Non-hydrogen-bonded secondary structure in beta-peptides: Evidence from circular dichroism of (S)-pyrrolidine-3 carboxylic acid oligomers and (S)-nipecotic acid oligomers

[GRAPHICS] Homooligomers of beta-amino acids (S)-3-pyrrolidine-3-carboxylic acid (PCA) and (S) nipecotic acid (Nip) were studied by circular dichroism (CD) in me thanol. In each series, a profound change in the far UV CD spectrum was obs erved from monomer to tetramer, but little change was observed from tetrame r to hexamer. A comparable pattern is observed in the CD spectra of short p roline oligomers. We conclude that both PCA and Nip oligomers with greater than or equal to four residues adopt a characteristic secondary structure.