| Abstract: | 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. |
