Spatial configurations, transformation, and reorganization of mesophase structures of polyaspartates-A highly intelligent molecular system

Insights into the helix‐sense inversion of poly(β‐phenethyl‐L‐aspartate) by two‐dimensional Raman correlation spectroscopy

“…The inversion of the main chain from right‐handed to left‐handed is triggered by the change from the trans state (180°) to the gauche − state (−60°) in the conformational mode of the χ1 bond in the side chain. The results obtained in this study support the mechanism of the helix‐sense inversion for polyaspartates proposed in previous studies …”

“…2 H nuclear magnetic resonance (NMR) studies using 2 H‐labeled PPLA have revealed that the orientation order of the main chain is maintained in the lyotropic liquid crystalline state during the helix‐sense reversal. The results of conformational analysis by the 2 H NMR technique indicated that the reversal of the helix‐sense could be primarily attributed to the difference in the conformation entropy of the side chain associated with the 2 opposite helical structures . Fourier transform infrared (FT‐IR) spectroscopy measurements performed in solution were consistent with the results of 2 H NMR analysis .…”

“…Finally, the screw‐sense inversion of the main chain occurs, and the stable left‐handed structure is formed. In previous studies on PPLA, the side‐chain conformations in the right‐handed and left‐handed helices were elucidated. It was mentioned that the driving force of the helix‐sense inversion might be traced back to the rotational characteristics around the C α ─C β bond, the first‐articulated bond ( χ1) of the side chain.…”

Polyaspartates as Thermoresponsive Enantiodifferentiating Helically Chiral Alignment Media for Anisotropic NMR Spectroscopy

“…The quadrupolar splitting changes drastically between 363 and 383 K indicating the helix reversal. In the transition range signals become broad as both ( P ‐ and M ‐helices) exist at the same time and therefore no reasonable data points could be extracted (for 2 H spectra see the Supporting Information). The high difference in magnitude of the quadrupolar splitting is indicative of a different induced orientational order at high temperatures (>383 K).…”

“…According to 2 H NMR observations of deuterium labelled polymer samples the orientational order of the α‐helical backbone is nearly invariant over the transition temperature whereas the sidechain orientations differ between the P ‐ and the M‐ α‐helical form . Molecular mechanics calculations and rotational isomeric state (RIS) simulations suggest an unwinding and rewinding of the α‐helices with three to four monomeric units being free from hydrogen bonds, connecting the two oppositely handed α‐helices . Energy calculations suggest that the energy difference between the M‐ and P ‐helix conformation is lower for PPLA than for PBLG suggesting why the transition occurs for PPLA at ordinary temperatures but not for PBLG …”