Potentiometric titration of poly‐S‐carboxymethyl‐L‐cysteine in aqueous NaCl solution

Abstract pH titration measurements of poly‐ S ‐carboxymethyl‐ L ‐cysteine were undertaken in the aqueous Nacl solution in relation to the β form–random coil transition. The titration curves show a marked molecular weight dependence because of the shortened chain length of materials. Comparison of the optical rotatory dispersion parameter a 0 with the titration curve reveals that the titration curve apparently reflects a β structure–random coil transition. The β form of this polymer is assumed to be an intramolecular β form, rather than a β structure stabilized by an intermolecular hydrogen bond, at least in the polymer concentration range considered here. The standard free energy change per amino acid residue for the transition from un‐ionized random coil to un‐ionized β form is estimated to be about −750 cal/mole residue in the range of 0.005–0.2 M NaCl concentration.