Appareillages et techniques pour études de routine de corps organiques cristallisant à basse température

Renaud, Michel; Fourme, R.

doi:10.1107/s0365110x67001380

Cited by 28 publications

(17 citation statements)

References 2 publications

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“…Single crystals were grown in sealed Lindemann glass capillaries (diameter 0.3 ram) directly on the goniometer head of Weissenberg and Buerger instruments. The attached cooling system gave a quasi-laminar flow of cold nitrogen which prevented any frosting of the sample (Renaud & Fourme, 1967); the goniometer head was held near room temperature by means of a built-in furnace. The temperature of the gas was monitored and the overall long-range fluctuations were estimated to be at most + 0.5 °K.…”

Section: Methodsmentioning

confidence: 99%

Crystal and molecular structure of diethyl ether at 128°K

André¹,

Fourme²,

Zechmeister³

1972

Acta Crystallogr Sect B

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Three-dimensional single-crystal X-ray diffraction data of the stable form of diethyl ether have been collected at 128 °K. The unit cell is orthorhombic, a = 11"81 (2), b = 8.07(2), c = 10.85(3) ~, space group P212~2~, Z= 8; there are two molecules in the asymmetric unit. The acentric structure has been solved by direct methods and refined to an R index of 0.052. Both molecules have approximately (C2v transtrans) symmetry and the rigid-body model is a good approximation to the thermal motion. For a planar molecule with five atoms, the normal equations matrix is singular and the molecular tensors have been found by a technique of regression on principal components. The packing is loose and this might explain the strong tendency of diethyl ether to give a vitreous form on cooling.

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Section: Methodsmentioning

confidence: 99%

Crystal and molecular structure of diethyl ether at 128°K

André¹,

Fourme²,

Zechmeister³

1972

Acta Crystallogr Sect B

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“…The conditions of the X-ray cryodiffraction depend on the specifications of these components. Cooling is achieved by a lamellar flux of liquid-nitrogen-cooled nitrogen (Renaud & Fourme, 1967). The temperature of the gas is controlled by varying the current in a heating element (H1).…”

Section: X-ray Diffractionmentioning

confidence: 99%

Freezing of aqueous specimens: an X‐ray diffraction study

Lepault

Bigot

Studer

et al. 1997

Journal of Microscopy

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SummaryThe effects on water of two cooling methods, immersion in a liquid cryogen and high-pressure freezing, were studied by X-ray cryodiffraction on different sucrose solutions. The nature of the ice formed by each method depends on both the sucrose concentration and the specimen thickness. In order to compare the two methods, we mainly studied specimens having a thickness of 0 . 2 mm. Under these conditions, freezing by immersion gives rise to hexagonal (IH), cubic (IC) and amorphous (IV) ices when the sucrose concentration (weight/weight) has a value within the range 0-30%, 30-60%, 60% and higher, respectively. The temperature of the phase transitions IV-IC, IC-IH depends on the sucrose concentration. High-pressure freezing gives rise to two specific forms of ice: an amorphous and a crystalline ice (ice III). Ice III is observed when pure water samples are high-pressure frozen provided that the sample temperature does not rise above ¹150 ЊC. Above this temperature, ice III transforms into hexagonal ice. Amorphous ice is formed when the sucrose concentration is higher than 20%. The amorphous ice formed under high pressure has a similar, but not identical, X-ray diffraction pattern to that of amorphous ice formed at atmospheric pressure. While the X-ray diffraction pattern of amorphous ice formed at atmospheric pressure (IV) shows a broad ring at a position corresponding to 0 . 37 nm, that of highpressure amorphous ice (IVHP) shows a broader ring, located at 0 . 35 nm. IVHP presents a phase transition (IVHP-IV) at temperatures that depend on the sucrose concentration. We also observed that some precautions have to be taken in order to minimize the alcohol contamination of high-pressure frozen samples. The icephase diagram presented in this paper should be taken into account in all methods dedicated to the structural study of frozen biological specimens.

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“…Single crystals were grown in sealed Lindemann glass capillaries (diameter: 0.2 mm) directly on the goniometer head of a precession camera. The attached cooling system gave a nearly laminar flow of cold nitrogen which prevented any frosting of the sample (Renaud & Fourme, 1967); the goniometer head was kept nearly at room temperature by means of a small built-in furnace. The temperature of the gas was continuously monitored and the overall long-range fluctuations were estimated to be at most + 0.5°K.…”

Section: Crystal and Molecular Structure Of Cyclohexane II Experimentalmentioning

confidence: 99%

Crystal structure of cyclohexane I and II

Kahn¹,

Fourme²,

André³

et al. 1973

Acta Crystallogr Sect B

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178

108

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Cyclohexane C6H12 (m.p. 279.8 °K) undergoes an isothermal transition at 186 °K. The so-called phase I is stable between 279.8 and 186°K, phase II below 186°K. Starting from a single crystal I grown by a zone melting technique at 187 °K, suitable single crystals II were obtained through a careful control of the phase transformation and annealing at 185 °K for two days. X-ray diffraction data have been collected at 195 and 115 °K by the low-temperature precession technique. At 115 °K, crystal data are: monoclinic cell, a= 11.23 (2), b = 6.44 (2), c= 8.20 (2) A, fl= 108.83 (17) °, Z= 4; space group Cc or C2/c (the analysis confirmed the centrosymmetric group). The crystal and molecular structures were refined to an R index of 0.061 ; the 'chair'-shaped molecule departs slightly but significantly from Dan symmetry. The rigid-body model is a good approximation for the thermal motion. At 195 °K, crystal data for the plastic phase I are: cubic cell, a = 8.61 (2)/~, Z= 4, space group Fm3m. Using the molecular shape previously found, two types of orientational disorder have been investigated: isotropic reorientations of the molecules about their centre of gravity (Pauling-Fowler model) and step reorientations between 24 equivalent positions (Frenkel model). In this case, the packing was found by a Monte-Carlo method coupled with a rigidgroup least-squares refinement. The Frenkel model gives a better agreement with experiment. A tentative interpretation of the transformation is given. The same general procedure can probably be applied to other plastic crystals.

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Appareillages et techniques pour études de routine de corps organiques cristallisant à basse température

Cited by 28 publications

References 2 publications

Crystal and molecular structure of diethyl ether at 128°K

Crystal and molecular structure of diethyl ether at 128°K

Freezing of aqueous specimens: an X‐ray diffraction study

Crystal structure of cyclohexane I and II

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