Polyelectrolyte behavior and conformation of poly‐ L ‐methionine S‐methylsulfonium salts in aqueous solution

The influence of the species of counterion on the polyelectrolyte behavior and the conformation of poly‐L‐methionine S‐methylsulfonium salts in aqueous solution was studied by viscometric, electrochemical, and optical measurements. The degree of binding of small counterions to charged polyions increases in the sequence: chloride ≲ bromide < iodide < thiocyanate. The conformations of chloride and bromide salts are independent of polymer concentration. On the contrary, iodide and thiocyanate salts indicate a conformational transition, probably from a random‐coil conformation to an intermolecularly stabilized β‐form, with the increase of polymer concentration. The results suggest the existence of a strong specific interaction between counterion and macroion in iodide and thiocyanate salt solutions at high polymer concentration.