Smell of Danger

Harvard Medical School scientists have discovered a single compound, found in high concentrations in the urine of carnivores, that lets rodents like rats and mice sense carnivores in general from a safe distance.
Mice have about 1200 kinds of odour receptors and 14 kinds of TAARs (Trace Amine-Associated Receptors), in comparison, humans have about 350 odour receptors and 5 TAARs because humans rely much more on sight than on smell.
Working with commercially available predator and prey urine, used by gardeners to keep pests out of their crops and by hunters to mask their own scent or as lures for prey, the scientists discovered that one of the 14 mice TAARs, TAAR4, detected the odour of several carnivores.
The compound that activates TAAR4 is 2-phenylethylamine, a product of protein metabolism.
Elevated levels of 2-phenylethylamine are found in many species of carnivores, but not found in non-carnivores (including rabbits and deer). In a series of behavior tests, rats and mice showed a clear, innate avoidance to the smell of 2-phenylethylamine.
The structural formula of 2-phenylethylamine is shown here.
2-phenylethylamine is an amine, consisting of a benzene ring and an aminoethyl group. It is a colourless liquid at room temperature, is strongly basic, and has a fishy odour to
humans, but has the smell of danger to mice and rats..


Reference
D. M. Ferrero, J. K. Lemon, D. Fluegge, S. L. Pashkovski, W. J. Korzan, S. R. Datta, M. Spehr, M. Fendt, S. D. Liberles. Detection and avoidance of a carnivore odor by prey. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1103317108

Further Reading
Amines
Functional Groups
Structural Isomers
Percentage Composition

Study Questions

1. Write the molecular formula for 2-phenylethylamine.
2. Draw a structural formula for a possible structural isomer of 2-phenylethylamine.
3. Calculate the percentage composition of 2-phenylethylamine.
4. Circle the functional group in the structural formula of 2-phenylethylamine.
5. Circle the benzene ring in the structural formula of 2-phenylethylamine.
6. Is 2-phenylethylamine a primary, secondary, or tertiary amine? Explain your answer.
7. 2-phenylethylamine is soluble in water and ethanol (ethyl alcohol). Explain why 2-phenylethylamine dissolves in water and ethanol.
8. Ethylamine, CH₃CH₂NH₂, has a boiling point of 17^oC and K_b=4.7 x 10^-4. Predict the boiling point and base dissociation constant for 2-phenylethylamine giving reasons for your answer.
   
9. Write a balanced chemical equation for the reaction between 2-phenylethylamine and hydrochloric acid.
10. Trimethylamine, a compound related to 2-phenylethylamine, activates TAAR5 receptors in humans.
    • Draw the structural formula for trimethylamine.
    • Give the molecular formula for trimethylamine.
    • Discuss the similarities between trimethylamine and 2-phenylethylamine.