6,6′-Dimethyl-1,1′,5,5′-tetraaza-6,6′-bi(bicyclo[3.1.0]hexane): synthesis and investigation of molecular structure by quantum-chemical calculations,NMR spectroscopy and X-ray diffraction analysis

Structural Chemistry - A new diaziridine derivative with two bicyclic diaziridine-containing moieties in one molecule,...     

The belok station for protein crystallography on the synchrotron radiation beam from the bending magnet in the Sibir-2 storage ring

Design modifications made in the initial project of the Belok station in the Sibir-2 storage ring and the alignment and calibration methods are considered. The main operating parameters of the station are reported. Protein single crystals in a capillary at T = 293 K and without a capillary at T = 95 K, powders (angular resolution Δ2? = 0.04°), and nanocrystalline Na and Cl₂ precipitates (sizes, shape, and orientation) in electron-irradiated NaCl crystals have been investigated. The problem of focusing of a short-wavelength synchrotron radiation beam with sagittal bending of the second crystal in the double-crystal monochromator at a limited source-to-sample distance is solved in the Belok project.     

Molecular structure of noradrenaline according to gas-phase electron diffraction data and quantum chemical calculations

1. Download : Download high-res image (90KB)
2. Download : Download full-size image

     

Molecular structure,conformation, and large amplitude motion of barbituric acid as studied by gas-phase electron diffraction and quantum chemical calculations

Structural Chemistry - B3LYP and MP2(Full) calculations with large basis sets predict the planar equilibrium structure of barbituric acid and reveal large amplitude ring puckering motion which is...     

Localized Blow-Up Regimes for Quasilinear Doubly Degenerate Parabolic Equations

Mathematical Notes - Singular blow-up regimes are studied for a wide class of second-order quasilinear parabolic equations. Energy methods are used to obtain exact (in a certain sense) estimates of...     

Molecular structure of carphedon as studied by gas electron diffraction and quantum chemical calculations

The gas-phase structure and conformational properties of carphedon (C₁₂H₁₄N₂O₂, phenylpiracetam, 2-oxo-4-phenyl-1-pyrrolidineacetamide) have been determined by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 with 6-31G and cc-pVDZ basis sets). Since quantum chemical calculations demonstrate that the orientation of the acetamide group is fixed by a strong intramolecular N–H(amide)···O(pyrrolidone) hydrogen bond, the number of possible conformers is reduced considerably. Depending on the conformation of the pyrrolidine ring, envelope with out-of-plane C4 atom and acetamide group on the same side of the plane (“+”) or envelope with C4 and acetamide group on opposite sides (“?”), and on the orientation of the phenyl ring, axial (Ax), or equatorial (Eq), four relevant conformations, Ax?, Ax+, Eq?, and Eq+, exist. According to both quantum chemical methods (B3LYP and MP2 with cc-pVDZ basis sets) these four conformers differ by less than 2 kcal/mol in free energies. However, the two methods predict different relative free energies. The GED data were analyzed with different models. With a single-conformer model the best fit of the experimental GED intensities (agreement factor R _f = 4 %) is obtained with the Ax+ conformer. Using a two-conformer model the fit improves considerable for a 50(11):50(11) mixture of Ax? and Eq+ conformers (R _f = 2.7 %). No further improvement is obtained with a three-conformer model and large uncertainties for relative contributions occur. The geometric parameters of gaseous carphedon are compared with those in the crystal phase, where two molecules are connected by two intermolecular N–H···O hydrogen bonds, and with gas-phase values of piracetam.     

Crystal monochromator with a large curvature of the sagittal bending

A new crystal monochromator is designed and tested. The crystal monochromator allows for the use of a large curvature of the sagittal bending and makes it possible to focus synchrotron radiation at a short wavelength and a limited distance from the synchrotron radiation source to the sample.     

Anisotropy of quasistatic magnetization-reversal processes in (210)-oriented iron-garnet films

An experimental study is made of the effect of an in-plane field H _p of various orientations on the domain structure and shape of the hysteresis loops of epitaxial iron garnet films with the (210) orientation. The characteristic of the magnetization reversal process (in fields somewhat lower than the anisotropy field) is taken to be the critical fields H _p1, H _p2, and H _p3, for which the magnetization reversal processes is interrupted at distinct stages. A method is proposed for constructing the phase diagram of the magnetic states of films, using measurements of the critical fields H _p for different amplitudes of the magnetization reversal field H _z . Two directions in the plane of the film are determined with an accuracy of a fraction of a degree from the hysteresis loops, where in the corresponding field Hp the transition from a single-domain state to a multidomain state occurs as a second-order phase transition. The characteristic changes in the shape of the hysteresis loop are consistent with the features in the reorganization of the domain structure of the (210) film. The preferential orientations of the stripe domain structure of the samples are determined relative to the crystal axes as determined by x-ray methods. Zh. Tekh. Fiz. 67, 32–35 (June 1997) Deceased     

Phragmen-Lindelof Principle for Some Quasilinear Evolution Equations of the Second Order

We consider the equation u _tt + A(u _t ) + B(u) = 0, where A and B are quasilinear operators with respect to the variable x of the second order and the fourth order, respectively. In a cylindrical domain unbounded with respect to the space variables, we obtain estimates that characterize the minimum growth of any nonzero solution of the mixed problem at infinity.__________Translated from Ukrains’kyi Matematychnyi Zhurnal, Vol. 57, No. 2, pp. 239–249, February, 2005.     

Experimental investigation of laval nozzles with gas blown asymmetrically

An experimental determination was made of the transverse forces resulting from asymmetric blowing of a transverse gas jet into the supersonic part of a Laval nozzle. The experimental data are generalized on the basis of the analogy between blowing and flow over an equivalent body and using the generalized theory of one-dimensional flows. An approximating dependence is obtained for determining the gain as a result of blowing.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 188–193, March–April, 1981.