The Separation of Racemic Crystals into Enantiomers by Chiral Block Copolymers

Abstract

A series of chiral double hydrophilic block copolymers (DHBCs) was synthesized and employed as additives in the crystallization of calcium tartrate tetrahydrate (CaT). We found that appropriate polymers can slow down the formation of the thermodynamically most stable racemic crystals as well as the formation of one of the pure enantiomeric crystals so that chiral separation by crystallization occurs even when racemic crystals can be formed. In addition, the presence of DHBCs results in major modifications of crystal morphology, creating unusual morphologies of higher complexity. Our study demonstrates the potential application of chiral DHBCs in the control of chirality throughout crystallization, in particular for racemic crystal systems, and also shows that enantiomeric excess of one enantiomer can be maximized by the kinetic control of crystallization.

Biomimetic Crystallization of Calcium Carbonate Spherules with Controlled Surface Structures and Sizes by Double-Hydrophilic Block Copolymers

“…Owing to the separation of the binding and the solvating moieties, these polymers turned out to be extraordinarily effective in crystallization control for calcium carbonate, [18,19] calcium phosphate, [20] barium sulfate, barium chromate, [21] zinc oxide, [22] CdWO 4 , [23] and even organic crystals. [24] A systematic study of the influence of various experimental parameters on the morphology and size of CaCO 3 crystals after room-temperature crystallization from water in the presence of poly(ethylene glycol)-block-poly(methacrylic acid) (PEG-b-PMAA) showed that all these morphologies are part of a more complex overall scenario. [25] However, the size of the particles was limited to a few micrometers.…”

Dutch Resolution of Racemates and the Roles of Solid Solution Formation and Nucleation Inhibition

“…For example, block polymers of polyethyleneglycol and polyethylenimine grafted with various chiral groups R * have been applied in the direct resolution of calcium tartrate and sodium ammonium tartrate (Pasteur's salt) as shown in Scheme 6 [61].…”

Polymer‐Controlled Biomimetic Mineralization of Novel Inorganic Materials

“…It has been shown that DHBCs [81,142,143] can exert a strong influence on the morphology and/or crystalline structure of inorganic particles such as CaCO 3 PbCO 3 , CdCO 3 , MnCO 3 [144], calcium phosphate [64], barium sulfate [152][153][154][155], barium chromate [67,156], barium titanate [157], calcium oxalate dihydrate [158], zinc oxide , cadmium tungstate [163], chiral organic crystals [164], as a template for silica formation [165] and even on the control of the structure of ice and water [166]. These results show that not only the shape control of primary nanocrystals is achieved, but also complicated superstructures can be produced through the mesoscale self-assembly of the "programmed" primary units.…”

“…In the crystallization of calcium tartrate tetrahydrate (CaT), it was found that appropriate chiral DHBCs can slow down the formation of the thermodynamically most stable racemic crystals as well as the formation of one of the pure enantiomeric crystals [164]. Therefore, chiral separation by crystallization occurs even when racemic crystals are thermodynamically favored.…”