Chiral Colloidal Molecules And Observation of The Propeller Effect

Abstract

Chiral molecules play an important role in biological and chemical processes, but physical effects due to their symmetry-breaking are generally weak. Several physical chiral separation schemes which could potentially be useful, including the propeller effect, have therefore not yet been demonstrated at the molecular scale. However, it has been proposed that complex nonspherical colloidal particles could act as “colloidal molecules” in mesoscopic model systems to permit the visualization of molecular phenomena that are otherwise difficult to observe. Unfortunately, it is difficult to synthesize such colloids because surface minimization generally favors the growth of symmetric particles. Here we demonstrate the production of large numbers of complex colloids with glancing angle physical vapor deposition. We use chiral colloids to demonstrate the Baranova and Zel’dovich (BaranovaN. B.Zel’dovichB. Y.BaranovaN. B.Zel’dovichB. Y.Chem. Phys. Lett.197857435) propeller effect: the separation of a racemic mixture by application of a rotating field that couples to the dipole moment of the enantiomers and screw propels them in opposite directions. The handedness of the colloidal suspensions is monitored with circular differential light scattering. An exact solution for the colloid’s propulsion is derived, and comparisons between the colloidal system and the corresponding effect at the molecular scale are made.

Magnetotactic bacteria

“…Indeed some of the best propellers selected from the random shapes show a weak resemblance to such slender helices. Propellers with helical shape as well as random shapes can only follow the rotation of the magnetic field up to a critical rotation frequency, for which the maximal speed is obtained [59,62]. If the field is rotated with a frequency exceeding this critical frequency, the propeller rotates with a smaller frequency and therefore also moves with reduced speed.…”

Optofluidic sorting of material chirality by chiral light

“…Importantly, the proposed optofluidic strategy does not require chiral-shaped microparticles and actually relies on the chirality of the medium, in contrast to previous experimental demonstrations of chiral sorting based on hydrodynamical effects [11][12][13]16 . Indeed, our method enables to sort material chirality by exploiting a universal feature of the light-matter interaction, namely the dependence of optical forces on the intrinsic handedness of matter and light.…”

“…In addition, hydrodynamic propeller effects driven by rotating electric fields have also been considered theoretically 14,15 . This principle has been demonstrated only recently by using screw-shaped micrometre-sized particles made of non-chiral medium subjected to the action of a rotating magnetic field 16 . Merging microfluidic and field-induced options into an optofluidic chiral sorting scheme may offer new possibilities for a technology that arouses interest regarding present achievements and promising developments (see ref.…”

Electric-field–induced assembly and propulsion of chiral colloidal clusters

“…Current strategies to make chiral structures are primarily based on photo or E-beam lithography (29,30), glancing-angle deposition (31), chemical etching (32), or templating methods using chiral molecules such as DNA (33). Nature, however, assembles simple and achiral building blocks into chiral structures with exquisite functionality.…”