer which are slightly sticky along their entire length. We examine the mean radius of gyration and the fractal dimension of the resulting aggregates and the dynamics of aggregation. The slightly sticky polymers and the polymers which are sticky only at the ends form aggregates with a higher fractal dimension than the polymers which are sticky along their entire length. However, the mean radius of gyration of the aggregates formed by polymers which are sticky only at the ends is significantly larger than that of the aggregates formed from slightly sticky polymers. The aggregation dynamics are also different for the polymers which are sticky only at the ends compared to the slightly sticky polymers. A single 'stickiness value' is therefore likely to be inadequate to describe a polymer. We also examine the effect of polymer rigidity; it seems that the effect of inhomogeneous stickiness is greater for almost-straight polymers than for coiled chains.     

叠氮二异丁基铝的构造及其缔合-解离平衡研究

叠氮二异丁基铝（DBAA）是一个新合成的化合物。通过相对分子质量的测定、氢－核磁共振谱和铝－核磁共振谱的测定,确定了DBAA三聚体的分子构造;在溶液中研究了DBAA的三聚体和单晶体之间的缔合－解离平衡。这个平衡受溶剂性质、温度的影响。借助铝－核磁共振谱和相对分子质量的测定计算了DBAA三聚体的解离平衡常数、解离焓和解离熵等热力学数据。     

What makes an N12 cage stable?

Much recent attention has been given to molecules containing only nitrogen atoms. Such molecules N(x) can undergo the reaction N(x) --> (x/2)N(2), which is very exothermic. These molecules are potential candidates for high energy density materials (HEDM). However, many all-nitrogen molecules dissociate too easily to be stable, practical energy sources. It is important to know which nitrogen molecules will be stable and which will not. In the current study, a variety of N(12) cages with all single bonds are examined by theoretical calculations to determine which ones are the most thermodynamically stable. Calculations are carried out using Hartree-Fock (HF) theory, gradient-corrected density functional theory (DFT), and Moller-Plesset perturbation theory (MP2 and MP4). Relative energies among the various isomers are calculated and trends are examined in order to determine which structural features lead to the most energetically favorable molecules.     

The formation of low-dimensional inorganic nanotube crystallites in carbon nanotubes

The filling of carbon nanotubes, which vary in diameter and morphology, is directly observed by molecular dynamics computer simulation with a potential model which thermodynamically favors a four-coordinate bulk crystal structure. Inorganic nanotube (INT) structures form which are based on percolating hexagonal nets. For small carbon nanotube diameters the filling is shown to proceed via an "internal wetting" mechanism, which depends on the internal carbon nanotube area rather than the free volume. Both single- and double-walled INTs are predicted to form. The atomistic formation mechanisms are discussed and an intermediate structure identified. The INT structures, including the observed intermediate, are discussed by reference to a simple energy landscape. The formation energetics are discussed in terms of a simple analytical model which combines the INT strain energy and the tube-tube interactions. An effective phase diagram, which predicts the INT morphologies as a function of carbon nanotube diameter, is derived and discussed with respect to the analytical model.     

SSC: a tool for constructing libraries for systematic screening of conformers

Even a relatively small molecule with 10-20 atoms might have a few local minima, which correspond to different conformers. The number of local minima quickly increases with molecular size and the most common algorithms, driven by calculated forces, frequently identify a minimum, which is closest to the initial structure, rather than the most stable conformer. Here we discuss how to perform a systematic search of the conformational space for a chain-like molecule. Our approach is fully automated and a user has control which chemical bonds will be probed and with which increments. Moreover, whole fragments of the molecule, which are adjacent to each selected rotational bond, are rotated in a properly selected cylindrical coordinate system and unchemical hybridizations and some "clashes" between neighboring groups, which are common when standard Z-matrices are used, are avoided. A library of potentially relevant conformers is created with a tool, which we call SSC, denoting Systematic Screening of Conformers. Each member of the library is prescreened at a predefined level of theory and the most promising conformers are identified. Finally, they are further evaluated at a higher level of theory to identify the most stable structures and their physicochemical properties. As an example, we demonstrate the results of this approach for 2'-deoxycytidine.     

The signal vs. concentration relationships in fluorimetry

Formulae for the fluorescence signal are derived which take into account some factors hitherto neglected. From these formulae conditions are deduced, for which a linear relationship exists between the concentration of the fluorescent components and the intensity of the fluorescence. In some cases of practical interest the fulfilment of these conditions cause too low a sensitivity. For such cases a method of optimization is outlined, by means of which the conditions are found which lead to the least deviation from linearity at the required sensitivity.     

Hypervirial analysis of enclosed quantum mechanical systems. III. Unsymmetrical boundary conditions

New theoretical developments based upon hypervirial analysis of enclosed systems are given. Systems which obey unsymmetrical boundary conditions are analyzed. Several results which were given by the authors in two previous communications are generalized.     

Regioselective rhodium-containing catalysts for ring-opening polymerizations and hydrosilylations

Organometallic rhodium complexes are described which are highly efficient initiators for the ring-opening polymerization of expoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon–hydrogen bonds must also be present. These same catalyst–cocatalyst mixtures are also highly active for hydrosilylation reactions. Other complexes bearing phosphine ligands have been discovered, which while active for hydrosilylation, are not catalysts for epoxide polymerizations. Polymer supported rhodium catalysts are also described which permit the synthesis of epoxy-functional silanes in high yields without competing ring-opening polymerization.     

On the theory of steady-state current flow through electrolytes

A method of solving electrodiffusion equations, which generalizes the method of joining asymptotic solutions, is developed. Approximate solutions for prelimit and beyond-limit currents are obtained. The limiting values of field strength at which a boundary layer is formed are found. The coordinates and field strength values at which the Boltzmann distribution of the concentration of species is observed are found.     

西红花有效成分合成研究进展

西红花主要有效成分为西红花酸和西红花糖苷,论文综述西红花酸和西红花糖苷生物合成和化学合成方法.在生物合成中最关键的是用葡萄糖糖基转移酶作催化剂将西红花酸转化为西红花糖苷;共轭多烯链化合物是合成西红花有效成分的起始物,在论文中概述了几种通过Wittig和Wittig-Horner 反应合成共轭多烯链化合物的路线.     

Gold ultra-microelectrode arrays: application to the steady-state voltammetry of hydroxide ion in aqueous solution.

Gold ultra-microelectrode arrays are used to explore the electrochemical oxidation of hydroxide ions and are shown to be analytical useful. Two types of ultra-microelectrode arrays are used; the first consist of 256 individual electrodes of 5 microm in radius, 170 of which are electrochemically active in a cubic arrangement which are separated from their nearest neighbour by a distance of 100 microm. The second array compromises 2597 electrodes of 2.5 microm in radius and of which 1550 of which are electrochemically active in a hexagonal arrangement separated by the nearest neighbour by 55 microm. Well defined voltammetric waves are found with peak currents proportional to the concentration of hydroxide ions in the range 50 microM to 1 mM. Detection limits of 20 microM using the 170 ultra-microelectrode and 10 microM with the 1550 ultra-microelectrode array are shown to be possible but with a higher sensitivity of 4 mA M(-1) observed using the 1550 ultra-microelectrode array compared to 1.2 mA M(-1) with the 170 ultra-microelectrode array.     

The classification of order-disorder transitions on surfaces

Order-disorder transitions occur in adsorbed systems of great diversity.However, the transitions themselves can be shown to fall into just a few classes which are characterized by differing critical properties. The particular class to which a given transition belongs is determined directly from the nature of the ordered state and substrate. The critical behavior of some of these classes is of great interest currently, and the observations of such transitions provide a test of the modern theory of critical phenomena. The simple but powerful ideas of Landau and Lifshitz which underlie the above classification are elucidated in the context of order-disorder transitions on surfaces. The “Landau rules” are derived, applied, and yield the several universality classes which can be observed in surface transitions. Specific applications are made to recent experiments, and some areas which call for experimental investigations are noted.     

Die Cardenolide und Pregnan-Glykoside der Wurzeln von Asclepias lilacina WEIMARCK. I. Isolierungen Glykoside und Aglykone, 290. Mitteilung

The dried roots of Asclepias lilacina contain ca. 14% glykosides, in which both cardenolides and ester glycosides of pregnane derivatives are present, the latter predominating. Uzarigenin, coroglaucigenin, and their corresponding glycosides ascleposide and frugoside, resp., were shown to be present; of these four, uzarigenin was isolated in crystalline form. The ester glycosides, some of which could be isolated in a crystalline state, are predominantly composed of the aglycones 20-O-acetyl-12-O-benzoyl-sarcostin and 12,20-di-O-benzoyl-sarcostin, besides which esters of desacetyl-metaplexigenin, lineolon, and dihydrosarcostin are also present. These aglycones are mostly attached to various trisaccharides which are composed of at least two 2-deoxy-sugar residues. Mild acid hydrolysis gave, besides the genins, 7 sugars, namely cymarose, oleandrose, digitoxose, 3-O-methyl-6-deoxy-D-allose (U3), as well as 3 unknown sugars U1, U2 and U5 which are probably disaccharides. U1 and U2 were isolated in crystalline form; they are isomeric and have been named asclepobiose and lilacinobiose; they are probably composed of units similar to those in the isomeric pachybiose.     

Electrochemical determination of sulfide and sulfite ions by pneumatoamperometry

Sulfide and sulfite ions in aqueous solution are converted through acidification to hydrogen sulfide and sulfur dioxide, which are purged from solution with nitrogen carrier gas. The volatile species are detected through oxidation in 1 M sulfuric acid at an anodically polarized platinum electrode separated from the gas stream by a gas-permeable polymer membrane. Mixtures of sulfide and sulfite are separated and determined independently through pH control during acidification. Interferences from metal ions, which form sulfide precipitates, and other anions, which form volatile species on acidification, are discussed.     

Sequence confirmation of modified oligonucleotides using IRMPD in the external ion reservoir of an electrospray ionization Fourier transform ion cyclotron mass spectrometer

Modified oligonucleotides continue to play an important role as antisense compounds that inhibit the expression of genes associated with metabolic disorders, cancer, and infectious diseases. Because the majority of modifications render these molecules refractory to standard enzymatic sequencing techniques, alternative sequencing methods which are fast and reliable are needed. In this work we explore how sugar and backbone modifications affect fragmentation patterns observed from oligonucleotides which are fragmented by infrared multiple photon dissociation in the external reservoir of an electrospray ionization Fourier transform ion cyclotron mass spectrometer. The modifications influence which fragment types (i.e., a(n)-B versus c(n)) dominate and the ease with which the oligonucleotides are fragmented. General observations for confirming the sequence of oligonucleotides are described.     

Synthesis and characterization of dicationic ionic liquids that contain both hydrophilic and hydrophobic anions

A series of dicationic ionic liquids, in which each dication is associated with both a hydrophobic anion and a hydrophilic anion, are synthesized. The thermal properties and solubility in organic solvents of these ILs are characterized. The ionic liquids show interesting properties, which are different from those of dicationic ionic liquids, in which each dication is associated with two identical anions.     

Rearrangements of 5-azidoisoxazoles

5-Azidoisoxazoles are prepared via displacement of a chlorine atom in 5-chloroisoxazoles with azide ion. These 5-azidoisoxazoles contain an unsaturated group (olefin, aldehyde, oxime or hydrazone) in the 4-position which participates during thermal decomposition of the azide. Two types of products are formed which are non-interconvertible: (i) bicyclic isoxazoles which result from direct attack of the azide or nitrene on the unsaturated group; (ii) monocyclic pyrroles and pyrazoles which result from ring opening followed by bond reorganization and subsequent ring closure. Mechanisms for the two discrete processes are discussed.     

3,3,3-Trifluoropropyl(methyl)cyclosiloxanes

Mixtures of cyclosiloxanes containing 3, 3, 3-trifluoropropyl(methyl)-and dimethylcyclosiloxanes units, are separated by vacuum distillation and GLC. Three hitherto undescribed compounds are isolated and characterized. Six new cyclosiloxanes are identified by indirect methods in cuts which are mixtures. Chromatography and fractional distillation give results which are in satisfactory agreement.