NEWS OF THE W EEK
call into question conclusions of a federal report
A
STUDY conducted by researchers at the
University of Missouri, Columbia, strikes at the heart of a federal panel’s conclusions about the health concerns of bisphenol A (BPA)—the high-production-volume chemical used to make polycarbonate plastic (Repro. Tox. DOI:10.1016/ j.reprotox.2008.01.001), say experts in the field. Last August, a panel appointed by the National Toxicology Program’s Center for the Evaluation of Risks to Human Reproduction (CERHR) reported that it had “some concern” that prenatal exposure to BPA causes neural and behavioral defects in infants and children, and “minimal” or “no concern” about any other health effects. It reached these conclusions by considering only those studies in which lab animals had been ex-
DNA-GUIDED CRYSTALLIZATION SELF-ASSEMBLY: Selective
biochemical interactions organize metal nanoparticles
D
NA’S KNACK for selective pairing of complementary strands can drive metal nanoparticles to assemble into crystals, according to two new studies in Nature (2008, 451, 549 and 553). The investigations demonstrate a strategy for producing novel self-assembling materials by chemically modifying nanoscale building blocks. In both studies, researchers grafted numerous strands of DNA onto gold particles with diameters in the range of 10 to 15 nm. The DNA-based tethers were composed of various segments and designed such that a relatively short section at the end of each strand would pair with a complementary section on another DNA-adorned nanoparticle. The pairing process—or hybridization reaction—forms DNA double helices and guides the tagged nanoparticles to line up in an orderly fashion in three dimensions, thereby forming micrometer-sized crystals. The investigations differed somewhat in their focus. In one case, researchers led by Oleg Gang at Brookhaven National Laboratory explored the temperature dependence of DNA-induced crystalliza-
Studies with baby mice show that multiple modes of exposure to BPA are of concern.
tion. They report that crystals form reversibly during heating and cooling cycles and that crystallization is affected by the length of a spacer segment within each DNA tether. Particles with long spacers (35 or 50 nucleobases) crystallize readily, whereas those with short or rigid spacers do not crystallize. Meanwhile, at Northwestern University, a team led by chemists Chad A. Mirkin and George C. Schatz probed the range of crystal structures that can be formed from a single type of nanoparticle. They find that when only one type of tether is used, the particles crystallize with a face-centered-cubic structure. But NEW TIES A new method uses strands of by combining nanoparDNA to guide nanoparticles into crystals. ticles with one type of tether with particles having a tether with a different DNA sequence, the nanoparticles form bodycentered-cubic crystals. Commenting in the same issue of Nature, University of Pennsylvania chemical engineering professor John C. Crocker notes that the method might be used with particles of nearly any material to make novel composites endowed with unusual electronic and optical properties.—MITCH JACOBY
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SHUTTERSTOCK
TOXICOLOGY: Research results may
posed orally to BPA and disregarding all experiments in which the animals had been injected or given the compound subcutaneously. Biologist Frederick S. vom Saal and colleagues at Missouri disagreed strongly with the CERHR conclusions because fetuses and newborns lack, or express at very low levels, the liver enzyme needed to deactivate BPA, in contrast to adults who metabolize it quickly. This fact, the researchers argue, indicates that exposure by any means will affect fetuses and newborns. To test this theory, vom Saal separated three-day-old mice into four groups. Two groups were exposed to oral doses of BPA. The other two groups were injected with BPA. Blood measurements of biologically active BPA over the next 24 hours showed that the route of administration made no difference, vom Saal says. “Vom Saal’s study is a very important piece of work,” Gail S. Prins, a professor of physiology at the University of Illinois, Chicago, says. It could invalidate the CERHR panel’s conclusions, she adds. “Our research shows that the decision by the CERHR panel is without merit and unsupported by the scientific literature,” vom Saal says.—BETTE HILEMAN
COURT ESY OF CHAD MIRKIN, N ORTHWESTERN UN IVERSIT Y
BISPHENOL A SAFETY
