PHOTO-STIMULATED COUPLED TRANSPORT OF ELECTRONS AND PROTONS ACROSS QUINONE-DOPED LIQUID POLYMER-SUPPORTED BIOMIMETIC MEMBRANE

A photo-stimulated reaction between EDTA as electron donor and anthraquinone-1,5-disulphonate as photosensitizer, both placed on one side of a liquid membrane supported by a nitrocellulose ultrafilter (ca. 0.1 mm thick), and ferricyanide as electron acceptor on its other side, has been carried out using 2,5-dichloro-1,4-benzoquinone as a lipophilic electron carrier in the hydrophobic membrane phase. The quinone-mediated electron transfer is coupled to active proton translocation and is directly monitored by pH measurements. A kinetic model of this multistep redox reaction is put forward, providing an explanation for the experimentally found dependence of the proton transfer rate on light intensity, electron donor and photosensitizer concentrations and on the membrane thickness. In terms of the model adopted, the reaction occurs mainly in a thin near-membrane water layer, this fact resulting in a large difference between the effective rate constants in this two-compartment system as compared with the same reaction in homogeneous solution. Depending on conditions, the net process may be kinetically controlled by the photochemical reaction itself, or by the dark chemical or transfer steps. In the last case the maximal net rate of the process is limited by the carrier diffusion in the membrane.