Chemical Education Today
Reports from Other Journals
Nature: Clean Up Your Act with Chemistry by Sabine Heinhorst and Gordon Cannon
Since the theme for this year’s National Chemistry Week and for this issue of the Journal of Chemical Education is “Chemistry Keeps Us Clean”, we have selected articles from Nature that relate to that topic in its broadest sense. One series of articles relates to cleaner energy; the topic of the final two articles can be classified under the subject of “cleaner-living” organisms. Cleaner Car Exhausts Cars and other vehicles emit gaseous combustion products that contribute to global warming and air pollution. While the catalytic converter has significantly reduced the emission of noxious gases such as CO, hydrocarbons, and NOx, currently used Pt- and Pd-based devices tend to lose efficiency over time due to aggregation of the finely dispersed metal particles and the concomitant decrease in surface area. To counteract this phenomenon, the precious metals are currently used in excess. A group of scientists from the Japan Atomic Energy Research Institute, Tokyo University of Science, and Daihatsu and Toyota Motor Companies have developed a porous ceramic material that contains 70–90% less of the precious metal than conventional catalytic converters (2002, 418, July 11, 164–167). The Pd-doped perovskite LaFe0.57Co0.38Pd0.05O3 is able to maintain its catalytic activity over time by responding to the fluctuations in redox state of the exhaust gas with fully reversible structural changes that prevent precious metal aggregation. The Pd atoms move out of the crystal lattice in a reducing atmosphere but are an integral part of the perovskite crystal in the oxidized state of the catalyst.
Cleaner Future Fuel Technologies To address the problem of dwindling supplies of fossil fuels and rapidly increasing demands for these non-renewable energy sources, efforts in this and many other countries to find a cleaner burning alternative fuel have concentrated on hydrogen because of its abundance and its clean combustion product, H2O. In his interesting News Feature (2001, 414, December 31, 682–684), Mark Schrope summarizes the logistic hurdles that have to be overcome to convert our current gasoline car industry to one that is based on hydrogen. Safe storage and transport of hydrogen gas, and the design of fuel tanks that are large enough to support several hours of uninterrupted driving are just some of the issues that need to be resolved before this new, cleaner fuel technology will find global acceptance. Although space considerations allow only a cursory reference, we would like to mention the excellent series of reviews in the November 15, 2001, issue of Nature (2001, 414, 331–377) on recent breakthroughs in materials development for clean energy technologies. An important issue to be considered in the development of a hydrogen-based fuel technology is the fact that an input of energy is required for the electrolysis of water to release H2 and O2 gas. The most attractive, because cheapest and vastly abundant, energy for this process is solar radiation. Although used in an ingenious manner by plants in photosynthesis, attempts to match, if not surpass, these biological water-splitting processes using semiconductor photocatalysts have been only marginally successful. One reason is the limited stability of some semiconductor materials in aqueous solutions. The large bandgaps of others exceed the energy of
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Figure 1. Model of the interaction between antimicrobial peptides and target lipid bilayers. Hydrophobic regions of the amphipathic peptide are shown in green. Basic, positively charged domains that interact with the negatively charged phospholipid head groups (yellow) in the outer leaflet of the membrane (A) are shown in red. Incorporation of the peptide into the membrane leads to strain (B) and formation of transient pores (C). Transport and integration of the peptide into the inner leaflet of the bilayer (D) can lead to interaction of the peptide with intracellular target molecules (E) and/or destruction of membrane integrity (F). Figure courtesy Michael Zasloff, Georgetown University Medical School.
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Journal of Chemical Education • Vol. 79 No. 10 October 2002 • JChemEd.chem.wisc.edu
Chemical Education Today
How Living Organisms “Clean Up” Microbes
Figure 2. Crystal structure of recombinant human lactoferrin with two bound ferric ions (Sun, X. L., Baker, H. M., Shewry, S. C., Jameson, G. B., Baker, E. N. Acta Crystallogr. D Biol. Crystallogr. 1999, 55, 403). Curled ribbons depict the α-helical regions. The β conformational portions of the peptide are shown as flat ribbons, and the two white spheres represent the bound ferric ions. Figure courtesy Michael Zasloff, Georgetown University Medical School.
most photons in the solar spectrum and therefore lower their energy conversion efficiency. Zou and colleagues from the National Institute of Advanced Industrial Science and Technology and from the National Institute for Materials Sciences in Japan report a series of novel photocatalysts that are stable in water and absorb visible light (2001, 414, December 6, 625–627; see also News and Views article by N. S. Lewis on pp 589–590). Nickel-doped indium–tantalum oxides of the formula In1-xNixTaO4 (x = 0–0.2) were subjected to reduction and subsequent oxidation to create a NiO surface that prevents reversal of the water electrolysis reaction. The watersplitting reaction catalyzed by these compounds is dependent on visible light and ceases in the dark. Although these new materials represent a significant advance in the field, more work is clearly needed to optimize the bandgap of photocatalysts, allowing them to utilize the visible range of the solar spectrum and convert the light energy more efficiently, thereby increasing their usefulness for large-scale hydrogen recovery from water.
The topic of the review article by Michael Zasloff from Georgetown University (2002, 415, January 24, 393–395) has nothing to do with clean energy but provides a synopsis of the defense mechanism used by multicellular organisms to protect themselves from invasion by the myriad microbes that surround them. The heroes of this innate immune system are the more than 500 known antimicrobial peptides that have very diverse amino acid sequences and three-dimensional structures. The most striking common feature of these molecules is their ability to adopt an amphipathic character, which is critical for their mode of action. Antimicrobial peptides interact specifically with the negatively charged outer half of the microbial plasma membrane of microbes and destroy the membrane’s integrity. Since membranes of multicellular organisms present their uncharged side to the outside, they are protected from potentially harmful encounters with these peptides. In humans and other mammals, antimicrobial peptides are found in epithelial cells of the skin, tongue, airways, and the gastrointestinal tract. Lactoferrin, which is secreted into the airways, is of particular interest for cystic fibrosis patients who often suffer from chronic lung infection due to colonization of their airways by biofilms of the pathogenic bacterium Pseudomonas aeruginosa that are resistant to various treatments. Singh and colleagues from the University of Iowa and Northwestern University showed that by chelating iron, lactoferrin increases the motility of the bacteria and prevents their aggregation into biofilms (2002, 417, May 30, 552–555). The fact that microbes very rarely become resistant to antimicrobial peptides makes these biopolymers attractive candidates for medical applications and for combinatorial approaches that could reveal novel antimicrobial activities. Sabine Heinhorst and Gordon Cannon are in the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043; email:
[email protected] and
[email protected].
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