Meeting Briefs from Anaheim
Evidence that chlorination may form mutagens Even in dilute aqueous systems, purine and pyrimidine bases commonly found in natural water systems react with chlorine to form compounds that are mutagenic when measured by the Ames test, according to Dr. Joseph P. Gould of Georgia Institute of Technology (Environmental Chemistry Division). Gould reacted the purine base caffeine and pyrimidines uracil and cytosine with chlorine. Caffeine and uracil formed simple chlorination mixtures, whereas cytosine produced a complex mixture containing as many as four different, very stable, chlorinated products. All of these compounds gave positive results in the Ames test for mutagenesis with the cytosine compounds being the strongest mutagens and the caffeine compound the weak est. Dechlorination before running the Ames test markedly reduced mutagenic activity in all cases, Gould found, suggesting that N-chloro compounds are a significant cause of the mutagenic activity. Reagent is good for transposing carbonyls Potassium 3-aminopropylamide (ΚΑΡΑ) reacts readily with vinyl ethers and vinyl sulfides, notes Dr. Charles A. Brown of IBM's research laboratory in San Jose, Calif. (Organic Chemistry Division). Though the ethers do yield some dienes, both ethers and sulfides give alkynes that are "exclusively terminal," meaning the triple bond is always at the end of the carbon chain. Brown calls this a "KAPA-catalyzed, acetylene zipper reaction." Because the terminal acetylene can be changed back into a carbonyl group, the entire re action series permits one to move the carbonyl group about the molecule. Yields in most steps are high (80 to 90% range), and reaction conditions mild. Microwave treatment improves soy proteins Microwave heating before hot water treatment produces soybean protein products superior to those obtained with hot water alone, University of Guelph (Ontario) food scien tists D. W. Stanley and D. L. Armstrong say (Agricultural & Food Chemistry Division). Although hot water is more ef fective in inactivating the lipoxidase enzymes that cause "beany" flavors, microwaves do a better job of inactivating trypsin inhibitors responsible for antinutritional effects. The combined treatment also gives higher yields of acid-precipitable protein. Cancer detected in humans by NMR Successful use of nuclear magnetic resonance to form cross-sectional images of the human body and to detect cancerous tissue noninvasive^ was announced by Dr. Raymond Damadian of State University of New York, Brooklyn (Nuclear Chemistry Division). The technique de rives from Damadian's 1971 discovery that NMR can dis criminate between normal tissue, containing 65% water, and malignant tissue, containing about 90%. Only recently,
however, has the Brooklyn group been able to build an NMR scanner large enough to accept the human body. This scanner is able to localize the origin of resonance signals within the human body because of a special magnetic field geometry: The field strength is large enough to initiate resonance only within a region 4 mm across. The chest images exhibited by Damadian resemble those now avail able via computerized axial tomography (CAT-scan). But Damadian emphasizes that NMR requires no computer re construction and no x-ray exposure to the patient, and it can provide a chemical analysis without biopsy. He expects the technique to be ready for clinical use in two to five years. Peroxide helps sun degrade pesticides When activated by sunlight, tiny amounts of hydrogen per oxide naturally present in water help break down persistent pesticides—even those that otherwise resist photodegradation—according to William M. Draper and Dr. Donald G. Crosby of the University of California, Davis (Pesticide Chemistry Division). Practical applications of this finding could result in improved decontamination of industrial ef fluents, more effective sewage treatment, and better design of pesticides, they say. Mass spectroscopy method gentle A new and very gentle method for performing mass spec troscopy on large biological molecules has been developed by Dr. Ronald MacFarlane of Texas A&M University (Nuclear Chemistry Division). The technique vaporizes and ionizes even very fragile molecules without breaking them apart. MacFarlane explains that fission fragments of californium-252 have energies in excess of 100 meV and are heavier than krypton. Striking a surface under study, they deposit their energy in a tri I Month of a second and blast a small area of surface molecules into a superheated, ionized plasma, which then can be accelerated in the spectrometer. With a sample of plant chlorophyll, for example, MacFarlane produced fragments containing up to four individual mole cules. He also found that the nuclear energy pulses were absorbed by the chlorophyll as if they were bursts of sun light, providing the first direct experimental confirmation of theories on how chlorophyll transfers energy from the leaf surface into the interior. Enzyme could aid shellfish processors A chitinase enzyme system obtained from bacteria could be used to treat shellfish waste, says Dr. Paul A. Carroad of the University of California, Davis (Agricultural & Food Chemistry Division). Chitin is the natural polymer that makes up a substantial part of the shells of shrimp, crab, and lob ster. Carroad is investigating the feasibility of using the enzyme to depolymerize shellfish chitin, with the hydrolysis products converted to useful commodities such as singlecell protein. This would help solve a serious waste disposal problem now faced by shellfish processors, he notes. March 27, 1978 C&EN
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Meeting Briefs from Anaheim
Test for breast cancer has promise A skin test to detect breast cancer has performed well in preliminary clinical trials, according to Dr. George F. Springer of Evanston Hospital, affiliated with Northwestern University of Illinois (Carbohydrate Chemistry Division). Of the slightly more than 100 patients that he and colleagues tested, all those actually afflicted with carcinoma showed positive in the skin test. Two women, who now show no sign of disease, tested "falsely" positive, and they will be watched for any cancer development. The test is "not yet fully standardized and requires studies on many more people." Such studies are under way at Northwestern and in collaboration with a group at Memorial Sloan Kettering Institute in New York City, but results are not available. The skin test relies on partial disappearance of a blood-type antigen in breast cancer patients. New mechanism for metal biomethylation offered A new mechanism for biomethylation of metals comes from the laboratory of Dr. John M. Wood at the Freshwater Biological Institute of the University of Minnesota (Inorganic Chemistry Division). For platinum methylation, both Pt(IV) and Pt(ll) oxidation states must be present for a methyl group to be transferred from the coenzyme vitamin B12 to the metal. Wood's group finds that Pt(ll) forms a one-to-one complex with the vitamin by forming an adduct to the corrin macrocycle of vitamin B12. NMR studies show a downfield shift in methyl resonance on the cobalt atom of the vitamin when this complex forms, indicating a change in electron density of the methyl group. This change makes the methyl group more liable to attack by Pt(IV) to form the methylplatinum product. Leukemia inhibitor made chemically Harringtonine, a promising antileukemia compound derived from a rare Asian plum-yew tree, has been made chemically from commercially available materials, report U.S. Department of Agriculture scientists Kenneth L. Mikolajczak and Cecil R. Smith Jr. (Medicinal Chemistry Division). Actually, their synthesis starts with ce.phalotaxine from the plum-yew tree, a natural product that other chemists have synthesized from commercially available materials. Although the synthetic approach to harringtonine is far from being perfected, extraction of the trees also is fraught with problems—25 trees yield a mere 36 grams. Another USDA group, also at the Peoria, III., lab, is studying tissue culture as a means of producing the drug. Radionuclides from lake core samples Radionuclides of a type found only in spent nuclear reactor fuel have been found in core samples from the Niagara River delta in Lake Ontario, according to Dr. Muralidhara B. Gavini 34
C&EN March 27, 1978
of Woods Hole Océanographie Institute (Nuclear Chemistry Division). The isotopes, which apparently began to accumulate in the sediments in 1966, include trace amounts of curium-244, an isotope not present in bomb test fallout. Other isotopes were also found, says Gavini, including cesium-137 and plutonium-239. He doesn't know if the radionuclides are concentrating in fish and other life forms, or if they present any direct threat to humans. However, Gavini does say that the trail of curium-244 can be traced upstream from the delta, back through the Niagara River, down the south shore of Lake Erie, and up to, but no farther than, the mouth of Cataraugus Creek in New York state. Cataraugus Creek, he notes, drains West Valley, N.Y. And in West Valley, he says, lies the abandoned nuclear fuel reprocessing plant formerly operated by Nuclear Fuel Services. GMP stacking may be helped by alkali metal ions The structures of nucleic polymers have been thought to be directed entirely by hydrogen bonding and base stacking forces. However, Dr. Thomas J. Pinnavaia and associates at Michigan State University find that, at least at high concentrations, alkali metal ions can influence the solution ordering of 5'-guanosine monophosphate (Inorganic Chemistry Division). Using proton magnetic spectroscopy, the chemists find that GMP salts containing alkali metal ions of intermediate size (Na+, K+, and Rb+) form highly ordered structures that are not formed by salts containing either the smaller lithium ion or the larger cesium ion. They postulate that the alkali metals bind to oxygen atoms of the guanine residues arranged in cyclic or cagelike arrays. It is further thought that stability of the polymer depends not only on interbase hydrogen bonding and stacking but on the ability of the alkali metal to occupy the network of holes formed within the arrays. Laser process purifies silane A process for purifying silane (SiH4) with ultraviolet laser energy is being developed by Dr. John Clark of Los Alamos Scientific Laboratory (Physical Chemistry Division). Silane is used in making silicon semiconductor devices and solar cells. Eliminating trace impurities would lead to better process quality control and higher efficiency in the final devices. Industry sources have told Clark that the savings could amount to $10 million per year. In the Los Alamos process, silane gas is illuminated by 193-nm light from an argonfluoride laser. Silane itself is relatively transparent at these wave lengths, but the major impurities—AsH3, PH3, and B2H6—are broken up. The resulting fragments polymerize into a gunky deposit on the walls. Clark and his colleagues have demonstrated the process on silane gas with 1 % impurities, but have yet to demonstrate it on commercial-grade gas where the impurities normally are at the parts-per-billion level.
