AbstractThe positive circular dichroism band observed near 228 nm with poly(L‐proline) responds in a similar fashion to HCl and CaCl2. The spectra in the HCl solutions are compatible with a simple binding equation and a pKnear −2 for the dissociation of a proton from a protonated peptide bond in poly(L‐proline). The data obtained in CaCl2is susceptible to the same analysis, suggesting a pKnear −1.5 for the dissociation of a calcium ion from its complex with poly(L