Science Concentrates IMAGING
▸ Photoacoustic molecular probe detects hypoxia
BIOCATALYSIS
▸ Chiral organoboranes built by bacteria
Twenty days after deposition on aluminum foil, a fingerprint developed with luminescent nanoparticles (green) has ridges with better definition than one dusted with commercial black powder (gray).
FORENSIC SCIENCE
Luminescent nanoparticles leave a glowing fingerprint Nanoparticles with long-lived luminescence have been shown to provide sharp images of otherwise invisible fingerprints, offering better resolution than does standard fingerprinting for forensic investigation, the researchers say (Anal. Chem. 2017, DOI: 10.1021/acs.analchem.7b03003). Quan Yuan of Wuhan University and colleagues synthesized Zn2GeO4 nanorods containing 1.0% gallium and 0.5% manganese that are similar to persistently luminescent nanoparticles they have used for biomedical imaging. The researchers modified the nanoparticle surface with activated esters that can bond to amino acids left behind in the ridges of fingerprints. Fingerprints developed with the glowing nanoparticles show more defined ridges than ones dusted with conventional black fingerprint powder. The particles also reveal clear fingerprints even 60 days after the prints are deposited—a potential benefit of this approach since the proteins, oils, and perspiration that form invisible fingerprints decompose over time, making the detection of aged prints with traditional techniques challenging. Yuan says a forensic research institute in Beijing is interested in further testing the nanoparticles.—MELISSAE FELLET, special to C&EN
Although there are natural products that contain boron, the organisms that make these compounds do so by using small molecules that react spontaneously with boric acid in the environment. No enzymes are involved. What’s more, natural CH3 organisms that create carbon-bo+ ron bonds, or organoboranes, are N – unknown. But that didn’t stop BH3 + Frances H. Arnold, S. B. Jennifer N Kan, Xiongyi Huang, and coworkCH3 ers at Caltech, who reasoned that
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C&EN | CEN.ACS.ORG | DECEMBER 4, 2017
(Nature 2017, DOI: 10.1038/nature24996). After genetic adjustments to the amino acids around the enzyme’s heme unit, the Caltech team was able to boost both the yield, enantioselectivity, and turnover of the biocatalyst. The researchers applied the bacterial catalyst to different boron reagents and diazoesters, creating a series of organoboranes. They also used trifluoromethyl-substituted (diazomethyl) benzene as a substrate to make chiral α-trifluoromethylated organoboranes—a valuable chiral building block. “Microorganisms are powerful alternatives to chemical methods for producing E. coli + CH3 pharmaceuticals, agrochemiengineered with N cals, materials and fuels,” the cytochrome c enzyme – researchers write. “Borylation N BH 2 chemistry can now be added to O H3C the vast synthetic repertoire of biology.”—BETHANY HALFORD O
with a little genetic tinkering they could create organoborane-making bacteria. The new approach could embellish current methods to make organoboranes, which are important synthetic building blocks for organic chemists. The researchers took Escherichia coli cells that were engineered with wild-type cytochrome c from the geothermal bacterium Rhodothermus marinus and incubated them with an N-heterocyclic carbene borane and a diazoester, finding they could create a chiral organoborane (reaction shown) in modest yield and with good enantioselectivity
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C R E D I T: A NA L . C H EM .
Hypoxia—damage to tissue caused by low oxygen levels—can be difficult to detect. Jefferson Chan and coworkers at the University of Illinois, Urbana-Champaign, have developed a small molecule probe they call HyP-1 that improves hypoxia detection by using photoacoustic imaging (Nat. Commun. 2017, DOI: 10.1038/s41467017-01951-0). In photoacoustic imaging, near-infrared light induces temperature and pressure changes in tissue that result in the production of ultrasound waves. Because sound scatters less in tissue than light does, the sound waves can be used to produce images from deep in tissue. HyP-1 contains an N-oxide trigger that undergoes reduction to the corresponding aniline (red-HyP-1) in the absence of oxygen. This reduction depends on competitive binding of oxygen to the heme iron in various enzymes. Because red-HyP-1 absorbs light at longer wavelengths than HyP-1 does, any photoacoustic signal produced by excitation at those longer wavelengths corresponds exclusively to red-Hyp-1, which indicates hypoxia. The researchers used HyP-1 to detect hypoxia in cultured cells, in tumors in mice, and in hind limb ischemia in mice. Although HyP-1 was designed for photoacoustic imaging, the fact that both it and red-HyP-1 fluoresce in the near-infrared means that the probe pair can also be used for comparative fluorescence imaging.—CELIA ARNAUD
