Volumetric and sonometric properties of ionic aminated resorcin[4]arenes in water and DMSO at 278.15 K to 303.15 K

Understanding supramolecular chemistry requires comprehensive knowledge of macrocycle behaviour in solution. This study reports standard molar volumes and compressibilities of the chloride salts of two cationic macrocycles C-methylresorcin[4]arene-tetraminoethylated-hydrochloride (TAE⋅(HCl)₄) and their C-ethyl analogue (ETAM⋅(HCl)₄) in aqueous and DMSO solutions. These quantities were obtained using density and speed of sound measurements at concentrations (0.005 to 0.08) mol⋅kg⁻¹ and temperatures in the range (278.15 to 308.15) K. NMR techniques were used to study the structures of the macrocycles in solution, while the corresponding compounds were characterised using mass spectrometry, thermogravimetry and differential scanning calorimetry. The partial molar quantities derived from the volumetric and sonometric data are discussed, along with relevant literature information, in terms of solute–solvent interactions. Structural modifications of macrocycles influence the standard molar compressibilities through changes in solvent organization around functional groups, intrinsic compressibility, and water molecules in the resorcinarene cavity. The effect of carbon chain length on the volumes and compressibilities of substituted resorcin[4]arenes is shown to depend on their location in the macrocycle, but not on the solvent. The standard molar volume is shown to be influenced by ionic moieties and intramolecular hydrogen bonds.