Chemistry in Pictures: Vapor diffusion

Tiffany Poynder had a nice surprise waiting for her in lab one recent Monday morning—crystals! Getting good crystals is always satisfying, and suggests that the compound in the vial is pure. But they’re crucial for Poynder, whose research is on perflourinated molecules that are difficult to isolate and characterize. Having nicely formed crystals to work with enabled her to use X-ray crystallography to identify what she had.

The crystallization setup shown in the photo is a classic called vapor diffusion. The molecule of interest is dissolved in a solvent or solvent mixture in the inner vial, which is left open. Then a different solvent, one that doesn’t dissolve the molecule well, goes around it in the outer vial, which is then capped tightly. Vapors of the outer solvent slowly mix in with the inner solvent (and vice versa), making the solvent in the inner vial less and less hospitable. Eventually the molecule can’t stay in solution, so it (hopefully) comes out as crystals.

Credit: Tiffany Poynder, @tiffany_poynder. Read more from this research: (Chem.–Eur. J. 2019, DOI: 10.1002/chem.201806110)

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