J. Am. Chem. SOC. zyxwvu 1984, 106, zyxwvu 4423-4421 4423 magnetic axes of the product diyl. It is possible that the symmetry of the photoexcited diazene is conferred upon the singlet diyl. The dinitrogen is certainly produced in its ground electronic state zyxwvuts ‘Z: +. (The first electronic excitation of zyxwvutsrq N2 to 3Zu+ is at 50 200 cm-’.) Approximate conservation of symmetry suggests that the polar zyxwvut x symmetry is conferred on the diyl fragment of the photodis- sociation. Acknowledgment. Support by the National Science Foundation under CHE-812006 and CHE-801 1399 is gratefully acknowl- edged. Registry No. 1, 32553-01-8; 2, 31689-32-4. Chemoreception by an Excitable Liquid Membrane: Characteristic Effects of Alcohols on the Frequency of Electrical Oscillation Kenichi Yoshikawa* and Yasuhiro Matsubara Contributionfrom the College of General Education, University of Tokushima, Minamijosanjima-cho, Tokushima 770, Japan. Received October 31, 1983 Abstract: Studies were made on oscillations across a liquid membrane consisting of an oil layer, nitrobenzene containing picric acid, between two aqueous layers: that on the left containing 5 mM CTAB plus an alcohol at various concentrations and that on the right containing 0.1 M sucrose. This system showed sustained rhythmic oscillations of electrical potential of 200-400 mV with an interval on the order of 1 min. The frequency of oscillations increased with increase in the concentration of the alcohol. The critical concentration of alcohols needed to induce oscillations decreased with an increase in their hydrophobicity. The oscillations can be explained by a mechanism of repetitive formation and abrupt destruction of a monolayer structure of CTAt on the interface between the organic and aqueous phases. The response to alcohols in the liquid membrane apparently resembled that of biological cheomoreceptive membranes. The possibility was suggested of developing a new type of chemical sensor with the ability to distinguish various chemical substances from the patterns of electrical oscillation that they induced. One of the most interesting phenomena in biological systems is excitability. There is much literature on electrical phenomena accompanying electrical excitation in biological membranes, but despite extensive studies on biooscillations, the physicochemical mechanisms of these phenomena are not yet clear. For an un- derstanding of the mechanism of biological excitation and/or oscillation, various types of artificial membranes with excitability have been investigated.’” Most of the artificial membranes examined were excitable under an external force, such as pres- sure,’*2 v~ltage,~,~ or electrical c ~rrent.~~~~~ In excitable biomem- branes, it is well established that the difference in the compositions of electrolytes, especially potassium and sodium ions, across the membranes is important. Investigations on “self-excitable” ar- tificial membranes are thus important in understanding the mechanism of excitation and/or oscillation in biological systems. However, there are very few report on this phenomenon in artificial membranes. Kobatake4 found that porous membranes doped with dioleylphosphate, DOPH-Millipore membranes, showed sponta- neous firing of an electrical potential when placed between so- lutions of different KCI concentrations. Pant and Rosenberg’ observed that a lipid bilayer membrane separating bathing solution compartments of potassium ferricyanide and potassium iodide could be set into sustained electrical oscillations when the pH’s of the two compartments were adjusted to 5 and 10, respectively. von Klitzing et aLs reported that voltage spikes were generated (1) Teorell, T. J. Gen. Physiol. 1959, 42, 831-845. (2) Arisawa, J.; Furukawa, T. J. Membr. Sci. 1977, 2, 303-307. (3) Monnier, A. M. Reu. Can. Biol. 1982, 41, 47-63. (4) Kobatake, Y. Adu. Chem. Phys. 1975, 29, 319-340. (5) Shashoua, zyxwvutsrqp V. E. Nature (London) 1967, 215, 846-847. (6) Mueller, P.; Rudin, D. 0. Nature (London) 1968, 217, 713-719. (7) Pant, H. C.; Rosenberg, B. Biochim. Biophys. Acta 1971, 225, 379-38 1. in a lipid bilayer membrane (black membrane) between aqueous solutions of different concentrations with KC1 or KH2P04, though they observed no dependence of these spikes on the electrolyte concentration. Recently, we9 found that electrochemical oscillations occur spontaneously even in a simple two-phase system consisting of an organic solution of picric acid in nitropropane and an aqueous solution of cetyltrimethylammonium bromide (CTAB). We also studiedlo an artificial liquid membrane consisting of an oil layer, nitrobenzene containing picric acid, imposed between two aqueous phases, one containing 5 mM CTAB and 5% ethanol. We found that this system showed rhythmic and sustained oscillations of electrical potential within the range of 150-300 mV with an interval of 2-3 min. No oscillations were observed in the absence of ethanol. As an extension of these studies, we investigated the effect of alcohols on the oscillations in the liquid membrane. The present paper reports the results of these experiments, indicating that the frequency of the oscillations depends on the concentration of alcohols, and that the threshold concentration needed to induce electrical oscillations decreases with an increase in the “hydrophobicity” of the alcohols. Experimental Section Experiments were performed in an apparatus with a U-shaped glass tube (12-mm inner diameter). The apparatus is shown schematically in Figure 1. A solution (4 mL) of 1.5 mM picric acid in nitrobenzene was placed in the base of the U cell. Aqueous solutions (10 mL each) were introduced simultaneously into the arms of the U cell above the organic phase without stirring. All measurements were carried out at 25 OC. The (8) von Klitzing, L.; Daber, M.; Bergeder, H. D. Biophysik (Berlin) 1973, (9) Yoshikawa, K. Matsubara, Y. J. Am. Chem. SOC. 1983, 105, (10) Yoshikawa, K.; Matsubara, Y. Biophys. Chem. 1983, 17, 183-185. 9, 166-171. 5967-5969. 0002-7863/84/1506-4423$01.50/0 0 1984 American Chemical Society