Single crystals of amylose V complexes with the 81 helical configuration can be obtained from aqueous solutions of amylose by using α-naphthol as a complexing agent. Morphological observations suggest that the differences in crystallization behavior among the α-naphthol complex and other complexes with alcohols are due to differences in solubility of the complexes in water. Electron diffraction studies indicate a two-dimensional tetragonal unit cell with a = b = 22.9 Å. It is deduced that the space group providing a satisfactory arrangement of two helices is one of the enantiomorphs P41212 and P43212. From x-ray diffraction it was found that the c axis spacing of the α-naphthol complex is equivalent to that in 61 and 71 helical amylose crystals. Consequently, the geometry of the helical configuration requires an integral number of glucose residues per turn. The true helical diameters of the n-butanol, isopropanol, and α-naphthol complexes were calculated from experimental data. The ratio was 6:7:8 and indicated that the helix of the α-naphthol complex has eight glucose residues per turn. The diversity of helical configurations in V amylose crystals is discussed. 相似文献
Summary: Solution‐grown lamellar crystals of poly(p‐dioxanone) (PPDX) have been crystallized isothermally from butane‐1,4‐diol at 100 °C. The crystal structure of PPDX has been determined by interpretation of X‐ray fiber diagrams of PPDX fibers and electron diffraction diagrams of lozenge‐shaped chain‐folder lamellar crystals. The unit cell of PPDX is orthorhombic with space group P212121 and parameters: a = 0.970 nm, b = 0.742 nm, and c (chain axis) = 0.682 nm. There are two chains per unit cell, which exist in an antiparallel arrangement.
Transmission electron micrograph of PPDX chain‐folded lamellar crystals obtained by isothermal crystallization and its electron diffraction diagram. 相似文献
The dependence of crystalline morphology of isotactic polypropylene crystallized from dilute solutions on its molecular weight and growing conditions and the mechanism of crystal growth were studied by electron microscopy and electron diffraction. Lathshaped lamellar crystals 150–300 A. in thickness are obtained from fractionated polypropylene powders of Mw (average molecular weight) = 600,000 and 240,000, but not from the samples of Mw = 82,000 and 44,000, by means of isothermal crystallization at 130°C. for 20 hr. in dilute α-chloronaphthalene solution (0.005 wt.-%). Precipitation of the fractionated polypropylene sample of Mw = 82,000 from a dilute solution of carbitol gives typical dendritic crystals under the same isothermal crystallizing conditions as mentioned above. The mode of chain folding in these crystals based on the orientation and the crystal structure of the lamellar crystals agrees with that proposed by Sauer, Morrow, and Richardson. From the morphological observations, the mechanism of growth pertinent to polypropylene lamellar crystals is presumed to be as follows: fibrils at first aggregate, then the molecular chains are folded to form small lamellae, and then these small lamellae accumulate compactly to grow to large, lath-shaped, lamellar crystals. 相似文献
Single crystals of a new barium oxogallate were obtained by growth from a melt at 1500 °C. The compound is monoclinic, with cell parameters a = 17.7447(10) Å, b = 10.6719(5) Å, c = 7.2828(5) Å, β = 98.962(7)°, V = 1362.3(2) Å3. The diffraction pattern shows systematic absences corresponding to the space group P121/c1. The structure was solved by direct methods followed by Fourier syntheses, and refined using a single crystal diffraction data set (R1 = 0.032 for 2173 reflections with I > 2σ(I)). The chemical composition derived from structure solution is Ba4Ga2O7, with a unit cell content of Z = 6. Main building units of the structure are GaO4 tetrahedra sharing one oxygen atom to form Ga2O7 groups. The Ga–O–Ga bridging angle of one of the two symmetrically independent groups is linear by symmetry. The dimers are crosslinked by barium cations coordinated by six to eight oxygen ligands. 相似文献
The molecular structure of 10-(1,3-Dithiolan-2-ylidene)-10H-indeno[1,2-f] -1,2,3,4,5-pentathiepin S7C12H89 has been determined by single crystal X-ray diffraction. The crystals are triclinic, space group PI, with two molecules in a unit cell of dimensions α = 8.931(2), b = 9.387(2), c = 10.175(2) Å, α = 75.73(2), β = 73.35(1), γ = 64.37(2)°. The structure was solved by direct methods, and refined to a final R value of 3.3% for 1925 independent reflections. The molecule consists of an indene core with a nearly co-planar dithiolane and a fused pentasulfide chain. The S5C2 ring is in the chair configuration, with an average S? S distance of 2.052 Å. There is no variation of bond lengths as is frequently seen in multi-sulfur chains. The indenone ring shows no evidence of any delocalization, while the dithiolane ring is disordered at the two methylene positions. No attempt was made to resolve the disorder, since it is frequently seen and has been thoroughly investigated previously. 相似文献
The morphology of solution grown single crystals of poly(p-dioxanone) was investigated. Different crystallization conditions (solvent, precipitant agent and temperature) were tested. Dendritic growth, screw dislocations and striations were observed. Crystals usually exhibited a lozenge morphology, whose apex angle changed with the crystallization conditions. In all cases, however, a single crystal electron diffraction pattern was recorded. Spherulitic morphologies were obtained by evaporation of formic acid solutions. Lamellae gave rise to well resolved electron diffraction patterns that allowed determination of the main packing characteristics. Patterns of tilted specimens helped establish an orthorhombic unit cell, whose parameters indicate a deviation from the all trans molecular conformation. Quantum mechanical calculations were performed on small model compounds to study the conformational preferences. Simulated diffraction patterns were consistent with a unit cell containing four repeat units and a P212121 space group. Molecular packing suggests the existence of different kinds of folds for an assumed adjacent reentry. Polyethylene decoration hardly highlighted a crystal sectorization. Also enzymatic degradation of lamellar crystals was evaluated by using a Pseudomonas cepacia lipase. 相似文献
The crystal structure of the Nb-methobromid of the alcaloid meloscin has been determined by three-dimensional X-ray crystallographic methods. The crystals belong to the orthorhombic space group P212121 with four molecules per unit cell. The cell constants are a = 10.01, b = 17.79, c = 11.43 Å. The absolute configuration has been obtained by the use of anomalous dispersion effects. 相似文献
For the first time, novel structural nanosized Y2O3 powders were successfully synthesized by the n-butanol soft-template method. X-ray diffraction, transmission electron microscopy, scanning electron microscopy and Raman
spectroscopy were used to characterize the products. The results indicate that these products (calcined at 700°C) were comprised
of many Y2O3 nanomembranes, and the nanomembranes could change into nanorods when calcined at 1000°C. Interestingly, differential thermal
analysis studies suggested that the nanosized Y2O3 crystals had intense catalytic activity on the thermal decomposition of ammonium perchlorate. 相似文献
Methyl acrylate, CH2CHCOOCH3, has been crystallized, and x-ray data have been collected at ?120°C. The crystals are orthorhombic, space group Pnma, with four molecules in the unit cell. The structure has been determined by using symbolic addition procedures, and refined to a final residual R factor of 0.10. The molecule is planar, and the intramolecular bond distances and angles are in good agreement with values obtained for the liquid monomer by electron diffraction techniques. Considerations of crystal geometry indicate that the packing hardly permits dimerization or polymerization of the molecules in regions of crystal perfection. 相似文献
Electron diffraction has been used to investigate the structure of a wide range of as-polymerized crystals of poly(4-hydroxybenzoate) [systematic name: poly(1,4-oxybenzoyl)]. The chemical composition and the degree of polymerization (DP) have been varied and some samples have been thermally treated. At room temperature two crystalline modifications with orthorhombic unit cells coexist. The chains adopt a 21 helical conformation in both forms, but there are differences for oligomer and polymer crystals. Oligomers of low DP have an extended chain-conformation, whereas in polymers a shortening of the repeat distance along the chain is observed as a function of both the DP and the crystallization conditions. From the most extensive data sets we have derived the lattice parameters a = 7.52, b = 5.70, and c = 12.49 Å for polymer crystals of phase I, and the subcell parameters for oligomer crystals of phase II a = 3.77, b = 11.06, and c = 12.89 Å. Both phases contain two chains per unit cell. In addition to modifications I and II several defect structures exist the unit cells of which contain more than two chains. At temperatures which depend on the degree of polymerization, a phase transition to a third modification takes place. The large difference between the densities of phase III as compared to both phase I and II suggests that torsional degrees of freedom exist in phase III which allow a certain mobility of the phenyl and ester groups. This mobility enables the end groups of adjacent layers in interlamellar regions of oligomer crystals to undergo transesterification reactions and therefore to increase the molecular weight of the samples. 相似文献
Morphology control for intense solid‐state phosphorescence of non‐emissive, but potentially emissive crystals of platinum complexes and the mechanistic rationale are described. A series of trans‐bis(salicylaldiminato)platinum(II) complexes bearing linear alkyl chains ( 1 a : n=5; 1 b : n=8; 1 c : n=12; 1 d : n=14; 1 e : n=16; 1 f : n=18) was synthesized and the solid‐state emission properties were examined by using crystals/aggregates prepared under various precipitation conditions. Crystals of 1 e , prepared using “kinetic” conditions including rapid cooling, high concentrations, and poor solvents, emit intensive yellow phosphorescence (λmax=545 nm) under UV irradiation at 298 K with an absolute quantum efficiency of 0.36, whereas all the crystals of 1 a – 1 f prepared using “thermodynamic” conditions including slow cooling, low concentrations, and good solvents were either non‐ or less emissive with Φ298K values of 0.12 ( 1 a ), 0.11 ( 1 b ), 0.10 ( 1 c ), 0.07 ( 1 d ), 0.02 ( 1 e ), and 0.02 ( 1 f ) under the same measurement conditions. The amorphous solid 1 e , prepared by rapid cooling and freeze‐drying, was also non‐emissive (Φ298K=0.02, 0.02). Temperature‐dependent emission spectra showed that the kinetic crystals of 1 e exhibit high heat‐resistance towards emission decay with increasing temperature, whereas the amorphous solid 1 e is entirely heat‐quenchable. This is a rare example of the change from a non‐emissive crystal into a highly emissive crystal by morphology control through crystal engineering. Emission spectra and powder X‐ray diffraction (XRD) patterns of the emissive, kinetic crystals of 1 e are clearly distinct from those of the less emissive, thermodynamic crystals of 1 a – 1 f . Single‐crystal XRD unequivocally establishes that the thermodynamic crystals of 1 d have a multilayered lamellar structure supported by highly regulated, consecutive π‐stacking interactions between imine moieties, whereas the kinetic crystals of 1 e have a face‐to‐edge lamellar structure with less stacking. These results lead to the conclusion that 1) morphology control of long‐chained complexes exclusively generates a metastable herringbone‐based lamellar packing motif that exhibits intense emission and high heat‐resistance, while 2) a thermodynamically stable, highly regulated, consecutive stacking motif is unfavorable for solid‐state emission. 相似文献
The exfoliation-reduction of VOPO4·2H2O in l-butanol oriso-butanol alone, and in a l-butanol/ethanol oriso-butanol/ethanol mixture, were conducted. Although all precursors were composed of a lamellar compound with intercalated alcohol molecules, VOHPO4·0.5H2O was formed when the exfoliation-reduction process was carried out in the mixed alcohol. All precursors transformed to a single phase of (VO)2P2O7 under the reaction conditions forn-butane oxidation, but the crystallinity of (VO)2P2O7 was different. The catalyst synthesized iniso-butanol/ethanol was well crystalline (VO)2P2O7, and exhibited higher selectivity to maleic anhydride than that synthesized iniso-butanol alone for then-butane oxidation. 相似文献
Pentacontane, hexacontane, 15-ketohentriacontane (palmitone), and solid solutions of the two n-paraffins were deposited from the vapor phase onto surfaces of potassium hydrogen phthalate (PHP) crystals and cleavage faces of potassium chloride (KCl) crystals in vacuo. Epitaxial growth, with molecular chains parallel to the substrates, occurs within a temperature range (e.g., 25–50°C for palmitone), and the epitaxial relationship between molecules and substrates was broken at higher temperatures. The electron diffraction patterns, similar to that of polyethylene, were obtained from all samples prepared at room temperature. The [100] or [130] directions of palmitone crystals are parallel to the substrate surface of PHP, and the [110] direction is parallel to that of KCl; the crystals in both cases are the orthorhombic form with lattice parameters a = 7.56 Å, b = 4.93 Å, c = 82.8 Å and a space group of Pna21. The (100) planes of n-paraffin crystals are parallel to the surface of PHP, and the crystals are again orthorhombic. Also, solid solutions of n-paraffins can be formed from the vapor phase, with the nucleation process on the two substrates being the same as for pure paraffins. 相似文献
The Layer Structure of Cyameluric Chloride C6N7Cl3 A solid state reaction of cyanuric chloride (trichloro‐s‐triazine C3N3Cl3) with sodium dicyanamide (NaN(CN)2) yielded some yellow, plate‐like crystals of cyameluric chloride (trichloro‐s‐heptazine C6N7Cl3). The crystal structure was determined by single crystal X‐ray diffraction at 220 K and was solved in the monoclinic space group C 2/c (no. 15) with Z = 24, a = 2319.4(4) pm, b = 1348.8(1) pm, c = 2063.4(3) pm, β = 118.38(2)° and V = 5.680(1) nm3. In the structure, the molecules of C6N7Cl3 are forming layers parallel to the ab‐plane, which are separated from each other by a gap of approximately 300 pm. In each of these layers, the molecules seem to be arranged around pseudo‐threefold axes, showing an almost trigonal structure pattern. 相似文献
Binary solid solutions of n-paraffins (n-C50H102/n-C60H122) epitaxially prepared on potassium hydrogen phthalate substrate from the vapor phase have been studied by electron diffraction to characterize their phase transitions and structure. The continuity of solid solution in the n-C50H102/n-C60H122 system is demonstrated once lamellar ordering of the crystal packing is achieved. However, such ordering is achieved only by annealing and proceeds through a series of intermediate chain packings. At first, the electron diffraction patterns from all samples prepared at room temperature resemble those from polyethylene, in which no spots corresponding to the interlayer spacings appear. Longitudinal chain translations are induced by annealing to cause the lamellar reflections to appear, while the “polyethylene” subcell reflections remain unsplit until the crystal structure with well-defined methyl end planes is reached. 相似文献
Crystal lattices for various polymorphs of poly(α-methly-α-ethyl-β-propiolactone) (PMEPL) are proposed on the basis of combined electron and x-ray diffraction data. Single crystal-like electron diffraction is observed from melt crystallized thin films of isotactic PMEPL and stereocomplex. Melt-crystallized isotactic PMEPL exhibits a monoclinic, pseudo orthorhombic lattice with the unit cell parameter c (4.75 Å) equivalent to the periodicity of the planar zigzag conformation typically obtained by sample elongation. The stereocomplex crystallizes in a distinctly different orthorhombic lattice with c = 7.1 Å, implying a 21 helical conformation. In addition, melt-crystallized mixtures of isotactic PMEPL and isotactic poly(α-methyl-α-n-propyl-β-propiolactone) (PMPPL) are examined by solid state 13C nuclear magnetic resonance spectroscopy and x-ray diffraction. These techniques reveal that, in such blends, the conformation and crystal structure found for isotactic PMEPL of a given chirality depends on the absolute configuration of the PMPPL present. In samples containing PMEPL and PMPPL of opposite absolute configuration, isotactic PMEPL crystallizes from the melt as a helix, in contrast to its behavior in the pure state, whereas PMPPL adopt the same helical conformation in the blend as when crystallized alone. 相似文献