Comparative studies on the self-assembling behaviors of cationic and catanionic surfactant-like peptides

In order to introduce ionic bonds into traditional surfactant-like peptide to develop self-assembling materials with better properties, a catanionic surfactant-like peptide A(6)K(+/-) was designed by removing the protecting -NH(2) at the C-terminus of the cationic surfactant-like peptide A(6)K. Both TEM and AFM observations revealed that A(6)K(+/-) could form longer nanofibers than A(6)K did. On mica surface, A(6)K could form membrane-like structures, which were likely formed by unassembled peptide monomers, while A(6)K(+/-) only formed regular nanofibers, suggesting the absence of unassembled monomers. Pyrene probe spectrofluorometry showed that A(6)K(+/-) had a much lower critical micelle concentration (CMC) than A(6)K. The self-assembling structures of A(6)K(+/-) were also more thermostable than those of A(6)K and could endure temperature as high as 80 degrees C. Furthermore, changing the pH value to extreme acid or basic has more complicated effects on A(6)K(+/-) than A(6)K. These results indicated that the coexistence of opposite charges in the head group of A(6)K(+/-) may help it to form nanostructures with better stability and pH-sensitivity, suggesting a novel approach to fabricate nanomaterials by catanionic surfactant-like peptides.