Abstract
Enantiomers share nearly identical physical properties but have different chiral geometries, making their identification and separation difficult. Here we show that when exposed to a rotating electric field, the left- and right-handed chiral molecules rotate with the field and act as microscopic propellers; moreover, owing to their opposite handedness, they propel along the axis of field rotation in opposite directions. We introduce a new molecular parameter called hydrodynamic chirality to characterize the coupling of rotational motion of a chiral molecule into its translational motion and quantify the direction and velocity of such motion. We demonstrate >80% enrichment level of counterpart enantiomers in solution without using chiral selectors or circularly polarized light. We expect our results to have an impact on multiple applications in drug discovery, analytical and chiral chemistry, including determination of absolute configuration, as well as in influencing the understanding of artificial and natural molecular systems where rotational motion of the molecules is involved.
Highlights
Enantiomers share nearly identical physical properties but have different chiral geometries, making their identification and separation difficult
Current separation methods typically rely on interactions with various chiral selectors, for example, chiral chromatography or recrystallization and related Viedma ripening[5,6], while determination of absolute configuration relies on X-ray crystallography and on chiroptical spectroscpy[7], which encompasses a range of spectroscopic techniques, including vibrational circular dichroism[8]
We first discuss the relationship between absolute configuration and handedness of a chiral molecule and its propulsion direction followed by the analysis of molecular dynamics simulations used for quantitative determination of rotational–translational coupling
Summary
Enantiomers share nearly identical physical properties but have different chiral geometries, making their identification and separation difficult. Chiral molecules can be envisaged as tiny propellers with their ‘handedness’ and propulsion direction being determined by absolute configuration of the molecule It has long been hypothesized by Baranova et al.[18], based on phenomenological theory, that the molecular ‘propeller effect’ may lead to separation of enantiomers exposed to radiofrequency electric fields of rotating polarization. There have been a few experimental studies on separation of macroscopic chiral objects (such as helical colloidal particles, model chiral helices, helical-shaped bacteria, 41 m) in helical flows, vortices, microfluidic shear flows and rotating magnetic fields[19,20,21,22]; overcoming Brownian diffusion that starts to dominate on nanoscale has been a challenge until now We show both theoretically and experimentally that the molecular propeller effect with rotating electric fields (REF) offers an important new chiral separation and analysis method. We mention how the molecular propeller effect can have an impact on the field of chiral separations and analysis
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