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JCE Featured Molecules
William F. Coleman
Molecular Models of Antioxidants and Radicals March Featured Molecules This month’s featured molecules come from the paper by John M. Berger, Roshniben J. Rana, Hira Javeed, Iqra Javeed, and Sandi L. Schulien (1) describing the use of DPPH to measure antioxidant activity. DPPH was one of the featured molecules in September 2007 (2) and the basics of antioxidant activity were introduced in last month’s column (3). In addition, some of the other molecules in the paper are already in the featured molecules collection (4). The remaining structures in the Figure 1 and Table 1 of the paper have been added to the collection. All structures have been optimized at the 6-311G(D,P) level. These molecules suggest a number of possible student activities, some reminiscent of previous columns and some new. (R,R,R)-α-tocopherol is one of the molecules in the mixture that goes by the name vitamin E. These molecules differ in the substituents on the benzene ring and on whether or not there are alternating double bonds in the phytyl tail. In (R,R,R)α-tocopherol the R’s refer to the three chiral carbon atoms in tail while α refers to the substituents on the ring. (R,R,R)-αTocopherol is the form found in nature. An interesting literature problem would be to have students learn more about the vitamin E mixture and the differing antioxidant activity of the various constituents. Additionally they could be asked to explore the difference between the word natural as used by a chemist, and “natural” as used on vitamin E supplements. Can students find regulations governing the use of the term “natural”? Can they suggest alternative legislation, and defend their ideas? If students read about vitamin C they will discover that only l-ascorbic acid is useful in the body. It would be interesting to extend the experiment described in the Berger et al. paper (1) to include d-ascorbic acid. How do the antioxidant abilities of the enantiomers, as determined by reaction with DPPH compare? Is this consistent with the behavior in the body? Why or why not?
Wellesley College Wellesley, MA 02481
Berger et al. mention two other stable neutral radicals, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and Fremy’s salt. In a reversal from the use of stable radicals to measure antioxidant properties, these two molecules have proven to be very versatile oxidation catalysts in organic synthesis, and would make a rich source of research papers for students in undergraduate organic courses. Literature Cited 1. Berger, J. M.; Rana, R. J.; Javeed, H.; Javeed, I.; Schulien, S. L. J. Chem. Educ. 2008, 85, 408. 2. Coleman, W. F. J. Chem. Educ. 2007, 84, 1496; http://www.jce. divched.org/JCEWWW/Features/MonthlyMolecules/2007/Sep/ (accessed Jan 2008). 3. Coleman, W. F. J. Chem. Educ. 2008, 85, 320; http://www.jce. divched.org/JCEWWW/Features/MonthlyMolecules/2008/Feb/ (accessed Jan 2008). 4. Coleman, W. F. J. Chem. Educ. 2007, 84, 1650; http://www.jce. divched.org/JCEWWW/Features/MonthlyMolecules/2007/Oct/ (accessed Jan 2008).
Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2008/Mar/abs464.html Full text (HTML and PDF) with links to cited URLs and JCE articles Supplement Find Molecular Models of Antioxidants in the JCE Digital Library at http://www.JCE.DivCHED.org/JCEWWW/Features/ MonthlyMolecules/2008/Mar/. Molecules added to the collection this month are: l-ascorbic acid (vitamin C); trans-cinnamic acid; citric acid monohydrate; Fremy’s salt (nitrosodisulfonate)dianion; hydroquinone; salicylic acid; TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) in its anion, cation, and neutral form; (R,R,R)-αtocopherol (vitamin E).
citric acid l-ascorbic
acid (vitamin C)
trans-cinnamic acid
salicylic acid
hydroquinone
(R,R,R)-α-tocopherol (vitamin E)
Antioxidants featured this month. Fully manipulable Jmol versions of these and many other molecules are available at http://www.JCE.DivCHED. org/JCEWWW/Features/MonthlyMolecules/.
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Journal of Chemical Education • Vol. 85 No. 3 March 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
