‘Tailor-made’ Polymers for the Removal of Lamellar Twinning: Resolution of α-Amino Acids by Entrainment

Abstract

ponents, as well as outgassing of CO 2 . Approximately 1 mg of vaterite spheroids was produced from 1 mL of supersaturated CaHCO 3 solution.Growth of the vaterite spheroids was followed in situ by optical microscopy and by removing samples at intervals of 2, 4, 6, and 18 h from an octane/SDS/CaHCO 3 microemulsion left partially uncovered at 25 C in a Petri dish. Samples of the uppermost dried powder layer, along with some of the thickening underlying microemulsion phase, were removed and immediately washed with methanol to remove SDS, filtered through a 1 mm poly(tetrafluoroethylene) (PTFE) membrane and rewashed with methanol. The remaining sediment was examined by SEM.Dissolution studies were undertaken by suspending the vaterite microsponges in distilled water. Samples were removed at various time intervals, dried in air and examined by SEM. Spheroids with an average size of 4.5 mm or 15 mm dissolved within 2 and 10 days, respectively.Control experiments on calcium carbonate crystallization were undertaken by mixing 0.5 g of SDS with 1.8 mL of supersaturated CaHCO 3 solution, prepared as above. A clear solution was obtained by probe sonication for 25 s, and the mixture left at 25 C in an open vial. The mixture transformed to a gel overnight. The precipitated CaCO 3 (vaterite) crystals were collected at intervals of 2, 4, 6, and 18 h by washing with methanol followed by sedimentation. Dissolution studies were performed by suspending the crystals, formed after 4 h, in distilled water for at least 1 day.Polymer-coated vaterite particles were prepared by adding 0.0011 g of the fully mineralized vaterite spheroids, 17.5 mm in diameter, to a saturated chlorobenzene solution of poly(vinyl chloride) (PVC) (M w = 95 000), followed by stirring for 2 h, sedimentation and air-drying of the inorganic material. The saturated PVC solution was prepared by adding 0.1 g of PVC to 25 mL of chlorobenzene, followed by overnight stirring, and removal of the saturated supernatent for further use. The PVC-coated vaterite spheres were then placed into 7 mL of distilled water and 1 mL liquid aliquots were removed at intervals of up to 7 days and the soluble Ca content analyzed by atomic absorption analysis. A control experiment involving the dissolution of 0.0013 g of uncoated 17.5 mm vaterite spheroids in 7 mL of distilled water was also undertaken.

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

“…This is likely due to adsorption to multiple binding sites (polydentate) in addition to the shielding of the crystal surface by the polymer backbone [58]. Polymeric additives also have been successfully applied to prevent lamellar twinning in the cases of methionine, cysteine and valine [60].…”

Biomimetic Polymers for Chiral Resolution and Antifreeze Applications

“…[131][132][133][134][135][136] They found that the incorporation of a small amount (up to a few percent) of enantiomerically-pure additives in the crystallization of chiral systems inhibits the crystallization of one enantiomer dramatically. In their study, Lahav and Leiserowitz encountered the interesting phenomenon of asymmetric induction on the crystallization of non-chiral photopolymerizable dienes into chiral crystals.…”

“…Zbaida and Lahav 133,[137][138] continued their research on chiral resolution by crystallization with "tailor-made" additives and extended it from low molecular-weight additives to polymeric-resolving agents. Zbaida described the resolution by the crystallization of a series of racemic compounds such as glutamic acid, threonine, asparagine monohydrate, and histidine, using soluble chiral polymers.…”

“…In a later publication, Zbaida demonstrated the use of soluble polymers based on R/L-lysine residues for the chiral separation of a lamellar twining racemate conglomerate of valine and methionine. 133 In a pioneer research, Mastai and Cölfen 139 presented chiral crystallization in the presence of DHBCs soluble chiral polymers in order to control chirality and to achieve racemate separation upon crystallization. In their study, a set of optically-active DHBCs were synthesized based on one polymer of PEG-b-PEI block (PEG poly(ethylene glycol), Mw=5,000 g mol -1 , PEI branched poly(ethyleneimine), M = 700 g mo -l ).…”

Asymmetric amplification in amino acidsublimation involving racemic compound to conglomerate conversion

“…16 One enantiomorph can thus operate as template for the crystallization of the other, yet obtaining the racemic conglomerate. Since the crystals of D,Lvaline are actually disordered, 17 they have not undergone spontaneous resolution.…”