SCIENCE & TECHNOLOGY CONCENTRATES
EACH STEP SLOWER THAN THE ONE BEFORE
Lei Li of Washington State University has been captivated by the idea of using smartphones to perform spectrophotometry since researchers at the University of Illinois, Urbana-Champaign (UIUC), introduced it a few years ago. Because smartphones are ubiquitous and inexpensive compared with conventional analytical instruments, smartphone spectrometers are promising tools for performing biosensing assays and medical diagnostics outside the clinic or laboratory. Li and his team are working to make Light travels these smartphone through a cuvette (left) and lenses devices even more in the black tube accessible with an before passing assist from another through the DVD cheap and common grating and into the technology—the DVD phone’s camera. (ACS Sens. 2016, DOI: 10.1021/acssensors.5b00204). UIUC-style smartphone spectrometers rely on diffraction gratings to spread white light into a rainbow spectrum before entering a phone’s camera lens. That spectrum can then be used in spectroscopic assays, such as ELISA. But commercial glass diffraction gratings cost around $100, Li says. Plastic chips cut from $1.00 DVDs can diffract light into useful spectra, the team demonstrated. The researchers spiked cuvettes of tap water with paraoxon and showed that their platform could detect the toxin at nanomolar concentrations, which is comparable to the performance of commercial instruments, Li tells C&EN.—MD
LI RESEARCH GROUP
Unlike conventional metabolic pathways that lead to a single product, diversitygenerating pathways produce many compounds. Understanding such diversity-generating pathways could help researchers develop combinatorial biosynthetic pathways. A team of researchers led by Baldomero M. Olivera and Eric W. Schmidt of the University of Utah shows how one such pathway from cyanobacteria differs significantly from conventional metabolic pathways. The researchers focused on the tru pathway, which synthesizes a diverse family of macrocyclic peptides called patellins (Proc. Natl. Acad. Sci. USA 2016, DOI: 10.1073/ pnas.1525438113). To study the four-enzyme pathway, the researchers expressed it in Escherichia coli bacteria. They found that they could greatly increase the yield of patellins by adding cysteine, which releases hydrogen sulfide that modulates the enzymes’ activity. In the process of figuring out the cysteine effect, they learned that each step in the pathway is much slower than the preceding steps. This results in the accumulation of intermediates, which is in sharp contrast to conventional pathways, in which the first step is usually the rate-limiting step to avoid such accumulation.—CHA
BIOSENSING GOES STRAIGHT TO DVD
O
Despite decades of work trying to control plague, the illness is still a major health concern in Madagascar. A 2014 outbreak in that country infected more than 335 people at its peak and claimed at least 79 lives, according to the World Health Organization. Plague is Cl primarily transmitted Cl Cl to people from rats Cl via the Oriental rat flea Xenopsylla cheopis. Efforts to keep Cl Cl the disease in check focus on controlling Dieldrin the flea population with insecticides. But a study by Adélaïde Miarinjara and Sébastien Boyer, of the Pasteur Institute of Madagascar, reveals that of 12 standard insecticides, six—including the most commonly used insecticide deltamethrin—are ineffective against local fleas (PLOS Neglected Trop. Dis. 2016, DOI: 10.1371/journal.pntd.0004414). Miarinjara
and Boyer studied eight flea populations from around the island and found that only one insecticide—dieldrin—was 100% effective on all populations. Dieldrin is an organochlorine compound that’s toxic to mammals and known to accumulate in the environment. It hasn’t been used in Madagascar since 1993. To prevent the spread of plague, Miarinjara and Boyer recommend exploring alternatives to insecticide dusting in homes, including rat control and insecticide-laced bait boxes for rats, which would reduce overall insecticide use.—BH
MOF MEMBRANES STAND UP TO WATER The impressive capacity of various metalorganic framework (MOF) compounds to adsorb gases—especially toxic gases such as ammonia—has raised interest in these porous solids for use as gas-mask filtraCEN.ACS.ORG
23
FEBRUARY 8, 2016
The structure (micrograph) and ammonia capacity of poly(vinylidene difluoride)-HKUST-1 membranes (2.5-cm square sample, blue), are unaffected by high levels of humidity.
tion materials. Filter materials are typically used as powders held in a canister fitted to the front of gas masks. But gas-mask designers aim to do away with the obtrusive canister, favoring instead a streamlined design in which the mask and filter are integrated into a low-profile unit. That design calls for making easily
JARED B. DECOSTE/ECBC
PLAGUE-CARRYING FLEAS RESIST INSECTICIDES
SCIENCE & TECHNOLOGY CONCENTRATES
processable MOF membranes, which has been challenging. A team led by Jared B. DeCoste of the Edgewood Chemical Biological Center at Aberdeen Proving Ground and Seth M. Cohen of the University of California, San Diego, reports success in making robust poly(vinylidene difluoride)HKUST-1 membranes (Chem. Sci. 2016, DOI: 10.1039/c5sc04368a). HKUST-1 is a copper-based MOF, in which paddle-wheel Cu dimers are linked by benzene-1,3,5-tricarboxylate units. High levels of humidity decompose powdered forms of HKUST-1, lowering gas-uptake capacity. In contrast, HKUST-1-polymer membranes retained their mechanical stability and theoretical ammonia capacities even after a monthlong exposure to 90% relative humidity.—MJ
NANOPARTICLES TRACK KIDNEY DISEASE Kidney disease is known as a silent killer. That’s because the markers physicians look for to diagnose the disease, such as urea and creatinine levels in the blood, often appear normal even when up to 75% of kidney function has been lost. One inexpensive, noninvasive method for imaging kidneys is to use near-infrared fluorescence imaging to follow an organic dye as it travels through the organs. But such dyes have problems: They often don’t provide enough contrast in the kidney, and they accumulate in background tissues. Researchers led by Jie Zheng of the University of Texas, Dallas, previously reported that glutathione-coated gold nanoparticles work better than the dyes as fluorescence imaging agents for cancer detection. The nanoparticles, Zheng notes, are inexpensive and clear the body easily. Now Zheng’s lab has shown that the nanoparticles can differentiate between various stages of kidney dysfunction in a mouse model (Angew. Chem. Int. Ed. 2016, DOI: 10.1002/ anie.201511148). If the results translate to people, doctors would be able to easily tell the difference among kidneys with normal function, mild dysfunction, and severe dysfunction—something they’re currently unable to do.—BH
WATER HELPS FORM SULFATE SALT IN AIR Sulfate salts in the atmosphere play a critical role in nucleating and enlarging
O H aerosol particles, N H O which can seed H S H precipitation, O H reflect or absorb H O solar radiation, and O H harm health. But H O the mechanisms H behind the formaIn a proposed tion of salts such as mechanism for ammonium sulfate atmospheric have yet to be fully NH4HSO4 detailed. Compuformation, one H2O tational work now (red) breaks apart to give OH– to SO3 indicates that amand H+ to another monium bisulfate H 2O (green). The can form from the H2O that receives pollutants ammonia the H+ transfers and sulfur trioxide, one of its original mediated by water H+ ions to NH3 to form NH4+. (J. Am. Chem. Soc. 2016, DOI: 10.1021/ jacs.5b13048). NH3 is emitted by agricultural operations and SO3 by fossil-fuel burning. A team at the University of Nebraska, Lincoln, led by Joseph S. Francisco and Xiao Cheng Zeng found that water molecules from a water trimer or droplet form a looplike network connecting NH3 and SO3 molecules. The network facilitates water-mediated proton transfer in which one water breaks apart, giving OH– to SO3 to form HSO4– and an H+ to another water. The water that receives the H+ transfers one of its original H+ ions to NH3 to form NH4+. The reaction has a low barrier and consequently may play a significant role in the formation of aerosol particles.—JK
leagues proposed this reaction pathway, noting that methanol is more reactive than methane. Methane, which exists in giant clouds in the interstellar medium, has long been presumed to be the starting block for the formation of more complex interstellar hydrocarbons. However, over the past two decades, astronomers have discovered interstellar clouds containing methanol as well. Olah’s group, citing results of their experiments and computations involving methanol carried out over the years, points out numerous ways in which methanol chemistry can lead to hydrocarbon production. For example, when methanol is exposed to intense radiation such as that in outer space, hydrocarbons can be formed through oligomerization of an intermediate, ethylene.—EKW
NANOCATALYSTS REVEAL STRUCTURE SENSITIVITY
A combined molecular-beam and quantum-simulation study that explores the catalytic behavior of tiny platinum clusters calls into question a well-established precept regarding the influence of structure on the reactivity of solid catalysts (Nat. Commun. 2016, DOI: 10.1038/ ncomms10389). Years of experiments have shown that platinum-catalyzed hydrogenation of ethylene to ethane does not depend on the surface structure of the platinum crystallites. This archetypal “structure-insensitive” reaction has long stood in contrast to structure-sensitive reactions, for example, ammonia syntheMETHANOL REACTIONS sis on iron crystals. These classifications have influenced strategies for enhancing IN SPACE catalyst performance. Now, a team led The radiation-induced conversion of by Ueli Heiz of the Technical University methanol may be an important pathof Munich and Uzi Landman of Georgia Tech has shown that ethylene hydrogena+ 2 ••CH2 + 2H3O 2 CH3OH2 tion is indeed sensitive to the structure of platinum particles, if those particles lie at the low end of the CH3OH2+ + H2C CH2 H3C CH CH2 + H3O+ nanoscale regime. By studying size-selected Interstellar radiation way for the platinum clusters comcan set off methanol’s production of posed of nine to 13 atoms, they found that conversion to hydrocarbons in the nine-atom cluster does not catalyze hydrocarbons. the interstellar ethylene hydrogenation but the larger environment, acparticles do catalyze the reaction with according to a new study (J. Am. Chem. Soc. tivity that increases with cluster size. Cal2016, DOI: 10.1021/jacs.6b00343). Uniculations show how the number of atoms versity of Southern California chemistry dictates cluster geometry, which controls professor George A. Olah, who won the the clusters’ electronic properties under1994 Nobel Prize in Chemistry, and colpinning surface catalysis.—MJ CEN.ACS.ORG
24
FEBRUARY 8, 2016
