PerspectiveChemical Structure

Absolute structure, at the nanoscale

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Science  17 May 2019:
Vol. 364, Issue 6441, pp. 632-633
DOI: 10.1126/science.aax5385

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In 1848, Louis Pasteur reported that sodium ammonium tartrate could crystallize in two distinct forms that are mirror images of each other, an observation that led to the discovery of molecular chirality. A chiral molecule and its mirror image are nonsuperposable and can have very different properties. This geometric property can result in chiral pairs (enantiomers) in which, for example, one version is sweet whereas the other is tasteless, or one is an effective drug whereas the other is toxic. It is therefore of vital importance to determine the absolute configuration of molecules. On page 667 of this issue, Brázda et al. (1) report the absolute structure of submicrometer-sized crystals of an organic pharmaceutical compound by means of electron diffraction, by taking advantage of the strong interaction between the molecules and the electron beam. This demonstration supports an approach that should have great value in assessing the therapeutic activity of drugs.