SCIENCE/TECHNOLOGY
New pyruvate aldolases have enhanced synthetic utility OH SCH 3 NH OH OCH 3 NHCH(CH3)2 !
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Pyruvate aldolases that are more flexible toward acceptance of diverse substrates have been found in hyperthermophilic microorganisms. The increased flexibility enhances the utility of this class of enzymes for catalyzing formation of precursor compounds used to make a wide range of biologically active compounds Note: Shaded regions in products denote structural contributions from precursors. Source: Eric J. Toone and Michael Shelton of Duke University, and Michael W. W. Adams and coworkers at the University of Georgia
machinery that underlies such functions. Tissue engineering is the manipulation or reconstruction of tissue function by biochemical and cellular approaches. An example is a device in which 36
JANUARY 11, 1993 C&EN
"Everything we're talking about . . . in cell and tissue engineering is molecular/' says chemical engineering professor Douglas A. Lauffenburger of the University of Illinois, UrbanaChampaign. "Even if we're talking about mechanical stimuli, they're transduced through molecular mechanisms. And chemical engineers are really the kind of engineers who are trained to deal with these kinds of phenomena." For example, the standard way biologists look at cell receptors is in terms of their type or specificity, explains cell biologist H. Steven Wiley of the University of Utah Medical Center, Salt Lake City. "The quantitative aspect of these receptor systems [was] completely unappreciated. Only when we started working with chemical engineers and started actually using quantitative approaches to these problems did we start to see far more information than we ever saw by looking at what receptors or substrates were triggered." Wiley adds: "I would submit to you that the collaboration of chemical engineers and biologists not only provides you with an enhanced way of doing your experiments, but it actually can yield unique insights into a system that absolutely cannot be obtained in any other way. We will find things out about these systems that will never be found out by the work of either the engineers by themselves or the biologists by themselves. The whole is far greater than the sum of its parts." •
dopamine-releasing cells are encapsulated within a selectively permeable membrane that protects them from a host organism's immune system. Such a device was recently implanted in animal models of Parkinson's disease.
Process makes (/-olefins from carboxylic acids A group of chemical researchers has developed a new process that makes it possible to synthesize an important class of petrochemicals from renewable resources. The technique efficiently converts carboxylic acids to 1-alkenes (a-olefins) having one less carbon atom. It is of potential importance industrially because billions of pounds of a-olefins are produced annually for making detergents, lubricants, plasticizers, and polyethylene, among other applications (C&EN, Oct. 8,1990, page 20). Details of the work by chemists Joseph A. Miller, Jeffrey A. Nelson,
ο
Georgia computational chemistry center opens A ribbon-cutting ceremony last month at the University of Georgia, Athens, marked the startup of a new Computational Center for Molecu lar Structure & Design. Participat ing in the dedication were (left to right) vice president for academic affairs William Prokasy, dean of arts and sciences Wyatt Anderson, chemistry professors J. Phillip Bowen and Norman L. Allinger, Geor gia Gov. Zell Miller, university president Charles Knapp, vice president for research Joe Key, physical plant director James TenBrook, and chemistry department head Charles Kutal. The computa tional chemistry center will be used to simulate and predict the behavior of molecular systems with potential pharmaceutical, bio medical, agricultural, and polymer applications. "Our goal [is not] to replace experimental research, but
and Michael P. Byrne of Henkel Re search Corp. (since renamed Cognis Inc.), in Santa Rosa, Calif., were re ported in the Jan. 1 issue of The Jour nal of Organic Chemistry [58, 18 (1993)]. Miller, the team's leader, is now employed at Exxon Chemical in Baytown, Tex. The new process is a catalytic tech nique that produces a-olefins—in high yields and with high purity— from carboxylic acids. Only minute quantities of by-products are generat ed, much less than the amounts typi cally obtained with current processes, according to Miller. The process also offers a "green" alternative to existing methods for making a-olefins because it can pro duce them from fatty acids (carboxyl ic acids from natural sources) instead of from petroleum. The technology is available for licensing through Henkel of Diisseldorf, Germany, Cognis' par ent company. In the reaction, an equimolar mix ture of a carboxylic acid and acetic an hydride is heated to 250 °C in the presence of a palladium or rhodium catalyst: RCH 2 CH 2 C0 2 H + (CH 3 CO) 2 0 -> RCH = CH 2 + CO + 2 CH3COOH This causes the carboxylic acid to un-
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to make it easier . . . by indicating which pathways might be more profitable to follow," notes center director Allinger. Codirector Bowen adds that "computational chem
Γν*>
istry methods have entered a new age and are quickly becoming an indispensable tool for doing modern chemical and biomedical research."
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JANUARY 11, 1993 C&EN
SCIENCE/TECHNOLOGY dergo decarbonylation and dehydration to a 1-alkene having one less carbon atom. Catalyst lifetimes are very long, Miller says, and the spent catalyst can be recovered for reuse. Previous decarbonylation-dehydration reactions of carboxylic acids to olefins were inefficient and relatively nonspecific toward formation of terminal olefins, according to the researchers. The Henkel process, they say, is much more efficient and produces compounds with terminal double bonds almost exclusively. The process also has potential for producing new types of linear (unbranched) oc-olefins. "Linear a-olefins commercially produced today are all ethylene-derived and hence are composed of an even number of carbon atoms," says Miller. "When carried out on naturally derived and readily available fatty acids, . . . the linear a-olefin products obtained from this new . . . technology have odd carbon chain lengths. Thus, the process is complementary to the present-day ethylene-based routes." Chemistry professor Richard F. Jordan of the University of Iowa, Iowa City, says, "Miller has developed an interesting procedure for catalytic conversion of long-chain carboxylic acids to odd-numbered, linear a-olefins. The overall process is highly selective and highly catalytic in palladium or rhodium, and is a big advance over similar reactions of carboxylic acids or acid chlorides." However, Jordan continues, "the reaction conditions (250 °C) would appear to me to be too vigorous for general application in the synthesis of fine chemicals." Joseph M. O'Connor, a chemistry professor at the University of Nevada, Reno, adds, "The work is exciting in that the chemistry is highly selective and involves a catalyst with good activity for executing a difficult and fundamentally important functional group interconversion. The process is certainly of interest to organometallic chemists from a mechanistic perspective and will no doubt stimulate further research in the area. The fact that naturally occurring, renewable fatty acids may be the starting materials is a significant feature in light of the growing importance of renewable resources." Stu Bonnmi
