Effects of acetylation and benzoylation on dye binding: Investigation of molecular alterations in models

Summary Previous investigations demonstrated significant differences in dye binding by acetylated and benzoylated tissues which could not be explained by blocking of -OH and -NH₂ groups. In order to obtain information concerning steric effects, we built models of unsubstituted, acetylated and benzoylated compounds. Acetylation or benzoylation of primary -OH groups in linear saccharides posed no steric problems. Acetylation of 2-and 3-OH groups caused slight crowding. Benzoylation of these groups could be accomplished only by straining of bonds and careful stacking of rings. It seems therefore unlikely that quantitative acetylation or benzoylation of polysaccharides is achieved under the conditions of histochemical technics. Correlation of observations on models with staining patterns of acetylated and benzoylated tissues indicated that alterations of dye binding are not necessarily due to inactivation of -OH and -NH₂ groups. Other factors, e.g. introduction of carbonyl groups, alterations of surface potentials of tissue structures, steric hindrance, interactions between aromatic rings in dyes and benzoylated tissues, can affect reactions of dyes with such modified tissues. These physical and chemical effects should be considered also in interpretations of histochemical reactions performed on acetylated or benzoylated sections.