Masking Effects of Odorants on a Malodorous Molecule in a Phospholipid Molecular Layer

1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC) molecular layer with the addition of trans-2-nonenal (NE) as a simple experimental model of epithelial cellular membrane damaged by malodorous substance was investigated to elucidate the masking effect of odorants (benzaldehyde (BA), methyl benzoate (MB), phenyl acetate (PA), linalool (LL), dihydromyrcenol (DM), tetrahydrolinalool (TL), and 3,7-dimethyl-1-octene (DO)). As for the surface pressure (Π)-area (A) isotherm of the DOPC monolayer, A at Π for the DOPC monolayer including NE were decreased by the aromatic compounds with electron-withdrawing substituents (BA, MB) in comparison with that with electron-donating substituent (PA). The decreases in A with the addition of acyclic terpenes with both double bonds and OH group (LL, DM) were larger than those with either double bond or OH groups (TL, DO). Similar trends to the changes in A of the Π-A isotherms were obtained in the peaks of the wavenumbers in Fourier transform infrared spectroscopy arising from the PO₂ ^- asymmetric stretching vibration mode of DOPC with the addition of NE and the odorants. These results suggest that odorants with the aromatic ring with electron-withdrawing substituent are easily eliminated from the DOPC membrane together with NE as the masking effect, rather than the aromatic ring with electron-donating substituent.