Vibrational circular dichroism of polypeptides. II. Solution amide II and deuteration results

Abstract

Abstract Vibrational CD (VCD) of amide I and II vibrations of several α‐helical polypeptides have been measured in solution. For the amide II as well as the amide I [previously published: Lal, B.B. & Nafie, L.A. (1982) Biopolymers 21 , 2161] we find the VCD to be characteristic of the polypeptide secondary structure. Amide II bands of right‐handed α helices were all found to have negative VCD and to have their maximum rotational strength for the parallel (low‐energy) component. However, left‐handed α helices formed from L ‐amino acids gave positive amide II bands at higher frequencies than found for the right‐handed helices, indicating that the VCD was sensitive to the stereochemical difference. The amide‐I VCD spectra of some deuterated right‐handed α‐helical polypeptides have a new negative feature to low frequency that does not reflect theoretical predictions but also appears to be stereochemically sensitive. Amide‐II and amide‐A VCD of a few deuterated polypeptides imply retention of the secondary‐structure‐dependent characteristics seen in the hydrogenated VCD.