ficial nonheme iron-oxo complexes have been hindered by the fact that the molecules tend to form unreactive, oxobridged dimers. The new synthetic monomelic ironyears for radiation to oxo complex, which doesn't suffer from decay to safe levels. The report urges such limitations, was created by associ DOE to fully integrate ate chemistry professor Andrew S. stewardship into clean Borovik and graduate student Cora E. MacBeth at the University of Kansas in up plans. DOE commissioned Lawrence, associate chemistry profes and agrees with much sor Michael P. Hendrich at Carnegie of the report, says Ger Mellon University in Pittsburgh, and ald G. Boyd, deputy as their colleagues. Knowledge about biological process sistant secretary for sci ence and technology in es gave them insight into how to design DOE's Office of Environmental Man the synthetic system, MacBeth says. agement. DOE must actively monitor 'The best way to couch it is to say that for "100, 200, or 1,000 years—whatever it's bioinspired," Borovik says. Their success hinges on the design it takes," he says, "but we think we can of a new ligand system—which col lay out a cost-effective program." Using the Hanford example, he says, leagues have described as elegant— 'We may find a better way to treat stron that forms a cavity, surrounding the ox tium in groundwater in the future, cut ygen atom of an Fe-0 unit with stabiliz ting costs and time." He argues, howev ing hydrogen bonds [Science, 2 8 9 , 938 er, that DOE can't wait for long. "We (2000) ]. The authors say this type of hy need to get the waste stable and in a safe drogen bonding near unsaturated metal centers is probably what's going on in condition quickly," he says. DOE created a Long-Term Steward the complex's biological analogs. Hy ship Office last November with a $5 mil drogen-bond donors have been pro lion yearly budget, Boyd points out. It posed in heme enzymes such as cyto will issue a stewardship assessment in chrome P450, and although the picture is muddier in the case of nonheme en October. Jeff'Johnson zymes, Borovik says, "there's a reason able amount of evidence that hydrogen bonds play a crucial role in regulating dioxygen activation." One unique aspect of the system But these intermediates have been is that two of the iron-oxo complexes notoriously difficult to pin down. The are formed from 0 2 activated by the structures of synthetic heme-based complex's precursor, as opposed to complexes have been moderately char the one complex formed in biological acterized, but the structures of non- systems. 'Without a doubt, these complexes heme-based complexes had until now only been inferred from mechanistic are benchmark structures for our un studies. And attempts to synthesize arti derstanding of nonheme metalloproteins and their 0 2 activation," notes Karl Wieghardt, chemistry profes sor and managing director at the Max Planck Institute of Radiation Chemistry, Mulheim an der Ruhr, Germany. Calling the research "a big ad vance in bioinorganic chemistry," H. Holden Thorp, associate chemistry professor at the University of North Carolina, Chapel Hill, says the ligand design has great tailoring potential. And the group members now want to do just that: By manipulating the ligands, they say they may be able to tune the molecule's reactivity. Elizabeth Wilson | Columbia River flows ο through DOE's Hanford I Nuclear Reservation.
of sale. The report singles out DOE's Oak Ridge facility in Tennessee, where land sold to a golf course developer carried the stipulation that contaminat ed groundwater not be tapped. Despite the restriction, however, the owner soon began drilling for water. The report also notes that technical solutions may not work or may take hundreds of years. It cites a groundwa ter containment operation at the Hanford Reservation in Washington state in tended to retard migration of strontium90 to the Columbia River. Strontium-90 has the benefit of a short, 29-year halflife, compared with other radioactive wastes, but the pump and reinject facili ty at Hanford will have to run for 300
Nature Spurs Design Of Iron-Oxo Complex Taking their inspiration from biological reactions, chemists have succeeded in synthesizing a unique artificial iron-oxy gen complex that's not only stable enough to be characterized, but also provides a new springboard for study and design of catalytic complexes. Nature routinely performs oxida tion with the help of iron-containing catalysts that activate molecular oxy gen. It's believed that heme enzymes such as cytochrome P450 and nonheme enzymes such as methane monooxygenase split 0 2 apart, grabbing one of the oxygens and forming an in termediate oxo complex. These com plexes then go on to perform chemical reactions, like the oxidation of meth ane to methanol. Top view ofiron-oxo complex reveals cavity formed by the ligand surrounding oxygen (red). Iron is shown as orange; carbon, gray; hydrogen, white; and nitrogen (barely visible), blue.
AUGUST 14, 2000 C&EN
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