Synthesis and conformational study of poly(L‐lysyl‐L‐valyl‐L‐lysine) in the solid state and in aqueous solution

Abstract

AbstractThe synthesis and some conformational properties of aqueous solutions of poly(L‐lysyl‐L‐valyl‐L‐lysine) at different ionization degrees, are reported. IR, UV, CD, and X‐ray measurements were performed on the sequential polypeptide in solution and in the solid state within the pH ranges of 6,4 to 7,2 (charged state) and of 10,4 to 11,0 (uncharged state). The presence of β‐ and probably α‐helical and random coil conformations is detected by IR spectroscopy in the solid state. X‐ray data show that the polymer in the charged form is likely packed as antiparallel β‐pleated sheets, whereas in the uncharged state there are some evidences for an α‐helical packing. The study of aqueous solutions of the polymer by UV spectroscopy seems to indicate that β‐ and a mixture of α‐ and β‐helices exist in the charged and uncharged state, respectively. However, the coexistence of random coil or other conformations cannot be excluded. The corresponding CD spectra support the interpretation supplied in the solid state. The results of this investigation further suggest that the introduction of valyl residues in a copolymer chain, containing residues which are α‐helix formers, favours the β‐conformation.