Helix-Sense Inversion in Polyaspartates

Abstract

Solid-state irreversible inversion of helix sense of poly(β-(p-chlorobenzyl) L-aspartate) and poly(β-(p-methylbenzyl) L-aspartate) was investigated by employing circular dichroism, infrared absorption, and X-ray diffraction techniques. The molecular conformation was the right-handed α-helix (αR) in the as-cast film prepared from the solution in chloroform. Heat treatment caused the transition from αR to the left-handed ω-helix (ωL). The crystal structure of the ωL forms was monoclinic (not tetragonal), i.e., the side chains do not form the fourfold helical structure. The right-to-left helix-sense inversion associated with the α-to-ω transition was supported by the conformation energy calculation.