The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Atsuo Tanaka - One of the best experts on this subject based on the ideXlab platform.
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Efficient kinetic resolution of organoSilicon compounds by stereoselective esterification with hydrolases in organic solvent
Applied Microbiology and Biotechnology, 2016Co-Authors: Akinori Uejima, Takuo Kawamoto, Toshiaki Fukui, Kenji Sonomoto, Eiichiro Fukusaki, Tetsuo Omata, Atsuo TanakaAbstract:Stereoselective esterification of three isomers of trimethylsilylpropanol, 1-trimethylsilyl-2-propanol, 1-trimethylsilyl-1-propanol, and 2-trimethylsilyl-1-propanol, was systematically studied with five kinds of hydrolases in an organic solvent system in connection with the structure of the compounds. The hydrolases were found to be able to esterify these organoSilicon compounds, even β-hydroxyalkylsilanes, which are unstable under the conditions of acid-catalysed esterification, and the highly optically active organoSilicon compounds were successfully prepared with the selected hydrolases. Even a primary alcohol, 2-trimethylsilyl-1-propanol, was stereoselectively esterified by lipase. Furthermore, comparative studies were made by using their carbon counterparts. The Silicon Atom in the substrates was found to enhance the enzyme stereoselectivity in some cases, but its effect on the substrate reactivity was dependent on the structure of the substrates. These results are discussed based on the specific characters of the Silicon Atom.
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Enzymatic preparation of optically active silylmethanol derivatives having a stereogenic Silicon Atom by hydrolase-catalyzed enantioselective esterification
Tetrahedron: Asymmetry, 1994Co-Authors: Toshiaki Fukui, Takuo Kawamoto, Atsuo TanakaAbstract:Abstract Kinetic resolution of ethylmethylphenylsilylmethanol, a primary alcohol having a stereogenic Silicon Atom, was tried by hydrolase-catalyzed enantioselective reactions. Among twenty kinds of hydrolases examined, a commercial crude papain preparation was found to exhibit the highest enantioselectivity with moderate activity toward the Silicon-containing alcohol on esterification with 5-phenylpentanoic acid in an organic solvent system, and the (+)-enantiomer of 92 %ee was obtained as the remaining substrate. Several silylmethanol derivatives could be also resolved by this enantioselective esterification, even though it was difficult to synthesize such chiral quaternary silanes with high optical purity by chemical methods due to the absence of leaving groups on the Silicon Atom. These results demonstrate that enzymes can recognize the configuration not only of carbon Atoms but also of Silicon Atoms, and indicate the usefulness of biocatalysts for preparing optically active silanes.
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Kinetic resolution of organoSilicon compounds by stereoselective dehydrogenation with horse liver alcohol dehydrogenase
Applied Microbiology and Biotechnology, 1992Co-Authors: Toshiaki Fukui, Min-hua Zong, Takuo Kawamoto, Atsuo TanakaAbstract:Streoselective dehydrogenation of three isomers of trimethylsilypropanol was carried out with horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) and optically active organoSilicon compounds were obtained in a water-organic solvent two-layer system with coenzyme regeneration. Furthermore, we examined the effects of the Silicon Atom on stereoselectivity of HLADH compared to the corresponding carbon compounds. Substitution of the Silicon Atom for the carbon Atom was found to improve the stereoselectivity of HLADH. For example, the optical purity of the remaining 1-trimethylsilyl-2-propanol was higher than 99% enantiomeric excess (ee) at 50% conversion, whereas that of the carbon analogue was 84% ee. This phenomenon was probably ascribable to the bulkiness of the organoSilicon compounds derived from their longer Si-C bond. Kinetic analysis in an aqueous monolayer system demonstrated that the specific properties of the Silicon Atom greatly affected the reactivity of these substrate compounds.
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Bioconversion of organoSilicon compounds by horse liver alcohol dehydrogenase: the role of the Silicon Atom in enzymatic reactions
Applied Microbiology and Biotechnology, 1991Co-Authors: Min-hua Zong, Toshiaku Fukui, Takuo Kawamoto, Atsuo TanakaAbstract:Bioconversion of three organoSilicon compounds of different chain length between the Silicon Atom and the hydroxyl group (Me3Si(CH2)nOH, n = 1–3) by horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) was studied. Furthermore, the effect of the Silicon Atom on the HLADH-catalysed reaction was examined in comparison with the corresponding carbon compounds. HLADH could catalyse the dehydrogenation of trimethylsilyeethanol (n = 2) and trimethylsilylpropanol (n = 3). Trimethylsilylethanol was a better substrate than both its carbon analogue, 3,3-dimethylbutanol, and ethanol. The improved activity of HLADH on trimethylsilylethanol could be accounted for by a higher affinity toward HLADH and a lower activation energy of the reaction by HLADH than those of the carbon counterpart. These are derived from physical properties of the Silicon Atom, that is, the lower electronegativity and the bigger radius than those of the carbon Atom. In contrast, HLADH showed no activity on trimethylsilylmethanol (n = 1), whereas it catalysed the dehydrogenation of the carbon analogue, 2,2-dimethylpropanol, fairly well. The reason for the inactivity of HLADH in the case of trimethylsilylmethanol based on the electric effect of the Silicon Atom is also discussed.
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Efficient optical resolution of 2-(4-chlorophenoxy)propanoic acid with lipase by the use of organoSilicon compounds as substrate: the role of Silicon Atom in enzymatic recognition
Journal of Biotechnology, 1991Co-Authors: Takuo Kawamoto, Kenji Sonomoto, Atsuo TanakaAbstract:Abstract Comparative studies were made of the use as acyl acceptor of organoSilicon compounds [Me 3 Si(CH 2 ) n OH] and the corresponding carbon compounds [Me 3 C(CH 2 ) n OH] in the stereoselective esterification of 2-(4-chlorophenoxy)propanoic acid by the use of lipase OF 360 of Candida cylindracea in water-saturated benzene. The organoSilicon compounds were effectively used as the substrates for the esterification of the d -acid enantiomer. Of the organoSilicon compounds of different chain-length between the Silicon Atom and the hydroxyl group, trimethylsilylmethanol ( n = 1) enabled the esterification reaction to be both fast and highly stereoselective, which was difficult with conventional substrates such as its carbon counterpart. On the other hand, no difference was observed between trimethylsilylethanol ( n = 2) and its carbon analogue (3,3-dimethylbutanol) in the enzymatic activity and the stereoselectivity. These results indicate that the Silicon Atom behaved as a mimic carbon Atom for lipase in the case of trimethylsilylethanol but was effective in enhancing the reactivity of trimethylsilylmethanol. The difference could be explained on the basis of the properties of Silicon Atom, such as its low electronegativity and big Atomic radius compared with the carbon Atom.
Muhammad Rafique - One of the best experts on this subject based on the ideXlab platform.
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first principles study on Silicon Atom doped monolayer graphene
Physica E-low-dimensional Systems & Nanostructures, 2018Co-Authors: Muhammad Rafique, Yong Shuai, Nayyar HussainAbstract:Abstract This paper illustrates the structural, electronic and optical properties of individual Silicon (Si) Atom-doped single layer graphene using density functional theory method. Si Atom forms tight bonding with graphene layer. The effect of doping has been investigated by varying the concentration of Si Atoms from 3.125% to 9.37% (i.e. From one to three Si Atoms in 4 × 4 pure graphene supercell containing 32 carbon Atoms), respectively. Electronic structure, partial density of states (PDOS) and optical properties of pure and Si Atom-doped graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with Si Atom doped graphene. It is revealed that upon Si doping in graphene, a finite band gap appears at the high symmetric K -point, thereby making graphene a direct band gap semiconductor. Moreover, the band gap value is directly proportional to the concentration of impurity Si Atoms present in graphene lattice. Upon analyzing the optical properties of Si Atom-doped graphene structures, it is found that, there is significant change in the refractive index of the graphene after Si Atom substitution in graphene. In addition, the overall absorption spectrum of graphene is decreased after Si Atom doping. Although a significant red shift in absorption is found to occur towards visible range of radiation when Si Atom is substituted in its lattice. The reflectivity of graphene improves in low energy region after Si Atom substitution in graphene. These results can be useful for tuning the electronic structure and to manipulate the optical properties of graphene layer in the visible region.
Nayyar Hussain - One of the best experts on this subject based on the ideXlab platform.
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first principles study on Silicon Atom doped monolayer graphene
Physica E-low-dimensional Systems & Nanostructures, 2018Co-Authors: Muhammad Rafique, Yong Shuai, Nayyar HussainAbstract:Abstract This paper illustrates the structural, electronic and optical properties of individual Silicon (Si) Atom-doped single layer graphene using density functional theory method. Si Atom forms tight bonding with graphene layer. The effect of doping has been investigated by varying the concentration of Si Atoms from 3.125% to 9.37% (i.e. From one to three Si Atoms in 4 × 4 pure graphene supercell containing 32 carbon Atoms), respectively. Electronic structure, partial density of states (PDOS) and optical properties of pure and Si Atom-doped graphene sheet were calculated using VASP (Vienna ab-initio Simulation Package). The calculated results for pure graphene sheet were then compared with Si Atom doped graphene. It is revealed that upon Si doping in graphene, a finite band gap appears at the high symmetric K -point, thereby making graphene a direct band gap semiconductor. Moreover, the band gap value is directly proportional to the concentration of impurity Si Atoms present in graphene lattice. Upon analyzing the optical properties of Si Atom-doped graphene structures, it is found that, there is significant change in the refractive index of the graphene after Si Atom substitution in graphene. In addition, the overall absorption spectrum of graphene is decreased after Si Atom doping. Although a significant red shift in absorption is found to occur towards visible range of radiation when Si Atom is substituted in its lattice. The reflectivity of graphene improves in low energy region after Si Atom substitution in graphene. These results can be useful for tuning the electronic structure and to manipulate the optical properties of graphene layer in the visible region.
Takuo Kawamoto - One of the best experts on this subject based on the ideXlab platform.
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Efficient kinetic resolution of organoSilicon compounds by stereoselective esterification with hydrolases in organic solvent
Applied Microbiology and Biotechnology, 2016Co-Authors: Akinori Uejima, Takuo Kawamoto, Toshiaki Fukui, Kenji Sonomoto, Eiichiro Fukusaki, Tetsuo Omata, Atsuo TanakaAbstract:Stereoselective esterification of three isomers of trimethylsilylpropanol, 1-trimethylsilyl-2-propanol, 1-trimethylsilyl-1-propanol, and 2-trimethylsilyl-1-propanol, was systematically studied with five kinds of hydrolases in an organic solvent system in connection with the structure of the compounds. The hydrolases were found to be able to esterify these organoSilicon compounds, even β-hydroxyalkylsilanes, which are unstable under the conditions of acid-catalysed esterification, and the highly optically active organoSilicon compounds were successfully prepared with the selected hydrolases. Even a primary alcohol, 2-trimethylsilyl-1-propanol, was stereoselectively esterified by lipase. Furthermore, comparative studies were made by using their carbon counterparts. The Silicon Atom in the substrates was found to enhance the enzyme stereoselectivity in some cases, but its effect on the substrate reactivity was dependent on the structure of the substrates. These results are discussed based on the specific characters of the Silicon Atom.
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Enzymatic preparation of optically active silylmethanol derivatives having a stereogenic Silicon Atom by hydrolase-catalyzed enantioselective esterification
Tetrahedron: Asymmetry, 1994Co-Authors: Toshiaki Fukui, Takuo Kawamoto, Atsuo TanakaAbstract:Abstract Kinetic resolution of ethylmethylphenylsilylmethanol, a primary alcohol having a stereogenic Silicon Atom, was tried by hydrolase-catalyzed enantioselective reactions. Among twenty kinds of hydrolases examined, a commercial crude papain preparation was found to exhibit the highest enantioselectivity with moderate activity toward the Silicon-containing alcohol on esterification with 5-phenylpentanoic acid in an organic solvent system, and the (+)-enantiomer of 92 %ee was obtained as the remaining substrate. Several silylmethanol derivatives could be also resolved by this enantioselective esterification, even though it was difficult to synthesize such chiral quaternary silanes with high optical purity by chemical methods due to the absence of leaving groups on the Silicon Atom. These results demonstrate that enzymes can recognize the configuration not only of carbon Atoms but also of Silicon Atoms, and indicate the usefulness of biocatalysts for preparing optically active silanes.
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Kinetic resolution of organoSilicon compounds by stereoselective dehydrogenation with horse liver alcohol dehydrogenase
Applied Microbiology and Biotechnology, 1992Co-Authors: Toshiaki Fukui, Min-hua Zong, Takuo Kawamoto, Atsuo TanakaAbstract:Streoselective dehydrogenation of three isomers of trimethylsilypropanol was carried out with horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) and optically active organoSilicon compounds were obtained in a water-organic solvent two-layer system with coenzyme regeneration. Furthermore, we examined the effects of the Silicon Atom on stereoselectivity of HLADH compared to the corresponding carbon compounds. Substitution of the Silicon Atom for the carbon Atom was found to improve the stereoselectivity of HLADH. For example, the optical purity of the remaining 1-trimethylsilyl-2-propanol was higher than 99% enantiomeric excess (ee) at 50% conversion, whereas that of the carbon analogue was 84% ee. This phenomenon was probably ascribable to the bulkiness of the organoSilicon compounds derived from their longer Si-C bond. Kinetic analysis in an aqueous monolayer system demonstrated that the specific properties of the Silicon Atom greatly affected the reactivity of these substrate compounds.
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Bioconversion of organoSilicon compounds by horse liver alcohol dehydrogenase: the role of the Silicon Atom in enzymatic reactions
Applied Microbiology and Biotechnology, 1991Co-Authors: Min-hua Zong, Toshiaku Fukui, Takuo Kawamoto, Atsuo TanakaAbstract:Bioconversion of three organoSilicon compounds of different chain length between the Silicon Atom and the hydroxyl group (Me3Si(CH2)nOH, n = 1–3) by horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) was studied. Furthermore, the effect of the Silicon Atom on the HLADH-catalysed reaction was examined in comparison with the corresponding carbon compounds. HLADH could catalyse the dehydrogenation of trimethylsilyeethanol (n = 2) and trimethylsilylpropanol (n = 3). Trimethylsilylethanol was a better substrate than both its carbon analogue, 3,3-dimethylbutanol, and ethanol. The improved activity of HLADH on trimethylsilylethanol could be accounted for by a higher affinity toward HLADH and a lower activation energy of the reaction by HLADH than those of the carbon counterpart. These are derived from physical properties of the Silicon Atom, that is, the lower electronegativity and the bigger radius than those of the carbon Atom. In contrast, HLADH showed no activity on trimethylsilylmethanol (n = 1), whereas it catalysed the dehydrogenation of the carbon analogue, 2,2-dimethylpropanol, fairly well. The reason for the inactivity of HLADH in the case of trimethylsilylmethanol based on the electric effect of the Silicon Atom is also discussed.
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Efficient optical resolution of 2-(4-chlorophenoxy)propanoic acid with lipase by the use of organoSilicon compounds as substrate: the role of Silicon Atom in enzymatic recognition
Journal of Biotechnology, 1991Co-Authors: Takuo Kawamoto, Kenji Sonomoto, Atsuo TanakaAbstract:Abstract Comparative studies were made of the use as acyl acceptor of organoSilicon compounds [Me 3 Si(CH 2 ) n OH] and the corresponding carbon compounds [Me 3 C(CH 2 ) n OH] in the stereoselective esterification of 2-(4-chlorophenoxy)propanoic acid by the use of lipase OF 360 of Candida cylindracea in water-saturated benzene. The organoSilicon compounds were effectively used as the substrates for the esterification of the d -acid enantiomer. Of the organoSilicon compounds of different chain-length between the Silicon Atom and the hydroxyl group, trimethylsilylmethanol ( n = 1) enabled the esterification reaction to be both fast and highly stereoselective, which was difficult with conventional substrates such as its carbon counterpart. On the other hand, no difference was observed between trimethylsilylethanol ( n = 2) and its carbon analogue (3,3-dimethylbutanol) in the enzymatic activity and the stereoselectivity. These results indicate that the Silicon Atom behaved as a mimic carbon Atom for lipase in the case of trimethylsilylethanol but was effective in enhancing the reactivity of trimethylsilylmethanol. The difference could be explained on the basis of the properties of Silicon Atom, such as its low electronegativity and big Atomic radius compared with the carbon Atom.
Toshiaki Fukui - One of the best experts on this subject based on the ideXlab platform.
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Efficient kinetic resolution of organoSilicon compounds by stereoselective esterification with hydrolases in organic solvent
Applied Microbiology and Biotechnology, 2016Co-Authors: Akinori Uejima, Takuo Kawamoto, Toshiaki Fukui, Kenji Sonomoto, Eiichiro Fukusaki, Tetsuo Omata, Atsuo TanakaAbstract:Stereoselective esterification of three isomers of trimethylsilylpropanol, 1-trimethylsilyl-2-propanol, 1-trimethylsilyl-1-propanol, and 2-trimethylsilyl-1-propanol, was systematically studied with five kinds of hydrolases in an organic solvent system in connection with the structure of the compounds. The hydrolases were found to be able to esterify these organoSilicon compounds, even β-hydroxyalkylsilanes, which are unstable under the conditions of acid-catalysed esterification, and the highly optically active organoSilicon compounds were successfully prepared with the selected hydrolases. Even a primary alcohol, 2-trimethylsilyl-1-propanol, was stereoselectively esterified by lipase. Furthermore, comparative studies were made by using their carbon counterparts. The Silicon Atom in the substrates was found to enhance the enzyme stereoselectivity in some cases, but its effect on the substrate reactivity was dependent on the structure of the substrates. These results are discussed based on the specific characters of the Silicon Atom.
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Enzymatic preparation of optically active silylmethanol derivatives having a stereogenic Silicon Atom by hydrolase-catalyzed enantioselective esterification
Tetrahedron: Asymmetry, 1994Co-Authors: Toshiaki Fukui, Takuo Kawamoto, Atsuo TanakaAbstract:Abstract Kinetic resolution of ethylmethylphenylsilylmethanol, a primary alcohol having a stereogenic Silicon Atom, was tried by hydrolase-catalyzed enantioselective reactions. Among twenty kinds of hydrolases examined, a commercial crude papain preparation was found to exhibit the highest enantioselectivity with moderate activity toward the Silicon-containing alcohol on esterification with 5-phenylpentanoic acid in an organic solvent system, and the (+)-enantiomer of 92 %ee was obtained as the remaining substrate. Several silylmethanol derivatives could be also resolved by this enantioselective esterification, even though it was difficult to synthesize such chiral quaternary silanes with high optical purity by chemical methods due to the absence of leaving groups on the Silicon Atom. These results demonstrate that enzymes can recognize the configuration not only of carbon Atoms but also of Silicon Atoms, and indicate the usefulness of biocatalysts for preparing optically active silanes.
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Kinetic resolution of organoSilicon compounds by stereoselective dehydrogenation with horse liver alcohol dehydrogenase
Applied Microbiology and Biotechnology, 1992Co-Authors: Toshiaki Fukui, Min-hua Zong, Takuo Kawamoto, Atsuo TanakaAbstract:Streoselective dehydrogenation of three isomers of trimethylsilypropanol was carried out with horse liver alcohol dehydrogenase (HLADH, EC 1.1.1.1.) and optically active organoSilicon compounds were obtained in a water-organic solvent two-layer system with coenzyme regeneration. Furthermore, we examined the effects of the Silicon Atom on stereoselectivity of HLADH compared to the corresponding carbon compounds. Substitution of the Silicon Atom for the carbon Atom was found to improve the stereoselectivity of HLADH. For example, the optical purity of the remaining 1-trimethylsilyl-2-propanol was higher than 99% enantiomeric excess (ee) at 50% conversion, whereas that of the carbon analogue was 84% ee. This phenomenon was probably ascribable to the bulkiness of the organoSilicon compounds derived from their longer Si-C bond. Kinetic analysis in an aqueous monolayer system demonstrated that the specific properties of the Silicon Atom greatly affected the reactivity of these substrate compounds.
