Effect of stereo-configurational difference of carbohydrate model compound on the reaction with active oxygen species under oxygen delignification conditions

Abstract

We examined how the stereo-configurational difference affects the reaction of a carbohydrate model compound with active oxygen species (AOS) generated in situ by reactions between O2 and a phenolic compound under conditions similar to those of oxygen delignification or with oxyl anion radical, the conjugate base of hydroxyl radical, generated by the decomposition of H2O2 under alkaline conditions. As the phenolic compound, 2,4,6-trimethylphenol or 4-hydroxy-3-methoxybenzyl alcohol (vanillyl alcohol) was used. The carbohydrate model compounds employed were methyl β-d-glucopyranoside (MGPβ) and its 4 epimers, methyl α-d-glucopyranoside (MGPα), methyl β-d-mannopyranoside (MMP), methyl β-d-allopyranoside (MAP), and methyl β-d-galactopyranoside (MGaP). Their stabilities were in the order of MGPα > MGPβ > MMP > MGaP > MAP, indicating that the reactivity of the carbohydrate model compound is significantly dependent on where the stereo-configurational difference is. Only the co-existence of MMP enhanced the degradation of MGPβ, when a pair of MGPβ and another carbohydrate model compound was reacted with the AOS. This result suggests that the profile of AOS in the system is dependent not only on the type of phenolic compound, the generator of AOS, but also on that of the carbohydrate model compound.