Structure-Tunable Glucan Oligomer Production from Glucose and Disaccharide Glycosylation in an Unacidified LiBr·3.2H2O Molten Salt Hydrate

Glucan oligomers are unique chemicals with versatile value-added applications in agriculture and healthcare depending on their specific glycosidic linkages. Glucose glycosylation shows high efficiency in glucan oligomer production, but the formed glycosidic bonds are generally random, which limits its application. To address this issue, we employed an unacidified molten salt hydrate (MSH) of LiBr·3.2H2O as the reaction medium and glucose/disaccharides as the substrate. Results showed that a 66.6% yield of glucan oligomer can be produced from glucose with a high selectivity of 93.2%, suggesting limited byproduct degradation. When maltose was used as the substrate, the initial α(1 → 4) glycosidic bonds were well preserved. Maltose was effectively converted into an α-type glucan oligomer consisting of 79.9% α(1 → 4) and 20.1% α(1 → 6) glycosidic linkages. The kinetic analysis revealed that the α(1 → 4) bond has a high activation energy of 57.9 kJ/mol, ensuring its chemical stability in unacidified LiBr·3.2H2O conversion. The unacidified MSH reaction medium presents a possibility of enhanced and structure-tunable glucan oligomer production via a glycosylation method.