Vibrational CD of polypeptides. X. A study of alpha-helical oligopeptides in solution

We have measured the vibrational CD (VCD) of a series of heterooligopeptides—o-nitrophenylsulfenyl(L -Met-L -Met-L -Leu) _n-OEt, n = 6,8,10,11–in the amide A, I, and II regions. These spectra are identical in shape and magnitude, within our signal to noise limits. The VCD in each band are of exactly the shape expected for a right-handed α-helix and imply that VCD of the polypeptide α-helix is relatively unaffected by chain length down to the 18-subunit level.