Thermodynamic evidence for nano-heterogeneity in solutions of the macrocycle C-butylresorcin[4]arene in non-aqueous solvents

Partial molar volumes and isentropic compressibilities of the macrocyclic calixarene C-butylresorcin[4]arene have been determined as functions of solute concentration and temperature in five non-aqueous solvents of widely differing character: ethanol, 1-propanol, acetonitrile, N,N-dimethylformamide and dimethylsulfoxide. Both thermodynamic parameters indicated the presence of solute aggregation in all of the studied solvents. Detailed analysis of the data implied that the aggregates formed contained significant amounts of solvent, suggesting that the solutions were nano-heterogeneous rather than conventional micellar. Differences among the solvents were consistent with their hydrogen-bond donor and acceptor properties.