≪Monocristaux≫ de copolymères triséquencés styrène/isoprène/styrène présentant la structure cylindrique III. Étude de la déformation par cisaillement

Résumé On a étudié par diffraction des rayons X aux petits angles des monocristaux de copolymère triséquencé styrène/isoprène/styrène présentant la structure cylindrique. On a porté l'attention sur la déformation structurale des systèmes sous l'effet d'une contrainte de cisaillement. On a montré que le réseau cristallin se déforme réversiblement de manière parfaitement affine.

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Summary This is a low-angle X-ray diffraction study of single-crystals obtained from styrene/isoprene/styrene three-block copolymers presenting the cylindrical structure. The structural deformation has been analyzed as a function of a shearing strain applied to the material. It has been shown that the crystal lattice deforms in a reversible and perfectly affine way.

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Zusammenfassung Mit Hilfe der Röntgenstrahlkleinwinkelstreuung haben wir die eine zylindrische Struktur zeigenden Polystyrol-Polyisopren-Polystyrol-Blockcopolymeren, die einen Zustand von Monokristallen darstellen, untersucht. Wir haben besonders die strukturellen Änderungen analysiert, die auftreten, wenn der Probe eine Scherung aufgezwungen ist. Es zeigt sich, daß sich das Kristallgitter reversibel und exakt affin verformt.

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Avec 9 figures et 2 tableaux     

Angle-resolved X-ray fluorescence spectrometry using synchrotron radiation at ELSA

Measurements on the centroid depth of ion-implanted phosphorus-in-silicon specimen by the method of angle-resolved, self-ratio X-ray fluorescence spectrometry (AR/SR/XFS) have been carried out using white synchrotron radiation (SR). The measurements were performed using a modified wavelength-dispersive fluorescence spectrometer. Problems due to the use of SR, like carbonaceous specimen contamination and sample heating were overcome by flooding the specimen chamber with helium and by pre-absorbing the non-exciting parts of the incident SR with suitable filters, respectively. The decaying primary intensity was monitored by measuring the compensation current of the photoelectrons emitted from a tungsten wire stretched across the primary beam. Results have been obtained for specimen with dose density levels of 10¹⁶ cm^–2 and 3×10¹⁵ cm^–2.     

Anionic polymerization with alkaline-earth counterion. I. Preparation and characterization of dicarbanionic oligostyrylbarium and -strontium in tetrahydrofuran

Dicarbanionic oligostyrylbarium or -strontium, PS⁼Ba⁺⁺ and PS⁼Sr⁺⁺, were prepared by reacting styrene with finely divided barium or strontium in THF or THP. The effects of reaction temperature, monomer, and metal concentration were described. Difunctionality of these living oligomers is confirmed from calculated and observed molecular weight data and also from conductivity measurements. λ_max of carbanions is found to vary with DP . At 25°C it decreases from 368 nm for dimers to 359 nm for DP > 10. As observed for monocarbanionic polystyrylbarium (PS^?)₂Ba⁺⁺, λ_max of PS⁼Ba⁺⁺ of high DP decreases with temperature, while λ_max of PS⁼Ba⁺⁺ of low DP increases with decreasing temperature. At ?100°C the difference between the two extreme values is about 30 nm. Similar results are obtained with PS⁼Sr⁺⁺. Such unusual spectral properties are interpreted, on the basis of excitation molecular theory, in terms of ring structures for the living oligomers.     

Reaktionen von (η2-Ethen)bis(triphenylphosphan)-platin(0) mit dimerem Hexafluorthioaceton Darstellung und Struktur von Platinacyclopentan- und -cyclopropanderivaten

Reactions of (η²-Ethene)bis(triphenylphosphane)platinum(0) with Dimeric Hexafluorothioacetone. Preparation and Structure of Platina Cyclopentane and Cyclopropane Derivatives The five-membered (CS)₂Pt ring 1 was obtained by the reaction of 2, 2, 4, 4-tetrakis(trifluoromethyl)-1,3-dithietane and (η²-ethene)bis(triphenylphosphane)platinum(0) at low temperatures. 1 is converted at its melting point to the three-membered CSPt ring derivative 2 , with elimination of one molecule of hexafluorothioacetone. 2 is also formed directly when the reaction is conducted at temperatures above +30°C. 2 was characterized by an X-ray Structural analysis.     

CAROTENOID TRIPLET STATE AND CHLOROPHYLL FLUORESCENCE QUENCHING IN CHLOROPLASTS AND SUBCHLOROPLAST PARTICLES

Abstract— Absorption changes attributed to the triplet state of carotenoids and to primary electron donors (P-700. P-680)^: and fluorescence quenching at several wavelengths have been measured with a single apparatus. following flash excitation with a dye or a ruby laser. Spinach chloroplasts as well as subchloroplast particles enriched in Photosystem-1 (F₁), Photosystem-2 (F₁) or the light-harvesting Chl a/h (F_III) have been examined at temperatures varying between 5 and 294 K.
The triplet state of carotenoids has been identified on the basis of its difference spectrum (having a peak at 515 nm) and decay kinetics (⋍ 7 µs at low temperature; accelerated by O₂ at 294 K). It is formed in all of the materials studied. The quantum yield of carotenoid triplet formation in chloroplasts increases at low temperature, but less than the fluorescence yield.
In most cases the fluorescence quenching recovers approximately with the same kinetics as the decay of the carotenoid triplets. The fluorescence recovery is, however, significantly faster for chloroplasts at 730 nm. Fluorescence quenching occurs in all types of materials. The ratio of fluorescence quenching to the concentration of carotenoid triplets varies with the material, being maximum in chloroplasts and minimum in F_m particles.
We conclude that the formation of the carotenoid triplet state is not limited to a few sites in the chloroplast and that a carotenoid triplet is a quencher of chlorophyll fluorescence. A detailed comparison of carotenoid triplets and fluorescence quenching gives some information concerning the organization of the pigments in the photosynthetic apparatus.     

Transitory forms of carotenoids: triplet state and radical cation

Abstract— Reactions between toluidine blue (a thiazine dye) and carotenoids (β-carotene and zeaxanthine) were studied by flash photolysis, in ethanolic solutions. Two types of reactions were evidenced:

• 1 a triplet-triplet energy transfer from the triplet state of monoprotonated toluidine blue to the carotenoid whose triplet state decays rapidly (t_1/2= 5μsec).
• 2 an electron transfer from the carotenoid to the mono- and bi-protonated triplet states of toluidine blue. This produces a radical-cation of the carotenoid (Car⁺) which decays slowly (t_1/2? 200 μsec) and has a strong absorption band around 900 nm.

     

Ion-implanted reference standards for use in microchemical analysis of materials

Summary A concise overview has been given of the present state of development of ion-implanted reference standards for the calibration of instrumental methods of microchemical characterization of solid materials.

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Ionen-implantierte Standardpräparate für die Mikroanalyse

Zusammenfassung Der gegenwärtige Entwicklungsstand ionenimplantierter Standardpräparate für die Eichung instrumenteller Mikromethoden der chemischen Feststoffanalyse wurde besprochen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Metal-insulator transition in the low-dimensional organic conductor (TMTSF)<Subscript>2</Subscript>FSO<Subscript>3</Subscript> probed by infrared microspectroscopy

We present measurements of the infrared response of the quasi-one-dimensional organic conductor (TMTSF)₂FSO₃ along (E ) and perpendicular (E ) to the stacking axis as a function of temperature. Above the metal-insulator transition related to the anion ordering the optical conductivity spectra show a Drude-like response. Below the transition an energy gap of about 1500 cm^-1 (185 meV) opens, leading to the corresponding charge transfer band in the optical conductivity spectra. The analysis of the infrared-active vibrations gives evidence for the long-range crystal structure modulation below the transition temperature and for the short-range order fluctuations of the lattice modulation above the transition temperature. We also report about a new infrared mode at around 710 cm-1 with a peculiar temperature behavior, which has so far not been observed in any other (TMTSF)₂X salt showing a metal-insulator transition. A qualitative model based on the coupling between the TMTSF molecule vibration and the reorientation of electrical dipole moment of the FSO₃ anion is proposed, in order to explain the anomalous behavior of this new mode.     

Understanding false positives in reporter gene assays: in silico chemogenomics approaches to prioritize cell-based HTS data

High throughput screening (HTS) data is often noisy, containing both false positives and negatives. Thus, careful triaging and prioritization of the primary hit list can save time and money by identifying potential false positives before incurring the expense of followup. Of particular concern are cell-based reporter gene assays (RGAs) where the number of hits may be prohibitively high to be scrutinized manually for weeding out erroneous data. Based on statistical models built from chemical structures of 650 000 compounds tested in RGAs, we created "frequent hitter" models that make it possible to prioritize potential false positives. Furthermore, we followed up the frequent hitter evaluation with chemical structure based in silico target predictions to hypothesize a mechanism for the observed "off target" response. It was observed that the predicted cellular targets for the frequent hitters were known to be associated with undesirable effects such as cytotoxicity. More specifically, the most frequently predicted targets relate to apoptosis and cell differentiation, including kinases, topoisomerases, and protein phosphatases. The mechanism-based frequent hitter hypothesis was tested using 160 additional druglike compounds predicted by the model to be nonspecific actives in RGAs. This validation was successful (showing a 50% hit rate compared to a normal hit rate as low as 2%), and it demonstrates the power of computational models toward understanding complex relations between chemical structure and biological function.