Science Concentrates SYNTHESIS
▸ Lighting up and tracking microRNA Researchers have developed a light-induced chemical reaction that visualizes RNA in live zebrafish embryos without interfering with cell processes. In previous work, the team applied the method to cells in culture. But now the researchers have developed the method as the first technique for detecting specific strings of nucleic acids in live vertebrates that doesn’t require genetically modifying the organisms. What’s more, the method is sensitive enough to visualize the expression of microRNAs, which are small noncoding RNAs that act as puppet masters of gene expression (ACS Cent. Sci. 2016, DOI: 10.1021/acscentsci.6b00054). Nicolas Winssinger, Marcos Gonzalez-Gaitan, and colleagues at the University of Geneva designed two nucleic acid probes that each
Nucleic acidbased probes illuminate expression of target microRNA sequences in neural cells (top) and cells involved in tail and fin development (bottom) in live zebrafish embryos. complement and bind to adjacent halves of a target microRNA sequence. The researchers conjugated one probe to a ruthenium complex that absorbs visible light and the other to a rhodamine dye that lights up when its azide bonds are cleaved. When the probes attach to the target sequence, the two reagents come close enough to react. Shining a light on the sample activates the ruthenium, which reduces the azide in the rhodamine conjugate and thereby allows it to fluoresce. The researchers designed probes against three different microRNAs: one expressed in neural cells, another in muscle cells, and a third in cells involved in forming the pectoral tail and fins. After the embryos were exposed to light for 30 minutes, confocal imaging revealed that each probe set illuminated the expected type of tissue and the probes tracked microRNA expression over time during embryo development.—ALLA
KATSNELSON, special to C&EN
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C&EN | CEN.ACS.ORG | JUNE 13, 2016
Chiral tertiary alcohols forged with copper To make a tertiary alcohol from a ketone, chemists will often use an organometallic reagent to muscle its way onto the ketone’s carbonyl carbon. But there are limitations to which substrates you can use in this reaction, because the organometallics will react with substituents other than the target carbonyl. Also, to do the reaction asymmetrically, which is desirable to make drug candidates, for
Ph + O P
Ph Ph = phenyl
Ph
CuH Ph
Ph
Ph Ph
HO
P Ph
example, chemists often have to add stoichiometric amounts of chiral additives. Seeking a method that overcomes these burdens, a team led by MIT’s Stephen L. Buchwald and the University of Pittsburgh’s Peng Liu has developed an asymmetric tertiary alcohol synthesis that uses catalytic amounts of copper hydride and a chiral phospholane ligand to couple a polyunsaturated hydrocarbon, such as an ene-yne, and a ketone (Science 2016, DOI: 10.1126/science.aaf7720). The reaction (one example shown) tolerates a range of coupling partners and proceeds in high yield and with high enantioselectivity. In many instances, the chemists built complex molecules with two adjacent chiral centers. With further ligand optimization, the reaction will become “a powerful tool for the asymmetric addition of olefin-derived nucleophiles to carbonyls that will be of broad synthetic utility,” the researchers believe.—BETHANY HALFORD
NANOMATERIALS
▸ Sticky nanopollen particles pack an antibacterial punch Supersticky nanoparticles that mimic the shape of pollen grains can deliver lysozyme—a protein found in tears and saliva— directly to bacteria in lab tests, boosting the protein’s antibacterial potency (J. Am. Chem.
Soc. 2016, DOI: 10.1021/jacs.6b00243). To make the particles, Chengzhong Yu of the University of Queensland and colleagues first created a polymer core and then coated it with a layer of silica mixed with the same polymer. Burning away the polymer left a hollow silica particle with a spiky, negatively charged surface to which the positively charged lysozyme molecules could stick. When naked spiky particles were incubated with Escherichia coli bacteria, almost 10 times as many adhered to the bacteria as smooth silica nanoparticles. Then when loaded with lysozyme, the spiky nanopollen particles completely inhibited bacterial activity for three days in culture, whereas smooth particles or free-floating lysozyme failed to fully inhibit bacterial growth. Yu’s team plans to test the lysozyme-loaded particles in place of antibiotics in animal feed as a way to combat the problem of antibiotic overuse in factory farming.—ALLA KATSNELSON,
special to C&EN Spiky silica nanoparticles, minus lysozyme, adhere to the surface of a rodshaped cell.
CREDIT: ACS CENT. SCI. (ZEBRAFISH) J. AM. CHEM. SOC. (NANOPOLLEN)
IMAGING
FORENSIC SCIENCE
CREDIT: OKSANA MIZINA/SHUTTERSTOCK (BLOODSTAIN) SCIENCE (ACTIVATION COMPLEX); NAT U RE (GLASS FILAMENT)
▸ Crime scene test puts blood on the clock A new forensic blood test could allow law enforcement to determine whether blood at a crime scene came from a minor or an adult and how recently the person parted with it (Anal. Chem. 2016, DOI: 10.1021/ acs.analchem.6b01169). Jan Halámek of the University at Albany, SUNY, and colleagues focused on alkaline phosphatase (ALP), an enzyme that hits peak levels in the blood during adolescence before decreasing sharply around age 17 for females and 18 for males. The researchers tested 100 samples of human serum spiked with randomly generated concentrations of ALP chosen to match natural enzyme levels found in juveniles and adults. The team determined the ALP concentrations with a known assay that is catalyzed by the enzyme: the conversion of p-nitrophenyl phosphate to p-nitrophenol, a yellow compound that can be measured using spectrophotometry. A statistical test on the measurements revealed that the assay had a 99% probability of differentiating young males from older ones and a 100% probability of differentiating young females from older ones, even after the samples sat on a lab bench near a window for 48 hours to simulate crime scene conditions. The researchers also developed a model based on ALP activity to predict how long blood has been at a crime scene.—
A glass filament, about 20 µm in diameter and shown as a black line, reversibly splits into uniform pieces when its polymer coating is stretched.
NANOMATERIALS
Opening and closing nano venetian blinds Researchers led by Soroush Shabahang and Ayman F. Abouraddy at the University of Central Florida are making nanoparticles with their bare hands––and some crafty materials science. To create uniform micro- and nanoscale structures, the team is simply stretching fibers and sheets made from a ductile polymer composite containing either a brittle core or coating (Nature 2016, DOI: 10.1038/nature17980). The team’s process is compatible with a variety of ductile materials, such as polycarbonate and polyethersulfone, that can be stretched at room temperature without breaking. The method also works with a variety of brittle materials, including glass, gold, and even ice. Stretching a fiber or sheet of one of the composites with a pair of pliers forces the polymer’s molecules into alignment, which causes the fiber or sheet to contract. But this contraction begins in a small region and then spreads outward like a wave, traveling through the polymer layer. This wave acts like a pair of scissors to cut the brittle component of the material into pieces at regular intervals, Abouraddy says. The researchers can then dissolve the polymer to retrieve the uniform brittle pieces, or instead they can repair the composite by heating it. This reversible snip-and-repair method opens and closes gaps in the brittle component, similar to opening and closing slats in venetian blinds, a process that could be useful for nanostructured dynamic camouflage, Abouraddy says.—MATT DAVENPORT
MELISSA PANDIKA, special to C&EN
BIOCHEMISTRY
▸ Transcription activation complex analyzed To better understand how DNA is transcribed into RNA, scientists have long been trying to obtain a detailed structure of a protein-DNA complex that initiates and regulates transcription of a specific gene. But such complexes have been hard to crystallize. Richard H. Ebright and coworkers at Rutgers University have now found a thermophilic bacterial complex that forms crystals readily and have determined its 4.4-Å structure (Science 2016, DOI: 10.1126/science.aaf4417). The complex includes a transcription activator
The detailed structure of thermophilic transcription activation complex; RNA polymerase is black, gray, and green; initiation factor is yellow; transcription activator protein is light blue; and DNA is red, pink, violet, and blue. protein, an initiation factor, RNA polymerase, a DNA template, and an RNA primer. The crystal structure reveals that a first set of protein-protein interactions between the activator and RNA polymerase helps the enzyme bind DNA and a second set of protein-protein interactions helps the enzyme unwind DNA so it can be transcribed. “It’s a lovely picture that you can tell is right” from decades of earlier biochemistry and genetics experiments on similar transcription activation complexes, comments transcription initiation
expert Deborah M. Hinton of the National Institute of Diabetes & Digestive & Kidney Diseases.—STU BORMAN JUNE 13, 2016 | CEN.ACS.ORG | C&EN
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