In this section, you will discuss the results of Noveduian, et al., and describe

Question

In this section, you will discuss the results of Noveduian, et al., and describe why the phenomenon is observed. The concept of the paper is shown below. Upon addition of a small excess of one environment of 1 or a different chiral species (such as phenylglycine), crystals of 1 with 100% enaetiometric excess can he obtained over time. The key to this theory and experiment selective crystallization. Read the Ostwald ripening attachment and explain why a large crystals more thermodynamically favorable than a small one. The experiment also relies on the fact that individual enantiomers crystallize together in a single crystal (i.e., the crystals are either all-$ or ail R, not a racemic crystal). Explain why this occurs; consider the solid state interaction of two molecules of the same handedness and different handedness. See McMurry. pagesl61-163. If there is only a small excess of one enantiomere in solution, can selective crystallization alone (i.e., in the absence of base) cause chirality enhancement? Discuss why the combination of added base (DBU in this case) and selective crystallization allows the enhancement of chirality of the system. Consider equilibrium effects and lessthanorequalto Chatelier's principle in your answer. This is a proof-of-principle experiment (i.e., it mimics the natural process, but several changes were made to allow study in a laboratory setting). To maximize the speed of the enhancement, glass beads and magnetic stirring were employed. How does this speed up the process? Is this a plausible method of mimicking natural evolution? Why did the researchers not simply perform the experiment as it would occur in prebiotic systems?

Explanation / Answer

Part 2 ) Enhancment of chiralty by crystallization

Crystallization is a technique used widely for the kinetic resolution of enantiomers from racemic mixture of isomers. The method involves, taking a racemic mixture of enantiomers and adding a slight excess crystal of one enantiomer into the solution of the two. The added crystals act as the nucelation site and direct the crystallization in the direction of the added enantiomer.

Addition of base such as DBU leads to epimerization of chiral center. So a chiral resolution with a base would keep inverting the configuration of the excess enantiomer until no more of the other isomer remains in solution. This is simultaneously done by the removal of the other enantiomer from the solution.

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