Enantiomeric Separation and the Hydrodynamic Properties of Chiral Molecules

Doctoral Dissertation


We present a model to explain the mechanism behind enantiomeric separation under either shear flow or local rotational motion in a fluid. Local vorticity of the fluid imparts molecular rotation that couples to translational motion, sending enantiomers in opposite directions. Translation-rotation coupling of enantiomers is explored using the molecular hydrodynamic resistance tensor, and a molecular equivalent of the pitch of a screw is introduced to describe the degree of translation-rotation coupling. Molecular pitch is a structural feature of the molecules and can be easily computed, allowing rapid estimation of the pitch for arbitrary molecules. We have computed this pitch for 85 drug-like molecules, and a wide range of chiral molecules with high symmetry axes. A competition model and continuum drift diffusion equations are developed to predict separation of realistic racemic mixtures. We find that enantiomeric separation on a centimeter length scale can be achieved in hours, using experimentally achievable vorticities. Additionally, we find that certain achiral objects can also exhibit a non-zero molecular pitch. We also present a theory for pitch, a matrix property which is linked to the coupling of rotational and translational motion of rigid bodies. The pitch matrix is a geometric property of objects in contact with a surrounding fluid, and it can be decomposed into three principal axes of pitch and their associated moments of pitch. The moments of pitch predict the translational motion in a direction parallel to each pitch axis when the object is rotated around that axis, and can be used to explain translational drift, particularly for rotating helices. We also provide a symmetrized boundary element model for blocks of the resistance tensor, allowing calculation of the pitch matrix for arbitrary rigid bodies. We analyze a range of chiral objects, including chiral molecules, helices, and propellers. Chiral objects with a C_n symmetry axis with n > 2 show additional symmetries in their pitch matrices. We also show that some achiral objects have non-vanishing pitch matrices, and use this result to explain recent observations of achiral microswimmers. We also discuss the small, but non-zero pitch of Lord Kelvin’s isotropic helicoid.


Attribute NameValues
Author Anderson D. S. Duraes
Contributor J. Daniel Gezelter, Research Director
Degree Level Doctoral Dissertation
Degree Discipline Chemistry and Biochemistry
Degree Name Doctor of Philosophy
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Defense Date
  • 2023-08-10

Submission Date 2023-08-11
  • Enantiomers, Chirality, Hydrodynamics, Low Reynolds Number, Molecular Dynamics, Reverse Nonequilibrium Molecular Dynamics

  • Theory of Pitch, Bead Models, Boundary Element Method, Resistance Tensor, Mobility Tensor

  • Swimmers, Achiral Swimmers, Non-Swimmers, Helices, Isotropic Helicoids

  • English

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