Figure 6. textbfDiscrimination of deuterated odorant.

Illustrated is here the principle of odorant discrimination through shape and vibrational frequency. Octanol receptors (light blue) and citronellyl nitrile receptors (pink) accommodate octanol, citronellyl nitrile, and deuterated octanol. Since the shape of octanol and citronellyl nitrile is similar, both odorants fit into either receptor. The receptors possess different Δε, i.e., the energy between the donor state D and acceptor state A, tuned to a certain vibration of the odorant. The ability of a receptor to respond to odorant binding is denoted with a green “+” sign, while the red “−” sign shows that the receptor is passive to the corresponding odorant binding. The characteristic vibrational energy of octanol, citronellyl nitrile, and deuterated octanol are denoted as ε_oct, ε_cn, and ε_oct−deu, respectively.