EXTREME WEATHER TIED TO HUMAN ACTIVITY
NANOFIX FOR A BROKEN HEART
Recent heat waves, droughts, and increasingly longer summers would likely not be happening without global warming caused by human-induced release of greenhouse gases, according to scientists at NASA’s Goddard Institute for Space Studies (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/ pnas.1205276109). Climate scientists have been hesitant to link extreme weather events, such as the heat wave and drought in Texas and Oklahoma in 2011, to humaninduced climate change rather than chalking them up to natural climate variability, in particular when the analysis is based on theory and climate-change computational models. NASA’s James E. Hansen and colleagues have now used only temperature data to compare weather anomalies during a base period of 1951–80 with anomalies since 1980. They found that extremely hot summers—those with temperatures three standard deviations greater than the mean temperature during the base period—affected less than 1% of Earth’s land surface during the base period. But these extreme events now affect 10% of the land. The researchers say their results are important to help form public policy, because actions to sufficiently curb greenhouse gas emissions are unlikely until the public, which typically takes its cues from local variability in weather, perceives that human-caused global climate change is under way.—SR
Patients recovering from a heart attack might one day get a helping hand from peptide-based nanofiber scaffolds (Sci. Transl. Med., DOI: 10.1126/ scitranslmed.3003841). A heart attack leaves cardiac muscle and blood vessels damaged, leading to scar tissue formation and sometimes causing heart dysfunction or failure. To help repair injured tissue after such an event, a research team led by Patrick C. H. Hsieh of Taiwan’s Academia Sinica tested a A pig’s cardiac tissue, damaged by a heart attack (left), can new therapy: The researchers inject- regrow blood vessels (right, labeled green) with the help of nanofiber-supported protein therapy. ed a peptide nanofiber gel containing the protein VEGF, or vascular endothelial growth factor, directly into the hearts of pigs just after a heart attack. After 28 days, the pig hearts functioned better and had increased blood vessel density compared with those of pigs given only VEGF or the nanofiber gel. The researchers think that because the nanofiber scaffold degrades slowly and releases VEGF over time it improves recruitment of healthy cells for repair. In a commentary, bioengineer Karen L. Christman of the University of California, San Diego, writes that the next steps for this therapy should be to monitor its effects over a longer period and to test whether it can be injected via a catheter. “With the addition of a few follow-up studies,” she says, “this technology has potential for near-future translation into people.”—LKW
By examining meteorite fragments, researchers have provided support for the idea that chiral amino acids essential to life on Earth originated by amplification of small enantiomeric excesses of the molecules (Meteorit. Planet. Sci.,
This fragment of the Tagish Lake meteorite has been kept in the cold since it crashed into the frozen lake in 2000.
MICHAEL HOLLY/U OF ALBE RTA
CHIRALITY VIA METEORITE
DOI: 10.1111/j.1945-5100.2012.01400.x). Daniel P. Glavin of NASA’s Goddard Space Flight Center and colleagues analyzed bits of the Tagish Lake meteorite, which crashed into the frozen surface of the Canadian lake in 2000. They found a large excess of l-aspartic acid and verified through carbon isotope measurements that the enrichment was not the result of any earthly contamination. It’s possible that water in the celestial body, present in liquid form in space as a result of heat given off from radioactivity, led to amplification of a small initial l-aspartic acid excess through crystallization, a process other groups have demonstrated experimentally, explains coauthor Aaron S. Burton. l-Alanine in the meteorite was not amplified, a result that can be explained by different crystallization behavior, he adds. Richard M. Kellogg of Dutch custom chemicals firm Syncom, an expert in homochirality, praises the work but notes that l-aspartic acid could also have been amplified by sublimation in ice.—CD
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POLYMER HEALING BY OLEFIN METATHESIS A way to efficiently repair cuts and cracks in polymers via the formation of new, strong carbon-carbon bonds has been devised by chemists at the University of California, Irvine (J. Am. Chem. Soc., DOI: 10.1021/ja306287s). Yi-Xuan Lu and Zhibin Guan came up with the strategy, which makes use of the olefin metathesis reaction to shuffle C=C bonds at the fracture interface of cross-linked polybutadiene. The researchers introduce a small amount—as little as 0.005%—of Grubbs secondgeneration ruthenium metathesis catalyst into the polymer. Wherever the polymer is cut, healing occurs by simply pressing the two fracture surfaces together with moderate pressure (10 to 30 kilopascal) and then waiting. The catalyst-loaded polymer repairs itself at temperatures as low as 5 °C, although it takes longer than healing at ambient temperature. Lu and Guan also show they can use the metathesis reaction to re-
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SCIENCE & TECHNOLOGY CONCENTRATES
SCIENCE & TECHNOLOGY CONCENTRATES
FUNCTIONALIZED GRAPHENE NANOBALLS
ACS NANO
A one-pot procedure converts solutions of graphene oxide and precursor ions to crumpled sheets of graphene decorated with nanocrystals, according to a study led by researchers at the University of Wisconsin, Milwaukee (ACS Nano, DOI: 10.1021/ Crumpled graphene sheets nn302818j). decorated with platinum The method form spontaneously in a builds on one-step procedure. work reported recently by other scientists that shows graphene sheets can be crumpled into nanosized balls that resist uncrumpling, aggregating, and stacking. The wadded-up form of carbon is endowed with high surface area, making it attractive for energy storage and other applications. But access to those applications typically requires additional chemical processing steps. UW Milwaukee’s Shun Mao and Junhong Chen and coworkers created a general method for making graphene nanoballs and functionalizing them with metals or metal oxides in a single step. The team reports that flowing aerosols of graphene oxide suspensions containing nanoparticle precursors through a furnace causes the aerosol droplets to rapidly evaporate. That process crumples and partially reduces the carbon flakes and triggers spontaneous growth of nanocrystals on the inner and outer surfaces of the balls. The researchers made supercapacitors and lithium-ion batteries from nanoballs coated with Mn3O4 and SnO2, respectively, and report that the devices outperform versions made from flat graphene sheets.—MJ
TOOTH ANALYSIS REVEALS ANCIENT DIETS The food preferences of two early human ancestors and another competing species have been elucidated by mass spectrometric analysis of their tooth enamel (Nature, DOI: 10.1038/nature11349). An international team led by Vincent Balter of École Normale Supérieure in Lyon, France, analyzed calcium, strontium, and barium isotopes in fossilized molars. The researchers discovered that two species of Australopithecus, a bipedal ancestor of the Homo lineage, and a concurrent competitor, Paranthropus, had much more diverse diets than their successors. Although all three hominins ranged over a similar-sized territory, Australopithecus ate a variety of both plants and meats before dying out 2 million years ago. On the other hand, the isotopic ratios from subsequent Homo ancestors show that modern human forebears had a predilection for meat—for example, low Ba/Ca levels are characteristic in carnivores, whereas higher Ba/Ca levels are characteristic in herbivores. The competing Paranthropus species preferred a more plant-based diet, the researchers note, which may have “contributed to its demise because it was unable to adapt to the changing environmental conditions that took place approximately 1 million years ago.”—SE
DOUBLE-HELIX INORGANIC STRUCTURES By computationally examining the twists and turns of imaginary inorganic molecules, a multinational research team has determined that simple inorganic compounds should be able to adopt double-helix structures similar to DNA (Angew. Chem. Int. Ed., DOI: 10.1002/ anie.201201843). Helical inorganic species are rare and typically involve complex molecular formulas. In addition, an atomiclevel structural model for an inorganic double helix hasn’t been proffered until now. Alexander I. Boldyrev of Utah State University, Andrew J. Morris and Chris J. Pickard of University College London, and colleagues found that bulk LiP and LixPx clusters, where x is seven or greater, adopt right- and left-handed double-helix structures in their lowest energy, most stable forms. Boldyrev notes that X-ray crystal structures for bulk LiP and LiAs reported decades ago indicate that the chains of
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The doublehelix structure of an infinite LiP chain.
the atoms are spiral and coaxial, but the researchers stopped short of labeling them as double-helix structures. Boldyrev acknowledges that the concept of inorganic double helices is controversial, adding that “we do not think that our double helix could be used by inorganic creatures as DNA on some other planet, but it is quite surprising to us that such unusually simple species might form a double helix.”—SR
TAKING A DIFFERENT TACK WITH AMYLOID-β Inhibiting the formation of amyloid-β, the peptide that clumps in the brains of patients with Alzheimer’s disease, has been a focus of drug designers for years. Rather than regulating amyloid-β directly, researchers at the University of Pennsylvania, led by Kurt R. Brunden, are now trying to control its production indirectly via an oxidative stress pathway in the body (ACS Chem. Neurosci., DOI: 10.1021/cn3000795). Neuroscientists have known that when amyloid-β clumps deposit in the brain, the peptide aggregates trigger formation of oxidized lipids such as isoprostane-2αIII. The Penn team,which also included chemists Carlo Ballatore and Amos B. Smith III, designed small molecules to block the thromboxane A2prostanoid (TP) receptor, a membrane protein whose activation by isoprostane-2αIII leads to an increase in amyloid-β production. Compounds that inhibit the TP receptor already existed, but they had a hard time penetrating the bloodbrain barrier. By replacing a carboxylic acid on one of those molecules with a nonacidic oxazole or thiazole group, the researchers synthesized a batch of lead compounds (one shown) that entered the brain in mice and bound tightly to both human and mouse TP receptors in cells.—LKW
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pair ruthenium-free cross-linked polybuta diene by simply applying a small amount of the catalyst to the fracture surfaces and pressing the wound shut. “The approach is simple, effective, and potentially applicable to a wide range of olefin-containing polymers such as polyisoprene, butyl rubber, polynorbornene, and other polymers containing double bonds amenable for metathesis,” they note.—BH
