Mechanical Stirring Induces Heteroaggregate Formation and Self‐assembly of Pseudoenantiomeric Oxymethylene Helicene Oligomers in Solution

Abstract

A mixture of pseudoenantiomeric oxymethylene helicene (P)‐pentamers and (M)‐hexamers formed heteroaggregates and self‐assembled as a result of mechanical stirring in solution at 25 °C. No aggregation occurred without stirring, and heteroaggregation was accelerated at high stirring rates. Repeatedly alternating between mechanical stirring and stopping respectively induced and then ceased the heteroaggregation. Sonication also promoted the heteroaggregation, which did not occur at high pressures or during centrifugation. Mechanisms based on friction due to mechanical stirring, which generated local and temporal high‐temperature domains, are considered. It is shown that different methods of mechanical stimulation, namely, stirring and surface contact, induce enantiomeric heteroaggregate formation.

Chemical Systems Involving Two Competitive Self-Catalytic Reactions

“…The mechanical stirring rate affected the formation of C and self-assembly. Without mechanical stirring, no self-assembly occurred at 25 °C after 150 h. 99 When the rate was reduced from 2000 to 1500 rpm, the process was retarded. Inversion of the stirring direction to counterclockwise provided the same CD spectra as those in the clockwise direction.…”

“…A pseudoenantiomer mixture of oxymethylenehelicene ( P )-pentamer ( P )- 3 and ( M )-hexamer ( M )- 4 formed hetero-double-helix, which self-assembled to form fibril films 98 and aggregates. 99 The ( P )- 3 /( M )- 4 mixture, analogous to the ( P )- 1 /( M )- 2 mixture, provided ( P *)-[( M )- 4 /( P )- 3 ], hetero-double-helix B , and ( M *)-[( M )- 4 /( P )- 3 ], hetero-double-helix C , in which the tentatively assigned ( P *) and ( M *) configurations are those of the helical senses. The ( P )- 3 /( M )- 4 mixture provides metastable random-coil 2 A in solution by simple heating and cooling procedures.…”

“…(a) CD spectra of the ( P )- 3 /( M )- 4 mixture in trifluoromethylbenzene (0.5 mM) in a glass vial during stirring at 2000 rpm. (b) AFM images of self-assembly materials after stirring for 9 h. This is reproduced from ref (99) with permission from John Wiley and Sons.…”

Synthesis and Self-Assembly of Chiral Cylindrical Molecular Complexes: Functional Heterogeneous Liquid-Solid Materials Formed by Helicene Oligomers

“…Hetero-double-helix and self-assembly gels formation in pseudo-enantiomeric mixtures of the oxymethylenehelicene ( P )-pentamer and ( M )-hexamer occurred at 25 °C in response to mechanical stirring ( Figure 30 ). This behavior is in contrast to the formation of fibril films on the solid surface at 5 °C ( Figure 29 ) [ 101 ].…”

Synthetic Chemical Systems Involving Self‐Catalytic Reactions of Helicene Oligomer Foldamers

“…In response to mechanical stirring, (P)-7/(M)-8 in solution forms hetero-double-helices and undergoes molecular self-assembly, which involves self-catalytic reactions. [48] (P)-7/(M)-8 in trifluoromethylbenzene was heated to 80°C and cooled to 25°C providing a metastable 2A(O) solution. The solution was mechanically stirred in a clockwise direction with a Teflon magnetic stirring bar at a rate of 2000 rpm.…”