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Analytical Chemistry

Ultrasensitive Crystal Probe

Optical method detects early onset of nucleation and crystallization of chiral compounds

by Mitch Jacoby
June 14, 2010 | APPEARED IN VOLUME 88, ISSUE 24

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Credit: Garth J. Simpson/Purdue U
As shown in these micrometer-sized sample maps, a nonlinear optical method detects the earliest stages of griseofulvin crystallization (colored spots at 0 min) while other methods indicate the sample is initially crystal free.
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Credit: Garth J. Simpson/Purdue U
As shown in these micrometer-sized sample maps, a nonlinear optical method detects the earliest stages of griseofulvin crystallization (colored spots at 0 min) while other methods indicate the sample is initially crystal free.

A novel laser-based method can detect nucleation and onset of crystallization of chiral compounds up to 100 million times more sensitively than conventional detection methods, according to researchers at Purdue University who developed the technique (Anal. Chem., DOI: 10.1021/ac100564f). The procedure provides an exceptionally sensitive way to probe nucleation and growth kinetics at the earliest stages of crystal formation. In addition, the technique may be useful for studying pharmaceutical agents, which often need to be inhibited from crystallizing to avoid reducing their bioavailability (C&EN, May 31, page 13). Purdue’s Duangporn Wanapun, Garth J. Simpson, Lynne S. Taylor, and coworkers melted samples of griseofulvin and chlorpropamide (antifungal and diabetes drugs, respectively) and then cooled the melts while probing them for crystal formation with their newly developed nonlinear optical imaging method. The method’s detection limit, roughly 1 part in 10 billion by volume, enabled the group to observe crystals with dimensions as small as 150 nm, they report. That limit is lower by a factor of 108 compared with common spectroscopy and diffraction methods and represents a five-order-of-magnitude improvement relative to optical microscopy.

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