MEETING BRIEFS FROM BOSTON
Vemonia oil shows promise as reactive monomer Progress to develop vernonia oil as a reactive monomer was described in separate papers by polymer chemistry professors Stoil K. Dirlikov of Eastern Michigan University, Ypsilanti, and Leslie H. Sperling of Lehigh University, Bethlehem, Pa. Pressed from seeds of the herb Vemonia galamensis, which thrives in arid climates, the oil contains 8 0 % of the triglyceride of c/s12,13-epoxy-c/5-9-octadecenoic acid. Yields are 2227 lb per acre, compared with 1926 lb per acre for soybean oil. Dirlikov estimates that the price may eventually be the same as for soybean oil. Melting point is 2 ° C ; viscosity is 300 centipoise at 10 ° C and 100 centipoise at 30 ° C . Dirlikov described use of the oil as a reactive diluent for high-solids, low-volatiles coatings and tough epoxy resins with low moisture absorption. Sperling reported making tough, resilient resins from interpen etrating network polymers of the oil with polystyrene.
Absolute configurations of secondary alcohols Absolute configurations of chiral secondary alcohols can be determined by measuring the rotations of their 2,4-dinitrobenzenesulfenates, according to organic chemistry professor Les lie E. Craine of Trinity College, Hartford, Conn. Working with undergraduate researchers Jonathan P. Mark, Scott A. Mitch ell, and Santiago R. Vicente, Craine reacted alcohols with commercially available 2,4-dinitrobenzenesulfenyl chloride. The sulfur atom is also chiral and adopts a configuration such that the most stable diastereoisomer predominates at equilibri um in solution. The Hartford chemists developed a rule to pre dict the most stable diastereoisomer according to the grouping of small, medium, and large groups about the carbinol carbon. Other workers had previously developed a similar method for chiral primary amines.
Inhibitor for hormone system sought A safe, effective inhibitor for the enzyme phospholipase A 2 (PLA2) could open up a whole new class of drugs, according to Edward A. Dennis, a professor of chemistry at the University of California, San Diego. Dennis and coworkers have devel oped a cell culture system that allows researchers to test and study potential PLA2 inhibitors in vitro. And they have studied a compound named manoalogue, a synthetic derivative of a nat ural chemical called manoalide found in South Pacific spong es, that inhibits the activity of PLA2 both in isolation and in cell culture. "We now have an inhibitor that we can use as a mod el to design other, possibly more effective inhibitors," Dennis says. PLA2 acts on lipids in the membranes of certain cells to release arachidonic acid, which is converted by another en zyme to prostaglandins. Nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen work by blocking the pathway to prostaglandin formation. However, no effective drugs exist to block two other pathways triggered by PLA2: conversion of arachidonic acid into leukotrienes, which are involved in pro cesses ranging from asthma and anaphylactic shock to inflam 62
May 7, 1990 C&EN
mation, and release of platelet activating factor (PAF), a potent hormone that is implicated in helping egg implantation and the establishment of pregnancy. Thus, Dennis explains, PLA2 is key to understanding not only what triggers premature labor but what intitiates normal labor and delivery.
Dynamics of hydrogen exchange reaction Theory and experiment on an isotopic variant of the hydrogen exchange reaction (D + H 2 —> DH + H) agree qualitatively, but some fine-tuning is needed in the theoretical equations used to simulate this system, say Robert E. Continetti, Barbara A. Balko, and Yuan T. Lee of the University of California, Berkeley. The motion of atoms and molecules in the reaction can be simulated theoretically, and experimental measurements can be used to test the accuracy of these simulations, explains Continetti. The researchers used a crossed molecular beam apparatus—a vacuum chamber in which a beam of D atoms crosses a beam of H 2 molecules—to measure the angular and energy distributions of scattered DH created in the reaction. Good qualitative agreement was seen between theory and ex periment, but significant discrepancies were observed for DH in the less populated, high-rotational energy states. "Although great strides have been made in the prediction of the dynamics of the simplest chemical reaction," says Continetti, "detailed experimental measurements show where further work is need ed by quantum chemists to obtain a more complete picture of the forces that govern how chemical reactions occur."
Monomer forms biodegradable polyesters A method to make 1,5-dioxepan-2-one as a monomer for bio degradable polyesters was described by polymer chemistry professor A.-C. Albertsson of the Royal Institute of Technolo gy, Stockholm, Sweden. The polyester may find use in surgery for resorbable sutures, ligature clamps, bone fixation plates, and controlled drug release. Working with T. Mathisen, Albertsson reacted β-chloropropionic acid with ethylene to make 1,5dichloropentan-3-one, which was hydrolyzed to tetrahydro-4Hpyran-4-one (THP). Oxidation of THP with m-chloroperbenzoic acid yielded the monomer in 45 to 4 8 % overall yield. Tin cat alysts polymerized the monomer in 9 0 % yield to an amor phous polyester with a glass transition temperature of —39 °C. Albertsson suggested that block copolymers with other mono mers may give elastomers in which both semicrystalline and soft segments are resorbable.
Stabilized hypofluorite oxidants do useful chemistry Researchers in Israel have prepared new oxidants containing the hypofluorite (OF) moiety and have shown they are stable enough to be used in organic synthesis. Fluorine chemist Shlomo Rozen and coworkers David Hebel and Moshe Kol of Tel Aviv University bubbled fluorine gas through a mixture of water and acetonitrile, producing a reagent they believe is a complex of hypofluorous acid (HOF) and acetonitrile. HOF by itself is
MEETING BRIEFS FROM BOSTON
extremely unstable. The as-formed solution of this complexed reagent, however, is stable enough to epoxidize olefins or hydroxylase unactivated carbon atoms in steroids and other molecules (by transferring HO + ). Epoxides or alcohols labeled with oxygen-18 can be prepared using this route by starting with 18 0-labeled water. By bubbling fluorine through a mixture of methanol and acetonitrile, the Israeli workers prepared a different oxidant, which they have good reason to believe is methyl hypofluorite (CH3OF). This molecule has been thought to be too unstable to exist because it would eliminate HF too readily. But complexed to acetonitrile, the reagent is stable enough at room temperature to add CH 3 0 and F across a double bond. When mixed with arènes such as mesitylene, it transfers a methoxy (CH 3 0 + ) group to the aromatic nucleus, producing HF as a by-product. Rozen says 1 9 F nuclear magnetic resonance data support a complex of CH 3 OF with acetonitrile.
Polyester/polysaccharide composite found Certain bacterial microorganisms have been found to produce a unique cellular composite material that consists of a polyester substituent associated with a polysaccharide backbone. The discovery was made by Arthur J. Stipanovic, Paul J. Giammatteo, Vincent P. Nero, and Peter D. Robison of Texaco Research Center, Beacon, N.Y. It is known that some bacteria store energy in the form of intracellular polyester granules and that others secrete polysaccharides extracellularly. However, the researchers say, "The occurrence of extracellular assemblies of polyesters and polysaccharides has not been previously reported, to our knowledge." Solid-state 1 3 C nuclear magnetic resonance spectroscopy was used to detect the complexes, and mass spectrometry was used to determine the structure of the polyester, which turns out to be composed of β-hydroxybutyrate monomelic subunits. Although specific ap plications of the materials have not yet been identified, the re searchers speculate that the complexes might help guide mi crobiologists in taxonomic classification of bacteria.
Blood vessel drug-delivery system promising A safer means to administer heparin for its potential activity against blood vessel diseases may be local, site-specific ther apy, according to a research team from Harvard Medical School's department of pathology headed by Morris J. Karnovsky and Elazer R. Edelman. The anticoagulant heparin, Edelman explains, has the additional benefit of preventing smooth muscle cell proliferation, a major factor contributing to the development of atherosclerosis. Standard heparin interferes with blood clotting and thus has the potential for causing bleed ing when administered intravenously. Chemical modification has removed much of the blood-thinning property from heparin while retaining various amounts of its antiproliferative activity, Edelman says. Working with rats, the team carried out experi ments to see if application of the drugs directly to the diseased portion of the blood vessel might increase their efficiency and reduce systemic complications. The heparins were embedded
in a polymer matrix of ethylene-vinyl acetate copolymer, where they resided in a network of pores and connecting channels in a dry particulate state until dissolved by fluid from the outside. The researchers found no effect on blood clotting, even from the standard anticoagulant heparin, yet both versions signifi cantly reduced proliferation of smooth muscle cells. Standard heparin inhibited 8 3 % of smooth muscle cells, and the chem ically altered heparin 68 %.
Full-text, on-line system being tested . . . All the text, formulas, and figures published in 20 American Chemical Society journals over the past seven years will be available this fall on the desktop computers of 150 Cornell University faculty members and students participating in the Chemistry On-line Retrieval Experiment (CORE), according to Jan K. Olsen, director of Cornell's Albert R. Mann Library. Olsen explains that CORE is a joint project by the library, ACS's R&D group, Chemical Abstracts Service, Bell Communications Research, and OCLC, a shared library cataloging service. ACS is providing CORE with computer tapes of the texts of each journal. However, because the tapes do not include graphics and chemical structures, a page-scanning system from Bell core is being used to integrate graphics with text. The absence of graphical material has been a major criticism of full-text, on-line systems. The complete database will be stored on magnetic media and optical discs. The CORE project will eval uate the usefulness of the full-text service to Cornell faculty and students and will investigate other questions related to on-line searching, including appropriate compensation to publishers for multiple use of copyrighted material and the virtues of different types of user interfaces.
. . . but use of full-text, on-line files is lagging Use of full-text, on-line, primary scientific databases today is much less than predictions in the early 1980s had indicated it would be, say Silas E. Hammond of Chemical Abstracts Ser vice and John A. Hearty of ACS. One reason for the slow growth is that the number of years of coverage of full-text files is still too low to interest most searchers. Although many bib liographic files (such as Biosis, Medline, and the Chemical Ab stracts Registry File) have 15 or more years of data available on-line, the full-text journal databases (such as Chemical Jour nals Online) have less than four years of coverage. Further more, whereas bibliographic files may cover thousands of jour nals, full-text files cover small sets of publications. In addition, full-text systems are incomplete because they usually do not contain graphics and tables. To turn the situation around and ensure the future of full-text searching, they say, database vendors should extend breadth of coverage; use data compres sion techniques to reduce storage costs; make graphics and tables available on-line; integrate full-text systems with biblio graphic and other types of files to facilitate multifile searching; and add user-friendly interfaces based on artificial intelligence software. May 7, 1990 C&EN 63
