Structural Features of β-Cyclodextrin Solvation in the Deep Eutectic Solvent, Reline

Abstract

The inherently amphiphilic nature of native cyclodextrins (CDs) determines their peculiar molecular encapsulation features, enabling applications such as targeted drug nanodelivery, aroma protection, etc. On the contrary, it may also lead to poor solubility in water and other organic solvents and to potentially detrimental flocking in these media, thus posing limitations to more extensive usage. Here we use small angle X-ray scattering to show that deep eutectic solvent reline (1:2 choline chloride:urea) succeeds in dissolving large amounts of β-CD (at least 800 mg/mL, compared with the solubility in water of 18 mg/mL), without aggregation phenomena occurring. At the microscopic level, molecular dynamics simulations highlight the complex interplay of hydrogen bonding-mediated hydrophilic interactions and hydrophobic force mitigation occurring between β-CD and reline components, leading to energetically favorable β-CD solvation. The possibility of achieving very high concentration conditions for unaggregated β-CD in an environmentally responsible media, such as reline, can open the way to new, so far unpredictable applications, addressing multiple societal challenges.