Advanced investigation of the adsorption process of geosmin molecules on polar bear and camel olfactory receptors: statistical physics treatment, in-depth DFT-modeling, and docking analysis.

To comprehend the olfaction process at a microscopic level, further elucidation of its multiple stages was essential. The content of this study served as an initial step towards achieving this goal via the examination of the adsorption of geosmin molecules on polar bear and camel olfactory receptors. The tested odorant, which is a common volatile sesquiterpenoid produced by microorganisms, was responsible for degrading the quality of various beverages, foods, and drinking water due to its unpleasant "earthy/musty" off-flavor. Indeed, the statistical physics modeling using the single layer model with two types of cavities was crucial to theoretically analyze the responsiveness of polar bear Ursus maritimus umOR11A1 and camel Camelus ferus cfOR11A1 to geosmin molecules. Indeed, fitting findings indicated that the values of the numbers of geosmin per binding cavity type 1 or 2 were lower than 1 for umOR11A1 (mixed orientations) and higher than 1 for cfOR11A1 (non-parallel orientations). The values of the molar adsorption energies relative to the two types of cavities, ranging from 10.97 to 21.69 kJ/mol, showed that process of adsorption was physical and exothermic. In addition, statistical physics modeling was also applied to theoretically characterize the two mammalian olfactory systems and quantitatively investigate the olfactory sensitivity. Additionally, a density functional theory (DFT) calculation incorporating the quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) have been conducted to enhance our understanding of the nature and types of forces contributing to the stability of the geosmin ligand. A docking study has been employed to elucidate the interaction mechanism between geosmin and both target receptors, Ursus maritimus umOR11A1 and Camelus ferus cfOR11A1, including a comparative description.