Exploring the mechanism of olfactory recognition in the initial stage by modeling the emission spectrum of electron transfer

Abstract

Olfactory sense remains elusive regarding the primary reception mechanism. Some studies suggest that olfaction is a spectral sense, the olfactory event is triggered by electron transfer (ET) across the odorants at the active sites of odorant receptors (ORs). Herein we present a Donor-Bridge-Acceptor model, proposing that the ET process can be viewed as an electron hopping from the donor molecule to the odorant molecule (Bridge), then hopping off to the acceptor molecule, making the electronic state of the odorant molecule change along with vibrations (vibronic transition). The odorant specific parameter, Huang-Rhys factor can be derived from ab initio calculations, which make the simulation of ET spectra achievable. In this study, we revealed that the emission spectra (after Gaussian convolution) can be acted as odor characteristic spectra. Using the emission spectrum of ET, we were able to reasonably interpret the similar bitter-almond odors among hydrogen cyanide, benzaldehyde and nitrobenzene. In terms of isotope effects, we succeeded in explaining why subjects can easily distinguish cyclopentadecanone from its fully deuterated analogue cyclopentadecanone-d28 but not distinguishing acetophenone from acetophenone-d8.

The ecology of electricity and electroreception

“…Whilst the detailed mechanisms of olfaction are still a matter of debate (Hoehn et al ., 2018; Liu, Fu & Li, 2020), electrostatics undoubtedly play some role at the molecular receptor level in terms of the substantial influence of electrostatics at this chemical scale. However, electrostatics may also impact the olfactory sense on a larger scale, by way of the interactions between the electrostatic charges carried by both the receptor organism and the odorant.…”

Implications of the simple chemical structure of the odorant molecules interacting with the olfactory receptor 1A1

“…When electron tunneling was first described, it was exclusively the purview of physicists [21], but it is now also a very important theme in chemistry and biology. Recently, efforts have been made to interpret similar bitter almond odors between hydrogen cyanide, benzaldehyde, and nitrobenzene using the emission spectra of electron tunneling [22]. Studies of electron transfer in proteins such as electron hopping in polypeptides, electron transfer in peptides such as amino acid relays, and light harvesting systems in photosynthesis have been reported several times [23].…”

The complexities of ligand/receptor interactions: Exploring the role of molecular vibrations and quantum tunnelling

“…Other approaches aiming to extend the VTO include correlating predicted vibrational modes in various types of odorant molecules alongside emission spectra of electron transfer to function. [ 104 ] Two more “out of the box” ideas have been proposed: the study of how a receptor influences the vibrational state of a ligand [ 105 ] and even fluorescence as a factor influencing receptor‐ligand interactions. [ 106 ]…”

“…This idea was applied to the VTO and can be easily adapted to in vivo experiments using organisms like Drosophila, other invertebrate models, and even vertebrates. [ 7–10,98,101,102,104 ] Experiments with planarians could provide valuable insight into this body of knowledge. The behavioral effects in planarians are thoroughly characterized, and this model may prove helpful for comparing nicotine/cotinine effects to the effects of deuterated nicotine/cotinine analogs (Figure 5).…”

“…This idea was applied to the VTO and can be easily adapted to in vivo experiments using organisms like Drosophila, other invertebrate models, and even vertebrates. [7][8][9][10]98,101,102,104] Experiments with planarians could provide valuable insight into this body of knowledge.…”