Inclusion compounds of N,N,N′,N′-tetracyclohexylfumaride with isomers of cresol and water

The crystal structures and thermal analyses of the host compound, N,N,N,N-tetracyclohexylfumaride, witho-cresol,p-cresol and water are reported and compared to that of them-cresol complex previously reported in an attempt to elucidate the reasons for host selectivity.     

Inclusion compounds of N,N,N′,N′-tetraisopropylfumaride with isomers of methyl phenol and water

The crystal structures and thermal analyses of the host compound, N,N,N,N-tetraisopropylfumaride, witho-cresol,m-cresol and water are reported and compared to that of thep-cresol complex previously reported in an attempt to elucidate the reasons for host selectivity.     

Structural regularities of helicoidally-like biopolymers in the framework of algebraic topology: II. α-Helix and DNA structures

The developed apparatus of the “structural application” of algebraic geometry and topology makes it possible to determine topologically stable helicoidally-like packings of polyhedra (clusters). A packing found is limited by a minimal surface with zero instability index; this surface is set by the Weierstrass representation and corresponds to the bifurcation point. The symmetries of the packings under consideration are determined by four-dimensional polyhedra (polytopes) from a closed sequence, which begins with diamondlike polytope {240}. One example of these packings is a packing of tetrahedra, which arises as a result of the multiplication of a peculiar starting aggregation of tetrahedra by a fractional 40/11 axis with an angle of helical rotation of 99°. The arrangement of atoms in particular positions of this starting aggregation allows one to obtain a model of the α-helix. This apparatus makes it possible to determine a priori the symmetry parameters of DNA double helices.     

Triplet Excitions in Crystalline Trans-Stilbene I. Spectroscopy of the So → T1 Transition

Abstract

The first singlet → triplet absorption of trans-stilbene has been studied between 10 and 300 K. The triplet exciton energy (energy of the lowest 0–0 line) is 17380 cm^?1 at 10 K, and does not change significantly with temperature. Vibrational A_g modes of 206. 1250 and 1570 cm^?1 are active. The Franck-Condon factor of the origin region is small. The low temperature spectra of the 0–0 and 206 cm^?1 regions show a doublet structure with a splitting of 82 ± 1 cm^?1 which is attributed to the site splitting. Further structure shown by the lines is discussed. The lines are approximately lorentzian. From curve fitting, line-widths and exciton-phonon coupling constants, increasing linearly with T, are deduced. Exciton-phonon coupling appears to be different on the two sites. The product of absorption coefficient at 4880 Å, α, by the total triplettriplet interaction rate constant has been measured at 295 K: αγ=2.3 ± 0.3. 10^?15 cm² sec^?1, corresponding for γ_total to a value of a few 10^?12 cm³ sec^?1.     

Stacking fault formation in Ni?Zn f.c.c. alloys

X-ray diffraction study of the fault formation in Ni Zn alloys is carried out. Approximative analyses are performed in order to distinguish the influences of the dispersity and the microdeformations. Correlation between the X-ray diffraction data and the free molar Gibbs energy is looked for.     

Quantitative UV–VIS spectroscopic studies of photo-thermo-refractive glasses. I. Intrinsic,bromine-related,and impurity-related UV absorption in photo-thermo-refractive glass matrices

The paper opens up a series of papers on the origin and parameters of spectral features forming the absorption of photo-thermo-refractive (PTR) glasses in the UV. Problems to be cleared for gaining further insight into the spectroscopic manifestations of species responsible for the photo-induced processes in PTR glasses are discussed. The samples of bromine-containing and bromine-free PTR glass matrices are synthesized and their absorption spectra in the 28,500 to 50,000 cm^–1 region are recorded. The dispersion analysis of the spectra is conducted based on the convolution model for the complex dielectric function of glasses. The matrix electronic transitions that set the real part of the complex dielectric function and form the intrinsic absorption tail of the matrix are simulated with a series of effective oscillators. Spectral features forming the total absorption spectrum of PTR glass matrices in the 28,500 to 50,000 cm^–1 region are deconvoluted. These features are (i) the intrinsic absorption tail, (ii) for the bromine-containing matrix, the low-wavenumber wing of an envelope around ~ 51,400 cm^–1 covering the bromine-related spectral feature(s), (iii) Fe²⁺- and Fe³⁺-related impurity bands, and also (iv) a structureless absorption mostly due to the high-wavenumber wings of other impurity bands below 28,500 cm^–1.     

Protein crystallization under microgravity conditions. Analysis of the results of Russian experiments performed on the International Space Station in 2005−2015

Conditions of mass transport to growing crystals have a considerable effect on the crystal size and quality. The reduction of convective transport can help improve the quality of crystals for X-ray crystallography. One approach to minimizing convective transport is crystallization in a microgravity environment, in particular, in space. The data obtained by our research team in protein crystallization experiments on the International Space Station are surveyed and analyzed.     

An X – Ray Study of the p-n-Alkoxycinnamic Acids. Part III.1

The effect upon molecular packing of increasing chain length in a homologous series of mesogens has been examined in the case of the p-n-alkoxycinnamic acids by determination of the crystal structures of the four nematogenic acids having two, four, six, and eight carbon atoms in the alkyl chain. The chains have the all-trans extended conformation, and the molecules exist in the crystal as planar hydrogen-bonded dimers. The dimers are arranged in end-to end fashion in parallel rows. Similar side-to-side packing of pairs of dimmers is found in each crystal structure giving a good fit between adjacent aromatic cores, but the amplitudes of thermal vibration of the chain carbon atoms increase markedly with increasing chain length, indicating a low packing efficiency for these moieties.     

Thermodynamic analysis of the W-Al2O3 system near the melting temperature of Al2O3. I. Evolution of the system in the pressure range of 1 × 10−1−1 × 10−4 bar

The changes in the main chemical reactions occurring upon the interaction between tungsten and the evaporation products of Al₂O₃ melt are considered at a fixed temperature (2400 K). The concentrations of the components coexisting in equilibrium in a closed system under isobaric-isothermal conditions are determined by stochastic simulation for low (× 10⁻¹−1 × 10⁻³ bar) and high (1 × 10⁻⁴ bar) vacuum. It is shown that the gas-liquid-solid system is in heterogeneous equilibrium for the basic component ratio W: Al₂O₃ = 1: 1 in the entire pressure range under consideration. A detailed study of the chemistry of this system should facilitate the choice of the optimal conditions for growing leucosapphire crystals from melt.     

Similar quartz crystallographic textures in rocks of continental earth’s crust (by neutron diffraction data): I. Quartz textures in monomineral rocks

Quartz crystallographic textures in different rocks have been investigated by neutron diffraction. Various types of crystallographic textures of quartz-bearing mineral associations in monomineral and multiphase rocks from a representative collection of samples have been revealed and classified. Experimental investigations have been performed on special neutron texture diffractometers designed at the Frank Laboratory of Neutron Physics and mounted in the seventh channel of the IBR-2 reactor at the Joint Institute for Nuclear Research (Dubna).     

Mathematical analysis of the reaction–diffusion of water in glass tubes

The diffusion and reaction of water with glass tubes are mathematically analyzed. A general mathematical model is developed that takes into account the absorption of molecular water from the vapour phase on to the glass tube surface, its subsequent diffusion, and both the forward and backward reactions of formation of the silanol groups. The general solutions are obtained numerically while analytical solutions are obtained for special cases of small time or fast reaction. An approximate integral solution is obtained for the latter and it is shown that the equilibrium model with fast reaction can be cast into a simple yet accurate algebraic form which is easy to implement. The models are applied to few cases of practical importance to optical fiber processing.     

Properties of Some Polarized Chromophores in Polyvinylpyrrolidone

Poor miscibility of highly polarized chromophores to polymer matrices is a crucial issue for EO polymer development. By using poly(N-vinylpyrrolidone) (PVP) as a matrix polymer, we were able to prepare the uniform film containing ammonium-borate type zwitterions or Disperse Red 1 (DR1). For zwitterions, corona poling was unsuccessful probably because of hygroscopic property of PVP and/or strong intermolecular interaction to form the antiparallel dimers. For DR1, we found apparent color change originated from the H-aggregate formation assisted by moisture, which is usable to detect humidity. On the other hand, a passivation layer is necessary to use PVP for the EO applications.     

Application of time–frequency wavelet analysis in the reflectometry of thin films

Crystallography Reports - The application of time–frequency wavelet analysis for solving the reflectometry inverse problem is considered. It is shown that a simultaneous transform of specular...     

Molecular complexes of sulfonamides. 3. Structure of 5-methoxysulfadiazine (form II) and its 1∶1 complex with acetylsalicylic acid

The X-ray structure of the biologically most active polymorph (Form II) of 5-methoxysulfadiazine (1) and that of the 11 complex between this sulfonamide and acetylsalicylic acid (2) are reported. The polymorph1 is monoclinic, space groupP2₁/c witha=13.086(2) Å,b=5.583(1) Å,c=17.222(3) Å, =99.98(1)°,Z=4 and occurs as centrosymmetric hydrogen bonded (N–H...N) dimers in the crystal. This arrangement differs from that observed in other polymorphs of the drug. Complex2 is triclinic, ,a=8.102(1)Å,b=12.033(1) Å,c=12.170(2) Å, =111.67(1)°, =93.77(1)°, =103.82(1)°,Z=2. Complexation involves linear intermolecular hydrogen bonds, N–H...O=C and N...O–H, between the amide group and pyrimidinyl N atom of the sulfonamide and the carboxylic group of the acetylsalicylic acid. On complexation to form2, neither molecular component undergoes any major structural change.     

Knoevenagel condensation catalyzed by K2NiP2O7. Synthesis of (E)-methyl-α-cyanocinnamates in high yields

The Knoevenagel reaction of benzaldehyde and several chloroderivatives with methyl cyanoacetate catalyzed by K₂NiP₂O₇ leads to methyl (E)--cyanocinnamate derivatives in 40 min with yields of 71.65–83.45%. Pure products are easily obtained in crystalline form, uncontaminated by side products or by stereoisomers. Methyl 2-chlorocyanocinnamate, methyl 2,4-dichlorocyanocinnamate, and a new polymorph of methyl cyanocinnamate have been characterized by single crystal X-ray diffraction.     

Similar quartz crystallographic textures in rocks of continental earth’s crust (by neutron diffraction data): III. Relation of quartz texture types with means and conditions of texture formation

Examples of different rocks collected in different regions of the continental earth’s crust are presented. Groups of quartz crystallographic textures of the same type are selected for these rocks. The relationship between the types of textures and the physical means and conditions of their formation is analyzed. The effect of the α-β phase transition in quartz on the texture transformations in rocks is considered.     

New chiral imines based on S-α-phenylethylamine and S-α-benzylethylamine in induced cholesteric and smectic mesophases: II. Behavior of chiral dopants in ester liquid-crystal systems

The temperature dependences of the pitch of induced helical structures in the ester liquid-crystal systems containing hydroxyphenyl benzoate derivatives and chiral N-aroyloxybenzylidene-S-α-phenylethylamines or N-aroyloxybenzylidene-S-α-benzylethylamines have been measured. The twisting power of chiral dopants is calculated and the temperature dependence of the helical pitch in the induced cholesteric (N ^*) and smectic C ^* mesophases is quantitatively characterized. The parameters A = dT _is/dC that characterize the effect of dopants on the thermal stability of the N ^* phases are determined from the concentration dependences of the cholesteric-isotropic transition temperature T _ts for the n-hexyloxyphenyl-n-butylbenzoate-chiral dopant systems. The results obtained are compared with the data for the 4-n-pentyl-4′-cyanobiphenyl (5CB)-based cholesteric systems induced by the chiral dopants under consideration.