Synthesis of spinacine and spinacine derivatives: crystal and molecular structures of Nπ-hydroxymethyl spinacine and Nα-methyl spinaceamine

The natural amino acid L-Spinacine (4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) has been synthesized following a new pathway which gives a chemically and optically pure product with an excellent yield. The crystal structures of a synthetic intermediate, N^π-hydroxymethyl-spinacine, and a spinacine derivative, N^α-methyl-spinaceamine, have been investigated through X-ray diffraction: Spi(πMeOH)·H₂O, monoclinicP2 _i,a=8.571(1),b=6.682(1),c=8.588(1) Å, and β=94.67(1)^o. Spm(αMe)·2HCl·H₂O, triclinicP l,a=7.492(4),b=10.799(3),c=7.040(2) Å, α=91.88(2), β=98.36(3) and γ=73.34(3)^o. Spi(πMeOH) crystallizes with a water molecule and displays a zwitterionic character. The carboxylate group is in equatorial position and forms a short electrostatic interaction of 2.618(2) Å between one of its oxygens and the protonated nitrogen of the tetrahydropyridine ring. The crystal packing is assured by strong O?H???O, O?H???N, N?H???N intermolecular hydrogen bonds and C?H???O close contacts. The biprotonated compounds Spm(αMe) crystallizes with two Cl^? anions and a water molecule. The positive charge on the imidazole ring is delocalized on the conjugated moiety N=C?N. The crystal is built up by clusters formed by two biprotonated Spm(αMe) molecules, four Cl^? anions and two water molecules linked together by hydrogen bonds.     

“Polyaniline”: Interconversion of Metallic and Insulating Forms

Abstract

“Polyaniline” has been synthesized in various forms both chemically and electrochemically in aqueous media. The qulnoid-benzenoid-diimine form, an insulator, is doped by dilute aqueous protonic acids to the metallic regime ([sgrave] = 5 ohm^?1cm^?1; compressed pellet) to give the corresponding iminium salt. This represents a new type of p-doping phenomenon in a conducting polymer. Both these forms are stable in the presence of air and/or water. The doping process is reversed by treatment with aqueous alkali. Cyclic voltammetry studies in an aqueous electrolyte show excellent reversibility between selected reduced and oxidized forms of polyaniline.     

Properties and structure of AsTe glasses: (I). Glass-forming ability and related properties

AsTe glasses have been investigated for determining the molecular mechanisms of glass formation and of crystallization. Stable and homogeneous bulk glasses are prepared throughout the range of concentration from 20 to 65 at % As, by using an improved quenching method. GFA (glass-forming ability) is determined with respect to the rate of cooling. Density, microhardness, T_g and ΔC_p at T_g are measured in the whole range of glass formation. Finally a quantitative analysis of the kinetics of crystallization is carried out. It appears that most properties which involve molecular motions exhibit anomalies for As₄₀ Te₆₀ composition (As₂Te₃ is the unique definite compound of the system). So GFA shows a sharp depression for this critical composition; similarly enthalpy and kinetics of crystallization are drastically modified at As₄₀Te₆₀. For Te-rich glasses, crystallization occurs at low temperature by homogeneous nucleation with a small energy of activation. For As-rich glasses, crystallization occurs at much higher temperatures. Above 200°C it is controlled by growth with an high activation energy which indicates deep rearrangements of the relative positions of the atoms by chemical diffusion. A coherent analysis of all the data is developed which shows that important differences of local order exist between amorphous and crystalline states and also between the two well-distinct types of glasses we are dealing with. The aim of paper II is to determine these differences from diffraction data.     

Crystal and Molecular Structure of 6,6′-Dimethoxy-gossypol:Acetic acid (1:1)

Abstract By crystallization from dilute solutions of acetic acid (2–4%) in diethyl ether, acetone, or methyl ethyl ketone, 6,6′-dimethoxy-gossypol forms a solvate with acetic acid in a one-to-one molar ratio. The compound crystallizes in the triclinic P space group and has unit cell dimensions of a = 7.5793(10) ?, b = 14.7211(19) ? and c = 14.740(2) ?, α = 106.260(3)°, β = 102.310(3)°, γ = 95.975(3)°, Z = 2. The structure was solved by direct methods and refined to an R1 value of 0.0394 on 4252 observed reflections. Enantiomeric pairs of dimethoxy-gossypol molecules form centrosymmetic dimers that are characterized by a pair of intermolecular hydrogen bonds and by hydrophobic stacking between pairs of naphthalene rings. The acetic acid molecule accepts a hydrogen bond from a gossypol hydroxyl group and donates to a hydrogen bond with one of the aldehyde groups of an adjacent gossypol molecule. Although there is less hydrogen bonding in this structure than in the gossypol:acetic acid (1:1) structure, the molecular packing of the two compounds is similar. Graphical abstract Crystal and molecular structure of 6,6′-dimethoxy-gossypol:acetic acid (1:1) Michael K. Dowd and Edwin D. Stevens The molecular structure of the acetic acid solvate of 6,6′-dimethoxy-gossypol is presented.      

The Life and Times of Vsevolod Konstantinovich Frederiks: 1885–1944

Abstract

The 17th International Liquid Crystal Confernce was held in Strasbourg, France from 19–24 July 1998. It was organized by all colleagues in Strasbourg involved in liquid crystal research with Antoine Skoulios as Conference Chairman, Daniel Guillon as Secretary, Stephane Mery and Paul Masson as Treasurers. This year, the ILCC attracted 897 participants, including 52 accompanying persons, from 38 countries. The largest representation of 130 delegates was from Japan followed by 118 from Germany, 115 from France, 94 from the UK and 77 from the USA. The scientific activities were structured around 10 main topics divided between 3 parallel sessions and 841 posters. The scientific report which follows has been written by Professor G. W. Gray and contains most of the highlights which were indicated to him by different experts on each of the coference topics.     

The resonant X-ray diffraction in Co-Åkermanite: Theory and experiment

The structural factors for X-ray resonant diffraction near the K-absorption edge of cobalt in Co-åkermanite have been calculated with allowance for the known data about its incommensurate 2D modulation. It is shown that the local symmetry of Co atoms in the basic structure does not allow any pure resonant reflections in the dipole-dipole approximation. However, pure resonant reflections of the h00 (h = 2n + 1) type are possible owing to the dipole-quadrupole contribution. The 5D formalism is used for the incommensurately modulated structure. It is shown that the displacement terms in the anisotropic tensor atomic factors could mainly contribute to the first-order satellites, providing pure resonant satellite reflections of the hhlm0 (m = 2n + 1) or h00m $\bar m$ (h = 2n + 1) types.     

Deposition of phosphorus doped a-Si:H and μc-Si:H using a novel linear RF source

A roll-to-roll PECVD system for thin film silicon solar cells on steel foil has been developed by ECN in collaboration with Roth and Rau AG. It combines MW–PECVD for fast deposition of intrinsic Si and novel linear RF sources, which apply very mild deposition conditions, for the growth of doped Si layers. The RF and MW sources can be easily scaled up to deposition widths of up to 150 cm. Here, we report on n-type doping, achieved by RF–PECVD from a H₂/SiH₄/PH₃ mixture in the reaction chamber. The best n-type a-Si:H layers showed E_act = 0.27 eV and σ_d = 2.7 × 10^?3 S/cm. Also thin layers down to 20 nm were of device quality and were deposited at a rate of 0.4 Å/s. Furthermore, n-type μc-Si:H layers with thicknesses of 150 nm, with E_act = 0.034 eV and σ_d = 2 S/cm were grown. Good quality n-type μc-Si:H layers can be made for layer thicknesses down to 50 nm at a rate of 0.15 Å/s. To conclude, the novel RF source is well-suited for the growth of n-doped a-Si:H and μc-Si:H layers for roll-to-roll solar cell production.     

Di-μ-sulphido-bis[4-methyl-piperidinedithiocarbamate tin(IV)]: Synthesis,characterization, and crystal and molecular structure

The title compound, C₁₅H₂₆SnN₂S₅Cl₂, was prepared, and characterized by means of X-ray and IR measurements. The crystals are monoclinic, space groupP2₁/n, (non standard setting ofP2₁/c, No. 14) witha=12.330(2),b=11.930(1),c=17.055(2) Å,=106.21(1)° andZ=4.The structure was solved by the heavy-atom method, and least-squares refinement of the structural parameters led to a conventionalR factor of 0.028 for 1284 independent reflections. The structure consists of discrete dimeric units with the metal coordinated to six sulphur atoms. The IR spectrum is consistent with the presence of the sulphur bridge atoms between the two metal ions.     

4,4′-Di(N)Hexoxybenzalazine: Crystal and Molecular Structure and Phase Characterization of the Liquid Crystalline Compound

Abstract

The crystal and molecular structure of the mesogenic title compound (HBA) is described. Lattice parameters are: space group P1, a = 9.003(2) Å, b = 8.850(2) Å, c = 8.510(2) Å, α = 79.63(1)°, β = 65.04(1)°, γ = 87.41(1)° (at T = 299 K). The molecules contain a centre of symmetry and the phenyl rings are coplanar. In order to obtain better structural data for a comparison with its methoxy derivative (MBA) a redetermination of this structure was carried out using a new data set. The melting enthalpy of HBA is 45(2) kJmol^?1 (127.8(5)°C) its clearing enthalpy is 1.5(4) kJmol^?1 (153.2(5) °C). The fluctuation wave-length 2π/q_‖ of 27(2) Å in the nematic state can be compared with the molecular length of 31.63 Å.     

Human 17β-hydroxysteroid dehydrogenase-ligand complexes: crystals of different space groups with various cations and combined seeding and co-crystallization

Human estrogenic 17β-hydroxysteroid dehydrogenase (17β-HSD1) is responsible for the synthesis of active estrogens that stimulate the proliferation of breast cancer cells. The enzyme has been crystallized using a Mg²⁺/PEG (3500)/β-octyl glucoside system [Zhu et al., J. Mol. Biol. 234 (1993) 242]. The space group of these crystals is C2. Here we report that cations can affect 17β-HSD1 crystallization significantly. In the presence of Mn²⁺ instead of Mg²⁺, crystals have been obtained in the same space group with similar unit cell dimensions. In the presence of Li⁺ and Na⁺ instead of Mg²⁺, the space group has been changed to P2₁2₁2₁. A whole data set for a crystal of 17ß-HSD1 complex with progesterone grown in the presence of Li⁺ has been collected to 1.95 Å resolution with a synchrotron source. The cell dimensions are a=41.91 Å, b=108.21 Å, c=117.00 Å. The structure has been preliminarily determined by molecular replacement, yielding important information on crystal packing in the presence of different cations. In order to further understand the structure–function relationship of 17β-HSD1, enzyme complexes with several ligands have been crystallized. As the steroids have very low aqueous solubility, we used a combined method of seeding and co-crystallization to obtain crystals of 17β-HSD1 complexed with various ligands. This method provides ideal conditions for growing complex crystals, with ligands such as 20α-hydroxysteroid progesterone, testosterone and 17β-methyl-estradiol-NADP⁺. Several complex structures have been determined with reliable electronic density of the bound ligands.     

Crystal structure of diheterolevulosan II: α-d-Fructofuranose-β-d-fructopyranose 1,2′:2,1′ dianhydride and molecular mechanics calculations on diheterolevulosan II and IV with chair and boat conformations of the central 1,4-dioxane ring

C₁₂H₂₀O₁₀,M _r=324.28, orthorhombic,P2₁2₁2₁,a=9.4476(8),b=10.2247(8),c=13.5827(11) Å,V=1312.07(18) ų,Z=4,D _x=1.642 g cm^?3, MoKα radiation (λ=0.71073 Å)μ=1.4 cm^?1,F(000)=688,T=295 K, finalR=0.041 for 1089 reflections withI≥2.5σa(I). The molecule consists of aβ-d-fructopyranose and a α-d-fructofuranose ring which are linked by a 1,4-dioxane ring. The pyranose ring and the dioxane ring both have a chair conformation, and the furanose ring has an envelope conformation. All six hydroxyl groups act as donors in intermolecular hydrogen bonding. Each molecule is hydrogen-bonded to eight neighbor molecules by fourteen hydrogen bonds, forming a three-dimensional framework. The hydrogen bonds of varying geometry give rise to five sharp hydroxyl stretch vibrations in the infrared spectrum. In diheterolevulosan IV the central dioxane ring is a boat. Molecular mechanics calculations on diheterolevulosan II and IV having different boat and chair conformations of the dioxane ring show that the lowest energy conformations correspond to the conformations observed in the crystal structure. For comparison the calculations also have been applied to 1,4-dioxane having boat and chair conformations.     

Inter-continental school of geometry and topology in soft matter,optics and biological systems: I-CAMP’14’s review

Two new 5‐substituted 1,3,4‐thiadiazole‐2‐carboxylate esters have been synthesized via ring closure of appropriate tricarbonyl precursors using Lawesson's reagent. The chemistry described is the first report of such methodology in the organic literature. The new materials display broad smectic C phases and show considerable potential for use in electrooptic display devices.     

Ca–Mg mixing in aluminosilicate glasses: An investigation using 17O MAS and 3QMAS and 27Al MAS NMR

To better understand non-framework cation mixing in Ca–Mg aluminosilicate glasses, ¹⁷O MAS and 3QMAS NMR studies were done on glasses on the Mg₃Al₂Si₃O₁₂–Ca₃Al₂Si₃O₁₂ join as well as several compositions with lower Al/Si ratios. While not all of the oxygen sites are fully resolved, the non-bridging oxygen associated with two Ca and one Mg cations is under-represented relative to that predicted by a model assuming random Ca/Mg mixing. Therefore, local non-bridging oxygen environments are rich in Mg, and extra Ca must be associated with charged bridging oxygens such as Al–O–Si. The deviation from random mixing increases as the Al/Si ratio decreases and as X_Mg approaches 0.50, suggesting a reduction in configurational entropy that may be compensated for by other sources, including mixing of network forming cations. Al–O–Al is detected, and appears to increase with increasing X_Mg and increasing Al/Si. High field ²⁷Al MAS NMR also shows that these glasses all have substantial concentrations of ^[5]Al, but no detectable ^[6]Al (0.5% detection limit). The amount of ^[5]Al increases non-linearly as X_Mg increases and very slightly as Al/Si increases.     

Ultrasonic wave velocities and attenuation in IVb-Vb-VIb chalcogenide glasses: 2–300 K

The velocities and attenuation of longitudinal and shear ultrasonic (12 MHz) waves have been measured for several chalcogenide glasses (Ge₁₀Si₁₂As₃₀Te₄₈, Ge₂₀As₃₀Se₅₀, Si₂₀As₃₂Te₄₈, Ge₁₀Si₁₂As₂₉Te₄₉, Ge₁₂S₁₄As₃₅Te₄₉). The bulk, shear and Young's moduli and the Poisson ratio are found to be insensitive to the glass composition. The temperature dependences of the longitudinal and shear-wave velocities are negative at higher temperatures and approach 0 K with a zero slope. The ultrasonic attenuation does not exhibit either the broad loss peak or the smaller low-temperature peak found in many other glasses: the elastic and anelastic behaviour is quite different from that of oxide glasses — no evidence for the existence of two-level systems has been obtained from the ultrasonic measurements.     

Precipitation of calcium carbonate particles by gas–liquid reaction: Morphology and size distribution of particles in Couette-Taylor and stirred tank reactors

The morphology and size of CaCO₃ precipitated by CO₂–Ca(OH)₂ reaction in stirred tank and Couette-Taylor reactors were experimentally investigated. The Taylor vortex in CT reactor encouraged more homogeneous mixing conditions, resulting in the production of smaller particles with a uniform shape throughout the reactor. However, in the stirred tank reactor, the local non-homogeneity of the mixing intensity led to the simultaneous production of cube-like and spindle-like particles at a high reactant concentration. The agglomeration of CaCO₃ resulted in a bimodal size distribution. However, the morphology and size of a single particle were predominantly changed by the excess species in the solution. The largest mean size and cube-like particles were observed under stoichiometric reaction conditions. As the excess species concentration increased, the morphology was transformed to a spindle-like shape and the mean size decreased due to selective adsorption of the excess species on the crystal faces.     

Crystal structures of 2,6- and 3,5-dichlorobenzoic acids: nonbonded Cl ⋅ ⋅ ⋅ Cl contacts

The crystal structures of 2,6-dichlorobenzoic acid (1) and 3,5-dichlorobenzoic acid (2) were obtained by single-crystal X-ray diffraction. Crystallization of 1 occurred in the centrosymmetric triclinic space group P1 (No. 2) with a = 7.2678(9), b = 9.8543(8), and c = 11.8290(11) Å = 95.000(7), = 104.262(10), and = 102.128(8); and Z = 4. Crystallization of 2 occurred in the monoclinic centrosymmetric space group P2₁/n (No. 14) with a = 3.7812(3), b = 13.996(2), and c = 14.514(2) Å = 95.183(8); and Z = 4. Chlorine substituents of four dimeric molecules of 2 formed square channels, ca. 3.54 Å on a side, which run parallel to the crystallographic a axis. Monomers of 1 and 2 formed centrosymmetric dimers via near-linear hydrogen bonds. Details of the structures and spectroscopic results are presented and discussed.     

Novel Methyl 4,6-O-benzylidene-3-ketoglucopyranosid-fused γ-lactam: Synthesis and Crystal Structure

Abstract  

The title compound methyl 4,6-O-benzylidene-3-ketoglucopyranosid-fused γ-lactam was synthesized from 2-oxoglucopyranoside in one pot via multi-step reaction sequence under mild conditions. It was characterized by HRMS, ¹H and ¹³C-NMR, IR, elemental analysis and single crystal X-ray diffraction. The crystal belongs to orthorhombic P2(1)2(1)2(1) space group with unit cell parameters a = 6.1840 (12) ?, b = 10.372 (2) ?, c = 25.702 (5) ?, V = 1648.5 (6) ?³, Z = 4, D_c = 1.343 Mg/m³, λ = 0.71073 ?, μ(Mo Kα) = 0.102 mm⁻¹, F(000) = 704. X-ray diffraction analysis reveals that the compound adopts chair-chair conformation. The newly formed γ-lactam moiety is fused to glucopyranoside ring by C2 to form spirosugar. The crystal structure is stabilized by N–H···O2 hydrogen bond.     

Atomic structure and chemical order in binary Ge–Te and As–Te glasses: A Te K-edge X-ray absorption fine structure spectroscopic study

The nearest-neighbor coordination environments of Te atoms in Ge_xTe_100?x glasses with x = 15 and 20 and in As_xTe_100?x glasses with 40 ? x ? 65 have been studied with Te K-edge EXAFS spectroscopy. The average coordination number of Te atoms in all glasses is found to be ～2.0 and no violation of the 8-N rule is observed. The compositional makeup of the first coordination shell of Te atoms indicates that chemical order is largely preserved in both glass-forming binary systems. Sudden changes in the Te coordination environment and violation of chemical order are observed at the stoichiometric As₄₀Te₆₀ glass implying formation of a constrained network. The compositional dependence of the physical properties in both systems can be correlated to short-range chemical order.