Hydrodynamic forces in stirred solutions induce chirality in some supramolecular species. Josep Ribo and colleagues, University of Barcelona, Spain, demonstrate that this chiral induction is a result of gradients of shear rate and viscous drag forces acting on the moving particles rather than the separation of enantiomorphic chiral objects in different regions of a stirred cuvette.
The gradients of shear rate and viscous drag create a net torque that may lead to folding and twisting of the particles. Chaotic flows are shown to lead to a racemic mixture of chiral shaped supramolecular species, and vertical flows to scalemic mixtures. Ascending and descending flows have different chiral signs and the circular dichroism reading depends on the relative weighting of these.
Control of chirality in the self-assembly processes could be achieved through flask shape and addition of reagents to defined regions of stirred solutions.