Synthesis of polyisocyanide derived from phenylalanine and its temperature‐dependent helical conformation

Abstract

Screw‐sense‐selective polymerization of the chiral isocyanide monomers derived from phenylalanine with NiCl2 as a catalyst in methanol to yield helical‐conjugated polyisocyanide was investigated with respect to the thermal stability of its helical conformation. Poly(1‐tert‐butoxycarbonyl‐2‐phenylethyl isocyanide) (poly1c) took a stable helical conformer independent of the polymerization temperature. In poly(1‐ethoxycarbonyl‐2‐phenylethyl isocyanide) (poly2c), which had slightly smaller side groups, the helical conformation was thermally destabilized. The specific rotation and circular dichroism of poly2c prepared at temperatures greater than 40 °C were considerably depressed in comparison with the values for poly2c prepared at or below room temperature. Additionally, poly2c prepared at low temperatures exhibited reversible temperature‐dependent specific rotation and circular dichroism, whereas poly1c showed few changes. It is suggested that polyisocyanide derived from phenylalanine takes various helical conformers (i.e., from tightly to loosely coiled helices), the thermal stability of which depends on the size of the side group. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 399–408, 2002

Conformational analysis of dipeptide‐derived polyisocyanides

“…8). The CD spectra of L,L ‐PIAS and L,L ‐PIAH show a strong Cotton effect around 310 nm in analogy to those of L,L ‐PIAA, L , D ‐PIAA, and L ‐PIGA, whereas such a Cotton effect is absent in the spectra of L , D ‐PIAS and D , L ‐PIAH, which show more of a resemblance to the spectrum obtained for L , D ‐PIAA after treatment with TFA and the spectrum of L ‐PIAG 38. Although the precise structures of these polymers were never elucidated, we tentatively attribute these differences to the presence of hydrogen‐bonding arrays in the former two polymers and the absence of such arrays in the latter two.…”

Water-Soluble Chiral Polyisocyanides Showing Thermoresponsive Behavior

“…The same result was also obtained for the polymer P1(d) with weak Cotton effects (Figure S4b). These results suggest the OEG-based bulky substituents, together with the strong hydrogen bondings between the pendant amide residues shielded with OEG units in these polymers, provide substantial barrier to prevent their chiral conformations from switching. ,, …”

Chiral Self-Assembly of Nanoparticles Induced by Polymers Synthesized via Reversible Addition–Fragmentation Chain Transfer Polymerization

“…This result confirms our hypothesis that even when syndiotacticity dominates, the preferred-handedness of a polymer main chain can only be preserved by the interactions of its bulky side groups. In the case of PIPEMA, the long side chain and bulky indole group have strong steric hindrance, which facilitates the main chain to preserve the preferred-handed conformation. − …”