Freeze trapping of reaction intermediates.

Structural intermediates in a biological reaction may be monitored by rapid spectroscopic or somewhat slower structural techniques. Intermediates may evolve in real time (no trapping), be stabilized by chemical manipulation of the reactants, the macromolecule or the solvent (chemical trapping), or be stabilized by lowering the temperature (freeze trapping). The last is beginning to be coupled with X-ray diffraction, electron cryomicroscopy and solid-state NMR approaches to characterize the trapped intermediates. Care in conducting such experiments, together with an awareness of possible artefacts, is essential if reliable structural results are to be obtained.