Abstract
Applying magnetic substrates, magnetized perpendicular to the surface, we were able to crystallize from racemic solution pure conglomerates of several molecules. The resolution is based on the spin-dependent charge reorganization (SDCR) effect. By having two surfaces with opposite magnetization, it was possible to simultaneously crystallize on each surface a different enantiomer. The method does not require any seeding or chemical modification and is generally employable to any conglomerate. A system is presented for performing the separation, while the racemic mixture flows between the two magnetic surfaces.
Highlights
Since the interaction strength of chiral molecules with the ferromagnetic substrate depends on the molecular properties, the system should be tuned for efficient separations to be achieved
When a chiral molecule approaches the ferromagnetic surface, charge is reorganized in the molecule to form an induced dipole due to the dispersive forces
Each pole of the induced electric dipole is associated with spin polarization so that there is one orientation of spin polarization associated with the positive pole and the opposite orientation associated with the negative pole
Summary
Crystallization is the most commonly used technique for the separation and purification of enantiopure molecules from a racemic mixture, whether it is by formation of a diastereomer by addition of a resolution agent[1] or by spontaneous resolution in the case of conglomerates.[2−4] Industrially, it has a great importance as most of the active pharmaceutical ingredients have in their preparation at least one crystallization step.[5−7] Since many enantiomeric drugs have different biological effects for the two enantiomers,[8−10] regulatory bodies are aiming for the development and commercialization of enantiopure active molecules rather than their racemic form,[11,12] giving even more importance to the development of efficient resolution techniques. The spin-polarized molecule interacts via spin-dependent exchange interaction with the spins of the magnetized surface The magnitude of this interaction depends on the relative orientations of the spin in the molecule and the spin in the ferromagnetic substrate.[17] In a way, the presence of a magnetized surface plays the same role of a crystal seed of one enantiomer, driving the separation process known as kinetic entrainment, where the crystallization of the selected enantiomer is kinetically favored to allow for the separation of enantiopure products.[18] Note that the same magnetic surface can be used to separate many different chiral materials. This method is general and allows one to obtain a highly pure material in a single separation stage
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