SCIENCE & TECHNOLOGY CONCENTRATES
High-resolution mass spectrometry is a wonder for identifying similar molecules in a mixture, but users of the technique still have a hard time distinguishing isomers. Oleg V. Boyarkin and Vladimir Kopysov of ETH Lausanne and Alexander Makarov of Thermo Fisher Scientific have found a way to improve structural identification of isomeric biomolecules by combining ultraviolet spectroscopy with high-resolution mass spec (Anal. Chem. 2015, DOI: 10.1021/ acs.analchem.5b00822). They use UV laser pulses to break apart cryogenically cooled ions and measure the mass spectrum of the resulting fragments with an Orbitrap mass spectrometer. The two-dimensional spectra provide structurally specific fingerprints, which the researchers used to distinguish peptide stereoisomers and peptides that differ only in the site of phosphorylation. They were even able to quantitate the relative composition of mixtures. “The fundamental science is very nice, but I do not envision this becoming a practical analytical method,” says James P. Reilly of Indiana University. Few peptide residues absorb UV light, and high-resolution UV spectra of various peptides are not predictable, Reilly notes. For most labs, the combination of a liquid helium-cooled ion storage system, an Orbitrap mass spectrometer, and a tunable UV laser would be prohibitively expensive, he says. But practicality, he adds, “is not everything.”—CHA
PEROVSKITE NANOWIRES WIN LASER BATTLE Lead halide perovskites are already famous for their ability to harvest solar energy, and now researchers are starting to show that the semiconductors make for promising lasers. Last year, British researchers demonstrated that lasers made with perovskite thin films and powered by light had a quantum efficiency of about 70%, meaning a laser emitted seven photons for every 10 absorbed. Chemists led by Song Jin of the University of Wisconsin, Madison, and Xiaoyang Zhu of Columbia University say they have now pushed that efficiency to nearly 100% using perovskite nanowires (Nat. Mater. 2015, DOI: 10.1038/ nmat4271). The team grew the wires by first depositing a film of lead acetate on a glass substrate and submerging the film in a concentrated methylammonium halide Perovskite solution. Lead slowly dissolved in the solution, allowing nanowires have single-crystal lead halide perovskite nanowires to grow. rectangular cross Each nanowire’s high crystalline quality contributes to sections. its quantum efficiency, which Zhu says is so high it’s “unheard of” in other semiconductor materials. The researchers are now working to power their lasers with electricity rather than light, which could pave the way to miniaturized optoelectronic devices.—MD
containing sulfur, selenium, or tellurium (M2E2 units) were discovered in 2001 and found to have unusual bond distances. That led to some ambiguity as to how to best describe the compounds’ electronic structure. Three possibilities emerged: singly bonded S22– units, three-electron A NEW SULFIDE IN TOWN half-bonded units that are formally S23– Chemists don’t take oxidation states with mixed-valent nickel atoms, and two lightly, and when someone suggests a new independent S2– units. The new paper one might be in the offing, provides crystallographic the extraordinary claim reand spectroscopic evidence quires extraordinary proof. supported by computaS A research team led by John tional analysis that all three Ni Ni F. Berry of the University of states are distinct and that S Wisconsin, Madison, is now M2E2 compounds occur in reporting its proof for a new quantized oxidation states, oxidation state for sulfur, S23– rather than displaying a (J. Am. Chem. Soc. 2015, DOI: continuum of E2 bonding Ni2.5+/Ni2.5+/S23– Subsulfide 10.1021/ja511607j). This subinteractions.—SR sulfide, as the researchers call it, joins the well-known sulfide, S2–, WIND AND RAIN POWER and disulfide, S22–, states. Berry says the initial suggestion for subsulfide, found in SMART WINDOWS a transition-metal complex in which an S2 unit coordinates to a pair of nickel atSo-called smart windows, which use redox oms, was controversial. Nickel complexes chemistry to darken with the flip of a switch, CEN.ACS.ORG
24
APRIL 20, 2015
have been a reality for several years. But efficiently powering them has been problematic. Using batteries for every window is impractical, and integrating them with solar cells inevitably obscures some of the window. Researchers at Georgia Tech, led by Zhong Lin Wang, believe they have a solution to this power problem. Wang’s group has been working on triboelectric nanogenerators, or TENGs, which are devices that convert motion into electricity. To make a self-powered smart window, they coupled a device that darkens as a result of redox chemistry to two types of TENGs (ACS Nano 2015, DOI: 10.1021/acsnano.5b00706). One of the TENGs sits atop the device and harvests electrostatic energy from falling raindrops. The other gathers energy when blowing wind moves two of the device’s layers, which are separated by tiny springs, across one another. Prussian blue nanoparticles, which can be reduced by the TENGS to colorless Prussian white nanoparticles, make up the color-changing layer of the window, and ZnHCF nanocubes constitute the device’s ion storage material. The researchers say they think TENGs will find use in
NAT. MATER.
TWO-PRONGED PEPTIDE FINGERPRINTING
SCIENCE & TECHNOLOGY CONCENTRATES
jacs.5b02313). To demonstrate the principle, which can be used to reduce waste and bypass purification steps, M. Ángeles Monge and coworkers at the Materials Science Institute of Madrid prepared three isostructural metal-organic framework (MOF) compounds, each containing one type of metal—aluminum, gallium, or indium. They used the MOFs individually to catalyze a one-pot Strecker reaction between benzaldehyde, trimethylsilyl cyanide, and aniline. The aluminum MOF generated an α-aminonitrile, the gallium MOF formed a cyanosilyl derivative, and the indium MOF yielded an imine. The team also prepared mixed indium-gallium MOFs in which the metals, located at equivalent lattice positions, were present in various ratios. They found that tuning the indium-to-gallium ratio altered the reaction rates and product selectivities. For example, a gallium-rich MOF functioned similarly to the aluminum compound and catalyzed formation of the α-aminonitrile in 96% yield in 30 minutes. In contrast, an indium-rich MOF led to just 64% yield after four days.—MJ
ANOTHER ROUTE TO PROTEIN DISPOSAL In the primary pathway for discarding proteins, cells tag targeted proteins with ubiquitin and deliver them to the proteasome, the cell’s garbage disposal. But there’s another protein disposal pathway that doesn’t involve ubiquitin and that uses only the central core of the proteasome, a portion called the 20S proteasome. Biologists previously thought this second pathway was a passive, unregulated process. Michal Sharon and coworkers of Israel’s Weizmann Institute of Science now report that the process is regulated at least in part by a Parkinson’s disease-related protein called DJ-1, which is in tissues throughout the human body (Nat. Commun. 2015, DOI: 10.1038/ncomms7609). The researchers found that DJ-1 both inhibits and indirectly activates protein degradation. It inhibits protein degradation by directly binding to the 20S proteasome. But during oxidative stress, DJ-1 activates a protein called Nrf2, which is itself an activator of the 20S proteasome. Sharon and coworkers are now studying where DJ-1 binds the proteasome to figure out the mechanism by which it exerts its effects.—CHA
O R1
R2
+ R3NH2 + (CH3)3SiCN
In
Ga
MOF catalyst
J. AM. CHEM. SOC.
Tuning the metal ion ratio in multimetal catalytic MOFs affects the outcome of these multicomponent reactions.
IMPROVED TOMOGRAPHY SEES THROUGH ART Museum conservators often want to visualize layers of varnish and paint on artwork, for example, when they need to replace varnish on an old masterpiece during restoration. A research team based in England has now improved a technique called ultrahighresolution Fourier domain optical coherence tomography so that it can see through a painting’s layers noninvasively—and with
ENZYME’S ELUSIVE PROTON DONOR FOUND
METAL SWITCHEROO TUNES SELECTIVITY Changing the ratio of metal ions in multimetal catalytic framework compounds can be an effective strategy for steering multicomponent reactions toward a desired product, according to researchers in Spain (J. Am. Chem. Soc. 2015, DOI: 10.1021/
C2-ene adduct as a molecular probe of the reaction has now enabled them to identify an active-site tyrosine as the elusive proton donor (Nat. Chem. Biol. 2015, DOI: 10.1038/ nchembio.1794). This new understanding also enabled them to reengineer the enzyme to catalyze the reaction with inverted stereochemistry.—SB
O PT. EXPR ESS
other self-powered systems such as flexible displays, wearable electronics, and energyefficient buildings.—BH
Researchers have identified the long-sought proton donor in enoyl-thioester reductase (ETR) enzymes, enabling them to reengineer the stereochemistry of the enzymes’ catalytic action. The work has implications for polyketide synthase-based synthesis of natural products and natural-product-like compounds because related reductases are major components of polyketide synthase enzyme complexes. In reactions catalyzed by ETRs, a proton from an active-site amino acid or water molecule is transferred to the α-carbon of the enoyl-thioester substrate. But scientists haven’t been able to pin down the identity of the proton donor. Tobias J. Erb of the Max Planck Institute for Terrestrial Microbiology, in Marburg, Germany, and coworkers provided experimental evidence for an earlier proposal that an R1 intermediate called a NR3 C2-ene adduct forms R2 between the substrate and NADPH in the R3 Si(CH3)3 reaction, suggesting it might be involved 1 2 in the proton-transfer R R process. Erb and coNC NHR3 workers’ use of this CEN.ACS.ORG
25
APRIL 20, 2015
the same depth resolu- Researchers used an improved tion (around 1 µm) tomography as traditional but technique to destructive sampling analyze the paint methods (Opt. Express and varnish 2015, DOI: 10.1364/ layers of “The Madonna and oe.23.010145). This Child” at the improved tool for culNational Gallery tural heritage science in London. comes courtesy of researchers developing tomography for visualizing tissue layers in the eye, notes the team, led by Haida Liang of Nottingham Trent University. Liang and her team needed to modify the eye technology to not lose sensitivity in deep paint layers. Then they demonstrated the technique’s strengths by visualizing the varnish and paint layers of “The Madonna and Child,” a painting from before 1600, perhaps by Raphael, at the National Gallery in London. The team compared the new method with a variety of other analysis techniques. The painting’s varnish is so yellowed that part of the Madonna’s dress now appears green instead of blue.—SE
