3-Cyclopropyl-1,2-dimethyldiaziridine: synthesis and study of molecular structure by gas electron diffraction method

The molecular structure and conformational behavior of 3-cyclopropyl-1,2-dimethyldiaziridine have been for the first time experimentally studied by gas-phase electron diffraction and quantum chemical calculations. The two most stable conformers at 298 K possess anti and gauche mutual ring orientation (with prevalence of the anti conformer) whereas only one anti conformer is observed in solution. The determined structural parameters of gaseous 3-cyclopropyl-1,2-dimethyldiaziridine have been compared with those for 3,3-bidiaziridine structural analogues in the crystal phase. The simple and convenient procedure for the synthesis of 3-cyclopropyl-1,2-dimethyldiaziridine comprising cyclopropane and diaziridine rings in one molecule was developed. The standard enthalpy of formation of 3-cyclopropyl-1,2-dimethyldiaziridine in the gas phase was calculated using Gaussian-4 theory, yielding value of 281.9?±?5.0 kJ/mol.     

Upgraded X-ray topography and microtomography beamline at the Kurchatov synchrotron radiation source

An upgraded X-ray Topography and Microtomography (XRT-MT) station is described, the parameters of the optical schemes and detectors are given, and the experimental possibilities of the station are analyzed. Examples of tomographic reconstructions are reported which demonstrate spatial resolutions of 2.5 and 10 μm at fields of view of 2.5 and 10 mm, respectively.     

Thermal strains in focusing channels of the stations for X-ray diffraction analysis in the Sibir-2 storage ring

The thermal load caused by the absorption of synchrotron radiation in X-ray optical elements of the Belok and RSA stations leads to optics elements heating and induces strains upon simultaneous cooling. The heating of the cooled first crystal in the double-crystal monochromator causes its bending and increases the reflected beam divergence, which, in turn, results in the monochromatic beam intensity loss [1]. Numerical simulation makes it possible to more accurately determine the strains, choose the optimal monochromator design, estimate the vertical sizes of the focal spot and wavelength resolution in the focusing channel, correctly design the system for cooling the mirror at the channel input, and choose a design providing the minimum temperature of the beam-limiting slit knives.     

Synthesis of imatinib: a convergent approach revisited

Abstract  A classical convergent approach for the synthesis of the anticancer drug imatinib has been substantially improved. Imatinib was assembled by coupling the amine and carboxylic acid precursors by using N,N′-carbonyldiimidazole (CDI) as a condensing agent. Both intermediates have been synthesized by novel efficient methods. Graphical abstract        

Diffusion versus absorption in semilinear parabolic problems

We study the limit, when $k\to \infty$, of the solutions $u=u_k$ of (E) ${?}_{t}u?\mathrm{\Delta }u+h(t)u^q=0$ in ${\mathbb{R}}^N\times (0,\infty )$, $u_k(?,0)=k{\delta }_0$, with $q>1$, $h(t)>0$. If $h(t)={\mathrm{e}}^{?\omega (t)/t}$ where $\omega >0$ satisfies to ${\int }_0^1\sqrt{\omega (t)}{t}^{\mathrm{?1}}\mathrm{d}t<\infty$, the limit function $u_{\infty }$ is a solution of (E) with a single singularity at $(0,0)$, while if $\omega (t)\equiv 1$, $u_{\infty }$ is the maximal solution of (E). We examine similar questions for equations such as ${?}_{t}u?\mathrm{\Delta }{u}^m+h(t)u^q=0$ with $m>1$ and ${?}_{t}u?\mathrm{\Delta }u+h(t){\mathrm{e}}^u=0$. To cite this article: A. Shishkov, L. Véron, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Extinction of solutions of semilinear higher order parabolic equations with degenerate absorption potential

We study the first vanishing time for solutions of the Cauchy–Dirichlet problem for the 2m-order (m ≥ 1) semilinear parabolic equation ${u_t + Lu + a(x) |u|^{q-1}u=0,\,0 < q < 1}We study the first vanishing time for solutions of the Cauchy–Dirichlet problem for the 2m-order (m ≥ 1) semilinear parabolic equation u_t + Lu + a(x) |u|^q-1u=0, 0 < q < 1{u_t + Lu + a(x) |u|^{q-1}u=0,\,0 < q < 1} with a(x) ≥ 0 bounded in the bounded domain W ì \mathbb R^N{\Omega \subset \mathbb R^N}. We prove that if N 1 2m{N \ne 2m} and ò₀¹ s^-1 (meas\nolimits {x ? W: |a(x)| ￡ s })^q ds < ￥, q = min(\frac2mN,1){\int_0^1 s^{-1} (\mathop{\rm meas}\nolimits \{x \in \Omega : |a(x)| \leq s \})^\theta {\rm d}s < \infty,\ \theta=\min\left(\frac{2m}N,1\right)}, then the solution u vanishes in a finite time. When N = 2m, the same property holds if ${\int_0^1 s^{-1} \left( \mathop{\rm meas}\nolimits \{x \in \Omega : |a(x)| \leq s \} \right) \ln \left( \mathop{\rm meas}\nolimits \{x \in \Omega : |a(x)| \leq s \} \right) {\rm d}s > - \infty}${\int_0^1 s^{-1} \left( \mathop{\rm meas}\nolimits \{x \in \Omega : |a(x)| \leq s \} \right) \ln \left( \mathop{\rm meas}\nolimits \{x \in \Omega : |a(x)| \leq s \} \right) {\rm d}s > - \infty}.     

Doppler-shifted cyclotron resonance in tungsten plates with atomic pure surface

The surface resistance of thin monocrystalline W plates as a function of the constant magnetic field H directed along the normal to the sample surface is studied in the r.f. spectrum region. The sample surface was cleaned in high vaccum (10^-11 torr) or coated with the monomolecular impurity film. The oscillating with the magnetic field part R_osc due to the Doppler-shifted cyclotron resonance is studied. The doppleron oscillation amplitude is found to depend on the surface state and increases with the crystal cleaning. The observed changes are caused by the increase of the specular reflection coefficient for resonance electrons. With the deviation of the magnetic field from the normal to the plate surface, the doppleron wave undergoes a collisionless magnetic Landau damping and the signal amplitude decreases down to values comparable with that of Gantmakher-Kaner oscillations. Cleaning of the surface (and related increase of specularity) gives rise to a further decrease of the doppleron amplitude and appearance of additional interference maxima induced by the Gantmakher-Kaner effect.     

Studying the spatial organization of membrane proteins by means of tritium stratigraphy: bacteriorhodopsin in purple membrane

The topography of bacteriorhodopsin (bR) in situ was earlier studied by using the tritium bombardment approach [Eur. J. Biochem. 178 (1988) 123]. Now, having the X-ray crystallography data of bR at atom resolution [Proc. Natl. Acad. Sci. 95 (1998) 11673], we estimated the influence of membrane environment (lipid and protein) on tritium incorporation into amino acid residues forming transmembrane helices. We have determined the tritium flux attenuation coefficients for residues 10-29 of helix A. They turned out to be low (0.04+/-0.02 A(-1)) for residues adjacent to the lipid matrix, and almost fourfold higher (0.15+/-0.05 A(-1)) for those oriented to the neighboring transmembrane helices. We believe that tritium incorporation data could help modeling transmembrane segment arrangement in the membrane.     

Gas phase electron diffraction analysis andab initio calculations of the molecular structure of 3,3-dimethyl-1-oxa-3-silacyclopentane

3,3-Dimethyl-1-oxa-3-silacyclopentane was synthesized, and its molecular structure was determined by gas phase electron diffractometry using ab initio calculations (GAUSSIAN-92, RHF method, 6-31G^* basis set). The six models derived from the gas phase electron diffraction analysis equally adequately (R≈3%) describe experimental data, whereas quantum chemical calculations lead to only one (O-envelope) conformer. The stereochemical data and the results of ab initio calculations confirm that the O-envelope is the best conformation; its geometrical parameters are as follows (bond lengths r_a in Å, and angles in degrees; total error in parentheses in units of the least significant digit): r(Si-C_cyc) 1.891(3) and 1.904; r(Si-C_Me) 1.877 and 1.879; r(C-C) 1.556(7); r(C-O) 1.431(3) and 1.445; r(C_cyc-H) 1.11(2); r(C_Me-H) 1.10(2); ϕ(O−C−C−Si) −33.0(14); ∠C_cycSiC_cyc 92.2(5); −33.0(14); ∠C_MeSiC_Me 107.2(8); ∠SiCC 102.6(6); ∠CCO 109.9(11); ∠HC_cycH 110.5(47); ∠SiC_MeH 111.6(14). Method for the synthesis of 3,3-dimethyl-1-oxa-3-silacyclopentane is given, and generalized notation for five-membered ring confor-mations is suggested. Moscow State University. Tromse University, Norway. Irkutsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 689–707, July–August, 1996. Translated by L. Smolina