Chiral Sign Induction by Vortices During the Formation of Mesophases in Stirred Solutions

Abstract

Achiral diprotonated porphyrins, forming homoassociates in aqueous solution, lead to spontaneous chiral symmetry breaking. The unexpected result is that the chirality sign of these homoassociates can be selected by vortex motion during the aggregation process. This result is confirmed by means of circular dichroism spectra. These experimental findings are rationalized in terms of the asymmetric influence of macroscopic forces on bifurcation scenarios and by considering the specific binding characteristics of the porphyrin units to form the homoassociates.

Mechanically Induced Homochirality in Nucleated Enantioselective Polymerization

“…One of the major aims of the present work was to address this issue (the formation of the homochiral polymers themselves), and especially in light of experimental techniques using hydrodynamic shear stresses for breaking up supramolecular structures. 25,26 The simulations suggest that the key necessary condition for achieving SMSB is the binary chain-fusion mechanism. Indeed, if we delete fusion from the overall scheme (k a = k −a = 0), racemic initial conditions lead to strictly racemic configuration for all time scales, including asymptotic times.…”

“…25 In an even earlier key experiment, hydrodynamic vortex motion was demonstrated to act as an environmental pressure to select one or the other handedness between two otherwise degenerate mirror symmetric supramolecular populations. 26 One of our main aims here is to explore the impact that both mechanically induced breakage in concert with fiber fusion have on the mirror symmetry breaking and subsequent chiral amplification. An important aspect of this work is that we consider the polymerization process in a closed system and include reversible reaction steps.…”

Experimental aspects of solid state circular dichroism

“…[59][60][61][62] As a caution: conventional stirring of a suspension in a cuvette may create vortices with induced supramolecular optical activity as pointed out recently. [63][64][65][66] Another recent application deals with nanocrystalline benzophenone 67 where CD spectra in Nujol mull and in suspension are compared, the experimental part is however not well described.…”

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] .…”