ИСТИНА

Chitosan depolymerization by nitrous acid (HNO2) or sodium nitrite in aqueous acidic media is a fast reaction even at room temperature. The molecular weight decreased almost linearly with the chitosan/NaNO2 ratio. The mechanism involves deamination of a D-glucosamine unit forming 2-formyl-2,5-anhydro-D-mannose containing highly reactive aldehyde group at the new chitosan chain end. The aldehyde group is capable to react with amino-group, and this reaction is a Schiff base reaction, similar to the non-enzymatic browning (Maillard’reaction), occurring at neutral and alkaline pH values. Since the terminal 2-formyl-2,5-anhydro-D-mannose unit is unstable and its decomposition can also produce 5-hydroxymethylfurfural, standard protocol has to include two additional steps: reduction of 2-formyl-2,5-anhydro-D-mannose to 2,5-anhydro-D-mannitol by the use of sodium borohydride and separation of oligochitosan from inorganic admixtures. Oligochitosan hydrolysed by nitrous acid can be stabilized and by means of reaction with hydroxylamine.