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A molecular propeller effect for chiral separation and analysis.

Clemens JB, Kibar O, Chachisvilis M - Nat Commun (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Dynamic Connections, LLC, 6150 Lusk Boulevard B104, San Diego, California 92121, USA.

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.

No MeSH data available.


Related in: MedlinePlus

Experimental set-up.(a) A three-dimensional slice of the separation chamber showing the four electrodes, A–D, surrounding the microfluidic capillary. (b) Cross-section schematic showing how the electric field rotates within the separation chamber at four selected time points during a single cycle, t1 to t4. At each time point, two electrodes are in the high-voltage state (+), and the opposite two electrodes are in a zero-voltage state (0). This results in a 90° rotation of the orientation of the electric field (E) within the separation chamber between each time point. (c) The voltage waveforms on each of the four electrode pairs during one full cycle of the electric field rotation. These square-like waveforms (1,100 V, 900 kHz) show the π/2 phase shift between electrodes A–D. The four time points, t1 to t4 from b are also shown. (d) Expected directions of motion of the S and R enantiomers of molecule I for the indicated direction of rotation of the REF (CW, curved black arrow). α is the relative angle between the electric dipole moment and electric field. Electric field rotates around the x axis in the plane zy. The grey arrows show the (opposite) directions of motion for the S and R enantiomers of molecule I. The structure of molecule I (S enantiomer) is also shown with the dipole moment direction indicated.
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f2: Experimental set-up.(a) A three-dimensional slice of the separation chamber showing the four electrodes, A–D, surrounding the microfluidic capillary. (b) Cross-section schematic showing how the electric field rotates within the separation chamber at four selected time points during a single cycle, t1 to t4. At each time point, two electrodes are in the high-voltage state (+), and the opposite two electrodes are in a zero-voltage state (0). This results in a 90° rotation of the orientation of the electric field (E) within the separation chamber between each time point. (c) The voltage waveforms on each of the four electrode pairs during one full cycle of the electric field rotation. These square-like waveforms (1,100 V, 900 kHz) show the π/2 phase shift between electrodes A–D. The four time points, t1 to t4 from b are also shown. (d) Expected directions of motion of the S and R enantiomers of molecule I for the indicated direction of rotation of the REF (CW, curved black arrow). α is the relative angle between the electric dipole moment and electric field. Electric field rotates around the x axis in the plane zy. The grey arrows show the (opposite) directions of motion for the S and R enantiomers of molecule I. The structure of molecule I (S enantiomer) is also shown with the dipole moment direction indicated.

Mentions: To experimentally confirm the molecular propeller effect, we have performed experiments on solutions of molecules I and II using the experimental apparatus depicted in Fig. 2a. The REF inside the microfluidic chamber is generated by applying π/2 phase-shifted voltages to the four pairs of electrodes surrounding the chamber (Fig. 2b,c). A small amount of a racemic solution was injected into the centre of separation chamber and exposed to the REF. Data in Fig. 3a show that the materials collected from the leading and trailing sides of the exposed sample (which was split into two halves at the centre of the absorption chromatogram) have finite and opposite signs of circular dichroism (CD) signal. If the rotation direction of the REF is inverted, the CD signals from the leading and trailing fractions are inverted too. Furthermore, when the experiment is performed on a pure enantiomer sample, no inversion of the CD signal for leading and trailing fractions occurs; these results unequivocally prove that exposure to the REF leads to enantiomeric separation of binaphthyl molecules. Importantly, the experimentally detected direction of propulsion of S and R enantiomers is the same as predicted by MD simulations (compare signs of Lrev in Fig. 1c,d and CD signals in Fig. 3a and Supplementary Fig. 3a; for example, the leading fraction is enriched with the S enantiomer for the clockwise (CW) REF, see Fig. 3a middle panel). This offers a new approach for determining absolute configuration of a chiral molecule.


A molecular propeller effect for chiral separation and analysis.

Clemens JB, Kibar O, Chachisvilis M - Nat Commun (2015)

Experimental set-up.(a) A three-dimensional slice of the separation chamber showing the four electrodes, A–D, surrounding the microfluidic capillary. (b) Cross-section schematic showing how the electric field rotates within the separation chamber at four selected time points during a single cycle, t1 to t4. At each time point, two electrodes are in the high-voltage state (+), and the opposite two electrodes are in a zero-voltage state (0). This results in a 90° rotation of the orientation of the electric field (E) within the separation chamber between each time point. (c) The voltage waveforms on each of the four electrode pairs during one full cycle of the electric field rotation. These square-like waveforms (1,100 V, 900 kHz) show the π/2 phase shift between electrodes A–D. The four time points, t1 to t4 from b are also shown. (d) Expected directions of motion of the S and R enantiomers of molecule I for the indicated direction of rotation of the REF (CW, curved black arrow). α is the relative angle between the electric dipole moment and electric field. Electric field rotates around the x axis in the plane zy. The grey arrows show the (opposite) directions of motion for the S and R enantiomers of molecule I. The structure of molecule I (S enantiomer) is also shown with the dipole moment direction indicated.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525176&req=5

f2: Experimental set-up.(a) A three-dimensional slice of the separation chamber showing the four electrodes, A–D, surrounding the microfluidic capillary. (b) Cross-section schematic showing how the electric field rotates within the separation chamber at four selected time points during a single cycle, t1 to t4. At each time point, two electrodes are in the high-voltage state (+), and the opposite two electrodes are in a zero-voltage state (0). This results in a 90° rotation of the orientation of the electric field (E) within the separation chamber between each time point. (c) The voltage waveforms on each of the four electrode pairs during one full cycle of the electric field rotation. These square-like waveforms (1,100 V, 900 kHz) show the π/2 phase shift between electrodes A–D. The four time points, t1 to t4 from b are also shown. (d) Expected directions of motion of the S and R enantiomers of molecule I for the indicated direction of rotation of the REF (CW, curved black arrow). α is the relative angle between the electric dipole moment and electric field. Electric field rotates around the x axis in the plane zy. The grey arrows show the (opposite) directions of motion for the S and R enantiomers of molecule I. The structure of molecule I (S enantiomer) is also shown with the dipole moment direction indicated.
Mentions: To experimentally confirm the molecular propeller effect, we have performed experiments on solutions of molecules I and II using the experimental apparatus depicted in Fig. 2a. The REF inside the microfluidic chamber is generated by applying π/2 phase-shifted voltages to the four pairs of electrodes surrounding the chamber (Fig. 2b,c). A small amount of a racemic solution was injected into the centre of separation chamber and exposed to the REF. Data in Fig. 3a show that the materials collected from the leading and trailing sides of the exposed sample (which was split into two halves at the centre of the absorption chromatogram) have finite and opposite signs of circular dichroism (CD) signal. If the rotation direction of the REF is inverted, the CD signals from the leading and trailing fractions are inverted too. Furthermore, when the experiment is performed on a pure enantiomer sample, no inversion of the CD signal for leading and trailing fractions occurs; these results unequivocally prove that exposure to the REF leads to enantiomeric separation of binaphthyl molecules. Importantly, the experimentally detected direction of propulsion of S and R enantiomers is the same as predicted by MD simulations (compare signs of Lrev in Fig. 1c,d and CD signals in Fig. 3a and Supplementary Fig. 3a; for example, the leading fraction is enriched with the S enantiomer for the clockwise (CW) REF, see Fig. 3a middle panel). This offers a new approach for determining absolute configuration of a chiral molecule.

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Dynamic Connections, LLC, 6150 Lusk Boulevard B104, San Diego, California 92121, USA.

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.

No MeSH data available.


Related in: MedlinePlus