Epimerization of aldoses catalysed by self-organized metallomicelles in an aqueous solution

Abstract

Nickel(II) complexes coordinated with long chain N-alkylated ethylenediamine ligands were synthesized. It was found that the complexes possessed a marked C-2 epimerization activity for aldoses in aqueous media. In contrast, a short chain diamine nickel(II) complex had little activity. The agreement between the formation of micelles and the enhancement of epimerization was clearly recognized. Amphiphilic complexes formed ‘metallomicelles’ which coordinated the aldoses and produced a new ternary complex composed of nickel, diamine and sugar. The stereospecific epimerization occurred in this aggregate accompanied by carbon skeleton rearrangement. One explanation for the high epimerizing ability of the amphiphilic nickel complex is the accumulation effect of nickel ion and ethylenediamine at the micelle surface.