Configurational characteristics of polypeptide chains has been thoroughly investigated in a series of elaborative work by Flory, Brant and Miller. On the basis of the conformational energy map calculated from the L-alanine residue, Flory stated that the preference for the right-handed α-helix usually exhibited by an L-polypeptide is seen to follow from the symmetry of rotations about the pair of bonds adjoining the α-carbon atom. A family of poly(L-aspartic acid ester)s are however known to exhibit exceptional behaviors to the above statement. They form an α-helix in either screw-sense depending on the chemical constitution of the pendant ester group, and often exhibit screw-sense inversion even in the solid state.<br/>The deuterium NMR analysis has been performed for poly(β-phenethyl L-aspartate) which forms lyotropic liquid crystalline phase in conventional organic solvents. From the observed D-NMR splittings, approximate values of the RIS fraction were estimated for each of the rotatable bonds. While the preferred form of the first two bonds were Χ1Χ2 = tt in the right-handed arrangement, those for the left-handed regime were Χ1Χ2 = g-t, being conformationally more proliferated.: the conformational free-energy difference between the two oppositely α-helical networks becomes zero at the transition temperature. Together with the evidence from other sources, a zipper-type transition scheme has been constructed and applied to the thermally-induced transitions characteristic of poly(aspartic acid ester)s.

α-Helix-sense inversion of polypeptides triggered by the side chain conformation

2019 Fall National Meeting

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