Abstract
Copolypeptides with alternating hydrophilic and hydrophobic residues were prepared, and their ability to form β-structures in aqueous solutions was investigated by circular dichroism. Optically pure samples of poly (Lys-Leu-Lys-Leu) and poly (Leu-Glu-Leu-Glu), obtained via the 2-hydroxyphenyl esters, undergo a coil-to-β transition in presence of salt. The β-structures obtained under identical conditions with partially racemized samples of poly (Leu-Lys)Np and poly (Leu-Glu)Np, prepared by polycondensation of the corresponding dipeptide p-nitrophenyl esters, appear to be less regular. Non-alternating poly (Gly-Lys-Leu-Lys-Leu) does not form β-structures in presence of NaCl as does alternating poly (Lys-Leu-Lys-Leu) indicating that the amino acid sequence can dramatically change the tendency to form β-structures.