Induced Charge Separation in Vesicles

Earlier sections demonstrated how by suitable design of the system it is possible to achieve light-induced separation of charges in energy storing redox reaction in aqueous micellar media. Similar studies have also been carried out in multiphase systems of unilamellar vesicles and liposomes. These systems differ from simple micelles in providing two aqueous phases (inner and outer) separated by a 

Idilayer formed by the lipid. In addition to vesicles and liposomes formed by biologically derived phospholipids, synthetic vesicles formed by surfactant derivatives such as dioctadecyl dimethyl ammonium chloride (DODAC) have been reported recently. Vesicles, unlike micelles are static entities and can accomodate a substantial number of guest molecules per aggregate. As in micelles, these systems can organise donors and acceptors, lower ionisation potentials and more importantly through their interfaces or electrical double layer allow for some kinetic control of electron transfers. 

The efficiency of light-induced charge separation and electron-transport through the bilayer lipid walls have been examined recent-ly3.3 3.39 for a variety of redox systems in lipid vesicles. Of particular interest has been the redox reactions sensitized by porphyrins such as chlorophyll-a and derivatives of RuCbpy) . Gratzel, Fendler and others have investigated recently electron-transfer and 

3 Charge Separation Phenomena in other Multiphase Systems 

Here the role of the particle is to couple the anodic oxidation of the reduced relay with H2 generation from water. The choice of the catalytic material may be based on the same considerations which apply for electrocatalytic reagents used on macroelectrodes the exchange current densities for the anodic and cathodic electron transfer steps must be high. Colloidal platin xm would then appear to be a suitable candidate to mediate reaction (6o). This fact was recognized already at the end of the last century when numerous examples for the intervention of finely divided Pt in the process of water reduction by agents such as Cr and V appeared in the german colloid literature.  

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