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C. De Rosa - One of the best experts on this subject based on the ideXlab platform.
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phase transition from a c centered to a b centered Orthorhombic crystalline Form of syndiotactic poly propylene
Macromolecular Chemistry and Physics, 1995Co-Authors: Finizia Auriemma, R. H. Lewis, Hans Wolfgang Spiess, C. De RosaAbstract:Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered Orthorhombic Form are here characterized through high resolution solid state 13 C NMR spectroscopy and wide angle X-ray diffraction. The 13 C NMR CP MAS (cross-polarization, magic angle spinning) spectra of highly disordered quench-precipitated s-PP samples (with a structure very close to a C-pseudo-centered orthrohombic Form) yield additional resonances beside those already reported in the literature for s-PP samples crystallized with the chains in a fully helical (TTGG) n conFormation (T : trans ; G : gauche). From the correlation of 13 C NMR CP MAS spectra with the X-ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C- to the B-pseudo-centered Orthorhombic Form starts to occur. Correspondingly, the aforementioned additional resonances in the 13 C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13 C NMR CP MAS spectrum of samles crystallized in the B-pseudo-centered structure. NMR and X-ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon ; at temperatures below 140°C for our samples, the variously sized C-pseudo-centered Orthorhombic crystallites melt and readily re-crystallize in the B-pseudo-centered Orthorhombic Form.
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Phase transition from a C‐centered to a B‐centered Orthorhombic crystalline Form of syndiotactic poly(propylene)
Macromolecular Chemistry and Physics, 1995Co-Authors: Finizia Auriemma, R. H. Lewis, Hans Wolfgang Spiess, C. De RosaAbstract:Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered Orthorhombic Form are here characterized through high resolution solid state 13 C NMR spectroscopy and wide angle X-ray diffraction. The 13 C NMR CP MAS (cross-polarization, magic angle spinning) spectra of highly disordered quench-precipitated s-PP samples (with a structure very close to a C-pseudo-centered orthrohombic Form) yield additional resonances beside those already reported in the literature for s-PP samples crystallized with the chains in a fully helical (TTGG) n conFormation (T : trans ; G : gauche). From the correlation of 13 C NMR CP MAS spectra with the X-ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C- to the B-pseudo-centered Orthorhombic Form starts to occur. Correspondingly, the aforementioned additional resonances in the 13 C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13 C NMR CP MAS spectrum of samles crystallized in the B-pseudo-centered structure. NMR and X-ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon ; at temperatures below 140°C for our samples, the variously sized C-pseudo-centered Orthorhombic crystallites melt and readily re-crystallize in the B-pseudo-centered Orthorhombic Form.
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On the crystal structure of the Orthorhombic Form of syndiotactic polystyrene
Polymer, 1992Co-Authors: C. De Rosa, M. Rapacciuolo, Gaetano Guerra, Vittorio Petraccone, P. CorradiniAbstract:The crystallization conditions for the preparation of different modifications of the Orthorhombic Form (β Form) of syndiotactic polystyrene (s-PS) are described. Crystallizing from the melt produces the β′ or α Form depending on the cooling rate. Crystallization by casting a film from o-dichlorobenzene solutions produces clathrate structures (δ Form) at low temperatures (T < 130°C) and ordered β″ modifications at higher temperatures. In particular, modification very close to the β″ limiting one are obtained in the temperature range 130–140°C. Recrystallization of the β Form has been detected by differential scanning calorimetry and studied by X-ray diffraction analysis of the annealed samples. These studies indicate that the recrystallization of the β′ Form in the melting region does not involve a β′ to β″ transition, but only morphological changes. Models for the chain packing of the limiting modifications of the β Form are suggested, by quantitative comparisons of the X-ray diffraction intensities and calculated structure factors.
Kazuaki Harata - One of the best experts on this subject based on the ideXlab platform.
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Structure of an Orthorhombic Form of xylanase II from Trichoderma reesei and analysis of thermal displacement.
Acta crystallographica. Section D Biological crystallography, 2006Co-Authors: Nobuhiko Watanabe, Toshihiko Akiba, Ryuta Kanai, Kazuaki HarataAbstract:An Orthorhombic crystal of xylanase II from Trichoderma reesei was grown in the presence of sodium iodide. Crystal structures at atomic resolution were determined at 100 and 293 K. Protein molecules were aligned along a crystallographic twofold screw axis, Forming a helically extended polymer-like chain mediated by an iodide ion. The iodide ion connected main-chain peptide groups between two adjacent molecules by an N-H...I-...H-N hydrogen-bond bridge, thus contributing to regulation of the molecular arrangement and suppression of the rigid-body motion in the crystal with high diffraction quality. The structure at 293 K showed considerable thermal motion in the loop regions connecting the beta-strands that Form the active-site cleft. TLS model analysis of the thermal motion and a comparison between this structure and that at 100 K suggest that the fluctuation of these loop regions is attributable to the hinge-like movement of the beta-strands.
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Structure of an Orthorhombic Form of xylanase II from Trichoderma reesei and analysis of thermal displacement.
Acta Crystallographica Section D Biological Crystallography, 2006Co-Authors: Nobuhiko Watanabe, Toshihiko Akiba, Ryuta Kanai, Kazuaki HarataAbstract:An Orthorhombic crystal of xylanase II from Trichoderma reesei was grown in the presence of sodium iodide. Crystal structures at atomic resolution were determined at 100 and 293 K. Protein molecules were aligned along a crystallographic twofold screw axis, Forming a helically extended polymer-like chain mediated by an iodide ion. The iodide ion connected main-chain peptide groups between two adjacent molecules by an N—H\cdotsI−\cdotsH—N hydrogen-bond bridge, thus contributing to regulation of the molecular arrangement and suppression of the rigid-body motion in the crystal with high diffraction quality. The structure at 293 K showed considerable thermal motion in the loop regions connecting the β-strands that Form the active-site cleft. TLS model analysis of the thermal motion and a comparison between this structure and that at 100 K suggest that the fluctuation of these loop regions is attributable to the hinge-like movement of the β-strands.
Nobuhiko Watanabe - One of the best experts on this subject based on the ideXlab platform.
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Structure of an Orthorhombic Form of xylanase II from Trichoderma reesei and analysis of thermal displacement.
Acta crystallographica. Section D Biological crystallography, 2006Co-Authors: Nobuhiko Watanabe, Toshihiko Akiba, Ryuta Kanai, Kazuaki HarataAbstract:An Orthorhombic crystal of xylanase II from Trichoderma reesei was grown in the presence of sodium iodide. Crystal structures at atomic resolution were determined at 100 and 293 K. Protein molecules were aligned along a crystallographic twofold screw axis, Forming a helically extended polymer-like chain mediated by an iodide ion. The iodide ion connected main-chain peptide groups between two adjacent molecules by an N-H...I-...H-N hydrogen-bond bridge, thus contributing to regulation of the molecular arrangement and suppression of the rigid-body motion in the crystal with high diffraction quality. The structure at 293 K showed considerable thermal motion in the loop regions connecting the beta-strands that Form the active-site cleft. TLS model analysis of the thermal motion and a comparison between this structure and that at 100 K suggest that the fluctuation of these loop regions is attributable to the hinge-like movement of the beta-strands.
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Structure of an Orthorhombic Form of xylanase II from Trichoderma reesei and analysis of thermal displacement.
Acta Crystallographica Section D Biological Crystallography, 2006Co-Authors: Nobuhiko Watanabe, Toshihiko Akiba, Ryuta Kanai, Kazuaki HarataAbstract:An Orthorhombic crystal of xylanase II from Trichoderma reesei was grown in the presence of sodium iodide. Crystal structures at atomic resolution were determined at 100 and 293 K. Protein molecules were aligned along a crystallographic twofold screw axis, Forming a helically extended polymer-like chain mediated by an iodide ion. The iodide ion connected main-chain peptide groups between two adjacent molecules by an N—H\cdotsI−\cdotsH—N hydrogen-bond bridge, thus contributing to regulation of the molecular arrangement and suppression of the rigid-body motion in the crystal with high diffraction quality. The structure at 293 K showed considerable thermal motion in the loop regions connecting the β-strands that Form the active-site cleft. TLS model analysis of the thermal motion and a comparison between this structure and that at 100 K suggest that the fluctuation of these loop regions is attributable to the hinge-like movement of the β-strands.
Gilles Precigoux - One of the best experts on this subject based on the ideXlab platform.
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Crystallization and preliminary X‐ray analysis of an Orthorhombic Form of horse‐spleen apoferritin
Acta Crystallographica Section D Biological Crystallography, 1996Co-Authors: B. Langois D'estaintot, Alain Dautant, Thierry Granier, Bernard Gallois, M.‐a. Michaux, Gilles PrecigouxAbstract:Horse-spleen apofemtin crystallizes in two different space groups: cubic F432 and tetragonal P42(1)2 while its iron-containing analogue is known to present a cubic and an Orthorhombic Form. Up to now, only the structure of the cubic Form has been fully investigated by X-ray diffraction, although some inFormation concerning the molecular packing of the two other Forms was deduced from analysis of X-ray photographs. While growing cubic crystals of horse-spleen apoferritin with Pt-mesoporphyrin IX, we obtained one crystal, with a diffraction limit of 2.4 A, belonging to the Orthorhombic P2(1)2(1)2 space group, with unit-cell dimensions a = 181.6, b = 128.9, c = 128.9 A. The orientation of the non-crystallographic axes of the molecule was determined by self-rotation Patterson function and the structure was determined by the molecular-replacement method. The asymmetric unit consists of half an apoferritin molecule. Refinement of the structure is in progress, some preliminary results of the molecular packing are given.
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Crystallization and preliminary X-ray analysis of an Orthorhombic Form of horse-spleen apoferritin.
Acta crystallographica. Section D Biological crystallography, 1996Co-Authors: B. Langois D'estaintot, Alain Dautant, Thierry Granier, Bernard Gallois, M A Michaux, Gilles PrecigouxAbstract:Horse-spleen apofemtin crystallizes in two different space groups: cubic F432 and tetragonal P42(1)2 while its iron-containing analogue is known to present a cubic and an Orthorhombic Form. Up to now, only the structure of the cubic Form has been fully investigated by X-ray diffraction, although some inFormation concerning the molecular packing of the two other Forms was deduced from analysis of X-ray photographs. While growing cubic crystals of horse-spleen apoferritin with Pt-mesoporphyrin IX, we obtained one crystal, with a diffraction limit of 2.4 A, belonging to the Orthorhombic P2(1)2(1)2 space group, with unit-cell dimensions a = 181.6, b = 128.9, c = 128.9 A. The orientation of the non-crystallographic axes of the molecule was determined by self-rotation Patterson function and the structure was determined by the molecular-replacement method. The asymmetric unit consists of half an apoferritin molecule. Refinement of the structure is in progress, some preliminary results of the molecular packing are given.
Finizia Auriemma - One of the best experts on this subject based on the ideXlab platform.
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phase transition from a c centered to a b centered Orthorhombic crystalline Form of syndiotactic poly propylene
Macromolecular Chemistry and Physics, 1995Co-Authors: Finizia Auriemma, R. H. Lewis, Hans Wolfgang Spiess, C. De RosaAbstract:Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered Orthorhombic Form are here characterized through high resolution solid state 13 C NMR spectroscopy and wide angle X-ray diffraction. The 13 C NMR CP MAS (cross-polarization, magic angle spinning) spectra of highly disordered quench-precipitated s-PP samples (with a structure very close to a C-pseudo-centered orthrohombic Form) yield additional resonances beside those already reported in the literature for s-PP samples crystallized with the chains in a fully helical (TTGG) n conFormation (T : trans ; G : gauche). From the correlation of 13 C NMR CP MAS spectra with the X-ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C- to the B-pseudo-centered Orthorhombic Form starts to occur. Correspondingly, the aforementioned additional resonances in the 13 C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13 C NMR CP MAS spectrum of samles crystallized in the B-pseudo-centered structure. NMR and X-ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon ; at temperatures below 140°C for our samples, the variously sized C-pseudo-centered Orthorhombic crystallites melt and readily re-crystallize in the B-pseudo-centered Orthorhombic Form.
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Phase transition from a C‐centered to a B‐centered Orthorhombic crystalline Form of syndiotactic poly(propylene)
Macromolecular Chemistry and Physics, 1995Co-Authors: Finizia Auriemma, R. H. Lewis, Hans Wolfgang Spiess, C. De RosaAbstract:Samples of highly syndiotactic poly(propylene) (s-PP) crystallized in a C-pseudo-centered Orthorhombic Form are here characterized through high resolution solid state 13 C NMR spectroscopy and wide angle X-ray diffraction. The 13 C NMR CP MAS (cross-polarization, magic angle spinning) spectra of highly disordered quench-precipitated s-PP samples (with a structure very close to a C-pseudo-centered orthrohombic Form) yield additional resonances beside those already reported in the literature for s-PP samples crystallized with the chains in a fully helical (TTGG) n conFormation (T : trans ; G : gauche). From the correlation of 13 C NMR CP MAS spectra with the X-ray diffraction profiles recorded at the same temperatures, it is possible to establish that at a given temperature (approximately 100°C, for our samples) a phase transition from the C- to the B-pseudo-centered Orthorhombic Form starts to occur. Correspondingly, the aforementioned additional resonances in the 13 C NMR CP MAS spectra progressively disappear with the onset of the phase transition. These extra resonances are indeed completely absent in the 13 C NMR CP MAS spectrum of samles crystallized in the B-pseudo-centered structure. NMR and X-ray diffraction data, according to differential scanning calorimetry, were interpreted with a recrystallization phenomenon ; at temperatures below 140°C for our samples, the variously sized C-pseudo-centered Orthorhombic crystallites melt and readily re-crystallize in the B-pseudo-centered Orthorhombic Form.
