Hydrophobic Vitamin B12. I. Preparation and Axial Ligation Behavior of Hydrophobic Vitamin B12r

Abstract

Heptamethyl cobyrinate perchlorate, [Cob(II)ester]ClO4, was prepared in a good yield from cyanocobalamin. This hydrophobic complex is structurally comparable to the base-off form of vitamin B12r. Thermodynamic parameters (ΔG, ΔH, and ΔS) for axial ligation of [Cob(II)ester]ClO4 with various amines in dichloromethane and toluene were determined by electronic spectroscopy. The isoequilibrium temperatures obtained from plots of ΔH vs. ΔS were 194±20 and 317±20 K in dichloromethane and toluene, respectively. The equilibrium is primarily controlled by entropy at ordinary temperatures and the logK1 value varies sensitively along with the change in pKa 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 logK1 value for [Cob(II)ester]ClO4, 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.

Organic/inorganic hybrid nanomaterials with vitamin B12functions

“…4. On the other hand, the incorporation behavior of HSA, which provides hydrophobic binding domain toward the hydrophobic vitamin B 12 , was different from that of organic media. [(CH 3 )Cob(III)7C n ester]ClO 4 was readily incorporated into HSA when the n-value of C n was equal to two or larger, but [(CH 3 4 , was dissolved in aqueous HSA solution, the absorption maxima of electronic spectrum was observed at 470, 510, and 540(sh) nm in visible light region.…”

“…[(CH 3 )Cob(III)7C n ester]ClO 4 was readily incorporated into HSA when the n-value of C n was equal to two or larger, but [(CH 3 4 , was dissolved in aqueous HSA solution, the absorption maxima of electronic spectrum was observed at 470, 510, and 540(sh) nm in visible light region. The shoulders at 510 and 540 nm are observed when an axial base is coordinated to cobalt(II) species of hydrophobic vitamin B 12 [12,13]. According to the electronic spectrum of hydrophobic vitamin B 12 derivative in aqueous HSA, an amino acid such as His in HSA is expected to coordinate to hydrophobic vitamin B 12 at one axial site.…”

“…The shoulders at 510 and 540 nm are observed when an axial base is coordinated to cobalt(II) species of hydrophobic vitamin B 12 [12,13]. According to the electronic spectrum of hydrophobic vitamin B 12 derivative in aqueous HSA, an amino acid such as His in HSA is expected to coordinate to hydrophobic vitamin B 12 at one axial site. The binding sites of HSA for hydrophobic vitamin B 12 are not clear at the present stage.…”

“…We have been interested in vitamin B 12 -dependent enzymes, involving the cobalt species as a catalytic center [1]. We have been dealing with a hydrophobic vitamin B 12 , heptamethyl cobyrinate perchlorate [Cob(II)7C 1 ester]ClO 4 , which has ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B 12 [2].…”

“…We have been dealing with a hydrophobic vitamin B 12 , heptamethyl cobyrinate perchlorate [Cob(II)7C 1 ester]ClO 4 , which has ester groups in place of the peripheral amide moieties of the naturally occurring vitamin B 12 [2]. In order to construct a good catalytic system, we prepared various nanomaterials with vitamin B 12 activities.…”