or more likely some derivative, eventually might find use as an enhancer of some drug's antitumor activity. Apart from utilitarian goals, a more general picture also is emerging. Cells seem to have a fairly large collection of small molecular control elements upon which they can draw to cope with environmental stresses. The cataloging of those molecules,
whether they're called alarmones or something else, could prove important to understanding how chemistry is coordinated in living cells. Bochner and Ames published some of their findings [Cell, 29,929 (1982)], and soon will have papers appearing in the Journal of Biological Chemistry. Jeffrey Fox, Washington
Search for methylene in space intensifies Like participants in some cosmic scavenger hunt, scientists from many countries are searching for proof that the highly reactive methylene radical, CH2, is one of the constituents of the great clouds found in interstellar space. Several recent developments, they hope, may be putting them within reach of that goal. In most scavenger hunts, searchers know what they are looking for but not where to find it. In this case, scientists know both what they are looking for—the methylene radical, and where it is—in interstellar clouds. Their problem is to come up with direct evidence that the radical actually is there. Few astronomers or radiochemists doubt that methylene is present in interstellar clouds, although there have been no direct observations of it as yet. Hydrogen is the most common element in these clouds, and carbon, too, is relatively abundant in them, explains Kenneth M. Evenson of the National Bureau of Standards' time and frequency division in Boulder, Colo. Many organic molecules have been detected, so if interstellar chemistry is anything like that on Earth, methylene radicals can be expected to be present to some degree in these clouds. In fact, complex theories holding that these clouds are coalescing into newly formed stars even calculate definite concentrations for the methylene radical in the clouds. Thus, among other things, detection and measurement of the radical in space would provide an independent verification of these theories of how stars are forming. But detecting methylene in interstellar space is no easy task. Even in the laboratory its electron spectrum was not identified until 1959. The methylene radical is very reactive, and hence short-lived. It also is small and light as radicals go, so its absorption lines are shifted from their expected positions. In interstellar regions, molecules and radicals have little energy, and
they rarely occupy excited electronic energy states, explains Trevor J. Sears of the National Research Council of Canada's Herzberg Institute of Astrophysics in Ottawa. So researchers have focused their attention on the portions of methylene's spectrum that come from its lowest energy transitions. These correspond to vibrational and rotational energy states of the radical. Normally, the rotational spectra of molecules fall roughly in the millimeter and submillimeter wavelengths, which are frequencies scanned by radio and far-infrared telescopes. Because methylene is so light, however, most of its known rotational transitions are in the microwave and submicrowave regions. One rotational transition does fall in the range of radiotélescopes—an absorption line at 68 GHz. This line is, in effect, a spectral signature for the methylene radical. Recently, chemists Frank J. Lovas and Richard D. Suenram of NBS's molecular spectroscopy division in Gaithersburg, Md., supplied radio astronomers with the exact location of this signature line. That accomplishment builds on five years of investigation by researchers at NBS, Herzberg Institute, and the University of Southampton in England. In 1977, Evenson and colleagues John A. Mucha and Donald A. Jennings began to map the far-infrared spectrum of the methylene radical, searching for clues to the radical's structure. Using a farinfrared laser magnetic resonance spectrometer, they were able to find the first purely rotational transition of the methylene radical to be identified. Unfortunately, although they knew that they had a part of the rotational spectrum of the radical, they could not tell which possible rotational transition was responsible for their line. Last year, the picture became clearer. Sears and his associates at Herzberg Institute, Phillip R. Bunker and A. Robert McKellar, used a
mid-infrared laser magnetic resonance spectrometer to locate several additional lines in the radical's spectrum. The two groups, working with theoretician John M. Brown of the University of Southampton, were able to assign spectral values to most of the rotational transitions for the lower-energy levels of the methylene radical spectrum. Based on this work, they predicted that the radical should have one rotational transition at a much lower frequency—in the microwave region. Lovas and Suenram, who already were working in this lower-frequency region, then began to look for this methylene signature line in laboratory experiments. Using a Stark resonance spectroscopy technique somewhat similar to Evenson's laser magnetic technique, they found the line at 68 GHz. Once the line definitely had been assigned to the spectrum of the methylene radical, the next step was to scan an interstellar cloud at this frequency to see if the line could be detected. The Herzberg Institute team performed this experiment last spring using the radiotélescope facilities at Kitt Peak, Ariz., but found nothing. Researchers, however, see this as only a temporary setback. Both Evenson and Sears say they are not really surprised that the 68-GHz line was not detectable. Even though it represents a very low-level rotational energy transition for the radical, its energy level still is too high to expect very many radicals to occupy this level in the low-energy conditions of interstellar space. Now the researchers have picked out another transition line to look for—one which, they argue, should be occupied more fully and therefore easier to detect. Their new target is a vibration-rotation transition that falls in the far-infrared region of the spectrum at about 3000 GHz. Unfortunately, Earth's atmosphere also absorbs strongly in this region, so detecting absorption from an interstellar cloud in this region is not possible from the ground. One solution is to observe from above the atmosphere. Physicist Charles H. Townes and his associates at the University of California, Berkeley, have perfected a method to do this that uses a telescope and Michaelson interferometer mounted in an airplane that flies above Earth's atmosphere. This group plans to search for this line in a flight late this summer. Rebecca Rawls, Washington Aug. 23, 1982 C&EN
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