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Jun Zhang - One of the best experts on this subject based on the ideXlab platform.
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ThermaL Behavior of PoLy(L-Lactide) Having Low L-Isomer Content of 94% after Compressed CO2 Treatment
Macromolecules, 2010Co-Authors: Qiaofeng Lan, Frans H. J. Maurer, Jun ZhangAbstract:The effect of compressed CO2 treatment on the thermaL behavior of poLy(L-Lactide) (PLLA) with Low L-Isomer content of 94% was studied by using differentiaL scanning caLorimetry (DSC) and temperature moduLated DSC. It was shown that the treated sampLes dispLayed rich thermaL transition signaLs during DSC heating, which is differ from the PLLA having high L-Isomer content, incLuding enthaLpy reLaxation, endothermic anneaLing, meLting-recrystaLLization process, and coLd crystaLLization. The resuLts suggested that the crystaLLine phase obtained has Less perfection and Low crystaLLinity regardLess of the treatment conditions because of the Low crystaLLizabiLity of the PLLA. This PLLA was induced to crystaLLize after treatment under CO2 at 2 MPa and temperature >= 65 degrees C and at pressures of 4-16 MPa and temperatures as Low as 0 degrees C. At 2 MPa, the aLpha crystaL form is formed predominantLy in the crystaLLized sampLes. The resuLts aLso indicated that the ELLA-CO2 system exhibited the property of retrograde vitrification.
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thermaL behavior of poLy L Lactide having Low L Isomer content of 94 after compressed co2 treatment
Macromolecules, 2010Co-Authors: Qiaofeng Lan, Frans H. J. Maurer, Jun ZhangAbstract:The effect of compressed CO2 treatment on the thermaL behavior of poLy(L-Lactide) (PLLA) with Low L-Isomer content of 94% was studied by using differentiaL scanning caLorimetry (DSC) and temperature moduLated DSC. It was shown that the treated sampLes dispLayed rich thermaL transition signaLs during DSC heating, which is differ from the PLLA having high L-Isomer content, incLuding enthaLpy reLaxation, endothermic anneaLing, meLting-recrystaLLization process, and coLd crystaLLization. The resuLts suggested that the crystaLLine phase obtained has Less perfection and Low crystaLLinity regardLess of the treatment conditions because of the Low crystaLLizabiLity of the PLLA. This PLLA was induced to crystaLLize after treatment under CO2 at 2 MPa and temperature >= 65 degrees C and at pressures of 4-16 MPa and temperatures as Low as 0 degrees C. At 2 MPa, the aLpha crystaL form is formed predominantLy in the crystaLLized sampLes. The resuLts aLso indicated that the ELLA-CO2 system exhibited the property of retrograde vitrification.
Keiichi Kawano - One of the best experts on this subject based on the ideXlab platform.
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Chymotrypsin inhibitory conformation of dipeptides constructed by side chain: side chain hydrophobic interactions
Journal of Molecular Recognition, 1993Co-Authors: Hiroshi Sakamoto, Yasuyuki Shimohigashi, Iori Maeda, Takeru Nose, Kinichi Nakashima, Ichiro Nakamura, Tomoshisa Ogawa, Motonori Ohno, Keiichi KawanoAbstract:A compLete series of configurationaLLy Isomers (L-L, L-D, D-L AND D-D) of a dipeptide Leu-Phe benzyL ester have been synthesized and assayed for chymotrypsin. In the conformationaL anaLysis by 400 MMz 1H NMR, the L-D and D-L Isomers, but not hte L-L and D-D Isomers, showed fairLy Large up fieLd shifts (0.2–0.4 ppm) of Leu-βCH2 and γCH proton signaLs, indicating the presence of shieLding effects from the benzene ring. In addition to distinct signaL spLitting of Phe-βCH2, the NOE enhancement observed between Leu-δCH3 and Phe-phenyL groups reveaLed that these groups are in cLose proximity. These data indicated that L-D and D-L Isomers from a hydrophobic core between side chains of adjacent Leu and Phe residues. When the dipeptides were examined for inhibition of chymotrypsin using Ac-Try-OEt as a substrate, the L-L Isomer showed no inhibition, itseLf becoming a substrate. However, the other three Isomers inhibited chymotrypsin in a competitive manner, and the D-L Isomer was strongest with Ki of 2.2 × 10−5M. It was found that the D-L Isomer was onLy sLowLy hydroLysed but the L(or D)-D Isomer was not. H-D-Phe-L-Leu-OBzL with the inverse sequence of H-D-Leu-L-Pre-OBzL inhibited chymotrypsin more strongLy (Ki = 6.3 × 10−6M). Since the free acid anaLogue of the D-L Isomer exhibited no inhibition, the benzyL ester moiety itseLf was thought to be invoLved in the enzyme inhibition. It is assumed that in the inhibitory conformation the ester-benzyL group fits the S1 site of chymotrypsin, whiLe the side chain-side chain compLexing hydrophobic core fits the S2 site.
Tetsuya Tosa - One of the best experts on this subject based on the ideXlab platform.
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D-ALanine production from DL-aLanine by Candida maLtosa with asymmetric degrading activity
Applied Microbiology and Biotechnology, 1992Co-Authors: Isao Umemura, Koji Yanagiya, Saburo Komatsubara, Tadashi Sato, Tetsuya TosaAbstract:To deveLop a practicaL process for d-aLanine production from dL-aLanine, we screened 107 yeasts for their asymmetric degrading activity against dL-aLanine. Candida maLtosa JCM1504 degraded the L-Isomer ten times more rapidLy than the d-Isomer. The ceLLs of this strain were used as a biocataLyst for eLiminating the L-Isomer. However, when the degradation reaction was conducted in the presence of a high concentration of dL-aLanine, the pH of the reaction mixture was rapidLy increased by the Liberation of ammonia from L-aLanine, and consequentLy the reaction stopped. This hindrance was overcome by controLLing the pH vaLue at 6.0 with H2SO4 during the reaction. AdditionaLLy, we found that the maximum rate of L-Isomer degradation was obtained at 30° C and pH 6.0 under conditions of high aeration (1.0 vvm) and agitation (1200 rpm). Under the optimaL conditions, the L-Isomer of 200 g dL-aLanine/L was compLeteLy degraded within 40 h and 90 g d-aLanine/L remained in the reaction mixture. d-ALanine was easiLy isoLated from the reaction mixture. The chemicaL and opticaL purity of the d-Isomer product so obtained was 99.0% and 99.9% enantiomeric excess, respectiveLy.
Si-jung Yeh - One of the best experts on this subject based on the ideXlab platform.
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Synthesis of Tc-D,D-HMPAO and Tc-L,L-HMPAO and their comparison of chemicaL and bioLogicaL properties.
Bioorganic & Medicinal Chemistry Letters, 1999Co-Authors: Hueisch-jy Ding, Ying-fong Huang, Cherng-chyi Tzeng, Li-mei Wei, Si-jung YehAbstract:Abstract Tc- d,d - and Tc- L,L -HMPAO were synthesized. The stabiLity of Tc- d,d - and Tc- L,L -HMPAO in vitro is simiLar to that of d,L-Isomers by the spectrophotometric and three strips methods. CerebraL uptake (%D in brain) for the L,L -Isomer is higer than the d,d - and d,L-Isomer in rats. DeLayed studies shows that Tc- L,L -HMPAO reveaLs Less washout and refLects a higher cerebraL deposition properties than the d,d - and d,L-Isomer.
Qiaofeng Lan - One of the best experts on this subject based on the ideXlab platform.
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ThermaL Behavior of PoLy(L-Lactide) Having Low L-Isomer Content of 94% after Compressed CO2 Treatment
Macromolecules, 2010Co-Authors: Qiaofeng Lan, Frans H. J. Maurer, Jun ZhangAbstract:The effect of compressed CO2 treatment on the thermaL behavior of poLy(L-Lactide) (PLLA) with Low L-Isomer content of 94% was studied by using differentiaL scanning caLorimetry (DSC) and temperature moduLated DSC. It was shown that the treated sampLes dispLayed rich thermaL transition signaLs during DSC heating, which is differ from the PLLA having high L-Isomer content, incLuding enthaLpy reLaxation, endothermic anneaLing, meLting-recrystaLLization process, and coLd crystaLLization. The resuLts suggested that the crystaLLine phase obtained has Less perfection and Low crystaLLinity regardLess of the treatment conditions because of the Low crystaLLizabiLity of the PLLA. This PLLA was induced to crystaLLize after treatment under CO2 at 2 MPa and temperature >= 65 degrees C and at pressures of 4-16 MPa and temperatures as Low as 0 degrees C. At 2 MPa, the aLpha crystaL form is formed predominantLy in the crystaLLized sampLes. The resuLts aLso indicated that the ELLA-CO2 system exhibited the property of retrograde vitrification.
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thermaL behavior of poLy L Lactide having Low L Isomer content of 94 after compressed co2 treatment
Macromolecules, 2010Co-Authors: Qiaofeng Lan, Frans H. J. Maurer, Jun ZhangAbstract:The effect of compressed CO2 treatment on the thermaL behavior of poLy(L-Lactide) (PLLA) with Low L-Isomer content of 94% was studied by using differentiaL scanning caLorimetry (DSC) and temperature moduLated DSC. It was shown that the treated sampLes dispLayed rich thermaL transition signaLs during DSC heating, which is differ from the PLLA having high L-Isomer content, incLuding enthaLpy reLaxation, endothermic anneaLing, meLting-recrystaLLization process, and coLd crystaLLization. The resuLts suggested that the crystaLLine phase obtained has Less perfection and Low crystaLLinity regardLess of the treatment conditions because of the Low crystaLLizabiLity of the PLLA. This PLLA was induced to crystaLLize after treatment under CO2 at 2 MPa and temperature >= 65 degrees C and at pressures of 4-16 MPa and temperatures as Low as 0 degrees C. At 2 MPa, the aLpha crystaL form is formed predominantLy in the crystaLLized sampLes. The resuLts aLso indicated that the ELLA-CO2 system exhibited the property of retrograde vitrification.
