Heat-induced conformation transition of the comb-branched β-glucan in dimethyl sulfoxide/water mixture

We studied the chain conformation transition of the comb-branched β-glucan (AF1) isolated from Auricularia auricula-judae by heating associated with dimethyl sulfoxide (DMSO). The results from ¹H NMR and differential scanning calorimeter (DSC) indicated that the reversible hydrogen bonds between side chains of AF1 and water clusters formed at relatively low temperatures. With increasing v_DMSO to 0.70, the transition temperature (T_m) increased from 9 to 71°C, and then decreased to 57°C with continuously increasing v_DMSO due to the competition between DMSO and water for forming hydrogen bonds. Additionally, the combined analysis of ¹³C NMR, viscosity and light scattering revealed an obvious stiff-to-flexible chain conformation transition of AF1, which occurred at 95-130°C, 120-145°C and 130-160°C with v_DMSO of 0.90, 0.85 and 0.70, respectively. This work demonstrated that AF1 has complex structure under different conditions, and the results obtained herein would benefit us to understand its specific behaviors including hollow fibril and anti-hepatoma activity.