Fragile to strong crossover and Widom line in supercooled water: A comparative study

The aim of this paper is to discuss the relationship between the dynamics and thermodynamics of water in the supercooled region. Reviewed case studies comprehend bulk water simulated with the SPC/E, TIP4P and TIP4P/2005 potentials, water at protein interfaces, and water in solution with electrolytes. Upon supercooling, the fragile to strong crossover in the α-relaxation of water is found to occur when the Widom line emanating from the liquid-liquid critical point is crossed. This appears to be a general characteristic of supercooled water, not depending on the applied interaction potential and/or different local environments.     

Indirect exciton transition in silicon under [111] uniaxial compression

Transverse electroabsorption and absolute absorption spectra in silicon at 1.8° K in the presence of [111] uniaxial compression are reported. The relative strengths of the phonon-assisted transitions and the change of exciton binding energy are found to be in agreement with predictions. The effect of strain upon spectral broadening is also discussed.     

n-Cotilting Modules and Pure-Injectivity

The author recently proved that 1-cotilting modules are pure-injective;however, the problem of determining whether n-cotilting modulesare pure-injective remained open. In this paper, necessary andsufficient conditions are given for the pure-injectivity ofn-cotilting modules. 2000 Mathematics Subject Classification16D90 (primary), 16D30 (secondary).     

Microwave-assisted synthesis of isonitriles: a general simple methodology

[reaction: see text] A facile conversion of formamides to isonitriles under very mild conditions and microwave irradiation is described. This simple and efficient method has been applied for the synthesis of both aliphatic and aromatic isonitriles in high yields.     

Terpene biosynthesis in the nudibranch Doriopsilla areolata

Biogenesis of the enantiomeric sesquiterpenes 1 and 5 of the marine nudibranch Doriopsilla areolata was investigated by feeding of [1-(13)C]glucose, [1,2-(13)C(2)]glucose, and [1,2-(13)C(2)]acetate. Evidence is presented that supports de novo origin of both compounds via mevalonic acid.     

中国南海裸鳃目软体动物美丽拟皮片鳃(Dermatobranchus orna-tus)及其可能的食源动物柳珊瑚Muricella sp.的化学成分研究

从中国南海的裸鳃目软体动物美丽拟皮片鳃(Dermatobranchus ornatus)中分离得到4个eunicellane型二萜: Ophirin (1), calicophirin B (2), 13-去乙酰氧基 calicophirin B (3)及3-去乙酰基-13-去乙酰氧基calicophirin B (4); 而由同时、同地采集到的柳珊瑚Muricella sp. 中则分离得到calicophirin B (2), 13-去乙酰氧基 calicophirin B (3), astrogorgin (5) 及类似物6. 这些化合物的结构经波谱学实验并与文献报道的数据相对照得以确定, 并首次对Ophirin (1) 的NMR数据进行了全归属. Ophirin (1) 的单晶X衍射实验不但进一步确证了化合物的结构, 而且使这一类化合物的立体结构表述得到修正. 本文是对Dermatobranchus属软体动物化学成分研究的首次报道; 研究提示, 美丽拟皮片鳃能通过选择适当的食物, 并将食物中有用的次生代谢产物转移、富集到身体的特定部位, 使之成为自身的化学防性物质. 美丽拟皮片鳃与Muricella 属柳珊瑚中共同出现的类似化合物支持二者间可能存在的捕食与被捕食的生态学关系.     

Tryptophan phosphorescence of ribonuclease T1 as a probe of protein flexibility

The phosphorescence properties of Trp-59 of ribonuclease T₁ fromAspergillus oryzae were monitored as a function of temperature, pH, salt concentration, and complex formation with substrate analogues and, also, in the presence of glycerol as viscogenic cosolvent. The results establish a rough correlation between the internal flexibility of the macromolecule, as derived from the triplet lifetime, and its stability (G orT _m ) toward unfolding. Below 10°C or in 70% glycerol the triplet probe distinguishes at least two gross conformations for the protein, which are characterized by a large difference in phosphorescence lifetime. It is pointed out that such structural heterogeneity does not correspond with the heterogeneity inferred from fluorescence decays and acrylamide quenching rates. Further, implications of the phosphorescence data with regard to the interpretation of acrylamide quenching of fluorescence are discussed.     

Selektive Bestimmung verschiedener Stickstoff-Formen mit der Mikrokjeldahl-Methode

Zusammenfassung Durch Anwendung der Methode vonDumas-Zimmermann und einer modifiziertenKjeldahl-Methode nebeneinander ist die selektive Bestimmung der verschiedenen Stickstoff-Formen in heterocyklischen Verbindungen möglich.Auf Grund der Ergebnisse, die einerseits bei Pyridin-, Chinolin- und Isochinolinverbindungen sowie anderseits bei hydrierten Ringsystemen erhalten wurden, werden einige Regeln festgesetzt, die den Anwendungsbereich des Verfahrens begrenzen.

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Summary By the joint application of theDumas-Zimmermann procedure and a modifiedKjeldahl method, it is possible to make a selective determination of the various forms of nitrogen in heterocyclic compounds. On the basis of the findings, which were obtained on one hand with pyridine-, quinoline-, and isoquinoline compounds, and with hydrogenated ring systems on the other, several rules were set up limiting the field of application of the procedure.

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Résumé Par emploi simultané de la méthodeDumas-Zimmermann et d'une méthode deKjeldahl modifiée, le dosage sélectif des différentes formes d'azote dans les composés hétérocycliques a été rendu possible. D'après les résultats, on a établi quelques règles qui limitent le domaine d'emploi des procédés. Ces résultats sont obtenus, d'une part avec la pyridine, la quinoléine, l'isoquinoléine, d'autre part, avec les cycles hydrogénés.