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Yasumasa Hamada - One of the best experts on this subject based on the ideXlab platform.
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Synthetic Studies on a Cyclic Hexadepsipeptide GE3: Stereoselective Construction of the Acyl Side Chain Segment
Synlett, 2002Co-Authors: Kazuishi Makino, Yoshiaki Henmi, Yasumasa HamadaAbstract:Stereoselective synthesis of the acyl side Chain Segment 2 of GE3 (1), a potent inhibitor of cell progression of the cell cycle from the Gl to S phase, has been achieved by using Sharpless' asymmetric dihydroxylation and Evans' and Paterson's stereoselective aldol methodologies.
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Synthesis of the acyl side Chain Segment of polyoxypeptins using regioselective ring-opening of chiral 2,3-epoxy alcohol
Tetrahedron Letters, 2002Co-Authors: Kazuishi Makino, Tatsuya Suzuki, Shinobu Awane, Osamu Hara, Yasumasa HamadaAbstract:(2S,3R)-3-hydroxy-3-methylproline ones. The intriguing biological activities coupled with the unique structure of polyoxypeptins prompted us to synthesize these novel cyclodepsipetides. As studies directed towards the total synthesis of the polyoxypeptins, we have already reported efficient synthesis of (2S,3S)-3hydroxyleucine 2a using dynamic kinetic resolution and (2S,3R)-3-hydroxy-3-methylproline using SmI2-mediated cyclization. 2f We describe here stereoselective synthesis of the acyl side Chain Segment 2 from chiral 2,3-epoxy alcohol 6, easily prepared by Sharpless asymmetric epoxidation, through a regioselective ring-opening reaction. Kobayashi and Kurosu have indepen
Kazuishi Makino - One of the best experts on this subject based on the ideXlab platform.
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Synthetic Studies on a Cyclic Hexadepsipeptide GE3: Stereoselective Construction of the Acyl Side Chain Segment
Synlett, 2002Co-Authors: Kazuishi Makino, Yoshiaki Henmi, Yasumasa HamadaAbstract:Stereoselective synthesis of the acyl side Chain Segment 2 of GE3 (1), a potent inhibitor of cell progression of the cell cycle from the Gl to S phase, has been achieved by using Sharpless' asymmetric dihydroxylation and Evans' and Paterson's stereoselective aldol methodologies.
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Synthesis of the acyl side Chain Segment of polyoxypeptins using regioselective ring-opening of chiral 2,3-epoxy alcohol
Tetrahedron Letters, 2002Co-Authors: Kazuishi Makino, Tatsuya Suzuki, Shinobu Awane, Osamu Hara, Yasumasa HamadaAbstract:(2S,3R)-3-hydroxy-3-methylproline ones. The intriguing biological activities coupled with the unique structure of polyoxypeptins prompted us to synthesize these novel cyclodepsipetides. As studies directed towards the total synthesis of the polyoxypeptins, we have already reported efficient synthesis of (2S,3S)-3hydroxyleucine 2a using dynamic kinetic resolution and (2S,3R)-3-hydroxy-3-methylproline using SmI2-mediated cyclization. 2f We describe here stereoselective synthesis of the acyl side Chain Segment 2 from chiral 2,3-epoxy alcohol 6, easily prepared by Sharpless asymmetric epoxidation, through a regioselective ring-opening reaction. Kobayashi and Kurosu have indepen
Susumu Kobayashi - One of the best experts on this subject based on the ideXlab platform.
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Synthetic study of polyoxypeptin: stereoselective synthesis of the acyl side-Chain Segment
Tetrahedron Letters, 2000Co-Authors: Yasuo Noguchi, Tatsuhiro Yamada, Hiromi Uchiro, Susumu KobayashiAbstract:Abstract The first synthesis of the acyl side-Chain Segment of polyoxypeptin, a potent inducer of apoptosis in human pancreatic carcinoma AsPC-1, was accomplished. The key feature of the present synthesis is the stereospecific palladium-catalyzed hydrogenolysis of ( Z )-alkenyloxirane to anti -hydroxyalkenoate by an improved method.
Xingyuan Zhang - One of the best experts on this subject based on the ideXlab platform.
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Annealing Effect on Chain Segment Motion and Charge Trapping and Detrapping in Nylon 1010
Journal of Macromolecular Science Part B, 2014Co-Authors: Shanna Zhang, Xingyuan ZhangAbstract:The Chain Segment motion and charge trapping and detrapping in nylon 1010 films were investigated by means of thermally stimulated depolarization current (TSDC). There were three current peaks (named α, ρ1, and ρ2 peaks, respectively) in the experimental TSDC spectra above room temperature. The α peak is attributed to a background dipole relaxation by the motion of Chain Segments and space charge contribution, the ρ1 peak is originated from a space charge trapped in the bulk amorphous regions and the interphase between crystalline and amorphous regions, the ρ2 peak is originated from space charge trapped in crystalline regions. By analyzing the characteristic parameters of these peaks, it was found that with in increase of the degree of crystallinity the activation energy of the a peak increased from 1.12 to 1.22 eV and the trap depth of the ρ2 peak increased from 2.70 to 2.82 eV, while the trap depth of the ρ1 peak decreased from 1.50 to 1.29 eV. Annealing induced a decrease of the Chain Segment mobility...
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Effect of alkane Chain Segment length on the crystallization kinetics of nylon 1010, 1013 and 1014
Polymer International, 2014Co-Authors: Long Zhang, Xingyuan Zhang, Yipeng Deng, Ruijie LiuAbstract:Isothermal and non-isothermal crystallization kinetics of long alkane Chain Segment nylon 1010, 1013 and 1014 were investigated by differential scanning calorimetry. The commonly used Avrami equation and that modified by Jeziorny were employed to fit the isothermal and non-isothermal crystallizations of nylon 1010, 1013 and 1014, respectively. It was found that the crystallization rate of nylon with a longer alkane Chain Segment was slower than that of nylon with a shorter one at a given cooling rate. The activation energies for the isothermal and non-isothermal crystallizations determined by the Arrhenius and the Kissinger methods, respectively, decreased with increase of the alkane Chain Segment length of nylon 1010, 1013 and 1014. Furthermore, the activation energy of the non-isothermal crystallization process of these nylons, determined by the isoconversional methods of Flynn and Wall and Ozawa, was found to be a decreasing function of the relative degree of crystallinity. © 2014 Society of Chemical Industry
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Annealing effect on Chain Segment motion and charge detrapping in polyamide 610
Journal of Applied Polymer Science, 2011Co-Authors: Xingyuan ZhangAbstract:The Chain Segment motion and charge detrapping in polyamide 610 films have been investigated by means of thermally stimulated depolarization current (TSDC) and wide-angle X-ray diffraction. There are three current peaks (namely α, ρ1, and ρ2 peaks) in the TSDC spectra above room temperature. α peak is attributed to a dipole relaxation by the motion of Chain Segments ρ1 peak is caused by space charge trapped in amorphous phase and the interphase between crystalline and amorphous phases, and ρ2 peak is brought about by space charge trapped in crystalline phase. By analyzing the characteristic parameters of these peaks, it is found that annealing induces the decrease of Chain Segment mobility and promotes the creation of structural traps in polyamide 610. The decrease of Chain Segment mobility in amorphous phase makes intensity of α peak weak and activation energy increscent. The higher the annealing temperature, the higher the degree of crystallinity, the more the charge carriers trapped in crystalline phase. So, the increase of degree of crystallinity makes intensity of ρ2 peak strong and increases the stability of trapped charge in the crystalline phase. The increase of annealing temperature makes intensity of ρ1 peak strong and decreases the stability of trapped charge in the amorphous phase and interphase. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
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Effect of Polarization Temperature on the Chain Segment Motion and Space Charge Detrapping in Polyamide 610 Film Electrets
Journal of Macromolecular Science Part B, 2011Co-Authors: Xingyuan ZhangAbstract:The effect of polarization temperature on the Chain Segment motion and charge trapping and detrapping in polyamide 610 films has been investigated by means of thermally stimulated depolarization current (TSDC) and wide-angle X-ray diffraction (WAXD). A small part of the amorphous phase of quenched polyamide 610 changes into the crystalline state with increasing polarization temperature. There are three current peaks (named α, ρ1, and ρ2 peak, respectively) in the TSDC spectra. The α peak corresponds to the glass transition, the ρ 1 peak is attributed to space charge trapped in the amorphous phase, and interphase between crystalline and amorphous phases, and the ρ 2 peak originates from space charge trapped in the crystalline phase. By analyzing the characteristic parameters of these peaks, it was found that the increase of polarization temperature induced a decrease of the Chain Segment mobility and promoted the creation of structural traps in polyamide 610. The decrease of the Chain Segment mobility in t...
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Gamma irradiation effect on Chain Segment motion and charge detrapping in polyamide 610
Radiation Physics and Chemistry, 2011Co-Authors: Xingyuan ZhangAbstract:Abstract Gamma irradiation effect on the Chain Segment motion and charge detrapping in polyamide 610 was investigated by means of thermally stimulated depolarization current (TSDC), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and gel fraction. There are four current peaks (named α, ρ 1 , ρ 2 and ρ 3 peak, respectively) in TSDC spectra of polyamide 610. The α peak corresponds to the glass transition, the ρ 1 peak is attributed to space charge trapped in the amorphous phase, the ρ 2 peak is originated from space charge trapped in the interphase between crystalline and amorphous regions and the ρ 3 peak is originated from space charge trapped in crystalline phase. With the increase of irradiation dose from 1.5 to 2 MGy, ρ 1 and ρ 2 peaks gradually merge into one single peak. With the increase of irradiation dose the degree of crosslinking in amorphous phase is more than that in interphase and then the trap depth of interphase is gradually close to that of amorphous phase. By analyzing the characteristic parameters of these peaks, it is found that gamma irradiation can reduce the mobility of Chain Segments and increase structural defects in polyamide 610. In addition, irradiation increases the stability of trapped charge in both amorphous phase and interphase, but not affecting the stability of trapped charge in crystalline phase.
B. Deloche - One of the best experts on this subject based on the ideXlab platform.
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Some remarks on the Chain Segment dynamics in confined polymers.
The European physical journal. E Soft matter, 2003Co-Authors: B. DelocheAbstract:Recently, the Chain dynamics of molten polymers in confined geometries has been investigated, using NMR. Some of these experiments have been performed on poydimethylsiloxane (PDMS) confined in planar nanolayers involving non-adsorbant solid surfaces. Here the data obtained on various PDMS systems are compared. The common property to these systems is that the local dynamics is anisotropic and the Chain Segments are undergoing uniaxial fluctuations around the normal n to the layers. Our data clearly show that the sign of the degree of orientational order S ( i.e. the direction of the fluctuations around n) and the broadening of the order distribution P( S) both result from the relative influence of the impenetrable interfaces and anchoring junctions on the Segment behaviour.
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Some remarks on the Chain Segment dynamics in confined polymers
The European Physical Journal E, 2003Co-Authors: B. DelocheAbstract:Recently, the Chain dynamics of molten polymers in confined geometries has been investigated, using NMR. Some of these experiments have been performed on poydimethylsiloxane (PDMS) confined in planar nanolayers involving non-adsorbant solid surfaces. Here the data obtained on various PDMS systems are compared. The common property to these systems is that the local dynamics is anisotropic and the Chain Segments are undergoing uniaxial fluctuations around the normal $\overrightarrow{\rm n}$ to the layers. Our data clearly show that the sign of the degree of orientational order S ( i.e. the direction of the fluctuations around $\overrightarrow{\rm n}$ ) and the broadening of the order distribution P ( S ) both result from the relative influence of the impenetrable interfaces and anchoring junctions on the Segment behaviour.
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End-Chain Segment ordering in lamellar sublayers of a diblock copolymer.
The European physical journal. E Soft matter, 2003Co-Authors: C. Lorthioir, P. Auroy, B. DelocheAbstract:The Segmental ordering within a lamellar polystyrene-polydimethylsiloxane diblock (PS-PDMS) was examined by NMR. A non-uniform stretching of the PDMS Chains was evidenced. Although Chain Segments displaying isotropic reorientational motions are present along the Chains, relaxation measurements on the free PDMS extremities demonstrate that these latter are oriented and submitted to a non-zero constraint. This specific result allows to precise some features of the order distribution within the lamellae.
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Chain Segment ordering in lamellar sublayers of block copolymers: A NMR study
The European Physical Journal E, 2002Co-Authors: C. Lorthioir, P. Auroy, B. Deloche, Y. GallotAbstract:The Chain Segment dynamics in the bulk lamellar phase of polystyrene-polydimethylsiloxane (PS-PDMS) block copolymers has been probed by NMR. The experiments were performed on a PS-PDMS diblock and on a PS-PDMS-PS triblock with twice the molecular weight. In the diblock, at room temperature, the PDMS block Segments undergo uniaxial reorientations around the normal to the lamellae. In the triblock, the reorientational motions exhibit a lower degree of symmetry: deviations from a uniaxial dynamics are observed. Such a behaviour originates in the anchorage of both PDMS Chain ends into the PS glassy layers.
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Chain Segment order in polymer thin films on a nonadsorbing surface: A NMR study
Physical review letters, 2000Co-Authors: S. Rivillon, P. Auroy, B. DelocheAbstract:The dynamics of polydimethylsiloxane Chains confined between air and a solid, wettable, and nonadsorbing surface is investigated using deuterium NMR. Chain Segments in such molten films undergo uniaxial reorientations around the normal to the surfaces. The influence of the film thickness proves this dynamic uniaxiality involves rapid Segment diffusion between both surfaces which impose a high degree of planar orientation. This Segmental ordering is observed over a thickness range which depends on the degree of Chain entanglements.