卤代化合物的光化学反应研究进展

介绍近年来卤代化合物在光照射下的偶联反应、醇解反应、消去反应、开环反 应，尤其是卤代杂环化合物的光化学反应，得到了许多用热反应或催化反应无法替 代的具有生物(理)活性的中间体．     

Determination of trace elements in Na-bentonitic clay by INAA in Turkey

Instrumental neutron activation analysis was applied to the determination of trace elements in a Na-bentonitic clay. The irradiation was done in the Triga Mark II type reactor of ITU Nuclear Energy Institute. The sample was irradiated in two steps for short- and long- lived isotopes. After irradiation, spectra were taken using a germanium detector, multichannel analyzer Canberra System 100 and a fitting program called Sampo 90. The spectra of short-lived isotopes were analyzed to determine Al, Mg, Na, K, Ca, Ti elements and Mn, V trace elements. The spectra of long-lived isotopes were analyzed to determine Sc, Br, Sb, Cs, La, Ce, Sm, Yb, Hf, Pa, Np trace elements.     

Analysis of RNA sequence structure maps by exhaustive enumeration I. Neutral networks

Summary Global relations between RNA sequences and secondary structures are understood as mappings from sequence space into shape space. These mappings are investigated by exhaustive folding of allGC andAU sequences with chain lengths up to 30. The computed structural data are evaluated through exhaustive enumeration and used as an exact reference for testing analytical results derived from mathematical models and sampling based on statistical methods. Several new concepts of RNA sequence to secondary structure mappings are investigated, among them that ofneutral networks (being sets of sequences folding into the same structure). Exhaustive enumeration allows to test several previously suggested relations: the number of (minimum free energy) secondary structures as a function of the chain length as well as the frequency distribution of structures at constant chain length (commonly resulting in generalized forms ofZipf's law).

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Analyse der Beziehungen zwischen RNA-Sequenzen und Sekundärstrukturen durch vollständige Faltung, 1. Mitt. Faltung, Neutrale Netzwerke

Zusammenfassung Die globalen Benziehungen zwischen RNA-Sequenzen und Sekundärstrukturen werden als Abbildungen aus einem Raum aller Sequenzen in einen Raum aller Strukturen aufgefaßt. Diese Abbildungen werden durch Falten aller binären Sequenzen desGC-undAU-Alphabets mit Kettenlängen bis zun=30 untersucht. Die berechneten Strukturdaten werden durch vollständiges Abzählen ausgewertet und als eine exakte Referenz zum Überprüfen analytischer Resultate aus mathematischen Modellen sowie zum Testen statistisch erhobener Proben verwendet. Einige neuartige Konzepte zur Beschreibung der Beziehungen zwischen Sequenzen und Strukturen werden eingehend untersucht, unter ihnen der Begriff derneutralen Netzwerke. Ein neutrales Netzwerk besteht aus allen Sequenzen, die eine bestimmte Struktur ausbilden. Vollständiges Abzählen ermöglicht beispielsweise die Bestimmung aller Strukturen minimaler freier Energie in Abhängigkeit von der Kettenlänge ebenso wie die Bestimmung der Häufigkeitsverteilungen der Strukturen bei konstanten Kettenlängen. Die letzteren folgen einer verallgemeinerten FormZipfschen Gesetzes.

     

In-depth analysis of glass fibers

Two types of commercial glass fibers were subjected to attack in strongly basic KOH solutions. The resulting leach solutions were analysed for Na, Ca, and Si. This showed that the corrosion process attacks the fibers incongruently. Although there are some distinct differences in the performance of these fibers, to a first approximation both types behave similarly. Further, the fibers were depth profiled using a recently developed SNMS technique for fiber in-depth analysis. This showed that both types of fibers behave in a quite dissimilar manner. The fibers were weathered already without any treatment. Although both fibers show alkali ion exchange and network splitting processes, on one of the fiber layers enriched in SiO₂, Fe₂O₃, and CaO are formed by a redeposition process from the leach solution.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Crystal Structure of (6S,9S,13R,14S)-7,8-Didehydro-3,7-dimethoxy-17-methylmorphinan-4,6-diol

1 INTRODUCTION (9S,13R,14S)-7,8-Didehydro-3,7-dimethoxy-4-hydroxy-17-methylmorphinan-6-one I is an impor- tant natural product that was used to ease pain, decrease blood pressure and diminish inflammation. In order to study the stereochemistry of the reduction of I with potassium boronhydride, the crystal structure of the title compound II was determined by X-ray diffraction method. 2 EXPERIMENTAL 2. 1 Instrument The melting point was measured on a Yanagimoto MP-500 apparatus…     

Quantitation in capillary electrophoresis-mass spectrometry

CE-MS has evolved into a strong alternative to LC-MS. Most of CE-MS applications deal with characterization and identification. However, quantitative aspects have gained importance in, e.g., pharmaceutical and biotechnological applications. Here we summarize and evaluate various methodological aspects in order to achieve sensitive and reproducible results. Similar to LC-MS, aspects of matrix influence on the electrospray process need to be carefully addressed when quantitative results are intended by CE-MS. Due to a more complicated coupling special emphasis needs to be put on the CE-MS interface. Generally linearity over more than three orders of magnitude can be achieved by CE-ESI-MS. Furthermore, a literature survey has been performed in order to give an overview over quantitative measurements performed by CE-MS. The precision can be doubled when changing from a structural related to an isotopically labeled internal standard. Thus a level of precision better than 5% RSD can be achieved.     

Adsorption kinetics, orientation, and self-assembling of N-acetyl-L-cysteine on gold: a combined ATR-IR, PM-IRRAS, and QCM study

The adsorption of N-acetyl-L-cysteine from ethanol solution on gold has been studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy, polarization modulation infrared reflection absorption spectroscopy, and a quartz crystal microbalance. After an initial fast adsorption, in situ ATR-IR revealed two considerably slower processes, besides further adsorption. The appearance of carboxylate bands and the partial disappearance of the carboxylic acid bands demonstrated that part of the molecules on the surface underwent deprotonation. In addition, the C=O stretching vibration of the carboxylic acid group shifted to lower and the amide II band to higher wavenumbers, indicating hydrogen-bonding interactions within the adsorbate layer. Based on the initial ATR-IR spectrum, which did not reveal deprotonation, the orientation of the molecule within the adsorbate layer was determined. For this, density functional theory was used to calculate the transition dipole moment vectors of the vibrational modes of N-acetyl-l-cysteine. The projections of the latter onto the z-axis of the fixed surface coordinate system were used to determine relative band intensities for different orientations of the molecule. The analysis revealed that the amide group is tilted with respect to and points away from the surface, whereas the carboxylic acid is in proximity to the surface, which is also supported by a shift of the C-O-H bending mode. This position of the acid group favors its deprotonation assisted by the gold surface and easily enables intermolecular interactions. Periodic acid stimuli revealed reversible protonation/deprotonation of part of the adsorbed molecules. However, only non-hydrogen-bonded carboxylic acid groups showed a response toward the acid stimuli.     

Fabrication of magnetically separable mesostructured silica with an open pore system

Magnetically separable mesostructured silica with an unobstructed pore system was fabricated through the deposition of cobalt nanoparticles on the outer surface of the submicron-sized silica particles. These cobalt nanoparticles were further protected by a nanometer-thick carbon shell against acid erosion. Due to the fact that the magnetic particles are grafted on the outer surface of the porous silica, the pores are still accessible for further modification, which could widen the application range of porous silica.     

CuO/γ-Al2O3单分散催化剂的XAFS研究

采用XAFS方法研究浸渍法制备并于低温焙烧的CuO/γ-Al2O3催化剂的局域结构.对于CuO负载量小于单层分散阈值的CuO/γ-Al2O3(0.4mmol/100m2),结果表明,CuO物种是以层状分散的孤立原子簇存在于γ-Al2O3载体表面,其第一近邻Cu-O配位环境的结构与晶态CuO的相似,键长和配位数分别为0.195nm和4.对于CuO负载量等于单层分散阈值的CuO/γ-Al2O3(0.8mmol/100m2),已有少量的CuO纳米颗粒生成.对于CuO负载量大于单层分散阈值的CuO/γ-Al2O3(1.2mmol/100m2),其结构与多晶CuO的相近.基于CuO在γ-Al2O3载体上的三种不同分散状态的结构特点,我们提出了CuO/γ-Al2O3催化剂的结构模型.     

Cation-induced collapse of low-molecular-weight polyacrylic acid in the dispersion of barium titanate

Observations on the steric layers formed by the adsorption of low-molecular-weight polyacrylic acid (PAA) were taken using the colloidal probe method in an atomic force microscope. The effects of divalent barium ions and of monovalent potassium ions at varying concentrations were observed on the repulsive interaction profiles. High ionic concentrations screened double-layer forces to small distances, whereby the acting forces were reduced to steric interactions. De Gennes scaling theory was used to model the effect of electrolyte on an aqueous barium titanate system, which was stabilized with PAA. The brush model was found to represent the force curves better than the mushroom model. The collapse of PAA layers with increasing salt approximated a grafted polymer brush in monovalent electrolyte, but the addition of barium ions caused markedly less steric collapse. It is suggested that the formation of a Ba(2+)-PAA complex in the adsorbed layer increases its compressibility parameter.