Experimental comparative study of solvent effects on the structure of two sulfonated resorcinarenes

Abstract

The conformational behaviours of two samples of sulfonated resorcin[4]arene, tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(butyl)resorcinarene and tetrasodium 5,11,17,23-tetrakissulfonatemethylen-2,8,14,20-tetra(2(methylthio)ethyl)resorcin[4]arene were studied in deuterated dimethylsulfoxide ((CD3)2SO), deuterated methyl alcohol (MeOD), and deuterium oxide (D2O). Our NMR analysis was based on the assignment of 1H and 13C signals of the molecules in the three solvents. In this way, different behaviours of the molecules were revealed in these solvents. In (CD3)2SO, it was possible to define stable crown conformational arrangements for both solutes, whereas in D2O, a greater conformational freedom was enabled by the signals of the methylene bridge and the aromatic region, and it was shown that sulfonated resorcinarene still had some conformational mobility at low temperatures. 13C NMR data confirmed the presence of two conformers in the aqueous solution. In the MeOD solution, one of these solutes exhibited two conformational forms, while for the other, only one conformational isomer was observed. Comparison of the behaviours of these two sulfonated resorcin[4]arenes allowed for seeing how the effect of the substituent on the lower rim played an important role in the stability of the conformers, and the study of the thermodynamic properties in water allowed for interpreting these results in terms of the interactions in solution.