✍ Scribed by L. Pospíšil; E. Müller; H.D. Dörfler
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1,ZDipalmitoyllecithine forms adsorbed films at electrodes in two distinct potential regions. At temperatures below the phase transition temperature the film at negative potentials is highly ordered and blocks the surface for electrode reactions. Potential steps between both regions enable us to monitor the random nucleation during the film transition by its influence upon the charge transfer process. The time distribution of current pulses obeys the Poisson distribution. The current power spectrum is given. INTRODUCTiON The occurrence of single molecular events is still a rather rare experimental observation. Recently it has been shown that electrochemical systems offer certain advantage in amplifying a single event to an experimentally observable effect. Examples of such measurements are found in studies of electrodeposition on small single crystal faces[l-3], of conductivity fluctuations at natural or artificial membranes[4-6] and of charge (or double-layer capacity) transients during the reorientation of an adsorbed film at electrodes[7-lo]. Here we report another example of observation of random events which are amplified to a measurable signal level by means of their influence on a suitable Faradaic process. In the present case the system responsible for stochastic behaviour is the phase transition of 1,2-dipalmitoyllecithine (1,2-DPL) fdm of molecules adsorbed on the mercury-90% ethanolic solution interface. By a proper choice of the temperature and the electrode potential the adsorbed lecithine film could be either in the highly ordered orientation or still in the adsorbed state, but with much less stiff chain configurations. Accordingly, the film of 1,2-DPL can either very strongly inhibit the electron transfer from, or to, the electrode or lose its blocking influence after the configuration change has taken place. Stochastic phenomena observed during the film transition bctween these two states are the subject of the present communication.
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