Chemistry of an Insect Wing Mast laboratary experiments in undergraduate chemistry begin with a 8ottle or two, bottles containing solutions and solid reagents needed t o carry out one sort of reaction or another. This is quite normal and expected for i t has been going on for years with generally suitable results. But some experiments don't have to start with a bottle a t all. It's possible t o get the ball rolling by swatting a fly, crushing a cockroach, or trapping a June bug. Almost any flying insect will do nicely as the source of raw material for a n interesting natural product experiment or project. One large, or several small, transparent flying wings ~. . will be sufficient for a chemical studv of these thin. sturdv. .. functional memhranes. The first steu after umcurine clean. drv. wines " is t o obtain an infrared soectruml which can be run directlv on the ~~~w i n e themselves hy simply placing them in the sample light beam. There is no need to use cells, discs, eylindera, or fancy hold~rs.Simply pin the wings to a thin piece of rardhonrd of &table size and slotted to matph the area of the rnfrared radiation. Hnving obtamed the spectra of 15 dtfferent species of insects-bugs, heetles, a wasp, dragunfllea, a cicada, and a katydid-and having found them all to be quite similar, I feel safe in predicting that any transparent insect wing will yield a suitable spectrum having an absorption maximum near 1640 cm-1 as shown in the figure. ~
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At this point the student may be asked to da a Little library work in an attempt to evaluate the spectrum. Before doing this, however, the student can save time by starting to hydrolyze the wings in eonstant-boiling HCI.2 Because of their small mass and great surface area, the wings can be digested, and the HC1 carefully evaporated in less then 3 hr. Any spines or large wing veins left untouched by the hydrolysis can be ignored. Addition of distilled water to the dark brown hydralysate followed by evaporation t o dryness is recommended. A stable stock solution can be prepared by dissolving the dry residue in 30 parts of 20% 2-propanol (30 ml of solvent per gram of dry residue, or more conveniently, per gram of original wing). Since the evaluation of the infrared spectrum will probably indicate peptides, the experiment can be concluded by carrying out paper or thin-layer chromatography on the stock solution and checking for various amino aeids.3A simple one-dimensional paper chromatogram with ninbydrin detection should reveal four to six different spots. A two-dimensional run should increase this number t o eight or nine and would include aspartic acid, arginine, lysine, glycine, alanine, proline, valine, tyrosine, and the nonseparating leucines. Excellent results were obtained with the following: (a) 17 X 17 cm Whatman 11 paper, ascending flow; (b) first solvent: t-butyl alcohol, cone. NHIOH (3:2 by val.); and (c) second solvent: ethyl acetate, formic acid, water (7:2:1 by vol.).
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Barker. Roy J.. J Insect I'hyaiul., 16, 19'21 (19701. 2Hailey, J . Leggett. "Techniques in Protein Chemistry,"Elsevrer Puhl. Co.. Amsterdam. 1962, p. 81. 'Fink. K., Clme. H. E:.. and Fmk, R. >I., Anol C h u m . 35,:I89r196R1. Thomas McCullough, C.S.C.
St. Edward's University Austin. Texas 78704
Volume 50. Number 2, February 1973
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