Screw-sense inversion characteristic of α-helical poly(β-p-chlorobenzyl L-aspartate) and comparison with other related polyaspartates

This is one of a series of studies on the reversal of the helix sense of polyaspartates originated from the pioneering work of Goodman and his associates in 1960s. Poly(β‐p‐chlorobenzyl L‐aspartate) (PClBLA) is one of the well‐studied polyaspartate derivatives in both solution and the solid state. The chemical structure of PClBLA differs from those of poly(β‐benzyl L‐aspartate) (PBLA) and poly(β‐phenethyl L‐aspartate) (PPLA) only at the terminal of the relatively long side chain. PBLA takes a left‐handed form (L) in conventional helicoidal solvents and does not exhibit any screw‐sense inversion. In contrast to PBLA, both PClBLA and PPLA form a right‐handed helix (R) in chlorinated alkane solvents and exhibits a reversal of α‐helix sense at higher temperatures. Yet the transition behaviors in the presence of denaturant acid are quite different between these two polymers. While PPLA exhibits transitions such as R → L → coil by lowering temperature, PClBLA directly goes into the coil state without showing the reentrant L form. The cause of these phenomenological differences among these polymers has been investigated by constructing the phase diagram. © 2005 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2005