Statistical physics modeling and interpretation of the adsorption of enantiomeric terpenes onto the human olfactory receptor OR1A1

The statistical physics approach has been well studied by our research team for liquid and gaseous adsorption systems. This treatment is based on the grand canonical partition function to give new interpretations of the adsorption process at molecular level for chemical senses: olfaction and taste. This work represents a contribution to understand the olfaction mechanism of four of enantiomeric terpenes by applying a statistical physics treatment that allows giving a physico-chemical meaning to parameters involved in the analytical model. It is possible to estimate the number of adsorbed molecules per site, the anchorage number, the receptor density, the concentration at half saturation and the molar adsorption energy. Through this selection of the best fitting model and through fitted values of these parameters, we showed that the adsorption of carvone and limonene enantiomers is not a multilayer process but a monolayer monosite process (monolayer adsorption model with identical and independent sites (n ≠ 1)). The physico-chemical model parameters can be used for the energetic characterization of the interactions between the carvone and the limonene enantiomers and the human olfactory receptor OR1A1 and the determination of an olfactory band of order of 14 kJ/mol, 7 kJ/mol, 9 kJ/mol, 8 kJ/mol for (R)-(−)-carvone, (S)-(+)-carvone, (R)-(+)-limonene and (S)-(−)-limonene, respectively, through the determination of the adsorption energy values and the adsorption energy distributions (AEDs). Thanks to the grand canonical formalism in statistical physics, the negative values of the Gibbs free enthalpy indicate that the adsorption process of the four enantiomeric terpenes onto the human olfactory receptor OR1A1 was spontaneous. The exothermic adsorption mechanism involved in the olfactory perception was explained via the negative values of the internal energy.