Anionic H-bonds improve the disorganization of starch in metal chloride hydrate-natural deep eutectic solvents

In this study, several kinds of metal chloride hydrates were added into NADESs (natural deep eutectic solvents) and a series of three constituent-NADESs (3c-NADESs) were successfully developed. The results suggested that the addition of metal chloride hydrates can significantly enhance the solubility of starch, such as, the solubility in MgCl₂-CGly-1 is 90.12 ± 3.49 g/100 g, which is 65 times higher than C-Gly (choline chloride-glycerol) (1.38 ± 0.65 g/100 g). The density functional calculation (DFT) suggested that a lower chloride occupancy of 3c-NADESs can provide more chloride ions used for the formation of hydrogen-bonding interaction with starch. Moreover, the molecular dynamic (MD) study demonstrates that Cl^- may play a key role as "chisel" during the dissolution of starch, which can efficiently destroy the intra- and intermolecular hydrogen bonds (HO⋯O) of starch, allowed the penetration of other components and prevent the recovery crystal of starch.