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Analytical Chemistry

Crystal Growth In Retrospect

New technique back tracks crystal’s life when in situ methods aren’t workable

by Sarah Everts
June 28, 2010 | A version of this story appeared in Volume 88, Issue 26

Just as tree rings reveal the secrets of a tree’s growth, a new technique that involves peering at a crystal’s cross section permits researchers to follow the growth of a crystal retrospectively (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201000952). Kenneth Harris of Cardiff University, in Wales, and François Guillaume of the University of Bordeaux, in France, hope the strategy will be useful when in situ methods aren’t workable, such as when crystal growth happens too fast or at temperatures too extreme for in situ equipment. To backtrack on a crystal’s life, the team studied urea inclusion compound crystals, which can grow only when molecules such as 1,8-dibromooctane or pentadecane occupy inclusion areas next to the urea. Since pentadecane preferentially slips into these spaces, its concentration in the crystal predominates over that of 1,8-dibromooctane in the early stages of growth. At later times, with less pentadecane available in the solution, 1,8-dibromooctane begins to populate more of the crystal’s inclusion spaces. Using Raman microspectrometry, the researchers measured the relative ratios of 1,8-dibromooctane and pentadecane in cross sections of the final crystal. Then, they mapped the concentration ratio to a color grid that reflects the deposition of these molecules in the growing crystal.

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