NEWS OF TH E WEEK
FOUR KILLED AT DUPONT PLANT
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AP
The workers who died were responding to a chemical leak at a DuPont plant in La Porte, Texas.
Methyl mercaptan is a colorless gas that can be easily ignited, according to the Agency for Toxic Substances & Disease Registry. It is toxic and can cause headaches, dizziness, nausea, vomiting, coma, or death. The DuPont facility, located east of Houston, uses INDUSTRIAL ACCIDENT: Methyl methyl mercaptan to manufacture insecticides and mercaptan leak appears to be fungicides, according to CSB. However, the chemical is responsible for deaths more widely known as the additive in natural gas that gives it a distinctive rotten cabbage smell. Methyl mercaptan was responsible for a deadly 2001 NVESTIGATORS FROM THE Chemical Safety & accident at an Atofina plant in Michigan. In that inciHazard Investigation Board (CSB) are in Texas prob- dent, workers died when the chemical ignited while a ing an apparent chemical leak that killed railcar was being unloaded, causing an exploS H four workers and injured a fifth at a DuPont sion. The accident killed three, injured sevC H plant in La Porte, Texas. eral others, and resulted in the evacuation of H The workers probably died from expo2,000 local residents. H sure to methyl mercaptan while responding Methyl mercaptan DuPont’s La Porte facility appears to have to a valve leak around been fined previously for safety violations by 4 AM on Nov. 15, according to the Texas Commission on Environmental Quality, acDuPont. The community around cording to reports from local news organizations. the plant was not at risk, the comCSB has conducted four previous investigations into pany adds. DuPont facilities, all in 2010. One of those accidents “Our goal in investigating this killed a worker in Belle, W.Va., and in another, a worker accident is to determine the root died in Buffalo. cause and make recommendations DuPont officials say they are working with local, to prevent any similar accidents state, and federal officials as they investigate the incithroughout the industry,” CSB dent. The company says it is conducting its own “topChairman Rafael Moure-Eraso says. to-bottom review.”—ANDREA WIDENER
TWISTED BY DESIGN MATERIALS SYNTHESIS: Polarized light
helps nanoparticles self-assemble into ribbons of controllable chirality N INTERNATIONAL RESEARCH team has
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coaxed semiconducting nanoparticles to self-assemble into helical ribbons using circularly polarized light (Nat. Mater. 2014, DOI: 10.1038/nmat4125). Such twisted inorganic nanostructures could be useful for chiral catalysis and optical data transmission, the researchers say, and their method’s high yield could make it suitable for mass production. Scientists have investigated the light-driven assembly of chiral organic molecules in the past, but they usually got a nearly even mixture of left- and right-handed ones. The surplus of molecules with the desired chirality rarely exceeded 1%, says Nicholas A. Kotov of the University of Michigan. He was convinced researchers would fare better using inorganic nanomaterials. To test that theory, his team started with aqueous NAT. MATER.
Electron microscopy helped researchers render the surfaces of left-handed (left) and right-handed ribbons.
CEN.ACS.ORG
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suspensions of cadmium telluride nanoparticles. The roughly 5-nm particles are inherently chiral thanks to subtle geometric asymmetries and therefore respond differently to different light polarizations. Left-handed particles, for instance, are more likely to absorb photons with a left-handed circular polarization. As the particles absorbed photons, they oxidized their thioglycolic acid coatings—coatings that kept the nanostructures dispersed. As more left-handed particles lost their coatings, they aggregated into lefthanded helical ribbons up to 3 µm long. When the team used light with a right-handed circular polarization, right-handed ribbons preferentially self-assembled. Using circularly polarized light, the team grew about 30% more structures whose chirality matched the light’s polarization than it did ribbons of the opposite chirality. “I have never seen such clear evidence of the influence of circularly polarized light on the formation of helical nanostructures,” says Luis M. Liz-Marzán, a nanomaterials scientist at the Centre for Cooperative Research in Biomaterials (CIC biomaGUNE) in Spain, who was not involved in the study. Kotov says he’s interested in extending this approach to other materials and seeing how finely researchers can tune their control over chirality to make increasingly complex nanostructures. “All semiconductors and metals have strong photochemical and optical activity,” he says. “There are a lot of possibilities here.”—MATT DAVENPORT
NOVEMBER 24, 2014
