Sodium Taurocholate-Induced Lamellar-Micellar Phase Transitions of DPPC

The thermotropic transitions of 1,2-dipalmitoylphosphatidylcholine (DPPC) and the structural changes of its lamellar phases have been studied between 0 and 50°C by both DSC and synchrotron small angle X-ray diffraction/scattering as a function of temperature (XRDT) and sodium taurocholate concentration [TC] in the 0–40 mM range ([DPPC]=50 mM) at pH 7.4. The existence of multiple phase transitions (up to 5 peaks within a 5°C interval) in a narrow domain of temperature between 25 and 42°C depending on the [TC]/[lipid] ratio was observed in the DSC curves. XRDT showed that at low ratios they might correspond to transitions between lamellar phases, the structural characteristics of which are given. At higher ratios a lamellar to micellar transition was observed, and the temperature at which it was observed decreased as a function of the TC content. The relationships with DPPC vesicle bilayer permeabilization and solubilization are discussed.     

Shape resonances in photoionization of diatomic molecules: An example in thed inner shell ionization of the hydrogen halides

A classification of the shape resonances in the photoionization of diatomic molecules into two types is proposed: the well known molecular shape resonances which appear in the σ _u channel for the photoionization of the σ _g shells of light molecules like 3σ _g in N₂ or in O₂, and the atomic-like shape resonances. To illustrate this last class of shape resonances, calculations in the frozen core static exchange approximation of thed inner shell photoionization cross sections, σ, and of the angular distribution parameters, β, are performed for both HBr and HI. In our model, the σ and β curves look roughly like that of the isoelectronic Kr and Xe rare gases, but in order to obtain quantitative agreement with experiment, an approach including interchannel interactions, i.e. similar to that used for the halogen atoms would be probably necessary.     

Macro lattice from segregated amorphous phases of a three block copolymer

Summary Extruded plugs of the styrene-butadiene-styrene amorphous copolymer Kraton 102 were found to exhibit discrete X-ray reflections in the low angle region such as are characteristic of an individual single crystal. This crystal lattice is hexagonal, with a lateral lattice spacing of 300 and an infinite period along the hexagonal axis which coincides with the extrusion direction. Annealing improved the crystal perfection, in fact a large portion of the macroscopic sample could become a single crystal. The orientation of the lattice could be influenced by deformation procedures in a consistent fashion. The diffraction effects are consistent with the styrene phase being in the form of cylinders. The cylinder diameter was estimated both from the lattice spacing coupled with the known molecular composition, and from missing reflections: both methods gave a diameter of close to 150 . Some suggestions are made on the molecular origin of this remarkable ordering phenomenon, together with pointing out some of the possible further consequences of such an order.

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Zusammenfassung Extrudierte pfropfenartige Proben von einem amorphen Block-Copolymeren Styrol-butadien-styrol (Kraton 102) ergaben diskrete Röntgenreflexe im Kleinwinkelbereich, wie sie im Weitwinkelbereich für Einzelkristalle charakteristisch sind. Das Kristallgitter ist hexagonal, lateraler Gitterabstand 300 , unendliche Periode entlang der hexagonalen Achse, die mit der Extrusionsrichtung zusammenfällt. Tempern verbesserte die Güte des Kristalls, so daß tatsächlich große Teile einer makroskopischen Probe sich zum Einzelkristall formen. Die Orientierung des Gitters kann auch durch Deformationsprozesse in konsistenter Weise beeinflußt werden. Die Beugungseffekte lassen sich deuten, wenn man für die Styrolphase Anordnungen zylindrischer Form annimmt. Der Durchmesser der Zylinder wurde geschätzt aus den Gitterabständen und den bekannten Molekulargewichtszusammensetzungen, sowie aus den fehlenden Reflexionen. Beide ergeben den Wert von ungefähr 150 . Einige Vorschläge werden über den molekularen Ursprung dieses bemerkenswerten Ordnungsphänomens gebracht, zusammen mit weiteren möglichen Konsequenzen einer solchen Ordnung.

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With 5 figures in 9 details     

A maximum likelihood estimator to distinguish single molecules by their fluorescence decays

We have developed a maximum likelihood estimator to distinguish between similar molecules at the single molecule level based upon fluorescence decay measurements. Time resolved fluorescence measurements for single Rhodamine 6G and tetramethylrhodamine isothiocyanate molecules in fluid flow are derived from time-correlated single photon counting. A maximum likelihood estimator is developed and applied to data from a mixture of molecules. Single molecules are identified and distinguished by their fluorescence time decays. Comparison is made between identification error rates and theoretical predictions. To our knowledge, this is the first reported example of single molecule identification by fluorescence decay in a mixture.     

CCR5 antagonists: 3-(pyrrolidin-1-yl)propionic acid analogues with potent anti-HIV activity

[reaction: see text] A novel approach to alpha,alpha-disubstituted-beta-amino acids (beta(2,2)-amino acids) was employed in the synthesis of a series of 3-(pyrrolidin-1-yl)propionic acids possessing high affinity for the CCR5 receptor and potent anti-HIV activity. The rat pharmacokinetics for these new analogues featured higher bioavailabilities and lower rates of clearance as compared to cyclopentane 1.     

Crystal structure, morphology and composition of magnetron sputtered tungsten carbide films

Summary It is shown that small variations of the deposition parameters during magnetron sputtering of tungsten carbide thin films may result in drastic changes of film properties. An increasing working gas pressure for example lowers stress and hardness values. Simultaneously, the texture of the WC_1–x cristallites turns from 200 preferential orientation to 111, whereas the composition of the films does not change. In reactive sputtering with a tungsten target there is a narrow range from 2 to 3% C₂H₂ gas admixture to the working gas where the films are stochiometric (WC) and hard, and grain size and morphology are similar to that of non-reactively sputtered films. The generation of different crystallite structures and orientations in the range of 0–3% C₂H₂ admixtures are used to produce a multiphase thin film with extremely low crack propagation.     

Neue Phellandren-Derivate aus dem Wurzelöl von Angelica archangelicaL

New Phellandrene Derivatives from the Root Oil of Angelica archangelica L . 2-Nitro-1,5-p-menthadiene ( 5 ), trans- and cis-6-nitro-1(7), 2-p-menthadiene ( 6 and 7 ), trans-1(7), 5-p-menthadien-2-yl acetate ( 9 ) and a formal phellandrene derivative, 7-isopropyl-5-methyl-5-bicyclo [2.2.2]octen-2-one ( 16 ), have been identified in the root oil of Angelica archangelica L . Starting from (?)-(R)-α-phellandrene ( 1 ) (R)- 5 , (4R, 6S)- 6 /(4R, 6R)- 7 , (2S, 4R)- 9 and (1R, 4R, 7R)- 16 as well as (2S, 4R)- 11 , (2R, 4R)- 12 and (2R, 4R)- 10 have been prepared.