ビタミンB_<12>およびその関連化合物の化学的研究 : (XXVI)上下配位子を異にするコリノイドの吸収スペクトルと電荷状態との関係

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This paper deals with so called red-yellow shift, the color change of corrinoid compounds caused by pH change. The relation between absorption spectrum and electronic charge in cyanocobalamin, monocyano-monoaquocobinamide, methylcobalamin and monomethyl-monoaquocobinamide was examined in a range of pH 1〜11. A spectral change accompanied with a charge change was found to occur at pH 2.5〜3.5 and at pH 8〜9 respectively in methylcobalamin and in monocyano-monoaquocobinamide, while cyanocobalamin was always neutral and red in the whole pH range, and monomethyl-monoaquocobinamide was always positive and yellow above pH 3. Although the results described above suggested that the yellow color was due to the protonation, monomethyl-monothiocyanatocobinamide was found to be neutral in spite of its yellow color, the absorption maximum being at 475mμ. Considering that the absorption maximum of monomethyl-monopyridinocobinamide and monomethyl-monocyanocobinamide was at 523mμ and at 580mμ respectively, it is concluded that the visible absorption spectrum of a corrinoid compound with a certain upper ligand depends upon the lower ligand very much. The color change caused by protonation can be thus explained as a result of a replacement of the lower ligand.
日本ビタミン学会の論文
1966-06-25