Chemical Education Today
Reports from Other Journals
Research Advances by Angela G. King
Mass Spectrometric Monitoring of Animal Feed for BSE Spread With the recent detection in the U.S. of mad cow disease, the common name for bovine spongiform encephalopathy (BSE), there is increased demand to prevent its spread since BSE infection in humans is linked to the onset of a variant of Creutzfeldt–Jakob disease. BSE is a progressive infectious neurodegenerative disease caused by a prion, a modified form of a normal cell protein. Using products derived from scrapie-infected sheep as animal feed is currently thought to have started the spread of BSE, and thus many governments have or are considering banning the inclusion of animal products in food consumed by animals in the food production industry. The European Union has such a ban in place and currently polices it with a feed sampling program that detects animal products in livestock food through immunoassay, polymerase chain reaction (PCR), and microscopy. These methods are costly and may not detect animal protein that has been rendered at high temperatures. Now researchers in London have developed an emerging technology that utilizes mass spectrometry to detect processed animal protein (PAP) in animal feed. This work identified a set of fingerprints for peptides produced by the hydrolysis of gelatine, a derivative of the major animal protein collagen, using the soft ionization techniques of matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry (MALDI–TOF MS) and liquid chromatography electrospray ionization mass spectrometry (LC–ESI MS). Optimal results are obtained by incubating samples with 3 M HCl at 95 ⬚C for 40 minutes. The marker peptides are detectable at 100 ng/mL and a peptide fingerprint of gelatine can be obtained from feed spiked with the animal protein. The amount of animal protein in the feed can be determined by the ratio of the hydrolyzed gelatine signal at m/z 1044 to an internal standard signal at m/z 556. The detection of gelatine hydrolysis products in real samples of animal feed is difficult because the feed matrix is quite complex, so fractionation of the digested peptides was carried out before the analysis. Use of MALDI– TOF MS and LC–ESI MS has the advantages of a quick processing time and very low cost per analysis. Current work on this project includes sequencing the gelatine-derived peptides and assaying real animal feed processed with known quantities of animal meat and bone meal.
3. An undergraduate lab using these techniques is available. See Counterman, A.; Thompson, M.; Clemmer, D. Identifying a Protein by MALDI–TOF Mass Spectrometry: An Experiment for the Undergraduate Laboratory. J. Chem. Educ. 2003, 80, 177–180. 4. A feature on mad on cow disease aimed at grades 6–10 is available in Current Science 2004, 89, 10–11.
Ancient Oceans Had Less Oxygen For billions of years after life arose on earth, it barely evolved. Recent work by a team of geochemists helps explain why evolution may have been delayed. Most geologists agree that there was essentially no dissolved oxygen in the Earth’s oceans until about two billion years ago, and that Earth’s oceans have had relatively high concentrations of oxygen for the last half billion years. The amount of dissolved oxygen in the oceans in the interim mid-Proterozoic period has been unclear and the subject of much debate. The level of oxygen present during this time has evolutionary implications, since essential trace metals are redox sensitive. In oxygenated water, molybdenum is commonly present as the molybdate anion, MoO42⫺, an anion so stable it causes molybdenum to be the most abundant transition metal in today’s oceans. Molybdenum is carried in rivers to the ocean, where it can stay in solution for hundreds of thousands of years, mixing throughout the world’s oceans, and becoming a global indicator of ocean conditions. However, molybdenum is removed from solution under euxinic (anoxic and sulfidic) conditions, such as those present in the Black Sea. Although less than 0.5% of the modern seafloor is covered by euxinic waters, the sedimentation of molybdenum that occurs there accounts for 10–50% of the annual removal of Mo from ocean waters. Thus the Mo budget is very sensitive to the presence of euxinic bottom waters. The ratio of Mo isotopes found in sedimentary rock also appears to be redox sensitive. Gail Arnold, the lead author of the breakthrough publication, and her collaborators used Multiple Collector Inductively Coupled Plasma Mass Spectrometry (MC–ICPMS) to examine the isotopic composition of molybdenum in rock and sediment samples. Variations in the isotopic composition of Mo are reported as
More Information 1. Ocana, M.; Neubert, H.; Przyborowska, A.; Parker, R.; Bramley, P.; Halket, J.; Patel, R. BSE Control: Detection of Gelatine-Derived Peptides in Animal Feed by Mass Spectrometry. Analyst 2004, 129, 111–115. 2. Vestling, M. Using Mass Spectrometry for Proteins. J. Chem. Educ. 2003, 80, 122.
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The similarity in δ97/95Mo of anoxic sediments and seawater is demonstrated by analyzing samples taken from the modern ocean floor. Euxinic sediment samples have heavier
Vol. 81 No. 9 September 2004
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www.JCE.DivCHED.org
Chemical Education Today
Reports from Other Journals More Information 1. Arnold, G.; Anbar, A.; Barling, J.; Lyons, T. Molybdenum Isotope Evidence for Widespread Anoxia in Mid-Proterozoic Oceans. Science 2004, 304, 87–90. 2. Related information can be found in Lucas, C.; Walsh, K. Organometallic Chemistry of Molybdenum. J. Chem. Educ. 1987, 64, 265–266.
A Model for the Formation of Piezoelectric Single-Crystal Nanorings and Nanobows
Molybdenum isotope compositions of sources, sinks, and reservoirs important to the ocean’s Mo budget. Open circles represent the mean of replicate measurements for single samples. Reprinted with permission from Arnold, G.; Anbar, A.; Barling, J.; Lyons, T. Molybdenum Isotope Evidence for Widespread Anoxia in MidProterozoic Oceans. Science 2004, 304, 87–90. Copyright 2004 AAAS.
Mo present (δ97/95Mo ⬇ 1.52‰), nearly identical to that of seawater, while samples from oxic, Mn-rich sites, represented by Mn nodules and crusts from the Atlantic and Pacific Oceans, have an average δ97/95Mo value of ᎑0.47‰. Samples from the Cariaco Basin, second only to the Black Sea in euxinic conditions, yielded δ97/95Mo with striking similarity to the data from Black Sea samples. The isotopic difference between euxinic and Mn-oxide rich sediments is thought to be the result of isotopic fractionation as Mo is removed from seawater to Mn-oxide rich sediments. Comparing the data from modern ocean samples to data generated from black shale samples over a billion years old, collected from northern Australia’s Velkerri and Wollogorang formations, indicates the mid-Proterozoic ocean had much less oxygen compared to today. δ97/95Mo values from the ancient samples were 1.1% lighter than samples from the euxininic Black Sea. Stable sulfur isotopes from the Australian samples show that the ancient rocks formed in locations that were not isolated from the ocean during sedimentation. Thus these values indicate a global lack of oxygen in seawater, not an isolated region. Hence, the Mo isotope system is useful in determining the amount of oxygen in earth’s ocean waters.
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Piezoelectric materials generate electricity or electric polarity in dielectric crystals when subjected to mechanical stress, or create stress when subjected to an applied voltage. Zinc oxide (ZnO) is a known semiconducting and piezoelectric material that can be used in sensing, photonics, and acoustic devices. Zinc oxide has a noncentro symmetric Wurzite crystal structure with a hexagonal Bravais lattice and can be represented schematically as alternating planes of tetrahedrally coordinated Zn2⫹ and O2᎑ ions. The oppositely charged ions create polar surfaces on the crystal along the c-axis. By rolling up single crystal nanobelts, the polar surfaces of ZnO are thought to cause the formation of seamless structures, including nanorings, nanospirals, and nanoloops. There are two possible explanations of the spontaneous bending of thin polar surface-dominated (PSD) sheets into nanorings. The electrostatic polar charge model proposes that for nanobelts of
