Structure cristalline et polymorphisme du nitrate de cadmium anhydre

Cd(NO₃)₂ undergoes a phase transition at 160°C. The high temperature form is cubic and isomorphic with M(NO₃)₂ (M = Ba, Ca, Sr, Pb). The crystal structure of the low temperature phase has been solved by X-ray diffraction at 20°C, using 774 independent reflections collected with a 4-circle diffractometer. The dimensions of the orthorhombic unit cell are: $\text{a ? c = 7.5073 (14)}$ Å, b = 15.3692 (35) Å, Z = 8, space group Pca2₁. The structure has been refined to the final weighted R = 0.044. The cadmium atoms are nearly in a face-centered arrangement. Each cadmium is octahedrally surrounded by six oxygen, the CdO distances varying from 2.34 to 2.46 Å. Each nitrate group belongs through its three oxygens to three different octahedra. The structural change cubic Cd(NO₃)₂ → orthorhombic Cd(NO₃)₂ is characterized by a small rotation of NO₃ groups in their plane; the face-centered array of cadmium atoms is only slightly modified. The coordination of cadmium atoms changes from 12 to 6, and the approximate doubling of parameter (b) as well as the difference of symmetry can be explained by two different directions of rotation of the NO₃ groups situated in the same plane.     

Tandem radical and non-radical reactions mediated with thiols--a new method of cleavage of allylic amines

Thiyl radical promotes the isomerisation of allylic amines into enamines via two consecutive hydrogen atom abstraction steps, and the subsequent polar addition of the corresponding thiol to the enamine results in the cleavage of the C-N bond via a thioaminal intermediate: this reaction provides a mild, metal-free methodology for the deprotection of allylated primary and secondary amines.     

Synthesis of beta-amino-alpha-hydroxy esters and beta-amino-alpha-azido ester by Sharpless asymmetric aminohydroxylation, byproducts analysis

[reaction: see text] Synthesis of enantiomerically pure beta-amino-alpha-hydroxy esters (1, 2) and beta-amino-alpha-azido ester (3) using Sharpless AA as a key step is described. A hitherto unreported side reaction, the oxidation of the beta-hydroxy-alpha-amino ester (5) into the alpha,alpha-di-tert-butyloxycarbamoyl-beta-ketoester (8) under AA conditions, is documented.     

Model-based measurement uncertainty evaluation,with applications in testing

Basic concepts and implementations of the model-based approach to uncertainty evaluation are discussed. One implementation is that of the law of propagation of uncertainty with the use of the central limit theorem as recommended in the Guide to the expression of uncertainty in measurement (GUM). Another is the propagation of distributions, the subject of a supplemental guide to the GUM, which is at an advanced stage of development. It falls in the category of other analytical and numerical methods indicated in the GUM. Two testing applications are used to illustrate the principles: tennis-ball rebound and tensile strength.

Étude thermochimique des alliages de gallium et de sodium

Enthalpies of mixing of liquid alloys of gallium and sodium and enthalpies of formation ΔH_f of the two compounds NaGa₄ and Na₅Ga₈ of this binary system were determined calorimetrically at 723 K. Referred to the simple constituants in the liquid state, the following values were found:

By means of quantitative thermal differential analysis, the value for the melting enthalpy of Na₅Ga₈ was found to be (13.5±0.5) kJ mol^?1.     

Zinc(II) and cadmium(II) complexes containing the 2-{2-[3-(triethoxysilyl)-propylthio]ethylamino}ethylamino ligand

The new 2-{2-[3-(triethoxysilyl)propylthio]ethylamino}ethylamino SNN ligand, has been synthesized and fully characterized. Its donor properties towards zinc(II) and cadmium(II) have been investigated in order to simulate the metal uptake behavior in environmental applications. It reacts with ZnX₂ (X = Cl, Br and I) and CdCl₂ to form monomeric molecular complexes, MX₂(SNN)₂. Mass, i.r., ¹H- and ¹³C{¹H}-n.m.r. spectroscopies and elemental analyses reveal that, in these complexes, the metal attains its highest coordination number by linking to two nitrogen atoms of the ethylenediamine portion, and to two halogen atoms. The SNN ligand thus behaves as a bidentate four electrons donor, the thioether sulfur atom still remaining available for further coordination.     

Competition of natural polyamines with dimethylsilyl analogues and monovalent cations in presence of a charged dipalmitoylphosphatidylglycerol monolayer

The interaction at the air/water interface of dipalmitoylphosphatidylglycerol (DPPG) with natural and dimethylsilyl polyamines are investigated first in the presence of NaCl in the subphase. Next, experiments are performed to study the competition between natural polyamines and dimethylsilyl analogues. The results obtained by surface pressure and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) with NaCl, are compared with those obtained with distilled water. A decrease of the DPPG mean molecular area is observed due to the local diminution of the Na⁺ concentration close to the polar head group and the simultaneous onset of interactions between the amino group of natural polyamines and the polar head group of DPPG. The same effects occur with azhepsi, followed by an insertion of the hydrophobic dimethylsilyl group. Near the polar head groups DPPG, a substitution of the Na⁺ by the amino groups of polyamines occurs.

For the competition experiments, whereas a partial substitution is possible after putrescine and spermine adsorption, it is almost complete after spermine adsorption. Since the number of amino groups of azhepsi and spermine are the same, hydrophobic interactions due to the presence of dimethylsilyl group occur between azhepsi and the alkyl chains of DPPG. This favoured insertion of azhepsi provides a basis for understanding of the action of dimethylsilyl derivatives in the case of an antitumour strategy.     

From central to planar chirality,the first example of atropenantioselective cycloetherification

Using chiral quaternary ammonium hydroxide as base, cycloetherification of linear achiral diarylheptanoid 5, by way of an intramolecular SNAr reaction, provides enantiomerically enriched cyclophane 6 in good to excellent yield.