Articles Alert

The Scientist has asked a group of experts to comment periodically upon recent articles that they have found noteworthy. Their selections, presented herein every issue, are neither endorsements of content nor the result of systematic searching. Rather, the list represents personal choices of articles the columnists believe the scientific community as a whole may also find interesting. Reprints of any articles cited here may be ordered through The Genuine Article, 3501 Market St., Philadelphia, Pa. 19104, or by telephoning (215) 386-4399. Author: SIMON SILVER Department of Microbiology & Immunology University of Illinois Chicago When liposomes containing color-tagged serium albumin were placed within alginate microcapsules, their survival time increased from hours to days, both in vitro and in mice. Coating the liposomes with phospholipase resulted in their release after a controllable delay. This system might develop into timed and delayable packages for release of drugs and hormones. P.G. Kibat, Y. Igari, M.A. Wheatley, H.N. Eisen, R. Langer, "Enzymatically activated microencapsulated liposomes can provide pulsatile drug release," FASEB Journal, 4, 2533-9, May 1990. (Massachusetts Institute of Technology, Cambridge; Children's Hospital Medical Center, Boston) A chance, but highly specific, recognition of T cell receptors by staphylococcal food poisoning and shock-inducing toxins may explain the initial pathology of this diverse group of bacterial toxins. These toxins show amino acid sequence relationships to an invariant component of the major histocompatibility complex. P. Marrack, J. Kappler, "The staphylococcal enterotoxins and their relatives," Science, 248, 705-11, 11 May 1990. (University of Colorado Health Sciences Center, Denver) The relationship between chloroquine resistance in the malarial parasite and multiple drug resistance (mdr) in human tumor cells may undergo some changes. There is an apparent inconsistency between new epidemological data, which show that chloroquine resistance is associated in nature with variants of the trypanosome mdr-like gene, and results of a laboratory genetic cross in which the two were not linked. T.E. Wellems, L.J. Panton, I.Y. Gluzman, V.E. do Rosario, et al., "Chloroquine resistance not linked to mdr-like genes in a Plasmodium falciparum cross," Nature, 345, 253-5, 17 May 1990. (National Institutes of Health, Bethesda, Md.; Washington University, St. Louis) S.J. Foote, D.E. Kyle, R.K. Martin, A.M.J. Oduola, et al., "Several alleles of the multidrug-resistance gene are closely linked to chloroquine resistance in Plasmodium falciparum," Nature, 345, 255-8, 17 May 1990. (Walter and Eliza Hall Institute of Medical Resarch, Melbourne, Australia; et al.) Environmental and population microbiologists may avoid difficulties in isolating and growing pure cultures by switching to polymerase chain reaction (PCR) analysis of highly conserved (16S rRNA) sequences and measurements of total environmental RNA. PCR analysis of marine and hot spring microbes is seen in readily cultivated bugs: Perhaps 80 percent of bacteria present will not readily grow. S.J. Giovannoni, T.B. Britschgi, C.L. Moyer, K.G. Field, "Genetic diversity in Sargasso Sea bacterioplankton," Nature, 345, 60-3, 3 May 1990. (Oregon State University, Corvalis) D.M. Ward, R. Weller, M.M. Bateson, "16S rRNA sequences reveal numerous uncultured microorganisms in a natural community," Nature, 345, 63-5, 3 May 1990. (Montana State University, Bozeman) Department of Biology King's College London, U.K. Stromatolites, formed by successive layers of microbes building up into stratified fossil communities, are the earliest records of primitive ecosystems. Structural studies continue to reveal more details of early evolution, but some interesting recent findings are derived from work on carbon isotope ratios. Changes in this area may reflect decreasing carbon dioxide levels in the atmosphere of the Precambrian earth. D.J. Des Marais, "Microbial mats and the early evolution of life, Trends in Ecology and Evolution, 5, 140-4, May 1990. (NASA Ames Research Center, Moffett Field, Calif.) Leatherback turtles, which are among the largest reptiles still surviving on earth, have a very wide geographic range - from the tropics to the Arctic. One of their most interesting physiological features is their ability to maintain elevated body temperatures in cold water and to keep cool in warm waters. This is achieved in part by their large body size and also by their possession of insulating outer tissues. Such studies may contribute to discussions of how dinosaurs coped with a range of climatic environments. F.V. Paladino, M.P. O'Connor, J.R. Spotila, "Metabolism of leatherback turtles, gigantothermy, and thermoregulation of dinosaurs," Nature, 344, 858-60, 26 April 1990. (Purdue University, Indiana; Drexel University, Philadelphia) Global fertility (birth rates per 1,000 head of population) has been declining worldwide since the end of the last World War. The region of Africa south of the Sahara Desert, however, has been the exception. Social systems prevail here that still ensure benefits from having large families. This is likely to result in severe pressure on environmental resources. If trends continue, by the end of the next century, Africa will contain almost a quarter of the world's population. J.C. Caldwell, P. Caldwell, "High fertility in Sub-Saharan Africa," Scientific American, 262, 118-25, May 1990. (Australian National University and National Center for Epidemiology and Population Health, Canberra) Information now available from the study of trapped bubbles in ice cores takes the atmospheric record of methane back 160,000 years. There is a close similarity between methane levels in the trapped gases and the temperature curve (inferred from deuterium concentration). Warmer conditions led to the formation of more wetlands, which in turn led to greater methane production; but this had a positive feedback, since the methane acts as a greenhouse gas. J. Chappellaz, J.M. Barnola, D. Raynaud, Y.S. Korotkevich, C. Lorius, "Ice-core record of atmospheric methane over the past 160,000 years," Nature, 345, 127-31, 10 May 1990. (Laboratoire de Glaciologie et Géophysique de l'Environnement, St. Martin d'H`res, France; Arctic and Antarctic Research Institute, Leningrad) Most of the world's cuckoos are extremely host-specific, but there is still argument as to the advantages of such specificity. Egg mimickry is possible if a cuckoo species restricts its attention to one host. This means that not only the host, but also any subsequent cuckoo who is up to the same game, will fail to reject the invasive egg. Specificity also promotes development of a stable balance between the host species and its parasite. L.C. Brooker, M.G. Brooker, "Why are cuckoos host specific?" Oikos, 57, 301-9, April 1990. (CSIRO, Midland, Australia) Species of oak tree with big acorns tend to occupy larger geographic areas on the North American continent than their smaller-seeded counterparts. There are two possible explanations: Either the large fruits were more attractive to birds and animals, leading to faster dispersal after the last glaciation and hence earlier establishment, or the large seed, with its greater resources, has competitive advantages for the germinating seedling. The latter proposal is perhaps more likely. M.A. Aizen, W.A. Patterson III, "Acorn size and geographical range in the North American oaks (Quercus L.)," Journal of Biogeography, 17, 327-32, May 1990. (University of Massachusetts, Amherst) Department of Chemistry University of Pittsburgh Pittsburgh The Cieplak model for ã-facial selectivity in nucleophilic additions to carbonyls has been rapidly gaining popularity. However, ab initio molecular orbital calculations on simple but representative models are not consistent with predictions of the Cieplak model. Instead, these calculations support the traditional Felkin-Anh-Eisenstein model. S.S. Wong, M.N. Padden-Row, "Theoretical evidence in support of the Anh-Eisenstein electronic model in controlling ã-facial stereoselectivity in nucleophilic additions to carbonyl compounds," Journal of the American Chemical Society, Chemical Communications, 6, 456-8, 15 March 1990. (University of New South Wales, Kensington, Australia) Even though it is a common reaction, little is known about the stereochemistry of enammonium-iminium tautomerization. Nuclear magnetic resonance (NMR) spectroscopy studies on labeled substrates reveal that this tautomerization underlies a fascinating stereoselective series of transformations. K.L. Sorgi, C.A. Maryanoff, D.F. McComsey, D.W. Graden, B.E. Maryanoff, "Asymmetric induction in an enammonium-iminium rearrangement. Mechanistic insight via NMR, deuterium labeling, and reaction rate studies. Application to the stereoselective synthesis of pyrroloisoquinoline antidepressants," Journal of the American Chemical Society, 112, 3567-79, 25 April 1990. (McNeil Pharmaceutical, Janssen Research Foundation, Spring House, Pa.) à-azidoimides of either configuration (R) or (S) can be generated from the same chiral imide enolate. Since conversions of the imides to à-amino acids occur without racemization, this is one of the most flexible, practical methods for electrophilic amination of a carboxylate derivative. D.A. Evans, T.C. Britton, J.A. Ellmar, L. Dorow, "The asymmetric synthesis of à-amino acids. Electrophilic azidation of chiral imide enolates, a practical approach to the synthesis of (R) and (S)-à-azido carboxylic acids," JACS, 112, 4011-30, 9 May 1990. (Harvard University, Cambridge, Mass.) Most currently available alcohol dehydrogenases reduce prochiral ketones to optically active alcohol by delivering a pro-(R) hydrogen atom. A new alcohol dehydrogenase isolated from Pseudomonas should be especially valuable, because it usually delivers a pro-(S) hydrogen atom. G.-J. Shen, Y.-F. Wang, C. Bradshaw, C.-H. Wong, "A new NAD-dependent alcohol dehydrogenase with opposite facial selectivity useful for asymmetric reduction and cofactor regeneration," Journal of the Chemical Society, Chemical Communications, 6, 677-9, 1 May 1990. (Research Institute of Scripps Clinic, La Jolla, Calif.) IBM Research Division Thomas J. Watson Research Center Yorktown Heights, N.Y. Artificial structures (superlattices, quantum wells, and so forth) grown by molecular beam epitaxy (MBE) have allowed the observation of novel quantum phenomena. Though "quantum beats" is an old phenomenon observed in molecules, it has not been observed resulting from extended states in solids. Quantum beats have been recently reported in MBE-grown structures arising from interference of excitons with slightly different confinement energy due to well-width fluctations. E.O. G”bel, K. Leo, T.C. Damen, J. Shah, et al., "Quantum beats of excitons in quantum wells," Physical Review Letters, 64, 1801-4, 9 April 1990. (AT&T Bell Laboratories, Holmdel, N.J.; Rutgers University, Piscataway, N.J.; Fraunhofer-Institut fur angewandte Festk”rperphysik, Freiburg, W.Ger.) When a stack of crystalline membranes is tethered, strange things can happen! One such thing is a phase transition, that is, to a "new phase of matter," as a recent paper reports. Characteristics of this new phase feature no first-order elastic couplings and a translational order that falls off algebraically. J. Toner, "New phase of matter in lamellar phases of tethered, crystalline membranes," Physical Review Letters, 64, 1741-4, 9 April 1990. (IBM Watson Research Center, Yorktown Heights, N.Y.) It used to be the challenge: Can you find a way to "unpin" the Fermi level at a GaAs surface? Ways were recently found, but the mechanisms remain elusive. A new paper gives valuable insights and proposes that decomposition of H2O and the subsequent role of hydrogen are the key to the puzzle. N.A. Ives, G.W. Stupian, M.S. Leung, "Effects of hydrogen on the photochemical unpinning of gallium arsenide," Applied Physics Letters, 56, 1537-9, 16 April 1990. (Aerospace Corp., El Segundo, Calif.) Atomic force microscopy is gradually maturing. The latest observations of gold atoms on samples submerged in water promise the possibility of atomic-resolution studies of metal electrodes in electrochemical baths. S. Manne, H.J. Butt, S.A.C. Gould, P.K. Hansma, "Imaging metal atoms in air and water using the atomic force microscope," Applied Physics Letters, 56, 1758-9, 30 April 1990. (University of California, Santa Barbara) "Can a computer have a mind?" is the central issue posed and discussed in the new best-stelling book by Roger Penrose, The Emperor's New Mind (New York: Oxford University Press, 1989). An incisive review appeared in Science, concluding that the value of the book lies in the fact that "it puts into the center of natural science questions that so far have been asked mainly by philosophers and children." W.H. Zurek, "Physics, mathematics, and minds," Science, 248, 880-1, 18 May 1990. (Los Alamos National Laboratory, N.Mex.)

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