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New Crystalline Form (new + crystalline_form)
Selected AbstractsHetero-Seeding and Solid Mixture to Obtain New Crystalline FormsCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2009Dario Braga Prof. Abstract Para -methyl benzyl alcohol (p -MeBA,II) and para -chloro benzyl alcohol (p -ClBA) are quasi-isostructural and share the same hydrogen-bond patterns, but their crystals are not isomorphous. No new polymorphs could be obtained by conventional polymorph screening based on different solvents and different crystallization conditions. Formation of a new polymorph of p -MeBA named p -MeBA,I, isomorphous with the crystal of p -ClBA, was induced by hetero-seeding with a small quantity of powdered p -ClBA added to a supersaturated solution of p -MeBA in hexane, while seeding of p -ClBA with p -MeBA,II failed to give a new phase of p -ClBA isomorphous with known crystalline p -MeBA,II. Mixed crystals of p -MeBA and p -ClBA were also prepared with different p -MeBA/p -ClBA ratios to understand the role of the different functional groups in the crystal structure. Crystal phases were characterized by combined use of single-crystal and powder X-ray diffraction, differential scanning calorimetry, and solid-state NMR spectroscopy. [source] Ab initio structure determination of phase II of racemic ibuprofen by X-ray powder diffractionACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2010Patrick Derollez Annealing of the quenched ibuprofen at 258,K yielded a new crystalline form, called phase II. Powder X-ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position-sensitive detector CPS120. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with rigid-body constraints for the phenyl group and soft restraints on the other interatomic bond lengths and bond angles. The cell volume is 5% larger than that of the conventional phase I at 258,K. It is also shown that the orientation of the propanoic acid group is drastically changed with respect to phase I, leading to strong modifications of the orientation of the O,H...O hydrogen bonds with respect to the chains of dimers. These structural considerations could explain the metastable character of this phase II. [source] Polymorphs of DABCO monohydrate as structural analogues of NaClACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2010Barbara Wicher A new crystalline form of 1,4-diazabicyclo[2.2.2]octane (DABCO) monohydrate, C6H12N2·H2O, crystallizing in the space group P31, has been identified during screening for cocrystals. There are three DABCO and three water molecules in the asymmetric unit, with two DABCO molecules exhibiting disorder over two positions related by rotation around the N...N axis. As in the monoclinic C2/c (Z, = 2) polymorph, the molecular components are connected via O,H...N hydrogen bonds into a polymeric structure that consists of linear O,H...N(CH2CH2)3N...H,O segments, which are approximately mutually perpendicular. The two polymorphic forms of DABCO monohydrate can be considered as structural analogues of NaCl, with the nearly globular DABCO molecules showing distorted cubic closest packing and all octahedral interstices occupied by water molecules. [source] A new polymorph of benzene-1,2-diamine: isomorphism with 2-aminophenol and two-dimensional isostructurality of polymorphsACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2010Agnieszka Czapik A new crystalline form of benzene-1,2-diamine, C6H8N2, crystallizing in the space group Pbca, has been identified during screening for cocrystals. The crystals are constructed from molecular bilayers parallel to (001) that have the polar amino groups directed to the inside and the aromatic groups, showing a herringbone arrangement, directed to the outside. The known monoclinic form and the new orthorhombic polymorph exhibit two-dimensional isostructurality as the crystals consist of nearly identical bilayers. In the monoclinic form, neighbouring bilayers are generated by a unit translation along the a axis, whereas in the orthorhombic form they are generated by a c -glide. Moreover, the new form of benzene-1,2-diamine is essentially isomorphous with the only known form of 2-aminophenol. [source] Effect of long-term natural aging on the thermal, mechanical, and viscoelastic behavior of biomedical grade of ultra high molecular weight polyethyleneJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010H. Fouad Abstract In the total joint prostheses, Ultra High Molecular Weight Polyethylene (UHMWPE) may undergo an oxidative degradation in the long term. The overall properties of UHMWPE are expected to be altered due to the oxidative degradation. The goal of this study is to investigate the effects of natural aging up to 6 years in air on the thermal, mechanical, and viscoelastic properties of UHMWPE that was used in total joint replacement. The changes in UHMWPE properties due to aging are determined using Differential Scanning Calorimetry (DSC), uniaxial tensile tests, and Dynamic Mechanical Analysis (DMA). The DSC results show that the lamellar thickness and degree of crystallinity of UHMWPE specimens increase by 38% and 12% due to aging. A small shoulder region in the DSC thermograms is remarked for aged specimens, which is an indication of formation of new crystalline forms within their amorphous region. The tensile properties of aged and nonaged UHMWPE specimens show a significant decrease in the elastic modulus, yield, fracture stresses, and strain at break due to aging. The DM testing results indicate that the storage modulus and creep resistance of UHMWPE specimens decrease significantly due to aging. Also, it is remarked that the , relaxation peak for aged UHMWPE specimens occurs at lower temperature compared to nonaged ones. The significant reduction in the strength and creep resistance of UHMWPE specimens due to aging would affect the long-term clinical performance of the total joint replacement and should be taken into consideration during artificial joint design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] | ||||||||||