Choline-peptides (ChPep) have recently been presented as a means to advance biocompatible ionic liquids (ILs). Although these ILs found their applications in blends with water, the resulting systems are yet unexplored at the molecular level, a knowledge that is key to understanding and rationalizing novel applications. Thus, building on prior molecular dynamics insights for neat ChPep, we examined 5 ChPep, H2O binaries with a focus on their nano-structuration. Upon addition, water disperses unevenly within the polar IL network, preferentially near anionic charge centers. With increasing dilution, the ion pairs become progressively isolated and their interactions weakened, yielding five structural regimes with two key transitions: ∼70%n/n (ionic polar network disruption) and ∼95%n/n (ion pair dissociation). For the series of phenylalaninate and di-phenylalaninate-based ILs (ChP and ChPP), the apolar domains conformed by phenyl rings (Pher) remain continuous at low dilutions but present different disruption regimes: While the ∼95%n/n dilution of ChPP is still dominated by a unique aggregate, that of ChP presents a broken apolar network. In fact, both the uneven breakage of Pher–Pher and Pher–Ch+ complexes in ChPP and a greater and more stretchable polar network lead to an apolar aggregate more regularly distributed at the 96%n/n blend. Greater dilutions do prompt the fracture of the ChPP Pher-based domain into the small clusters still observable in 99. 6%n/n. Overall, this work describes how water reorganizes both polar and apolar motifs in ChPep, H2O and delineates different composition-dependent regimes, insights that can be, for instance, used to sketch more suitable hydrotrope solvents for pharmaceutical formulation.
Morandeira et al. (Thu,) studied this question.