Polymorph selection of magnesium under different pressures: A simulation study

Molecular dynamics simulations were used to investigate the influence of pressure on the structural properties and dynamics of magnesium(Mg)during rapid solidification.The dynamics analysis revealed that,with an increase in pressure,the dynamics of Mg melt slowed down sharply and the dynamical heterogeneities increased,leading to a denser structure.Atom-level structural analysis using the cluster-type index method suggested that the predominant structure transformed from hexagonal closed-packed to face-centered cubic with increasing pressure from 0 GPa to 5 GPa,and then transformed to the A15 complex crystal structure as the pressure increased above 10 GPa.In addition,the nature of polymorph selection was investigated by analyzing the phonon dispersion of Mg under different pressures.These findings provide a novel insight into polymorphic transitions of Mg under pressure and guide the selection of Mg polymorphs for practical applications.     

Crystal structures of two polymeric 1,5-naphthalenedisulfonate-coordinated transition metal complexes

Two 1,5-naphthalenedisulfonate(1,5-nds)-coordinated polymeric complexes [Cu(1,5-nds) (H₂O)₄]_n and [Cd(1,5-nds)(H₂O)₂]_n were synthesized and their structures characterized by single-crystal structure analysis. The Cu(II) complex [Cu(1,5-nds)(H₂O)₄]_n is obtained both from CuCl or CuCl₂ reacting with 1,5-naphthalenedisulfonic acid at 80^∘C. It is a one-dimensional polymer in which Cu(II) is coordinated by four water molecules and two sulfonate oxygen atoms in the trans positions. The interaction between sulfonate and Cu(II) is different in complexes obtained from different reaction temperature. While the three-dimensional Cd(II) complex [Cd(1,5-nds)(H₂O)₂]_n is a polymorph of the reported two-dimensional layer structure, in which Cd(II) is coordinated by two water molecules in the trans positions and four different sulfonate groups, the same as that observed in the two-dimensional polymorph. However, the 1,5-nds ligands connect Cd(II) centers belonging to different layers, resulting in the three-dimensional framework.     

Potential polymorphs of aspirin

Aspirin is only found experimentally in one crystal structure. In this article, the method of Karfunkel and Gdanitz is used to predict potential polymorphs of aspirin. The known structure, containing a nonplanar conformer is found, along with a number of other low energy structures, many of which are based on a planar conformer. Semiempirical and ab initio calculations show that the planar conformer is less stable than the experimentally known one. Force field calculations suggest that the planar conformer is more stable. The lattice energy of the experimentally known crystal structure is 1.4 kcal/mol lower than any of the potential crystal structures, even though there are a number of structures with lower total (lattice+intramolecular) energies. Conformational maps indicate that another stable conformation occurs within a few kilocalories per mole of the known structure. Polymorphs are predicted for this conformer, but it is found to pack poorly. It is proposed that routes to producing polymorphs of aspirin might be found if consideration is given to promoting the stability of the planar conformer with appropriate solvents or additives. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 262–273, 1999     

Elastic modulus of the crystalline regions of polyimide derived from poly(amic acid)–biphtalic dianhydride and p-phenylene diamine

The elastic modulus E_l of the crystalline regions in the direction parallel to the chain axis was measured by X-ray diffraction for polyimide derived from polyamic acid (biphthalic dianhydride and p-phenylene diamine). These specimens were cured by two different routes: curing at 200 °C, and at 400 °C for 1 h, respectively (2STEPS), and curing from 80 °C to 400 °C stepwise (nine steps) for 1 h at each step (STEPWISE). The E_l values of 54–169 GPa were obtained for the STEPWISE specimen and 80–178 GPa for the 2STEPS specimen, depending on the meridional reflection employed for measurement of the E_l value. A linear relationship between the E_l value and the fiber identity period was obtained from each meridional diffraction, such that the E_l value increased with an increase in the fiber identity period. The E_l value of the fully extended structure was estimated to be 210 GPa. These are considered to be due to the coexistence of polymorphs with different skeletal structures. The crystalline regions of the 2STEPS specimen seems to consist of a more extended skeleton than those of the STEPWISE specimen. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3294–3301, 1999     

亚微米级型CL-20的制备、表征与性能

采用超临界气体抗溶剂（gas anti-solvent, GAS）技术制备了平均粒径为721.9 nm的亚微米级型六硝基六氮杂异伍兹烷（CL-20）,应用傅立叶变换红外光谱（Fourier translation infrared spectrum, FT-IR）,对亚微米级CL-20的晶型进行了鉴别,并进行了小隔板试验、撞击感度和爆发点测试。研究结果表明,细化后的亚微米级型CL-20冲击波感度的隔板厚度降低了58.6%,撞击感度的特性落高提高了84.1%,而爆发点保持不变。     

Structure determination of phase II of the antifungal drug griseofulvin by powder X‐ray diffraction

Two new crystalline polymorphs of the widely used antifungal drug griseofulvin (phases II and III), which originate from the crystallization of the melt, have been detected recently. The crystal structure of phase II of griseofulvin {systematic name: (2S,6′R)‐7‐chloro‐2′,4,6‐trimethoxy‐6′‐methyl‐3H,4′H‐spiro[1‐benzofuran‐2,1′‐cyclohex‐2‐ene]‐3,4′‐dione}, C₁₇H₁₇ClO₆, has been solved by powder X‐ray diffraction (PXRD). The PXRD pattern of this new phase was recorded at room temperature using synchrotron radiation. The starting structural model was generated by a Monte Carlo simulated annealing method. The final structure was obtained through Rietveld refinement with soft restraints for interatomic bond lengths and angles, except for the aromatic ring, where a rigid‐body constraint was applied. The symmetry is orthorhombic (space group P2₁2₁2₁) and the asymmetric unit contains two molecules.     

ZrO2晶型对Ni/ZrO2催化剂CO甲烷化性能的影响

采用浸渍法制备了四方相ZrO2(t-ZrO2)和单斜相ZrO2(m-ZrO2)负载的Ni含量为10%的催化剂,在连续流动微反装置上考察了Ni/m-ZrO2以及不同温度焙烧Ni/t-ZrO2催化剂的CO甲烷化催化活性.采用N2物理吸附-脱附、H2-TPR、XRD、CO-TPSR及原位漫反射傅里叶变换红外光谱等技术对催化剂进行了表征.结果表明,在CO体积分数为1%,空速为20 000 h-1,常压的反应条件下,当CO转化率为50%时,Ni/m-ZrO2-673和Ni/t-ZrO2-673催化剂的反应温度分别为445 K和488 K,Ni/m-ZrO2-673催化剂的CO甲烷化活性远高于Ni/t-ZrO2-673催化剂.随焙烧温度的升高,Ni/t-ZrO2催化剂的CO甲烷化活性评价显著升高,产生这一现象的原因是在高温焙烧过程中Ni/t-ZrO2催化剂表面的t-ZrO2已转化为m-ZrO2,以m-ZrO2为载体的催化剂因m-ZrO2表面具有较多的配位不饱和O2-碱性中心和配位不饱和Zr4+-O2-位点而表现出高的CO甲烷化活性.     

Synthesis,characterization and thermal analysis of ursolic acid solid forms

This study performed a solid‐state characterization of ursolic acid (UA) crystalline forms, a poorly water‐soluble triterpene with anticancer activity. Two new polymorphs (form I, II), two new solvates (propanol and isopropanol solvates), and a known ethanol solvate were determined and elucidated using a combination of multi‐techniques, including X‐ray single crystal and powder diffraction, Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A colorless single crystal of UA was grown from a propanol solution, and its crystalline structure was determined through X‐ray single crystal diffraction. It was determined that the propanol solvate was crystallized in the orthorhombic space group P2₁2₁2₁ with unit‐cell parameters a = 7.17200 (8) Å, b = 12.24100 (16) Å, c = 33.8950 (4) Å and Z = 4. The ethanol solvate and propanol solvate were isomorphous crystals. The results of the thermal analysis demonstrate that form I is a meta‐stable form, while form II is a stable form that is monotropically related.     

Comparison of the crystal structures of the potent anticancer and anti‐angiogenic agent regorafenib and its monohydrate

Regorafenib {systematic name: 4‐[4‐({[4‐chloro‐3‐(trifluoromethy)phenyl]carbamoyl}amino)‐3‐fluorophenoxy]‐1‐methylpyridine‐2‐carboxamide}, C₂₁H₁₅ClF₄N₄O₃, is a potent anticancer and anti‐angiogenic agent that possesses various activities on the VEGFR, PDGFR, raf and/or flt‐3 kinase signaling molecules. The compound has been crystallized as polymorphic form I and as the monohydrate, C₂₁H₁₅ClF₄N₄O₃·H₂O. The regorafenib molecule consists of biarylurea and pyridine‐2‐carboxamide units linked by an ether group. A comparison of both forms shows that they differ in the relative orientation of the biarylurea and pyridine‐2‐carboxamide units, due to different rotations around the ether group, as measured by the C—O—C bond angles [119.5 (3)° in regorafenib and 116.10 (15)° in the monohydrate]. Meanwhile, the conformational differences are reflected in different hydrogen‐bond networks. Polymorphic form I contains two intermolecular N—H…O hydrogen bonds, which link the regorafenib molecules into an infinite molecular chain along the b axis. In the monohydrate, the presence of the solvent water molecule results in more abundant hydrogen bonds. The water molecules act as donors and acceptors, forming N—H…O and O—H…O hydrogen‐bond interactions. Thus, R₄²(28) ring motifs are formed, which are fused to form continuous spiral ring motifs along the a axis. The (trifluoromethyl)phenyl rings protrude on the outside of these motifs and interdigitate with those of adjacent ring motifs, thereby forming columns populated by halogen atoms.     

Characterization of Green Paints in Ming and Qianlong Dynasties’ Lin’xi Pavilion by Complimentary Techniques

During conservation of the painted ceiling decoration of Lin’xi Pavilion in the Forbidden City, two distinct paint campaigns were isolated as a unique case study into architectural paint materials during both the Ming and Qing dynasties. Paint samples and cross sections from both paint generations were analyzed with SEM-EDX, time of flight-secondary ion mass spectrometry (ToF-SIMS), XRD, FTIR, and Raman spectroscopies. Similar organic and inorganic materials characteristic of these time periods were identified. The pigments of interest found in both paint generations were botallackite and atacamite polymorphs. This suggests a shift from natural mineral sources to synthetic copper-based pigments for these larger architectural projects.