著者

村上 幸人 久枝 良雄 尾崎 俊章 横野 照尚 谷 祐太郎

出版者

公益社団法人 日本化学会

雑誌

日本化学会誌(化学と工業化学) (ISSN:03694577)

巻号頁・発行日

vol.1988, no.4, pp.445-451, 1988-04-10 (Released:2011-05-30)

参考文献数

27

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ビタミンB12誘導体の反応性に関するアキシアル配位塩基の効果を明らかにするために,α-配位座に分子内塩基を有する疎水性ビタミンB12[Cob(II)(α-Im)6C1ester]ClO4,β-配位座に分子内塩基を有する疎水性ビタミンB12[Cob(II)(β-Im)6C2ester]ClO4,配位塩基でキャップした疎本性ビタミンB12[Cob(II)(Im:cap)5C1ester]CIO4,を合成した。電子スピン共鳴(以下ESRと略記する)スペクトルおよびサイクリックボルタンメトリーによる検討から,これらの錯体はほぼ完全なbase-on型で存在し,分子内配位塩基をもたない疎水性ビタミンB12[Cob(II)7C1ester]ClO4に50倍モルのN-ひメチルイミダゾールを添加した状態に匹敵することを明らかにした。アルキル化反応においては,コバルト+1価は四配位構造のためアキシアル配位塩基の影響は小さいが,アルキル錯体の光開裂反応におヘセいては,アキシアル配位塩基の立体的および電子的効果により反応はいちじるしく促進された。また,β-配位面側に分子内配位塩基が導入された錯体では,コパルト-炭素結合生成反応が抑制された。

著者

久枝 良雄 嶌越 恒

出版者

The Society of Synthetic Organic Chemistry, Japan

雑誌

有機合成化学協会誌 (ISSN:00379980)

巻号頁・発行日

vol.63, no.8, pp.780-790, 2005-08-01 (Released:2009-11-13)

参考文献数

27

被引用文献数

3 3

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Vitamin B12-dependent enzymes, involving the cobalt species as a catalytic center, mediate various molecular transformations in vivo. In order to use vitamin B12 derivatives (cobalamins) as green catalysts, various studies have been carried out such as a chemical modification of cobalamin or the fixation of B12 derivative on electrodes.The Co (I) species of vitamin B12 derivative is widely known as a supernucleophile that forms an alkylated complex by reaction with an alkyl halide. Such reaction is efficient for dehalogenation of various organic halides. Therefore, vitamin B12 derivatives can be used as catalysts for reductive degradation of organic pollutant such as DDT. In addition, the alkylated complex is a useful reagent for forming radical species as the cobalt-carbon bond is readily cleaved homolytically by photolysis or electrolysis. Therefore, the application of the alkylated complex to organic synthesis is quite interesting from the viewpoint of a radical-forming reagent. This review article summarizes recent progress in homogeneous and heterogeneous catalytic reactions mediated by vitamin B12 derivatives.

著者

久枝 良雄

出版者

Japan Society of Coordination Chemistry

雑誌

Bulletin of Japan Society of Coordination Chemistry (ISSN:18826954)

巻号頁・発行日

vol.54, pp.10-21, 2009-11-30 (Released:2010-04-16)

参考文献数

69

被引用文献数

6 6

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This account describes a current summary of our research on the development of bio-inspired catalysts with vitamin B12 enzyme functions for degradation of environmental pollutants. We have been interested in vitamin B12-dependent enzymes, involving the cobalt species as a catalytic center, and dealing with a hydrophobic vitamin B12, heptamethyl cobyrinate perchlorate, which has ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B12. In order to construct a good catalytic system, we prepared various nanomaterials with vitamin B12 activities. For example, a vesicle-type artificial enzyme composed of peptide lipids and hydrophobic vitamin B12, a vitamin B12-ruthenium photo-sensitizer system, a vitamin B12-titanium dioxide hybrid catalyst and so on. These bio-inspired catalysts are very interesting from the viewpoint of green chemistry. 1,1-bis(4-chlorophenyl)- 2,2,2-trichloroethane (DDT) is characterized by a pronounced insecticidal property and has been used worldwide for the last several decades despite its known hazardous effects on human health and wildlife. Because of recent environmental concerns, there is pressing need for efficient methods for degradation of such chlorinated compounds accumulated in the soil. DDT was degradated effectively by the electrochemical method and the bio-inspired catalysts with vitamin B12 function. Such vitamin B12 derivatives also can apply the detoxification of inorganic arsenic by the methylation.