Re-entrant supramolecular interactions in inverse-melting α-cyclodextrin·4-methylpyridine·water mixtures: an NMR study.

Inverse melting α-cyclodextrin·4-methylpyridine·H2O ternary mixtures were studied via solution, high-resolution magic-angle-spinning and 2D-NOESY NMR spectroscopy with the aim of unveiling the supramolecular driving force for the unusual inverse-melting phase transition. The role of solvent-solvent interactions as well as solvent-solute interactions in the emergence of the inverse-melting phenomenon is revealed. A surprising re-entrant solvent-solvent interaction is found in the system and in the 4-methylpyridine·water solvent system, supporting the non-coincidental relationship between inverse melting and re-entrant phase transitions, at least in the present system.