IMAGING
CREDIT: NAT. BIOMED. ENG (TUMOR); PATRICK CRAMER/AAAS (EXPRESSOME)
▸ Quantum dots could expand live imaging When it comes to imaging live tissue, short-wavelength infrared (SWIR) radiation penetrates farther and scatters less than more-traditional near-IR and visible light. But a lack of agents that fluoresce brightly in the SWIR region (about 1,000 to 2,000 nm) has impeded the development of this type of imaging in the body. Moungi G. Bawendi, Oliver T. Bruns, and Thomas S. Bischof of MIT and coworkers have now created quantum dots that could expand SWIR live imaging This vasculature, at (Nat. Biomed. the edge of a tumor Eng. 2017, DOI: in a live mouse, was 10.1038/s41551mapped with SWIR017-0056). They emitting quantum coated InAs dots. cores with CdSe, CdS, CdSeZnSe, or CdS-ZnSe single or double layers and derivatized the resulting quantum dots with organic functional groups to customize them—for instance, to have long blood circulation times. The quantum dots emit SWIR radiation about an order of magnitude more strongly, are more stable, and have narrower and more tunable emission spectra than previous SWIR probes. In live imaging, the quantum dots also allow faster acquisition speeds and higher sensitivity than previous SWIR emitters. In live mice and in real time, the researchers used the emitters to measure metabolic turnover rates in several organs simultaneously, to quantify heartbeat and breathing rates, and to map brain vasculature. The quantum dots have constituents such as cadmium that aren’t necessarily suitable for human use, but the researchers hope to eventually make versions of the particles that are safe for use in the clinic.—STU
BORMAN
NANOMATERIALS
▸ Carbon nanobelt fashioned at last Decades before nanoscientists zapped graphite with an electrical discharge to
STRUCTURAL BIOLOGY
In bacteria, transcription and translation are coupled Just when you thought the fundamental processes of gene transcription and translation could offer no more surprises, researchers report that RNA polymerase and the ribosome, the macromolecules responsible for transcription and translation, respectively, can be physically coupled in bacteria. The conjoined machinery was named the “expressome” by Patrick Cramer of the Max Planck Institute for Biophysical Chemistry, Robert Landick of the University of Wisconsin, Madison, and colleagues, who solved the 7.6-Å-resolution coupled structure using cryo-electron microscopy (Science 2017, DOI: 10.1126/ Shown in these two views of the expressome, RNA science.aal3059). polymerase (top) is coupled to the ribosome (bottom) Textbooks worldin bacteria. The overall megamachine sequesters 30 wide describe the mRNA nucleotides within. transcription of DNA into mRNA by RNA polymerase as a separate process from the subsequent translation of mRNA into a protein by the ribosome. Decades ago, scientists observed that “these two processes may be coupled in bacteria,” Cramer tells C&EN. But most scientists thought it was just the rates of the processes that might be coupled. “We show it is also a physical coupling,” Cramer adds. The expressome is unlikely to be found in multicellular creatures, such as humans, where transcription and translation occur in separate cellular compartments. But, Cramer adds that the expressome may be widespread in bacteria and Archaea, something he hopes the research community will further investigate.—SARAH EVERTS
make the first carbon nanotubes, synthetic cessive Wittig reactions followed by a nickchemists were trying to craft similar, smallel-catalyzed aryl-aryl coupling reaction (Scier structures in their reaction flasks. But ence 2017, DOI: 10.1126/science.aam8158). the belt-shaped compounds these chemists Although they synthesized the nanobelt in were trying to create entirely only 0.2% overall yield, the Nafrom fused benzene rings were goya researchers made enough tough to come by. Chemists of it to get crystals for X-ray observed one such structure analysis. The crystal structure fleetingly via mass spectromreveals that the bonds at the etry a decade ago, but no one nanobelt’s equator have benhas been able to synthesize and zene-like bond lengths of about isolate enough of these carbon 1.4 Å, while the remaining bonds Nanobelt nanobelts for further study— have single- and double-bond until now. Kenichiro Itami, Yasutomo Secharacters. The researchers believe the gawa, and coworkers at Nagoya University nanobelts could serve as seed molecules for managed to fashion a nanobelt out of 12 making structurally well-defined carbon aromatic rings (shown) via a series of sucnanotubes.—BETHANY HALFORD APRIL 17, 2017 | CEN.ACS.ORG | C&EN
9
