The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform
Michel Vert - One of the best experts on this subject based on the ideXlab platform.
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structure property relationships in the case of the degradation of massive poly α Hydroxy Acids in aqueous media
Journal of Materials Science: Materials in Medicine, 1990Co-Authors: Su Ming Li, Herve Garreau, Michel VertAbstract:A standard protocol is proposed which has been used to study comparatively the degradation mechanism of bioresorbable poly(α-Hydroxy Acids) with respect to macromolecular structural characteristics and solid-state morphologies. As a first approach, the hydrolytic degradation of poly(dl-lactic acid) (PLA50) parallelepipedic specimens (15 mm×10 mm×2 mm), processed by compression moulding and machining, was investigated in two aqueous media: iso-osmolar saline and pH 7.4 phosphate buffer. Various techniques (namely weighing, size-exclusion chromatography (SEC), potentiometry, cryometry and enzymatic assay) have been applied to these specimens in order to monitor the degradation. Data show conclusively that the degradation of massive PLA50 specimens proceeds more rapidly in the centre than at the surface. This feature has been related to the formation of an outer layer of slowly degrading polymer, which is caused by surface phenomena and entraps degrading macromolecules. Only oligomers can diffuse and dissolve in the surrounding media. Accordingly, the number of carboxylic groups present in the inner part of the degrading specimens becomes larger than at the surface and accelerates ester bond cleavage. The resultant autocatalytic mechanism explains well the fact that partially degraded PLA50 exhibits bimodal SEC chromatograms although this polymer is amorphous.
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Structure-property relationships in the case of the degradation of massive aliphatic poly-(α-Hydroxy Acids) in aqueous media - Part 1: Poly(dl-lactic acid)
Journal of Materials Science: Materials in Medicine, 1990Co-Authors: Su Ming Li, Herve Garreau, Michel VertAbstract:A standard protocol is proposed which has been used to study comparatively the degradation mechanism of bioresorbable poly(~-Hydroxy Acids) with respect to macromolecular structural characteristics and solid-state morphologies. As a first approach, the hydrolytic degradation of poly(gL-lactic acid) (PLA50) parallelepipedic specimens (15mm x 10mm x 2mm), processed by compression moulding and machining, was investigated in two aqueous media: iso-osmolar saline and pH 7.4 phosphate buffer. Various techniques (namely weighing, size-exclusion chromatography (SEC), potentiometry, cryometry and enzymatic assay) have been applied to these specimens in order to monitor the degradation. Data show conclusively that the degradation of massive PLA50 specimens proceeds more rapidly in the centre than at the surface. This feature has been related to the formation of an outer layer of slowly degrading polymer, which is caused by surface phenomena and entraps degrading macromolecules. Only oligomers can diffuse and dissolve in the surrounding media. Accordingly, the number of carboxylic groups present in the inner part of the degrading specimens becomes larger than at the surface and accelerates ester bond cleavage. The resultant autocatalytic mechanism explains well the fact that partially degraded PLA50 exhibits bimodal SEC chromatograms although this polymer is amorphous.
Yoshihiko Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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chemoselective catalytic oxidation of 1 2 diols to α Hydroxy Acids controlled by tempo clo2 charge transfer complex
ChemInform, 2015Co-Authors: Keisuke Furukawa, Masatoshi Shibuya, Yoshihiko YamamotoAbstract:A broad range of diversely substituted 1,2-diols, including optically active ones, are efficiently oxidized to the corresponding α-Hydroxy Acids.
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chemoselective catalytic oxidation of 1 2 diols to α Hydroxy Acids controlled by tempo clo2 charge transfer complex
Organic Letters, 2015Co-Authors: Keisuke Furukawa, Masatoshi Shibuya, Yoshihiko YamamotoAbstract:Chemoselective catalytic oxidation from 1,2-diols to α-Hydroxy Acids in a cat. TEMPO/cat. NaOCl/NaClO2 system has been achieved. The use of a two-phase condition consisting of hydrophobic toluene and water suppresses the concomitant oxidative cleavage. A study of the mechanism suggests that the observed selectivity is derived from the precise solubility control of diols and Hydroxy Acids as well as the active species of TEMPO. Although the oxoammonium species TEMPO+Cl– is hydrophilic, the active species dissolves into the organic layer by the formation of the charge-transfer (CT) complex TEMPO–ClO2 under the reaction conditions.
Su Ming Li - One of the best experts on this subject based on the ideXlab platform.
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structure property relationships in the case of the degradation of massive poly α Hydroxy Acids in aqueous media
Journal of Materials Science: Materials in Medicine, 1990Co-Authors: Su Ming Li, Herve Garreau, Michel VertAbstract:A standard protocol is proposed which has been used to study comparatively the degradation mechanism of bioresorbable poly(α-Hydroxy Acids) with respect to macromolecular structural characteristics and solid-state morphologies. As a first approach, the hydrolytic degradation of poly(dl-lactic acid) (PLA50) parallelepipedic specimens (15 mm×10 mm×2 mm), processed by compression moulding and machining, was investigated in two aqueous media: iso-osmolar saline and pH 7.4 phosphate buffer. Various techniques (namely weighing, size-exclusion chromatography (SEC), potentiometry, cryometry and enzymatic assay) have been applied to these specimens in order to monitor the degradation. Data show conclusively that the degradation of massive PLA50 specimens proceeds more rapidly in the centre than at the surface. This feature has been related to the formation of an outer layer of slowly degrading polymer, which is caused by surface phenomena and entraps degrading macromolecules. Only oligomers can diffuse and dissolve in the surrounding media. Accordingly, the number of carboxylic groups present in the inner part of the degrading specimens becomes larger than at the surface and accelerates ester bond cleavage. The resultant autocatalytic mechanism explains well the fact that partially degraded PLA50 exhibits bimodal SEC chromatograms although this polymer is amorphous.
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Structure-property relationships in the case of the degradation of massive aliphatic poly-(α-Hydroxy Acids) in aqueous media - Part 1: Poly(dl-lactic acid)
Journal of Materials Science: Materials in Medicine, 1990Co-Authors: Su Ming Li, Herve Garreau, Michel VertAbstract:A standard protocol is proposed which has been used to study comparatively the degradation mechanism of bioresorbable poly(~-Hydroxy Acids) with respect to macromolecular structural characteristics and solid-state morphologies. As a first approach, the hydrolytic degradation of poly(gL-lactic acid) (PLA50) parallelepipedic specimens (15mm x 10mm x 2mm), processed by compression moulding and machining, was investigated in two aqueous media: iso-osmolar saline and pH 7.4 phosphate buffer. Various techniques (namely weighing, size-exclusion chromatography (SEC), potentiometry, cryometry and enzymatic assay) have been applied to these specimens in order to monitor the degradation. Data show conclusively that the degradation of massive PLA50 specimens proceeds more rapidly in the centre than at the surface. This feature has been related to the formation of an outer layer of slowly degrading polymer, which is caused by surface phenomena and entraps degrading macromolecules. Only oligomers can diffuse and dissolve in the surrounding media. Accordingly, the number of carboxylic groups present in the inner part of the degrading specimens becomes larger than at the surface and accelerates ester bond cleavage. The resultant autocatalytic mechanism explains well the fact that partially degraded PLA50 exhibits bimodal SEC chromatograms although this polymer is amorphous.
Keisuke Furukawa - One of the best experts on this subject based on the ideXlab platform.
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chemoselective catalytic oxidation of 1 2 diols to α Hydroxy Acids controlled by tempo clo2 charge transfer complex
ChemInform, 2015Co-Authors: Keisuke Furukawa, Masatoshi Shibuya, Yoshihiko YamamotoAbstract:A broad range of diversely substituted 1,2-diols, including optically active ones, are efficiently oxidized to the corresponding α-Hydroxy Acids.
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chemoselective catalytic oxidation of 1 2 diols to α Hydroxy Acids controlled by tempo clo2 charge transfer complex
Organic Letters, 2015Co-Authors: Keisuke Furukawa, Masatoshi Shibuya, Yoshihiko YamamotoAbstract:Chemoselective catalytic oxidation from 1,2-diols to α-Hydroxy Acids in a cat. TEMPO/cat. NaOCl/NaClO2 system has been achieved. The use of a two-phase condition consisting of hydrophobic toluene and water suppresses the concomitant oxidative cleavage. A study of the mechanism suggests that the observed selectivity is derived from the precise solubility control of diols and Hydroxy Acids as well as the active species of TEMPO. Although the oxoammonium species TEMPO+Cl– is hydrophilic, the active species dissolves into the organic layer by the formation of the charge-transfer (CT) complex TEMPO–ClO2 under the reaction conditions.
Kai Chen - One of the best experts on this subject based on the ideXlab platform.
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palladium catalyzed c sp 3 h arylation of lactic acid efficient synthesis of chiral β aryl α Hydroxy Acids
Organic chemistry frontiers, 2016Co-Authors: Kai Chen, Xin Li, Shuoqing ZhangAbstract:A Pd-catalyzed arylation of lactic acid employing 8-aminoquinoline as the directing group has been reported. The protocol is found to be compatible with a broad range of synthetically useful functional groups, thus providing a practical route to chiral β-aryl-α-Hydroxy Acids. Further, the new reaction has also been applied to the synthesis of pharmaceutically important α-Hydroxy Acids, such as LY519818 and tesaglitazar.
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synthesis of chiral α Hydroxy Acids via palladium catalyzed c sp 3 h alkylation of lactic acid
Chemical Communications, 2016Co-Authors: Kai Chen, Xin Li, Shuoqing ZhangAbstract:Herein we report a Pd-catalyzed alkylation of lactic acid with the assistance of 8-aminoquinoline auxiliary. A wide range of alkyl iodides bearing β-hydrogen atoms are compatible with the reaction conditions, providing a practical and straightforward alternative to access chiral α-Hydroxy Acids (AHAs). The new reactions have been applied for the synthesis of isotope-labeled AHAs and a sugar-containing complex AHA.
