Spontaneous oscillation of membrane potential in surface modified polyamino acid membrance

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Chemically modified poly (gamma-methyl-L-glutamate) membranes having several lengths of diamine scgments were prepared. The membrane potential, DELTAphi, was measured in cells that consisted of two chambers separated by the membranes. The potential was measured using a digital multimeter with Ag/AgCl electrodes, and the data were transferred to a 32-bit personal computer.The modified membranes generated oscillation of membrane potential under a conceutration gradient of several salts, although nonmodified membranes showed constant potential. The oscillation of membrane potential is considered to be caused by the fluctuation of the fixed charge density originating from the themal fluctuation of partially ionized amine segments in the modified membranes. The amplitude of the oscillation was greater in the modified membranes having longer diamine segments.It was also influenced by the salts used, and the highest amplitude of the oscillation was observed when LiCl was used as the salt. The amplitudes of the oscillation of membrane potential measured using several salts were observed to increase in the following order at C_O=0.1M,C_1=1mM,_pH=10 and 25^OC : CsCl=KCl<<Na_2CO_3<NaNO_3=Na_2SO_4<<LiCl. Not only the anion but also the cation in the salts was found to affect the amplitude of the oscillation of membrane potential. The amplitudes of oscillation in the membrane potential were observed to be higher when the ionic radius of the cation in the salts was less and the hydration radious of the cation in the salts was higher in this study (i.e., CsCl=KCl<NaCl<LiCl).Fast Fourier transport analysis revealed that the oscillation of membrane potential is not chaotic but has specific frequencies. It might be possible to recognize a particular salt present in the solution from the information on the amplitude and the power spectrum of fast Fourier transport in the oscillation of membrane potential.