Raman studies of the helix‐to‐coil transition in poly‐L‐glutamic acid and poly‐L‐ornithine

The conformational transitions in water and in the solid state of poly‐ L ‐glutamic acid (PGA) and poly‐ L ‐ornithine (PO) have been studied by Raman spectroscopy. The Raman spectra of PGA, PO, and the monomer, dimer, and trimer of PGA in aqueous solutions and solid state are presented. The Raman spectral changes of PGA and PO were followed through the helix‐to‐coil transition induced by p H , temperature, and solvent composition. A hyperchromic shift in the intensity of the amide III line accompanying the helix‐to‐coil transition was observed. This hyperchromic intensity shift occurs abruptly as a function of p H but more slowly with heat denaturation of the alpha helix indicating that the Raman spectrum is sensitive to the transition mechanism. The high‐temperature coil and the charged coil may have different conformations as evidenced by different amide III frequencies but similar intensities in these two conformations.