Organic/inorganic hybrid nanomaterials with vitamin B₁₂ functions

A hybrid nanomaterial was prepared by human serum albumin (HSA) and vitamin B₁₂ derivatives. The incorporation of hydrophobic vitamin B₁₂ derivatives, which have ester groups in place of the peripheral amide moieties of the natural cobalamin, into HSA is primarily controlled by the hydrophobicity of the peripheral ester groups. Microenvironmental property around the hydrophobic vitamin B₁₂ in HSA was examined by fluorescence and fluorescence polarization measurements. The hydrophobic vitamin B₁₂ itself in HSA is in a microenvironment equivalent in medium polarity to dichloromethane. The molecular motion of hydrophobic vitamin B₁₂ in HSA was markedly suppressed under such microenvironmental conditions. Carbon-skeleton rearrangement reaction of an alkyl radical derived from an alkyl ligand bound to the hydrophobic vitamin B₁₂ was markedly favored in HSA aqueous solution, relative to the reactions in methanol and benzene. The 1,2-migration of the electron-withdrawing group arises from both the suppression of molecular motion and desolvation effects on the alkylated hydrophobic vitamin B₁₂ in HSA.