Emergence of Supramolecular Chirality by Flows

Abstract

Hydrodynamic forces in stirred solutions induce chirality in some supramolecular species of J-aggregates, as detected at the level of the electronic transition. However, the mechanism that explains the phenomenon remains to be elucidated, although the basic effect of hydrodynamic gradients of the shear rate is most probably the folding or bending of the nanoparticles in solution. Herein, we demonstrate a correlation between chiral flows in different regions of circular and square stirred cuvettes and the emergence of true circular dichroism (CD). The results show that chaotic flows lead to a racemic mixture of chiral shaped supramolecular species, and vortical flows to scalemic mixtures. In a magnetically stirred flask the descending and ascending flows are of different chiral sign and the CD reading depends on the weighting of these two flows of inverse chiral sign. The effect of the gradient of shear rates of the flows leading to chiral shape objects depends on the shape of the cuvette, which suggests that the flask shape and the controlled addition of reagents in defined regions of the stirred solutions may exert a control in self-assembly processes.

Using shape for self-assembly

“…Remarkably, similar effects have been reported for assemblies of chiral molecules, whose organization can depend on the orientation of the local fluid vorticity (i.e. clockwise flows versus counterclockwise flows) [128,129].…”

Stirring competes with chemical induction in chiral selection of soft matter aggregates

“…More striking is the report that the combination of soft aggregation and stirring may lead not only to chiral induction 22,23 but, more importantly, also to sign selection, in both three 24,25 and two dimensions 26,27 . Discussions on the true nature of such an enantioselection in three-dimensional aggregates have raised some controversy [28][29][30][31][32][33] . Recently, d'Urso et al 34 have hinted at the possibility to exert enantioselective control on the supramolecular assembly of achiral components doped with a chiral complex by means of vortex flow.…”

Selective chiral handedness induced in spin-coated polyaramide films

“…5 In fact, electrostatic J-aggregation of a 4-sulfonatophenylporphyrin in aqueous media has demonstrated that the sense of optical activity can be selected using the direction of rotary stirring. [6][7][8][9] The optical activity of a helical ribbon reflected the direction of the chirality induced in a stirred solution. 9 Furthermore, a hydrogen-bonded dendritic porphyrin wire gives a selective and reversible optically active solution, suggesting that rotational stirring is a potential tool for chiral induction.…”

“…[6][7][8][9] The optical activity of a helical ribbon reflected the direction of the chirality induced in a stirred solution. 9 Furthermore, a hydrogen-bonded dendritic porphyrin wire gives a selective and reversible optically active solution, suggesting that rotational stirring is a potential tool for chiral induction. 10,11 The dendritic porphyrin derivatives form optically active films whose enantiometric form is determined by the spinning direction.…”