NEWS OF THE WEEK es. He also doubts that IL-16 is the true HIV suppressor. "While these subDifferent kinds of stances can suppress the virus, in my hydrogen bonds exist opinion they are not behind the natural 7 response/ he says. "We are still lookX—H Y ing for the major mechanism that is working in asymptomatic people." In a normal hydrogen bond, the proton is In fact, there may not be a single joined by a covalent bond to one atom and HIV-suppressive factor, points out Anby a much weaker noncovalent interaction thony S. Fauci, head of the National Into another atom. stitute of Allergy & Infectious Diseases, in a commentary in Nature. "However," Fauci adds, "at the very least, the X H Y availability of ... HIV-suppressive factors alone or in combination will tell In a low-barrier hydrogen bond, the proton us a great deal ... and will provide interacts equally with two atoms. the framework for the development of strategies for therapy and vaccine development." Pamela Zurer have a major role in enzyme catalysis, notes John A. Gerlt, biochemistry professor at the University of Illinois, Urbana-Champaign. In 1993, Gerlt and the late Paul G. Gassman, chemistry professor at the University of Minnesota, proposed that Not all hydrogen hydrogen bonds are created created LBHB formation explains how unstable Not all bonds are equal, equal, and and aa lively lively debate debate has has focused focused enolate anions are created in enzymeon the importance of a special type of mediated reactions. Gerlt estimates that hydrogen bond in enzyme catalysis. the stabilization predicted by the StanNow, additional data for estimating the ford team—although much lower than effects of these so-called short and expected—could accelerate rates by strong hydrogen bonds have been ob- three orders of magnitude. tained by researchers working at StanThe Stanford experiments provide ford University. clear proof of LBHBs' stabilizing effect, Short and strong hydrogen bonds— but the extent may vary from system to also called low-barrier hydrogen bonds system, comments Perry A. Frey, bio(LBHBs)—are interactions between a chemistry professor at the University of proton and two bases of equal strength. Wisconsin, Madison. Frey tells C&EN Unlike in ordinary hydrogen bonds, that the new data support his earlier the proton in LBHBs is equally shared findings that the rate of chymotrypsinby the two bases and is equally likely mediated acylation decreases by four to to transfer to either base. five orders of magnitude when the Some scientists believe that LBHBs LBHB in chymotrypsin is disrupted. formed during an enzymatic reaction Such deceleration corresponds to a loss significantly stabilize the transition of 5 to 7 kcal per mole in transition-state state. The Stanford study of LBHBs in stabilization, he says. solution predicts that LBHB stabilizaOn the other hand, notes chemistry tion is about 4 to 5 kcal per mole— professor Ronald Kluger of the Univermuch lower than previous estimates of sity of Toronto, the Stanford findings up to 20 kcal per mole that were based "cannot account for accelerations reon gas-phase data. quiring intermediates to be stabilized Stanford assistant professor of chem- by 10 to 20 kcal per mole, as had been istry Dale G. Drueckhammer and grad- invoked by advocates of catalysis by uate student Benjamin Schwartz stud- LBHBs." ied the equilibria between cis and trans Indeed, says Steve Scheiner, chemisforms of two a,P-unsaturated diacids try professor at Southern Illinois Uniin protic and nonprotic solvents to versity, Carbondale, not all the stabilicompare the strength of an LBHB with zation observed by the Stanford rethat of a normal hydrogen bond [/. Am. searchers results from LBHBs. Part of Chem. Soc, 117, 11902 (1995)]. The re- it, he believes, may come from differsults support the theory that LBHBs ences in stabilities of the compounds
New data obtained for short, strong H bonds
8
DECEMBER 11,1995 C&EN
in various solvents—and perhaps only 1 or 2 kcal per mole can be attributed to LBHB formation. Thus, the new findings do not resolve the LBHB debate in enzyme catalysis. But as Gerlt tells C&EN, "As a result of this and future [similar] studies, we will have a better quantitative understanding of the energetics of enzyme-catalyzed reactions." Maureen Rouhi
U.S. and Europe boost chemical cooperation Cooperation between the U.S. and Europe will be boosted in more than 150 policy areas—many affecting the chemical industry and environmental protection— by a pact signed last week in Madrid. At a summit meeting, U.S. and European Union (EU) leaders adopted a political declaration, the "New Transatlantic Agenda," and a 21-page action plan to implement it. The agenda has broad goals, including promoting peace and democracy, responding to global challenges, and expanding world trade. But the pact also calls for the U.S. and EU to cooperate on exchanging information and reporting on global environmental issues—such as climate change, biodiversity, and stratospheric ozone depletion. In addition, the countries promise to reduce land-based sources of marine pollution and to encourage sustainable management of forests. Specifically affecting the chemical industry is a provision that the U.S. and EU "will work together to exchange ... sensitive information for the preclearance of shipments of essential and precursor chemicals used in the production of illegal drugs, and cooperate in joint training programs on chemical diversion control." Another provision calls for prior informed consent for trade in hazardous chemicals, harmonization of classification and labeling of chemicals, and reduction of risks from hazardous substances, especially from lead exposure. A third provision calls for coordinated initiatives to disseminate environmental technologies, especially by creating an international clearinghouse. The countries also pledge to counter proliferation of chemical and biological weapons and to engage in a dialogue to find ways to reduce greenhouse gas emissions.
According to Marybeth Kelliher, manager for international trade at the Chemical Manufacturers Association, CMA is already collaborating with chemical industries in Europe in the manner envisioned in the action plan. "Our negotiations are ongoing in all of these different areas, including tariffs, the environment, proliferation. We already have a number of forums in which to address these issues." But the action plan may enhance those efforts, she notes.
For example, CMA's chemical diversion work group meets frequently with the U.S. Drug Enforcement Administration to develop a system to track the domestic and international flow of precursor chemicals used to make illegal drugs. European company representatives recently attended one of these meetings. CMA is also taking part in an intergovernmental forum on chemical safety that is attempting to harmonize the U.S. and EU regulatory systems, including those for notification and labeling.
CMA also strongly supports the action plan's provisions on trade issues, Kelliher says. The countries pledge to complete the unfinished business of the Uruguay round of multilateral trade negotiations, sponsored by the General Agreement on Tariffs & Trade. CMA is especially interested in lowering tariffs on chemicals worldwide, so it hopes the action plan will accelerate those efforts through its emphasis on working through the World Trade Organization. Bet te Hileman
U.S., South Africa spur joint scientific efforts At a meeting last week of a top-level bilateral commission, the U.S. and South Africa agreed to spur cooperation in science and technology and a broad range of other areas, including several chemically related programs. Vice President Al Gore led a delegation to Pretoria for the second meeting of the U.S.-South Africa Binational Commission. Cochaired by Gore and South African Deputy President Thabo M. Mbeki, the commission was created at an October 1994 meeting between President Clinton and South African President Nelson Mandela and held its inaugural meeting last March in Washington, D.C. South Africa faces enormous tasks of national development after decades of apartheid. The commission is "a pioneering effort to forge a new partnership in the areas of greatest mutual interest and benefit to both peoples," Gore noted. Only Russia and Egypt have such high-level commissions with the U.S. The meeting was attended by officials who cochair the commission's five working committees: science and technology; sustainable energy development; business development; conservation, environment, and water; and human resources development and education. A sixth panel, on agriculture, was announced at the meeting. A highlight of the meeting was the signing by Gore and Mbeki of an umbrella environment, science, and technology agreement. The pact provides a framework and legal context, including intellectual property protection, for governmental joint efforts in areas ranging from energy research to climate prediction to biomedical research.
i
i
Gore and Mbeki exchange signed copies of cooperation pacts in Pretoria. Overseeing implementation of the pact will be the commission's science and technology panel, cochaired by presidential science adviser John H. Gibbons and South Africa's Minister for Arts, Culture, Science & Technology, Ben S. Ngubane. One top priority is education and capacity building in science and technology, seeking to create a new generation of scientific leaders. Committee members discussed an advanced training program in science and engineering for faculty at historically black and disadvantaged South African colleges. The panel also discussed a joint educational program in marine and environmental sciences. Officials signed a cooperative agreement in agricultural science and technology. Members discussed collaboration in biomedical sciences. And the panel will encourage South African students to study math and science by enabling them to hold a televised dialogue during a space shuttle flight next month with a black U.S. astronaut.
Work of the sustainable energy development committee was boosted by the visit of its cochairman, Secretary of Energy Hazel R. CLeary, to South Africa in August, which included the signing of 25 documents (C&EN, Sept. 4, page 21). The two countries have picked 20 key areas for cooperation, including a "fast track" coal-bed methane project, renewable energy technologies, clean-coal technology, and peaceful uses of nuclear energy. The two nations also signed an agreement on reduction of greenhouse gases and emissions. Deanna Behring, assistant director for international affairs at the White House Office of Science & Technology Policy, stresses that cooperation with South Africa is not a one-way street. It contains a number of unique research sites of interest to U.S. scientists. And, she says, "There are many fields in which South Africa is among the world leaders, from mining technology to astronomy." Richard Seltzer DECEMBER 11,1995 C&EN 9
