Specific adsorptions of bitter or odorous substances on a synthetic lipid multibilayer matrix (2C18N+2C1/PSS-) were detected by observing frequency changes of a multibilayer-coated quartz-crystal microbalance (QCM). Partition coefficient (P) and diffusion constants (D) of these substances in the lipid matrix could be obtained quantitatively by using the QCM method. There were good correlations between partition coefficients of various bitter or odor substances to the synthetic multibilayer film on the QCM and the intensity of bitter tastes or olfactory receptions in humans: the stronger the intensity of a bitter substance or odorant, the greater the adsorption on the lipid matrix. This indicates that the lipid-coated QCM acts as a sensitive and selective sensor for bitter taste and odor. Electric responses (changes of membrane potential and membrane resistance) of the 2C18N+2C1/PSS-film occurred consecutively by the adsorption of these substances. The bitter or odor substance showing the stronger intensity induced membrane potential change in lower concentrations. It was found that bitter substances having sterically bulky molecular structures adsorb on the surface of the lipid matrix, and the phase-boundary potential of the membrane is thereby changed. On the contrary, odor substances with relatively small or slender structures can penetrate into the lipid matrix and cause reduction of the membrane resistance (the increase of ion permeability). The selective adsorption behavior of bitter and odor substances by molecular shapes was confirmed by adsorption studies of simple C9-10 hydrophobic alcohols having various molecular structures.
The membrane potential and resistance of a bilayer-immobilized film changed on addition of bitter substances or odorants in aqueous solution; there was a good correlation between the minimum concentration of these additives for inducing the membrane potential and the bitter taste or olfactory threshold in man.
peaks and large frequency shift observed in the FT-IR spectra along with the occurrence of low-energy absorption bands (CT2 band) in the electronic absorption spectra (extending into IR region) indicate that these charge carriers are migrating along the TCNQ molecules. Thus, the TCNQ molecules are stacked in columns.This stacking is affected by the surrounding dications via the structural configuration and periodicity of the electric potential.The stoichiometry of TCNQ evaluated from the results of elemental analysis is, in most of the cases, close to 4.5. This number becomes smaller for shorter dications. It is known that in TCNQ salts, TCNQ molecules are sometimes arranged in tetrads or pentads in the TCNQ columns.5-7,14 Hence, it is reasonable to expect that there are two tetrads sharing an extra TCNQ molecule in the crystal lattice of these salts. Assuming a uniform distribution of charges among these TCNQ molecules, a value of -0.44 fractional charges is obtained. However, the fractional charge is evaluated to be -0.56 to -0.7 on the basis of the frequency shift of infrared peaks. Thus, neutral TCNQ molecules very likely exist in the stacks. Migration of charge from charged to neutral TCNQ molecules is indeed observed in the electronic absorption spectra (CT2 band). The difference in conductivity by 3 orders of magnitude for C3 and C4 salts could be due to the larger separation between the tetrads (CT2 bands located at ~2000 and >2500 nm, respectively).It would be very helpful to have single crystals of these salts to study their properties. More efforts are currently underway to obtain these and also for elucidation of the conduction mechanism. More affirmative evidence is needed to show if the length made by four or five singly bonded carbon atoms is the best match for giving high conductivities. This could be important in future design of polymeric conductors.
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