Normal Mode Spectrum of the Parallel-Chain fLSheet*

Normal mode calculations have been carried out for parallel-chain 8-sheet structures. These include the parallel-chain pleated sheet of poly(L-alanine) and the parallel-chain rippled sheet of polyglycine. Dipole derivative coupling has been included for amide I and I1 modes, and the effects of parallel-sheet and antiparallel-sheet arrangements of varying separation have been examined for the poly(i-alanine) case. Some amide and nonamide modes are distinctly different from their antiparallel-chain counterparts, thus providing a basis for distinguishing between such structures from their ir and Raman spectra. As in our previous studies, these results emphasize the need for both kinds of spectral data in order to draw definitive conclusions about conformation.