sample of the S-enantiomer from Thomas Haffner, 

 a chemist at the Berlin Technical University. The 

 stuff could all evaporate, so we don't dare sniff it. 



Now Guang performs the critical experiment. He 

 runs the commercial mixture of delta-decalactone 

 through the chiral column and, seventy-seven min- 

 utes after the process begins, two peaks emerge in the 

 area of the readout where delta-decalactone appears, 

 fifty seconds apart. When Guang spikes the com- 

 mercial mixture with the S-enantiomer, the first peak 

 enlarges. When he runs only the porcupine sample 

 through the chiral column, a single delta-decalactone 

 peak emerges, coinciding with the second peak of the 

 commercial mixture. The delta-decalactone from the 

 porcupine is therefore R-delta-decalactone. Guang 

 and I shake hands. The project is finished. 



What did we learn by assigning a chemical 

 name to an odor we already recognized? We 

 learned something about its uniqueness. The por- 

 cupine has a strong interest in sending an unam- 

 biguous message. A message that says "porcupine 

 here" is preferable to one that says "perhaps porcu- 

 pine here, perhaps something else." If a predator has 

 ever had a prior painful encounter with a porcu- 

 pine, the unique odor would be more likely to trig- 

 ger the impulse to retreat. 



A chenucal name is also a specific entry into the 

 large dictionary of natural odors. Smells make up a 

 rich natural language for most mammals, playing a 

 key role in social structure, navigation, and much 

 else. But people for the most part are insensible to 

 the variation and meaning of smells, both for our 

 species and others. At present, the best tool for learn- 

 ing the rudiments of such languages is chemistry. 



Chemistry will also help decipher other mysteries 

 of the porcupine, including the fluorescent charac- 

 teristics of porcupine quills — yet another mechanism 

 of warning oft nocturnal predators. That may be a 

 mystery I leave for another scientist. To him or to her, 

 I can offer a very good pair of used vinyl gloves. □ 



Chemical detective work identified the molecule responsible for the porcupine's 

 distinctive warning odor. The odor was one of eighty-nine volatile compounds 

 detected by a gas chromatograph-mass spectrometer (GC-MS) (a). Washing the 

 same mix of eighty-nine chemicals in three increasingly strong solvents led to 

 three extracts, one of which smelted of porcupine (b). The GC-MS showed that 

 the extract was made up of just three major organics, including the compound 

 delta-decalactone (c). A second run of the raw porcupine mixture of eighty-nine 

 chemicals through the GC-MS split the output simultaneously between a strip- 

 chart recorder and a human nose, confirming that the odor is delta-decalactone 

 (d). But a commercial sample of delta-decalactone didn't smell of porcupine (e). 

 The puzzle was resolved when the investigators realized that commercial delta-de- 

 calactone (purple) is made up of two distinct molecules that are mirror images of 

 each other. Once the two were separated (red, blue), the red component, identi- 

 fied as R-delta-decalactone, passed the smell test (f). 



R-delta-decalactone S-delta-decalactone 



March 2006 NATURAl HISTORY 



53 



