Molecular Mixers

Laboratory stir bars may soon come in a new size: nanoscopic. Researchers at the University of Groningen, in the Netherlands, have synthesized rodlike molecular rotors of differing lengths that could one day help control chemical reactions and drug delivery (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja507711h). Group leader Ben L. Feringa had previously helped develop a molecular motor that spins when illuminated with ultraviolet light. But the compact compound couldn’t agitate solvents. So the current team grafted arms in the form of flexible hexadecyl chains or rigid phenylene-ethynylene oligomers onto the rotating molecule, extending its reach by up to 32 Å. The researchers characterized the resulting rotation about the molecule’s axle using NMR and UV-Vis spectroscopy. They found that the rotor stir rate dropped in increasingly viscous solvents and that the slowing was more pronounced for the longer, more rigid molecules. However, the larger stirrers moved more solvent. Feringa says arm length and rigidity could thus become variables for researchers to tweak when designing future nanomixers.