Veithen et al (2015), writing about OR1D2’s broadly tuned agonist spectrum, claim that “the different agonists are not linked by a common organoleptic characteristic or note.” Here we present evidence, in the form of a differential experiment, to refute that statement.
The following mixtures were prepared: 1.) tetrahydromyrcenol 0.6g, bourgeonal 15% in EtOH 0.9g, floralozone 50% in EtOH 0.15g; 2.) the same ingredients and quantities again plus aldehyde C11 enic (undec-10-enal) 10% in EtOH 0.15g and aldehyde supra (undec-9-enal) 10% in EtOH 0.3g. Undecanal, an OR1D2 antagonist, was not available so the two undecenals were substituted which both have similar odors to undecanal.
When the odors of the two mixtures were compared, mixture 1 smelled bright and clean, like pine without the camphorous, or lemon-lime without the citrus, or peach without the fruity-lactonic, or rose without the floral. Mixture 2 smelled much more dull, having a fatty-soapy, slightly metallic character. Both mixtures were dominated by clean laundry, powdery, and aldehydic notes, but mixture 1 (the +1D2 mixture) showed a very clear but hard to describe “brightness” that mixture 2 (-1D2) lacked. Undecanal is not known to antagonize any other receptor besides OR1D2.
Moreover, once the experimenter’s nose was trained to the differential, the OR1D2 note could be smelled more strongly in tetrahydrolinalool (log10 EC50 -4.81) than in linalool (log10 EC50 -4.26); more strongly in phenethyl acetate (-3.91) than in phenethyl alcohol (unknown activity); strongly in neryl acetate (-3.25); and more strongly in (γ-undecalactone (-5.14) and δ-dodecalactone (-5.09) ) > γ-decalactone (-3.75), correlating with the odorants’ relative EC50s for OR1D2. Other OR1D2 agonists that we smelled all included the same “bright” note from the differential experiment.
Additionally, when phenethyl acetate was combined with aldehyde supra on a scent strip, the mixture lost the “brightness” of the acetate and smelled like phenethyl alcohol mixed with an aliphatic aldehyde.
Based on this experiment, we conclude that OR1D2 contributes a “bright” top note to odors, and we predict that phenethyl alcohol would not be an OR1D2 agonist.