n e w s o f t h e w e e k ^ '

cent unpublished research, he and his co­workers isolated a tin analog of Robin­son's compound—K2(RSnSnR), where R is the big ligand. They found that the Sn-Sn-C angle is about 109° and the Sn-Sn distance is marginally shorter than a sin­gle bond; formally, it is a double bond, albeit a very weak one.

Power also cites calculations by his col­league Thomas L. Allen, a professor emer­itus at UC Davis, that show that in model Sn2 and Ge2 compounds most relevant to Robinson's Ga2 compound, the species with a quasi-single bond and a lone pair of electrons on each metal atom is signif­icantly more stable than the triple-bonded species. The heavier the group 13 element, Power says, the less likely it is to π-bond. As a result, he believes that Robinson's Ga2 compound is closer to a single-bonded species. But, he adds, "no matter what you think the bonding is, it's still a very interesting compound" and it represents "a great contribution to group 13 chemistry."

Missouri's Atwood, although not famil­iar with the details of Power's argu­ments, opines that tin does not necessar­ily predict what gallium does. Nor does he find the nonlinearity of the Ga-Ga-C system to be worrisome. Basically, he thinks Robinson is on firm footing.

Robinson himself is confident that his admittedly "radical proposal" will eventu­ally be accepted by all chemists. "After all," he says, looking back, "some people did not believe that we had actually pre­pared cyclogallenes!"

Ron Dagani

Chemical Instruction' may have a role in antibody selectivity A fresh look at a 50-yearold question in immunochemistry is revealing new in­sights into the exquisite molecular selec­tivity of the immune system. By examin­ing crystal structures of the combining site of an antibody, a team of chemists at the University of California, Berkeley, finds that the binding mechanism of the anti­body changes as it matures [Science, 276, 1665 (1997)].

The study—by assistant professor Ray­mond C. Stevens, professor Peter G. Schultz, and their colleagues—revisits key aspects of a theory first proposed half a century ago by Iinus Pauling, among oth­ers, to explain the phenomenal ability of

antibodies to recognize specific molecules and bind to them.

The experiments may also provide im­portant insights for the field of combina­torial chemistry. As Schultz explains: "All the combinatorial systems that are being explored today are in some way derived from or inspired by the immune system."

It's almost impossible to fool the im­mune system. If an unknown molecule-even one that has never been synthesized before—is introduced into the body, a spe­cific population of antibodies will quickly develop that bind the molecule tightly and specifically. The question of how the sys­tem can handle such diversity has fascinat­ed and puzzled researchers for decades.

ο ο ε

Germllne antibody changes Its shape to bind to antigen (red). Mutations that take place as the antibody matures "preselect" this configuration, so that binding no longer involves a shape change. The antibody's heavy chain is shown in green, Its light chain In yellow.

In the 1940s, Pauling suggested that the antibody molecule can adopt differ­ent conformations and that the target mol­ecule acts as a template to direct the an­tibody to fold into the shape that comple­ments it best. An alternative explanation is that the immune system takes a combi­natorial approach, recombining a relative­ly small number of gene segments to make an enormous diversity of antibody molecules. That diversity is further ampli­fied through a process called somatic mu­tation as the antibodies mature.

The new experiments suggest that in some cases both mechanisms may oper­ate. "This study demonstrates that not only is sequence diversity important but, poten­tially, configurational diversity can be im­portant, too," Schultz says. "In this partic­ular case, we found that the precursor an­tibody did change configuration and become more complementary to the target mole­cule," he explains. "The somatic mutations refine the combining site and lock it into a

configuration that closely complements the shape of the target molecule."

The Berkeley chemists investigated a cat­alytic antibody raised against a phospho-nate molecule that is the transition-state an­alog for the hydrolysis of a nitrophenyl ester. They solved the crystal structure for the antibody in four forms: the immature— or germline—antibody bound and not bound to the transition-state analog and the mature, fully mutated antibody bound and not bound to the same analog. When bound to the target, the mature and imma­ture antibodies have the same shape. The researchers found that the immature anti­body changes shape when it binds, but the mature antibody doesn't. The nine muta­

tions that occurred during c maturation, in effect, locked I the antibody into the config­

uration it needed to tightly bind the analog.

It makes sense that there's more than just sequence di­versity involved in the im­mune system's ability to rec­ognize molecules, Schultz says. Chemists have success­fully mimicked the immune system's ability to combinato-rialry generate 1010 to 1014 dif­ferent sequences, he notes, "but the immune system does more with the diversi­ty it generates than we have been able to do with diversi­ty generated synthetically in the test tube. I think we are now starting to get at some

of the molecular mechanisms that the im­mune system uses to do that."

Rebecca Rawls

Huntsman perseveres, gets Rexene After nearly a year of contentious, on-again, off-again discussions that included a brewing proxy fight, an agreement was reached last week that will allow Hunts­man Corp. to acquire Rexene Corp.

The $l6-per-share, $300 million cash part of the deal has already been ap­proved by the boards of directors of both companies. It still must be approved by Rexene's shareholders in a special meet­ing to be held later in the year. The deal also includes Huntsman's assumption of about $300 million in debt held by Dallas-based Rexene. Huntsman expects to close the transaction, subject to regulatory ap-

10 JUNE 16, 1997 C&EN

Jon Huntsman: extraordinary synergies

proval, during the latter part of this year's third quarter.

Clearly alluding to the lengthy negoti­ations between the two firms, Huntsman Chairman and Chief Executive Officer Jon M. Huntsman says, "We have maintained our interest in Rexene because of the ex­traordinary synergies and efficiencies that would result from a merger of our two companies." Huntsman Corp. made its first bid—at $14 per share—on July 17 last year.

As part of the acquisition, Salt Lake City-based Huntsman Corp. will receive Rex-ene's Odessa, Texas, plant, which has annu­al capacity for 600 million lb of ethylene, 430 million lb of polyethylene, 320 million lb of styrene, 240 million lb of propylene, and 210 million lb of polypropylene. Rex­ene also has 65 million lb per year of amor­phous poly(oc-olefin) capacity and 75 mil­lion lb per year of flexible polyolefin capac­ity at Odessa, which Huntsman will also acquire as part of the deal.

In addition, Rexene produces polyethyl­ene and polypropylene plastic films at four U.S. sites—Chippewa Falls, Wis.; Clearfield, Utah; Dalton, Ga.; and Harrington, Del.— and in Scunthorpe, England. The combined annual plastic films capacity at the five sites is 255 million lb.

Acquisition of Rexene s polyethylene facility puts Huntsman into that business for the first time. "While today we are not a market leader in this field," says Huntsman Corp. President and Chief Op­erating Officer Peter R. Huntsman, "we are beginning as we did with polystyrene and polypropylene. Our future growth will be controlled, but aggressive."

Huntsman Corp. is talking with An­drew J. Smith, Rexene's chairman and CEO,

and others in key positions about their stay­ing on after the transaction is closed.

The deal obviated the need for a June 12 special meeting with shareholders at which Wyser-Pratte & Co. and Spear Leeds & Kellogg—both large Rexene sharehold­ers—were to present a proposal to re­place Rexene's board with a board that would sell the company. Rexene called off the meeting.

George Peaff

New engineering college incubates education reform

The legacy of a man born in a primitive lumber camp in I860 will provide more than $250 million to support innovative engineering and science programs in Mas­sachusetts and Florida. The F. W. Olin Foundation, New York City, will spend more than $200 million to set up a new engineering college in Needham, Mass., a suburb of Boston. The foundation also plans to grant up to $50 million to Flori­da Institute of Technology in Melbourne, including $21 million to build an ad­vanced engineering complex and a life sciences laboratory.

Franklin W. Olin, an engineer and in­dustrialist who founded an explosives company in 1892 that went on to be­come Olin Corp., a diversified chemicals producer, started his foundation in 1938. With its $200 million grant, the founda­tion aims to "establish a new paradigm for undergraduate engineering educa­tion," says its president, Lawrence W. Mi-las. The foundation, he explains, wants to put into practice engineering educa­tion reforms advanced by the National Sci­ence Foundation, which has proposed that the education of engineers "become more cross-disciplinary, more hands-on, that there be more experience working in teams, and that students get greater communication skills."

Milas says the new college will put students in labs "actually doing engineer­ing, rather than reading from a book or listening passively to a lecture." That's a good idea, says Marshall M. Lin, NSF's di­vision director for engineering education and centers. Students who choose engi­neering "are pretty eager to get their hands on something and build it," he points out, but conventional education de­lays that experience until the last year of college. "That's like a baseball training

schedule where you tell people to run, jump, and catch for the first four weeks, without letting them play games. A base­ball team like that would lose half its play­ers pretty quickly."

The Franklin W. Olin College of Engi­neering in Needham will be built on land bought from Babson College. Once the land purchase is approved, the college will be incorporated, a president and fac­ulty hired, and curricula developed. Be­ginning approximately in 2001, the school will take in up to a maximum of 800 stu­dents and may be tuition-free. Milas says the foundation expects its initial invest­ment to last about 10 years, but it hopes to attract other funders.

The proximity to Babson—which was the most highly ranked independent under­graduate business college in America in U.S. News & World Reports most recent sur­vey (Sept. 16, 1996)—is no accident, the foundation says. The two colleges hope to bridge the gap between technology and business, and they will develop joint pro­grams to improve the education of engi­neers and business managers.

Sophie Wilkinson

Mercury poisoning fatal to chemist Karen E. Wetterhahn, professor of chem­istry and Albert Bradley Third Century Pro­fessor in the Sciences at Dartmouth Col­lege, died June 8 at age 48 from mercury poisoning.

Wetterhahn's research and teaching in­terests spanned the fields of inorganic chemistry, biochemistry, and chemical toxicology. Her work involved under­standing how elevated levels of heavy met­als interfere with such processes as cell metabolism and the transfer of genetic information. That work was the direct cause of her death.

"Karen was the acknowledged interna­tional expert in chromium carcinogenic­ity," notes John S. Winn, chairman of the Dartmouth chemistry department. But she "started this project in mercury chemis­try when she began a sabbatical at Har­vard in the fall of '95. The work involved doing some model compound studies, some structure and kinetic studies with Steve Lippard's group at MIT—Karen had gotten her Ph.D. with Lippard when he was at Columbia [University].

"That work led to the need to do some mercury NMR characterization of these model compounds. The only reason she

JUNE 16, 1997 C&EN 11