Seeing Superstructure

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Science  06 Apr 2001:
Vol. 292, Issue 5514, pp. 15
DOI: 10.1126/science.292.5514.15b

Polymers with π-conjugated backbones tend to form helical superstructures that can alternate between left- or right-handed forms. Bulk probes such as circular dichroism can reveal the net handedness of these polymers, but measuring the structural details underlying helicity and understanding how it can switch will require direct methods. Shinohara et al. synthesized a polyphenylacetylene that has both main-chain and side-chain chirality. Using scanning tunneling microscopy (STM), they resolved two helical chains that intertwined with quaternary or interchain helical interactions to form a right-handed superhelix with a pitch of 2 nanometers. This structure was readily altered by the STM, so further work will aim at fixing polymers to the substrate to probe superhelicity in more detail and to image transitions between right- and left-handed helices. — MSL

J. Am. Chem. Soc., in press.

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