Issue Date: May 14, 2007
Sorting Nanotube Isomers
Optical isomers of single-walled carbon nanotubes (SWNTs) now can be sorted from one another for the first time, thanks to a pair of chiral diporphyrin "tweezers" developed by researchers in Japan (Nat. Nanotechnol., DOI: 10.1038/nnano.2007.142). Commercially available SWNTs usually are a jumble of nanotubes of various lengths and diameters, and this lack of uniformity can make product development difficult. Nanotubes also possess a helical twist-either right- or left-handed-that gives them optical activity. Using one or the other of the chiral diporphyrin molecules, a group led by Xiaobin Peng and Naoki Komatsu of Shiga University of Medical Science was able to separate the optical isomers. The sorting process takes advantage of the diporphyrins' affinity to bind more tightly to one of the two helices (one diporphyrin shown). The researchers suspended the SWNTs and a chiral diporphyrin in methanol, followed by sonication and centrifugation. The resulting supernatant liquid is enriched with the preferred diporphyrin-SWNT complex. The diporphyrin is easily washed away, leaving behind the SWNT isomer.
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