Intensities and other spectral parameters of infrared amide bands of polypeptides in the α‐helical form

Intensities and other spectral parameters of infrared amide I and II bands of α‐helical polypeptides in solutions have been determined for poly(γ‐benzylglutamate), poly(γ‐ethylglutamate), and polymethionine in chloroform, polylysine, poly(glutamic acid), and fibrillar protein tropomyosin from rabbit muscles in heavy water. The majority of spectral parameters are characteristic. The half‐width of the amide I band was found to vary in the range of 15–40 cm−1 for different polypeptides in the different solutions. The correlation between this parameter of the amide I band and the stability of the α‐helix was estimated. A new weak band near 1537 cm−1 of unknown origin was observed for the hydrogen form of polypeptides in the α‐helical state.