Insights into the molecular association of aqueous deep eutectic solvents using cell permeability

Deep eutectic solvents are increasingly of interest across a range of fields, from energy storage, to cryopreservation, to chemical extraction. However, many fundamental characteristics are still unknown, or worse, assumed, leaving many questions unanswered and unasked. One of these is whether or not the components of deep eutectic solvents associate with each other when in dilute solutions. In this paper shrink-swell experiments are used to examine the permeability of a deep eutectic solvent composed of proline and ethylene glycol, using two mammalian cell types. Using the deep eutectic composition, as well as other ratios of the components, it was found that proline did not permeate while ethylene glycol does permeate. This demonstrates that at least for this deep eutectic solvent, the components act independently when in dilute solution. This has implications for the fundamental understanding of solvent behaviour as well as specific applications such as cryopreservation which rely on cell permeation of active agents.