Selective acetylation of mannuronic acid residues in calcium alginate gels

Abstract

Treatment of non-aqueous spherical beads of calcium alginate, or alginic acid gel, with acetic anhydride in pyridine results in acetylation without degradation. The degree and pattern of substitution were investigated using n.m.r. spectroscopy and degradation with specific enzymes. At low degrees of acetylation, substitution occurred almost exclusively on the mannosyluronic acid residues. At high degrees of acetylation, only a minor proportion of the isolated guluronic acid residues was substituted. The presence of O-acetyl groups inhibited depolymerisation by alginate lyases.