Poly(DL-proline), a synthetic polypeptide behaving as an ion channel across membranes: conformational studies on ion complexes of the tetramer Boc(D-Pro-L-Pro)2OCH3

Theoretical and experimental conformational analyses by circular dichroism and NMR spectroscopy of poly(DL-proline) and its tetrameric derivative are reported. The tetramer Boc(D-Pro-L-Pro)zOCH, conformations were investigated in different solvents and in the presence of Ba2+ and Ca2+ ions to explain the ability of poly(m-proline) to increase the ion permeability across bilayer membranes. Both theoretical and experimental data indicate the formation of dimeric and monomeric complexes between tetramer and cations in solution when the tetramer is in the all-trans conformation of the peptide bonds. The results of this analysis allow confirmation of the channel model, previously proposed on the basis of the phenomenological behavior of poly(DL-proline) in membranes.