n e w s of t h e w e e k sisting of dumbbell-shaped molecular the switching to just one, ideally, and to use nanometer-scale wires. chains with captive rings. 'The best wires we can think of for Rotaxanes can switch between two states, but in the past this behavior has getting down to true molecular dimenbeen observed only for rotaxanes in solu- sions are carbon nanotubes," Heath says. tion, and they couldn't be hooked into ex- 4 We're hard at work trying to incorporate ternal circuits. In the new devices, the ro- those into our devices right now." taxanes are instead laid down as self"Demonstrating this using a single assembled monolayers inside sandwiches layer of molecules is a really significant of metal and metal oxide electrodes. The achievement," says chemistry professor devices are then combined into logic ar- James M. Tour of Rice University, Housrays and connected by conventional litho- ton, a specialist in molecular electronics. graphic wires to form circuits. He agrees that "what's left to be done is to In operation, an electrical signal oxi- scale the size down to one or a few moledizes the rotaxane monolayer, causing a cules and to have it work more than major conformational change. The once." But still, he says, "certainly this is change acts like a switch in that it caus- an important stepping stone toward a moes a significant increase in the circuit's lecular electronic system." resistance. An advantage of the design Organic molecule-based computing, is that the switch-open and switch- Heath says, "would require almost no closed resistances of the devices' two energy, and you would have fantastic states are easy to discriminate. They dif- computational power—way beyond fer by more than a factor of 10. whatever silicon would give you." A moThe switching phenomenon is cur- lecular computer can theoretically run rently a one-time thing, but the scien- 109 times faster than a silicon-based tists hope to develop it into a reversible computer, he notes. 'That's nine orders process. In addition, each device con- of magnitude of playground available to tains about 108 rotaxane molecules, and you, and we know silicon is only going the attached lithographic wires are of to improve by about one additional ormicrometer dimensions, but the re- der of magnitude. That's a big opportusearchers hope eventually to reduce the nity, and it's why we got into this game." number of molecules needed to perform Stu Borman
Glickman: biotech tools must benefit farmers
able nontransgenic traits developed over the years, he said (see page 42). The first of the studies assessing the impact of transgenic crops on farmers was conducted by Leonard P. Gianessi, a research associate with the National Center for Food & Agricultural Policy, Washington, D.C. He analyzed crop data for the Biotechnology Industry Organization and found highly variable results for several Bt crops. Compared with profits from conventional corn, Bt corn growers earned $72 million in extra income in 1997, but USDA beefs up biotech regulatory process earned $26 million less than conventional The Department of Agriculture is taking ucts over a long period of time" for their corn growers in 1998 because the slight a number of steps to strengthen the regu- effects on health, agricultural pests, and yield advantage from Bt corn did not comlation of genetically modified foods and the environment. The debate over the pensate for the extra cost of the seed. On feed. Many of the changes are aimed at effect on monarch butterflies of corn ge- the other hand, Bt cotton farmers, in the bolstering the scientific basis for approval netically modified to make toxin from aggregate, used less insecticide and of transgenic crops, ensuring consumer Bacillus thuringiensis (Bt) "underscores earned extra profits of $92 million in 1998. acceptance, and overcoming opposition the need to develop a comprehensive Gianessi stresses that because condito such crops in the European Union. approach to evaluating long-term . . . ef- tions such as weather and the diversity That opposition has resulted in the loss of fects of biotech products," he said. and numbers of pests vary from year to hundreds of millions of dollars in U.S. agProducers of biotech products year, 10 years of data will be required ricultural exports. should "report any unexpected or po- for an accurate assessment of Bt crops. Throughout his announcement of the tentially adverse effects" to USDA "imIn the second study, Charles M. Bennew policies, made July 13 at the Nation- mediately upon discovery," Glickman brook, former director of the National al Press Club, Washington, D.C., USDA said. He promised that USDA will take Academy of Sciences' Board on AgriculSecretary Daniel R. Glickman stressed steps to make sure there is a clear separa- ture and now a consultant, analyzed data the "awesome potential" of agricultural tion in the department between those who from more than 8,200 university-run soybiotechnology. However, on the same regulate genetically engineered products bean trials and USDA crop data gathered day, two studies not sponsored by USDA and those who promote trade in them. in 1998 and found that soybeans engiwere released exploring the costs and And it will set up an advisory committee neered to resist the herbicide Roundup benefits from the use of transgenic crops. on biotechnology. produced yields 5 to 10% smaller than Neither report's conclusions were comGlickman warned that seed produc- conventional seeds and required two to pletely sanguine. ers need to ensure that "biotechnology five times as much weed killer as convenGlickman called for "an independent becomes a tool that results in greater, tional soybeans. These data "show that scientific review of USDA's biotech ap- not fewer, options for farmers." USDA is some of the rosy claims biotech compaproval process." He proposed the "es- already hearing complaints from farm- nies have been making about their prodtablishment of regional centers around ers who say they now have to buy bio- ucts are wrong," Benbrook says. the country to evaluate biotech prod- tech seeds to get the more highly desirBette Hileman 12 JULY 19,1999 C&EN
