Chemical Education Today
Reports from Other Journals
Nature: Chemical and Biological Recycling, and Novel Micro- and Nanodevices by Sabine Heinhorst and Gordon C. Cannon
After perusing this year’s Nature issues for articles that are related to recycling through chemistry, the Earth Day theme of this JCE issue, we decided to report on two advances: the more efficient generation of hydrogen, a recyclable energy source; and the remarkable way in which certain bacteria recycle the greenhouse gas, methane. In addition, we have included two articles that point the way to ever smaller analytical and mechanical devices of the future. Photocatalytic Water Splitting The first article we chose is in the “Recycling through Chemistry” category. The brief communication (2006, 440, March 16, 295) by a group of scientists from the University of Tokyo, Nagaoka University of Technology, and the Japan Science and Technology Corporation describes a novel photocatalyst that brings clean, recyclable hydrogen-based energy technology a step closer to reality; more information on hydrogen as an energy source is at http://www.hydrogen.energy.gov/index.html (accessed Nov 2006). Loading of a solid (Ga1-xZnx)(N1-xOx) solution with Rh–Cr mixed oxide nanoparticles yields a crystalline photocatalyst that supports the splitting of water into H2 and O2 gas in the presence of visible light. With a 2.5% quantum efficiency for light in the range of 420–440 nm, this photocatalyst is an order of magnitude more efficient than those previously described. The improved catalytic efficiency and stable activity (ⱖ 35 h) of the Rh–Cr oxide-modified solid (Ga1⫺xZnx)(N1⫺xOx) solution suggests that this photocatalyst holds promise in supporting efficient solar energypowered hydrogen generation in the future.
921) managed to enrich a consortium of two extremely slowgrowing microbial species from the anoxic sediment of a freshwater canal that is rich in nitrogen and methane from agricultural runoff and microbial activity (Figure 1B). The researchers were able to follow the consortium’s N2 production and nitrite and methane utilization under controlled anaerobic growth conditions in the laboratory and show that timing and stoichiometry of N2 evolution mirror the disappearance of CH4 and NO2⫺ from the culture medium, consistent with the proposed reaction shown in Figure 1A. As determined by DNA sequence analysis, the consortium consists mainly of two “partners in crime”: an archaeon, and a bacterium that belongs to an elusive group of unculturable species. Their unique ability to couple the anaerobic oxida-
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Biological Methane Recycling Methane is a powerful greenhouse gas whose atmospheric concentration has increased by 150% since 1750 (http:// www.epa.gov/methane/index.html (accessed Nov 2006)). The gas is produced by biological processes, predominantly the metabolism of methanogenic bacteria in natural wetlands (Figure 1B), and by anthropogenic processes related to energy consumption and production, agriculture, and waste management (http://www.eia.doe.gov/oiaf/1605/ggccebro/ chapter1.html (accessed Nov 2006)). Removal of methane occurs predominantly via chemical reactions in the atmosphere, but some remarkable biological methane “sinks” have recently been discovered that may prove to be significant players in the global biogeochemical carbon cycle. The newest of these biological methane recycling processes is the anaerobic oxidation of the gas coupled to nitrite or nitrate reduction. Over a period of 16 months, Raghoebarsing and colleagues from Radboud University Nijmegen and the Royal Netherlands Institute for Sea Research (2006, 440, April 13, 918– www.JCE.DivCHED.org
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Figure 1. Anaerobic bacterial methane recycling. A. The reactions catalyzed by a newly discovered bacterial consortium that is able to anaerobically oxidize methane through coupling to the reduction of nitrate or nitrite. B. Bacterial activity related to nitrogen and methane metabolism in the oxic and anoxic zones of a freshwater body receiving considerable agricultural runoff. The figure was modified from the News and Views commentary by Thauer and Shima (2006, 440, April 13, 878–879).
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Reports from Other Journals tion of methane to denitrification is not only remarkable from a scientific point of view but may constitute an important process for global methane recycling that counteracts the global warming trend. A Miniature Chemical Motor Eelkema and colleagues from the University of Groningen, Eindhoven University of Technology, and the Phillips Research Laboratory in the Netherlands have developed a remarkable light-driven nanomachine that is able to move much larger objects, such as a m-size glass rod (2006, 440, March 9, 163). The machine consists of the synthetic motor molecule 9-(2-phenyl-2,3-dihydro-cyclopenta[a]naphtalen-1-ylidene)-9H-fluorene (Figure 2) dispersed in a liquid crystalline film. The motor molecules aid in the helical alignment of the liquid crystal film parallel to the surface. Irradiation with 365 nm UV light induces isomerization around the double bond (shaft) in the motor that connects its rotor portion to the stator (Figure 2), and thermal
Figure 2. The light-driven rotating nanomotor 9-(2-phenyl-2,3dihydro-cyclopenta[a]naphthalen-1-ylidene)-9H-fluorene.
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isomerization at 20 ⬚C completes rotation of the rotor in the same net direction after removal of the light source. This molecular motion in turn causes a collective re-orientation of the film surface from a right- to a left-handed helical arrangement. Glass rods sprinkled onto the film surface are rotated at an average speed of 0.67 rpm during the film re-orientation process. When the enantiomer of the molecule shown in Figure 2 is incorporated into the liquid crystal film, liquid crystal reorientation and glass rod rotation proceed in the opposite direction. Microfluidics—Innovations and Applications Finally, we want to mention the series of excellent reviews on recent advances and potential future benefits of microfluidics technology (2006, 442, July 27, 368–418). The topics covered in these articles range from applications of microfluidics technology to analysis and control of chemical reactions (even at the single molecule scale), to guidance of cell growth, and sorting of cell types. Most intriguing, however, is the potential use of this technology for the development of medical diagnostic devices. If sufficiently inexpensive, robust, user-friendly, and portable detectors for bacterial or viral pathogens can be developed. Such devices could potentially find widespread use in remote locations and settings that lack refrigerated high-tech instrumentation. They would undoubtedly have a significant positive impact on health care in developing countries. Sabine Heinhorst and Gordon C. Cannon are members of the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043;
[email protected];
[email protected].
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