news of the week MAY 24, 2010 EDITED BY WILLIAM G. SCHULZ & ALICIA J. CHAMBERS
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C12H25O ered dendrimers in 1979. “It’s O O the first step toward a huge C12H25O family of dendrimersome structures. I can see an endO O C12H25O less number of libraries that SUPRAMOLECULAR CHEMISTRY: Selfone can construct by varying assembled dendrimer-based structures the structures of Janus denC12H25O O could deliver drugs, other substances drimers, so this paper is just O C12H25O the tip of the iceberg.” O O Liposomes and polymerC12H25O INY BUBBLES and other nanostructures that somes—synthetic vesicles form spontaneously when highly branched made from phospholipids and bifunctional compounds are put in water have polymers, respectively—have similar uses as delivery been discovered and characterized. The nanostrucvehicles but several drawbacks: Liposomes tend to be tures may be more broadly useful for delivering drugs unstable and have short lifetimes; polymersome memand other substances than similar nanostructures branes are too thick to accommodate biological recepmade from phospholipids or polymers. tor and pore-forming proteins; and both liposomes and The new nanostructures form from “Janus polymersomes adopt a wide range of sizes when they dendrimers”—dendrimers (repetitively branched form and are difficult to derivatize. molecules) that branch out from a point and are amDendrimersomes are stable for longer periods of phiphilic (polar on one side and nonpolar time, are highly uniform in size, have MORE ONLINE on the other). Chemistry professor Virgil the proper dimensions to accommodate Percec of the University of Pennsylvania membrane-spanning proteins, and are and coworkers report in Science that a new family of easily functionalized. vesicles, tubes, disks, and other shapes—which they Several groups have been studying Janus dendrimers call “dendrimersomes”—self-assemble from the Janus for nearly two decades, although they were so named dendrimers in water (2010, 328, 1009). more recently. In the new study, Percec and coworkers Dendrimersomes can act as hosts for a variety of synthesized more than 100 Janus dendrimers, screened guest molecules and could therefore have widespread them for supramolecular self-assembly in water, and applications as delivery vehicles for drugs, genes, imfound that all adopted useful shapes. aging compounds, diagnostic agents, cosmetics, and The technique is reminiscent of the versatility with other substances. which “globular proteins can assemble into viral capsids “This is truly groundbreaking work,” says Donald A. and other complex biological nanostructures,” says Tomalia of Central Michigan University, who discovKaren L. Wooley, a polymer chemist and nanomedicine expert at Texas A&M University. Jan C. M. van Hest, a specialist in bioinspired NANOSTRUCTURE Dendrimersome cross-section materials at Radboud University Nijmegen, in shows its cell-membrane-like bilayer. the Netherlands, says it’s noteworthy that “dendrimersomes can be tailor-made with a high level of size control. Creating monodisperse vesicles is always difficult, but seems to be easier with Janus dendrimers.” Dendrimersomes “are truly unique and highly differentiated from traditional liposomes and polymersomes, which are very fragile and very polydisperse,” Tomalia says. “They are incredibly robust and very monodisperse, and they allow you to do chemistry on the surface.” Tomalia believes it will be possible to select Janus dendrimers with specific sizes, shapes, and surface chemistries and then use them as building blocks to create dendrimersomes with designed structural and functional characteristics.—STU
COURTESY OF VIRGIL PERCEC
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BORMAN WWW.CEN-ONLINE.ORG
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MAY 24, 2010
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Janus dendrimers are amphiphilic, with nonpolar (red) and polar (blue) ends.
