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The fluorescence excitation and dispersed fluorescence spectra of jet-cooled 4-dimethylamino-7-azaindole dimer are recorded to investigate the effect of a substitution of a dimethylamino group into the 4-position of the hydrogen atom of the 7-azaindole on the excited-state double proton transfer (ESDPT). The substitution of the dimethylamino group drastically suppresses the ESDPT reaction.

To obtain an information on the membrane charge around the interface, we measured the membrane potential and ζ-potential of cellulose acetate in aqueous NaCl solution at 34℃. The ζ-potential was negative but nearly equal to zero. The Donnan potential obtained from the analysis of the membrane potential was also negative, but the absolute magnitude was much larger than ζ-potential. As the results of analysis, it was found that the cellulose acetate membrane itself had no fixed charge and the effective membrane charge was due to the Cl^- ions adsorbed by the membrane. The saturated adsorption amount expressed in surface density and the adsorption coefficient within the membrane were the same as those at the surface. It was, therefore, concluded that even if the surface density of adsorbed ions within the membrane is as small as at the membrane surface, the membrane charge strongly affects the Donnan potential. This is because the Donnan potential was affected not by the charge density expressed in surface density but by the charge density in volume density. Within the membrane, the charge density in volume density becomes very large since the pore radius is extremely small, even if the adsorbed amount in surface density was small.

The membrane potential of rabbit nasal mucosa was measured in vitro to investigate the electrical properties of the tissue. The influence of bile salts, that are enhancers for nasal absorption of peptide drugs, on the nasal mucosa was also studied from the viewpoint of membrane potential. The nasal mucosa membrane was negatively charged. The membrane charge density (θ∗) was − 3.4 mmol 1 in KCl solution and − 3.5 mol 1 in NaCl solution. These membrane potentials of the nasal membrane for isotonic solution were not changed by pretreatment with 1% ( w v ) bile salts (sodium glycocholate and dehydrocholate). The membrane potential of nasal mucosa for NaCl and KCl deviated from the simple Donnan equilibrium theorem in the region of low bulk concentration, whereas the membrane potential of the cellulose membrane obeyed the theorem over all the bulk solution concentrations. This difference may be a result of the variation in the amount o ions adsorbed on the nasal mucosa membrane.

From microelectrophoretic measurements on multilamellar liposomes as a function of lipid composition and pH of the medium, the pH dependence of the ζ-potential was found to be the same for liposomes in both the absence and presence of insulin. For liposomes without insulin, it is concluded that dicetyl phosphate (DCP) is incorporated at the external surface of bilayers consisting of phosphatidylcholine and cholesterol. Furthermore, the apparent pKa for the -PO4H group of DCP in liposomes was 4.5. On the other hand, insulin entrapped in liposomes did not affect the ζ-potential of liposomes. The amount of entrapped insulin solution was the same as that of entrapped calcein solution, the latter being known to be distributed in the internal aqueous compartment of liposomes. By means of incubating the mixed solution of empty liposomes and insulin, the equilibrium constant for adsorption (k) and the amount of insulin adsorbed to liposomes at saturation (X∞) could be determined from Langmuir plots. The present data suggest that the polar regions of the insulin molecule do not occur at the liposomal surface. This may be the result of the interaction between insulin and liposomes being hydrophobic in nature.