The concept of supramolecular
solvents has been recently introduced,
and the extended liquid-state window accessible for mixtures of functionalized
cyclodextrins (CDs) with hydrogen bond (HB) donor species, e.g., levulinic
acid, led to the debut of supramolecular deep eutectic solvents (SUPRA-DES).
These solvents retain CD’s inclusion ability and complement
it with enhanced solvation effectiveness due to an extended HB network.
However, so far, these promising features were not rationalized in
terms of a microscopic description, thus hindering a more complete
capitalization. This is the first joint experimental and computational
study on the archetypal SUPRA-DES: heptakis(2,6-di-O-methyl)-β-CD/levulinic acid (1:27). We used X-ray scattering
to probe CD’s aggregation level and molecular dynamics simulation
to determine the nature of interactions between SUPRA-DES components.
We discover that CDs are homogeneously distributed in bulk and that
HB interactions, together with the electrostatic ones, play a major
role in determining mutual interaction between components. However,
dispersive forces act in synergy with HB to accomplish a fundamental
task in hindering hydrophobic interactions between neighbor CDs and
maintaining the system homogeneity. The mechanism of mutual solvation
of CD and levulinic acid is fully described, providing fundamental
indications on how to extend the spectrum of SUPRA-DES combinations.
Overall, this study provides the key to interpreting structural organization
and solvation tunability in SUPRA-DES to extend the range of sustainable
applications for these new, unique solvents.