Direct assignment of the absolute configuration of molecules from crystal morphology

Abstract

A method for direct assignment of the absolute configuration of molecules and the absolute structures of polar crystals, independent to that of Bijvoet, is described. The method correlates between the two-dimensional packing arrangement of specific faces, that delineate crystals during their growth and dissolution, with molecules present in the environment. The structural information stored in these faces is transferred to "tailor-made" molecules added to the solvent by controlled morphological changes induced to the growing crystals and by the creation of etch pits at specific crystal faces during their dissolution. In addition, the "tailor-made" molecules are occluded enantioselectively as guests within specific sectors of the host crystals. The method is illustrated for a variety of molecules and crystals including the assignment of the absolute configuration of several alpha-amino acids as "tailor-made" additives in centrosymmetric crystals of glycine and serine, for the absolute structure of polar crystals of sugars and alpha-amino acids and consequently the absolute configuration of molecules packed in such crystals.

Absolute Asymmetric Reduction Based on the Relative Orientation of Achiral Reactants

“…In principle, the product enantiomer that will form in excess can be predicted if one knows which enantiotopic surface is exposed to the solution. [35] The ee values are surprisingly high relative to those found in most other absolute asymmetric syntheses, especially if one takes into account that the orientation of the polished end face in the present set of experiments was only controlled by the naked eye (with an uncertainty of approximately 208) and that the tilt of the molecular planes with respect to the needle axis was not corrected for. We also conducted a number of control experiments in which we exposed either BC powder or unsealed BC crystals to a solution of NaBH 4 .…”

Synthesis and characterization of MgSO4·5Mg(OH)2·2H2O flake powders

“…3.1.5 Influence of crystal additives on morphology of products The growth habit of crystals is often modified by their growing environment. For example, the habit may be modified by the presence of crystal additives or impurities [22], which bind to the growth sites and reduce the rate of attachment of solute molecules. For the improvement of magnesium oxysulfate crystallization, NaH 2 PO 4 and Na 3 PO 4 were utilized as crystal modifiers in the hydrothermal synthesis process.…”

On the Centenary of Emanuel Gil‐Av, Former Professor of the Weizmann Institute of Science and Pioneer of Enantioselective Chromatography

“…Emanuel Gil‐Av and Zeev Vager recognized the opportunity of this approach to determine the absolute configuration of single enantiomers of a small ionized chiral molecule by direct three‐dimensional visualization. Previously, absolute configurations were only accessible by indirect methods, such as anomalous X‐ray scattering, chiroptical methods, or from crystal morphology studies, also developed at the Weizmann Institute by Meir Lahav and associates . As a chiral projectile of the required low molecular weight, Gil‐Av originally suggested monodeuterooxirane.…”

“…Previously,a bsolute configurations were only accessible by indirect methods, such as anomalous X-ray scattering,c hiroptical methods, or from crystal morphology studies,a lso developed at the WeizmannI nstitute by Meir Lahava nd associates. [80] As ac hiral projectile of the required low molecular weight, Gil-Avo riginally suggested monodeuterooxirane.L ater at Tübingen University, trans-(R,R)-2,3-dideuterooxiranew as considered instead (Figure 18, bottom right) as it could be directly correlated with the stereochemical key compound D-(+)-glyceraldehyde, which had been used 1917 by Wohl and Momber as as tereochemical reference standard for all sugars, based on the original configurational assignment of glucoseb y Emil Fischer in 1891. [81] Thus,d extrorotatory glyceraldehyde had arbitrarilyb een assigned as havingt he D-configuration ( Figure 18, bottom left).…”