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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