Improving upon self-assembly

Inspired by the principle of the vernier scale for making precise measurements, chemists have reported a technique for using smaller templates to assemble rings of subunit molecules larger than the templates, thus providing a way to make large molecules from smaller molecules that is more precise than random self-assembly. From ScienceNews, written by Rachel Ehrenber “Building big molecules bottom-up“:

Just tossing mortar and bricks together won’t yield a tidy structure, but chemists must often resort to similar measures when building molecules the size of proteins, the workhorses of cells. Now researchers have developed a cleaner strategy for constructing such compounds. By employing one kind of molecule as a template, scientists can string together small biologically important molecules into larger ringed structures with unprecedented precision and no mess, a team reports in the Jan. 6 Nature [abstract].

The new technique hits a previously inaccessible sweet spot, yielding hefty molecules that approach the size of proteins, the macromolecules that are the movers and shakers of the cellular world. The method could become a broadly used tool for building big molecular structures, including more templates to build even larger compounds. And because the rings are built from strands of compounds of the same class as the pigment chlorophyll, the large loops may exhibit unusual electrical properties and could help researchers better understand how the pigments that drive photosynthesis harvest light.

“We’d like to think the use would be very general — there’s no reason it shouldn’t be,” says chemist Harry Anderson of the University of Oxford in England, who led the new work. “People often want to make objects that are a particular size and shape.” …

In the example published, the researchers used a template molecule with six binding sites for porphyrin molecules and building block strands of four porphyrin molecules each. Because six is not a multiple of four, three building block strands wrapped around two template molecules to give a one-to-one correspondence between number of binding sites and number of porphyrins so that after the strands were joined and the templates removed, the product was a ring of 12 porphyrin molecules 4.7 nm in diameter. Clearly a neat trick, but it will be interesting to see just how general this approach will prove to be and just how varied will be the molecular architectures produced.

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