Helical Poly(β-peptides): The Helix−Coil Transition of Poly(α-alkyl-β-aspartate)s in Solution

The helix−coil conformational transition taking place in a family of poly(β-peptide)s, namely, poly(α-alkyl-β-aspartate)s (Mw > 100 000), upon addition of acid or by changes in temperature has been investigated. Results obtained for a set of optically pure polymers differing in the size and shape of the alkyl side chain evidenced that the transition is a phenomenon common to all poly(β-l-aspartate)s. Experimental conditions required for transition were found to be independent of the constitution of the poly(β-peptide). Investigation of poly(β-d,l-aspartate)s with different enantiomeric composition and configurational sequence revealed the occurrence of the helix−coil transition in block stereocopolymers for any d/l ratio but not in stereocopolymers with a statistical distribution of the antipode units.