In the Classroom
highlights
edited by
projects supported by the NSF division of undergraduate education
Susan H. Hixson National Science Foundation Arlington, VA 22230
Curtis T. Sears, Jr.
Theme-Based Bidisciplinary Chemistry Laboratory Modules
Georgia State University Atlanta, GA 30303
Phyllis A. Leber* and Sandra K. Szczerbicki Department of Chemistry, Franklin & Marshall College, Lancaster, PA 17604-3003 A thematic approach to each of the two introductory chemistry laboratory sequences, general and organic chemistry, not only provides an element of cohesion but also stresses the role that chemistry plays as the “central science” and emphasizes the intimate link between chemistry and other science disciplines. Thus, in general chemistry the rubric “Environmental Chemistry” affords connections to the geosciences, whereas experiments on the topic of “Plant Assays” bridge organic chemistry and biology. By establishing links with other science departments, the theme-based laboratory experiments will satisfy the following multidisciplinary criteria: (i) to demonstrate the general applicability of core methodologies to the sciences, (ii) to help students relate concepts to a broader multidisciplinary context, (iii) to foster an attitude of both independence and cooperation that can transcend the teaching laboratory to the research arena, and (iv) to promote greater cooperation and interaction between the science departments. Fundamentally, this approach has the potential to impact the chemistry curriculum significantly by including student decision-making in the experimental process. Furthermore, the incorporation of GC-MS, a powerful tool for separation and identification as well as a stateof-the-art analytical technique, in the modules will enhance the introductory general and organic chemistry laboratory sequences by making them more instrumentintensive and by providing a reliable and reproducible means of obtaining quantitative analyses. Each multifaceted module has been designed to meet the following criteria: (i) a synthetic protocol including full spectral characterization of products, (ii) quantitative and statistical analyses of data, and (iii) construction of a database of results. The database will provide several concrete functions. It will foster the idea that science is a continuous incremental process building on the results of earlier experimentalists, it will reinforce an understanding of the scientific method by allowing students to propose testable hypotheses based on previous work, and it will generate a large body of quantitative data that can be used to illustrate the fundamentals of data analysis, including statistical measures of uncertainty. We have already developed several “Environmental Chemistry” modules for general chemistry, including monitoring for orthophosphate and nitrate concentrations in water using colorimetric analyses and assaying for gasoline contamination in water and soil samples using GC-MS. Another module dealing with herbicide residues in soil is still being explored. *Corresponding author.
1130
However, we purposefully choose here to emphasize the two modules that are under development for implementation in the organic chemistry laboratory sequence. The first “Plant Assay” project focuses on fatty acid methyl esters (FAMEs) and involves three discrete phases: (i) synthesis and characterization of FAME standards, (ii) isolation of the fatty acids (as FAMEs) from a variety of different plant leaves that will be collected by BIO 110 students on field trips, and (iii) qualitative and quantitative analysis of the plant leaf extract for whole-leaf lipid composition. Acid-catalyzed Fischer esterification of carboxylic acids in methanol is a standard methodology for the preparation of methyl esters. A textbook procedure (1) for the synthesis of ethyl laurate has been employed, with good success, to prepare eight FAMEs in yields of ca. 70%. Conversion of leaf phospholipids to FAMEs proceeds readily via a transesterification reaction. Treatment of the whole leaf in a methanolic HCl solution for an hour at 80 °C (2) is sufficient after extraction in hexane to provide a suitable sample for GCMS analysis. Preliminary results obtained with an HP GCD system indicate that GC-MS will afford highly reliable quantitative data on FAME lipid composition. Possible extensions of the project include using boron trifluoride in methanol to effect transesterification (3) and examining the effect of variations in leaf type and season on lipid composition. A second “Plant Assay” study involves preparing and characterizing analogs of naphthalene-1-acetamide, which is the active growth-promoting ingredient in commercial preparations such as Transplantone® and Rootone®. There are two direct methods for synthesizing the amide from the native plant growth regulator (“auxin”) or carboxylic acid: acid-catalyzed hydrolysis of the nitrile or ammonolysis of the acid chloride derivative, prepared in situ from the acid by treatment with thionyl chloride (4). In the spring of 1996, organic chemistry students synthesized the amide derivatives of a number of auxins via the acid chloride intermediate, which is more efficiently prepared using oxalyl chloride (40–60% overall yield) instead of thionyl chloride (20– 40% overall yield), or via nitrile hydrolysis (72–99% yield). Plant bioassays, based on measurement of pea stem segment elongation (5) have only been performed on the acetamide derivatives of three auxins, indole-3-acetic acid (IAA), naphthalene-1-acetic acid (1-NAA), and naphthalene-2-acetic acid (2-NAA). In comparison with the control, indole-3-acetamide and naphthalene-1-acetamide promoted growth by 50% and 90%, respectively. The acetamide of 2-NAA impeded growth by 30% relative to the control, an observation consistent with the known antiauxin activity of 2-NAA (6). Acquisition of the nec-
Journal of Chemical Education • Vol. 73 No. 12 December 1996
In the Classroom
essary imaging system for the teaching laboratory will enable students to extend these quantitative studies to other auxin conjugates. Acknowledgment We are grateful to the NSF for financial support through the Division of Undergraduate Education (DUE9455693 and DUE-9550890).
Literature Cited 1. Mayo, D. W.; Pike, R. M.; Trumper, P. K. Microscale Organic Laboratory, 3rd ed; John Wiley & Sons: New York, 1994; pp 202–203. 2. Browse, J.; McCourt, P. J.; Somerville, C. R. Anal. Biochem. 1986, 152, 141. 3. Rodig, O. R.; Bell, C. E., Jr.; Clark, A. K. Organic Chemistry Laboratory; Saunders: Philadelphia, 1990; p 455. 4. Reference 3, pp 361–365. 5. Ballal, S.; Ellias, R.; Fluck, R.; Jameton, R.; Leber, P.; Lirio, R.; Salama, D. Plant Physiol. Biochem. 1993, 31, 249–255. 6. Venis, M. A.; Napier, R. M. Plant Growth Regulation 1991, 10, 329–340.
Vol. 73 No. 12 December 1996 • Journal of Chemical Education
1131
