Aspects of spontaneous separation of enantiomers in two- and three-dimensional crystals

From Homochiral Clusters to Racemate Crystals: Viable Nuclei in 2D Chiral Crystallization

“…22,25 Based on general symmetry arguments, it has been proposed that confinement at surfaces should favor conglomerate formation. 26,27 Our study here shows that, at least for apolar molecules, the match of the footprint with the substrate surface plays a more important role. Because monolayer or the nuclei at the surface serve as template for further three-dimensional growth, the new insight into 2D crystallization reported here are useful for crystallization in general.…”

Molecular asymmetry in extraterrestrial organic chemistry: An analytical perspective

“…For example, were centers of asymmetry present on such surfaces, their diastereomeric interactions with chiral molecules might have influenced enantiomeric ratios by either favoring reactions of a preferentially adsorbed enantiomer or allowing the one left in solution to further react. These processes would have the same result of a preferential survival of one enantiomer but not necessarily require initial ee in the adsorbed molecule, as long as the configuration of mineral centers was not randomly distributed, i.e., the symmetry breaking Under laboratory conditions, it has also been shown that the unimolecular assembling of chiral molecules on surfaces may facilitate the separation of their enantiomers in two dimensions, because of their planar confinement and resulting enhancement of chiral interactions (e.g., Kuzmenko et al, 1998;Fasel et al, 2006). In these two-dimensional arrangements, in fact, all the symmetry elements of threedimensional crystals are not allowed and even prochiral molecules have been shown to spontaneously form planar conglomerates, i.e., localized homochiral crystal structures (e.g., Ernst, 2010).…”

Crystal engineering based on mirror image recognition

“…In this presentation the inclusion of both metal centres and chromophores into GS networks is discussed. Metal centres can be included through use of sulfonated phosphine ligands such as PPh 2 (C 6 H 4 SO 3 -m) [2,3], though in such cases the strong N-H×××O hydrogen bonds of the GS array can be compromised by weaker interactions involving the phenyl rings. Chromophores can be included into GS networks through use of sulfonated indicators such as methyl orange, Na[O 3 SC 6 H 4 N=NC 6 H 4 NMe 2 ].…”

“…Chromophores can be included into GS networks through use of sulfonated indicators such as methyl orange, Na[O 3 SC 6 H 4 N=NC 6 H 4 NMe 2 ]. The guanidinium derivative of methyl orange has been shown by powder X-ray diffraction and diffuse reflectance UV-visible spectroscopy to react sequentially with HCl and NH 3 . In addition, the tolerance of the GS network to substitution on the guanidinium cation has been examined.…”

“…Opposite chirality offers the possibility to design binary crystals based on the favourable interaction between opposite enantiomers. We have exploited the statistical preference for heterochiral crystals [1][2][3] as a design tool to generate predictable molecular assemblies [4][5][6][7]. Preferred mirror image recognition in the solid extends to closely related compounds of opposite chirality, so-called quasiracemates [8,9].…”