Dipeptide Crystals For Gas Storage

Nanochannels that form in biomolecular crystals may be useful for separating, purifying, and storing gases such as methane, hydrogen, and carbon dioxide under mild conditions, according to Piero Sozzani and colleagues at the University of Milano Bicocca, in Italy (Chem. Commun., DOI: 10.1039/b820200a). Researchers have proposed numerous porous materials for gas storage, but many of these materials require unfavorable synthesis conditions, contain heavy-metal ions, or are not biodegradable. Sozzani and coworkers prepared four dipeptides that crystallize with chiral channels suitable for encapsulating gases. A network of hydrogen bonds holds the peptides together, creating the permanent channels with hydrophobic internal surfaces. The researchers found that the channels in a dipeptide crystal composed of isoleucine and valine, for example, can hold as many moles of CH₄ as H₂ and selectively absorbs CO₂ over CH₄. They further noted that some of the dipeptides tested had better capacity for CH₄ than other porous materials such as zeolites and certain metal-organic frameworks. With the variety of peptides that are available, the nanochannels could be customized to fit specific gases, Sozzani says.