Templating: Small templates and building blocks combine to make extra-large structures
A circular templating approach yields 4.7-nm-diameter macrocycles from small, easily prepared templates, reports a group of British researchers (Nature, DOI: 10.1038/nature09683).
The method is based on Vernier complexes, which are precise assemblies generated by the coming together of components with different numbers of binding sites—for example, different four- and six-membered building blocks. Past experiments with Vernier systems, however, have all involved linear complexes. In the new work, a group led by Harry L. Anderson, a chemistry professor at Oxford University, experimented with radial templates and linear building blocks to produce 12-membered porphyrin nanorings.
Realizing that Vernier complexes can be circular “is a significant step forward in the science of template-directed synthesis,” says J. Fraser Stoddart, a chemistry professor at Northwestern University. The technique should enable and ease the preparation of macromolecules with consistent size and shape, he adds.
Anderson and coworkers used a circular hexapyridyl template with six binding sites. They combined the template with four-membered zinc porphyrin chains, with the porphyrins linked by butadiyne groups. Three porphyrin tetramers can bind around and occupy all of the binding sites on two of the templates, linking the two in the process. The researchers then oxidatively coupled the template-bound porphyrin tetramers to form a figure-eight compound. Dissociating the porphyrins from the templates produced a 12-membered, π-conjugated porphyrin nanoring, among the largest of similar macrocycles ever synthesized. … rest