Phenomenon of Optical Self-Purification of Chiral Non-Racemic Compounds

Abstract

Owing to a faster rate of sublimation of the racemic form as compared to the optically pure form, optical purification occurred without any external action or special environmental condition. We believe that the phenomenon of optical self-purification reported here deserves further systematic study as possibly one of the mechanisms leading to the emergence and maintenance of prebiotic homochirality.

Evolução biomolecular homoquiral: a origem e a amplificação da quiralidade nas moléculas da vida

“…Os autores observaram que a substância sublimada possuía apenas 35% ee. 16 Quando a sublimação foi realizada em vaso aberto (pressão ambiente), partindo do derivado de ácido lático com 80% ee, obtiveram um material não sublimado Os autores demonstraram que as pressões de vapor dos enantiô-meros e de suas misturas variam significativamente, e podem depender principalmente da entalpia da decomposição do composto racêmico e da temperatura do processo. As diferenças relevantes nas interações intramoleculares entre enantiômeros e racematos são suficientes para produzir enantiosseparações espontâneas, mesmo sob influências físicas aquirais.…”

Self-disproportionation of enantiomers (SDE) of chiral sulfur-containing compounds via achiral chromatography

“…2 At the same time, considering the role of amino acids in the emergence of life, they put forward an idea that such processes could have occurred under prebiotic conditions, providing significant amounts of highly enantiomerically enriched compounds leading eventually to biological homochirality. 3 Soon thereafter, Dreiding et al reported 4 that chromatography on silica gel of a chiral hydrindandione also gave fractions that showed dispersion of ees. The similar chromatographic behaviour of a mixture of 14 C-labeled racemic N-acetylvaline tert-butyl ester with the unlabeled (S)-enantiomer on silica gel was described by Hara et al 5 and for a cineole derivative by Carman.…”

“…19 The SDE of chiral crystalline compounds results from the essential differences in the crystallographic structures of racemates and enantiomerically pure crystals (named as conglomerates), which are expressed as the Wallach rule. 3,[20][21] It is obvious that racemates and conglomerates always show different physicochemical properties such as melting point, density, sublimation and solubility rates and these differences can be used for the purpose of enantiomeric purification. However, SDE via density gradient centrifugation 22 or SDE via sublimation [23][24][25] are far much less known, but can be quite successfully used for It is also obvious that the well-defined preferences for dynamic homochiral/heterochiral molecular associations for chiral compounds in liquid state or in solution can be considered as the equivalent of the distinct crystallographic structures observed in the solid state.…”

Crystal structure of rac-4,4,4-trifluoro-3-hydroxy-3-methylbutanoic acid, C5H7O2F3

“…To allow for comparisons of metrical parameters of the carboxylic-acid-derived ligand in envisioned coordination compounds, the crystal and molecular structure of the free ligand was determined. The crystal structure of several related compounds such as 2-hydroxy-2-(tri uoromethyl)proprionic acid [2], rac-3,3,3-tri uorolactic acid [3] In the crystal, a series of classical hydrogen bonds can be observed. These are either intramolecular -as observed in between one alcoholic hydroxyl group as donor and the carbonyl-type oxygen atom as acceptor -or intermolecular.…”