Increasing the greenness of an organic acid through deep eutectic solvation and further polymerisation

Acrylic acid (AA) is an important and widely used industrial chemical, but its high toxicity renders its use incompatible with the concept of green development. By leveraging its terminal carboxyl group and unsaturated bond, we designed and explored a new strategy to increase the greenness of AA via its eutectic melting using a quaternary ammonium salt (choline chloride) to form a deep eutectic solvent (DES), followed by polymerisation of the DES to form a polymer (poly(DES)). The greenness of AA, DES, and poly(DES) was evaluated via an in vitro test using MGC80-3 cells and an in vivo test using Kunming mice. The toxicity improved from Grade 2 (moderately toxic) for AA to Grade 1 (slightly toxic) for DESs and Grade 0 (non-toxic) for poly(DES) in the in vitro test. Moreover, the poly(DES)s showed a lower toxicity in mice than the DESs in the in vivo test. Thus, greenness enhancement was successfully achieved, with the greenness following the order AA < DES < poly(DES). Furthermore, the mechanisms underlying the change in toxicity were explored through microscopy and flow cytometry, which revealed that the DES can permeate the MGC80-3 cell membrane during the G₀/G₁ phase to adversely affect DNA synthesis in the S phase, but the poly(DES) cannot. Finally, the green poly(DES), which showed good adsorption properties and flexible functionality, was successfully applied as a carrier or excipient of drugs. Through the novel strategy reported herein, greenness enhancement and the broadening of the application scope of a toxic organic acid were achieved, making such acids applicable for green development.