Summary: The annealing and melting behavior of poly[(R)‐3‐hydroxybutyrate] (P(3HB)) single crystals were followed in real time by synchrotron small‐ (SAXS) and wide‐angle X‐ray scattering (WAXS) measurements. The real‐time SAXS measurements revealed that the P(3HB) single crystal exhibits a discontinuous increase of lamellar thickness during heating. The structural changes as observed by SAXS and WAXS were in response to the thermal properties of single crystals characterized by differential scanning calorimetry.
A series of two‐dimensional small‐angle X‐ray scattering patterns of P(3HB) single crystal mats during the lamellar thickening process. 相似文献
Summary: In a low‐molecular‐weight polyethylene‐block‐poly(ethylene oxide) (PE‐b‐PEO) diblock copolymer, two pathway‐dependent melting processes were observed: Upon slow heating, the PE lamellar crystals melted at ≈97 °C into a disordered state. However, when the temperature rapidly jumped to above the melting point (e.g., 100 °C), the PE lamellar crystals transformed directly into an ordered lamellar melt, followed by an isothermal conversion into a disordered melt. This isothermal order‐to‐disorder transition was explained by superheating of the PE crystals using a G‐T diagram.
A schematic G‐T diagram explaining the pathway‐dependent double melting for a crystalline polyethylene‐block‐poly(ethylene oxide) copolymer. 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
A structural comparison of three different crystalline forms of poly(β‐propiolactone) (PPL) was carried out by wide‐angle X‐ray diffraction, Fourier‐transform infrared spectroscopy, and differential scanning calorimetry. The α‐form in a hot‐drawn and annealed film represents a 21 helix conformation. The β‐form in a cold‐drawn and annealed film represents a planar zigzag conformation. The γ‐form in an oriented sedimented mat of solution‐grown chain‐folded lamellar crystals also implies a planar zigzag conformation. The solution‐cast film depicts similar outlines with the γ‐form in lamellar crystals in all the experimental measurements, suggesting that the molecular chain in the solution‐cast film has a planar zigzag conformation. While elongation at break decreased, tensile strength and Young's modulus increased with an increase in the crystallinity, independent of the crystalline forms. The influence of the enzymatic degradation of these crystal structures has been investigated by using an extracellular PHB depolymerase purified from Ralstonia pickettii T1. The rate of degradation was in the order of β‐form > α‐form > solution‐cast (γ‐form) film, and the different surface morphologies after partial enzymatic degradation were observed in scanning electron micrographs. It is suggested that the crystal structure is one of the important factors for determining the rate of degradation together with crystallinity.
Enzymatic degradation profiles of poly(β‐propiolactone) films. 相似文献
The crystal structure of the title compound, C38H32, presents a novel framework that combines the functionalities of a 1,6‐diarene‐substituted 1,2‐dihydronaphthalene (DHN) with a 1,4‐distyrylbenzene (DSB) to form a crossed bis‐diarene. The lamellar crystal structure is held together by arene–arene interactions. While the orientations of the phenyl rings of the DSB units alternate within both the R and the S substructures, the homochiral substructures feature opposing polarity along the long axes of the DHN‐based diarenes. 相似文献
The fact that molecular crystals exist as different polymorphic modifications and the identification of as many polymorphs as possible are important considerations for the pharmaceutic industry. The molecule of N‐benzyl‐4‐hydroxy‐1‐methyl‐2,2‐dioxo‐1H‐2λ6,1‐benzothiazine‐3‐carboxamide, C17H16N2O4S, does not contain a stereogenic atom, but intramolecular hydrogen‐bonding interactions engender enantiomeric chiral conformations as a labile racemic mixture. The title compound crystallized in a solvent‐dependent single chiral conformation within one of two conformationally polymorphic P212121 orthorhombic chiral crystals (denoted forms A and B). Each of these pseudo‐enantiomorphic crystals contains one of two pseudo‐enantiomeric diastereomers. Form A was obtained from methylene chloride and form B can be crystallized from N,N‐dimethylformamide, ethanol, ethyl acetate or xylene. Pharmacological studies with solid–particulate suspensions have shown that crystalline form A exhibits an almost fourfold higher antinociceptive activity compared to form B. 相似文献
This study of 3‐(5‐phenyl‐1,3,4‐oxadiazol‐2‐yl)‐2H‐chromen‐2‐one, C17H10N2O3, 1 , and 3‐[5‐(pyridin‐4‐yl)‐1,3,4‐oxadiazol‐2‐yl]‐2H‐chromen‐2‐one, C16H9N3O3, 2 , was performed on the assumption of the potential anticancer activity of the compounds. Three polymorphic structures for 1 and two polymorphic structures for 2 have been studied thoroughly. The strongest intermolecular interaction is stacking of the `head‐to‐head' type in all the studied crystals. The polymorphic structures of 1 differ with respect to the intermolecular interactions between stacked columns. Two of the polymorphs have a columnar or double columnar type of crystal organization, while the third polymorphic structure can be classified as columnar‐layered. The difference between the two structures of 2 is less pronounced. Both crystals can be considered as having very similar arrangements of neighbouring columns. The formation of polymorphic modifications is caused by a subtle balance of very weak intermolecular interactions and packing differences can be identified only using an analysis based on a study of the pairwise interaction energies. 相似文献
A photochromic diarylethene, 1,2‐bis(5‐phenyl‐2‐propyl‐3‐thienyl)perfluorocyclopentene ( 1a ), was found to have two polymorphic crystal forms, α‐ and β‐crystals. From X‐ray crystallographic analysis, the space groups of α‐ and β‐crystals were determined to be P21/c and C2/c, respectively. The difference between two crystal forms is ascribed to the orientation of two of four molecules in the unit cell. The thermodynamic phase transition from α‐ to β‐forms occurred via a crystal‐to‐crystal process, as confirmed by differential scanning calorimetry measurements, optical microscopic observations in the reflection mode and under crossed Nicols, and powder X‐ray diffraction measurements. The movement of the molecules in the crystal was evaluated by analyzing the change of face indices before and after the phase transition. 相似文献
The effect of casting solvent on the morphology of sulfonated polystyrene‐block‐poly(ethylene‐ran‐butylene)‐block‐polystyrene (SSEBS) was investigated using transmission electron microscopy and small‐angle X‐ray scattering. Proton conductivities and methanol permeabilities were measured and the related impact on morphological changes is discussed. SSEBS is transformed from a well‐ordered lamellar to a disordered structure as the concentration of MeOH in MeOH/THF mixtures increases. 相似文献
Single crystals of two liquid crystal compounds, 5‐{[4′‐(((pentyl)oxy)‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne (A3EO5) and 5‐{[(4′‐nonyloxy‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne (A3EO9), have been prepared by solution growth technique. The morphologies and structures of A3EO5 and A3EO9 crystals were investigated by wide angle X‐ray diffraction (WXRD), atom force microscope (AFM) and transmission electron microscope (TEM). In contrast to the same series of compounds which have a longer alkyl tail, 5‐{[(4′‐heptoxy‐4‐biphenylyl)carbonyl]oxy}‐1‐pentyne (A3EO7), 5‐{[(4′‐heptoxy‐4‐biphenylyl)oxy]carbonyl}‐1‐pentyne (A3E′O7) and A3EO9, A3EO5 shows strikingly different crystalline behavior. The former three compounds have only one crystal form, whereas A3EO5 exhibits polymorphism. Specifically, A3EO5 crystals grown from toluene solution show two crystal forms. The first one is crystal I which adopts a monoclinic P112/m space group with unit cell parameters of a?5.79 Å, b?8.34 Å, c?43.92 Å, γ?96°, and the other one is crystal II which adopts a monoclinic P112 space group with unit cell parameters of a?5.55 Å, b?7.38 Å, c?31.75 Å, γ?94°. When using dioxane as the solvent to grow A3EO5 crystal, we can selectively obtain crystal I. A3EO5 melt‐grown crystals also have two crystal forms which derive from crystal I and crystal II, respectively. The different crystalline behavior of the compounds should correlate with their different electron dipole moment resulting from the different length of alkyl tail. 相似文献
Enzymatic degradation behavior of a lamella of single crystals of poly(R)‐3‐hydroxybutyrate (P(3HB)) with an extracellular polyhydroxybutyrate (PHB) depolymerase purified from Alcaligenes faecalis T1 has been investigated by atomic force microscopy (AFM) in order to obtain further information for the chain packing state of P(3HB) in a lamellar single crystal. Two kinds of P(3HB) single crystals with different molecular weights, denoted respectively as H‐ and L‐P(3HB) for high and low molecular weights, respectively, were prepared. The enzymatic treatment was conducted for P(3HB) single crystals adsorbed on a surface of highly ordered pyrolytic graphite. The enzymatic degradation of both P(3HB) single crystals generates several crevices crosswise across the crystal at an early stage. Subsequently, the enzymatic degradation yields numbers of cracks lengthwise along the crystal. In addition to these common features, the interval between cracks crosswise across a lamella in H‐P(3HB) single crystal is longer than that in L‐P(3HB) single crystal, and each crack has V‐shaped and rectangular shaped morphology for H‐ and L‐P(3HB) single crystals, respectively. Based on these results, it is concluded that a lamella of P(3HB) single crystal has straight degradation pathways, that may correspond to a switchboard region, along the long axis of the crystal, independent of molecular weight of P(3HB) samples, and that a H‐P(3HB) single crystal has broader degradation pathways with longer intervals crosswise across the crystal than a L‐P(3HB) single crystal. 相似文献
Self‐assembly of poly(2‐vinylpyridine)‐block‐poly(ϵ‐caprolactone) (P2VP‐b‐PCL) diblock copolymer in the presence of a selective solvent is investigated by transmission electron microscopy and atomic force microscopy. Addition of water into a P2VP‐b‐PCL solution in N,N‐dimethylformamide at 20 °C produces elongated truncated lozenge shaped single crystals of uniform size and shape in large quantities. The single crystals are composed of PCL single‐crystal layer sandwiched between two P2VP layers tethered on the top and bottom basal surfaces. The formation of the single crystals is found to depend on the temperature. These findings provide a facile approach to the preparation of uniform single crystals in large quantities.
Derivatives of 4‐hydroxypyrimidine are an important class of biomolecules. These compounds can undergo keto–enol tautomerization in solution, though a search of the Cambridge Structural Database shows a strong bias toward the 3H‐keto tautomer in the solid state. Recrystallization of 2‐amino‐5,6‐dimethyl‐4‐hydroxypyrimidine, C6H9N3O, from aqueous solution yielded triclinic crystals of the 1H‐keto tautomer, denoted form (I). Though not apparent in the X‐ray data, the IR spectrum suggests that small amounts of the 4‐hydroxy tautomer are also present in the crystal. Monoclinic crystals of form (II), comprised of a 1:1 ratio of both the 1H‐keto and the 3H‐keto tautomers, were obtained from aqueous solutions containing uric acid. Forms (I) and (II) exhibit one‐dimensional and three‐dimensional hydrogen‐bonding motifs, respectively. 相似文献
On crystallization from CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2, 6‐chloro‐5‐hydroxy‐2‐pyridone, C5H4ClNO2, (I), undergoes a tautomeric rearrangement to 6‐chloro‐2,5‐dihydroxypyridine, (II). The resulting crystals, viz. 6‐chloro‐2,5‐dihydroxypyridine chloroform 0.125‐solvate, C5H4ClNO2·0.125CHCl3, (IIa), 6‐chloro‐2,5‐dihydroxypyridine carbon tetrachloride 0.125‐solvate, C5H4ClNO2.·0.125CCl4, (IIb), 6‐chloro‐2,5‐dihydroxypyridine 1,2‐dichloroethane solvate, C5H4ClNO2·C2H4Cl2, (IIc), and 6‐chloro‐2,5‐dihydroxypyridine 1,1,2,2‐tetrachloroethane solvate, C5H4ClNO2·C2H2Cl4, (IId), have I41/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent‐free crystals with P21/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion‐related molecules form R22(8) dimers via pairs of N—H...O hydrogen bonds. The dimers are linked by O—H...O hydrogen bonds into R46(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel‐containing pyridine solvate crystals, viz. (IIa)–(IId), two independent host molecules form an R22(8) dimer via a pair of O—H...N hydrogen bonds. One molecule is further linked by O—H...O hydrogen bonds to two 41 screw‐related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O—H...O hydrogen bonded to two related equivalents to form tetrameric R44(28) rings. The dimers are π–π stacked with inversion‐related dimers, which in turn stack the R44(28) rings along c to form continuous solvent‐accessible channels. CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2 solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels. 相似文献