Unconventional, Amphiphilic Polymers Based on Chiral Poly(ethylene oxide) Derivatives. 2. Ordering and Assembly

Abstract

The poly(ethylene oxide) derivatives 1-3 (Figure 1) aresin designssynthetic analogues of coiled-coil-forming peptides. A comparative optical rotatory dispersion (ORD) study and TEM measurements have been used to investigate the ordering and assembly processes that are involved in the aggregation of these amphiphilic polymers 1-3 in H2O. ORD measurements have shown that various ethylene oxide derivatives display an inversion of optical rotation upon complexation with KSCN, i.e. upon adoption of a helical conformation. This observation has led to the proposal that polymers 1-3 are helically ordered in H2O, since the methyl-substituted polymer 3 exhibits an inversion of optical rotation on going from apolar (THF) to polar (H2O) solvents; phase separation prohibits the detection of such an inversion for the isobutyl-substituted polymers 1 and 2. TEM studies on surfaces onto which polymers 1-3 were deposited from aqueous solutions revealed granular and threadlike aggregates. The formation of the threadlike higher structures requires a directionality in the assembly process. Such a directionality could be provided by the formation of coiled-coil tertiary structures. However, substantial evidence for the formation of coiled coils or other specific tertiary structures is lacking.

Inversion of Optical Activity of Chiral Polythiophene Aggregates by a Change of Solvent

“…Similarly, the odd or even position of a chiral center in the side chain of polyisocyanides has been shown to cause an alternating optical activity via an inversion of the sense of the prevailing helix . Interestingly, some examples are known of a (reversible) inversion of optical activity in polymers, by changing the nature of the medium without affecting even a single stereocenter . The inversion of the poly(dGC) double helix from right-handed B-DNA into left-handed Z-DNA at high-salt concentrations is probably the best known example in this respect .…”

“…2 Interestingly, some examples are known of a (reversible) inversion of optical activity in polymers, by changing the nature of the medium without affecting even a single stereocenter. 3 The inversion of the poly-(dGC) double helix from right-handed B-DNA into lefthanded Z-DNA at high-salt concentrations is probably the best known example in this respect. 4 Similar inversions have been established for poly[(S)-diphenyl-(1-methylpyrrolin-2-yl)methyl methacrylate] by changing the acidity of the solution and for poly(L-proline).…”

Preparation and chiro‐optical characterization of polyaniline doped with (+) or (−)‐2‐pyrrolidone‐5‐carboxylic acid (PCA)

“…Interestingly, some examples are known of a reversible inversion of optical activity in polymers by changing the nature of medium 45. Recently, inversion of configuration has been reported for π‐conjugated polymers carrying optically active side chains 46.…”

Helicity Control of π‐Stacked Assemblies of Oligo(para‐phenylene) Derivatives Using Photoresponsive Chiral Moieties at Terminal Sites

“…Many researchers have brought about chirality control in π‐conjugated systems and polymers by changing the nature of the environment without affecting their stereocenters . These changes in chirality have been generated by varying parameters such as the temperature, pH, and salt concentration .…”