Hydrophobic vitamin B12. I. Preparation and axial ligation behavior of hydrophobic vitamin B12r.
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概要
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Heptamethyl cobyrinate perchlorate, [Cob(II)ester]ClO<SUB>4</SUB>, was prepared in a good yield from cyanocobalamin. This hydrophobic complex is structurally comparable to the base-off form of vitamin B<SUB>12r</SUB>. Thermodynamic parameters (Δ<I>G</I>, Δ<I>H</I>, and Δ<I>S</I>) for axial ligation of [Cob(II)ester]ClO<SUB>4</SUB> with various amines in dichloromethane and toluene were determined by electronic spectroscopy. The isoequilibrium temperatures obtained from plots of Δ<I>H</I> <I>vs.</I> Δ<I>S</I> were 194±20 and 317±20 K in dichloromethane and toluene, respectively. The equilibrium is primarily controlled by entropy at ordinary temperatures and the log<I>K</I><SUB>1</SUB> value varies sensitively along with the change in p<I>K</I><SUB>a</SUB> of amine in dichloromethane, while the equilibrium values were almost invariant to the choice of amine in toluene because the measurements were carried out near the isoequilibrium temperature. The log<I>K</I><SUB>1</SUB> value for [Cob(II)ester]ClO<SUB>4</SUB>, different from the case of cobalt(II)-porphyrin complexes, depends on the nature of solvent used and undergoes wide variations. The possible functions of equatorial ligands involved in these two different complexes in the axial ligation behavior were discussed.
- 公益社団法人 日本化学会の論文
著者
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Hisaeda Yoshio
Department Of Applied Chemistry Graduate School Of Engineering Kyushu University
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Murakami Yukito
Department Of Chemical Science And Technology Faculty Of Engineering Kyushu University
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Kajihara Akiro
Department of Organic Synthesis, Faculty of Engineering, Kyushu University
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