simple method makes cell skeleton mimics
TRANSCRIPT
page 6). But then the $4.2 billion global settlement to compensate implant recipients for alleged damages began to unravel. The settlement included implant and material makers Bristol-Myers Squibb, Baxter Health Care, 3M, and Dow Corning. It did not include Dow Chemical, which never made implants.
The federal judge overseeing the settlement said in June that the fund was not large enough to compensate eligible women among the 248,500 U.S. women who had applied for compensation. Efforts to salvage a settlement including Bristol-Myers Squibb and Baxter Health Care, but not Dow Coming, are still under way. In April, the same federal judge also decided breast implant suits against Dow Chemical could go to trial under the laws of some states.
Marc Rcisch
Simple method makes cell skeleton mimics No sooner was Halloween over last week than a team of materials chemists at the University of Toronto announced discovery of a quick and simple method for making "skeletons in the beaker/' The "skeletons" are self-assembling inorganic materials whose elaborate shapes and patterns mimic those in the exoskeletons of single-cell marine organisms like diatoms and radiolaria.
Besides aiding understanding of how nature builds skeletal structures, the work could lead to materials with novel electronic, optical, or other properties, says Toronto materials chemistry professor Geoffrev A. Ozin. Such materials might have an important impact on computer chips, bone replacement materials, industrial catalysts, separation technology, and "smart" materials that respond to changes in their environment. One chemist familiar with the work calls it "extremely exciting."
Nature uses simple, abundant minerals such as silica, calcium carbonate, and calcium phosphate to construct "an extraordinary array of exquisite architectures," Ozin notes. These architectures are seen in bones, teeth, seashells, sea urchins, corals, opals, and the microskele-tons of single-cell organisms. The multilevel complexities of these structures have both delighted and puzzled scientists.
But despite much effort, chemists
Colonzed scanning electron microscope images of the surfaces of synthetic aluminophosphate spheroids reveal a pattern of micrometer bowls (left) and of "meshed" bowls that resemble the silica microskeletons of radiolanan, a single-cell organism (right). The tivo patterns are produced using slightly different chemical systems.
haven't come close to matching nature's architectural feats. One of the biggest challenges is how to control the complexity and shape of such so-called hierarchical materials.
Now, the tide is beginning to turn, says Ozin, thanks to a "new materials synthesis paradigm" that he, graduate student Scott Oliver, and other coworkers have developed over the past three years. The method can "mimic nature's dexterity for sculpting biominerals" with intricate structural features that span three size realms—the nanoscopic (less than 10 A), mesoscopic (10 to 1,000 A), and macroscopic (more than 1,000 A).
Overall, Ozin says, many of the artificial skeletons his group has generated bear a striking resemblance to naturally occurring structures, such as the delicate "lacelike" microskeletons of diatoms and radiolaria, the exquisitely sculpted spicules of marine sponges, the quiltlike patterns seen in sea urchins, and the star-dodecahedral patterns of certain rushes.
Ozin's new approach to materials synthesis is detailed in several papers—the first of which was published last week [Nature, 378, 47 (1995)]. Co-authored with Oliver, Alex Kuperman, Neil Coombs, and Alan Lough, the paper describes synthesis of well-ordered, stacked aluminophosphate structures using self-assembled organic vesicles (hollow sacs) as templates.
The recipe, notes Nature chemistry editor Philip Ball in the same issue, "sounds alarmingly simple: throw together phosphoric acid and pseudo-boehmite (a hydrated aluminum oxide) in tetraethylene glycol in the presence of an alkylamine; heat, dry, and [crystal
lize]." The millimeter-sized aluminophosphate spheroids produced show intricate surface features like disks, ridges, pores, platelets, and honeycomb arrays.
Ozin believes that the alkylammoni-um dihydrogen phosphate bilayers, which initially form, interact with the tetraethylene glycol to produce contiguous arrays of vesicles around which the aluminophosphate is deposited. The bowl-shaped craters on these spheroids, he thinks, are the imprints of vesicles packed together like soap bubbles. And the finer scale patterns may arise from precipitation of aluminophosphate into specific domains in the vesicle walls. But this explanation is still speculative.
Although heating is a necessary step in the chemistry detailed in the Nature paper, Ozin tells C&EN that subsequent papers will describe room-temperature reactions with a number of other chemical systems.
Ron Dagani
Praxair makes hostile bid for CBI Industries Praxair has made a hostile $2.1 billion bid for Oakbrook, Ill-based CBI Industries, parent to carbon dioxide maker Liquid Carbonic. The cash tender offer to CBI stockholders comes after failure of six months of merger negotiations between the two and of a bid to CBTs board of directors.
Liquid Carbonic is the largest carbon dioxide business worldwide. Praxair is a power in the air separation business but lacks carbon dioxide capabilities. Its only major stake in carbon dioxide
NOVEMBER 6, 1995 C&EN 7