HELIX-SENSE INVERSION IN POLYASPARTATES

Solid-state irreversible inversion of helix sense of poly(beta-(p-chlorobenzyl) L-aspartate) and poly(beta-(p-methylbenzyl) L-aspartate) was investigated by employing circular dichroism, infrared absorption, and X-ray diffraction techniques. The molecular conformation was the right-handed alpha-helix (alpha(R)) in the as-cast film prepared from the solution in chloroform. Heat treatment caused the transition from alpha(R) to the left-handed omega(L)-helix (omega(L)). The crystal structure of the omega(L) 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 alpha-to-omega transition was supported by the conformation energy calculation.