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News Scan Briefs: Iron-Tough Paper; DEET-free Repellent; Artificial Corneas

Biology -- Repellents -- Materials -- Neuropsychology

Reconstructing the Very First Cell
Unlike modern cells, with their mitochondria, pores, nuclei and such, the very first cell, which emerged some 3.5 billion years ago, was simple. It probably consisted of just a membrane with genetic information inside—raising the question of how it could take in nutrients and reproduce. Harvard Medical School researchers have built a model of what the first cell may have looked like. Using fatty acids that likely existed on a primeval Earth, they created a membrane porous enough to let in nutrients but strong enough to protect the genetic material inside. In a test tube of water, the fatty acids formed into a ring around a strip of DNA. The investigators also added nucleotides—units of genetic material—which entered the cell, latched onto the DNA and replicated it over 24 hours. Scientists now must figure out how the original and copycat DNA strands can separate, which would enable the cell to divide and reproduce. The study turned up in the June 12 Nature.

DEET Beaters
New mosquito repellents work more than three times as long as DEET, currently the most widely used such chemical and the gold standard by which to judge alternatives. Researchers discovered them using an artificial neural network, which they first trained by supplying it with the molecular structures of 150 known repellents. The neural network then scanned a library of roughly 2,000 untested piperidines, compounds related to the active ingredient in black pepper that can ward off insects. Human volunteers then wore arm patches impregnated with the best candidates and held their arms motionless in cages filled with roughly 500 mosquitoes for one minute each day. While DEET repelled mosquito attacks for an average of 17.5 days, some of the new compounds lasted for up to 73 days, scientists at the University of Florida and the U.S. Department of Agriculture found. Buzz about the findings in the May 27 Proceedings of the National Academy of Sciences USA.

Iron-Tough Paper
Paper may not become obsolete after all—a new type can resist tearing better than cast iron. Materials made from cellulose fibers can be very strong, but they can also be brittle, ripping apart fairly easily when pulled. Now investigators at the Royal Institute of Technology in Stockholm and their colleagues have devised “nano­paper” that is remarkably tough. To make these sheets, the researchers treated wood pulp with enzymes and then pulverized it. Paper is typically made from fibers tens of microns in diameter, but the nanopaper swirls cellulose fibers together into tangles that are 10 to 40 nanometers wide. Its high tensile strength is likely explained by its weblike structure and the way the fibers adhere to one another. The recipe for the paper, which could find use as a construction material, was printed up in the June 9 issue of Biomacromolecules.

Is That Your Final Offer?
Serotonin, a chemical that in the brain affects mood, also seems to control behavioral reactions to unfairness. Researchers at the University of Cambridge depleted the serotonin levels of volunteers in part by feeding them a cocktail of amino acids that lacked tryptophan, an ingredient that the body needs to make serotonin. The volunteers then played an ultimatum game, in which they had to decide whether to accept an offer by a “proposer” to split, however unevenly, a pot of money. Rejection of the offer meant that no one got anything. Lack of serotonin, the experimenters found, made refusal more likely—for instance, 82 percent of serotonin-deprived individuals refused a 20 percent piece of the pie, compared with 67 percent of normal subjects given the same ultimatum. Take it or leave it from the study published online June 5 by Science.

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