The Changing Shapes of Molecules

recise diagnostics are important for conveying information about an ob-ject’s properties. In retail stores, bar codes are used to identify goods. Similarly, spectra are widely used in chemistry to iden-tify molecular properties. On page 924 of this issue, Dian et al. (1) report the use of a new spectroscopic technique that makes it much easier to identify the shapes of mole-cules as they change. Like any good diagnostic, molecular spectroscopy needs to be fast, sensitive, and selective. Several different types of spec-troscopy can elucidate molecular proper-ties, but the finest level of molecular detail—the molecule’s shape—can best be identified by microwave spectroscopy. Traditionally, this technique provides excel-lent selectivity and sensitivity but suffers limitations in speed. The new microwave spectroscopic technique used by Dian et al. dramatically enhances the speed of acquir-ing rotational spectra without sacrificing sensitivity or selectivity. Molecular shape plays an important role in chemical reactivity. Nowhere is this more apparent than in biochemistry. For example, biopolymers are dominated by L-amino acids and D-sugars, whereas their mirror image molecules are nearly absent (2). Subtle shape differences also have big effects for fatty acids. Those with hydrogen atoms located on opposite sides of the carbon-carbon double bond are more likely to raise bodily LDL cholesterol levels than are those that have the hydrogens on the same side (3). The complete determination of the three-dimensional molecular geometry by A new microwave spectrometer enables the geometries of molecules to be tracked as they interconvert between different shapes