Binding of methylene blue to polyelectrolytes containing sulfonate groups

The interaction between methylene blue (MB) and poly(sodium 4-styrenesulfonate) (PSS), poly(sodium vinylsulfonate) (PVS), and the more hydrophobic poly[sodium 2-(N-acrylamido)-2-methyl-propanesulfonate] (PAMPS), is investigated. The main driving forces for the interaction with PSS are supposed to be short-range aromatic/aromatic interactions, which explain the smaller dissociation constant, the resistance to the cleaving effect of NaCl, and the prevention of MB self-aggregation around the macromolecules under a moderate excess of the polymer. On the contrary, as a consequence of long-range interactions, a higher local concentration of MB around PAMPS and, more significantly, around PVS results in MB self-aggregation that can be quenched in the presence of NaCl.