KOH/thiourea aqueous solution: A potential solvent for studying the dissolution mechanism and chain conformation of corn starch

Non-derivatizing, high-efficiency and low-toxicity solvents are important for studying the dissolution behavior and potential applications of starch. In this study, we investigated the starch dissolution mechanism and molecular conformation in KOH/thiourea aqueous solutions and compared these with KOH/urea and KOH aqueous solutions. Solubility analysis revealed that the KOH/thiourea solution demonstrates a better ability to dissolve corn starch than KOH/urea and KOH solutions. Rheological behavior and dynamic and static light scattering indicated that starch is stable in KOH/thiourea solution and exists as a regular star structure. Fourier transform infrared spectroscopy, 13C NMR, and molecular dynamics simulations indicated that hydrated K+ and OH- destroy the strong starch hydrogen bond interactions; thiourea hydrate self-assembles into a shell surrounding the starch-KOH complex through interaction with KOH, whereas there is no direct strong interaction between urea and KOH. Therefore, adding thiourea to a KOH solution can promote dissolution and prevent self-aggregation of the starch chain.