Self-assembly of 2-(guanidiniocarbonyl)-pyrrole-4-carboxylate in dimethyl sulfoxide: an entropy driven oligomerization

The self-assembly of 2-(guanidiniocarbonyl)-pyrrole-4-carboxylate (2), which is a heteroditopic zwitterion with self-complementary binding groups, was studied in DMSO. Through intermolecular ion pairing between the carboxylate of one and the guanidinium group of another molecule, 2 forms linear chain like oligomers in solution as can be seen from the corresponding shift changes in the NMR spectrum. Concentration dependent NMR studies at different temperatures allowed us to calculate the corresponding binding constants and thermodynamic parameters for this association process. These data show that the oligomerization is endothermic and therefore an entropy-driven process. The release of ordered solvent molecules into the bulk solution during complexation is hence responsible for the oligomerization.