Self-assembly of a triple-zwitterion in polar solutions: hierarchical formation of nanostructures

The self-assembly of triple-zwitterion 1 in dimethyl sulfoxide is described. 1 forms dimers which polymerize upon increasing concentration into flexible twisted ribbons. These ribbons finally coil into soft nanospheres. The step-wise aggregation process is primarily based on the very strong tendency of the self-complementary guanidiniocarbonyl pyrrole carboxylate zwitterion to form H-bond assisted ion paired dimers (K > 10(10) M-1 in DMSO). Using a variety of analytical techniques such as diffusion ordered NMR spectroscopy (DOSY NMR), small angle neutron scattering (SANS), as well as atomic force microscopy (AFM) and molecular modelling for visualization, a consistent picture of the hierarchical self-assembly process of triple-zwitterion 1 in solution is obtained.