Crystalline sponge with guaiazulene guests (light blue). Image from Nature

Cyrstallographers everywhere will attest to how hard it can be to get some molecules to crystalize. Sometimes, there might not even be enough material there to attempt crystallization. Someone is working on a solution though. C&EN reports that researchers have generated a nanoscale scaffold that captures molecules in pores and allows x-ray crystal data to be collected on samples with as little as 80ng of material. From the magazine:

In X-ray crystallography, X-rays are shot through a single crystal of a compound. How they bounce, or diffract in crystallographic lingo, reveals the structure of the molecule that makes up the crystal. The technique has helped scientists visualize innumerable molecules, including antibiotics, industrial catalysts, and even artificial sweeteners.

A team led by Makoto Fujita, of the University of Tokyo, in Japan, reports it can use porous metal frameworks with large cavities as “crystalline sponges” that soak up guest molecules within their voids, putting the molecules in an ordered array that can be studied via X-ray crystallography (Nature, DOI: 10.1038/nature11990). The technique works on as little as 80 ng of material.

In one example, the researchers used a zinc-based crystalline sponge to soak up just 5 µg of miyakosyne A, a scarce marine natural product with a central methyl group that had defied stereochemical assignment. Using their crystal-free crystallographic technique, the team was able to identify the compound’s stereochemistry.