The reaction between neutral salts and fibrous proteins. I. The model system sodium poly‐ L ‐glutamate‐LiBr‐H2O

The effects of concentrated aqueous solutions of a neutral salt, lithium bromide, on randomly coiled sodium poly‐L‐glutamate have been followed using high resolution infrared and nuclear magnetic resonance spectroscopy. The results suggest that two processes are taking place. First, at low concentrations 0–4M LiBr, a simple electrolyte effect occurs in which some water is removed from the polymer by an electrostriction effect. Second, a more intense interaction (>4M LiBr), apparently cooperative, occurs in which the competition for the available water in the system forces the electrolyte to form an association with the peptide group either as a fully or partially hydrated species. It is proposed that the anion is associated with the nitrogen atom of the peptide group and the cation is situated within the vicinity of the carbonyl oxygen.