Dissipation enhanced vibrational sensing in an olfactory molecular switch

Abstract

Motivated by a proposed olfactory mechanism based on a vibrationally-activated molecular switch, we study electron transport within a donor-acceptor pair that is coupled to a vibrational mode and embedded in a surrounding environment. We derive a polaron master equation with which we study the dynamics of both the electronic and vibrational degrees of freedom beyond previously employed semiclassical (MarcusJortner) rate analyses. We show: (i) that in the absence of explicit dissipation of the vibrational mode, the semiclassical approach is generally unable to capture the dynamics predicted by our master equation due to both its assumption of one-way (exponential) electron transfer from donor to acceptor and its neglect of the spectral details of the environment; (ii) that by additionally allowing strong dissipation to act on the odorant vibrational mode we can recover exponential electron transfer, though typically at a rate that differs from that given by the Marcus-Jortner expression; (iii) that the ability of the molecular switch to discriminate between the presence and absence of the odorant, and its sensitivity to the odorant vibrational frequency, are enhanced significantly in this strong dissipation regime, when compared to the case without mode dissipation; and (iv) that details of the environment absent from previous Marcus-Jortner analyses can also dramatically alter the sensitivity of the molecular switch, in particular allowing its frequency resolution to be improved. Our results thus demonstrate the constructive role dissipation can play in facilitating sensitive and selective operation in molecular switch devices, as well as the inadequacy of semiclassical rate equations in analysing such behaviour over a wide range of parameters.

Dissipative vibrational model for chiral recognition in olfaction

“…They found that the rate of odorant-mediated inelastic ET is larger than the rate of elastic one. Following this approach, in a very recent work, Chȩcińska and co-workers examined dynamically dissipative role of environment in vibration-based olfactory recognition and showed that the strong coupling to the environment can enhance the odorant frequency resolution in the ET rates [11].…”

Experimental evaluation of the generalized vibrational theory of G protein-coupled receptor activation

“…Recently, Reese et al (81) addressed several of these concerns, showing that the binding effects of the receptor have a nonzero-all but negligible-effect on the ligand, that dynamic fluctuations have a very small effect on the transfer, and that the reorganization energy (λ) for an OR can conform to λ 1 kcal/mol. Concerns of electron density leaking into the environment were previously addressed through coupling a vibrational bath with the electron transfer (80), and such studies have shown that environmentalinduced dissipation could enhance the vibrational signaling (82). Evaluating the reliability of the electron delivery mechanism cannot be addressed until the complete structure of the OR is known and models account for all cofactors including the possible effects of perireceptor molecular species, as there is evidence that NADPH and other oxidative processes are important in GPCR activation (59).…”

“…Thus, a molecule must both fit into the active site with the correct orientation and have a vibrational mode capable of assisting in an IET process to activate the protein. Working within Turin's hypothesis, several theoretical expansions have been undertaken to account for specific considerations of the system, including charge transfer rates (60,80), receptor effects (80)(81)(82), and chiral effects (83).…”

Molecular recognition in olfaction

“…However, for the reverse process the odourant must provide the energy. Since the odourant will re-equilibrate with the receptor very rapidly after excitation [55], the reverse process is frustrated. Thus we can ignore any coherence between the electron jumping from D to A and the reverse process, and so can describe it in terms of a transition rate.…”

“…Of course, at equilibrium the same argument holds for the electrons; however, there are electrochemical processes that operate in living cells that can generate electrons of increased energy. We note that immediately following the transition, the molecule is in a vibrationally excited state, so the reverse process is then rapid; however, this can be suppressed by interactions of the molecule with its environment [55]. (3) Third, D and A and must not be coupled strongly to their environment:…”