A POTENTIOMETRIC AND CD STUDY ON THE β‐RANDOM COIL TRANSITION OF POLY‐L‐TYROSINE IN AQUEOUS SOLUTION

The pH induced coil-β transition of poly-L-tyrosine has been investigated by potentiometric and CD techniques. The “poly-electrolyte” plot pKα vs. a shows the characteristic behaviour of polypeptides undergoing a conformational transition. CD measurements carried out on samples of the polymer solution under titration indicated that the polymer conformation changes within the same range of degrees of ionization as the titration curve exhibits the characteristic “hump”. Taking into account literature data on the aggregation process during the titration, the conclusion was made that β-structure formation parallels aggregation. The stability of the β-structure of (L-Tyr)r was found to decrease by increasing the temperature to 60°C. These results are discussed in terms of the solvation effects of the polymer side-chains.