Enantiomeric segregation

In the host/additive systems described above, such as (/ ,S)-ser/(/ ,S)-thr and glycine/(/ ,S)-a-amino acids, the change in crystal habit and the enantiomeric segregation of occluded additive indicates that only a subset of the possible symmetry-related sites may be occupied by an additive depending on through which faces the additives are occluded. Such an effect would lead to a reduction in the overall symmetry of the host/additive crystal. 

Selection-coupled analysis/phase segregation. One strategy for simplifying the analytical challenge is to use phase segregation. Three subclasses are possible. In the first of these, a phase transition is part of the selection process. This includes not only the familiar crystallization-induced enantiomeric enrichment discussed above but also the experiments (primarily employed in experiments directed toward the production of novel materials) such as those described by Lehn and coworkers in 2005. In this study, an acylhydrazone library was created from guanosine hydrazide and a mixture of aldehydes (Fig. 1.22) in the presence of metal ions, formation of G-quartet structures led to the production of a gel. 

The [ C]-(2S,2 S)-(-)-t/treo-enantiomer did not bind, indicating that the (2/ ,2 R)-(+)-t/treo-enantiomer 1 is the active form. Thus, to segregate the desired pharmacological activities from side effects, there is a great interest for preparing enantiomerically pure (2R,2 R)-(+)-t/treo-methylphenidate hydrochloride (1) on a large scale. 

The transformation of racemic chemistry to chiral biology remain an unsolved mystery of nature, but the spontaneous segregation of a racemic mixture into enantiomers in 2D and 3D might have played an important role [33]. To address this problem the molecular structures (at the air-water interface) of racemic and enantiomerically resolved monolayers have been explored, e.g., a-amino acids with a long alkyl chain residue. A brief overview of pure derivatives of amino acids, peptides and proteins characterised at the air-water interface is presented. 

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