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In the Laboratory
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JCE Featured Molecules
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Molecular Models of Rosmarinic Acid and DPPH
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William F. Coleman
Department of Chemistry, Wellesley College, Wellesley, MA 02481
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September 2007
Vol. 84 No. 9
p. 1496
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| Full Text |
The paper by Canelas and da Costa (1) introduces students to the antioxidant rosmarinic acid, and its interaction with the free radical DPPH. Those two molecules are the featured species this month. The original paper shows the 2-dimensional structure of the cis isomer of rosmarinic acid, although the trans isomer exhibits very similar antioxidant properties. Calculations at the DFT/B3LYP 631-G(d) level show that the trans isomer is more stable than the cis isomer in the gas phase, a situation that is expected to carry over into solution. Many antioxidants are phenols, and rosmarinic acid has four such groups available for radical formation. A DFT study by Cao et al. (2) examines the relative stabilities of the radicals formed from loss of each of the phenolic hydrogens. That paper focuses on the trans isomer, and a useful student project would be to repeat the calculations with the cis isomer. An HPLC separation of the isomers of rosmarinic acid has been published (3), and might well lead to an extension of the experiment described in ref 1 in which relative antioxidant efficiencies of the two isomers could be evaluated.
cis-rosmarinic acid 
trans-rosmarinic acid DPPH has been used extensively as a standard for determining antioxidant activity. An examination of the molecular orbital occupied by the lone electron shows significant delocalization, providing a partial explanation for the stability of the neutral radical. Our gas phase structure for DPPH, also at the DFT/B3LYP 631-G(d) level, is quite consistent with several crystal structures on DPPH and DPPH in the presence of another species (4). Students can examine the structures of trans- and cis- rosmarinic acid and the free radical DPPH in Jmol or Chime, along with other molecules in the collection, at the JCE Digital Library Web site.
Literature Cited
- Canelas, V.; da Costa, C. T. J. Chem Educ. 2007, 84, 1502–1504.
- Cao, Huai; Cheng, Wei-Xian; Li, Cong; Pan, Xu-Lin; Xie, Xiao-Guang; Li, Tao-Hong. J. Mol. Structure: THEOCHEM 2005, 719 (1–3), 177–183.
- Caniova, A.; Brandstetrova, E. J. Liquid Chrom. and Related Tech. 2001, 24, 2647–2659.
- See for example Williams, D. E. J. Am. Chem. Soc. 1967, 89, 4280 and Kiers, C. T.; de Boer, J. L.; Olthof, R.; Spek, A. L. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1976, 32, 2297.
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| More Information |
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Citation |
Coleman, William F. J. Chem. Educ. 2007, 84, 1496.
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Keywords |
Computer-Based Learning; Hands-On Learning / Manipulatives; Upper-Division Undergraduate
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History |
Created:
Last Updated: |
7/23/2007
8/16/2007
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 Caution! | | Experiments, laboratory exercises, lecture demonstrations, and other descriptions of the use of chemicals, apparatus, instruments, computers, and computer interfaces are presented in the Journal of Chemical Education as illustrative of new or improved ideas or concepts in chemistry instruction and are directed at qualified teachers. Although every effort is made to assure and encourage safe practices and safe use of chemicals, the Journal of Chemical Education cannot assume responsibility for uses made of its published materials. Many chemicals are hazardous. Precautions for the safe use of hazardous chemicals and directions for their proper disposal are described in the Material Safety Data Sheets and on the labels. We strongly urge all those planning to use materials from our pages to make choices and to develop procedures for laboratory and classroom safety in accordance with local needs and situations. |
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